Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

PRIMA-1 as a cancer therapy restoring mutant p53: a review

PRIMA-1 as a cancer therapy restoring mutant p53: a review BioscienceHorizons Volume 8 2015 10.1093/biohorizons/hzv006 Review article PRIMA-1 as a cancer therapy restoring mutant p53: a review Emily J. Lewis* University of Exeter Medical School, Exeter, Devon EX1 2LU, England *Corresponding author: St Luke’s Campus, Magdalen road, Exeter, Devon EX1 2LU, England. Email: ejl213@exeter.ac.uk Supervisor: Emma Taylor, University of Exeter Medical School, Exeter, Devon EX1 2LU, England. With a continuing increase in the prevalence of cancer, there is an increasing pressure to produce novel cancer therapies. The production of targeted cancer therapies could lead to the replacement of conventional cancer chemotherapy and, conse- quently, the minimization of the associated distressing side effects. This review addresses the process of restoring a mutant tumour suppressor protein, p53, in the apoptosis pathway as a potential therapeutic target for cancer therapy. Current litera- ture highlights the small molecule PRIMA-1 as a particularly promising novel cancer therapy; however, there are currently many potential therapies being investigated; CP-31398 is another small molecule with potential anti-cancer effects. PRIMA-1 acts to restore the mutant p53 by modifying thiol groups in the core domains of the protein. Its success is well documented, with many studies in different cancer models proving its effectiveness. This, however, is not unanimous, with some questions being raised about its efficacy and other aspects such as possible resistance mechanisms as well as potentially harmful degra - dation products. This said, PRIMA-1 has entered Stage II clinical trials and with more data collected on in vivo models and potential complications of the drug, it could ultimately provide an alternative to conventional cancer chemotherapy. This could therefore help to prevent cancer patients suffering the displeasing side effects with which it is associated. Key words: cancer therapy, targeted therapy, PRIMA-1, p53 Submitted on 24 September 2014; accepted on 7 September 2015 Introduction Carelle et al. (2002) documented these with the most distress- ing side effects including the loss of hair, weight gain and loss There are >200 types of cancer that caused an estimated 12.7 of sexual feeling. To try and minimize the side effects associ- million new cases in 2008 (Cancer Research UK, 2014). With ated with current chemotherapy methods, researchers are this, cancer incidence rates have increased by 33% in the UK now exploring the use of drug targeting for the development since the 1970s (Cancer Research UK, 2014), and this is set to of novel therapies. Targeted cancer therapies use specific mol - increase with an ageing population. As a result, the pressure ecules involved in the development of the tumour as targets to for the discovery of novel treatments is ever increasing. halt its proliferation (National Cancer Institute, 2014b). Current chemotherapy methods, among other advances, have Success in this field has resulted from the use of both thera - led to a 2-fold increase in the survival rates in the UK in the peutic antibodies and small molecules acting on a range of last 40 years meaning that half of the people diagnosed with targets to effectively prevent the proliferation of tumours cancer now survive for at least 5 years after diagnosis (Cancer while aiming to lower the toxicity of the drugs (Wu, Chang Research UK, 2014). With this said, chemotherapy has long and Huang, 2006). This review will look at some of these been associated with side effects that can dramatically reduce developing methods focusing on targeting the absence of suf- the quality of life of cancer patients, due to the lack of specific - ficient apoptosis, one of the hallmarks of cancer, (see Fig.  1) ity of chemotherapy causing other dividing cells to be affected. (Hanahan and Weinberg, 2011) with a reduction in tumour © The Author 2015. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Review article Bioscience Horizons • Volume 8 2015 Figure 1. The hallmarks of cancer. This schematic shows the hallmarks of cancer. The red box on the diagram highlights ‘Resisting cell death’, which is the hallmark targeted by the methods studied in this review. Reprinted from Cell, 144/5, Hanahan, D., Weinberg, R.A., Hallmarks of cancer: the next generation, 646–674, copyright (2011), with permission from Elsevier. size considered evidence of a regression of malignant cells. mechanism and finally inhibiting mdm2, which is in itself an The apoptosis pathway is modified in a number of ways in inhibitor of p53. Shchors et al. (2013) used a genetically engi- cancerous cells, but this review will centre on the protein p53. neered mouse model that pharmacologically restores p53 The location of p53 in the apoptosis pathway has been high- function. They were able to activate and deactivate cancerous lighted in Fig. 2. p53 is involved in many physiological pro- effects that established the mechanism of reactivation of the cess but is mainly categorized as a tumour suppressor. It is tumour suppressor. This literature review will explore the res- involved in cell fate by integrating various forms of cell signal- toration of the mutated protein to its wild-type form as a ling mechanisms, including but not limited to nutrient, cyto- novel target for cancer