Recovery of phospho-ERK activity allows melanoma cells to escape from BRAF inhibitor therapy

Inhibition of autophagy enhances the effects of the AKT inhibitor MK-2206 when combined with paclitaxel and carboplatin in BRAF wild-type melanoma

This study investigates the mechanism of action behind the long-term responses (12-16 months) of two BRAF WT melanoma patients to the AKT inhibitor MK-2206 in combination with paclitaxel and carboplatin. Although single agent MK-2206 inhibited phospho-AKT signaling, it did not impact in vitro melanoma growth or survival. The combination of MK-2206 with paclitaxel and carboplatin was cytotoxic in long-term colony formation and 3D spheroid assays, and induced autophagy. Autophagy was initially protective with autophagy inhibitors and deletion of ATG5 found to enhance cytotoxicity. Although prolonged autophagy induction (>6 days) led to caspase-dependent apoptosis, drug resistant clones still emerged. Autophagy inhibition enhanced the cell death response through reactive oxygen species and could be reversed by anti-oxidants. We demonstrate for the first time that AKT inhibition in combination with chemotherapy may have clinical activity in BRAF WT melanoma and show that an autophagy inhibitor may prevent resistance to these drugs.

The GIST of targeted therapy for malignant melanoma

The high response rates to the tyrosine kinase inhibitor imatinib in KIT-mutated gastrointestinal stromal tumors (GIST) has led to a paradigm shift in cancer treatment. In a parallel fashion, the field of melanoma is shifting with the utilization of targeted therapy to treat BRAF-mutated melanoma. We reviewed published literature in PubMed on GIST and melanoma, with a focus on both past and current clinical trials. The data presented centers on imatinib, vemurafenib, and most recently dabrafenib, targeting KIT and BRAF mutations and their outcomes in GIST and melanoma. The BRAF(V600E) melanoma mutation, like the KIT exon 11 mutation in GIST, has the highest response to therapy. High response rates with inhibition of KIT in GIST have not been recapitulated in KIT-mutated melanoma. Median time to resistance to targeted agents occurs in ~7 months with BRAF inhibitors and 2 years for imatinib in GIST. In GIST, the development of secondary mutations leads to resistance; however, there have been no similar gatekeeper mutations found in melanoma. Although surgery remains an important component of the treatment of early GIST and melanoma, surgeons will need to continue to define the thresholds and timing for operation in the setting of metastatic disease with improved targeted therapies. Combination treatment strategies may result in more successful clinical outcomes in the management of melanoma in the future.

BRAF and beyond: Tailoring strategies for the individual melanoma patient

Until recently, options for therapy in metastatic melanoma were limited. The understanding of immune check-point blockade and the discovery of molecular pathways involving driver mutations like BRAF has transformed the therapeutic landscape in this disease. Ipilimumab was the first drug shown to improve survival while vemurafenib demonstrated rapid responses never seen before in melanoma. Drugs from these classes and others are now in advanced stages of development and primed to positively impact patient survival in an incremental fashion. In this review, we highlight some of the developments during this renaissance in melanoma therapy and discuss agents of promise. Clinical challenges we face include individualizing therapy for patients, overcoming resistance to molecularly targeted therapy and developing rationale combinations or sequences of drugs. A concerted bench and bedside effort in this direction will undoubtedly keep melanoma in the forefront in an era of personalized medicine.

The role of mitogen- and stress-activated protein kinase pathways in melanoma

Recent discoveries have increased our comprehension of the molecular signaling events critical for melanoma development and progression. Many oncogenes driving melanoma have been identified, and most of them exert their oncogenic effects through the activation of the RAF/MEK/ERK mitogen-activated protein kinase (MAPK) pathway. The c-Jun N-terminal kinase (JNK) and p38 MAPK pathways are also important in melanoma, but their precise role is not clear yet. This review summarizes our current knowledge on the role of the three main MAPK pathways, extracellular regulated kinase (ERK), JNK, and p38, and their impact on melanoma biology. Although the results obtained with BRAF inhibitors in melanoma patients are impressive, several mechanisms of acquired resistance have emerged. To overcome this obstacle constitutes the new challenge in melanoma therapy. Given the major role that MAPKs play in melanoma, understanding their functions and the interconnection among them and with other signaling pathways represents a step forward toward this goal.

