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The potential for BRAF V600 inhibitors in advanced cutaneous melanoma: rationale and latest evidence:

The potential for BRAF V600 inhibitors in advanced cutaneous melanoma: rationale and latest... 432949 TAM C Therapeutic Advances in Medical Oncology Review Ther Adv Med Oncol The potential for BRAF V600 inhibitors in (2012) 0(0) 61 –73 DOI: 10.1177/ advanced cutaneous melanoma: rationale 1758834011432949 © The Author(s), 2011. Reprints and permissions: and latest evidence http://www.sagepub.co.uk/ journalsPermissions.nav Charlotte Lemech, Jeffrey Infante and Hendrik-Tobias Arkenau Abstract: Historically, patients with advanced cutaneous melanoma have a poor prognosis and limited treatment options. The discovery of selective v-raf murine sarcoma viral oncogene homolog B1 (BRAF) V600 mutation as an oncogenic mutation in cutaneous melanoma and the importance of the mitogen-activated protein kinase (MAPK) pathway in its tumourigenesis have changed the treatment paradigm for melanoma. Selective BRAF inhibitors and now MEK inhibitors have demonstrated response rates far higher than standard chemotherapeutic options and we review the phase I–III results for these agents in this article. The understanding of mechanisms of resistance that may occur upstream, downstream, at the BRAF level or bypassing the MAPK pathway provides a platform for rational drug development and combination therapies. Keywords: BRAF inhibitor, BRAF V600E, cutaneous melanoma, ipilimumab, MEK inhibitor, resistance, vemurafenib Correspondence to: Introduction 2010] and more recently in the first-line setting in Hendrik-Tobias Arkenau Malignant melanoma is the sixth most common combination with dacarbazine [Robert et al. 2011]. MD PhD Sarah Cannon Research type of new cancer in the UK and the fifth most In addition, the selective v-raf murine sarcoma viral UK, 93 Harley Street, common in the USA [National Cancer Institute, oncogene homolog B1 (BRAF) inhibitor, vemu- London W1G 6AD, UK; and University College London, 2010]. Although it is the least common skin cancer, rafenib (PLX4032), has also demonstrated an OS London, UK. cutaneous melanoma is the most life threatening benefit compared with dacarbazine in the first-line tobias.arkenau@ with metastases present in 10–15% of patients at setting [Chapman et al. 2011]. Thus, it is the advent sarahcannonresearch. co.uk diagnosis [National Cancer Institute - Surveillance of immunotherapy and agents targeting specific Charlotte Lemech MBBS Epidemiology and End Results, 2010]. The annual genetic aberrations that have significantly improved BSc(med) Sarah Cannon Research incidence of melanoma is escalating and in the UK outcomes in malignant melanoma. UK, London and University the incidence rates have increased more rapidly College London, London, than any of the top 10 cancers in men and women UK Jeffrey Infante MD [Cancer Research UK, 2010]. Patients with Melanoma: a heterogeneous disease Sarah Cannon Research advanced or metastatic disease confined to the skin, Although genetic aberrations and abnormal Institute, Nashville, TN, USA subcutis and lymph nodes have a median overall activity in the mitogen-activated protein kinase survival (OS) of 12 months compared with only (MAPK) pathway drive tumourigenesis in the 4–6 months for patients with visceral disease [Balch majority of cutaneous melanomas, there is an et al. 2001]. In this setting, the reported OS rates increasing body of evidence that other pathways from studies with various chemotherapeutic agents, and immunological mechanisms contribute to its including dacarbazine and temozolamide, as well as complexity. immune modulators, is between 6 and 10 months [Chapman et al. 1999; Eigentler et al. 2003; Aberrant activation of the MAPK pathway has Middleton et al. 2000]. The cytotoxic T -lymphocyte been demonstrated in over 80% of cutaneous antigen 4 (CTLA-4) antibody, ipilimumab, was the melanomas due to abnormalities at various levels first agent to demonstrate a benefit in OS in previ- along the RAS-RAF-MEK-ERK pathway [Platz ously treated metastatic melanoma [Hodi et al. et al. 2008]. http://tam.sagepub.com 61 Therapeutic Advances in Medical Oncology 0 (0) Activation of the Rat Sarcoma (RAS) family Another frequently occurring mutation is the GTPases by growth factors or by RAS mutation is CKIT mutation, specifically in melanomas of both the first step driving this pathway. Activated RAS ultraviolet (UV)-protected sites, acral and mucosal proteins can complex with and activate members melanomas (in 36% and 39%, respectively), as well of the RAF kinase family (ARAF, BRAF and as melanoma on chronically sun-damaged skin CRAF), causing subsequent phosphorylation (28%) [Curtin et al. 2006]. and activation of MEK 1 and MEK2, followed by extracellular signal-regulated kinases (ERK1 and Increased copy number of GAB2, a scaffolding ERK2) [Davies et al. 2002]. In turn, this leads to protein that mediates interactions with various phosphorylation of the erythroblast transformation signalling pathways, including RAS-RAF-MEK- specific (ETS) protein family, nuclear transcrip- ERK and phosphoinositide 3-kinase (PI3K)- tion factor activation, expression of cell-cycle AKT signalling, has also been demonstrated in up regulators such as cyclin D, finally leading to to 26% of acral and mucosal melanomas and is cell-cycle progression and regulation of cellular mutually exclusive of BRAF, NRAS and KIT differentiation, senescence and apoptosis/survival mutations [Chernoff et al. 2009]. NRAS muta- [Platz et al. 2008]. Although activity along this tions have been demonstrated in 20–29% of pathway is essential for normal cell function, melanomas of all subtypes and are associated abnormal activation of the MAPK pathway due with a higher Clark level of invasion and older age to mutations and aberrations at various levels has compared with BRAF mutation tumours [Curtin been implicated in a number of cancer types, not et al. 2006; Edlundh-Rose et al. 2006]. only malignant melanoma but also colorectal cancer and borderline ovarian cancer, among Improved understanding of the genetic heteroge- others [Davies et al. 2002]. neity in melanoma, the detection of oncogenic mutations and the ability to target these mutations Mutations along the MAPK pathway and other has dramatically expanded the treatment options genetic alterations have been documented in available for this disease. varying frequencies in primary and metastatic melanomas based on site, previous sun exposure, skin damage and other factors [Curtin et al. 2005, Types of BRAF mutations Long et al. 2011a]. BRAF is a serine/threonine protein kinase, encoded on chromosome 7q34, that activates the MAPK/ The BRAF mutation is among the most studied, ERK signalling pathway. There are now over 100 occurring in 36–59% of primary melanomas somatic mutations identified in BRAF [Wellcome and 42–66% of metastatic melanomas [Houben Trust Sanger Institute, 2011]. et al. 2004; Jakob et al. 2011; Long et al. 2011a] and has been characterized as an oncogenic The most common somatic mutation, found in mutation [Davies et al, 2002.; Karasarides et al. 66–90% of BRAF-mutant melanomas [Cheng 2004]. The BRAF mutation has been demon- et al. 2011; Wellcome Trust Sanger Institute, strated to occur more frequently in intermit- 2011; Long et al. 2011a], occurs in the activating tently sun-exposed sites (i.e. trunk) and sites segment in exon 15 and involves the substitution without chronic sun-induced damage and are of glutamic acid for valine at codon 600 (GTG also present in 10–15% of primary cases of to GAG, known as V600E] [Davies et al. 2002; mucosal and acral melanomas [Curtin et al. Platz et al. 2008]. This leads to elevated kinase 2005; Long et al. 2011a]. activity compared with BRAF wild type (wt) dis- ease, stimulated phosphorylation of downstream In contrast, mutational analyses of melanoma in endogenous ERK and subsequent cellular prolif- patients with high sun exposure and chronic sun- eration and survival [Davies et al. 2002; Dhomen induced skin damage more often have high cyclin and Marais, 2009]. D1 (CCND1) and cyclin-dependent kinase 4 (CDK4) gene copy numbers. Increased CCND1 A number of other clinically relevant, but less copy number has also been demonstrated in common mutations have also been described, acral melanoma (44%), lentigo maligna melanoma including V600K and V600G/R. The V600K (10%) and superficial spreading melanoma (6%) mutation has been reported in 16–30% of patients [Sauter et al. 2002]. with BRAF-mutant metastatic melanoma [Cheng 62 http://tam.sagepub.com C Lemech, J Infante et al. et al. 2011; Long et al. 2011; Rubinstein et al. showed disease stabilization in a few unselected 2010; Thomas et al. 2007]. It involves two point patients with advanced melanoma, but without mutations (GTG to AAG) resulting in a substi- any impact on survival [Eisen et al. 2006]. Another tution of lysine for valine. The frequency of phase II study of sorafenib in combination with non-V600E mutations is particularly important dacarbazine in patients with untreated melanoma when interpreting the clinical trials of the BRAF showed an improvement in median progression- inhibitors, which vary in the mutation subtypes free survival (PFS), but this did not translate into that are included. an OS benefit [McDermott et al. 2008]. In addi- tion, there was no activity demonstrated in a In primary melanomas, BRAF-mutant status has phase III trial in the second-line setting combining been associated with younger age (age ≤40 years), sorafenib with carboplatin and paclitaxel [Hauschild histopathologic subtype (superficial spreading et al. 2009]. and nodular melanoma), presence of mitoses, single or occult primary melanoma and truncal location [Long et al. 2011b]. Recent data in BRAF inhibitors patients with advanced disease demonstrate