therapy to supplement or even replace kine and hormone levels. The underlying mechanisms remain conventional chemotherapy methods that have undesirable unclear; however, it is thought that the TP53 gene can encode side effects. different isoforms that modulate the activity of p53, either promoting cell survival or death, depending on cell context PRIMA-1 mechanism of action and external stresses by differentially regulating gene tran- scription (Surget et al., 2013). It is normally kept at low levels There have been a number of clinical trials on drugs targeted through ubiquitation and proteasomal degradation in the cell at restoring mutant p53 proteins in cancerous cells. The most but becomes up-regulated by stress signals, often induced by promising thus far is PRIMA-1, which is a small molecule DNA damage (Selivanova et al., 1999). Once activated it leads therapy that entered its second phase of clinical trials in 2011 MET to a pathway of downstream effects including physiological (Aprea, 2012). PRIMA-1 is converted to PRIMA-1 , the functions and the induction of apoptosis which halts cancer methylated form of the drug, which works in a variety of ways progression (Martinez, 2010). In cancerous cells, p53 is often to restore p53 (Lambert et al., 2009). One proposed mecha- MET mutated and so this pathway does not proceed, which can nism of action is that the PRIMA-1 covalently binds to result in uncontrolled cell proliferation of cells with damaged and modifies thiol groups in the central domain of the mutated DNA that may include mutations in oncogenes or tumour protein (Lambert et al., 2009). This therefore causes reactiva- suppressor genes. Subsequently, this may lead to the forma- tion of the p53 protein that should subsequently regain its tion of a tumour. Hollstein et al. (1991) estimated that up to ability to induce apoptosis. There has been a range of papers 50% of human cancers have a mutation in p53, and this is investigating the therapeutic possibilities of PRIMA-1 in a therefore a promising target for novel cancer therapies with- number of different cancers. out causing the death of healthy cells as seen with traditional chemotherapy. So far there have been three main methods for The effect of p53 expression levels targeting p53 in cancerous cells. The first technique is to reac - tivate the apoptosis pathway by modifying mutant p53; the One seminal paper is the study by Bykov et al. (2002) which second is to reintroduce the p53 protein by an exogenous is a statistical analysis of the data provided on the drug by the 2 Bioscience Horizons • Volume 8 2015 Review article conditions (Bykov et al., 2002) and Zandi et al. (2011) per- formed some analysis on a xenograft model, but there is a lack of in vivo evidence. Lambert et al. (2009) drew a conclusion that ‘conversion of PRIMA-1 occurs even more efficiently in living cells than in vivo’; however, analysis from living H1299- HIS175 cells was the only evidence given. An animal model study by Watanabe et  al. (2011) that found no significant decrease in tumour size when mice were injected with PRIMA-1 raised further concerns. With this said, the results of this study did not show a significant decrease in tumour size of 1.48 mm, but with only eight mice in each of the drug and control categories, it is imperative that more research is done into the in vivo effects of the drug during its clinical trial phases (Aprea, 2012). The main implications of the deficiency of in vivo analysis are that potential side effects could go unnoticed before the drug is administered to humans. Mouse models may identify some potential problem areas; however, as shown in the TGN 1412 study, mouse models cannot be entirely relied on to highlight any potential complications (Suntharalingam et al., 2006). Furthermore, a lack of identifi - cation of severe side effects would undermine the purpose of this novel targeted drug. Timescales of drug action In addition, the identification needs to be undertaken over a long period of time to observe complications that may arise further down the line of treatment. Lambert et al. (2009) took measurements up to 24 h, and this was increased to 10 days in the Zandi et al. (2011) paper; however, few long-term studies Figure 2. Apoptosis intrinsic pathway. This diagram shows the of the potential effects of PRIMA-1, either advantageous or intrinsic pathway of apoptosis. The red box denotes the location of the otherwise, are freely available. Rao et al. (2013) compared the p53 in the apoptosis intrinsic pathway. From this diagram, the role of chemopreventive effect of PRIMA-1 with another small- p53 as an inducer of the apoptosis pathway is evident. molecule p53-restoring drug, CP-31398, performing a longer trial on the effects of PRIMA-1. In this trial, however, other National Cancer Institute. Human tumour cell lines were used effects of the drug were not monitored and the trial took place to find growth inhibition profiles for PRIMA-1 and 44 other in a mouse model (Rao et al. 2013). The study involved mix- commonly used cancer therapies, p53 expression levels and ing the p53 modulators with food and measuring the tumour population doubling time as a measure of the size of the size on the lungs after both 20 and 32 weeks. Photographs of tumour. The study however only analysed cell lines with the lungs are shown in the study by Rao et al. (Fig. 2). From mutant protein levels exceeding 1 unit, determined by western these, it