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Therapeutic potential of TAS-102 in the treatment of gastrointestinal malignancies:

Therapeutic potential of TAS-102 in the treatment of gastrointestinal malignancies: 603313 TAM0010.1177/1758834015603313Therapeutic Advances in Medical OncologyG. J. Peters research-article2015 Therapeutic Advances in Medical Oncology Review Ther Adv Med Oncol Therapeutic potential of TAS-102 in the 2015, Vol. 7(6) 340 –356 DOI: 10.1177/ treatment of gastrointestinal malignancies © The Author(s), 2015. Reprints and permissions: http://www.sagepub.co.uk/ Godefridus J. Peters journalsPermissions.nav Abstract: Fluoropyrimidines form the mainstay in treatment of gastrointestinal malignancies. For decades 5-fluorouracil (5FU), was the major fluoropyrimidine. Currently it is usually given in a combination with leucovorin and oxaliplatin, i.e. FOLFOX, or irinotecan, i.e. FOLFIRI, or all three, i.e. FOLFIRINOX, but gradually it has been replaced by oral fluoropyrimidine prodrug formulations, such as tegafur-uracil and S-1 (both contain ftorafur), and capecitabine (Xeloda®). Novel drugs such as the antivascular endothelial growth factor antibody, bevacizumab, and the anti-epidermal growth factor receptor antibody, cetuximab, are often combined with one of these treatment options. However, when resistance emerged, no alternatives were available. TAS-102, a combination of trifluorothymidine and the thymidine phosphorylase inhibitor TPI in a 1:0.5 ratio, is a novel oral formulation, which is active in 5FU- resistant models, both in vitro and in xenograft models. In addition to inhibition of thymidylate synthase, the major mechanism of action of classical fluoropyrimidines, TAS-102’s major mechanism of action is incorporation into DNA, thereby causing DNA damage. TAS-102 also follows an alternative activation pathway via thymidine kinase, and is not a substrate for dihydropyrimidine dehydrogenase. All together this explains the efficacy in 5FU-resistant models. In early clinical studies, the twice-daily schedule (5 days on, 2 days rest) for 2 weeks every 4 weeks, led to a significant disease control rate in various malignancies. This schedule showed consistent activity in two randomized trials on fluoropyrimidine refractory colorectal cancer patients, reflected by an increase of 2–3 months in overall survival in the TAS-102 group compared with placebo. Considering the impressive preclinical potential of various combinations TAS-102 has the promise to become an alternative for 5FU-resistant cancer. Keywords: clinical trials, colorectal cancer, combination studies, DNA damage, TAS-102, thymidine phosphorylase inhibitor, trifluorothymidine Correspondence to: Introduction clinical evaluation was discontinued because of a Godefridus J. Peters PhD TAS-102 is an oral formulation that combines sev- poor pharmacokinetic profile and side effects. Department of Medical Oncology, VU University eral attractive features of the cytotoxic pyrimidine However, some of the administration schedules Medical Center, De analog 5-trifluoro-2’-deoxythymidine (trifluoro- resulted in a reduction of tumor size (8 out of 23 Boelelaan 1117, PO Box 7057, 1007 MB thymidine [TFT]; trifluridine [F TdR]; 5-trifluo- breast cancers and 1 out of 6 colon cancers) Amsterdam, The romethyl-2’-deoxyuridine [CFdUrd]; FTD; [Ansfield and Ramirez, 1971]. It was shown that Netherlands gj.peters@vumc.nl 2’-deoxy-5-(trifluoromethyl)uridine [F Thd]) and TFT can be phosphorylated by thymidine kinase the potent thymidine phosphorylase (TP) inhibitor to its active monophosphate form mediating TPI (tipiracil hydrochloride), in a molar ratio cytotoxicity [Heidelberger et  al. 1965], and it of 1:0.5 [Temmink et  al. 2007b] (Figure 1). It was as effective against adenocarcinoma cells as has successfully completed two randomized 5-fluoro-2’-deoxyuridine (FdUrd) [Heidelberger phase II/III studies [Yoshino et  al. 2012; Mayer and Anderson, 1964]. TFT is registered as et al. 2015]. Viroptic® [De Clercq, 2004], for use against herpes simplex virus infections and was previously approved Although TFT was synthesized by Heidelberger by the US Food and Drug Administration in 1980 and colleagues [Heidelberger et al. 1964], its initial for the treatment of primary keratoconjunctivitis 340 http://tam.sagepub.com GJ Peters serves as the co-factor for the reductive methyla- tion of dUMP to thymidine monophosphate CF HN (dTMP) (Figure 2). Inhibition of TS leads to HN intracellular depletion of deoxythymidine triphos- O N O N phate (dTTP), and subsequent dUMP accumula- HO CH tion, resulting in uracil misincorporation into the NH HCl DNA leading to DNA damage [Wilson et  al. 2014; Peters et al. 2009]. In an animal model con- tinuous treatment with TFT led to an accumula- OH H tion of dUMP [Tanaka et  al. 2014]. Normally TPI TFT dUMP can be broken down to deoxyuridine, TAS-102= T FT + TPI which will be excreted into plasma, resulting in increased deoxyuridine plasma levels, which can (1:0.5 ra o) be considered as a biomarker for effective TS Figure 1. Composition of TAS-102. inhibition [Peters et al. 2009]. This effect was also observed in animals and patients treated with a specific TS inhibitor such as raltitrexed, nola- trexed, or pemetrexed [Peters et  al. 2009; Ford and epithelial keratitis [Carmine et al. 1982]. TAS- et al. 2002]. 102 is currently registered in Japan as Lonsurf® for third-line treatment of colorectal cancer. The In addition to TFT-mediated TS inhibition, TFT current review summarizes the mechanism of itself can be incorporated into DNA [Fujiwara action of the individual components of TAS-102, and Heidelberger, 1970], for which evidence is TFT and TPI, and its development as an alterna- accumulating that this is the main mechanism of tive treatment for colorectal cancer. action of the drug. TFT is incorporated into DNA as the triphosphate form of TFT (TFT-TP) TFT-mediated cytotoxicity [Temmink et al. 2005; Emura et al. 2004c], caus- TFT shares some similarities to 5-fluorouracil ing cell death due to DNA strand-break forma- (5FU), but its differences seem responsible for its tion [Emura et  al. 2004d; Suzuki et  al. 2011; successful application as an anticancer drug [De Matsuoka et  al. 2015]. This incorporation into Bruin et  al. 2006]. The mechanism of action of DNA was related to the antitumor activity of TFT is depicted in Figure 2. TFT is phosphoryl- TAS-102 in in vivo mouse models [Tanaka et al. ated by thymidine kinase 1 (TK1) to its active 2014]. TAS-102 showed a dose-dependent and monophosphate-derivative TFT-MP, which similar antitumor effect against 5FU-resistant inhibits thymidylate synthase (TS) [Reyes and DLD-1 colon tumors (tumor growth inhibition Heidelberger, 1965; Sakamoto et al. 2015]. TS is rate 73.2% at 150 mg/kg/day) and the parent one of the rate-limiting enzymes in pyrimidine de DLD-1 tumors (tumor growth inhibition rate novo deoxynucleotide synthesis and therefore it 73.4% at 150 mg/kg/day) [Emura et al. 2004d], in plays a central role in DNA synthesis as a target contrast to conventional 5FU (continuous infu- for chemotherapeutic approaches [Van Triest and sion; inhibition rate 28.2% versus 62.3%, respec- Peters, 1999]. TFT-MP does not form a ternary tively), or an analog such as tegafur-uracil (UFT) complex and binds covalently to the active site of (inhibition rate 12.9% versus 61.2%, respectively). TS (tyrosine 146), thereby inhibiting its activity DLD-1/FdUrd resistant and DLD-1 parent [Santi and Sakai, 1971; Eckstein et  al. 1994]. tumors were similarly sensitive to TAS-102, but TFT-MP is a potent reversible inhibitor of TS DLD-1/FdUrd tumors were resistant to UFT. with a Ki of 0.38 nM [Reyes and Heidelberger, Also another 5FU-resistant model (the gastric 1965], and its activity remains inhibited when a cancer xenograft NUGC-3/5FU) was similarly constant influx of TFT is present; removal of the sensitive to oral TFT but cross-resistant to compound leads to a rapid recovery of TS activity FdUrd and TS-1. Intracellular TFT-TP is rapidly [Santi and Sakai, 1971; Temmink et  al. 2004]. eliminated from tumor cells after the removal of This is in contrast to the 5FU derivative, 5-fluoro- TFT from the culture medium, but TFT incor- 2’-deoxyuridine-5’-monophosphate (FdUMP), poration into DNA continued to increase during which inhibits TS after formation of a ternary 8 h TFT exposure of NUGC-3 human gastric complex with 5,10-methylene-tetrahydrofolate cancer cells. TFT was incorporated in a time- (CH -THF), thereby enhancing and prolonging dependent manner and not in a concentration- this inhibition [Peters et al. 2002]. CH -THF also dependent manner [Emura et  al. 2004c; Tanaka http://tam.sagepub.com 341 Therapeutic Advances in Medical Oncology 7(6) et  al. 2014]. Incorporated TFT into the DNA is cause a chain-terminating effect. From the pre- retained for at least 80% up to 24 h after the sent data it can be concluded that the DNA- wash-out procedure. These observations indi- targeted effects of TAS-102 are specific for cancer cated that TFT incorporation into DNA is impor- cells, determine the antitumor effects, and are tant. This incorporation led to inhibition of chk-1 enhanced by the inhibition of TS. phosphorylation and an increase in AP sites [Suzuki et  al. 2011]. In addition, tumor-bearing mice treated with TAS-102 at a repeated dosing TFT resistance of 75 mg/kg/day or 150 mg/kg/day showed a sig- Most chemotherapeutic regimens in the treatment nificantly higher incorporation of TFT into DNA of gastrointestinal cancer patients are 5FU-based. of the tumor compared with single dosing [Emura The presence of a fluoropyrimidine is indispensa- et al. 2004c; T anaka et al. 2014], while higher dos- ble to obtain a maximal effect. To improve treat- ing also led to an accumulation of dUMP, indicat- ment of colorectal cancer it is important that an ing inhibition of TS in vivo [Tanaka et al. 2014]. alternative chemotherapeutic regimen, such as TFT induced pronounced DNA damage due to TAS-102, also exhibits antitumor effects against enhanced DNA fragmentation resulting in most 5FU-sensitive, and more favorably, against potent antitumor activity. This indicates that mul- 5FU-resistant tumor cells. Indeed a high dose tiple daily dosing may result in better clinical level of TFT alone (200 mg/kg/day) resulted in benefits for TAS-102-treated cancer patients. tumor growth-inhibition rates of about 70% for However, although it has been reported that both 5FU-sensitive and 5FU-resistant NUGC-3 TFT-TP is a substrate for DNA polymerase α gastric cancer cells (NUGC-3/5FU) implanted [Sakamoto et al. 2015], and causes DNA damage, subcutaneously in nude mice [Emura et al. 2004d]. it is not yet known whether TFT-TP is a substrate Similar data were found for FdUrd-resistant for other DNA polymerases, and whether it might DLD-1 colorectal cancer cells (DLD-1/FdUrd) in deoxyuridine TAS-102 TPI TFT TF- dUMP thymine TS TFT-MP dTMP thymidine TFT-TP dTDP TPI dR-1-P thymine dTTP dRibose TFT incorporated into DNA; Angiogenesis? DNA damage: cell death Figure 2. Metabolism and mechanism of action of TAS-102. Trifluorothymidine (TFT) can be phosphorolyzed by thymidine phosphorylase (TP) to trifluorothymine which can be inhibited by TPI. TAS-102 is the combination of TFT and TPI (a thymidine phosphorylase inhibitor). TFT is phosphorylated by thymidine kinase 1 (TK1) to TFT-MP, which is a reversible inhibitor of thymidylate synthase (TS), which leads to depletion of thymidine monophosphate (dTMP), but an accumulation of 2’-deoxyuridine-5’-monophosphate (dUMP) (and deoxyuridine outside the cell and in plasma). TFT-MP can be phosphorylated to TFT-TP, which can be incorporated into DNA, causing DNA damage, and induce a DNA damage-response signaling, leading to G2-M accumulation and cell death. Depletion of deoxythymidine triphosphate (dTTP) by inhibition of TS, will enhance the incorporation of TFT-TP into DNA. An alternative source for dTMP is thymidine, which can be phosphorylated to dTMP by TK1. However, degradation of thymidine by TP to thymine also leads to the formation of deoxyribose-1-P (dRib-1-P), which can be degraded to deoxyribose (dRibose), and may be responsible for angiogenic effects. TPI will also inhibit this step when patients are treated with TAS-102 (adapted from [Peters et al. 2002]). 342 http://tam.sagepub.com GJ Peters mice treated with 150 mg/kg/day TFT. The resist- patients was less than 15 min [Dexter et al. 1972]; ance mechanisms of both tumors are different TFT is phosphorolyzed to trifluorothymine [Inaba et al. 1996; Murakami et al. 2000], showing (TF-Thy), which can be hydrolyzed to 5-carboxy- an advantage for TAS-102 over 5FU in uracil with the loss of the inorganic fluoride. Initial 5FU-resistant tumor cells, while TAS-102 was studies on mice have already demonstrated that also effective in vivo against 5FU-sensitive tumors the TFT degradation product TF-Thy and its cat- from different tissue types, such as human pancre- abolite 5-carboxyuracil were formed mainly in the atic and esophageal tumor cells [Emura et  al. liver, spleen, and intestines [Heidelberger et  al. 2004a, 2004d]. 1965]. Similar to normal nucleosides [Peters, 2014], TFT can easily cross the blood–brain bar- Also in vitro TFT was active against 5FU-resistant rier in low micromolar concentrations and is also DLD-1 cells (DLD-1/5FU) [Emura et al. 2004a]. predominantly metabolized to TF-Thy in the brain In DLD-1/TFT cells no increase in TS was found, [Pouremad et al. 1999]. Besides TF-Thy, the dihy- but TK activity was decreased significantly (37- dro-species of TFT and TF-Thy, the reductive cat- fold). Also H630 human colorectal carcinoma cells abolites α-trifluoromethyl-β-ureidopropionic made resistant to TFT using either a long-term acid (F MUPA) and α-trifluoromethyl-β-alanine continuous exposure schedule (H630-cTFT) or (F MBA) were detected in liver extracts. Low lev- short-term repeated exposure schedule (H630- els of fluoride ions were detected in serum and 4TFT), showed different mechanisms of resistance urine, but also in brain and liver extracts. Early [Temmink et  al. 2010]. The H630-4TFT cells clinical pharmacology studies with TFT showed exposed to TFT on a short-term basis (250 µM that the only metabolites detected in urine and TFT 4 h/week) had normal TS levels, but no TK serum samples of treated cancer patients were activity, similar to the DLD-1/TFT-resistant cells. unmodified TFT, TF-Thy, and 5-carboxyuracil H630-cTFT cells growing in medium ultimately [Heidelberger et al. 1965; Dexter et al. 1972]. containing 20 µM TFT did not have altered TS and TK levels but showed a disturbed signal trans- In a series of novel orally active 6-methylene- duction with upregulated secretory phospholipase bridged, uracil-derived inhibitors of human TP A2 expression. In both H630- TFT-resistant cell [Fukushima et  al. 2000; Yano et  al. 2004], the lines no change in TP levels was observed, although most potent human TP inhibitor was the this was less relevant, because a high TP expression 5-chloro-6-(2-iminopyr rolidin-1-yl)methyl- in colorectal cancer cells hardly influences the sen- 2,4(1H,3H)-pyrimidine dione hydrochloride sitivity to TFT [Temmink et  al. 2005; De Bruin (TPI; tipiracil hydrochloride) with an IC of 35 et  al. 2003]. In agreement with the DLD-1/TFT nM for TP, which was a poor inhibitor of uridine cells, both H630-derived TFT-resistant cell lines phosphor ylase (UP) (IC > 100 µM) [Fukushima were not cross-resistant to 5FU or the folate-based et  al. 2000], a pyrimidine phosphorylase also direct TS inhibitor GW1843, but the TK-deficient known to cleave thymidine (TdR) and other variants were cross-resistant to FdUrd (about 160- pyrimidine nucleosides. The Ki value for TPI fold). In contrast to the DLD-1/5FU, 5FU-resistant using recombinant human TP was 17 nM. TPI H630 cells (H630-R10) with increased TS levels was a potent inhibitor of TFT phosphorolysis in were cross-resistant to FdUrd and TFT, but this extracts from human liver, small intestine, and was dependent on exposure time [Temmink et al. tumor tissues. At equimolar doses TPI increased 2005]. C and area under curve (AUC) of orally max administered TFT to rodents or monkeys (10 It can be concluded that TAS-102 is active in mg/kg) [Fukushima et al. 2000; Y ano et al. 2004], 5FU-resistant models, while resistance to TFT is which was most pronounced in monkeys (Figure 3), multifactorial but different from 5FU. This offers due to differences in expression of pyrimidine opportunities to use this information to select phosphorylases in these animals [Ackland and patients for the best treatment option. Peters, 1999; Cao and Pizzorno, 2004; Pugmire and Ealick, 2002]. Pharmacokinetics studies were also designed to optimize the molar drug ratio of TPI increases bioavailability of TFT in vivo TFT:TPI to reach maximal TFT plasma levels. The main pharmacokinetics of TFT [Dexter et al. With a TFT:TPI molar ratio of 1:0.5 optimal 1972] resemble that of most antimetabolites with a TFT concentrations in the plasma were obtained short half-life [Peters et  al. 1993]. The mean [Emura et  al. 2005], and this formulation was plasma half-life of single TFT injected to cancer developed as TAS-102. At a co-administration of http://tam.sagepub.com 343 Therapeutic Advances in Medical Oncology 7(6) (a) (b) 40 16 35 14 30 12 25 10 20 8 15 6 10 4 5 2 0123 45 67 8 Time after administration (min) Time after administration (hr) Figure 3. Effect of TPI on trifluorothymidine (TFT) pharmacokinetics. Plasma TFT levels in mice (a) and monkeys (b) were measured following oral administration in the presence and absence of TPI. TFT (black circles) was administered in doses of 50 mg/kg (normal mice) or 10 mg/kg (normal monkeys), or in combination with an equimolar amount of TPI (white circles). Values are means of several experiments (n = six mice; n = three monkeys). (Data adapted from [Fukushima et al. 2000] with permission.) 