BRAF The two most advanced agents currently in mutation rates greater than 80% in those less than clinical development are the selective BRAF 40 years, with V600E more common at younger inhibitors, vemurafenib (PLX4032, RG 7204) ages and V600K more common at older ages and GSK2118436 (GSK436). [Menzies et al. 2011]. Other reported associated factors include fewer markers of chronic sun Vemurafenib is an orally available, highly potent, damage in surrounding skin, higher total body ATP-competitive inhibitor of mutant BRAF. The nevus counts, early life UV exposure and histo- phase I (dose extension phase), II and III trials for pathologic findings, including heavy melaniza- this agent included patients with BRAF V600E- tion and prominent upward scatter of melanocytes mutant metastatic melanoma, confirmed by [Liu et al. 2006; Thomas et al. 2007; Viros et al. means of a polymerase chain reaction (PCR) 2008]. assay (cobas 4800 BRAF V600 Mutation Test, Roche Molecular Systems Inc., Pleasanton, CA, BRAF mutations are a negative marker for sur- USA). This assay involves hybridizing a probe, vival with a strong association with inferior OS specific to the 1799T→A substitution that results demonstrated in the metastatic setting [Houben in the V600E BRAF mutation, with DNA isolated et al. 2004; Long et al. 2011b; Flaherty, 2011]. It from formalin-fixed, paraffin-embedded tumour has also been demonstrated that patients with tissue and determining the presence or absence of BRAF mutation treated with a BRAF inhibitor amplification after repeated chain-reaction cycles. have an improved OS compared with those with Patients with other DNA alterations giving rise BRAF wt and BRAF-mutant status not receiving to V600E and non-V600E mutations were thus a BRAF inhibitor [Long et al. 2011a], findings excluded. which have been confirmed in later phase trials. The phase I study included a dose-escalation Early preclinical studies of RAF inhibition phase (from 160 mg twice daily to 1120 mg twice demonstrated that specific inhibitory nucleic daily) and dose-extension phase (recommended acids or chemical RAF inhibition in cell lines phase II dose of 960 mg twice daily) and demon- and xenograft models caused growth arrest and strated a response rate (RR) of 69% (11 of 16 induction of apoptosis [Calipel et al. 2003; patients) in the dose-escalation phase and 81% Hoeflich et al. 2006]. (26 of 32 patients) in the dose-extension phase. At the time of publication, the estimated median The earliest clinical trials of RAF inhibition with PFS was more than 7 months with duration of metastatic melanoma involved the multiple tyros- response ranging from 2 months to over 18 ine kinase inhibitor sorafenib. Although it was ini- months [Flaherty et al. 2010]. tially developed as a RAF inhibitor, sorafenib has inhibitory effects on vascular endothelial growth The subsequent BRAF in Melanoma 2 (BRIM- factor receptor 2 (VEGFR2), VEGFR3, platelet- 2) phase II study included 132 patients and derived growth factor receptor β (PDGFRβ), showed RR of 53%, stable disease (SD) in a fur- cKIT and fms-like tyrosine kinase receptor 3 ther 29%, median PFS of 6.7 months and OS at (FLT3). A randomized phase II study of sorafenib 6 and 12 months of 77% and 58%, respectively. http://tam.sagepub.com 63 Therapeutic Advances in Medical Oncology 0 (0) At the time of the report, the median OS had not and the subgroup of patients with a V600K muta- been reached [Ribas et al. 2011]. tion demonstrated a RR of 44% (four of nine). The recent phase III BRAF Inhibitor in Melanoma Overall GSK436 was very well tolerated with 3 trial (BRIM-3) compared vemurafenib (960 mg side effects similar to those described with twice daily) with dacarbazine (1000 mg/m ) as vemurafenib, including skin changes (37%, one first-line treatment in patients with BRAF V600E- G3), low-grade cutaneous SCC (two patients), mutant metastatic melanoma [Chapman et al. headache (19%, one G3), nausea (18% G1), 2011]. The RR was 48% for vemurafenib and fatigue (15% G1) and vomiting (13%, four G2). 5% for dacarbazine with a significant prolonged Although the majority of side effects are similar median PFS of 5.3 months in the vemurafenib between the two BRAF inhibitors, vemurafenib arm compared with 1.6 months on dacarbazine is associated with photosensitivity in up to 30% [hazard ratio (HR) 0.26; 95% confidence interval of patients (12% G2 or G3) while pyrexia is (CI) 0.20–0.33, p < 0.0001]. Treatment with reported in 15% (2% G3) on GSK436. vemurafenib resulted in a 63% relative risk reduc- tion for death and a 74% risk reduction for either Interestingly, in the dose-escalation phase with death or disease progression. At 6 months, the OS GSK436, a cohort of 10 patients with previously was 84% for patients who received vemurafenib untreated brain metastases also demonstrated a compared with 64% for patients who received significant RR to treatment. There was a reduction dacarbazine. The adverse events (AEs) were con- in size of the brain metastases in 9 of 10 patients, sistent with those previously described in earlier ranging from a 20% to a 100% reduction in brain trials and included grade 2 (G2) and G3 arthral- metastases that were 3–15 mm in size prior to gias (18% and 3%), rash (10% and 8%), photo- treatment. The reduction in brain metastases sensitivity (12% G2 or G3), fatigue (11% and correlated with extra-cranial response [Long et al. 2%), cutaneous squamous-cell carcinoma (SCC, 2010]. 12%), keratoacanthoma (2% and 6%), nausea (7% and 1%) and diarrhoea (5% and <1%). Dose Further studies of GSK436 that have completed interruption and modification were required in accrual and may be reported in 2012 include 38% of patients. GSK436 versus dacarbazine in previously untreated patients with BRAF-mutant advanced or meta- Interestingly, BRIM-3 also included 10 patients static melanoma, as well as a study of GSK436 in with a V600K mutation, 4 of whom demonstrated BRAF-mutant metastatic melanoma to the brain a good clinical response. Comparison of the PCR [ClinicalTrials.gov Identifier NCT01227889]. assay (cobas 4800 BRAF V600 Mutation Test) and Sanger sequencing has demonstrated higher Importantly, the response to BRAF inhibition sensitivity in the detection of V600E mutations with improvement in symptoms and performance with the PCR test; however, 6.8% of samples status is usually rapid, occurring within the identified by the PCR assay were shown to have a first 2 weeks, and has shown concordance with V600K rather than V600E mutation, confirmed fluorodeoxyglucose positron emission tomogra- on Sanger sequencing [Bloom et al. 2011]. phy (FDG-PET) response [McArthur et al. 2010]. Interestingly, heterogeneous FDG-PET GSK436 is an ATP-competitive, reversible inhib- response at day 15 of treatment has been demon- itor of mutant BRAF V600E, as well as V600K strated in up to 26% of patients in a substudy of and V600G kinases. A phase I–II trial enrolled 61 23 patients, with significantly shorter time to patients including 52 with BRAF-mutant mela- progression compared with those with a homog- noma [Kefford et al. 2010]. There was a high RR enous FDG-PET response [Carlino et al. 2011]. with 18 of 30 patients (60%) demonstrating par- tial response (PR) at first restaging during weeks As evidenced with both selective BRAF inhibi- 8–9. The PFS at the expanded dose of 150 mg tors, though less commonly with GSK436 twice daily was 8.3 months. [Kefford et al. 2010], the increased incidence of cutaneous SCC generally develops between In the dose expansion cohort of 20 patients, 77% weeks 2 and 14 and is hypothesized to be due to had a BRAF V600E mutation and 19% had a upstream RAS mutations in pre-existing SCC V600K mutation [Kefford, 2010]. Patients with a skin lesions, occurring in approximately 15% of BRAF V600E mutation demonstrated RR of 77% patients. Selective inhibition of downstream BRAF 64 http://tam.sagepub.com C Lemech, J Infante et al. can lead to CRAF signalling by mutant RAS with patients) and a further 18% had SD [Falchook subsequent development of SCCs [Arkenau et al. et al. 2010]. 2010]. The majority of these SCCs are keratoa- canthoma type, well differentiated with no meta- The most common AEs were an acneiform rash static potential and can be treated with surgical (all grade 85%; ≥G3 2%) usually on the face, excision [Flaherty et al. 2010]. torso and arms, diarrhoea (all grade 48%; ≥G3 2%), fatigue (all grade 37%; ≥G3 7%) and nausea (all grade 20%; ≥G3 0). Less common events MEK inhibitors requiring monitoring in future studies included In addition to inhibiting BRAF signalling with left ventricular systolic dysfunction (9 of 162 selective BRAF inhibitors, preclinical and clini- patients), central serous retinopathy (3 of 162 cal evidence also supports the antiproliferative patients, at dose levels higher than 2 mg daily) activity of MEK inhibitors in melanoma [Zhang and retinal vein occlusion (1 of 162 patients at et al. 2003]. 