is clear to see that both the p53 modulators decreased blotting. As a result, no conclusion can be drawn about the the size of the tumours and also that CP-31398 may in fact be efficacy of PRIMA-1 in cell lines where p53 expression had the more effective option, despite it being less well researched reached very low levels or stopped completely, and the authors at present (Rao et al. 2013). suggested that the efficacy would depend on the levels of mutant p53 in the cell. This was contested by Zandi et  al. Models of drug selectivity (2011) who selected cell lines with low or undetectable levels of p53 and reported a signic fi ant increase in the proportion of With this shortage of availability of in vivo evidence, a model Sub-G0/G1 apoptotic cells in the tumour after undertaking investigating drug selectivity could be used to get an insight cell cycle analysis. into the likelihood of complications occurring. The expecta- tion is then that the higher the selectivity of the drug, the less side effects it will cause as a result of acting on healthy cells. In vivo drug effects This was tested by Bykov et  al., (2002) using a Wilcoxon A further problem of using selected cell lines for the studies of matched paired test; for results, see figure 3 in Bykov et al., PRIMA-1 is a lack of evidence of the effects of the drug in vivo (2002). PRIMA-1 had a target selectivity that was higher than and in human subjects. Lambert et al. (2009) incubated sam- the current cancer therapies in colon cancer, NSCLC and mel- ples at 37°C and kept them at pH 7.4 to simulate human anomas with selective advantages over certain therapies in 3 Review article Bioscience Horizons • Volume 8 2015 other cancers. A P-value of 0.04 was also calculated which Fig.  1). It would therefore be imperative that the effects of was interpreted as being a statistically significant preference of these unknown compounds were investigated fully, as well as PRIMA-1 for mutant-p53 strains over non-mutated p53 those of the PRIMA itself, to ensure that the drug will be suit- (Bykov et al., 2002). It should however be noted that a P-value able for clinical use. Lambert et  al. (2009) also stated that of 0.04, although significant, is often only defined as ‘some another breakdown product of PRIMA-1 is formaldehyde. evidence of a difference’ (Crocker and Weedon, 2010). The Formaldehyde has been classified as a known human carcino - selectivity shown by PRIMA-1 may have other benefits as well gen by the International Agency for Research on Cancer as the limitation of side effects. The high selectivity of the drug (National Cancer Institute, 2014a); however, the potential may also have positive repercussions with respect to drug implications of this have not yet been assessed in a PRIMA-1 resistance, which is becoming an ever-increasing problem in study. all aspects of medicine. Conclusion Resistance to PRIMA-1 In conclusion, cancer is a disease that is hugely prevalent, with An inevitable increase in resistance to cancer chemotherapy cases increasing year on year. Treatment has progressed in drugs as their prescription is increasing is another motivation recent years, with chemotherapy now available to treat most for developing novel cancer therapies. To investigate the pos- cancers with an increasing success rate. Despite this improve- sible resistance mechanisms to PRIMA-1, Bykov et al. (2002) ment, the afflicting associated side effects with chemotherapy performed the Compare algorithm of the NCI database in leave many opportunities for innovation. Drug targeting is reverse (Paull et  al., 1989). They found that resistance to proving to offer many potential alternatives, with targeting PRIMA-1 could be caused by insulin-like growth receptor the apoptosis pathway being one of the most explored. (p = 0.35) and a proto-oncogene tyrosine kinase (p = 0.44), as PRIMA-1 exploits the high occurrence of a mutated p53 pro- well as by more universal resistance mechanisms such as tein in cancers and acts to restore the mutated protein to its efflux pumps and a multi-drug-resistant protein ( Bykov et al., wild-type state. The restored p53 can then resume its role 2002). N-acetylcysteine was also identified as blocking apop - inducing apoptosis to prevent superfluous cell proliferation. tosis induced by PRIMA-1 (Lambert et al., 2009, see figure 3). There have been a number of studies investigating the possi- More research would have to be done into the potential effect bility of PRIMA-1, and other p53-modulating drugs such as of these resistance mechanisms on the suitability of the drug CP-31398, as novel cancer therapies to replace chemotherapy. as a cancer therapy. Data would need to be collected to inves- Combining the results of these studies provides an overall tigate the effect of these mechanisms in vivo and whether the positive outlook on the potential of these therapies with just a level of resistance would affect its therapeutic potential or few obstacles being presented before the therapy can be put whether further actions could be taken to prevent these mech- into clinical use. It is therefore suggested that further investi- anisms affecting the efficacy of PRIMA-1. gations are made into the in vivo effects of the drug, especially in the long term, with a focus of identifying other possible A cluster analysis was performed by Bykov et  al. (2002) effects of the drugs. which could provide an insight into the chances of a large-scale resistance to