1 M TFT (10 mg/kg) and > 0.5 M TPI, a maxi- incorporation of TFT into DNA [Temmink et al. mum and constant level of 15 µg TFT/ml was 2005]. Probably TK1 has favorable enzyme prop- found, associated with a maximally augmented erties for the TFT-activation pathway by being antitumor activity for gastrointestinal cancer cells maximally saturated, which is hardly influenced xenografted into mice [Emura et  al. 2005]. by TFT degradation by TP. TPI only affected Steady levels of TFT in plasma obtained with a TFT-mediated cytotoxicity at very short expo- divided dosing of TFT within an adequate time sures in cells expressing very high TP [Temmink period resulted in optimal DNA incorporation et al. 2005]. This means that the mode of in vitro and subsequent antitumor activity [Emura et  al. cytotoxicity exerted by TFT is also dependent on 2004c]. the exposure times used. The effect of TPI was not dependent on the activity of TP, since all High TdR levels may reduce the antitumor effect models displayed different activities of TP. of TFT. Administration of TAS-102 will not only inhibit TFT degradation but can also inhibit TdR It can be concluded that the addition of TPI degradation, which can lead to an increase of improved the pharmacology of TFT drastically, intracellular TdR [Emura et al. 2004b]. TAS-102 by almost completely inhibiting TFT degrada- or TPI will not affect the concentration of uridine tion, prolonging its half-life and drug exposure, or deoxycytidine, since TPI does not inhibit UP and enhanced its incorporation into DNA. or deoxycytidine degradation. However, it is pos- sible that TAS-102 can increase the deoxyuridine concentration since it causes a dUMP accumula- Tumor angiogenesis tion [Tanaka et al. 2014]. TPI is a potent inhibitor of TP, also known as platelet-derived endothelial cell growth factor The addition of TPI is only important for in vivo (PDECGF) [Ackland and Peters, 1999; studies, since in vitro studies showed that, despite Moghaddam and Bicknell, 1992], which is an high TFT phosphorolysis, high TP-expressing angiogenesis growth factor [Miyazono et  al. colorectal Colo320TP1 and nonsmall cell lung 1987]. Angiogenesis is an important process in H460TP2 cancer cells are not more resistant to stimulating tumor vascularization and targeting TFT, while addition of TPI did not increase TFT angiogenesis is an important novel therapeutic sensitivity [Temmink et al. 2005; De Bruin et al. approach [Ellis, 2004]. Most anti-angiogenic 2003]. A moderate almost two-fold increase in drugs target growth factors (and their receptors) formation of active TFT metabolites was found, or inhibit endothelial cell proliferation or/and sig- although it was not related to increased nal transduction. Vascular endothelial growth 344 http://tam.sagepub.com TFT levels (µg/ml) TFT levels (µg/ml) GJ Peters factor (VEGF), but also fibroblast growth factor activation of focal adhesion kinase (FAK) and (FGF), PDECGF, and their tyrosine kinase p70/S6, the downstream kinase of the mechanis- receptors are the major regulators of angiogenesis tic target of rapamycin (mTOR), which regulates [Manetti and Botta, 2003; George, 2001]. TP/ cell proliferation, metabolism, and also angiogen- PDECGF overexpression is often associated with esis. mTOR and FAK seem responsible for the VEGF overexpression. Bevacizumab (Avastin®) invasive potential of TP. TPI can block these pro- depletes VEGF levels and is effective in combina- cesses and, in vivo [Emura et  al. 2005; Akiyama tion with 5FU-based regimens for colorectal can- et al. 2004; T akao et al. 2000], it was demonstrated cer. Thymidine exposure of TP-overexpressing that TPI significantly inhibited PDECGF/ cells leads to an increase of various angiogenic TP-induced neovascularization in a dose-depend- factors (bFGF, interleukin-8, and tumor necrosis ent manner in mice models. In a specific model, factor [TNF]-α, but not VEGF), which enhanced with KB cells transfected with TP leading to a migration and invasion of human umbilical vein clinically not relevant overexpression of TP (KB/ endothelial cells [Bijnsdorp et al. 2011]. TP cells), TPI decreased the growth rate of these KB/TP cells and increased the apoptotic index, In addition to VEGF, increased TP/PDECGF indicating a potential antitumor activity of TPI as expression is seen in colorectal tumor tissue com- a single agent [Takao et al. 2000]. pared with normal tissue [Takebayashi et  al. 1996b], and high PDECGF/TP levels are a prog- TAS-102 was also able to reduce the number of nostic factor for poor survival in colorectal liver metastases in a nude mouse model [Emura [Takebayashi et  al. 1996a] and gastric cancers et al. 2004a]; TPI alone decreased the chemotac- [reviewed in De Bruin et al. 2006]. PDECGF/TP tic motility and basement membrane invasion of is also overexpressed in tumor-infiltrating cells the above-mentioned KB/TP cells [Takao et  al. (mainly macrophages) and colon cancer cells 2000], suppressed the number of liver metastases themselves [De Bruin et al. 2006; Van Triest et al. macroscopically, and markedly diminished the 2000; Takahashi et  al. 1996]. High blood vessel invasive activity [Sato et  al. 2003]. Due to the density is well correlated with increased potent anti-invasive and antimetastatic activity of PDECGF/TP expression and is associated with TPI, TAS-102 may have multiple mechanisms of metastasis formation in several tumors [Takahashi action in clinical use. et al. 1996, 2003]. Both VEGF and PDECGF/TP are important in human angiogenesis induced by The expression of TP in tumors shows a larger both tumor and normal cells and therefore these variation between malignancies with the same factors and their receptors are good targets for pathology, but also between different types of antiangiogenic therapy [De Bruin et  al. 2006]. tumors [De Bruin et  al. 2006]. When TP is low, Tumor growth and metastasis are dependent on a chemotherapeutic drugs often upregulate sufficient blood supply and therefore inhibition of PDECGF/TP [Endo et al. 1999; Fukushima et al. tumor-induced angiogenesis in combination with 2002]. This is an advantage for the oral 5FU classic cytotoxic chemotherapy may be a strategy prodrug capecitabine ((+)-pentyl 1-(5-deoxy-β- to improve survival for patients with solid tumors, D-ribofuranosyl)-5-fluoro-1,2-dihydro-2-oxo-4- as was already shown in preclinical models when pyrimidinecarbamate) [Van Cutsem et  al. 2001; an anti-angiogenic agent was combined with Hoff et al. 2001], which is activated by PDECGF/ cytotoxic agents [Zondor and Medina, 2004; TP and for which a low expression negatively Kabbinavar et al. 2005]. influences therapeutic outcome of capecitabine- based chemotherapy [Ackland and Peters, 1999]. The downstream mediator of PDECGF/TP However, activation of the capecitabine interme- 2-deoxy-D-ribose is rapidly formed [Bijnsdorp diate 5-fluoro-5’-deoxyuridine (5’DFUR) to 5FU et  al. 2010a] (Figure 2), and its increased levels can also be mediated by UP [Cao and Pizzorno, promote angiogenesis by enhancing chemotaxis 2004; Temmink et al. 2006a, 2007a], but TPI is a of vascular endothelial cells [Uchimiya et  al. poor inhibitor of UP [Fukushima et  al. 2000]. 2002], which may confer resistance to apoptosis Since TFT is a poor substrate for UP, a high activ- induced by hypoxia [Ikeda et  al. 2002]. ity of UP will unlikely affect the efficacy of TFT. Deoxyribose has shown angiogenic properties in In vivo data showed that TAS-102 is only effective various in vitro and in vivo studies [Seeliger et al. in inducing cytotoxicity when systemic TPI is pre- 2004; Hotchkiss et  al. 2003], and it was shown sent, but acts against both undetectable and high that it can stimulate invasion and migrations by TP-expressing colon cancer cells. http://tam.sagepub.com 345 Therapeutic Advances in Medical Oncology 7(6) Table 1. Effective combinations of trifluorothymidine or TPI (in vitro) or TAS-102 (in vivo) with conventional chemotherapy targeted against DNA and novel therapeutics targeting protein kinases. Drug Combination drug Model system In vitro/in Outcome Postulated Reference vivo mechanism Trifluorothymidine Oxaliplatin Colon cancer In vitro Synergistic Increased DNA Temmink et al. adducts [2007d] TAS-102 Oxaliplatin Colon and In vivo Synergistic Nukatsuka et al. gastric cancer [2015a] Trifluorothymidine Irinotecan Colon cancer In vitro Synergistic Increased DNA Temmink et al. damage and [2007c] apoptosis TAS-102 Irinotecan Colon and In vivo Nukatsuka et al. gastric cancer [2015b] Trifluorothymidine Docetaxel Colon cancer In vitro Synergistic Cell-cycle arrest; Bijnsdorp et al. cell kill [2008] Trifluorothymidine Antifolates Colon cancer In vitro Synergistic/ DNA damage Temmink et al. additive [2006b] TPI Rapamycin Colon cancer In vitro Synergistic TPI prevents Bijnsdorp and autophagy Peters [2011] Trifluorothymidine Tumor necrosis Lung cancer In vitro Synergistic Induction caspase Azijli et al. [2014] pathway factor-related apoptosis-inducing ligand (TRAIL) Trifluorothymidine Radiation Colon cancer In vitro Synergistic Decreased repair El-Naggar et al. DNA damage [2014] TAS-102 Radiation Colon cancer In vivo Sensitization Angiogenesis and Miyatani et al. [2012] decreased DNA repair Trifluorothymidine Erlotinib Colon cancer In vitro Synergistic S-phase arrest; no Bijnsdorp et al. DNA repair [2010b] TAS-102 Cetuximab, Colon cancer In vivo Tsukihara et al. panitumumab [2015] TAS-102 Bevacizumab Colon cancer In vivo Increased TFT- Tsukihara et al. phosphates [2015] PDECGF/TP clearly promotes angiogenesis, [Temmink et  al. 2006b], oxaliplatin [Temmink possibly in conjunction with other growth factors. et  al. 2007d], or irinotecan (CPT-11) [Temmink This pro-angiogenic effect seems to be mediated et  al. 2007c], in different schedules in order to by breakdown products of thymidine, such as determine their interactions. At low folate condi- deoxyribose-1-phosphate. Inhibition of thymi- tions TFT and folate-based TS inhibitors (e.g. dine phosphorolysis by TPI has an anti-angio- raltitrexed) showed schedule-dependent syner- genic effect. Whether inhibition of angiogenesis gism in growth inhibition, two-sided TS inhibi- contributes to the antitumor activity of TAS-102 tion, and DNA damage induction, whereas at in patients needs further investigation. high folate conditions only additive effects were seen [Temmink et al. 2006b]. Combination studies The sensitivity of colon cancer cells to oxaliplatin Novel treatment options often consist of combi- could be increased by simultaneous exposure to nations of drugs in which current chemothera- TFT [Temmink et  al. 2007d], resulting in peutic regimens are combined with, for example, increased Pt-DNA-adduct formation, and subse- protein kinase-targeting drugs, immunotherapy, quent increased DNA damage induction and or radiation therapy. TAS-102 is an excellent can- apoptosis induction. The TFT-oxaliplatin combi- didate for combination with other cytotoxic nation was dose-schedule dependent, since TFT agents. In in vitro studies potential TAS-102 com- pre-incubation decreased oxaliplatin-induced binations were extensively investigated by combi- cytotoxicity to colorectal cancer cells. Recently it nations with other anticancer agents (Table 1). was also shown that this combination was syner- TFT was combined with other TS inhibitors gistic in vivo [Nukatsuka et  al. 2015a]. For the 346 http://tam.sagepub.com GJ Peters combination of TFT and SN38, the active metab- the repair of radiation-induced DNA damage, olite of irinotecan, the most pronounced synergis- and that TPI would have no effect, which was tic interactions were found when colorectal cancer indeed observed in vivo (TAS-102) [Miyatani cells were pre-incubated with TFT before SN38 et al. 2012], and in vitro [El-Naggar et al. 2014]. exposure, which resulted in increased DNA strand-break formation and cell death [Temmink In summary TAS-102 has the potential to increase et al. 2007c]. Also in several in vivo models of colo- the effect of a variety of different drugs, affecting rectal and gastric cancer the combination of TAS- their mechanism of action at critical points such 102 and irinotecan was superior to single agents as DNA repair of drug-induced lesions. The syn- without increased toxicity [Nukatsuka et  al. ergism of drugs used in common combination in 2015b]. TFT induces an uncommon effect on the colorectal cancer, such as oxaliplatin and irinote- cell cycle (G2-M accumulation and tetraploidy) can, is especially promising. [Bijnsdorp et  al. 2010c], which explains why the combination docetaxel appeared to be schedule dependent. A pre-incubation of docetaxel fol- Clinical trials lowed by TFT was synergistic, due to increased cell kill, polynucleation, and mitotic spindle inhi- Early phase I and II studies bition, accompanied by phosphorylation of chk2 The initial antitumor effects of TFT against colon and dephosphorylation of cdc25 [Bijnsdorp et al. cancer were reported in 1971, where it was shown 2008]. The reverse sequence was antagonistic. that repeated administration of TFT can produce TFT’s mechanism of cell kill was mediated by the reduction in tumor size of patients with breast intrinsic pathway (via the mitochondrial and colon cancer [Ansfield and Ramirez, 1971]. cytochrome c pathway, leading to caspase 9 cleav- However, systemic administration of TFT alone age). This is probably related to the TFT-induced (2.5 mg/kg/day) in divided doses every 3 h for p-53-dependent arrest in the G2 phase that was 8–13 days, resulted in severe bone-marrow associated with a proteasome-dependent decrease depression. TFT-mediated side effects were pri- in cyclin B1 [Matsuoka et  al. 2015]. It seemed marily confined to the hematopoietic system with likely that additional induction of the extrinsic less damage of the gastrointestinal tract compared pathway via caspase 8 cleavage would be effective. with 5FU and FdUrd [Ansfield and Ramirez, Indeed TNF-related apoptosis-inducing ligand 1971; Dexter et al. 1972]. The TFT early clinical (TRAIL), a specific inducer of the extrinsic path- trials were discontinued because of the short half- way, via binding to the death receptors 4 and 5, life due to its rapid clearance and extensive degra- was synergistic with TFT [Azijli et  al. 2014]. dation by PDECGF/TP in vivo. This likely Since many colorectal patients are sensitive to the resulted in the moderate antitumor efficacy that anti-epidermal growth factor receptor (EGFR) was observed (Table 2). antibody cetuximab (in case tumor KRAS is wild type), the combination of TFT with an EGFR TFT re-entered clinical development as TAS- inhibitor was also investigated. The small mole- 102, and in several US phase I clinical trials dos- cule EGFR inhibitor erlotinib showed synergism ing was optimized (summarized in Table 2). In in cells with a wild-type EGFR and additivity in the first phase I trial (TAS102-9801) TAS-102 cells with a mutant EGFR [Bijnsdorp et  al. was orally administered to patients with solid 2010b], erlotinib appeared to inhibit the prosur- tumors once daily for 14 days every 3 weeks. The vival pathway (AKT and MAPK) induced by maximum-tolerated dose (MTD) was 50 mg/m / TFT. Likewise in vivo combinations of TAS-102 day with granulocytopenia as the dose-limiting with the anti-EGFR antibodies cetuximab and toxicity (DLT) at 100 mg/m /day [Hong et  al. panitumumab resulted in a more than additive 2006]. In this schedule drug accumulation was activity, while the combination of bevacizumab observed, since the AUC increased 2–2.5-fold with TAS-102 was more effective [Tsukihara et al. after 2 weeks, possibly explaining the toxicity. In 4 2015]. Interestingly bevacizumab increased the out of 14 patients a stable disease (SD) was formation of TFT phosphate. Since many nucleo- observed. In the second trial (TAS102-9802) side analogs are excellent radiosensitizers, and once-daily TAS-102 was given orally (50–110 mg/ since 5FU is used for the treatment of patients m /day) to patients with gastrointestinal malig- with rectal cancer, TAS-102 was investigated for nancies for 5 days/week for 2 weeks repeated its potential radiosensitizing effect [Miyatani et al. every 4 weeks [Overman et  al. 2008b]. This 2012]. It was reasoned that TFT would inhibit schedule with the 2-day treatment rest allowed http://tam.sagepub.com 347 Therapeutic Advances in Medical Oncology 7(6) 348 http://tam.sagepub.com Table 2. Overview of phase I and II studies with TAS-102 at different schedules. Study Dose/scheme Maximum Dose-limiting Patients/disease Efficacy Reference tolerated toxicity dose Phase I/II Trifluorothymidine alone 2.5 Every 3 h; 2.5 mg/kg/ Bone marrow 6 colon 23 breast Some short PR Ansfield et al. [1971] mg/kg/day 8–13 days day Phase I Once daily for 14 days every 3 weeks 50 mg/m / Granulocytopenia 14 various 4 stable Hong et al. [2006] (9801) (50–100 mg/m /day) day disease Phase I Once daily for 5 days for 2 weeks every 4 100 mg/m / Granulocytopenia 24 various 7 stable Overman et al. (9802) weeks (50–110 mg/m /day day disease [2008b] Phase I Once daily for 5 days for 1 week every 3 160 mg/m / Granulocytopenia 39 various 11 stable Overman et al. (9803) weeks (100–180 mg/m /day) day disease [2008b] Phase I Twice daily for 5 days for 2 weeks every 4 50 mg/m / Granulocytopenia 19 breast 12 stable Green et al. [2006] (9804) weeks (50–80 mg/m /day) day disease Phase I Three times daily for 5 days for 2 weeks 70 mg/m / Granulocytopenia 15 mostly 9 stable Overman et al. (9805) every 4 weeks (60–80 mg/m /day) day gastrointestinal disease [2008a] Phase 1 Twice daily for 5 days for 2 weeks every 4 70 mg/m / Neutropenia 21 gastrointestinal (18 12 stable Doi et al. [2012] (J001) weeks (30–70 mg/m /day) day colorectal) disease Phase II Twice daily for 5 days for 2 weeks every 4 18 gastric 1 stable Mayer et al. [2015] (9806) weeks (50 mg/m /day) disease (supplementary data) The studies 9801–9806 (TAS102-9801 to TAS102-9806) were performed in the US; study J001 was a Japanese study; PR, partial response. GJ Peters the administration of higher doses of TAS-102 in the US studies grades 1 and 2 toxicity consisted compared with the continuous daily schedule. of nausea (66%), fatigue (64%), and neutropenia Granulocytopenia was dose limiting, while in 7 (55%), which were also seen as grades 3 and 4, out of 24 patients SD was observed. In a third but in general treatment-related toxicities were phase I study (TAS102-9803) patients with solid reversible. tumors received TAS-102 once daily (doses rang- 2 2 ing from 100 mg/m /day to 140 mg/m /day for 5 In a phase II study in the US (TAS102-9806) 18 days every 3 weeks) in order to determine the patients (most pretreated with a fluoropyrimidine MTD [Overman et al. 2008b]. At 120 mg/m /day regimen and progressive) with gastric cancer were patients experienced severe granulocytopenia, treated with the twice-daily schedule at 50 mg/ which was considered to be the DLT. Other tox- m /day. All patients progressed within four cycles, icities observed included neutropenia, mild to and the study was closed early (see supplemen- moderate nausea, vomiting, diarrhea, fatigue, and tary data of Mayer and colleagues [Mayer et  al. rash. Out of 39 patients, SD was observed in 11 2015]). The toxicity profile was similar to that of patients. the phase I studies. In general the MTD in US patients was lower than in the Japanese study, Other TAS-102 phase I trials applied two or three which is most likely not due to the ethnic back- times a day administration schedules, since divided ground but to the difference in pretreatment; daily dosing of TFT resulted in higher antitumor most US patients received more pretreatments. activity in preclinical studies due to increased For example, a median of more than five prior incorporation of TFT into DNA. Furthermore, treatments was given to patients with breast the previous once-daily TAS-102 phase I trials cancer in the TAS102-9804 study, including showed a short TFT half-life (about 2 h). A phase cyclophosphamide, which can compromise the I trial (TAS102-9805) was carried out at the bone-marrow reserve. A phase I study (TAS102- University of Texas MD Anderson Cancer Center 101) in the USA preceding the RECOURSE (Houston, TX, USA) using a three-times daily phase III study was limited to patients with meta- 2 2 (60–80 mg/m /day) schedule (5 days/week for 2 static colon cancer. The dose of 70 mg/m /day weeks repeated every 4 weeks) with 15 patients was shown to be tolerable, underlining that toxic- with solid tumors receiving TAS-102 orally. It was ity was related to pretreatment. concluded that TAS-102 was well tolerated with manageable hematologic (most common grade 3/4 neutropenia) and nonhematologic (e.g. nau- Pharmacokinetics sea, vomiting, fatigue, colitis) toxicities [Overman The pharmacokinetics of TAS-102 was investi- et  al. 2008a]. SD was observed in nine patients. gated in the phase I studies but most extensively The suggested phase II TAS-102 dose was 70 mg/ in the J001 study in which TAS-102 was given at 2 2 m /day. Another phase I trial (TAS102-9804) was 30–70 mg/m /day in a twice-daily schedule for 5 carried out to determine the phase II dose and the days during 2 weeks repeated every 4 weeks [Doi DLT in 19 patients with metastatic breast cancer et  al. 2012]. The pharmacokinetics in Japanese [Green et  al. 2006]. Patients received TAS-102 patients seemed comparable to that in US 2 2 orally at an initial dose level of 80 mg/m /day in a patients, for example, at 50 mg/m /day plasma twice-daily schedule (5 days/week for 2 weeks levels were comparable with those of patients in repeated every 4 weeks). Clinical activity (12 SD) the same schedule [Green et  al. 2006]. TFT was seen including prolonged disease control (> showed a slightly nonlinear pharmacokinetics, 12 weeks). It was concluded that TAS-102 is an for example, the C increased from 1009 (at 30 max 2 2 active agent against heavily pretreated metastatic mg/m /day) to 3338 ng/ml at 70 mg/m /day; for breast cancer patients, with primarily hematologic the AUC these values were 2037–8678 ng*h/ 0–10 toxicities (mainly grade 3/4 granulocytopenia and ml. The pharmacokinetics was performed on grade 4 thrombocytopenia), and the recom- days 1 and 12, enabling the investigation of mended dose was 50 mg/m /day using this sched- potential accumulation as was observed in the ule. In a Japanese phase I study (J001) TAS-102 first phase I studies. Also in this study an accu- was also given in the same schedule twice daily mulation of the drug was observed, which was (30–70 mg/m /day) to 21 patients with gastroin- most pronounced at the highest dose of 70 mg/ testinal malignancies (mainly colorectal cancer), m /day, for example, the C (reached between max resulting in a higher MTD of 70 mg/m /day, with 1.3 and 1.9 h) increased from 3338 ng/ml to 11 patients with SD [Doi et al. 2012]. In summary 4752 ng/ml. The increase in AUC was more 0–10 http://tam.sagepub.com 349 Therapeutic Advances in Medical Oncology 7(6) pronounced (also at the lower levels) and 2 days rest for 2 weeks and repeated after 4 weeks. increased from 8678 ng*h/ml to 20,950 ng*h/ In the Japanese study the disease control rate ml, with a tendency that the T½ also increased, (DCR) was 43.8% versus 10.5% (p < 0.0001), but only up to 1.5-fold, and was about 2 h at 12 respectively. The overall survival (OS) was 9.0 days. Interestingly the metabolite trifluorothy- months and 6.6 months (hazard ratio [HR] = mine decreased after 12 days to about 60% of 0.56; 95% confidence interval: 0.39–0.81; p = that at day 1. The C of TPI was about 70 ng/ 0.0011), respectively. For progression-free sur- max ml and was reached after about 2.3 h, with no vival (PFS) these values were 2.0 months and 1.0 significant difference between day 1 and day 12, months (HR = 0.41), respectively. In the TAS- although the AUC tended to increase from 102 group an improved OS was observed in 0–10 281 ng*h/ml to 317 ng*h/ml at the 70 mg/m / patients with wild-type and mut-KRAS, but it day dose. For both the C and AUC a linear was more pronounced and consistent in the mut- max 0–10 significant inverse relationship (r = -0.678 and KRAS group (HR wt/mt = 1.48; p = 0.045). The r = -0.753, respectively; both p < 0.001) was safety profile was comparable with that observed observed with the relative change in neutrophil in the earlier US and Japanese phase I and II count. A recent mass-balance study in patients studies, with bone-marrow suppression and gas- showed that 60% of the dose of TFT was recov- trointestinal events. ered, mostly in urine, and excreted as TFT itself, trifluorothymine, and TFT glucuronide, In the RECOURSE study a similar protocol was while TPI was mostly recovered in feces as TPI used as in the J003 study, using the same dose (70 and partially as 6-hydroxymethyluracil [Lee mg/m /day), randomized in a 2:1 ratio (534 versus et al. 2015a, 2015b], which was in line with the 266 patients) [Mayer et  al. 2015]. All patients early historical data [Heidelberger et  al. 1965; were progressive on systemic anticancer treat- Dexter et al. 1972]. ment (e.g. fluoropyrimidines, oxaliplatin, irinote- can, bevacizumab), having received at least two The clinical development of TAS-102 was guided regimens but the majority received four regimens. by its preclinical pharmacology, showing that a The KRAS wild-type patients (278 versus 144 in twice-daily administration would yield a better each arm, respectively) received an anti-EGFR incorporation into DNA, which is responsible for antibody and a subgroup also received regorafenib its antitumor activity. This twice-daily schedule of (91 and 53, respectively). Also in this worldwide TAS-102 was well tolerated and yielded similar study (Japan, USA, Europe, Australia) TAS-102 pharmacokinetics in the USA and Japan. showed favorable activity in view of OS (7.1 versus 5.3 months; HR = 0.68; p < 0.001), PFS (2.0 versus 1.7 months; HR = 0.48; p < 0.001), and a Randomized phase II and III studies DCR of 44% versus 16% (p < 0.001). Even when These dose-finding and early efficacy studies corrected for three prognostic factors (i.e. time were followed by two placebo-controlled studies; since diagnosis of first metastasis, Eastern a randomized Japanese study (J003) and a world- Cooperative Oncology Group (ECOG) perfor- wide phase III study (RECOURSE protocol) mance status, and number of metastatic sites), the (Figure 4). In both studies the efficacy of TAS- effect of TAS-102 treatment was maintained (HR 102 was evaluated in patients with metastatic = 0.69). The effect was independent of pretreat- colorectal cancer, progressive on at least two ment (e.g. KRAS status, anti-EGFR antibody chemotherapeutic regimens. In the J003 study treatment, regorafenib). Also in this worldwide [Yoshino et al. 2012], all patients (112 in the TAS- study, the safety was comparable with the earlier 102 group and 57 in the placebo group) were phase I and II studies, with hematologic toxicity refractory or intolerant on treatment regimens in the TAS-102 group (e.g. grade 3 neutropenia including a fluoropyrimidine, oxaliplatin, and in 38% of the patients), but no toxicities typical irinotecan. The majority of the patients (87 in the for fluoropyrimidines, such as hand–foot syn- TAS-102 and 47 in the placebo group) also drome (typical for capecitabine), stomatitis, or received the anti-VEGF antibody bevacizumab coronary spasm. A population pharmacokinetic and a subgroup the anti-EGFR antibody, cetuxi- analysis showed that pharmacokinetic parameters mab (71 in the TAS-102 and 34 in the placebo did not vary with race, age, gender, or hepatic group, although 54 and 24 patients were KRAS functions, that dosing according to body surface wild-type, respectively). TAS-102 was given orally area is adequate; renal function was the primary twice daily (70 mg/m /day) for 5 days a week with determinant of the pharmacokinetics of TAS-102 350 http://tam.sagepub.com GJ Peters Figure 4. Efficacy of TAS-102 in colorectal cancer patients, progressive on multiple treatment regimens including a fluoropyrimidine, irinotecan, or oxaliplatin. The upper curve shows the overall survival curve of the Japanese J003 study [Yoshino et al. 2012], while the lower curve shows the overall survival curves of the worldwide RECOURSE study [Mayer et al. 2015]. (Figures reproduced with permission.) indicating that renal function should be monitored Conclusion and future directions in patients on TAS-102 treatment [Cleary et  al. The novel formulation TAS-102 is promising 2015]. because of its activity in colorectal cancer patients progressive on classical fluoropyrimi- The two randomized studies yielded almost dine therapies. Its mechanism of action is dis- completely identical results, with a comparable tinct from 5FU as has been shown in various increase in OS and a similar safety profile. studies [Peters and Bijnsdorp, 2012]. In multiple http://tam.sagepub.com 351 Therapeutic Advances in Medical Oncology 7(6) studies it has been shown that 5FU’s activity is et  al. 2015], showing a DCR of 64% by central related to the inhibition of TS, but not on its assessment and 72% by investigator assessment, incorporation into RNA or DNA. Although a median OS of 11 months, no drug–drug inter- TAS-102 inhibits TS (although transiently), its action, and acceptable toxicity. Other possibili- antitumor activity was most clearly related to its ties are combining TAS-102 with the anti-EGFR incorporation into DNA. It is not clear whether antibodies cetuximab or panitumumab or with its angiogenic effects contributed to the efficacy the small-molecule inhibitors of the EGFR of the treatment. Other differences include the tyrosine kinase domain gefitinib or erlotinib, or different activation pathways. 5FU is dependent one of the new second- or third-generation on either a phosphoribosyl transferase or UP/ EGFR inhibitors. uridine kinase, but TFT on TK1. Interestingly, 5FU is protected by autophagy, but TFT is not Conflict of interest statement and is therefore several fold more active in clo- The author received consulting fees from Taiho nogenic assays, which reveal such a difference Pharmaceutical and in the past (more than 4 [Bijnsdorp et al. 2010c]. years ago) financial support for research. Future studies should not only explore combi- Funding nations, but also identify predictive parameters This research received no specific grant from any to select patients likely to benefit from TAS- funding agency in the public, commercial, or not- 102. These include the equilibrative nucleoside for-profit sectors. transporter and concentrative nucleoside trans- porter [Takahashi et al. 2015], and its activation (catalyzed by TK1) [Sakamoto et al. 2015], while References positron emission tomography, using 3’-fluoro- Ackland, S. and Peters, G. (1999) Thymidine 3’[18F]-thymidine (FLT), may help to charac- phosphorylase: its role in sensitivity and resistance to terize these processes in patients [Lee et  al. anticancer drugs. Drug Resist Update 2: 205–214. 2015a, 2015b] TAS-102 appeared to upregulate Akiyama, S., Furukawa, T., Sumizawa, T., FLT accumulation in tumors. Evaluation of Takebayashi, Y., Nakajima, Y., Shimaoka, S. et al. DNA damage in surrogate tissues and plasma (2004) The role of thymidine phosphorylase, an thymidine can reveal limiting metabolic and angiogenic enzyme, in tumor progression. Cancer Sci mechanistic factors, while accumulation of sug- 95: 851–857. ars (e.g. deoxyribose) in plasma can give some Ansfield, F. and Ramirez, G. (1971) Phase I and II insight into potential other effects, such as on studies of 2’-deoxy-5-(trifluoromethyl)-uridine (NSC- angiogenesis. Due to the inclusion of TPI, which 75520). Cancer Chemother Rep 55: 205–208. has clearly shown anti-angiogenic effects in pre- clinical studies, evaluation of several other angi- Azijli, K., Van Roosmalen, I., Smit, J., Pillay, S., ogenic factors could be included. Fukushima, M., de Jong, S. et al. (2014) The novel thymidylate synthase inhibitor trifluorothymidine (TFT) and TRAIL synergistically eradicate non-small Although TAS-102 showed benefit against gas- cell lung cancer cells. Cancer Chemother Pharmacol 73: trointestinal malignancies, preclinical studies 1273–1278. clearly showed efficacy against other cancers, while its efficacy in preclinical models shows Bijnsdorp, I., Azijli, K., Jansen, E., Wamelink, M., great potential in future clinical drug combina- Jakobs, C., Struys, E. et al. (2010a) Accumulation of thymidine-derived sugars in thymidine phosphorylase tion studies, both with conventional cytotoxic overexpressing cells. Biochem Pharmacol 80: 786–796. agents and signaling targeted therapy, as well as radiotherapy. A combination of these treatments Bijnsdorp, I., Capriotti, F., Kruyt, F., Losekoot, may help to prevent recurrence of tumors due to N., Fukushima, M., Griffioen, A. et al. (2011) drug resistance. Specifically TAS-102 has great Thymidine phosphorylase in cancer cells stimulates potential to improve the treatment of gastroin- human endothelial cell migration and invasion by the secretion of angiogenic factors. Br J Cancer 104: testinal malignancies when combined with other 1185–1192. agents, such as with the VEGF inhibitor bevaci- zumab or the DNA synthesis inhibitors oxalipl- Bijnsdorp, I., Kruyt, F., Fukushima, M., Smid, atin or irinotecan. Recently the first promising K., Gokoel, S. and Peters, G. (2010b) Molecular results of the combination of TAS-102 (70 mg/ mechanism underlying the synergistic interaction m /day) and bevacizumab were reported [Kuboki between trifluorothymidine and the epidermal growth 352 http://tam.sagepub.com GJ Peters factor receptor inhibitor erlotinib in human colorectal of thymidylate synthase by 5-(trifluoromethyl)-2’- cancer cell lines. Cancer Sci 101: 440–447. deoxyuridine 5’-monophosphate. Biochemistry 33: 15086–15094. Bijnsdorp, I., Kruyt, F., Gokoel, S., Fukushima, M. and Peters, G. (2008) Synergistic interaction of Ellis, L. (2004) Angiogenesis and its role in colorectal trifluorothymidine with docetaxel (Taxotere®) after tumor and metastasis formation. Semin Oncol 31: 3–9. sequential scheduling. Cancer Sci 99: 2302–2309. El-Naggar, M., Ebbing, E., Bijnsdorp, I., Van den Bijnsdorp, I. and Peters, G. (2011) Deoxyribose Berg, J. and Peters, G. (2014) Radiosensitization protects against rapamycin induced cytotoxicity in by thymidine phosphorylase inhibitor in thymidine colorectal cancer cells in vitro. Nucleosides Nucleotides phosphorylase negative and overexpressing bladder Nucleic Acids 30: 1197–1202. cancer cell lines. Nucleosides Nucleotides Nucleic Acids 33: 413–421. Bijnsdorp, I., Peters, G., Temmink, O., Fukushima, M. and Kruyt, F. (2010c) Differential activation Emura, T., Murakami, Y., Nakagawa, F., Fukushima, of cell death and autophagy results in an increased M. and Kitazato, K. (2004a) A novel antimetabolite, cytotoxic potential for trifluorothymidine compared to TAS-102 retains its effect on FU-related resistant 5-fluorouracil in colon cancer cells. Int J Cancer 126: cancer cells. Int J Mol Med 13: 545–549. 