2 mg daily). Importantly, central serous retinopa- thy is reversible on drug cessation [Infante et al. The earliest MEK inhibitors in preclinical and 2010]. Retinal vein occlusion is not reversible; clinical development were PD98059, UO126 however, the one patient affected had a significant and CI-1040 [Messersmith et al. 2006]; however improvement in vision with intraocular anti- limited clinical activity did not warrant further VEGF therapy [Infante et al. 2010]. investigation of these agents. Further single-agent activity is being assessed in PD0325901 was a second-generation MEK an ongoing phase III trial, randomizing patients inhibitor also evaluated in phase I and II trials with to GSK1120212 versus first or second-line some preliminary evidence of response and disease chemotherapy. stabilization in patients with metastatic melanoma [Lorusso et al. 2005]. Dose-limiting diarrhoea and rash prevented further dose escalation and phase II Combination therapy with MEK and trials were suspended due to the occurrence of reti- BRAF inhibitors nal vein thrombosis in several patients. There is early clinical evidence that the combina- tion of BRAF and MEK inhibitors shows clinical AZD6244 was another MEK inhibitor assessed activity in BRAF V600-mutant melanoma with in early phase trials. The phase I trial enrolled a lower incidence of rash and BRAF-induced 57 patients, 20 of whom (35%) had melanoma hyperproliferative skin lesions [Infante et al. 2011]. [Adjei et al. 2008]. One patient had an objective The rationale for combining both agents is based response and seven patients achieved disease on preclinical studies that demonstrate potential stabilization after two cycles. A further rand- reduction in drug resistance as well as decreased omized phase II study comparing AZD6244 and incidence of BRAF inhibitor induced hyperprolif- temozolamide demonstrated an RR of 12% (5 erative skin changes and SCCs. Preliminary results of 42 patients) in BRAF-mutant metastatic mel- at doses of GSK436 150 mg twice daily and anoma [Dummer et al. 2008] but no significant GSK1120212 2 mg daily (19 patients) showed a difference in the primary endpoint of PFS. complete response (CR) rate of 11%, a total RR Further single-agent clinical trials have not been (CR + PR) of 74% and clinical benefit rate (CR + pursued but phase II combination trials with PR + SD) of 100%. Compared with single-agent dacarbazine, docetaxel and temsirolimus are toxicities there was also a lower incidence of rash currently underway in BRAF-mutant metastatic (all grade 25%; ≥G3 2%) and hyperproliferative melanoma in the first-line setting [ClinicalTrials. skin lesions. Other common G2 toxicities were gov Identifier NCT00936221, ClinicalTrials. pyrexia (11%), vomiting (4%) and fatigue (4%). gov Identifier NCT01256359, ClinicalTrials. Significantly, only 1 of 109 patients developed cuta- gov Identifier NCT01166126 respectively.]. neous SCC, supporting the preclinical evidence that the combination leads to reduction of SCCs, The phase I–II study of the MEK inhibitor potentially by switching off the CRAF-activated GSK1120212 in patients with advanced BRAF- pathway through downstream MEK inhibition. mutant melanoma showed good tolerability and encouraging RRs. At the recommended phase II A number of clinical trials assessing the combi- dose of 2 mg once daily, RRs were 40% (8 of 20 nation of BRAF and MEK inhibitors or the http://tam.sagepub.com 65 Therapeutic Advances in Medical Oncology 0 (0) combination of inhibitors of the MAPK pathway response. Cyclin D1 and Ki67 staining on IHC with other agents are underway. The combination were also decreased, consistent with reduced of vemurafenib with the MEK inhibitor GDC0973 proliferation. There were no significant effects on is being assessed in patients with BRAF V600E- phosphorylation of AKT or on phosphatase and mutant metastatic melanoma whose disease has tensin homolog (PTEN) expression. Interestingly, progressed after treatment with vemurafenib. on progression, some but not all tumours were Vemurafenib is also being studied in combination found to have a return of ERK and MEK phos- with ipilimumab. phorylation, indicating the presence of both ERK-dependent and ERK-independent mecha- More general studies that may show relevance in nisms of resistance. Sequenom analysis demon- the setting of melanoma include studies of MEK strated the presence of NRAS G12R mutation in inhibitors (e.g. GSK1120212 or GDC0973) and 1 of 11 patients and MEK P124S mutation in 1 PI3K inhibitors (e.g. BKM120 or GDC0941) in of 28 patients with resistant tumours. One patient advanced solid tumours. Other novel agents in was shown to have PTEN loss and an increase in development have dual BRAF and CRAF activ- phosphorylated AKT (pAKT) at progression, ity and include PLX4720 and RAF265. indicating the PI3K-AKT-mammalian target of rapamycin (mTOR) pathway may act as a bypass signalling pathway. Sequenom analysis also con- Resistance to BRAF inhibitors firmed BRAF V600E mutation was present in all Recent studies investigating primary and second- progression samples (10/10). ary resistance to BRAF inhibition have identified both upstream, downstream and bypass mecha- An exploratory tumour gene analysis of patients nisms that act in an ERK-dependent or ERK- treated in the GSK436 phase I–II trial also independent manner [Corcoran et al. 2011], as demonstrated several potential mechanisms of illustrated in Table 1. Primary resistance, when resistance, including alterations in PTEN and patients have progressive disease as their best mutations in CDK4 and β-catenin [Nathanson response to treatment, is present in less than 15% et al. 2011]. A MEK2 mutation was demon- of patients treated with BRAF or MEK inhibitors strated in a tumour sample of one patient with for BRAF V600-mutant metastatic melanoma SD. Pretreatment analysis demonstrated that [Chapman et al. 2011; Flaherty et al. 2010; abnormal PTEN (deleted or mutant) was asso- Kefford et al. 2010; Ribas et al. 2011]. However, ciated with shorter PFS. Analysis of array-based secondary or acquired resistance develops in the comparative genomic hybridization also demon- majority of patients after an initial response, with strated that patients with CDKN2A or KIT the duration of this response ranging between 2 deletion had a shorter PFS. months and 1.8 years with a median of 8–9 months [Flaherty et al. 2010]. The results of the above studies suggest mecha- nisms of resistance that may occur upstream As part of the phase I vemurafenib trial, the effect (NRAS mutation) or downstream of BRAF along on key signalling pathways and mechanisms of the MAPK pathway (MEK mutation), as well as acquired resistance were investigated [McArthur alternative bypass signalling pathways through et al. 2011]. Formalin-fixed paraffin-embedded the PI3K-AKT pathway and through abnormali- samples were obtained from a total of 23 patients ties in CDK4/cyclin D1. Further resistance (5 patients from the dose-escalation cohort and mechanisms have also been investigated in mela- 18 patients from the melanoma expansion cohort) noma cell lines, tumour models and through at three different time points; at baseline, at day individual case reports [Corcoran et al. 2010; 15 of treatment and at disease progression while Emery et al. 2009; Johannessen et al. 2010; Little still receiving vemurafenib. Immunohistochemical et al. 2011; Montagut et al. 2008; Nazarian et al. (IHC) staining for a number of different molecu- 2010; Wagle et al. 2011]. The majority of these lar markers was performed as well as Sequenom data focus on mechanisms of acquired resistance, MassARRAY of over 400 mutations in genes, though some overlap with primary resistance including BRAF, RAS, PIK3CA, AKT1/2 and exists. CDK4. At day 15, phosphorylated ERK (pERK) and phosphorylated MEK (pMEK) were mark- These substudies also demonstrate the necessity edly reduced, consistent with decreased signal- of longitudinal tumour biopsies to fully charac- ling downstream and correlating with tumour terize the activity of targeted agents, investigate 66 http://tam.sagepub.com C Lemech, J Infante et al. http://tam.sagepub.com 67 Table 1. Possible mechanisms of resistance to selective BRAF inhibitors and potential therapeutic combinations. Level of resistance Genetic mutation/alteration Status of ERK Potential combination therapy Reference pathway Upstream in the NRAS mutation (e.g. G12R, Dependent BRAFi + MEKi [Adjei et al. 2008; McArthur et al. 2011; MAPK pathway Q61K) Nazarian et al. 2010] PDGFRβ upregulation Independent PDGFRβ inhibitor ± BRAFi [Corcoran et al. 2011; Nazarian et al. BRAFi + IGF1Ri 2010] Other RTK upregulation Independent BRAFi + PI3K/AKT/dual mTORi [Corcoran et al. 2011; Villanueva (e.g. IGF1R signalling) et al. 2010] At the RAF level BRAF amplification Dependent BRAFi + MEKi [Corcoran et al. 2010; Little et al. 2011] Elevated CRAF activity Dependent BRAFi + MEKi or [Johannessen et al. 2010] CRAFi/nonselective RAFi [Montagut et al. 2008; Johannessen et Increased COT/Tpl2 levels Dependent BRAFi + MEKi al. 2010] (also acts downstream in the MAPK pathway) Downstream in the MEK1 mutation (e.g. P124L, Dependent BRAFi and MEKi for P124L mt [Corcoran et al. 2011; Emery et al. MAPK pathway P124S, C121S) (not C121S) 2009; McArthur et al. 2011; Wagle et al. 2011] Bypass pathway PTEN loss Independent BRAFi/MEKi + PI3K/mTORi [Nathanson et al. 2011; Paraiso et al. signalling 2011] PI3K-AKT pathway activation Independent BRAFi/MEKi + PI3K/AKT/mTORi BRAF/MEKi + PI3K/AKTi AKT3 mutation Independent BRAFi + IGF1Ri or PI3K/AKTi [Jiang et al. 2011] IGF1R signalling Independent BRAFi + mTORi [Shao and Aplin, 2010] CDK4 mutation/cyclin D1 Independent [Villanueva et al. 2010] amplification BRAFi/MEKi + imatinib Co-overexpression of KIT/ Independent [Smalley et al. 2008b, 2008a] CDK4 BRAFi, selective v-raf murine sarcoma viral oncogene homolog B1 inhibitor; CDK4, cyclin-dependent kinase 4; ERK, extracellular signal-regulated kinase; IGF1R, insulin-like growth factor 1 receptor; MAPK, mitogen-activated protein kinase; MEKi, MEK inhibitor; mTORi, mammalian target of rapamycin inhibitor; PDGFRβ, platelet-derived growth factor receptor β; PI3K, phosphoinositide 3-kinase; PTEN, phosphatase and tensin homolog; RTK, receptor tyrosine kinase. Therapeutic Advances in Medical Oncology 0 (0) resistance mechanisms and formulate rational mediated through mutations in MEK [Corcoran drug combinations for future studies. et al. 2011; Emery et al. 2009; Wagle et al. 2011]. Point mutations in MEK1 have been shown to cause secondary resistance to both BRAF inhibi- Mechanisms of resistance at the BRAF level tion and MEK inhibition in the clinical setting Secondary mutations in BRAF, as well as BRAF [Emery et al. 2009; Wagle et al. 2011]. A MEK amplification have