Novel ATP-competitive MEK inhibitor E6201 is effective against vemurafenib-resistant melanoma harboring the MEK1-C121S mutation in a preclinical model

Many clinical cases of acquired resistance to the BRAF inhibitor vemurafenib have recently been reported. One of the causes of this acquired resistance is the BRAF downstream kinase point mutation MEK1-C121S. This mutation confers resistance to not only vemurafenib, but also to the allosteric MEK inhibitor selumetinib (AZD6244). Here, we investigated the pharmacologic activities and effectiveness of the novel MEK inhibitor E6201 against BRAF (v-raf murine sarcoma viral oncogene homolog B1)-V600E mutant melanoma harboring the MEK1-C121S mutation. A cell-free assay confirmed that E6201 is an ATP-competitive MEK inhibitor, meaning it has a different binding mode with MEK compared with allosteric MEK inhibitors. E6201 is more effective against BRAF-V600E mutant melanoma compared with BRAF wild-type melanoma based on MEK inhibition. We found that the acquired MEK1-C121S mutation in BRAF-V600E mutant melanoma conferred resistance to both vemurafenib and selumetinib but not E6201. The effectiveness of E6201 in this preclinical study is a result of its binding with MEK1 far from the C121S point mutation so the mutation is unable to influence the MAPK pathway inhibitory activity. These results support further clinical investigation of E6201.

New insights into the molecular pathogenesis of langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is a rare proliferative disorder characterized by an accumulation of cells sharing the major phenotypic features of cutaneous Langerhans cells. Given its variable clinical evolution, ranging from self-limiting lesions to multisystemic forms with a poor prognosis, in the last decades it has been debated whether LCH might not have a neoplastic rather than an inflammatory nature. However, although the fundamental events underlying the pathogenesis of LCH are still elusive, recent advances have strikingly improved our understanding of the disease. In particular, the identification of multiple interplays between LCH cells and their tumor microenvironment, along with the recognition of the lesional cytokine storm as a key determinant of LCH progression, has substantiated new opportunities for devising targeted therapeutic approaches. Strikingly, the detection of the rapidly accelerated fibrosarcoma isoform B(V600E) gain-of-function mutation as a genetic alteration recurring in more than 50% of patients has fueled the paradoxical picture of LCH as a tumor of the antigen-presenting cells that can evade rejection by the immune system. Thus, new evidence regarding the ontogeny of LCH cells, as well as a better understanding of the putative immune system frustrating strategy in LCH, may help to define the precise pathogenesis.

Frontline approach to metastatic BRAF-mutant melanoma diagnosis, molecular evaluation, and treatment choice

An estimated 76,100 patients will be diagnosed with invasive melanoma in the United States in 2014, and 9,710 patients will die from the disease. In almost all cases, the cause of death is related to the development of widespread metastatic disease. Although death rates from most types of cancer have steadily decreased in the United States--a 20% decrease during two decades from a peak of 215.1 deaths per 100,000 population in 1991 to 171.8 in 2010--death rates from melanoma have steadily increased during the same time, especially among males. The news regarding melanoma is far from all bad. Increases in our understanding of the human immune system have led to the development of new immunotherapeutic drugs such as ipilimumab, which has been shown to improve survival in phase III trials in metastatic melanoma, and anti-programmed death 1 (anti-PD1) antibodies, recently hailed by ASCO as one of the past year's most noteworthy clinical cancer advances. However, no discovery has influenced and, indeed, transformed the management of metastatic melanoma more than the identifıcation of activating mutations in the BRAF gene in the mitogen-activated protein kinase (MAPK) pathway, which occur in about half of cutaneous melanomas and can be targeted with small molecule inhibitors of the BRAF protein, the downstream MEK protein, or both. This article will address how patients with metastatic melanoma are evaluated for their mutation status and how the presence of a targetable mutation influences therapeutic decisions regarding systemic therapy and even surgery.

[Cellular and molecular mechanisms of carcinogenic side effects and resistance to BRAF inhibitors in metastatic melanoma with BRAFV600 mutation: state of the knowledge]

Cutaneous melanoma is a malignant tumor with a high metastatic potential. If an early treatment is associated with a favorable outcome, the prognosis of metastatic melanoma remains poor. Advances in molecular characterization of cancers, notably the discovery of BRAF gene mutations in metastatic melanoma, allowed to the recent development of targeted therapies against mutated BRAF protein. Despite high tumor response rates observed in clinical trials, these new drugs are associated with frequent secondary tumor resistance occurrence and paradoxical carcinogenic side effects. The cellular and molecular mechanisms of these carcinogenic side effects and secondary resistance are not yet fully elucidated and are actually intensely studied. This review of the literature focus on the mechanisms of these carcinogenic side effects and on the tumor resistance associated with anti-BRAF targeted therapies.