PRIMA-1. Clustering was performed according Author’s biography to Ward’s method, and a dendogram was generated showing 44 therapies and their relation to PRIMA-1 (Bykov et  al. E.J.L. is a student at the University of Exeter Medical School (2002), see figure 4). As can be seen from the figure, PRIMA-1 where she is currently studying Medical Sciences, a transla- clusters away from many other commonly used therapies, only tional science degree investigating the science underpinning showing similarities to the purine analogues. This could be a medicine and clinical practice. Her specific interests are in potential benefit with respect to multi-drug resistance mecha - cancer biology, pharmacology and microbiology. E.J.L. aspires nisms, as tumour cells would have to evolve different resis- to study postgraduate medicine. She would also like to main- tance mechanisms to PRIMA-1 than conventional cancer tain an involvement in clinical research while practicing. She therapies to avoid being affected by the novel drug. wrote up this paper and has primary responsibility for its final content. Other potential issues References As well as potential issues concerning resistance, the Lambert et al. (2009) study on PRIMA-1 has raised a few further pos- Aprea.com. (2012) Aprea announces positive data from a clinical Phase sible shortcomings of the drug. At 15 min, a sample of the I/II study with APR-246 | Aprea. [Online], accessed at: http://aprea. solution containing PRIMA-1 and its degradation products com/2012/aprea-announces-positive-data-from-a-clinical-phase-iii- was analysed using mass spectrometry and nuclear magnetic study-with-apr-246/ (10 Mar 2014). resonance. This showed the mixture to contain three com- pounds, methylene quinuclidinone and two unknown com- Bykov, V., Issaeva, N., Selivanova, G. et al. (2002) Mutant p53-dependent pounds. (For their structures, see Lambert et  al. (2009), growth suppression distinguishes PRIMA-1 from known anticancer 4 Bioscience Horizons • Volume 8 2015 Review article drugs: a statistical analysis of information in the National Cancer development of mean graph and COMPARE algorithm, Journal of the Institute database, Carcinogenesis, 23 (12), 2011–2018. National Cancer Institute, 81 (14), 1088–1092. Cancer.gov Formaldehyde and Cancer Risk – National Cancer Institute. Rao, C., Pattlolla, J., Qian, L. et al. (2013) Chemopreventive effects of the (2014a) [Online], accessed at: http://www.cancer.gov/cancertopics/ p53-modulating agents CP-31398 and Prima-1 in tobacco carcinogen- factsheet/Risk/formaldehyde (11 Mar 2014). induced lung tumorigenesis in A/J mice, Neoplasia, 15 (9), 1018–1027. Cancer.gov Targeted Cancer Therapies – National Cancer Institute. Selivanova, G., Ryabchenko, L., Jansson, E. et al. (1999) Reactivation of (2014b) [Online], accessed at: http://www.cancer.gov/cancertopics/ mutant p53 through interaction of a C-terminal peptide with the factsheet/Therapy/targeted (9 Mar 2014). core domain, Molecular and Cellular Biology, 19 (5), 3395–3402. Cancerresearchuk.org All cancers combined key facts: Cancer Research Shchors, K., Persson, A. I., Rostker, F. et al. (2013) Using a preclinical mouse UK. [Online], accessed at: http://www.cancerresearchuk.org/cancer- model of high-grade astrocytoma to optimize p53 restoration ther- info/cancerstats/keyfacts/Allcancerscombined/ (6 Mar 2014). apy, Proceedings of the National Academy of Science of the United States of America, 110 (16), 1480–1489. Carelle, N., Piotto, E., Bellanger, A. et al. (2002) Changing patient perceptions of the side effects of cancer chemotherapy, Cancer, 95 (1), 155–163. Suntharalingam, G., Perry, M., Ward, S. et al. (2006) Cytokine storm in a phase 1 trial of the anti-CD28 monoclonal antibody TGN1412, Crocker, G. and Weedon, M. (2010) Interpretation of P-values, BclinSci New England Journal of Medicine, 355 (10), 1018–1028. Statistics Workshop, 6, 141. Surget, S., Khoury, M. and Bourdon, J. (2013). Uncovering the role of p53 Hanahan, D. and Weinberg, R. (2011) Hallmarks of cancer: the next splice variants in human malignancy: a clinical perspective, generation, Cell, 144 (5), 646–674. OncoTargets and Therapy, 7, 57. Hollstein, M., Sidransky, D., Vogelstein, B. et al. (1991) p53 mutations in Watanabe, F., Chade, D., Reis, S. et al. (2011) Curcumin, but not Prima-1, human cancers, Science, 253 (5015), 49–53. decreased tumor cell proliferation in the syngeneic murine ortho- topic bladder tumor model, Clinics, 66 (12), 2121–2124. Lambert, J., Gorzov, P., Veprintsev, D. et al. (2009) PRIMA-1 reactivates mutant p53 by covalent binding to the core domain, Cancer Cell, 15 Wu, H., Chang, D. and Huang, C. (2006) Targeted-therapy for cancer, (5), 376–388. Journal of Cancer Molecules, 2 (2), 57–66. Martinez, J. (2010) Restoring p53 tumor suppressor activity as an anti- Zandi, R., Selivanova, G., Christensen, C. et al. (2011) PRIMA-1Met/APR- cancer therapeutic strategy, Future Oncology, 6 (12), 1857–1862. 246 induces apoptosis and tumor growth delay in small cell lung Paull, K., Shoemaker, R., Hodes, L. et al. (1989) Display and analysis of pat- cancer expressing mutant p53, Clinical Cancer Research, 17 (9), terns of differential activity of drugs against human tumor cell lines: 2830–2841. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Bioscience Horizons Oxford University Press

PRIMA-1 as a cancer therapy restoring mutant p53: a review

Bioscience Horizons , Volume 8 – Nov 11, 2015

Loading next page...