2457–2468. Emura, T., Nakagawa, F., Fujioka, A., Ohshimo, Cao, D. and Pizzorno, G. (2004) Uridine H. and Kitazato, K. (2004b) Thymidine kinase and phosphorylase: an important enzyme in pyrimidine thymidine phosphorylase level as the main predictive metabolism and fluoropyrimidine activation. Drugs parameter for sensitivity to TAS-102 in a mouse Today (Barc) 40: 431–443. model. Oncol Rep 11: 381–387. Carmine, A., Brogden, R., Heel, R., Speight, T. and Emura, T., Nakagawa, F., Fujioka, A., Ohshimo, Avery, G. (1982) Trifluridine: a review of its antiviral H., Yokogawa, T., Okabe, H. et al. (2004c) An activity and therapeutic use in the topical treatment of optimal dosing schedule for a novel combination viral eye infections. Drugs 23: 329–353. antimetabolite, TAS-102, based on its intracellular metabolism and its incorporation into DNA. Int J Mol Cleary, J., Mayer, R., Van Cutsem, E., Yamashita, Med 13: 249–255. F. and Yoshisue, K., Ieiri, I. et al. (2015) Population pharmacokinetic (PK) analysis of TAS-102 in Emura, T., Suzuki, N., Fujioka, A., Ohshimo, H. and patients (pts) with metastatic colorectal cancer Fukushima, M. (2005) Potentiation of the antitumor (mCRC): results from 3 phase 1 trials and the phase activity of alpha, alpha, alpha-trifluorothymidine by 3 RECOURSE trial. J Clin Oncol 33(Suppl.): abstract the co-administration of an inhibitor of thymidine phosphorylase at a suitable molar ratio in vivo. Int J Oncol 27: 449–455. De Bruin, M., Temmink, O., Hoekman, K., Pinedo, H. and Peters, G. (2006) Role of platelet Emura, T., Suzuki, N., Yamaguchi, M., Ohshimo, derived endothelial cell growth factor/thymidine H. and Fukushima, M. (2004d) A novel combination phosphorylase in health and disease. Cancer Ther 4: antimetabolite, TAS-102, exhibits antitumor activity 99–124. in FU-resistant human cancer cells through a mechanism involving FTD incorporation in DNA. Int De Bruin, M., van Capel, T., van der Born, K., J Oncol 25: 571–578. Kruyt, F., Fukushima, M., Hoekman, K. et al. (2003) Role of platelet-derived endothelial cell growth Endo, M., Shinbori, N., Fukase, Y., Sawada, N., factor/thymidine phosphorylase in fluoropyrimidine Ishikawa, T., Ishitsuka, H. et al. (1999) Induction of sensitivity. Br J Cancer 88: 957–964. thymidine phosphorylase expression and enhancement of efficacy of capecitabine or 5’-deoxy-5-fluorouridine De Clercq, E. (2004) Antiviral drugs in current by cyclophosphamide in mammary tumor models. Int clinical use. J Clin Virol 30: 115–133. J Cancer 83: 127–134. Dexter, D., Wolberg, W., Ansfield, F., Helson, L. and Ford, H., Mitchell, F., Cunningham, D., Farrugia, Heidelberger, C. (1972) The clinical pharmacology D., Hill, M., Rees, C. et al. (2002) Patterns of of 5-trifluoromethyl-2’-deoxyuridine. Cancer Res 32: elevation of plasma 2’-deoxyuridine, a surrogate 247–253. marker of thymidylate synthase (TS) inhibition, Doi, T., Ohtsu, A., Yoshino, T., Boku, N., Onozawa, after administration of two different schedules Y., Fukutomi, A. et al. (2012) Phase I study of TAS- of 5-fluorouracil and the specific TS inhibitors 102 treatment in Japanese patients with advanced raltitrexed (Tomudex) and ZD9331. Clin Cancer Res solid tumours. Br J Cancer 107: 429–434. 8: 103–109. Eckstein, J., Foster, P., Finer-Moore, J., Wataya, Y. Fujiwara, Y. and Heidelberger, C. (1970) and Santi, D. (1994) Mechanism-based inhibition Fluorinated pyrimidines. 38. The incorporation http://tam.sagepub.com 353 Therapeutic Advances in Medical Oncology 7(6) of 5-trifluoromethyl-2’-deoxyuridine into the Ikeda, R., Furukawa, T., Kitazono, M., Ishitsuka, K., deoxyribonucleic acid of vaccinia virus. Mol Pharmacol Okumura, H., Tani, A. et al. (2002) Molecular basis 6: 281–291. for the inhibition of hypoxia-induced apoptosis by 2-deoxy-D-ribose. Biochem Biophys Res Commun 291: Fukushima, M., Okabe, H., Takechi, T., Ichikawa, 806–812. W. and Hirayama, R. (2002) Induction of thymidine phosphorylase by interferon and taxanes occurs Inaba, M., Mitsuhashi, J., Sawada, H., Miike, N., only in human cancer cells with low thymidine Naoe, Y., Daimon, A. et al. (1996) Reduced activity phosphorylase activity. Cancer Lett 187: 103–110. of anabolizing enzymes in 5-fluorouracil-resistant human stomach cancer cells. Jpn J Cancer Res 87: Fukushima, M., Suzuki, N., Emura, T., Yano, 212–220. S., Kazuno, H., Tada, Y. et al. (2000) Structure and activity of specific inhibitors of thymidine Kabbinavar, F., Hambleton, J., Mass, R., Hurwitz, phosphorylase to potentiate the function of antitumor H., Bergsland, E. and Sarkar, S. (2005) Combined 2’-deoxyribonucleosides. Biochem Pharmacol 59: analysis of efficacy: the addition of bevacizumab to 1227–1236. fluorouracil/leucovorin improves survival for patients with metastatic colorectal cancer. J Clin Oncol 23: George, D. (2001) Platelet-derived growth factor 3706–3712. receptors: a therapeutic target in solid tumors. Semin Oncol 28: 27–33. Kuboki, Y., Nishina, T., Shinozaki, E., Yamazaki, K., Shitara, K., Okamoto, W. et al. (2015) An investigator Green, M., Pusztai, L., Theriault, R., Adinin, R., initiated multicenter phase I/II study of TAS-102 Hofweber, M., Fukushima, M. et al. (2006) Phase I with bevacizumab for metastatic colorectal cancer study to determine the safety of oral administration of refractory to standard therapies (C-TASK FORCE). J TAS-102 on a twice daily (BID) schedule for five days Clin Oncol 33(Suppl.): abstract 3544. a week (wk) followed by two days rest for two wks, every (Q) four wks in patients (pts) with metastatic Lee, H., Oh, S., Lee, E., Chung, J., Kim, Y., Ryu, J. breast cancer (MBC). Proc Am Soc Clin Oncol et al. (2015a) Positron emission tomography imaging (abstract 10576). of human colon cancer xenografts in mice with [(18) F]fluorothymidine after TAS-102 treatment. Cancer Heidelberger, C. and Anderson, S. (1964) Chemother Pharmacol 75: 1005–1013. Fluorinated pyrimidines. XXI. The tumor inhibitory activity of 5-trifluoromethyl-2’-deoxyuridine. Cancer Lee, J., Seraj, J., Yoshida, K., Narurkar, M. and Res 24: 1979–1985. Mizuguchi, H., Strychor, S. et al. (2015b) Mass balance study of TAS-102 using 14C labeling Heidelberger, C., Boohar, J. and Kampschroer, analyzed by accelerator mass spectrometry. J Clin B. (1965) Fluorinated pyrimidines. XXIV. In vivo Oncol 33(Suppl.): abstract 2563. metabolism of 5-trifluoromethyluracil-2-C-14 and 5-trifluoromethyl-2’-deoxyuridine-2-C-14. Cancer Res Manetti, F. and Botta, M. (2003) Small-molecule 25: 377–381. inhibitors of fibroblast growth factor receptor (FGFR) tyrosine kinases (TK). Curr Pharm Des 9: 567–581. Heidelberger, C., Parsons, D. and Remy, D. (1964) Syntheses of 5-trifluoromethyluracil and Matsuoka, K., Iimori, M., Niimi, S., Tsukihara, H., 5-trifluoromethyl-2’-deoxyuridine. J Med Chem 55: Watanabe, S., Kiyonari, S. et al. (2015) Trifluridine 1–5. induces p53-dependent sustained G2 phase arrest with its massive misincorporation into DNA and few Hoff, P., Ansari, R., Batist, G., Cox, J., Kocha, W., DNA strand breaks. Mol Cancer Ther 14: 1004–1013. Kuperminc, M. et al. (2001) Comparison of oral capecitabine versus intravenous fluorouracil plus Mayer, R., Van Cutsem, E., Falcone, A., Yoshino, T., leucovorin as first-line treatment in 605 patients with Garcia-Carbonero, R., Mizunuma, N. et al. (2015) metastatic colorectal cancer: results of a randomized Randomized trial of TAS-102 for refractory metastatic phase III study. J Clin Oncol 19: 2282–2292. colorectal cancer. N Engl J Med 372: 1909–1919. Hong, D., Abbruzzese, J., Bogaard, K., Lassere, Y., Miyatani, T., Kurita, N., Utsunomiya, T., Iwata, T., Fukushima, M., Mita, A. et al. (2006) Phase I study Nishioka, M., Yoshikawa, K. et al. (2012) Platelet- to determine the safety and pharmacokinetics of oral derived endothelial cell growth factor/thymidine administration of TAS-102 in patients with solid phosphorylase inhibitor augments radiotherapeutic tumors. Cancer 107: 1383–1390. efficacy in experimental colorectal cancer. Cancer Lett 318: 199–205. Hotchkiss, K., Ashton, A. and Schwartz, E. (2003) Thymidine phosphorylase and 2-deoxyribose Miyazono, K., Okabe, T., Urabe, A., Takaku, F. and stimulate human endothelial cell migration by specific Heldin, C. (1987) Purification and properties of an activation of the integrins alpha 5 beta 1 and alpha V endothelial cell growth factor from human platelets. J beta 3. J Biol Chem 278: 19272–19279. Biol Chem 262: 4098–4103. 354 http://tam.sagepub.com GJ Peters Moghaddam, A. and Bicknell, R. (1992) Expression of trifluorothymidine metabolism in rat brain. NMR of platelet-derived endothelial cell growth factor in Biomed 12: 373–380. Escherichia coli and confirmation of its thymidine Pugmire, M. and Ealick, S. (2002) Structural phosphorylase activity. Biochemistry 31: 12141–12146. analyses reveal two distinct families of nucleoside Murakami, Y., Kazuno, H., Emura, T., Tsujimoto, phosphorylases. Biochem J 361: 1–25. H., Suzuki, N. and Fukushima, M. (2000) Different Reyes, P. and Heidelberger, C. (1965) Fluor- mechanisms of acquired resistance to fluorinated inated pyrimidines. XXVI. Mammalian thymidylate pyrimidines in human colorectal cancer cells. Int J synthetase: its mechanism of action and inhibition Oncol 17: 277–283. by fluorinated nucleotides. Mol Pharmacol 1: Nukatsuka, M., Nakagawa, F., Matsuoka, K., 14–30. Tsukihara, K. and Takechi, T. (2015a) Efficacy Sakamoto, K., Yokogawa, T., Ueno, H., Oguchi, K., of combination chemotherapy using a novel oral Kazuno, H., Ishida, K. et al. (2015) Crucial roles of chemotherapeutic agent, TAS-102, with oxaliplatin on thymidine kinase 1 and deoxyUTPase in incorporating human colorectal or gastric cancer and 5FU-resistant the antineoplastic nucleosides trifluridine and gastric cancer xenografts. Proc Annu Meet Am Assoc 2’-deoxy-5-fluorouridine into DNA. Int J Oncol 46: Cancer Res 56: abstract 2557. 2327–2334. Nukatsuka, M., Nakagawa, F., Saito, H., Sakata, Santi, D. and Sakai, T. (1971) Thymidylate M., Uchida, J. and Takechi, T. (2015b) Efficacy synthetase. Model studies of inhibition by of combination chemotherapy using a novel oral 5-trifluoromethyl-2’-deoxyuridylic acid. Biochemistry chemotherapeutic agent, TAS-102 with irinotecan 10: 3598–3607. hydrochloride on human colorectal and gastric cancer xenografts. Anticancer Res 35: 1437–1445. Sato, J., Sata, M., Nakamura, H., Inoue, S., Wada, T., Takabatake, N. et al. (2003) Role of thymidine Overman, M., Kopetz, S., Varadhachary, G., phosphorylase on invasiveness and metastasis in lung Fukushima, M., Kuwata, K., Mita, A. et al. (2008a) adenocarcinoma. Int J Cancer 106: 863–870. Phase I clinical study of three times a day oral administration of TAS-102 in patients with solid Seeliger, H., Guba, M., Koehl, G., Doenecke, A., tumors. Cancer Invest 26: 794–799. Steinbauer, M., Bruns, C. et al. (2004) Blockage of 2-deoxy-D-ribose-induced angiogenesis with Overman, M., Varadhachary, G., Kopetz, S., rapamycin counteracts a thymidine phosphorylase- Thomas, M., Fukushima, M., Kuwata, K. et al. based escape mechanism available for colon cancer (2008b) Phase 1 study of TAS-102 administered once under 5-fluorouracil therapy. Clin Cancer Res 10: daily on a 5-day-per-week schedule in patients with 1843–1852. solid tumors. Invest New Drugs 26: 445–454. Suzuki, N., Nakagawa, F., Nukatsuka, M. and Peters, G. (2014) Novel developments in the use of Fukushima, M. (2011) Trifluorothymidine exhibits antimetabolites. Nucleosides Nucleotides Nucleic Acids potent antitumor activity via the induction of DNA 33: 358–374. double-strand breaks. Exp Ther Med 2: 393–397. Peters, G., Backus, H., Freemantle, S., van Triest, B., Takahashi, Y., Bucana, C., Liu, W., Yoneda, J., Codacci-Pisanelli, G., van der Wilt, C. et al. (2002) Kitadai, Y., Cleary, K. et al. (1996) Platelet-derived Induction of thymidylate synthase as a 5-fluorouracil endothelial cell growth factor in human colon cancer resistance mechanism. Biochim Biophys Acta 1587: angiogenesis: role of infiltrating cells. J Natl Cancer 194–205. Inst 88: 1146–1151. Peters, G. and Bijnsdorp, I. (2012) TAS-102: more Takahashi, Y., Ellis, L. and Mai, M. (2003) The than an antimetabolite. Lancet Oncol 13: e518–e519. angiogenic switch of human colon cancer occurs Peters, G., Honeywell, R., Leon, L., Van simultaneous to initiation of invasion. Oncol Rep 10: Groeningen, C., Jansen, G., Ylstra, B. et al. (2009) 9–13. Role of pharmacodynamic, pharmacogenetic Takahashi, K., Yoshisue, K., Chiba, M., Nakanishi, and pharmacogenomic biomarkers of cancer T. and Tamai, I. (2015) Involvement of concentrative chemotherapy with antifolates. Pteridines 20: nucleoside transporter 1 in intestinal absorption of s115–s127. trifluridine using human small intestinal epithelial Peters, G., Schornagel, J. and Milano, G. (1993) cells. J Pharm Sci 104: 3146–3153. Clinical pharmacokinetics of anti-metabolites. Cancer Takao, S., Akiyama, S., Nakajo, A., Yoh, H., Surv 17: 123–156. Kitazono, M., Natsugoe, S. et al. (2000) Suppression Pouremad, R., Bahk, K., Shen, Y., Knop, R. and of metastasis by thymidine phosphorylase inhibitor. Wyrwicz, A. (1999) Quantitative 19F NMR study Cancer Res 60: 5345–5348. http://tam.sagepub.com 355 Therapeutic Advances in Medical Oncology 7(6) Takebayashi, Y., Akiyama, S., Akiba, S., Yamada, oxaliplatin-induced cytotoxicity to colorectal cancer K., Miyadera, K., Sumizawa, T. et al. (1996a) cells. Br J Cancer 96: 231–240. Clinicopathologic and prognostic significance of Temmink, O., Hoogeland, M., Fukushima, M. an angiogenic factor, thymidine phosphorylase, in and Peters, G. (2006b) Low folate conditions may human colorectal carcinoma. J Natl Cancer Inst 88: enhance the interaction of trifluorothymidine with 1110–1117. antifolates in colon cancer cells. Cancer Chemother Takebayashi, Y., Yamada, K., Miyadera, K., Pharmacol 57: 171–179. Sumizawa, T., Furukawa, T., Kinoshita, F. et al. Tsukihara, H., Nakagawa, F., Sakamoto, K., Ishida, (1996b) The activity and expression of thymidine K., Tanaka, N., Okabe, H. et al. (2015) Efficacy phosphorylase in human solid tumours. Eur J Cancer of combination chemotherapy using a novel oral 32A: 1227–1232. chemotherapeutic agent, TAS-102, together with Tanaka, N., Sakamoto, K., Okabe, H., Fujioka, A., bevacizumab, cetuximab, or panitumumab on human Yamamura, K., Nakagawa, F. et al. (2014) Repeated colorectal cancer xenografts. Oncol Rep 33: 2135– oral dosing of TAS-102 confers high trifluridine 2142. incorporation into DNA and sustained antitumor Uchimiya, H., Furukawa, T., Okamoto, M., activity in mouse models. Oncol Rep 32: Nakajima, Y., Matsushita, S., Ikeda, R. et al. (2002) 2319–2326. Suppression of thymidine phosphorylase-mediated angiogenesis and tumor growth by 2-deoxy-L-ribose. Temmink, O., Bijnsdorp, I., Prins, H., Losekoot, N., Cancer Res 62: 2834–2839. Adema, A., Smid, K. et al. (2010) Trifluorothymidine resistance is associated with decreased thymidine Van Cutsem, E., Twelves, C., Cassidy, J., Allman, kinase equilibrative nucleoside transporter expression D., Bajetta, E., Boyer, M. et al. (2001) Oral or increased secretory phospholipase A2. Mol Cancer capecitabine compared with intravenous fluorouracil Ther 9: 1047–1057. plus leucovorin in patients with metastatic colorectal cancer: results of a large phase III study. J Clin Oncol Temmink, O., Comijn, E., Fukushima, M. and 19: 4097–4106. Peters, G. (2004) Intracellular thymidylate synthase inhibition by trifluorothymidine in FM3A cells. Van Triest, B. and Peters, G. (1999) Thymidylate Nucleosides Nucleotides Nucleic Acids 23: 1491–1494. synthase: a target for combination therapy and determinant of chemotherapeutic response in Temmink, O., De Bruin, M., Comijn, E., Fukushima, colorectal cancer. Oncology 57: 179–194. M. and Peters, G. (2005) Determinants of trifluorothymidine sensitivity and metabolism in colon Van Triest, B., Pinedo, H., Blaauwgeers, J., van and lung cancer cells. Anticancer Drugs 16: 285–292. Diest, P., Schoenmakers, P., Voorn, D. et al. (2000) Prognostic role of thymidylate synthase, thymidine Temmink, O., De Bruin, M., Laan, A., Turksma, A., phosphorylase/platelet-derived endothelial cell growth Cricca, S., Masterson, A. et al. (2006a) The role of factor, and proliferation markers in colorectal cancer. thymidine phosphorylase and uridine phosphorylase Clin Cancer Res 6: 1063–1072. in (fluoro)pyrimidine metabolism in peripheral blood mononuclear cells. Int J Biochem Cell Biol 38: 1759– Wilson, P., Danenberg, P., Johnston, P., Lenz, H. and Ladner, R. (2014) Standing the test of time: targeting thymidylate biosynthesis in cancer therapy. Nat Rev Temmink, O., de Bruin, M., Turksma, A., Cricca, Clin Oncol 11: 282–298. S., Laan, A. and Peters, G. (2007a) Activity and substrate specificity of pyrimidine phosphorylases Yano, S., Kazuno, H., Sato, T., Suzuki, N., Emura, and their role in fluoropyrimidine sensitivity in colon T., Wierzba, K. et al. (2004) Synthesis and evaluation cancer cell lines. Int J Biochem Cell Biol 39: 565–575. of 6-methylene-bridged uracil derivatives. Part 2: optimization of inhibitors of human thymidine Temmink, O., Emura, T., De Bruin, M., Fukushima, phosphorylase and their selectivity with uridine M. and Peters, G. (2007b) Therapeutic potential phosphorylase. Bioorg Med Chem 12: 3443–3450. of the dual-targeted TAS-102 formulation in the treatment of gastrointestinal malignancies. Cancer Sci Yoshino, T., Mizunuma, N., Yamazaki, K., Nishina, 98: 779–789. T., Komatsu, Y., Baba, H. et al. (2012) TAS-102 Temmink, O., Hoebe, E., Fukushima, M. and Peters, monotherapy for pretreated metastatic colorectal G. (2007c) Irinotecan-induced cytotoxicity to colon cancer: a double-blind, randomised, placebo- cancer cells in vitro is stimulated by pre-incubation controlled phase 2 trial. Lancet Oncol 13: 993–1001. with trifluorothymidine. Eur J Cancer 43: 175–183. Zondor, S. and Medina, P. (2004) Bevacizumab: Visit SAGE journals online Temmink, O., Hoebe, E., van der Born, K., an angiogenesis inhibitor with efficacy in colorectal http://tam.sagepub.com Ackland, S., Fukushima, M. and Peters, G. (2007d) and other malignancies. Ann Pharmacother 38: SAGE journals Mechanism of trifluorothymidine potentiation of 1258–1264. 356 http://tam.sagepub.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Therapeutic Advances in Medical Oncology SAGE