been surmised as possible pri- point mutation has been implicated in acquired mary or secondary resistance mechanisms, as resistance to MEK inhibition [Emery et al. 2009] has been demonstrated with secondary EGFR while another MEK1 mutation, P124L, led to mutations in non-small cell lung cancer. There is both resistance to MEK inhibition and cross evidence in mouse models regarding secondary resistance to BRAF inhibition [Emery et al. 2009]. BRAF mutations [Whittaker et al. 2010] and in In addition, the point mutation C121S has been BRAF-mutant colorectal cancer cell lines regard- demonstrated in a post-relapse biopsy in a patient ing BRAF amplification [Corcoran et al. 2010; on the BRAF inhibitor vemurafenib [Wagle et al. Little et al. 2011] that suggests these mecha- 2011] and further analysis demonstrated it could nisms may play a role in resistance to BRAF or confer resistance to both RAF and MEK inhibi- MEK inhibition. To date, however, there is limited tion. Interestingly, the combination of BRAF and clinical evidence from patients’ tumour biopsies MEK inhibition was able to overcome resist- to support these preclinical findings. ance conferred by the MEK1 P124L mutation in BRAF-mutant melanoma cells [Emery et al. 2009]. Elevated activity of the alternative RAF isoform, CRAF, has also been identified in preclinical The significance of MEK2 mutations in mediat- studies as a possible mechanism of both primary ing sensitivity or resistance is currently unknown. and secondary resistance through reactivation of the MAPK pathway [Johannessen et al. 2010; Montagut et al. 2008]. These findings require fur- Mechanisms of resistance upstream of ther validation in prospective analysis of tumour BRAF in the MAPK pathway tissue and biopsies on progression but suggest NRAS mutations have been demonstrated in vitro that there may be therapeutic potential in com- and in vivo to cause resistance to BRAF inhibition bining a nonselective RAF inhibitor or selective [Nazarian et al. 2010]. NRAS Q61K mutation was CRAF inhibitor with a MEK or BRAF inhibitor. demonstrated in preclinical cell line models to confer resistance to vemurafenib, supported by its Another resistance mechanism that acts both isolation in a nodal biopsy from a patient whose at the level of BRAF and downstream in the disease had progressed after an initial response to MAPK pathway is mediated by COT/Tpl2. treatment. The NRAS mutation is thought to COT/Tpl2, encoded by MAP3K8, activates ERK signal through RAF isoforms other than BRAF, and the MAPK pathway primarily through MEK- leading to persistently elevated pMEK and pERK dependent mechanisms but is RAF independent levels despite BRAF inhibition [Nazarian et al. [Johannessen et al. 2010]. There is both preclin- 2010]. Interestingly, these cell lines may retain ical and clinical evidence [Johannessen et al. sensitivity to MEK inhibition [Adjei et al. 2008]. 2010] demonstrating elevated COT/Tpl2 levels in resistant cell lines and biopsy specimens. It is PDGFRβ upregulation, insulin-like growth fac- hypothesized that high COT levels cause MEK tor 1 receptor (IGF1R) activation and signalling hyperactivation, thus mediating resistance to both through other receptor tyrosine kinase (RTK) BRAF and MEK inhibition. Consistent with this pathways have also been investigated as ERK- hypothesis, combined BRAF and MEK inhibition independent mechanisms of resistance, acting has been demonstrated to overcome COT-induced upstream of BRAF in the MAPK pathway and resistance in experimental models [Johannessen mediating alternative pathways that bypass MAPK et al. 2010]. [Corcoran et al. 2011; Nazarian et al. 2010]. Nazarian and colleagues [Nazarian et al. 2010] Mechanisms of resistance downstream demonstrated that overexpression of PDGFRβ of BRAF in the MAPK pathway resulted in acquired resistance to vemurafenib Current preclinical and clinical evidence dem- in BRAF-mutant melanoma cell lines despite onstrates that downstream resistance is primarily persistent pERK suppression, consistent with 68 http://tam.sagepub.com C Lemech, J Infante et al. ERK independence. Additionally, 4 of 11 clinical [Smalley et al. 2008a] also demonstrated that co- postrelapse biopsies from patients with melanoma overexpression of KIT/CDK4 also led to decreased treated with vemurafenib showed increased sensitivity to BRAF inhibition in preclinical PDGFRβ expression relative to pretreatment models but may increase sensitivity to imatinib. biopsies. Although, the existence of this KIT/CDK4 sub- group has been confirmed in human melanoma samples, the clinical significance of these preclini- Mechanisms bypassing BRAF cal findings requires further investigation. signalling Signalling via the PI3K-AKT-mTOR pathway has been described as an escape pathway in vari- Future strategies ous tumour models [Gopal et al. 2010; Shao and Increased understanding of the molecular path- Aplin, 2010; Villanueva et al. 2010]. ways and aberrations in advanced and metastatic cutaneous melanoma has changed the treatment IGF1R signalling has been demonstrated as an paradigm for a large subset of patients with mela- ERK-independent mechanism of resistance and noma. However, there remain several challenges. also plays a critical role in the PI3K-AKT-mTOR This review outlines a subset of possible strate- pathway. gies to overcome resistance mechanisms that inevitably develop to BRAF and MEK inhibition. In preclinical models, Villanueva and colleagues Further challenges include combining immune [Villanueva et al. 2010] identified IGF1R acti- therapy with inhibitors of the MAPK pathway, as vation with enhanced IGF1R/PI3K signalling well as treating those patients who do not have a as a key RTK-driven acquired mechanism of BRAF mutation. resistance that could be overcome by combined IGF1R/PI3K and MEK inhibition. A number of Intensive study continues into the complex resist- other preclinical studies have also demonstrated ance mechanisms of BRAF inhibition. Whether aberrant activation in the PI3K-AKT pathway, by inhibiting both the MAPK and bypass path- evidenced by elevated pAkt, which contributes to ways, such as with BRAF-MEK and PI3K-AKT- both primary and secondary resistance and may mTOR inhibition, or by targeting IGF1R or other be overcome through combining RAF and PI3K- RTKs, a combination of these agents may be AKT inhibition [Jiang et al. 2011; Shao and effective for overcoming secondary resistance to Aplin, 2010]. PTEN loss and subsequent lack of BRAF inhibition and may be utilized in an earlier inhibition on the PI3K-AKT-mTOR pathway setting to prevent or delay resistance [Corcoran has also been demonstrated to confer acquired et al. 2011]. Importantly, obtaining biopsies lon- resistance to BRAF inhibition in preclinical mod- gitudinally during a patient’s treatment course is els [Paraiso et al. 2011] and could be reversed key to this process. The combination of molecu- with dual treatment with PLX4720 and a PI3K lar characterization in the preclinical and clinical inhibitor [Paraiso et al. 2011]. setting can further enhance identification of clini- cally relevant mutations and possible treatment Signalling via the PI3K-AKT-mTOR pathway options [Wagle et al. 2011]. mediates an important MAPK- independent mechanism of resistance and demonstrates a com- Improved understanding of the effect of BRAF plex crosstalk between these pathways [Corcoran inhibition on immune response and T-cell func- et al. 2011]. Measurement of pERK and pAKT to tion will also provide a rationale for the combina- determine pathway activity may therefore help to tion of these approaches. Treatment with selective guide therapeutic choices and combinations of BRAF inhibitors has been shown to preserve selective BRAF, MEK or PI3K/AKT inhibitors, T-cell function whereas treatment with MEK but this data require further clinical confirmation. inhibitors may impair T-cell function [Boni et al. 2010]. Improved recognition by antigen-specific Finally, dysregulation of CDK4 or cyclin D1 has T cells and increased intratumoural and peritu- also been implicated in BRAF inhibitor resistance. moural lymphocytes occurs early after exposure In preclinical models, cyclin D1 overexpression to BRAF inhibition. Conversely, patients who demonstrated increased resistance, particularly in develop resistance to BRAF inhibition demon- the presence of CDK4 mutation/overexpression strate a decrease in intratumoural and peritu- [Smalley et al. 2008b]. Smalley and colleagues moural lymphocytes [Boni et al. 2010; Long et al. http://tam.sagepub.com 69 Therapeutic Advances in Medical Oncology 0 (0) mediates cell proliferation and transformation through 2011b]. Together, these early data provide a the MEK/ERK pathway. J Biol Chem rationale for the combination of ipilimumab and 278: 42409–42418. BRAF inhibition. Cancer Research UK (2010) Skin Cancer – UK Understanding the oncogenic drivers of mela- Incidence Statistics. Available at: http://info. noma, the complex mechanisms of resistance, the cancerresearchuk.org/cancerstats/types/skin/incidence/ (accessed 29 November 2011). interaction between signalling pathways and the immune system and integration of new genomic Carlino, M.S., Saunders, C.A.,Gebski, V., technologies has increased exponentially over the Menzies, A.M., Ma, B., Lebowitz, P.F., et al. last few years and provides a rationale for the (2011) Heterogeneity of FDG-PET response to current combination studies, with further clinical GSK2118436, an inhibitor of oncogenic mutant correlation required to strengthen the rationale for BRAF-kinase in BRAF-mutant metastatic melanoma. J Clin Oncol 29(Suppl.): abstract 8539. future studies. Chapman, P.B., Einhorh, L.H., Meyers, M.L., Funding Saxman, S., Destro, A.N., Panageas K.S., et al. 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The potential for BRAF V600 inhibitors in advanced cutaneous melanoma: rationale and latest evidence:

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432949 TAM C Therapeutic Advances in Medical Oncology Review Ther Adv Med Oncol The potential for BRAF V600 inhibitors in (2012) 0(0) 61 –73 DOI: 10.1177/ advanced cutaneous melanoma: rationale 1758834011432949 © The Author(s), 2011. Reprints and permissions: and latest evidence http://www.sagepub.co.uk/ journalsPermissions.nav Charlotte Lemech, Jeffrey Infante and Hendrik-Tobias Arkenau Abstract: Historically, patients with advanced cutaneous melanoma have a poor prognosis and limited treatment options. The discovery of selective v-raf murine sarcoma viral oncogene homolog B1 (BRAF) V600 mutation as an oncogenic mutation in cutaneous melanoma and the importance of the mitogen-activated protein kinase (MAPK) pathway in its tumourigenesis have changed the treatment paradigm for melanoma. Selective BRAF inhibitors and now MEK inhibitors have demonstrated response rates far higher than standard chemotherapeutic options and we review the phase I–III results for these agents in this article. The understanding of mechanisms of resistance that may occur upstream, downstream, at the BRAF level or bypassing the MAPK pathway provides a platform for rational drug development and combination therapies. Keywords: BRAF inhibitor, BRAF V600E, cutaneous melanoma, ipilimumab, MEK inhibitor, resistance, vemurafenib Correspondence to: Introduction 2010] and more recently in the first-line setting in Hendrik-Tobias Arkenau Malignant melanoma is the sixth most common combination with dacarbazine [Robert et al. 2011]. MD PhD Sarah Cannon Research type of new cancer in the UK and the fifth most In addition, the selective v-raf murine sarcoma viral UK, 93 Harley Street, common in the USA [National Cancer Institute, oncogene homolog B1 (BRAF) inhibitor, vemu- London W1G 6AD, UK; and University College London, 2010]. Although it is the least common skin cancer, rafenib (PLX4032), has also demonstrated an OS London, UK. cutaneous melanoma is the most life threatening benefit compared with dacarbazine in the first-line tobias.arkenau@ with metastases present in 10–15% of patients at setting [Chapman et al. 2011]. Thus, it is the advent sarahcannonresearch. co.uk diagnosis [National Cancer Institute - Surveillance of immunotherapy and agents targeting specific Charlotte Lemech MBBS Epidemiology and End Results, 2010]. The annual genetic aberrations that have significantly improved BSc(med) Sarah Cannon Research incidence of melanoma is escalating and in the UK outcomes in malignant melanoma. UK, London and University the incidence rates have increased more rapidly College London, London, than any of the top 10 cancers in men and women UK Jeffrey Infante MD [Cancer Research UK, 2010]. Patients with Melanoma: a heterogeneous disease Sarah Cannon Research advanced or metastatic disease confined to the skin, Although genetic aberrations and abnormal Institute, Nashville, TN, USA subcutis and lymph nodes have a median overall activity in the mitogen-activated protein kinase survival (OS) of 12 months compared with only (MAPK) pathway drive tumourigenesis in the 4–6 months for patients with visceral disease [Balch majority of cutaneous melanomas, there is an et al. 2001]. In this setting, the reported OS rates increasing body of evidence that other pathways from studies with various chemotherapeutic agents, and immunological mechanisms contribute to its including dacarbazine and temozolamide, as well as complexity. immune modulators, is between 6 and 10 months [Chapman et al. 1999; Eigentler et al. 2003; Aberrant activation of the MAPK pathway has Middleton et al. 2000]. The cytotoxic T -lymphocyte been demonstrated in over 80% of cutaneous antigen 4 (CTLA-4) antibody, ipilimumab, was the melanomas due to abnormalities at various levels first agent to demonstrate a benefit in OS in previ- along the RAS-RAF-MEK-ERK pathway [Platz ously treated metastatic melanoma [Hodi et al. et al. 2008]. http://tam.sagepub.com 61 Therapeutic Advances in Medical Oncology 0 (0) Activation of the Rat Sarcoma (RAS) family Another frequently occurring mutation is the GTPases by growth factors or by RAS mutation is CKIT mutation, specifically in melanomas of both the first step driving this pathway. Activated RAS ultraviolet (UV)-protected sites, acral and mucosal proteins can complex with and activate members melanomas (in 36% and 39%, respectively), as well of the RAF kinase family (ARAF, BRAF and as melanoma on chronically sun-damaged skin CRAF), causing subsequent phosphorylation (28%) [Curtin et al. 2006]. and activation of MEK 1 and MEK2, followed by extracellular signal-regulated kinases (ERK1 and Increased copy number of GAB2, a scaffolding ERK2) [Davies et al. 2002]. In turn, this leads to protein that mediates interactions with various phosphorylation of the erythroblast transformation signalling pathways, including RAS-RAF-MEK- specific (ETS) protein family, nuclear transcrip- ERK and phosphoinositide 3-kinase (PI3K)- tion factor activation, expression of cell-cycle AKT signalling, has also been demonstrated in up regulators such as cyclin D, finally leading to to 26% of acral and mucosal melanomas and is cell-cycle progression and regulation of cellular mutually exclusive of BRAF, NRAS and KIT differentiation, senescence and apoptosis/survival mutations [Chernoff et al. 2009]. NRAS muta- [Platz et al. 2008]. Although activity along this tions have been demonstrated in 20–29% of pathway is essential for normal cell function, melanomas of all subtypes and are associated abnormal activation of the MAPK pathway due with a higher Clark level of invasion and older age to mutations and aberrations at various levels has compared with BRAF mutation tumours [Curtin been implicated in a number of cancer types, not et al. 2006; Edlundh-Rose et al. 2006]. only malignant melanoma but also colorectal cancer and borderline ovarian cancer, among Improved understanding of the genetic heteroge- others [Davies et al. 2002]. neity in melanoma, the detection of oncogenic mutations and the ability to target these mutations Mutations along the MAPK pathway and other has dramatically expanded the treatment options genetic alterations have been documented in available for this disease. varying frequencies in primary and metastatic melanomas based on site, previous sun exposure, skin damage and other factors [Curtin et al. 2005, Types of BRAF mutations Long et al. 2011a]. BRAF is a serine/threonine protein kinase, encoded on chromosome 7q34, that activates the MAPK/ The BRAF mutation is among the most studied, ERK signalling pathway. There are now over 100 occurring in 36–59% of primary melanomas somatic mutations identified in BRAF [Wellcome and 42–66% of metastatic melanomas [Houben Trust Sanger Institute, 2011]. et al. 2004; Jakob et al. 2011; Long et al. 2011a] and has been characterized as an oncogenic The most common somatic mutation, found in mutation [Davies et al, 2002.; Karasarides et al. 66–90% of BRAF-mutant melanomas [Cheng 2004]. The BRAF mutation has been demon- et al. 2011; Wellcome Trust Sanger Institute, strated to occur more frequently in intermit- 2011; Long et al. 2011a], occurs in the activating tently sun-exposed sites (i.e. trunk) and sites segment in exon 15 and involves the substitution without chronic sun-induced damage and are of glutamic acid for valine at codon 600 (GTG also present in 10–15% of primary cases of to GAG, known as V600E] [Davies et al. 2002; mucosal and acral melanomas [Curtin et al. Platz et al. 2008]. This leads to elevated kinase 2005; Long et al. 2011a]. activity compared with BRAF wild type (wt) dis- ease, stimulated phosphorylation of downstream In contrast, mutational analyses of melanoma in endogenous ERK and subsequent cellular prolif- patients with high sun exposure and chronic sun- eration and survival [Davies et al. 2002; Dhomen induced skin damage more often have high cyclin and Marais, 2009]. D1 (CCND1) and cyclin-dependent kinase 4 (CDK4) gene copy numbers. Increased CCND1 A number of other clinically relevant, but less copy number has also been demonstrated in common mutations have also been described, acral melanoma (44%), lentigo maligna melanoma including V600K and V600G/R. The V600K (10%) and superficial spreading melanoma (6%) mutation has been reported in 16–30% of patients [Sauter et al. 2002]. with BRAF-mutant metastatic melanoma [Cheng 62 http://tam.sagepub.com C Lemech, J Infante et al. et al. 2011; Long et al. 2011; Rubinstein et al. showed disease stabilization in a few unselected 2010; Thomas et al. 2007]. It involves two point patients with advanced melanoma, but without mutations (GTG to AAG) resulting in a substi- any impact on survival [Eisen et al. 2006]. Another tution of lysine for valine. The frequency of phase II study of sorafenib in combination with non-V600E mutations is particularly important dacarbazine in patients with untreated melanoma when interpreting the clinical trials of the BRAF showed an improvement in median progression- inhibitors, which vary in the mutation subtypes free survival (PFS), but this did not translate into that are included. an OS benefit [McDermott et al. 2008]. In addi- tion, there was no activity demonstrated in a In primary melanomas, BRAF-mutant status has phase III trial in the second-line setting combining been associated with younger age (age ≤40 years), sorafenib with carboplatin and paclitaxel [Hauschild histopathologic subtype (superficial spreading et al. 2009]. and nodular melanoma), presence of mitoses, single or occult primary melanoma and truncal location [Long et al. 2011b]. Recent data in BRAF inhibitors patients with advanced disease demonstrate BRAF The two most advanced agents currently in mutation rates greater than 80% in those less than clinical development are the selective BRAF 40 years, with V600E