Clinicopathological relevance of BRAF mutations in human cancer

BRAF represents one of the most frequently mutated protein kinase genes in human tumours. The mutation is commonly tested in pathology practice. BRAF mutation is seen in melanoma, papillary thyroid carcinoma (including papillary thyroid carcinoma arising from ovarian teratoma), ovarian serous tumours, colorectal carcinoma, gliomas, hepatobiliary carcinomas and hairy cell leukaemia. In these cancers, various genetic aberrations of the BRAF proto-oncogene, such as different point mutations and chromosomal rearrangements, have been reported. The most common mutation, BRAF V600E, can be detected by DNA sequencing and immunohistochemistry on formalin fixed, paraffin embedded tumour tissue. Detection of BRAF V600E mutation has the potential for clinical use as a diagnostic and prognostic marker. In addition, a great deal of research effort has been spent in strategies inhibiting its activity. Indeed, recent clinical trials involving BRAF selective inhibitors exhibited promising response rates in metastatic melanoma patients. Clinical trials are underway for other cancers. However, cutaneous side effects of treatment have been reported and therapeutic response to cancer is short-lived due to the emergence of several resistance mechanisms. In this review, we give an update on the clinical pathological relevance of BRAF mutation in cancer. It is hoped that the review will enhance the direction of future research and assist in more effective use of the knowledge of BRAF mutation in clinical practice.

Synchronous BRAF(V600E) and MEK inhibition leads to superior control of murine melanoma by limiting MEK inhibitor induced skin toxicity

The BRAF inhibitor (BRAFi) treatment has led to impressive responses in BRAF^V600E mutation-positive melanomas, but responses are not durable in many patients. As most of the BRAFi escape mechanisms involve ERK reactivation, combinations with MEK inhibitors (MEKi) are currently tested to improve BRAFi-mediated response durations. Additionally, such a combination is expected to reduce MEKi-induced skin toxicities, as these drugs are thought to have antagonistic effects on ERK activation in keratinocytes. However, preclinical in vivo data exploring the combination of BRAFi and MEKi to achieve improved tumor control in the absence of skin toxicities are limited. Using a murine Tyr::CreER^T2;Pten^LoxP/LoxP;Braf^CA/+ melanoma model, we have determined the effect of BRAFi and MEKi treatment and their combination on melanoma control and occurrence of adverse events. We found that the MEKi dosed beyond the maximum tolerable dose (MTD) led to stronger control of tumor growth than did the BRAFi, but mice had to be removed from treatment because of skin toxicity. The combination of BRAFi and MEKi reduced MEKi-associated skin toxicity. This allowed high and long-term dosing of the MEKi, resulting in long-term tumor control. In contrast to previous hypotheses, the addition of a BRAFi did not restore the MEKi-mediated downregulation of pERK1/2 in skin cells. Our data describe, for the first time, the alleviation of MEKi-mediated dose-limiting toxicity by addition of a BRAFi in a mouse melanoma model. Additional clinical Phase I studies should be implemented to explore MEKi dosing beyond the single drug MTD in combination with BRAFi.

Combined PKC and MEK inhibition in uveal melanoma with GNAQ and GNA11 mutations

Uveal melanoma (UM) is a genetically and biologically distinct type of melanoma, and once metastatic there is no effective treatment currently available. Eighty percent of UMs harbor mutations in the Gαq family members GNAQ and GNA11. Understanding the effector pathways downstream of these oncoproteins is important to identify opportunities for targeted therapy. We report consistent activation of the protein kinase C (PKC) and MAPK pathways as a consequence of GNAQ or GNA11 mutation. PKC inhibition with AEB071 or AHT956 suppressed PKC and MAPK signalling and induced G1 arrest selectively in melanoma cell lines carrying GNAQ or GNA11 mutations. In contrast, treatment with two different MEK inhibitors, PD0325901 and MEK162, inhibited the proliferation of melanoma cell lines irrespective of their mutation status, indicating that in the context of GNAQ or GNA11 mutation MAPK activation can be attributed to activated PKC. AEB071 significantly slowed the growth of tumors in an allograft model of GNAQ(Q209L)-transduced melanocytes, but did not induce tumor shrinkage. In vivo and in vitro studies showed that PKC inhibitors alone were unable to induce sustained suppression of MAP-kinase signaling. However, combinations of PKC and MEK inhibition, using either PD0325901or MEK162, led to sustained MAP-kinase pathway inhibition and showed a strong synergistic effect in halting proliferation and in inducing apoptosis in vitro. Furthermore, combining PKC and MEK inhibition was efficacious in vivo, causing marked tumor regression in a UM xenograft model. Our data identify PKC as a rational therapeutic target for melanoma patients with GNAQ or GNA11 mutations and demonstrate that combined MEK and PKC inhibition is synergistic, with superior efficacy compared to treatment with either approach alone.