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603313 TAM0010.1177/1758834015603313Therapeutic Advances in Medical OncologyG. J. Peters research-article2015 Therapeutic Advances in Medical Oncology Review Ther Adv Med Oncol Therapeutic potential of TAS-102 in the 2015, Vol. 7(6) 340 –356 DOI: 10.1177/ treatment of gastrointestinal malignancies © The Author(s), 2015. Reprints and permissions: http://www.sagepub.co.uk/ Godefridus J. Peters journalsPermissions.nav Abstract: Fluoropyrimidines form the mainstay in treatment of gastrointestinal malignancies. For decades 5-fluorouracil (5FU), was the major fluoropyrimidine. Currently it is usually given in a combination with leucovorin and oxaliplatin, i.e. FOLFOX, or irinotecan, i.e. FOLFIRI, or all three, i.e. FOLFIRINOX, but gradually it has been replaced by oral fluoropyrimidine prodrug formulations, such as tegafur-uracil and S-1 (both contain ftorafur), and capecitabine (Xeloda®). Novel drugs such as the antivascular endothelial growth factor antibody, bevacizumab, and the anti-epidermal growth factor receptor antibody, cetuximab, are often combined with one of these treatment options. However, when resistance emerged, no alternatives were available. TAS-102, a combination of trifluorothymidine and the thymidine phosphorylase inhibitor TPI in a 1:0.5 ratio, is a novel oral formulation, which is active in 5FU- resistant models, both in vitro and in xenograft models. In addition to inhibition of thymidylate synthase, the major mechanism of action of classical fluoropyrimidines, TAS-102’s major mechanism of action is incorporation into DNA, thereby causing DNA damage. TAS-102 also follows an alternative activation pathway via thymidine kinase, and is not a substrate for dihydropyrimidine dehydrogenase. All together this explains the efficacy in 5FU-resistant models. In early clinical studies, the twice-daily schedule (5 days on, 2 days rest) for 2 weeks every 4 weeks, led to a significant disease control rate in various malignancies. This schedule showed consistent activity in two randomized trials on fluoropyrimidine refractory colorectal cancer patients, reflected by an increase of 2–3 months in overall survival in the TAS-102 group compared with placebo. Considering the impressive preclinical potential of various combinations TAS-102 has the promise to become an alternative for 5FU-resistant cancer. Keywords: clinical trials, colorectal cancer, combination studies, DNA damage, TAS-102, thymidine phosphorylase inhibitor, trifluorothymidine Correspondence to: Introduction clinical evaluation was discontinued because of a Godefridus J. Peters PhD TAS-102 is an oral formulation that combines sev- poor pharmacokinetic profile and side effects. Department of Medical Oncology, VU University eral attractive features of the cytotoxic pyrimidine However, some of the administration schedules Medical Center, De analog 5-trifluoro-2’-deoxythymidine (trifluoro- resulted in a reduction of tumor size (8 out of 23 Boelelaan 1117, PO Box 7057, 1007 MB thymidine [TFT]; trifluridine [F TdR]; 5-trifluo- breast cancers and 1 out of 6 colon cancers) Amsterdam, The romethyl-2’-deoxyuridine [CFdUrd]; FTD; [Ansfield and Ramirez, 1971]. It was shown that Netherlands gj.peters@vumc.nl 2’-deoxy-5-(trifluoromethyl)uridine [F Thd]) and TFT can be phosphorylated by thymidine kinase the potent thymidine phosphorylase (TP) inhibitor to its active monophosphate form mediating TPI (tipiracil hydrochloride), in a molar ratio cytotoxicity [Heidelberger et  al. 1965], and it of 1:0.5 [Temmink et  al. 2007b] (Figure 1). It was as effective against adenocarcinoma cells as has successfully completed two randomized 5-fluoro-2’-deoxyuridine (FdUrd) [Heidelberger phase II/III studies [Yoshino et  al. 2012; Mayer and Anderson, 1964]. TFT is registered as et al. 2015]. Viroptic® [De Clercq, 2004], for use against herpes simplex virus infections and was previously approved Although TFT was synthesized by Heidelberger by the US Food and Drug Administration in 1980 and colleagues [Heidelberger et al. 1964], its initial for the treatment of primary keratoconjunctivitis 340 http://tam.sagepub.com GJ Peters serves as the co-factor for the reductive methyla- tion of dUMP to thymidine monophosphate CF HN (dTMP) (Figure 2). Inhibition of TS leads to HN intracellular depletion of deoxythymidine triphos- O N O N phate (dTTP), and subsequent dUMP accumula- HO CH tion, resulting in uracil misincorporation into the NH HCl DNA leading to DNA damage [Wilson et  al. 2014; Peters et al. 2009]. In an animal model con- tinuous treatment with TFT led to an accumula- OH H tion of dUMP [Tanaka et  al. 2014]. Normally TPI TFT dUMP can be broken down to deoxyuridine, TAS-102= T FT + TPI which will be excreted into plasma, resulting in increased deoxyuridine plasma levels, which can (1:0.5 ra o) be considered as a biomarker for effective TS Figure 1. Composition of TAS-102. inhibition [Peters et al. 2009]. This effect was also observed in animals and patients treated with a specific TS inhibitor such as raltitrexed, nola- trexed, or pemetrexed [Peters et  al. 2009; Ford and epithelial keratitis [Carmine et al. 1982]. TAS- et al. 2002]. 102 is currently registered in Japan as Lonsurf® for third-line treatment of colorectal cancer. The In addition to TFT-mediated TS inhibition, TFT current review summarizes the mechanism of itself can be incorporated into DNA [Fujiwara action of the individual components of TAS-102, and Heidelberger, 1970], for which evidence is TFT and TPI, and its development as an alterna- accumulating that this is the main mechanism of tive treatment for colorectal cancer. action of the drug. TFT is incorporated into DNA as the triphosphate form of TFT (TFT-TP) TFT-mediated cytotoxicity [Temmink et al. 2005; Emura et al. 2004c], caus- TFT shares some similarities to 5-fluorouracil ing cell death due to DNA strand-break forma- (5FU), but its differences seem responsible for its tion [Emura et  al. 2004d; Suzuki et  al. 2011; successful application as an anticancer drug [De Matsuoka et  al. 2015]. This incorporation into Bruin et  al. 2006]. The mechanism of action of DNA was related to the antitumor activity of TFT is depicted in Figure 2. TFT is phosphoryl- TAS-102 in in vivo mouse models [Tanaka et al. ated by thymidine kinase 1 (TK1) to its active 2014]. TAS-102 showed a dose-dependent and monophosphate-derivative TFT-MP, which similar antitumor effect against 5FU-resistant inhibits thymidylate synthase (TS) [Reyes and DLD-1 colon tumors (tumor growth inhibition Heidelberger, 1965; Sakamoto et al. 2015]. TS is rate 73.2% at 150 mg/kg/day) and the parent one of the rate-limiting enzymes in pyrimidine de DLD-1 tumors (tumor growth inhibition rate novo deoxynucleotide synthesis and therefore it 73.4% at 150 mg/kg/day) [Emura et al. 2004d], in plays a central role in DNA synthesis as a target contrast to conventional 5FU (continuous infu- for chemotherapeutic approaches [Van Triest and sion; inhibition rate 28.2% versus 62.3%, respec- Peters, 1999]. TFT-MP does not form a ternary tively), or an analog such as tegafur-uracil (UFT) complex and binds covalently to the active site of (inhibition rate 12.9% versus 61.2%, respectively). TS (tyrosine 146), thereby inhibiting its activity DLD-1/FdUrd resistant and DLD-1 parent [Santi and Sakai, 1971; Eckstein et  al. 1994]. tumors were similarly sensitive to TAS-102, but TFT-MP is a potent reversible inhibitor of TS DLD-1/FdUrd tumors were resistant to UFT. with a Ki of 0.38 nM [Reyes and Heidelberger, Also another 5FU-resistant model (the gastric 1965], and its activity remains inhibited when a cancer xenograft NUGC-3/5FU) was similarly constant influx of TFT is present; removal of the sensitive to oral TFT but cross-resistant to compound leads to a rapid recovery of TS activity FdUrd and TS-1. Intracellular TFT-TP is rapidly [Santi and Sakai, 1971; Temmink et  al. 2004]. eliminated from tumor cells after the removal of This is in contrast to the 5FU derivative, 5-fluoro- TFT from the culture medium, but TFT incor- 2’-deoxyuridine-5’-monophosphate (FdUMP), poration into DNA continued to increase during which inhibits TS after formation of a ternary 8 h TFT exposure of NUGC-3 human gastric complex with 5,10-methylene-tetrahydrofolate cancer cells. TFT was incorporated in a time- (CH -THF), thereby enhancing and prolonging dependent manner and not in a concentration- this inhibition [Peters et al. 2002]. CH -THF also dependent manner [Emura et  al. 2004c; Tanaka http://tam.sagepub.com 341 Therapeutic Advances in Medical Oncology 7(6) et  al. 2014]. Incorporated TFT into the DNA is cause a chain-terminating effect. From the pre- retained for at least 80% up to 24 h after the sent data it can be concluded that the DNA- wash-out procedure. These observations indi- targeted effects of TAS-102 are specific for cancer cated that TFT incorporation into DNA is impor- cells, determine the antitumor effects, and are tant. This incorporation led to inhibition of chk-1 enhanced by the inhibition of TS. phosphorylation and an increase in AP sites [Suzuki et  al. 2011]. In addition, tumor-bearing mice treated with TAS-102 at a repeated dosing TFT resistance of 75 mg/kg/day or 150 mg/kg/day showed a sig- Most chemotherapeutic regimens in the treatment nificantly higher incorporation of TFT into DNA of gastrointestinal cancer patients are 5FU-based. of the tumor compared with single dosing [Emura The presence of a fluoropyrimidine is indispensa- et al. 2004c; T anaka et al. 2014], while higher dos- ble to obtain a maximal effect. To improve treat- ing also led to an accumulation of dUMP, indicat- ment of colorectal cancer it is important that an ing inhibition of TS in vivo [Tanaka et al. 2014]. alternative chemotherapeutic regimen, such as TFT induced pronounced DNA damage due to TAS-102, also exhibits antitumor effects against enhanced DNA fragmentation resulting in most 5FU-sensitive, and more favorably, against potent antitumor activity. This indicates that mul- 5FU-resistant tumor cells. Indeed a high dose tiple daily dosing may result in better clinical level of TFT alone (200 mg/kg/day) resulted in benefits for TAS-102-treated cancer patients. tumor growth-inhibition rates of about 70% for However, although it has been reported that both 5FU-sensitive and 5FU-resistant NUGC-3 TFT-TP is a substrate for DNA polymerase α gastric cancer cells (NUGC-3/5FU) implanted [Sakamoto et al. 2015], and causes DNA damage, subcutaneously in nude mice [Emura et al. 2004d]. it is not yet known whether TFT-TP is a substrate Similar data were found for FdUrd-resistant for other DNA polymerases, and whether it might DLD-1 colorectal cancer cells (DLD-1/FdUrd) in deoxyuridine TAS-102 TPI TFT TF- dUMP thymine TS TFT-MP dTMP thymidine TFT-TP dTDP TPI dR-1-P thymine dTTP dRibose TFT incorporated into DNA; Angiogenesis? DNA damage: cell death Figure 2. Metabolism and mechanism of action of TAS-102. Trifluorothymidine (TFT) can be phosphorolyzed by thymidine phosphorylase (TP) to trifluorothymine which can be inhibited by TPI. TAS-102 is the combination of TFT and TPI (a thymidine phosphorylase inhibitor). TFT is phosphorylated by thymidine kinase 1 (TK1) to TFT-MP, which is a reversible inhibitor of thymidylate synthase (TS), which leads to depletion of thymidine monophosphate (dTMP), but an accumulation of 2’-deoxyuridine-5’-monophosphate (dUMP) (and deoxyuridine outside the cell and in plasma). TFT-MP can be phosphorylated to TFT-TP, which can be incorporated into DNA, causing DNA damage, and induce a DNA damage-response signaling, leading to G2-M accumulation and cell death. Depletion of deoxythymidine triphosphate (dTTP) by inhibition of TS, will enhance the incorporation of TFT-TP into DNA. An alternative source for dTMP is thymidine, which can be phosphorylated to dTMP by TK1. However, degradation of thymidine by TP to thymine also leads to the formation of deoxyribose-1-P (dRib-1-P), which can be degraded to deoxyribose (dRibose), and may be responsible for angiogenic effects. TPI will also inhibit this step when patients are treated with TAS-102 (adapted from [Peters et al. 2002]). 342 http://tam.sagepub.com GJ Peters mice treated with 150 mg/kg/day TFT. The resist- patients was less than 15 min [Dexter et al. 1972]; ance mechanisms of both tumors are different TFT is phosphorolyzed to trifluorothymine [Inaba et al. 1996; Murakami et al. 2000], showing (TF-Thy), which can be hydrolyzed to 5-carboxy- an advantage for TAS-102 over 5FU in uracil with the loss of the inorganic fluoride. Initial 5FU-resistant tumor cells, while TAS-102 was studies on mice have already demonstrated that also effective in vivo against 5FU-sensitive tumors the TFT degradation product TF-Thy and its cat- from different tissue types, such as human pancre- abolite 5-carboxyuracil were formed mainly in the atic and esophageal tumor cells [Emura et  al. liver, spleen, and intestines [Heidelberger et  al. 2004a, 2004d]. 1965]. Similar to normal nucleosides [Peters, 2014], TFT can easily cross the blood–brain bar- Also in vitro TFT was active against 5FU-resistant rier in low micromolar concentrations and is also DLD-1 cells (DLD-1/5FU) [Emura et al. 2004a]. predominantly metabolized to TF-Thy in the brain In DLD-1/TFT cells no increase in TS was found, [Pouremad et al. 1999]. Besides TF-Thy, the dihy- but TK activity was decreased significantly (37- dro-species of TFT and TF-Thy, the reductive cat- fold). Also H630 human colorectal carcinoma cells abolites α-trifluoromethyl-β-ureidopropionic made resistant to TFT using either a long-term acid (F MUPA) and α-trifluoromethyl-β-alanine continuous exposure schedule (H630-cTFT) or (F MBA) were detected in liver extracts. Low lev- short-term repeated exposure schedule (H630- els of fluoride ions were detected in serum and 4TFT), showed different mechanisms of resistance urine, but also in brain and liver extracts. Early [Temmink et  al. 2010]. The H630-4TFT cells clinical pharmacology studies with TFT showed exposed to TFT on a short-term basis (250 µM that the only metabolites detected in urine and TFT 4 h/week) had normal TS levels, but no TK serum samples of treated cancer patients were activity, similar to the DLD-1/TFT-resistant cells. unmodified TFT, TF-Thy, and 5-carboxyuracil H630-cTFT cells growing in medium ultimately [Heidelberger et al. 1965; Dexter et al. 1972]. containing 20 µM TFT did not have altered TS and TK levels but showed a disturbed signal trans- In a series of novel orally active 6-methylene- duction with upregulated secretory phospholipase bridged, uracil-derived inhibitors of human TP A2 expression. In both H630- TFT-resistant cell [Fukushima et  al. 2000; Yano et  al. 2004], the lines no change in TP levels was observed, although most potent human TP inhibitor was the this was less relevant, because a high TP expression 5-chloro-6-(2-iminopyr rolidin-1-yl)methyl- in colorectal cancer cells hardly influences the sen- 2,4(1H,3H)-pyrimidine dione hydrochloride sitivity to TFT [Temmink et  al. 2005; De Bruin (TPI; tipiracil hydrochloride) with an IC of 35 et  al. 2003]. In agreement with the DLD-1/TFT nM for TP, which was a poor inhibitor of uridine cells, both H630-derived TFT-resistant cell lines phosphor ylase (UP) (IC > 100 µM) [Fukushima were not cross-resistant to 5FU or the folate-based et  al. 2000], a pyrimidine phosphorylase also direct TS inhibitor GW1843, but the TK-deficient known to cleave thymidine (TdR) and other variants were cross-resistant to FdUrd (about 160- pyrimidine nucleosides. The Ki value for TPI fold). In contrast to the DLD-1/5FU, 5FU-resistant using recombinant human TP was 17 nM. TPI H630 cells (H630-R10) with increased TS levels was a potent inhibitor of TFT phosphorolysis in were cross-resistant to FdUrd and TFT, but this extracts from human liver, small intestine, and was dependent on exposure time [Temmink et al. tumor tissues. At equimolar doses TPI increased 2005]. C and area under curve (AUC) of orally max administered TFT to rodents or monkeys (10 It can be concluded that TAS-102 is active in mg/kg) [Fukushima et al. 2000; Y ano et al. 2004], 5FU-resistant models, while resistance to TFT is which was most pronounced in monkeys (Figure 3), multifactorial but different from 5FU. This offers due to differences in expression of pyrimidine opportunities to use this information to select phosphorylases in these animals [Ackland and patients for the best treatment option. Peters, 1999; Cao and Pizzorno, 2004; Pugmire and Ealick, 2002]. Pharmacokinetics studies were also designed to optimize the molar drug ratio of TPI increases bioavailability of TFT in vivo TFT:TPI to reach maximal TFT plasma levels. The main pharmacokinetics of TFT [Dexter et al. With a TFT:TPI molar ratio of 1:0.5 optimal 1972] resemble that of most antimetabolites with a TFT concentrations in the plasma were obtained short half-life [Peters et  al. 1993]. The mean [Emura et  al. 2005], and this formulation was plasma half-life of single TFT injected to cancer developed as TAS-102. At a co-administration of http://tam.sagepub.com 343 Therapeutic Advances in Medical Oncology 7(6) (a) (b) 40 16 35 14 30 12 25 10 20 8 15 6 10 4 5 2 0123 45 67 8 Time after administration (min) Time after administration (hr) Figure 3. Effect of TPI on trifluorothymidine (TFT) pharmacokinetics. Plasma TFT levels in mice (a) and monkeys (b) were measured following oral administration in the presence and absence of TPI. TFT (black circles) was administered in doses of 50 mg/kg (normal mice) or 10 mg/kg (normal monkeys), or in combination with an equimolar amount of TPI (white circles). Values are means of several experiments (n = six mice; n = three monkeys). (Data adapted from [Fukushima et al. 2000] with permission.) 