more common at younger inhibitors, vemurafenib (PLX4032, RG 7204) ages and V600K more common at older ages and GSK2118436 (GSK436). [Menzies et al. 2011]. Other reported associated factors include fewer markers of chronic sun Vemurafenib is an orally available, highly potent, damage in surrounding skin, higher total body ATP-competitive inhibitor of mutant BRAF. The nevus counts, early life UV exposure and histo- phase I (dose extension phase), II and III trials for pathologic findings, including heavy melaniza- this agent included patients with BRAF V600E- tion and prominent upward scatter of melanocytes mutant metastatic melanoma, confirmed by [Liu et al. 2006; Thomas et al. 2007; Viros et al. means of a polymerase chain reaction (PCR) 2008]. assay (cobas 4800 BRAF V600 Mutation Test, Roche Molecular Systems Inc., Pleasanton, CA, BRAF mutations are a negative marker for sur- USA). This assay involves hybridizing a probe, vival with a strong association with inferior OS specific to the 1799T→A substitution that results demonstrated in the metastatic setting [Houben in the V600E BRAF mutation, with DNA isolated et al. 2004; Long et al. 2011b; Flaherty, 2011]. It from formalin-fixed, paraffin-embedded tumour has also been demonstrated that patients with tissue and determining the presence or absence of BRAF mutation treated with a BRAF inhibitor amplification after repeated chain-reaction cycles. have an improved OS compared with those with Patients with other DNA alterations giving rise BRAF wt and BRAF-mutant status not receiving to V600E and non-V600E mutations were thus a BRAF inhibitor [Long et al. 2011a], findings excluded. which have been confirmed in later phase trials. The phase I study included a dose-escalation Early preclinical studies of RAF inhibition phase (from 160 mg twice daily to 1120 mg twice demonstrated that specific inhibitory nucleic daily) and dose-extension phase (recommended acids or chemical RAF inhibition in cell lines phase II dose of 960 mg twice daily) and demon- and xenograft models caused growth arrest and strated a response rate (RR) of 69% (11 of 16 induction of apoptosis [Calipel et al. 2003; patients) in the dose-escalation phase and 81% Hoeflich et al. 2006]. (26 of 32 patients) in the dose-extension phase. At the time of publication, the estimated median The earliest clinical trials of RAF inhibition with PFS was more than 7 months with duration of metastatic melanoma involved the multiple tyros- response ranging from 2 months to over 18 ine kinase inhibitor sorafenib. Although it was ini- months [Flaherty et al. 2010]. tially developed as a RAF inhibitor, sorafenib has inhibitory effects on vascular endothelial growth The subsequent BRAF in Melanoma 2 (BRIM- factor receptor 2 (VEGFR2), VEGFR3, platelet- 2) phase II study included 132 patients and derived growth factor receptor β (PDGFRβ), showed RR of 53%, stable disease (SD) in a fur- cKIT and fms-like tyrosine kinase receptor 3 ther 29%, median PFS of 6.7 months and OS at (FLT3). A randomized phase II study of sorafenib 6 and 12 months of 77% and 58%, respectively. http://tam.sagepub.com 63 Therapeutic Advances in Medical Oncology 0 (0) At the time of the report, the median OS had not and the subgroup of patients with a V600K muta- been reached [Ribas et al. 2011]. tion demonstrated a RR of 44% (four of nine). The recent phase III BRAF Inhibitor in Melanoma Overall GSK436 was very well tolerated with 3 trial (BRIM-3) compared vemurafenib (960 mg side effects similar to those described with twice daily) with dacarbazine (1000 mg/m ) as vemurafenib, including skin changes (37%, one first-line treatment in patients with BRAF V600E- G3), low-grade cutaneous SCC (two patients), mutant metastatic melanoma [Chapman et al. headache (19%, one G3), nausea (18% G1), 2011]. The RR was 48% for vemurafenib and fatigue (15% G1) and vomiting (13%, four G2). 5% for dacarbazine with a significant prolonged Although the majority of side effects are similar median PFS of 5.3 months in the vemurafenib between the two BRAF inhibitors, vemurafenib arm compared with 1.6 months on dacarbazine is associated with photosensitivity in up to 30% [hazard ratio (HR) 0.26; 95% confidence interval of patients (12% G2 or G3) while pyrexia is (CI) 0.20–0.33, p < 0.0001]. Treatment with reported in 15% (2% G3) on GSK436. vemurafenib resulted in a 63% relative risk reduc- tion for death and a 74% risk reduction for either Interestingly, in the dose-escalation phase with death or disease progression. At 6 months, the OS GSK436, a cohort of 10 patients with previously was 84% for patients who received vemurafenib untreated brain metastases also demonstrated a compared with 64% for patients who received significant RR to treatment. There was a reduction dacarbazine. The adverse events (AEs) were con- in size of the brain metastases in 9 of 10 patients, sistent with those previously described in earlier ranging from a 20% to a 100% reduction in brain trials and included grade 2 (G2) and G3 arthral- metastases that were 3–15 mm in size prior to gias (18% and 3%), rash (10% and 8%), photo- treatment. The reduction in brain metastases sensitivity (12% G2 or G3), fatigue (11% and correlated with extra-cranial response [Long et al. 2%), cutaneous squamous-cell carcinoma (SCC, 2010]. 12%), keratoacanthoma (2% and 6%), nausea (7% and 1%) and diarrhoea (5% and <1%). Dose Further studies of GSK436 that have completed interruption and modification were required in accrual and may be reported in 2012 include 38% of patients. GSK436 versus dacarbazine in previously untreated patients with BRAF-mutant advanced or meta- Interestingly, BRIM-3 also included 10 patients static melanoma, as well as a study of GSK436 in with a V600K mutation, 4 of whom demonstrated BRAF-mutant metastatic melanoma to the brain a good clinical response. Comparison of the PCR [ClinicalTrials.gov Identifier NCT01227889]. assay (cobas 4800 BRAF V600 Mutation Test) and Sanger sequencing has demonstrated higher Importantly, the response to BRAF inhibition sensitivity in the detection of V600E mutations with improvement in symptoms and performance with the PCR test; however, 6.8% of samples status is usually rapid, occurring within the identified by the PCR assay were shown to have a first 2 weeks, and has shown concordance with V600K rather than V600E mutation, confirmed fluorodeoxyglucose positron emission tomogra- on Sanger sequencing [Bloom et al. 2011]. phy (FDG-PET) response [McArthur et al. 2010]. Interestingly, heterogeneous FDG-PET GSK436 is an ATP-competitive, reversible inhib- response at day 15 of treatment has been demon- itor of mutant BRAF V600E, as well as V600K strated in up to 26% of patients in a substudy of and V600G kinases. A phase I–II trial enrolled 61 23 patients, with significantly shorter time to patients including 52 with BRAF-mutant mela- progression compared with those with a homog- noma [Kefford et al. 2010]. There was a high RR enous FDG-PET response [Carlino et al. 2011]. with 18 of 30 patients (60%) demonstrating par- tial response (PR) at first restaging during weeks As evidenced with both selective BRAF inhibi- 8–9. The PFS at the expanded dose of 150 mg tors, though less commonly with GSK436 twice daily was 8.3 months. [Kefford et al. 2010], the increased incidence of cutaneous SCC generally develops between In the dose expansion cohort of 20 patients, 77% weeks 2 and 14 and is hypothesized to be due to had a BRAF V600E mutation and 19% had a upstream RAS mutations in pre-existing SCC V600K mutation [Kefford, 2010]. Patients with a skin lesions, occurring in approximately 15% of BRAF V600E mutation demonstrated RR of 77% patients. Selective inhibition of downstream BRAF 64 http://tam.sagepub.com C Lemech, J Infante et al. can lead to CRAF signalling by mutant RAS with patients) and a further 18% had SD [Falchook subsequent development of SCCs [Arkenau et al. et al. 2010]. 2010]. The majority of these SCCs are keratoa- canthoma type, well differentiated with no meta- The most common AEs were an acneiform rash static potential and can be treated with surgical (all grade 85%; ≥G3 2%) usually on the face, excision [Flaherty et al. 2010]. torso and arms, diarrhoea (all grade 48%; ≥G3 2%), fatigue (all grade 37%; ≥G3 7%) and nausea (all grade 20%; ≥G3 0). Less common events MEK inhibitors requiring monitoring in future studies included In addition to inhibiting BRAF signalling with left ventricular systolic dysfunction (9 of 162 selective BRAF inhibitors, preclinical and clini- patients), central serous retinopathy (3 of 162 cal evidence also supports the antiproliferative patients, at dose levels higher than 2 mg daily) activity of MEK inhibitors in melanoma [Zhang and retinal vein occlusion (1 of 162 patients at et al. 2003]. 