Targeted therapy in melanoma

Since the discovery of activating mutations in the BRAF oncogene in melanoma, there has been remarkable progress in the development of targeted therapies for unresectable and metastatic melanoma. We review the latest developments in our understanding of the role of BRAF/MEK/ERK pathway signaling in melanoma, and the development of inhibitors of this pathway. We also explore alternative mutations seen in melanoma, such as NRAS, KIT, GNAQ, and GNA11, and the drug development that is ongoing based on this biology. Strategies for the management of the vexing clinical problem of BRAF inhibitor resistance, primarily via combination therapy, are outlined. With the recent approval of the BRAF inhibitor vemurafenib for stage IV metastatic melanoma, use of this agent is expanding in the United States. Thus, management of the skin toxicities of this agent, such as squamous cell carcinomas, "acneiform" eruptions, hand-foot syndrome, and panniculitis, will be a growing problem facing dermatologists today. We discuss the toxicities of targeted agents in use for melanoma, in particular the dermatologic effects and the management of these skin toxicities.

Stat3-targeted therapies overcome the acquired resistance to vemurafenib in melanomas

Vemurafenib (PLX4032), a selective inhibitor of Braf, has been approved by the US Food and Drug Administration for the treatment of unresectable or metastatic melanoma in patients with Braf(V600E) mutations. Many patients treated with vemurafenib initially display dramatic improvement, with decreases in both risk of death and tumor progression. Acquired resistance, however, rapidly arises in previously sensitive cells. We attempted to overcome this resistance by targeting the signal transducer and activator of transcription 3 (STAT3)-paired box homeotic gene 3 (PAX3)-signaling pathway, which is upregulated, owing to fibroblast growth factor 2 (FGF2) secretion or increased kinase activity, with the Braf(V600E) mutation. We found that activation of Stat3 or overexpression of PAX3 induced resistance to vemurafenib in melanoma cells. In addition, PAX3 or Stat3 silencing inhibited the growth of melanoma cells with acquired resistance to vemurafenib. Furthermore, treatment with the Stat3 inhibitor, WP1066, resulted in growth inhibition in both vemurafenib-sensitive and -resistant melanoma cells. Significantly, vemurafenib stimulation induced FGF2 secretion from keratinocytes and fibroblasts, which might uncover, at least in part, the mechanisms underlying targeting Stat3-PAX3 signaling to overcome the acquired resistance to vemurafenib. Our results suggest that Stat3-targeted therapy is a new therapeutic strategy to overcome the acquired resistance to vemurafenib in the treatment of melanoma.

Trametinib: first global approval

Trametinib is an orally bioavailable mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor with antineoplastic activity. The compound specifically binds to MEK1 and MEK2, resulting in inhibition of growth factor-mediated cell signalling and cellular proliferation in various cancers. Originally developed by Japan Tobacco, GlaxoSmithKline has licensed exclusive worldwide rights to the compound and conducted development in a number of different cancer types. Trametinib, as a monotherapy, has been approved in the US for the treatment of unresectable or metastatic malignant melanoma with BRAF V600E or V600K mutations, as detected by an FDA-approved test. The compound, as a monotherapy, has also been submitted for regulatory review in the EU for BRAF mutation-positive malignant melanoma, and is in phase III development in Europe, Argentina, Canada and Oceania. Phase II development is underway for pancreatic cancer, non-small cell lung cancer and relapsed or refractory leukaemias. GlaxoSmithKline is also developing trametinib for use in combination with dabrafenib in BRAF V600 mutation-positive metastatic cutaneous melanoma; the combination is at the preregistration stage in the EU and a phase III clinical programme is underway worldwide. Phase II development for this combination is also underway in colorectal cancer. Several phase I trials have also been initiated to evaluate trametinib in combination with other drugs for the treatment of various solid tumours and haematological malignancies. A paediatric oral solution formulation has been assessed against the oral tablet formulation in a phase I trial. This article summarizes the milestones in the development of trametinib leading to this first approval for unresectable or metastatic BRAF mutation-positive malignant melanoma.