 
/lp/oxford-university-press/prima-1-as-a-cancer-therapy-restoring-mutant-p53-a-review-5ACtOjgMNK
Publisher
Oxford University Press
Copyright
The Author 2015. Published by Oxford University Press.
eISSN
1754-7431
DOI
10.1093/biohorizons/hzv006
Publisher site
See Article on Publisher Site

Abstract

BioscienceHorizons Volume 8 2015 10.1093/biohorizons/hzv006 Review article PRIMA-1 as a cancer therapy restoring mutant p53: a review Emily J. Lewis* University of Exeter Medical School, Exeter, Devon EX1 2LU, England *Corresponding author: St Luke’s Campus, Magdalen road, Exeter, Devon EX1 2LU, England. Email: ejl213@exeter.ac.uk Supervisor: Emma Taylor, University of Exeter Medical School, Exeter, Devon EX1 2LU, England. With a continuing increase in the prevalence of cancer, there is an increasing pressure to produce novel cancer therapies. The production of targeted cancer therapies could lead to the replacement of conventional cancer chemotherapy and, conse- quently, the minimization of the associated distressing side effects. This review addresses the process of restoring a mutant tumour suppressor protein, p53, in the apoptosis pathway as a potential therapeutic target for cancer therapy. Current litera- ture highlights the small molecule PRIMA-1 as a particularly promising novel cancer therapy; however, there are currently many potential therapies being investigated; CP-31398 is another small molecule with potential anti-cancer effects. PRIMA-1 acts to restore the mutant p53 by modifying thiol groups in the core domains of the protein. Its success is well documented, with many studies in different cancer models proving its effectiveness. This, however, is not unanimous, with some questions being raised about its efficacy and other aspects such as possible resistance mechanisms as well as potentially harmful degra - dation products. This said, PRIMA-1 has entered Stage II clinical trials and with more data collected on in vivo models and potential complications of the drug, it could ultimately provide an alternative to conventional cancer chemotherapy. This could therefore help to prevent cancer patients suffering the displeasing side effects with which it is associated. Key words: cancer therapy, targeted therapy, PRIMA-1, p53 Submitted on 24 September 2014; accepted on 7 September 2015 Introduction Carelle et al. (2002) documented these with the most distress- ing side effects including the loss of hair, weight gain and loss There are >200 types of cancer that caused an estimated 12.7 of sexual feeling. To try and minimize the side effects associ- million new cases in 2008 (Cancer Research UK, 2014). With ated with current chemotherapy methods, researchers are this, cancer incidence rates have increased by 33% in the UK now exploring the use of drug targeting for the development since the 1970s (Cancer Research UK, 2014), and this is set to of novel therapies. Targeted cancer therapies use specific mol - increase with an ageing population. As a result, the pressure ecules involved in the development of the tumour as targets to for the discovery of novel treatments is ever increasing. halt its proliferation (National Cancer Institute, 2014b). Current chemotherapy methods, among other advances, have Success in this field has resulted from the use of both thera - led to a 2-fold increase in the survival rates in the UK in the peutic antibodies and small molecules acting on a range of last 40 years meaning that half of the people diagnosed with targets to effectively prevent the proliferation of tumours cancer now survive for at least 5 years after diagnosis (Cancer while aiming to lower the toxicity of the drugs (Wu, Chang Research UK, 2014). With this said, chemotherapy has long and Huang, 2006). This review will look at some of these been associated with side effects that can dramatically reduce developing methods focusing on targeting the absence of suf- the quality of life of cancer patients, due to the lack of specific - ficient apoptosis, one of the hallmarks of cancer, (see Fig.  1) ity of chemotherapy causing other dividing cells to be affected. (Hanahan and Weinberg, 2011) with a reduction in tumour © The Author 2015. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Review article Bioscience Horizons • Volume 8 2015 Figure 1. The hallmarks of cancer. This schematic shows the hallmarks of cancer. The red box on the diagram highlights ‘Resisting cell death’, which is the hallmark targeted by the methods studied in this review. Reprinted from Cell, 144/5, Hanahan, D., Weinberg, R.A., Hallmarks of cancer: the next generation, 646–674, copyright (2011), with permission from Elsevier. size considered evidence of a regression of malignant cells. mechanism and finally inhibiting mdm2, which is in itself an The apoptosis pathway is modified in a number of ways in inhibitor of p53. Shchors et al. (2013) used a genetically engi- cancerous cells, but this review will centre on the protein p53. neered mouse model that pharmacologically restores p53 The location of p53 in the apoptosis pathway has been high- function. They were able to activate and deactivate cancerous lighted in Fig. 2. p53 is involved in many physiological pro- effects that established the mechanism of reactivation of the cess but is mainly categorized as a tumour suppressor. It is tumour suppressor. This literature review will explore the res- involved in cell fate by integrating various forms of cell signal- toration of the mutated