1 M TFT (10 mg/kg) and > 0.5 M TPI, a maxi- incorporation of TFT into DNA [Temmink et al. mum and constant level of 15 µg TFT/ml was 2005]. Probably TK1 has favorable enzyme prop- found, associated with a maximally augmented erties for the TFT-activation pathway by being antitumor activity for gastrointestinal cancer cells maximally saturated, which is hardly influenced xenografted into mice [Emura et  al. 2005]. by TFT degradation by TP. TPI only affected Steady levels of TFT in plasma obtained with a TFT-mediated cytotoxicity at very short expo- divided dosing of TFT within an adequate time sures in cells expressing very high TP [Temmink period resulted in optimal DNA incorporation et al. 2005]. This means that the mode of in vitro and subsequent antitumor activity [Emura et  al. cytotoxicity exerted by TFT is also dependent on 2004c]. the exposure times used. The effect of TPI was not dependent on the activity of TP, since all High TdR levels may reduce the antitumor effect models displayed different activities of TP. of TFT. Administration of TAS-102 will not only inhibit TFT degradation but can also inhibit TdR It can be concluded that the addition of TPI degradation, which can lead to an increase of improved the pharmacology of TFT drastically, intracellular TdR [Emura et al. 2004b]. TAS-102 by almost completely inhibiting TFT degrada- or TPI will not affect the concentration of uridine tion, prolonging its half-life and drug exposure, or deoxycytidine, since TPI does not inhibit UP and enhanced its incorporation into DNA. or deoxycytidine degradation. However, it is pos- sible that TAS-102 can increase the deoxyuridine concentration since it causes a dUMP accumula- Tumor angiogenesis tion [Tanaka et al. 2014]. TPI is a potent inhibitor of TP, also known as platelet-derived endothelial cell growth factor The addition of TPI is only important for in vivo (PDECGF) [Ackland and Peters, 1999; studies, since in vitro studies showed that, despite Moghaddam and Bicknell, 1992], which is an high TFT phosphorolysis, high TP-expressing angiogenesis growth factor [Miyazono et  al. colorectal Colo320TP1 and nonsmall cell lung 1987]. Angiogenesis is an important process in H460TP2 cancer cells are not more resistant to stimulating tumor vascularization and targeting TFT, while addition of TPI did not increase TFT angiogenesis is an important novel therapeutic sensitivity [Temmink et al. 2005; De Bruin et al. approach [Ellis, 2004]. Most anti-angiogenic 2003]. A moderate almost two-fold increase in drugs target growth factors (and their receptors) formation of active TFT metabolites was found, or inhibit endothelial cell proliferation or/and sig- although it was not related to increased nal transduction. Vascular endothelial growth 344 http://tam.sagepub.com TFT levels (µg/ml) TFT levels (µg/ml) GJ Peters factor (VEGF), but also fibroblast growth factor activation of focal adhesion kinase (FAK) and (FGF), PDECGF, and their tyrosine kinase p70/S6, the downstream kinase of the mechanis- receptors are the major regulators of angiogenesis tic target of rapamycin (mTOR), which regulates [Manetti and Botta, 2003; George, 2001]. TP/ cell proliferation, metabolism, and also angiogen- PDECGF overexpression is often associated with esis. mTOR and FAK seem responsible for the VEGF overexpression. Bevacizumab (Avastin®) invasive potential of TP. TPI can block these pro- depletes VEGF levels and is effective in combina- cesses and, in vivo [Emura et  al. 2005; Akiyama tion with 5FU-based regimens for colorectal can- et al. 2004; T akao et al. 2000], it was demonstrated cer. Thymidine exposure of TP-overexpressing that TPI significantly inhibited PDECGF/ cells leads to an increase of various angiogenic TP-induced neovascularization in a dose-depend- factors (bFGF, interleukin-8, and tumor necrosis ent manner in mice models. In a specific model, factor [TNF]-α, but not VEGF), which enhanced with KB cells transfected with TP leading to a migration and invasion of human umbilical vein clinically not relevant overexpression of TP (KB/ endothelial cells [Bijnsdorp et al. 2011]. TP cells), TPI decreased the growth rate of these KB/TP cells and increased the apoptotic index, In addition to VEGF, increased TP/PDECGF indicating a potential antitumor activity of TPI as expression is seen in colorectal tumor tissue com- a single agent [Takao et al. 2000]. pared with normal tissue [Takebayashi et  al. 1996b], and high PDECGF/TP levels are a prog- TAS-102 was also able to reduce the number of nostic factor for poor survival in colorectal liver metastases in a nude mouse model [Emura [Takebayashi et  al. 1996a] and gastric cancers et al. 2004a]; TPI alone decreased the chemotac- [reviewed in De Bruin et al. 2006]. PDECGF/TP tic motility and basement membrane invasion of is also overexpressed in tumor-infiltrating cells the above-mentioned KB/TP cells [Takao et  al. (mainly macrophages) and colon cancer cells 2000], suppressed the number of liver metastases themselves [De Bruin et al. 2006; Van Triest et al. macroscopically, and markedly diminished the 2000; Takahashi et  al. 1996]. High blood vessel invasive activity [Sato et  al. 2003]. Due to the density is well correlated with increased potent anti-invasive and antimetastatic activity of PDECGF/TP expression and is associated with TPI, TAS-102 may have multiple mechanisms of metastasis formation in several tumors [Takahashi action in clinical use. et al. 1996, 2003]. Both VEGF and PDECGF/TP are important in human angiogenesis induced by The expression of TP in tumors shows a larger both tumor and normal cells and therefore these variation between malignancies with the same factors and their receptors are good targets for pathology, but also between different types of antiangiogenic therapy [De Bruin et  al. 2006]. tumors [De Bruin et  al. 2006]. When TP is low, Tumor growth and metastasis are dependent on a chemotherapeutic drugs often upregulate sufficient blood supply and therefore inhibition of PDECGF/TP [Endo et al. 1999; Fukushima et al. tumor-induced angiogenesis in combination with 2002]. This is an advantage for the oral 5FU classic cytotoxic chemotherapy may be a strategy prodrug capecitabine ((+)-pentyl 1-(5-deoxy-β- to improve survival for patients with solid tumors, D-ribofuranosyl)-5-fluoro-1,2-dihydro-2-oxo-4- as was already shown in preclinical models when pyrimidinecarbamate) [Van Cutsem et  al. 2001; an anti-angiogenic agent was combined with Hoff et al. 2001], which is activated by PDECGF/ cytotoxic agents [Zondor and Medina, 2004; TP and for which a low expression negatively Kabbinavar et al. 2005]. influences therapeutic outcome of capecitabine- based chemotherapy [Ackland and Peters, 1999]. The downstream mediator of PDECGF/TP However, activation of the capecitabine interme- 2-deoxy-D-ribose is rapidly formed [Bijnsdorp diate 5-fluoro-5’-deoxyuridine (5’DFUR) to 5FU et  al. 2010a] (Figure 2), and its increased levels can also be mediated by UP [Cao and Pizzorno, promote angiogenesis by enhancing chemotaxis 2004; Temmink et al. 2006a, 2007a], but TPI is a of vascular endothelial cells [Uchimiya et  al. poor inhibitor of UP [Fukushima et  al. 2000]. 2002], which may confer resistance to apoptosis Since TFT is a poor substrate for UP, a high activ- induced by hypoxia [Ikeda et  al. 2002]. ity of UP will unlikely affect the efficacy of TFT. Deoxyribose has shown angiogenic properties in In vivo data showed that TAS-102 is only effective various in vitro and in vivo studies [Seeliger et al. in inducing cytotoxicity when systemic TPI is pre- 2004; Hotchkiss et  al. 2003], and it was shown sent, but acts against both undetectable and high that it can stimulate invasion and migrations by TP-expressing colon cancer cells. http://tam.sagepub.com 345 Therapeutic Advances in Medical Oncology 7(6) Table 1. Effective combinations of trifluorothymidine or TPI (in vitro) or TAS-102 (in vivo) with conventional chemotherapy targeted against DNA and novel therapeutics targeting protein kinases. Drug Combination drug Model system In vitro/in Outcome Postulated Reference vivo mechanism Trifluorothymidine Oxaliplatin Colon cancer In vitro Synergistic Increased DNA Temmink et al. adducts [2007d] TAS-102 Oxaliplatin Colon and In vivo Synergistic Nukatsuka et al. gastric cancer [2015a] Trifluorothymidine Irinotecan Colon cancer In vitro Synergistic Increased DNA Temmink et al. damage and [2007c] apoptosis TAS-102 Irinotecan Colon and In vivo Nukatsuka et al. gastric cancer [2015b] Trifluorothymidine Docetaxel Colon cancer In vitro Synergistic Cell-cycle arrest; Bijnsdorp et al. cell kill [2008] Trifluorothymidine Antifolates Colon cancer In vitro Synergistic/ DNA damage Temmink et al. additive [2006b] TPI Rapamycin Colon cancer In vitro Synergistic TPI prevents Bijnsdorp and autophagy Peters [2011] Trifluorothymidine Tumor necrosis Lung cancer In vitro Synergistic Induction caspase Azijli et al. [2014] pathway factor-related apoptosis-inducing ligand (TRAIL) Trifluorothymidine Radiation Colon cancer In vitro Synergistic Decreased repair El-Naggar et al. DNA damage [2014] TAS-102 Radiation Colon cancer In vivo Sensitization Angiogenesis and Miyatani et al. [2012] decreased DNA repair Trifluorothymidine Erlotinib Colon cancer In vitro Synergistic S-phase arrest; no Bijnsdorp et al. DNA repair [2010b] TAS-102 Cetuximab, Colon cancer In vivo Tsukihara et al. panitumumab [2015] TAS-102 Bevacizumab Colon cancer In vivo Increased TFT- Tsukihara et al. phosphates [2015] PDECGF/TP clearly promotes angiogenesis, [Temmink et  al. 2006b], oxaliplatin [Temmink possibly in conjunction with other growth factors. et  al. 2007d], or irinotecan (CPT-11) [Temmink This pro-angiogenic effect seems to be mediated et  al. 2007c], in different schedules in order to by breakdown products of thymidine, such as determine their interactions. At low folate condi- deoxyribose-1-phosphate. Inhibition of thymi- tions TFT and folate-based TS inhibitors (e.g. dine phosphorolysis by TPI has an anti-angio- raltitrexed) showed schedule-dependent syner- genic effect. Whether inhibition of angiogenesis gism in growth inhibition, two-sided TS inhibi- contributes to the antitumor activity of TAS-102 tion, and DNA damage induction, whereas at in patients needs further investigation. high folate conditions only additive effects were seen [Temmink et al. 2006b]. Combination studies The sensitivity of colon cancer cells to oxaliplatin Novel treatment options often consist of combi- could be increased by simultaneous exposure to nations of drugs in which current chemothera- TFT [Temmink et  al. 2007d], resulting in peutic regimens are combined with, for example, increased Pt-DNA-adduct formation, and subse- protein kinase-targeting drugs, immunotherapy, quent increased DNA damage induction and or radiation therapy. TAS-102 is an excellent can- apoptosis induction. The TFT-oxaliplatin combi- didate for combination with other cytotoxic nation was dose-schedule dependent, since TFT agents. In in vitro studies potential TAS-102 com- pre-incubation decreased oxaliplatin-induced binations were extensively investigated by combi- cytotoxicity to colorectal cancer cells. Recently it nations with other anticancer agents (Table 1). was also shown that this combination was syner- TFT was combined with other TS inhibitors gistic in vivo [Nukatsuka et  al. 2015a]. For the 346 http://tam.sagepub.com GJ Peters combination of TFT and SN38, the active metab- the repair of radiation-induced DNA damage, olite of irinotecan, the most pronounced synergis- and that TPI would have no effect, which was tic interactions were found when colorectal cancer indeed observed in vivo (TAS-102) [Miyatani cells were pre-incubated with TFT before SN38 et al. 2012], and in vitro [El-Naggar et al. 2014]. exposure, which resulted in increased DNA strand-break formation and cell death [Temmink In summary TAS-102 has the potential to increase et al. 2007c]. Also in several in vivo models of colo- the effect of a variety of different drugs, affecting rectal and gastric cancer the combination of TAS- their mechanism of action at critical points such 102 and irinotecan was superior to single agents as DNA repair of drug-induced lesions. The syn- without increased toxicity [Nukatsuka et  al. ergism of drugs used in common combination in 2015b]. TFT induces an uncommon effect on the colorectal cancer, such as oxaliplatin and irinote- cell cycle (G2-M accumulation and tetraploidy) can, is especially promising. [Bijnsdorp et  al. 2010c], which explains why the combination docetaxel appeared to be schedule dependent. A pre-incubation of docetaxel fol- Clinical trials lowed by TFT was synergistic, due to increased cell kill, polynucleation, and mitotic spindle inhi- Early phase I and II studies bition, accompanied by phosphorylation of chk2 The initial antitumor effects of TFT against colon and dephosphorylation of cdc25 [Bijnsdorp et al. cancer were reported in 1971, where it was shown 2008]. The reverse sequence was antagonistic. that repeated administration of TFT can produce TFT’s mechanism of cell kill was mediated by the reduction in tumor size of patients with breast intrinsic pathway (via the mitochondrial and colon cancer [Ansfield and Ramirez, 1971]. cytochrome c pathway, leading to caspase 9 cleav- However, systemic administration of TFT alone age). This is probably related to the TFT-induced (2.5 mg/kg/day) in divided doses every 3 h for p-53-dependent arrest in the G2 phase that was 8–13 days, resulted in severe bone-marrow associated with a proteasome-dependent decrease depression. TFT-mediated side effects were pri- in cyclin B1 [Matsuoka et  al. 2015]. It seemed marily confined to the hematopoietic system with likely that additional induction of the extrinsic less damage of the gastrointestinal tract compared pathway via caspase 8 cleavage would be effective. with 5FU and FdUrd [Ansfield and Ramirez, Indeed TNF-related apoptosis-inducing ligand 1971; Dexter et al. 1972]. The TFT early clinical (TRAIL), a specific inducer of the extrinsic path- trials were discontinued because of the short half- way, via binding to the death receptors 4 and 5, life due to its rapid clearance and extensive degra- was synergistic with TFT [Azijli et  al. 2014]. dation by PDECGF/TP in vivo. This likely Since many colorectal patients are sensitive to the resulted in the moderate antitumor efficacy that anti-epidermal growth factor receptor (EGFR) was observed (Table 2). antibody cetuximab (in case tumor KRAS is wild type), the combination of TFT with an EGFR TFT re-entered clinical development as TAS- inhibitor was also investigated. The small mole- 102, and in several US phase I clinical trials dos- cule EGFR inhibitor erlotinib showed synergism ing was optimized (summarized in Table 2). In in cells with a wild-type EGFR and additivity in the first phase I trial (TAS102-9801) TAS-102 cells with a mutant EGFR [Bijnsdorp et  al. was orally administered to patients with solid 2010b], erlotinib appeared to inhibit the prosur- tumors once daily for 14 days every 3 weeks. The vival pathway (AKT and MAPK) induced by maximum-tolerated dose (MTD) was 50 mg/m / TFT. Likewise in vivo combinations of TAS-102 day with granulocytopenia as the dose-limiting with the anti-EGFR antibodies cetuximab and toxicity (DLT) at 100 mg/m /day [Hong et  al. panitumumab resulted in a more than additive 2006]. In this schedule drug accumulation was activity, while the combination of bevacizumab observed, since the AUC increased 2–2.5-fold with TAS-102 was more effective [Tsukihara et al. after 2 weeks, possibly explaining the toxicity. In 4 2015]. Interestingly bevacizumab increased the out of 14 patients a stable disease (SD) was formation of TFT phosphate. Since many nucleo- observed. In the second trial (TAS102-9802) side analogs are excellent radiosensitizers, and once-daily TAS-102 was given orally (50–110 mg/ since 5FU is used for the treatment of patients m /day) to patients with gastrointestinal malig- with rectal cancer, TAS-102 was investigated for nancies for 5 days/week for 2 weeks repeated its potential radiosensitizing effect [Miyatani et al. every 4 weeks [Overman et  al. 2008b]. This 2012]. It was reasoned that TFT would inhibit schedule with the 2-day treatment rest allowed http://tam.sagepub.com 347 Therapeutic Advances in Medical Oncology 7(6) 348 http://tam.sagepub.com Table 2. Overview of phase I and II studies with TAS-102 at different schedules. Study Dose/scheme Maximum Dose-limiting Patients/disease Efficacy Reference tolerated toxicity dose Phase I/II Trifluorothymidine alone 2.5 Every 3 h; 2.5 mg/kg/ Bone marrow 6 colon 23 breast Some short PR Ansfield et al. [1971] mg/kg/day 8–13 days day Phase I Once daily for 14 days every 3 weeks 50 mg/m / Granulocytopenia 14 various 4 stable Hong et al. [2006] (9801) (50–100 mg/m /day) day disease Phase I Once daily for 5 days for 2 weeks every 4 100 mg/m / Granulocytopenia 24 various 7 stable Overman et al. (9802) weeks (50–110 mg/m /day day disease [2008b] Phase I Once daily for 5 days for 1 week every 3 160 mg/m / Granulocytopenia 39 various 11 stable Overman et al. (9803) weeks (100–180 mg/m /day) day disease [2008b] Phase I Twice daily for 5 days for 2 weeks every 4 50 mg/m / Granulocytopenia 19 breast 12 stable Green et al. [2006] (9804) weeks (50–80 mg/m /day) day disease Phase I Three times daily for 5 days for 2 weeks 70 mg/m / Granulocytopenia 15 mostly 9 stable Overman et al. (9805) every 4 weeks (60–80 mg/m /day) day gastrointestinal disease [2008a] Phase 1 Twice daily for 5 days for 2 weeks every 4 70 mg/m / Neutropenia 21 gastrointestinal (18 12 stable Doi et al. [2012] (J001) weeks (30–70 mg/m /day) day colorectal) disease Phase II Twice daily for 5 days for 2 weeks every 4 18 gastric 1 stable Mayer et al. [2015] (9806) weeks (50 mg/m /day) disease (supplementary