Molecular-targeted agents combination therapy for cancer: developments and potentials

Although chemotherapy has advanced into the era of targeted drugs, the antitumor efficacies of current therapies are limited, most likely because of the high degree of cancer clonal heterogeneity, intratumor genetic heterogeneity and cell signal complexity. As shutdown of a single target does not necessarily eradicate the cancer, the use of combinations of molecular-targeted agents (MATs) has been proposed, and some pioneering research has been conducted to examine the efficacy of this strategy. In this article, the clinical and preclinical studies that are underway in an attempt to improve the anticancer efficacy of chemotherapies through combination strategies are summarized. Studies of combining cytotoxic agents with MATs, coinhibiting two or more targets in a single pathway or coinhibiting parallel or compensatory pathways as well as specific combinations will be introduced, and the antitumor potentials of each combination strategy will be evaluated.

The evolution of S100B inhibitors for the treatment of malignant melanoma

Malignant melanoma continues to be an extremely fatal cancer due to a lack of viable treatment options for patients. The calcium-binding protein S100B has long been used as a clinical biomarker, aiding in malignant melanoma staging and patient prognosis. However, the discovery of p53 as a S100B target and the consequent impact on cell apoptosis redirected research efforts towards the development of inhibitors of this S100B-p53 interaction. Several approaches, including computer-aided drug design, fluorescence polarization competition assays, NMR, x-ray crystallography and cell-based screens have been performed to identify compounds that block the S100B-p53 association, reactivate p53 transcriptional activities and induce cancer cell death. Eight promising compounds, including pentamidine, are presented in this review and the potential for future modifications is discussed. Synthesis of compound derivatives will likely exhibit increased S100B affinity and mimic important S100B-target dynamic properties that will result in high specificity.

Update on the targeted therapy of melanoma

Melanoma is the most aggressive of the cutaneous malignancies, causing more than 9,000 deaths in the past year in the United States. Historically, systemic therapies have been largely ineffective, because melanoma is usually resistant to cytotoxic chemotherapy. However, during the past few years, several targeted therapies have proved effective in this challenging disease. These recent advances have been facilitated by an improved understanding of the driving genetic aberrations of melanoma, particularly mutations in the mitogen-activated protein kinase (MAPK) pathway. Vemurafenib, a BRAF inhibitor, demonstrated an overall survival advantage in phase III trials and is an appropriate option for first-line therapy in metastatic BRAF mutant melanoma. Dabrafenib, another BRAF inhibitor, and trametinib, a MEK inhibitor, also have been shown to be effective in phase III trials for BRAF mutant melanoma and may be additional treatment options as monotherapy or in combination pending regulatory approval. Additionally, imatinib is a promising targeted therapy for patients whose tumors harbor a KIT mutation in exons 11 and 13. Although these targeted agents cause objective responses and clinical benefit in patients with metastatic melanoma, resistance invariably develops. New targets and strategies to overcome acquired resistance are urgently needed. Furthermore, no effective targeted therapy has been developed for NRAS mutant tumors or in melanomas with as yet unknown driver mutations. In this review, we discuss current molecular targeted treatment options and promising ongoing research to develop new strategies to treat melanoma.

Paradoxical oncogenesis--the long-term effects of BRAF inhibition in melanoma

The clinical benefits of BRAF inhibition in patients with advanced-stage BRAF-mutant melanoma are now well established. Although the emergence of cutaneous squamous-cell carcinomas (SCCs) and secondary melanomas in patients on BRAF-inhibitor therapy have been well described, reports are emerging of additional secondary premalignant and malignant events, including RAS-mutant leukaemia, the metastatic recurrence of RAS-mutant colorectal cancer and the development of gastric and colonic polyps. In most cases, paradoxical MAPK activation--resulting from the BRAF-inhibitor-mediated homodimerization and heterodimerization of nonmutant RAF isoforms--seems to underlie the development of these secondary tumours. Although evidence supports that therapy with the simultaneous administration of BRAF and MEK inhibitors abrogates the onset of treatment-induced SCCs, whether combination treatment will limit the emergence of all BRAF-inhibitor-driven pathologies is unclear. In this Review, we describe the clinical and mechanistic manifestations of secondary cancers that have thus far been observed to arise as a consequence of BRAF inhibition. We discuss the concept of pre-existing populations of partly transformed cells with malignant potential that might be present in various organ systems, and the rationale for novel therapeutic strategies for the management of BRAF-inhibitor-induced neoplasia.