protein to its wild-type form as a ling mechanisms, including but not limited to nutrient, cyto- novel target for cancer therapy to supplement or even replace kine and hormone levels. The underlying mechanisms remain conventional chemotherapy methods that have undesirable unclear; however, it is thought that the TP53 gene can encode side effects. different isoforms that modulate the activity of p53, either promoting cell survival or death, depending on cell context PRIMA-1 mechanism of action and external stresses by differentially regulating gene tran- scription (Surget et al., 2013). It is normally kept at low levels There have been a number of clinical trials on drugs targeted through ubiquitation and proteasomal degradation in the cell at restoring mutant p53 proteins in cancerous cells. The most but becomes up-regulated by stress signals, often induced by promising thus far is PRIMA-1, which is a small molecule DNA damage (Selivanova et al., 1999). Once activated it leads therapy that entered its second phase of clinical trials in 2011 MET to a pathway of downstream effects including physiological (Aprea, 2012). PRIMA-1 is converted to PRIMA-1 , the functions and the induction of apoptosis which halts cancer methylated form of the drug, which works in a variety of ways progression (Martinez, 2010). In cancerous cells, p53 is often to restore p53 (Lambert et al., 2009). One proposed mecha- MET mutated and so this pathway does not proceed, which can nism of action is that the PRIMA-1 covalently binds to result in uncontrolled cell proliferation of cells with damaged and modifies thiol groups in the central domain of the mutated DNA that may include mutations in oncogenes or tumour protein (Lambert et al., 2009). This therefore causes reactiva- suppressor genes. Subsequently, this may lead to the forma- tion of the p53 protein that should subsequently regain its tion of a tumour. Hollstein et al. (1991) estimated that up to ability to induce apoptosis. There has been a range of papers 50% of human cancers have a mutation in p53, and this is investigating the therapeutic possibilities of PRIMA-1 in a therefore a promising target for novel cancer therapies with- number of different cancers. out causing the death of healthy cells as seen with traditional chemotherapy. So far there have been three main methods for The effect of p53 expression levels targeting p53 in cancerous cells. The first technique is to reac - tivate the apoptosis pathway by modifying mutant p53; the One seminal paper is the study by Bykov et al. (2002) which second is to reintroduce the p53 protein by an exogenous is a statistical analysis of the data provided on the drug by the 2 Bioscience Horizons • Volume 8 2015 Review article conditions (Bykov et al., 2002) and Zandi et al. (2011) per- formed some analysis on a xenograft model, but there is a lack of in vivo evidence. Lambert et al. (2009) drew a conclusion that ‘conversion of PRIMA-1 occurs even more efficiently in living cells than in vivo’; however, analysis from living H1299- HIS175 cells was the only evidence given. An animal model study by Watanabe et  al. (2011) that found no significant decrease in tumour size when mice were injected with PRIMA-1 raised further concerns. With this said, the results of this study did not show a significant decrease in tumour size of 1.48 mm, but with only eight mice in each of the drug and control categories, it is imperative that more research is done into the in vivo effects of the drug during its clinical trial phases (Aprea, 2012). The main implications of the deficiency of in vivo analysis are that potential side effects could go unnoticed before the drug is administered to humans. Mouse models may identify some potential problem areas; however, as shown in the TGN 1412 study, mouse models cannot be entirely relied on to highlight any potential complications (Suntharalingam et al., 2006). Furthermore, a lack of identifi - cation of severe side effects would undermine the purpose of this novel targeted drug. Timescales of drug action In addition, the identification needs to be undertaken over a long period of time to observe complications that may arise further down the line of treatment. Lambert et al. (2009) took measurements up to 24 h, and this was increased to 10 days in the Zandi et al. (2011) paper; however, few long-term studies Figure 2. Apoptosis intrinsic pathway. This diagram shows the of the potential effects of PRIMA-1, either advantageous or intrinsic pathway of apoptosis. The red box denotes the location of the otherwise, are freely available. Rao et al. (2013) compared the p53 in the apoptosis intrinsic pathway. From this diagram, the role of chemopreventive effect of PRIMA-1 with another small- p53 as an inducer of the apoptosis pathway is evident. molecule p53-restoring drug, CP-31398, performing a longer trial on the effects of PRIMA-1. In this trial, however, other National Cancer Institute. Human tumour cell lines were used effects of the drug were not monitored and the trial took place to find growth inhibition profiles for PRIMA-1 and 44 other in a mouse model (Rao et al. 2013). The study involved mix- commonly used cancer therapies, p53 expression levels and ing the p53 modulators with food and measuring the tumour population doubling time as a measure of the size of the size on the lungs after both 20 and 32 weeks. Photographs of tumour. The study however only analysed cell lines with the lungs are shown