2 mg daily). Importantly, central serous retinopa- thy is reversible on drug cessation [Infante et al. The earliest MEK inhibitors in preclinical and 2010]. Retinal vein occlusion is not reversible; clinical development were PD98059, UO126 however, the one patient affected had a significant and CI-1040 [Messersmith et al. 2006]; however improvement in vision with intraocular anti- limited clinical activity did not warrant further VEGF therapy [Infante et al. 2010]. investigation of these agents. Further single-agent activity is being assessed in PD0325901 was a second-generation MEK an ongoing phase III trial, randomizing patients inhibitor also evaluated in phase I and II trials with to GSK1120212 versus first or second-line some preliminary evidence of response and disease chemotherapy. stabilization in patients with metastatic melanoma [Lorusso et al. 2005]. Dose-limiting diarrhoea and rash prevented further dose escalation and phase II Combination therapy with MEK and trials were suspended due to the occurrence of reti- BRAF inhibitors nal vein thrombosis in several patients. There is early clinical evidence that the combina- tion of BRAF and MEK inhibitors shows clinical AZD6244 was another MEK inhibitor assessed activity in BRAF V600-mutant melanoma with in early phase trials. The phase I trial enrolled a lower incidence of rash and BRAF-induced 57 patients, 20 of whom (35%) had melanoma hyperproliferative skin lesions [Infante et al. 2011]. [Adjei et al. 2008]. One patient had an objective The rationale for combining both agents is based response and seven patients achieved disease on preclinical studies that demonstrate potential stabilization after two cycles. A further rand- reduction in drug resistance as well as decreased omized phase II study comparing AZD6244 and incidence of BRAF inhibitor induced hyperprolif- temozolamide demonstrated an RR of 12% (5 erative skin changes and SCCs. Preliminary results of 42 patients) in BRAF-mutant metastatic mel- at doses of GSK436 150 mg twice daily and anoma [Dummer et al. 2008] but no significant GSK1120212 2 mg daily (19 patients) showed a difference in the primary endpoint of PFS. complete response (CR) rate of 11%, a total RR Further single-agent clinical trials have not been (CR + PR) of 74% and clinical benefit rate (CR + pursued but phase II combination trials with PR + SD) of 100%. Compared with single-agent dacarbazine, docetaxel and temsirolimus are toxicities there was also a lower incidence of rash currently underway in BRAF-mutant metastatic (all grade 25%; ≥G3 2%) and hyperproliferative melanoma in the first-line setting [ClinicalTrials. skin lesions. Other common G2 toxicities were gov Identifier NCT00936221, ClinicalTrials. pyrexia (11%), vomiting (4%) and fatigue (4%). gov Identifier NCT01256359, ClinicalTrials. Significantly, only 1 of 109 patients developed cuta- gov Identifier NCT01166126 respectively.]. neous SCC, supporting the preclinical evidence that the combination leads to reduction of SCCs, The phase I–II study of the MEK inhibitor potentially by switching off the CRAF-activated GSK1120212 in patients with advanced BRAF- pathway through downstream MEK inhibition. mutant melanoma showed good tolerability and encouraging RRs. At the recommended phase II A number of clinical trials assessing the combi- dose of 2 mg once daily, RRs were 40% (8 of 20 nation of BRAF and MEK inhibitors or the http://tam.sagepub.com 65 Therapeutic Advances in Medical Oncology 0 (0) combination of inhibitors of the MAPK pathway response. Cyclin D1 and Ki67 staining on IHC with other agents are underway. The combination were also decreased, consistent with reduced of vemurafenib with the MEK inhibitor GDC0973 proliferation. There were no significant effects on is being assessed in patients with BRAF V600E- phosphorylation of AKT or on phosphatase and mutant metastatic melanoma whose disease has tensin homolog (PTEN) expression. Interestingly, progressed after treatment with vemurafenib. on progression, some but not all tumours were Vemurafenib is also being studied in combination found to have a return of ERK and MEK phos- with ipilimumab. phorylation, indicating the presence of both ERK-dependent and ERK-independent mecha- More general studies that may show relevance in nisms of resistance. Sequenom analysis demon- the setting of melanoma include studies of MEK strated the presence of NRAS G12R mutation in inhibitors (e.g. GSK1120212 or GDC0973) and 1 of 11 patients and MEK P124S mutation in 1 PI3K inhibitors (e.g. BKM120 or GDC0941) in of 28 patients with resistant tumours. One patient advanced solid tumours. Other novel agents in was shown to have PTEN loss and an increase in development have dual BRAF and CRAF activ- phosphorylated AKT (pAKT) at progression, ity and include PLX4720 and RAF265. indicating the PI3K-AKT-mammalian target of rapamycin (mTOR) pathway may act as a bypass signalling pathway. Sequenom analysis also con- Resistance to BRAF inhibitors firmed BRAF V600E mutation was present in all Recent studies investigating primary and second- progression samples (10/10). ary resistance to BRAF inhibition have identified both upstream, downstream and bypass mecha- An exploratory tumour gene analysis of patients nisms that act in an ERK-dependent or ERK- treated in the GSK436 phase I–II trial also independent manner [Corcoran et al. 2011], as demonstrated several potential mechanisms of illustrated in Table 1. Primary resistance, when resistance, including alterations in PTEN and patients have progressive disease as their best mutations in CDK4 and β-catenin [Nathanson response to treatment, is present in less than 15% et al. 2011]. A MEK2 mutation was demon- of patients treated with BRAF or MEK inhibitors strated in a tumour sample of one patient with for BRAF V600-mutant metastatic melanoma SD. Pretreatment analysis demonstrated that [Chapman et al. 2011; Flaherty et al. 2010; abnormal PTEN (deleted or mutant) was asso- Kefford et al. 2010; Ribas et al. 2011]. However, ciated with shorter PFS. Analysis of array-based secondary or acquired resistance develops in the comparative genomic hybridization also demon- majority of patients after an initial response, with strated that patients with CDKN2A or KIT the duration of this response ranging between 2 deletion had a shorter PFS. months and 1.8 years with a median of 8–9 months [Flaherty et al. 2010]. The results of the above studies suggest mecha- nisms of resistance that may occur upstream As part of the phase I vemurafenib trial, the effect (NRAS mutation) or downstream of BRAF along on key signalling pathways and mechanisms of the MAPK pathway (MEK mutation), as well as acquired resistance were investigated [McArthur alternative bypass signalling pathways through et al. 2011]. Formalin-fixed paraffin-embedded the PI3K-AKT pathway and through abnormali- samples were obtained from a total of 23 patients ties in CDK4/cyclin D1. Further resistance (5 patients from the dose-escalation cohort and mechanisms have also been investigated in mela- 18 patients from the melanoma expansion cohort) noma cell lines, tumour models and through at three different time points; at baseline, at day individual case reports [Corcoran et al. 2010; 15 of treatment and at disease progression while Emery et al. 2009; Johannessen et al. 2010; Little still receiving vemurafenib. Immunohistochemical et al. 2011; Montagut et al. 2008; Nazarian et al. (IHC) staining for a number of different molecu- 2010; Wagle et al. 2011]. The majority of these lar markers was performed as well as Sequenom data focus on mechanisms of acquired resistance, MassARRAY of over 400 mutations in genes, though some overlap with primary resistance including BRAF, RAS, PIK3CA, AKT1/2 and exists. CDK4. At day 15, phosphorylated ERK (pERK) and phosphorylated MEK (pMEK) were mark- These substudies also demonstrate the necessity edly reduced, consistent with decreased signal- of longitudinal tumour biopsies to fully charac- ling downstream and correlating with tumour terize the activity of targeted agents, investigate 66 http://tam.sagepub.com C Lemech, J Infante et al. http://tam.sagepub.com 67 Table 1. Possible mechanisms of resistance to selective BRAF inhibitors and potential therapeutic combinations. Level of resistance Genetic mutation/alteration Status of ERK Potential combination therapy Reference pathway Upstream in the NRAS mutation (e.g. G12R, Dependent BRAFi + MEKi [Adjei et al. 2008; McArthur et al. 2011; MAPK pathway Q61K) Nazarian et al. 2010] PDGFRβ upregulation Independent PDGFRβ inhibitor ± BRAFi [Corcoran et al. 2011; Nazarian et al. BRAFi + IGF1Ri 2010] Other RTK upregulation Independent BRAFi + PI3K/AKT/dual mTORi [Corcoran et al. 2011; Villanueva (e.g. IGF1R signalling) et al. 2010] At the RAF level BRAF amplification Dependent BRAFi + MEKi [Corcoran et al. 2010; Little et al. 2011] Elevated CRAF activity Dependent BRAFi + MEKi or [Johannessen et al. 2010] CRAFi/nonselective RAFi [Montagut et al. 2008; Johannessen et Increased COT/Tpl2 levels Dependent BRAFi + MEKi al. 2010] (also acts downstream in the MAPK pathway) Downstream in the MEK1 mutation (e.g. P124L, Dependent BRAFi and MEKi for P124L mt [Corcoran et al. 2011; Emery et al. MAPK pathway P124S, C121S) (not C121S) 2009; McArthur et al. 2011; Wagle et al. 2011] Bypass pathway PTEN loss Independent BRAFi/MEKi + PI3K/mTORi [Nathanson et al. 2011; Paraiso et al. signalling 2011] PI3K-AKT pathway activation Independent BRAFi/MEKi + PI3K/AKT/mTORi BRAF/MEKi + PI3K/AKTi AKT3 mutation Independent BRAFi + IGF1Ri or PI3K/AKTi [Jiang et al. 2011] IGF1R signalling Independent BRAFi + mTORi [Shao and Aplin, 2010] CDK4 mutation/cyclin D1 Independent [Villanueva et al. 2010] amplification BRAFi/MEKi + imatinib Co-overexpression of KIT/ Independent [Smalley et al. 2008b, 2008a] CDK4 BRAFi, selective v-raf murine sarcoma viral oncogene homolog B1 inhibitor; CDK4, cyclin-dependent kinase 4; ERK, extracellular signal-regulated kinase; IGF1R, insulin-like growth factor 1 receptor; MAPK, mitogen-activated protein kinase; MEKi, MEK inhibitor; mTORi, mammalian target of rapamycin inhibitor; PDGFRβ, platelet-derived growth factor receptor β; PI3K, phosphoinositide 3-kinase; PTEN, phosphatase and tensin homolog; RTK, receptor tyrosine kinase. Therapeutic Advances in Medical Oncology 0 (0) resistance mechanisms and formulate rational mediated through mutations in MEK [Corcoran drug combinations for future studies. et al. 2011; Emery et al. 2009; Wagle et al. 2011]. Point mutations in MEK1 have been shown to cause secondary resistance to both BRAF inhibi- Mechanisms of resistance at the BRAF level tion and MEK inhibition in the clinical setting Secondary mutations in BRAF, as well as BRAF [Emery et al. 2009; Wagle et al. 2011]. A MEK amplification have been surmised as possible pri- point mutation has been implicated in acquired mary or secondary resistance mechanisms, as resistance to MEK inhibition [Emery et al. 2009] has