data) The studies 9801–9806 (TAS102-9801 to TAS102-9806) were performed in the US; study J001 was a Japanese study; PR, partial response. GJ Peters the administration of higher doses of TAS-102 in the US studies grades 1 and 2 toxicity consisted compared with the continuous daily schedule. of nausea (66%), fatigue (64%), and neutropenia Granulocytopenia was dose limiting, while in 7 (55%), which were also seen as grades 3 and 4, out of 24 patients SD was observed. In a third but in general treatment-related toxicities were phase I study (TAS102-9803) patients with solid reversible. tumors received TAS-102 once daily (doses rang- 2 2 ing from 100 mg/m /day to 140 mg/m /day for 5 In a phase II study in the US (TAS102-9806) 18 days every 3 weeks) in order to determine the patients (most pretreated with a fluoropyrimidine MTD [Overman et al. 2008b]. At 120 mg/m /day regimen and progressive) with gastric cancer were patients experienced severe granulocytopenia, treated with the twice-daily schedule at 50 mg/ which was considered to be the DLT. Other tox- m /day. All patients progressed within four cycles, icities observed included neutropenia, mild to and the study was closed early (see supplemen- moderate nausea, vomiting, diarrhea, fatigue, and tary data of Mayer and colleagues [Mayer et  al. rash. Out of 39 patients, SD was observed in 11 2015]). The toxicity profile was similar to that of patients. the phase I studies. In general the MTD in US patients was lower than in the Japanese study, Other TAS-102 phase I trials applied two or three which is most likely not due to the ethnic back- times a day administration schedules, since divided ground but to the difference in pretreatment; daily dosing of TFT resulted in higher antitumor most US patients received more pretreatments. activity in preclinical studies due to increased For example, a median of more than five prior incorporation of TFT into DNA. Furthermore, treatments was given to patients with breast the previous once-daily TAS-102 phase I trials cancer in the TAS102-9804 study, including showed a short TFT half-life (about 2 h). A phase cyclophosphamide, which can compromise the I trial (TAS102-9805) was carried out at the bone-marrow reserve. A phase I study (TAS102- University of Texas MD Anderson Cancer Center 101) in the USA preceding the RECOURSE (Houston, TX, USA) using a three-times daily phase III study was limited to patients with meta- 2 2 (60–80 mg/m /day) schedule (5 days/week for 2 static colon cancer. The dose of 70 mg/m /day weeks repeated every 4 weeks) with 15 patients was shown to be tolerable, underlining that toxic- with solid tumors receiving TAS-102 orally. It was ity was related to pretreatment. concluded that TAS-102 was well tolerated with manageable hematologic (most common grade 3/4 neutropenia) and nonhematologic (e.g. nau- Pharmacokinetics sea, vomiting, fatigue, colitis) toxicities [Overman The pharmacokinetics of TAS-102 was investi- et  al. 2008a]. SD was observed in nine patients. gated in the phase I studies but most extensively The suggested phase II TAS-102 dose was 70 mg/ in the J001 study in which TAS-102 was given at 2 2 m /day. Another phase I trial (TAS102-9804) was 30–70 mg/m /day in a twice-daily schedule for 5 carried out to determine the phase II dose and the days during 2 weeks repeated every 4 weeks [Doi DLT in 19 patients with metastatic breast cancer et  al. 2012]. The pharmacokinetics in Japanese [Green et  al. 2006]. Patients received TAS-102 patients seemed comparable to that in US 2 2 orally at an initial dose level of 80 mg/m /day in a patients, for example, at 50 mg/m /day plasma twice-daily schedule (5 days/week for 2 weeks levels were comparable with those of patients in repeated every 4 weeks). Clinical activity (12 SD) the same schedule [Green et  al. 2006]. TFT was seen including prolonged disease control (> showed a slightly nonlinear pharmacokinetics, 12 weeks). It was concluded that TAS-102 is an for example, the C increased from 1009 (at 30 max 2 2 active agent against heavily pretreated metastatic mg/m /day) to 3338 ng/ml at 70 mg/m /day; for breast cancer patients, with primarily hematologic the AUC these values were 2037–8678 ng*h/ 0–10 toxicities (mainly grade 3/4 granulocytopenia and ml. The pharmacokinetics was performed on grade 4 thrombocytopenia), and the recom- days 1 and 12, enabling the investigation of mended dose was 50 mg/m /day using this sched- potential accumulation as was observed in the ule. In a Japanese phase I study (J001) TAS-102 first phase I studies. Also in this study an accu- was also given in the same schedule twice daily mulation of the drug was observed, which was (30–70 mg/m /day) to 21 patients with gastroin- most pronounced at the highest dose of 70 mg/ testinal malignancies (mainly colorectal cancer), m /day, for example, the C (reached between max resulting in a higher MTD of 70 mg/m /day, with 1.3 and 1.9 h) increased from 3338 ng/ml to 11 patients with SD [Doi et al. 2012]. In summary 4752 ng/ml. The increase in AUC was more 0–10 http://tam.sagepub.com 349 Therapeutic Advances in Medical Oncology 7(6) pronounced (also at the lower levels) and 2 days rest for 2 weeks and repeated after 4 weeks. increased from 8678 ng*h/ml to 20,950 ng*h/ In the Japanese study the disease control rate ml, with a tendency that the T½ also increased, (DCR) was 43.8% versus 10.5% (p < 0.0001), but only up to 1.5-fold, and was about 2 h at 12 respectively. The overall survival (OS) was 9.0 days. Interestingly the metabolite trifluorothy- months and 6.6 months (hazard ratio [HR] = mine decreased after 12 days to about 60% of 0.56; 95% confidence interval: 0.39–0.81; p = that at day 1. The C of TPI was about 70 ng/ 0.0011), respectively. For progression-free sur- max ml and was reached after about 2.3 h, with no vival (PFS) these values were 2.0 months and 1.0 significant difference between day 1 and day 12, months (HR = 0.41), respectively. In the TAS- although the AUC tended to increase from 102 group an improved OS was observed in 0–10 281 ng*h/ml to 317 ng*h/ml at the 70 mg/m / patients with wild-type and mut-KRAS, but it day dose. For both the C and AUC a linear was more pronounced and consistent in the mut- max 0–10 significant inverse relationship (r = -0.678 and KRAS group (HR wt/mt = 1.48; p = 0.045). The r = -0.753, respectively; both p < 0.001) was safety profile was comparable with that observed observed with the relative change in neutrophil in the earlier US and Japanese phase I and II count. A recent mass-balance study in patients studies, with bone-marrow suppression and gas- showed that 60% of the dose of TFT was recov- trointestinal events. ered, mostly in urine, and excreted as TFT itself, trifluorothymine, and TFT glucuronide, In the RECOURSE study a similar protocol was while TPI was mostly recovered in feces as TPI used as in the J003 study, using the same dose (70 and partially as 6-hydroxymethyluracil [Lee mg/m /day), randomized in a 2:1 ratio (534 versus et al. 2015a, 2015b], which was in line with the 266 patients) [Mayer et  al. 2015]. All patients early historical data [Heidelberger et  al. 1965; were progressive on systemic anticancer treat- Dexter et al. 1972]. ment (e.g. fluoropyrimidines, oxaliplatin, irinote- can, bevacizumab), having received at least two The clinical development of TAS-102 was guided regimens but the majority received four regimens. by its preclinical pharmacology, showing that a The KRAS wild-type patients (278 versus 144 in twice-daily administration would yield a better each arm, respectively) received an anti-EGFR incorporation into DNA, which is responsible for antibody and a subgroup also received regorafenib its antitumor activity. This twice-daily schedule of (91 and 53, respectively). Also in this worldwide TAS-102 was well tolerated and yielded similar study (Japan, USA, Europe, Australia) TAS-102 pharmacokinetics in the USA and Japan. showed favorable activity in view of OS (7.1 versus 5.3 months; HR = 0.68; p < 0.001), PFS (2.0 versus 1.7 months; HR = 0.48; p < 0.001), and a Randomized phase II and III studies DCR of 44% versus 16% (p < 0.001). Even when These dose-finding and early efficacy studies corrected for three prognostic factors (i.e. time were followed by two placebo-controlled studies; since diagnosis of first metastasis, Eastern a randomized Japanese study (J003) and a world- Cooperative Oncology Group (ECOG) perfor- wide phase III study (RECOURSE protocol) mance status, and number of metastatic sites), the (Figure 4). In both studies the efficacy of TAS- effect of TAS-102 treatment was maintained (HR 102 was evaluated in patients with metastatic = 0.69). The effect was independent of pretreat- colorectal cancer, progressive on at least two ment (e.g. KRAS status, anti-EGFR antibody chemotherapeutic regimens. In the J003 study treatment, regorafenib). Also in this worldwide [Yoshino et al. 2012], all patients (112 in the TAS- study, the safety was comparable with the earlier 102 group and 57 in the placebo group) were phase I and II studies, with hematologic toxicity refractory or intolerant on treatment regimens in the TAS-102 group (e.g. grade 3 neutropenia including a fluoropyrimidine, oxaliplatin, and in 38% of the patients), but no toxicities typical irinotecan. The majority of the patients (87 in the for fluoropyrimidines, such as hand–foot syn- TAS-102 and 47 in the placebo group) also drome (typical for capecitabine), stomatitis, or received the anti-VEGF antibody bevacizumab coronary spasm. A population pharmacokinetic and a subgroup the anti-EGFR antibody, cetuxi- analysis showed that pharmacokinetic parameters mab (71 in the TAS-102 and 34 in the placebo did not vary with race, age, gender, or hepatic group, although 54 and 24 patients were KRAS functions, that dosing according to body surface wild-type, respectively). TAS-102 was given orally area is adequate; renal function was the primary twice daily (70 mg/m /day) for 5 days a week with determinant of the pharmacokinetics of TAS-102 350 http://tam.sagepub.com GJ Peters Figure 4. Efficacy of TAS-102 in colorectal cancer patients, progressive on multiple treatment regimens including a fluoropyrimidine, irinotecan, or oxaliplatin. The upper curve shows the overall survival curve of the Japanese J003 study [Yoshino et al. 2012], while the lower curve shows the overall survival curves of the worldwide RECOURSE study [Mayer et al. 2015]. (Figures reproduced with permission.) indicating that renal function should be monitored Conclusion and future directions in patients on TAS-102 treatment [Cleary et  al. The novel formulation TAS-102 is promising 2015]. because of its activity in colorectal cancer patients progressive on classical fluoropyrimi- The two randomized studies yielded almost dine therapies. Its mechanism of action is dis- completely identical results, with a comparable tinct from 5FU as has been shown in various increase in OS and a similar safety profile. studies [Peters and Bijnsdorp, 2012]. In multiple http://tam.sagepub.com 351 Therapeutic Advances in Medical Oncology 7(6) studies it has been shown that 5FU’s activity is et  al. 2015], showing a DCR of 64% by central related to the inhibition of TS, but not on its assessment and 72% by investigator assessment, incorporation into RNA or DNA. Although a median OS of 11 months, no drug–drug inter- TAS-102 inhibits TS (although transiently), its action, and acceptable toxicity. Other possibili- antitumor activity was most clearly related to its ties are combining TAS-102 with the anti-EGFR incorporation into DNA. It is not clear whether antibodies cetuximab or panitumumab or with its angiogenic effects contributed to the efficacy the small-molecule inhibitors of the EGFR of the treatment. Other differences include the tyrosine kinase domain gefitinib or erlotinib, or different activation pathways. 5FU is dependent one of the new second- or third-generation on either a phosphoribosyl transferase or UP/ EGFR inhibitors. uridine kinase, but TFT on TK1. Interestingly, 5FU is protected by autophagy, but TFT is not Conflict of interest statement and is therefore several fold more active in clo- The author received consulting fees from Taiho nogenic assays, which reveal such a difference Pharmaceutical and in the past (more than 4 [Bijnsdorp et al. 2010c]. years ago) financial support for research. Future studies should not only explore combi- Funding nations, but also identify predictive parameters This research received no specific grant from any to select patients likely to benefit from TAS- funding agency in the public, commercial, or not- 102. These include the equilibrative nucleoside for-profit sectors. transporter and concentrative nucleoside trans- porter [Takahashi et al. 2015], and its activation (catalyzed by TK1) [Sakamoto et al. 2015], while References positron emission tomography, using 3’-fluoro- Ackland, S. and Peters, G. (1999) Thymidine 3’[18F]-thymidine (FLT), may help to charac- phosphorylase: its role in sensitivity and resistance to terize these processes in patients [Lee et  al. anticancer drugs. Drug Resist Update 2: 205–214. 2015a, 2015b] TAS-102 appeared to upregulate Akiyama, S., Furukawa, T., Sumizawa, T., FLT accumulation in tumors. Evaluation of Takebayashi, Y., Nakajima, Y., Shimaoka, S. et al. DNA damage in surrogate tissues and plasma (2004) The role of thymidine phosphorylase, an thymidine can reveal limiting metabolic and angiogenic enzyme, in tumor progression. Cancer Sci mechanistic factors, while accumulation of sug- 95: 851–857. ars (e.g. deoxyribose) in plasma can give some Ansfield, F. and Ramirez, G. (1971) Phase I and II insight into potential other effects, such as on studies of 2’-deoxy-5-(trifluoromethyl)-uridine (NSC- angiogenesis. Due to the inclusion of TPI, which 75520). Cancer Chemother Rep 55: 205–208. has clearly shown anti-angiogenic effects in pre- clinical studies, evaluation of several other angi- Azijli, K., Van Roosmalen, I., Smit, J., Pillay, S., ogenic factors could be included. Fukushima, M., de Jong, S. et al. (2014) The novel thymidylate synthase inhibitor trifluorothymidine (TFT) and TRAIL synergistically eradicate non-small Although TAS-102 showed benefit against gas- cell lung cancer cells. Cancer Chemother Pharmacol 73: trointestinal malignancies, preclinical studies 1273–1278. clearly showed efficacy against other cancers, while its efficacy in preclinical models shows Bijnsdorp, I., Azijli, K., Jansen, E., Wamelink, M., great potential in future clinical drug combina- Jakobs, C., Struys, E. et al. (2010a) Accumulation of thymidine-derived sugars in thymidine phosphorylase tion studies, both with conventional cytotoxic overexpressing cells. Biochem Pharmacol 80: 786–796. agents and signaling targeted therapy, as well as radiotherapy. A combination of these treatments Bijnsdorp, I., Capriotti, F., Kruyt, F., Losekoot, may help to prevent recurrence of tumors due to N., Fukushima, M., Griffioen, A. et al. (2011) drug resistance. Specifically TAS-102 has great Thymidine phosphorylase in cancer cells stimulates potential to improve the treatment of gastroin- human endothelial cell migration and invasion by the secretion of angiogenic factors. Br J Cancer 104: testinal malignancies when combined with other 1185–1192. agents, such as with the VEGF inhibitor bevaci- zumab or the DNA synthesis inhibitors oxalipl- Bijnsdorp, I., Kruyt, F., Fukushima, M., Smid, atin or irinotecan. Recently the first promising K., Gokoel, S. and Peters, G. (2010b) Molecular results of the combination of TAS-102 (70 mg/ mechanism underlying the synergistic interaction m /day) and bevacizumab were reported [Kuboki between trifluorothymidine and the epidermal growth 352 http://tam.sagepub.com GJ Peters factor receptor inhibitor erlotinib in human colorectal of thymidylate synthase by 5-(trifluoromethyl)-2’- cancer cell lines. Cancer Sci 101: 440–447. deoxyuridine 5’-monophosphate. Biochemistry 33: 15086–15094. Bijnsdorp, I., Kruyt, F., Gokoel, S., Fukushima, M. and Peters, G. (2008) Synergistic interaction of Ellis, L. (2004) Angiogenesis and its role in colorectal trifluorothymidine with docetaxel (Taxotere®) after tumor and metastasis formation. Semin Oncol 31: 3–9. sequential scheduling. Cancer Sci 99: 2302–2309. El-Naggar, M., Ebbing, E., Bijnsdorp, I., Van den Bijnsdorp, I. and Peters, G. (2011) Deoxyribose Berg, J. and Peters, G. (2014) Radiosensitization protects against rapamycin induced cytotoxicity in by thymidine phosphorylase inhibitor in thymidine colorectal cancer cells in vitro. Nucleosides Nucleotides phosphorylase negative and overexpressing bladder Nucleic Acids 30: 1197–1202. cancer cell lines. Nucleosides Nucleotides Nucleic Acids 33: 413–421. Bijnsdorp, I., Peters, G., Temmink, O., Fukushima, M. and Kruyt, F. (2010c) Differential activation Emura, T., Murakami, Y., Nakagawa, F., Fukushima, of cell death and autophagy results in an increased M. and Kitazato, K. (2004a) A novel antimetabolite, cytotoxic potential for trifluorothymidine compared to TAS-102 retains its effect on FU-related resistant 5-fluorouracil in colon cancer cells. Int J Cancer 126: cancer cells. Int J Mol Med 13: 545–549. 