in the study by Rao et al. (Fig. 2). From mutant protein levels exceeding 1 unit, determined by western these, it is clear to see that both the p53 modulators decreased blotting. As a result, no conclusion can be drawn about the the size of the tumours and also that CP-31398 may in fact be efficacy of PRIMA-1 in cell lines where p53 expression had the more effective option, despite it being less well researched reached very low levels or stopped completely, and the authors at present (Rao et al. 2013). suggested that the efficacy would depend on the levels of mutant p53 in the cell. This was contested by Zandi et  al. Models of drug selectivity (2011) who selected cell lines with low or undetectable levels of p53 and reported a signic fi ant increase in the proportion of With this shortage of availability of in vivo evidence, a model Sub-G0/G1 apoptotic cells in the tumour after undertaking investigating drug selectivity could be used to get an insight cell cycle analysis. into the likelihood of complications occurring. The expecta- tion is then that the higher the selectivity of the drug, the less side effects it will cause as a result of acting on healthy cells. In vivo drug effects This was tested by Bykov et  al., (2002) using a Wilcoxon A further problem of using selected cell lines for the studies of matched paired test; for results, see figure 3 in Bykov et al., PRIMA-1 is a lack of evidence of the effects of the drug in vivo (2002). PRIMA-1 had a target selectivity that was higher than and in human subjects. Lambert et al. (2009) incubated sam- the current cancer therapies in colon cancer, NSCLC and mel- ples at 37°C and kept them at pH 7.4 to simulate human anomas with selective advantages over certain therapies in 3 Review article Bioscience Horizons • Volume 8 2015 other cancers. A P-value of 0.04 was also calculated which Fig.  1). It would therefore be imperative that the effects of was interpreted as being a statistically significant preference of these unknown compounds were investigated fully, as well as PRIMA-1 for mutant-p53 strains over non-mutated p53 those of the PRIMA itself, to ensure that the drug will be suit- (Bykov et al., 2002). It should however be noted that a P-value able for clinical use. Lambert et  al. (2009) also stated that of 0.04, although significant, is often only defined as ‘some another breakdown product of PRIMA-1 is formaldehyde. evidence of a difference’ (Crocker and Weedon, 2010). The Formaldehyde has been classified as a known human carcino - selectivity shown by PRIMA-1 may have other benefits as well gen by the International Agency for Research on Cancer as the limitation of side effects. The high selectivity of the drug (National Cancer Institute, 2014a); however, the potential may also have positive repercussions with respect to drug implications of this have not yet been assessed in a PRIMA-1 resistance, which is becoming an ever-increasing problem in study. all aspects of medicine. Conclusion Resistance to PRIMA-1 In conclusion, cancer is a disease that is hugely prevalent, with An inevitable increase in resistance to cancer chemotherapy cases increasing year on year. Treatment has progressed in drugs as their prescription is increasing is another motivation recent years, with chemotherapy now available to treat most for developing novel cancer therapies. To investigate the pos- cancers with an increasing success rate. Despite this improve- sible resistance mechanisms to PRIMA-1, Bykov et al. (2002) ment, the afflicting associated side effects with chemotherapy performed the Compare algorithm of the NCI database in leave many opportunities for innovation. Drug targeting is reverse (Paull et  al., 1989). They found that resistance to proving to offer many potential alternatives, with targeting PRIMA-1 could be caused by insulin-like growth receptor the apoptosis pathway being one of the most explored. (p = 0.35) and a proto-oncogene tyrosine kinase (p = 0.44), as PRIMA-1 exploits the high occurrence of a mutated p53 pro- well as by more universal resistance mechanisms such as tein in cancers and acts to restore the mutated protein to its efflux pumps and a multi-drug-resistant protein ( Bykov et al., wild-type state. The restored p53 can then resume its role 2002). N-acetylcysteine was also identified as blocking apop - inducing apoptosis to prevent superfluous cell proliferation. tosis induced by PRIMA-1 (Lambert et al., 2009, see figure 3). There have been a number of studies investigating the possi- More research would have to be done into the potential effect bility of PRIMA-1, and other p53-modulating drugs such as of these resistance mechanisms on the suitability of the drug CP-31398, as novel cancer therapies to replace chemotherapy. as a cancer therapy. Data would need to be collected to inves- Combining the results of these studies provides an overall tigate the effect of these mechanisms in vivo and whether the positive outlook on the potential of these therapies with just a level of resistance would affect its therapeutic potential or few obstacles being presented before the therapy can be put whether further actions could be taken to prevent these mech- into clinical use. It is therefore suggested that further investi- anisms affecting the efficacy of PRIMA-1. gations are made into the in vivo effects of the drug, especially in the long term, with a focus of identifying other possible A cluster analysis was performed by Bykov et  