been demonstrated with secondary EGFR while another MEK1 mutation, P124L, led to mutations in non-small cell lung cancer. There is both resistance to MEK inhibition and cross evidence in mouse models regarding secondary resistance to BRAF inhibition [Emery et al. 2009]. BRAF mutations [Whittaker et al. 2010] and in In addition, the point mutation C121S has been BRAF-mutant colorectal cancer cell lines regard- demonstrated in a post-relapse biopsy in a patient ing BRAF amplification [Corcoran et al. 2010; on the BRAF inhibitor vemurafenib [Wagle et al. Little et al. 2011] that suggests these mecha- 2011] and further analysis demonstrated it could nisms may play a role in resistance to BRAF or confer resistance to both RAF and MEK inhibi- MEK inhibition. To date, however, there is limited tion. Interestingly, the combination of BRAF and clinical evidence from patients’ tumour biopsies MEK inhibition was able to overcome resist- to support these preclinical findings. ance conferred by the MEK1 P124L mutation in BRAF-mutant melanoma cells [Emery et al. 2009]. Elevated activity of the alternative RAF isoform, CRAF, has also been identified in preclinical The significance of MEK2 mutations in mediat- studies as a possible mechanism of both primary ing sensitivity or resistance is currently unknown. and secondary resistance through reactivation of the MAPK pathway [Johannessen et al. 2010; Montagut et al. 2008]. These findings require fur- Mechanisms of resistance upstream of ther validation in prospective analysis of tumour BRAF in the MAPK pathway tissue and biopsies on progression but suggest NRAS mutations have been demonstrated in vitro that there may be therapeutic potential in com- and in vivo to cause resistance to BRAF inhibition bining a nonselective RAF inhibitor or selective [Nazarian et al. 2010]. NRAS Q61K mutation was CRAF inhibitor with a MEK or BRAF inhibitor. demonstrated in preclinical cell line models to confer resistance to vemurafenib, supported by its Another resistance mechanism that acts both isolation in a nodal biopsy from a patient whose at the level of BRAF and downstream in the disease had progressed after an initial response to MAPK pathway is mediated by COT/Tpl2. treatment. The NRAS mutation is thought to COT/Tpl2, encoded by MAP3K8, activates ERK signal through RAF isoforms other than BRAF, and the MAPK pathway primarily through MEK- leading to persistently elevated pMEK and pERK dependent mechanisms but is RAF independent levels despite BRAF inhibition [Nazarian et al. [Johannessen et al. 2010]. There is both preclin- 2010]. Interestingly, these cell lines may retain ical and clinical evidence [Johannessen et al. sensitivity to MEK inhibition [Adjei et al. 2008]. 2010] demonstrating elevated COT/Tpl2 levels in resistant cell lines and biopsy specimens. It is PDGFRβ upregulation, insulin-like growth fac- hypothesized that high COT levels cause MEK tor 1 receptor (IGF1R) activation and signalling hyperactivation, thus mediating resistance to both through other receptor tyrosine kinase (RTK) BRAF and MEK inhibition. Consistent with this pathways have also been investigated as ERK- hypothesis, combined BRAF and MEK inhibition independent mechanisms of resistance, acting has been demonstrated to overcome COT-induced upstream of BRAF in the MAPK pathway and resistance in experimental models [Johannessen mediating alternative pathways that bypass MAPK et al. 2010]. [Corcoran et al. 2011; Nazarian et al. 2010]. Nazarian and colleagues [Nazarian et al. 2010] Mechanisms of resistance downstream demonstrated that overexpression of PDGFRβ of BRAF in the MAPK pathway resulted in acquired resistance to vemurafenib Current preclinical and clinical evidence dem- in BRAF-mutant melanoma cell lines despite onstrates that downstream resistance is primarily persistent pERK suppression, consistent with 68 http://tam.sagepub.com C Lemech, J Infante et al. ERK independence. Additionally, 4 of 11 clinical [Smalley et al. 2008a] also demonstrated that co- postrelapse biopsies from patients with melanoma overexpression of KIT/CDK4 also led to decreased treated with vemurafenib showed increased sensitivity to BRAF inhibition in preclinical PDGFRβ expression relative to pretreatment models but may increase sensitivity to imatinib. biopsies. Although, the existence of this KIT/CDK4 sub- group has been confirmed in human melanoma samples, the clinical significance of these preclini- Mechanisms bypassing BRAF cal findings requires further investigation. signalling Signalling via the PI3K-AKT-mTOR pathway has been described as an escape pathway in vari- Future strategies ous tumour models [Gopal et al. 2010; Shao and Increased understanding of the molecular path- Aplin, 2010; Villanueva et al. 2010]. ways and aberrations in advanced and metastatic cutaneous melanoma has changed the treatment IGF1R signalling has been demonstrated as an paradigm for a large subset of patients with mela- ERK-independent mechanism of resistance and noma. However, there remain several challenges. also plays a critical role in the PI3K-AKT-mTOR This review outlines a subset of possible strate- pathway. gies to overcome resistance mechanisms that inevitably develop to BRAF and MEK inhibition. In preclinical models, Villanueva and colleagues Further challenges include combining immune [Villanueva et al. 2010] identified IGF1R acti- therapy with inhibitors of the MAPK pathway, as vation with enhanced IGF1R/PI3K signalling well as treating those patients who do not have a as a key RTK-driven acquired mechanism of BRAF mutation. resistance that could be overcome by combined IGF1R/PI3K and MEK inhibition. A number of Intensive study continues into the complex resist- other preclinical studies have also demonstrated ance mechanisms of BRAF inhibition. Whether aberrant activation in the PI3K-AKT pathway, by inhibiting both the MAPK and bypass path- evidenced by elevated pAkt, which contributes to ways, such as with BRAF-MEK and PI3K-AKT- both primary and secondary resistance and may mTOR inhibition, or by targeting IGF1R or other be overcome through combining RAF and PI3K- RTKs, a combination of these agents may be AKT inhibition [Jiang et al. 2011; Shao and effective for overcoming secondary resistance to Aplin, 2010]. PTEN loss and subsequent lack of BRAF inhibition and may be utilized in an earlier inhibition on the PI3K-AKT-mTOR pathway setting to prevent or delay resistance [Corcoran has also been demonstrated to confer acquired et al. 2011]. Importantly, obtaining biopsies lon- resistance to BRAF inhibition in preclinical mod- gitudinally during a patient’s treatment course is els [Paraiso et al. 2011] and could be reversed key to this process. The combination of molecu- with dual treatment with PLX4720 and a PI3K lar characterization in the preclinical and clinical inhibitor [Paraiso et al. 2011]. setting can further enhance identification of clini- cally relevant mutations and possible treatment Signalling via the PI3K-AKT-mTOR pathway options [Wagle et al. 2011]. mediates an important MAPK- independent mechanism of resistance and demonstrates a com- Improved understanding of the effect of BRAF plex crosstalk between these pathways [Corcoran inhibition on immune response and T-cell func- et al. 2011]. Measurement of pERK and pAKT to tion will also provide a rationale for the combina- determine pathway activity may therefore help to tion of these approaches. Treatment with selective guide therapeutic choices and combinations of BRAF inhibitors has been shown to preserve selective BRAF, MEK or PI3K/AKT inhibitors, T-cell function whereas treatment with MEK but this data require further clinical confirmation. inhibitors may impair T-cell function [Boni et al. 2010]. Improved recognition by antigen-specific Finally, dysregulation of CDK4 or cyclin D1 has T cells and increased intratumoural and peritu- also been implicated in BRAF inhibitor resistance. moural lymphocytes occurs early after exposure In preclinical models, cyclin D1 overexpression to BRAF inhibition. Conversely, patients who demonstrated increased resistance, particularly in develop resistance to BRAF inhibition demon- the presence of CDK4 mutation/overexpression strate a decrease in intratumoural and peritu- [Smalley et al. 2008b]. Smalley and colleagues moural lymphocytes [Boni et al. 2010; Long et al. http://tam.sagepub.com 69 Therapeutic Advances in Medical Oncology 0 (0) mediates cell proliferation and transformation through 2011b]. Together, these early data provide a the MEK/ERK pathway. J Biol Chem rationale for the combination of ipilimumab and 278: 42409–42418. BRAF inhibition. Cancer Research UK (2010) Skin Cancer – UK Understanding the oncogenic drivers of mela- Incidence Statistics. Available at: http://info. noma, the complex mechanisms of resistance, the cancerresearchuk.org/cancerstats/types/skin/incidence/ (accessed 29 November 2011). interaction between signalling pathways and the immune system and integration of new genomic Carlino, M.S., Saunders, C.A.,Gebski, V., technologies has increased exponentially over the Menzies, A.M., Ma, B., Lebowitz, P.F., et al. last few years and provides a rationale for the (2011) Heterogeneity of FDG-PET response to current combination studies, with further clinical GSK2118436, an inhibitor of oncogenic mutant correlation required to strengthen the rationale for BRAF-kinase in BRAF-mutant metastatic melanoma. J Clin Oncol 29(Suppl.): abstract 8539. future studies. Chapman, P.B., Einhorh, L.H., Meyers, M.L., Funding Saxman, S., Destro, A.N., Panageas K.S., et al. 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Journal

Therapeutic Advances in Medical Oncology – SAGE

Published: Dec 19, 2011

Keywords: BRAF inhibitor; BRAF V600E; cutaneous melanoma; ipilimumab; MEK inhibitor; resistance; vemurafenib

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