2457–2468. Emura, T., Nakagawa, F., Fujioka, A., Ohshimo, Cao, D. and Pizzorno, G. (2004) Uridine H. and Kitazato, K. (2004b) Thymidine kinase and phosphorylase: an important enzyme in pyrimidine thymidine phosphorylase level as the main predictive metabolism and fluoropyrimidine activation. Drugs parameter for sensitivity to TAS-102 in a mouse Today (Barc) 40: 431–443. model. Oncol Rep 11: 381–387. Carmine, A., Brogden, R., Heel, R., Speight, T. and Emura, T., Nakagawa, F., Fujioka, A., Ohshimo, Avery, G. (1982) Trifluridine: a review of its antiviral H., Yokogawa, T., Okabe, H. et al. (2004c) An activity and therapeutic use in the topical treatment of optimal dosing schedule for a novel combination viral eye infections. Drugs 23: 329–353. antimetabolite, TAS-102, based on its intracellular metabolism and its incorporation into DNA. Int J Mol Cleary, J., Mayer, R., Van Cutsem, E., Yamashita, Med 13: 249–255. F. and Yoshisue, K., Ieiri, I. et al. (2015) Population pharmacokinetic (PK) analysis of TAS-102 in Emura, T., Suzuki, N., Fujioka, A., Ohshimo, H. and patients (pts) with metastatic colorectal cancer Fukushima, M. (2005) Potentiation of the antitumor (mCRC): results from 3 phase 1 trials and the phase activity of alpha, alpha, alpha-trifluorothymidine by 3 RECOURSE trial. J Clin Oncol 33(Suppl.): abstract the co-administration of an inhibitor of thymidine phosphorylase at a suitable molar ratio in vivo. Int J Oncol 27: 449–455. De Bruin, M., Temmink, O., Hoekman, K., Pinedo, H. and Peters, G. (2006) Role of platelet Emura, T., Suzuki, N., Yamaguchi, M., Ohshimo, derived endothelial cell growth factor/thymidine H. and Fukushima, M. (2004d) A novel combination phosphorylase in health and disease. Cancer Ther 4: antimetabolite, TAS-102, exhibits antitumor activity 99–124. in FU-resistant human cancer cells through a mechanism involving FTD incorporation in DNA. Int De Bruin, M., van Capel, T., van der Born, K., J Oncol 25: 571–578. Kruyt, F., Fukushima, M., Hoekman, K. et al. (2003) Role of platelet-derived endothelial cell growth Endo, M., Shinbori, N., Fukase, Y., Sawada, N., factor/thymidine phosphorylase in fluoropyrimidine Ishikawa, T., Ishitsuka, H. et al. (1999) Induction of sensitivity. Br J Cancer 88: 957–964. thymidine phosphorylase expression and enhancement of efficacy of capecitabine or 5’-deoxy-5-fluorouridine De Clercq, E. (2004) Antiviral drugs in current by cyclophosphamide in mammary tumor models. Int clinical use. J Clin Virol 30: 115–133. J Cancer 83: 127–134. Dexter, D., Wolberg, W., Ansfield, F., Helson, L. and Ford, H., Mitchell, F., Cunningham, D., Farrugia, Heidelberger, C. (1972) The clinical pharmacology D., Hill, M., Rees, C. et al. (2002) Patterns of of 5-trifluoromethyl-2’-deoxyuridine. Cancer Res 32: elevation of plasma 2’-deoxyuridine, a surrogate 247–253. marker of thymidylate synthase (TS) inhibition, Doi, T., Ohtsu, A., Yoshino, T., Boku, N., Onozawa, after administration of two different schedules Y., Fukutomi, A. et al. (2012) Phase I study of TAS- of 5-fluorouracil and the specific TS inhibitors 102 treatment in Japanese patients with advanced raltitrexed (Tomudex) and ZD9331. Clin Cancer Res solid tumours. Br J Cancer 107: 429–434. 8: 103–109. Eckstein, J., Foster, P., Finer-Moore, J., Wataya, Y. Fujiwara, Y. and Heidelberger, C. (1970) and Santi, D. (1994) Mechanism-based inhibition Fluorinated pyrimidines. 38. The incorporation http://tam.sagepub.com 353 Therapeutic Advances in Medical Oncology 7(6) of 5-trifluoromethyl-2’-deoxyuridine into the Ikeda, R., Furukawa, T., Kitazono, M., Ishitsuka, K., deoxyribonucleic acid of vaccinia virus. Mol Pharmacol Okumura, H., Tani, A. et al. (2002) Molecular basis 6: 281–291. for the inhibition of hypoxia-induced apoptosis by 2-deoxy-D-ribose. Biochem Biophys Res Commun 291: Fukushima, M., Okabe, H., Takechi, T., Ichikawa, 806–812. W. and Hirayama, R. (2002) Induction of thymidine phosphorylase by interferon and taxanes occurs Inaba, M., Mitsuhashi, J., Sawada, H., Miike, N., only in human cancer cells with low thymidine Naoe, Y., Daimon, A. et al. (1996) Reduced activity phosphorylase activity. Cancer Lett 187: 103–110. of anabolizing enzymes in 5-fluorouracil-resistant human stomach cancer cells. Jpn J Cancer Res 87: Fukushima, M., Suzuki, N., Emura, T., Yano, 212–220. S., Kazuno, H., Tada, Y. et al. (2000) Structure and activity of specific inhibitors of thymidine Kabbinavar, F., Hambleton, J., Mass, R., Hurwitz, phosphorylase to potentiate the function of antitumor H., Bergsland, E. and Sarkar, S. (2005) Combined 2’-deoxyribonucleosides. Biochem Pharmacol 59: analysis of efficacy: the addition of bevacizumab to 1227–1236. fluorouracil/leucovorin improves survival for patients with metastatic colorectal cancer. J Clin Oncol 23: George, D. (2001) Platelet-derived growth factor 3706–3712. receptors: a therapeutic target in solid tumors. Semin Oncol 28: 27–33. Kuboki, Y., Nishina, T., Shinozaki, E., Yamazaki, K., Shitara, K., Okamoto, W. et al. (2015) An investigator Green, M., Pusztai, L., Theriault, R., Adinin, R., initiated multicenter phase I/II study of TAS-102 Hofweber, M., Fukushima, M. et al. (2006) Phase I with bevacizumab for metastatic colorectal cancer study to determine the safety of oral administration of refractory to standard therapies (C-TASK FORCE). J TAS-102 on a twice daily (BID) schedule for five days Clin Oncol 33(Suppl.): abstract 3544. a week (wk) followed by two days rest for two wks, every (Q) four wks in patients (pts) with metastatic Lee, H., Oh, S., Lee, E., Chung, J., Kim, Y., Ryu, J. breast cancer (MBC). Proc Am Soc Clin Oncol et al. (2015a) Positron emission tomography imaging (abstract 10576). of human colon cancer xenografts in mice with [(18) F]fluorothymidine after TAS-102 treatment. Cancer Heidelberger, C. and Anderson, S. (1964) Chemother Pharmacol 75: 1005–1013. Fluorinated pyrimidines. XXI. The tumor inhibitory activity of 5-trifluoromethyl-2’-deoxyuridine. Cancer Lee, J., Seraj, J., Yoshida, K., Narurkar, M. and Res 24: 1979–1985. Mizuguchi, H., Strychor, S. et al. (2015b) Mass balance study of TAS-102 using 14C labeling Heidelberger, C., Boohar, J. and Kampschroer, analyzed by accelerator mass spectrometry. J Clin B. (1965) Fluorinated pyrimidines. XXIV. In vivo Oncol 33(Suppl.): abstract 2563. metabolism of 5-trifluoromethyluracil-2-C-14 and 5-trifluoromethyl-2’-deoxyuridine-2-C-14. Cancer Res Manetti, F. and Botta, M. (2003) Small-molecule 25: 377–381. inhibitors of fibroblast growth factor receptor (FGFR) tyrosine kinases (TK). Curr Pharm Des 9: 567–581. Heidelberger, C., Parsons, D. and Remy, D. (1964) Syntheses of 5-trifluoromethyluracil and Matsuoka, K., Iimori, M., Niimi, S., Tsukihara, H., 5-trifluoromethyl-2’-deoxyuridine. J Med Chem 55: Watanabe, S., Kiyonari, S. et al. (2015) Trifluridine 1–5. induces p53-dependent sustained G2 phase arrest with its massive misincorporation into DNA and few Hoff, P., Ansari, R., Batist, G., Cox, J., Kocha, W., DNA strand breaks. Mol Cancer Ther 14: 1004–1013. Kuperminc, M. et al. (2001) Comparison of oral capecitabine versus intravenous fluorouracil plus Mayer, R., Van Cutsem, E., Falcone, A., Yoshino, T., leucovorin as first-line treatment in 605 patients with Garcia-Carbonero, R., Mizunuma, N. et al. (2015) metastatic colorectal cancer: results of a randomized Randomized trial of TAS-102 for refractory metastatic phase III study. J Clin Oncol 19: 2282–2292. colorectal cancer. N Engl J Med 372: 1909–1919. Hong, D., Abbruzzese, J., Bogaard, K., Lassere, Y., Miyatani, T., Kurita, N., Utsunomiya, T., Iwata, T., Fukushima, M., Mita, A. et al. (2006) Phase I study Nishioka, M., Yoshikawa, K. et al. (2012) Platelet- to determine the safety and pharmacokinetics of oral derived endothelial cell growth factor/thymidine administration of TAS-102 in patients with solid phosphorylase inhibitor augments radiotherapeutic tumors. Cancer 107: 1383–1390. efficacy in experimental colorectal cancer. Cancer Lett 318: 199–205. Hotchkiss, K., Ashton, A. and Schwartz, E. (2003) Thymidine phosphorylase and 2-deoxyribose Miyazono, K., Okabe, T., Urabe, A., Takaku, F. and stimulate human endothelial cell migration by specific Heldin, C. (1987) Purification and properties of an activation of the integrins alpha 5 beta 1 and alpha V endothelial cell growth factor from human platelets. J beta 3. J Biol Chem 278: 19272–19279. Biol Chem 262: 4098–4103. 354 http://tam.sagepub.com GJ Peters Moghaddam, A. and Bicknell, R. (1992) Expression of trifluorothymidine metabolism in rat brain. NMR of platelet-derived endothelial cell growth factor in Biomed 12: 373–380. Escherichia coli and confirmation of its thymidine Pugmire, M. and Ealick, S. (2002) Structural phosphorylase activity. Biochemistry 31: 12141–12146. analyses reveal two distinct families of nucleoside Murakami, Y., Kazuno, H., Emura, T., Tsujimoto, phosphorylases. Biochem J 361: 1–25. H., Suzuki, N. and Fukushima, M. (2000) Different Reyes, P. and Heidelberger, C. (1965) Fluor- mechanisms of acquired resistance to fluorinated inated pyrimidines. XXVI. Mammalian thymidylate pyrimidines in human colorectal cancer cells. Int J synthetase: its mechanism of action and inhibition Oncol 17: 277–283. by fluorinated nucleotides. Mol Pharmacol 1: Nukatsuka, M., Nakagawa, F., Matsuoka, K., 14–30. Tsukihara, K. and Takechi, T. (2015a) Efficacy Sakamoto, K., Yokogawa, T., Ueno, H., Oguchi, K., of combination chemotherapy using a novel oral Kazuno, H., Ishida, K. et al. (2015) Crucial roles of chemotherapeutic agent, TAS-102, with oxaliplatin on thymidine kinase 1 and deoxyUTPase in incorporating human colorectal or gastric cancer and 5FU-resistant the antineoplastic nucleosides trifluridine and gastric cancer xenografts. Proc Annu Meet Am Assoc 2’-deoxy-5-fluorouridine into DNA. Int J Oncol 46: Cancer Res 56: abstract 2557. 2327–2334. Nukatsuka, M., Nakagawa, F., Saito, H., Sakata, Santi, D. and Sakai, T. (1971) Thymidylate M., Uchida, J. and Takechi, T. (2015b) Efficacy synthetase. Model studies of inhibition by of combination chemotherapy using a novel oral 5-trifluoromethyl-2’-deoxyuridylic acid. Biochemistry chemotherapeutic agent, TAS-102 with irinotecan 10: 3598–3607. hydrochloride on human colorectal and gastric cancer xenografts. Anticancer Res 35: 1437–1445. Sato, J., Sata, M., Nakamura, H., Inoue, S., Wada, T., Takabatake, N. et al. (2003) Role of thymidine Overman, M., Kopetz, S., Varadhachary, G., phosphorylase on invasiveness and metastasis in lung Fukushima, M., Kuwata, K., Mita, A. et al. (2008a) adenocarcinoma. Int J Cancer 106: 863–870. Phase I clinical study of three times a day oral administration of TAS-102 in patients with solid Seeliger, H., Guba, M., Koehl, G., Doenecke, A., tumors. Cancer Invest 26: 794–799. Steinbauer, M., Bruns, C. et al. (2004) Blockage of 2-deoxy-D-ribose-induced angiogenesis with Overman, M., Varadhachary, G., Kopetz, S., rapamycin counteracts a thymidine phosphorylase- Thomas, M., Fukushima, M., Kuwata, K. et al. based escape mechanism available for colon cancer (2008b) Phase 1 study of TAS-102 administered once under 5-fluorouracil therapy. Clin Cancer Res 10: daily on a 5-day-per-week schedule in patients with 1843–1852. solid tumors. Invest New Drugs 26: 445–454. Suzuki, N., Nakagawa, F., Nukatsuka, M. and Peters, G. (2014) Novel developments in the use of Fukushima, M. (2011) Trifluorothymidine exhibits antimetabolites. Nucleosides Nucleotides Nucleic Acids potent antitumor activity via the induction of DNA 33: 358–374. double-strand breaks. Exp Ther Med 2: 393–397. Peters, G., Backus, H., Freemantle, S., van Triest, B., Takahashi, Y., Bucana, C., Liu, W., Yoneda, J., Codacci-Pisanelli, G., van der Wilt, C. et al. (2002) Kitadai, Y., Cleary, K. et al. (1996) Platelet-derived Induction of thymidylate synthase as a 5-fluorouracil endothelial cell growth factor in human colon cancer resistance mechanism. Biochim Biophys Acta 1587: angiogenesis: role of infiltrating cells. J Natl Cancer 194–205. Inst 88: 1146–1151. Peters, G. and Bijnsdorp, I. (2012) TAS-102: more Takahashi, Y., Ellis, L. and Mai, M. (2003) The than an antimetabolite. Lancet Oncol 13: e518–e519. angiogenic switch of human colon cancer occurs Peters, G., Honeywell, R., Leon, L., Van simultaneous to initiation of invasion. Oncol Rep 10: Groeningen, C., Jansen, G., Ylstra, B. et al. (2009) 9–13. Role of pharmacodynamic, pharmacogenetic Takahashi, K., Yoshisue, K., Chiba, M., Nakanishi, and pharmacogenomic biomarkers of cancer T. and Tamai, I. (2015) Involvement of concentrative chemotherapy with antifolates. Pteridines 20: nucleoside transporter 1 in intestinal absorption of s115–s127. trifluridine using human small intestinal epithelial Peters, G., Schornagel, J. and Milano, G. (1993) cells. J Pharm Sci 104: 3146–3153. Clinical pharmacokinetics of anti-metabolites. Cancer Takao, S., Akiyama, S., Nakajo, A., Yoh, H., Surv 17: 123–156. Kitazono, M., Natsugoe, S. et al. (2000) Suppression Pouremad, R., Bahk, K., Shen, Y., Knop, R. and of metastasis by thymidine phosphorylase inhibitor. Wyrwicz, A. (1999) Quantitative 19F NMR study Cancer Res 60: 5345–5348. http://tam.sagepub.com 355 Therapeutic Advances in Medical Oncology 7(6) Takebayashi, Y., Akiyama, S., Akiba, S., Yamada, oxaliplatin-induced cytotoxicity to colorectal cancer K., Miyadera, K., Sumizawa, T. et al. (1996a) cells. Br J Cancer 96: 231–240. Clinicopathologic and prognostic significance of Temmink, O., Hoogeland, M., Fukushima, M. an angiogenic factor, thymidine phosphorylase, in and Peters, G. (2006b) Low folate conditions may human colorectal carcinoma. J Natl Cancer Inst 88: enhance the interaction of trifluorothymidine with 1110–1117. antifolates in colon cancer cells. Cancer Chemother Takebayashi, Y., Yamada, K., Miyadera, K., Pharmacol 57: 171–179. Sumizawa, T., Furukawa, T., Kinoshita, F. et al. Tsukihara, H., Nakagawa, F., Sakamoto, K., Ishida, (1996b) The activity and expression of thymidine K., Tanaka, N., Okabe, H. et al. (2015) Efficacy phosphorylase in human solid tumours. Eur J Cancer of combination chemotherapy using a novel oral 32A: 1227–1232. chemotherapeutic agent, TAS-102, together with Tanaka, N., Sakamoto, K., Okabe, H., Fujioka, A., bevacizumab, cetuximab, or panitumumab on human Yamamura, K., Nakagawa, F. et al. (2014) Repeated colorectal cancer xenografts. Oncol Rep 33: 2135– oral dosing of TAS-102 confers high trifluridine 2142. incorporation into DNA and sustained antitumor Uchimiya, H., Furukawa, T., Okamoto, M., activity in mouse models. Oncol Rep 32: Nakajima, Y., Matsushita, S., Ikeda, R. et al. (2002) 2319–2326. Suppression of thymidine phosphorylase-mediated angiogenesis and tumor growth by 2-deoxy-L-ribose. Temmink, O., Bijnsdorp, I., Prins, H., Losekoot, N., Cancer Res 62: 2834–2839. Adema, A., Smid, K. et al. (2010) Trifluorothymidine resistance is associated with decreased thymidine Van Cutsem, E., Twelves, C., Cassidy, J., Allman, kinase equilibrative nucleoside transporter expression D., Bajetta, E., Boyer, M. et al. (2001) Oral or increased secretory phospholipase A2. Mol Cancer capecitabine compared with intravenous fluorouracil Ther 9: 1047–1057. plus leucovorin in patients with metastatic colorectal cancer: results of a large phase III study. J Clin Oncol Temmink, O., Comijn, E., Fukushima, M. and 19: 4097–4106. Peters, G. (2004) Intracellular thymidylate synthase inhibition by trifluorothymidine in FM3A cells. Van Triest, B. and Peters, G. (1999) Thymidylate Nucleosides Nucleotides Nucleic Acids 23: 1491–1494. synthase: a target for combination therapy and determinant of chemotherapeutic response in Temmink, O., De Bruin, M., Comijn, E., Fukushima, colorectal cancer. Oncology 57: 179–194. M. and Peters, G. (2005) Determinants of trifluorothymidine sensitivity and metabolism in colon Van Triest, B., Pinedo, H., Blaauwgeers, J., van and lung cancer cells. Anticancer Drugs 16: 285–292. Diest, P., Schoenmakers, P., Voorn, D. et al. (2000) Prognostic role of thymidylate synthase, thymidine Temmink, O., De Bruin, M., Laan, A., Turksma, A., phosphorylase/platelet-derived endothelial cell growth Cricca, S., Masterson, A. et al. (2006a) The role of factor, and proliferation markers in colorectal cancer. thymidine phosphorylase and uridine phosphorylase Clin Cancer Res 6: 1063–1072. in (fluoro)pyrimidine metabolism in peripheral blood mononuclear cells. Int J Biochem Cell Biol 38: 1759– Wilson, P., Danenberg, P., Johnston, P., Lenz, H. and Ladner, R. (2014) Standing the test of time: targeting thymidylate biosynthesis in cancer therapy. Nat Rev Temmink, O., de Bruin, M., Turksma, A., Cricca, Clin Oncol 11: 282–298. S., Laan, A. and Peters, G. (2007a) Activity and substrate specificity of pyrimidine phosphorylases Yano, S., Kazuno, H., Sato, T., Suzuki, N., Emura, and their role in fluoropyrimidine sensitivity in colon T., Wierzba, K. et al. (2004) Synthesis and evaluation cancer cell lines. Int J Biochem Cell Biol 39: 565–575. of 6-methylene-bridged uracil derivatives. Part 2: optimization of inhibitors of human thymidine Temmink, O., Emura, T., De Bruin, M., Fukushima, phosphorylase and their selectivity with uridine M. and Peters, G. (2007b) Therapeutic potential phosphorylase. Bioorg Med Chem 12: 3443–3450. of the dual-targeted TAS-102 formulation in the treatment of gastrointestinal malignancies. Cancer Sci Yoshino, T., Mizunuma, N., Yamazaki, K., Nishina, 98: 779–789. T., Komatsu, Y., Baba, H. et al. (2012) TAS-102 Temmink, O., Hoebe, E., Fukushima, M. and Peters, monotherapy for pretreated metastatic colorectal G. (2007c) Irinotecan-induced cytotoxicity to colon cancer: a double-blind, randomised, placebo- cancer cells in vitro is stimulated by pre-incubation controlled phase 2 trial. Lancet Oncol 13: 993–1001. with trifluorothymidine. Eur J Cancer 43: 175–183. Zondor, S. and Medina, P. (2004) Bevacizumab: Visit SAGE journals online Temmink, O., Hoebe, E., van der Born, K., an angiogenesis inhibitor with efficacy in colorectal http://tam.sagepub.com Ackland, S., Fukushima, M. and Peters, G. (2007d) and other malignancies. Ann Pharmacother 38: SAGE journals Mechanism of trifluorothymidine potentiation of 1258–1264. 356 http://tam.sagepub.com

Journal

Therapeutic Advances in Medical Oncology – SAGE

Published: Sep 10, 2015

Keywords: clinical trials; colorectal cancer; combination studies; DNA damage; TAS-102; thymidine phosphorylase inhibitor; trifluorothymidine

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