al. (2002) effects of the drugs. which could provide an insight into the chances of a large-scale resistance to PRIMA-1. Clustering was performed according Author’s biography to Ward’s method, and a dendogram was generated showing 44 therapies and their relation to PRIMA-1 (Bykov et  al. E.J.L. is a student at the University of Exeter Medical School (2002), see figure 4). As can be seen from the figure, PRIMA-1 where she is currently studying Medical Sciences, a transla- clusters away from many other commonly used therapies, only tional science degree investigating the science underpinning showing similarities to the purine analogues. This could be a medicine and clinical practice. Her specific interests are in potential benefit with respect to multi-drug resistance mecha - cancer biology, pharmacology and microbiology. E.J.L. aspires nisms, as tumour cells would have to evolve different resis- to study postgraduate medicine. She would also like to main- tance mechanisms to PRIMA-1 than conventional cancer tain an involvement in clinical research while practicing. She therapies to avoid being affected by the novel drug. wrote up this paper and has primary responsibility for its final content. Other potential issues References As well as potential issues concerning resistance, the Lambert et al. (2009) study on PRIMA-1 has raised a few further pos- Aprea.com. (2012) Aprea announces positive data from a clinical Phase sible shortcomings of the drug. At 15 min, a sample of the I/II study with APR-246 | Aprea. [Online], accessed at: http://aprea. solution containing PRIMA-1 and its degradation products com/2012/aprea-announces-positive-data-from-a-clinical-phase-iii- was analysed using mass spectrometry and nuclear magnetic study-with-apr-246/ (10 Mar 2014). resonance. This showed the mixture to contain three com- pounds, methylene quinuclidinone and two unknown com- Bykov, V., Issaeva, N., Selivanova, G. et al. (2002) Mutant p53-dependent pounds. (For their structures, see Lambert et  al. (2009), growth suppression distinguishes PRIMA-1 from known anticancer 4 Bioscience Horizons • Volume 8 2015 Review article drugs: a statistical analysis of information in the National Cancer development of mean graph and COMPARE algorithm, Journal of the Institute database, Carcinogenesis, 23 (12), 2011–2018. National Cancer Institute, 81 (14), 1088–1092. Cancer.gov Formaldehyde and Cancer Risk – National Cancer Institute. Rao, C., Pattlolla, J., Qian, L. et al. (2013) Chemopreventive effects of the (2014a) [Online], accessed at: http://www.cancer.gov/cancertopics/ p53-modulating agents CP-31398 and Prima-1 in tobacco carcinogen- factsheet/Risk/formaldehyde (11 Mar 2014). induced lung tumorigenesis in A/J mice, Neoplasia, 15 (9), 1018–1027. Cancer.gov Targeted Cancer Therapies – National Cancer Institute. Selivanova, G., Ryabchenko, L., Jansson, E. et al. (1999) Reactivation of (2014b) [Online], accessed at: http://www.cancer.gov/cancertopics/ mutant p53 through interaction of a C-terminal peptide with the factsheet/Therapy/targeted (9 Mar 2014). core domain, Molecular and Cellular Biology, 19 (5), 3395–3402. Cancerresearchuk.org All cancers combined key facts: Cancer Research Shchors, K., Persson, A. I., Rostker, F. et al. (2013) Using a preclinical mouse UK. [Online], accessed at: http://www.cancerresearchuk.org/cancer- model of high-grade astrocytoma to optimize p53 restoration ther- info/cancerstats/keyfacts/Allcancerscombined/ (6 Mar 2014). apy, Proceedings of the National Academy of Science of the United States of America, 110 (16), 1480–1489. Carelle, N., Piotto, E., Bellanger, A. et al. (2002) Changing patient perceptions of the side effects of cancer chemotherapy, Cancer, 95 (1), 155–163. Suntharalingam, G., Perry, M., Ward, S. et al. (2006) Cytokine storm in a phase 1 trial of the anti-CD28 monoclonal antibody TGN1412, Crocker, G. and Weedon, M. (2010) Interpretation of P-values, BclinSci New England Journal of Medicine, 355 (10), 1018–1028. Statistics Workshop, 6, 141. Surget, S., Khoury, M. and Bourdon, J. (2013). Uncovering the role of p53 Hanahan, D. and Weinberg, R. (2011) Hallmarks of cancer: the next splice variants in human malignancy: a clinical perspective, generation, Cell, 144 (5), 646–674. OncoTargets and Therapy, 7, 57. Hollstein, M., Sidransky, D., Vogelstein, B. et al. (1991) p53 mutations in Watanabe, F., Chade, D., Reis, S. et al. (2011) Curcumin, but not Prima-1, human cancers, Science, 253 (5015), 49–53. decreased tumor cell proliferation in the syngeneic murine ortho- topic bladder tumor model, Clinics, 66 (12), 2121–2124. Lambert, J., Gorzov, P., Veprintsev, D. et al. (2009) PRIMA-1 reactivates mutant p53 by covalent binding to the core domain, Cancer Cell, 15 Wu, H., Chang, D. and Huang, C. (2006) Targeted-therapy for cancer, (5), 376–388. Journal of Cancer Molecules, 2 (2), 57–66. Martinez, J. (2010) Restoring p53 tumor suppressor activity as an anti- Zandi, R., Selivanova, G., Christensen, C. et al. (2011) PRIMA-1Met/APR- cancer therapeutic strategy, Future Oncology, 6 (12), 1857–1862. 246 induces apoptosis and tumor growth delay in small cell lung Paull, K., Shoemaker, R., Hodes, L. et al. (1989) Display and analysis of pat- cancer expressing mutant p53, Clinical Cancer Research, 17 (9), terns of differential activity of drugs against human tumor cell lines: 2830–2841.

Journal

Bioscience HorizonsOxford University Press

Published: Nov 11, 2015

There are no references for this article.