Pharmacodynamic effects and mechanisms of resistance to vemurafenib in patients with metastatic melanoma

PURPOSE To assess pharmacodynamic effects and intrinsic and acquired resistance mechanisms of the BRAF inhibitor vemurafenib in BRAF(V600)-mutant melanoma, leading to an understanding of the mechanism of action of vemurafenib and ultimately to optimization of metastatic melanoma therapy. METHODS In the phase II clinical study NP22657 (BRIM-2), patients received oral doses of vemurafenib (960 mg twice per day). Serial biopsies were collected to study changes in mitogen-activated protein kinase (MAPK) signaling, cell-cycle progression, and factors causing intrinsic or acquired resistance by immunohistochemistry, DNA sequencing, or somatic mutation profiling. Results Vemurafenib inhibited MAPK signaling and cell-cycle progression. An association between the decrease in extracellular signal-related kinase (ERK) phosphorylation and objective response was observed in paired biopsies (n = 22; P = .013). Low expression of phosphatase and tensin homolog showed a modest association with lower response. Baseline mutations in MEK1(P124) coexisting with BRAF(V600) were noted in seven of 92 samples; their presence did not preclude objective tumor responses. Acquired resistance to vemurafenib associated with reactivation of MAPK signaling as observed by elevated ERK1/2 phosphorylation levels in progressive lesions and the appearance of secondary NRAS(Q61) mutations or MEK1(Q56P) or MEK1(E203K) mutations. These two activating MEK1 mutations had not previously been observed in vivo in biopsies of progressive melanoma tumors. CONCLUSION Vemurafenib inhibits tumor proliferation and oncogenic BRAF signaling through the MAPK pathway. Acquired resistance results primarily from MAPK reactivation driven by the appearance of secondary mutations in NRAS and MEK1 in subsets of patients. The data suggest that inhibition downstream of BRAF should help to overcome acquired resistance.

Targeted therapy and immunotherapy in advanced melanoma: an evolving paradigm

Metastatic melanoma is one of the most challenging malignancies to treat and often has a poor outcome. Until recently, systemic treatment options were limited, with poor response rates and no survival advantage. However, the treatment of metastatic melanoma has been revolutionized by developments in targeted therapy and immunotherapy; the BRAF inhibitor, vemurafenib, and anticytotoxic T-lymphocyte antigen 4 antibody, ipilimumab, are the first agents to demonstrate a survival benefit. Despite the success of these treatments, most patients eventually progress, and research into response and resistance mechanisms, rationally designed combination therapies and evaluation of the role of these agents in the adjuvant setting is critically important.

An unholy alliance: cooperation between BRAF and NF1 in melanoma development and BRAF inhibitor resistance

In this issue of Cancer Discovery, 2 studies provide new evidence implicating loss of the tumor suppressor neurofibromin (NF1) in the biologic behavior of cutaneous melanoma. The first study from Maertens and colleagues describes a new transgenic mouse model in which mutant BRAF cooperates with NF1 loss to drive melanoma development through the abrogation of oncogene-induced senescence. The second, from Whittaker and colleagues, used a high-throughput short hairpin RNA screening approach to identify NF1 loss as a key mediator of acquired and intrinsic BRAF inhibitor resistance. Together these studies provide new insights into the signaling that underlies melanoma initiation and progression and suggests novel therapeutic strategies for patients whose melanomas are BRAF-mutant/NF1-deficient.

Anti-apoptotic proteins on guard of melanoma cell survival

Apoptosis plays a pivotal role in sustaining proper tissue development and homeostasis. Evading apoptosis by cancer cells is a part of their adaption to microenvironment and therapies. Cellular integrity is predominantly maintained by pro-survival members of Bcl-2 family and IAPs. Melanoma cells are characterized by a labile and stage-dependent phenotype. Pro-survival molecules can protect melanoma cells from apoptosis and mediate other processes, thus enhancing aggressive phenotype. The essential role of Bcl-2, Mcl-1, Bcl-X(L), livin, survivin and XIAP was implicated for melanoma, often in a tumor stage-dependent fashion. In this review, the current knowledge of pro-survival machinery in melanoma is discussed.

BRAF inhibition increases tumor infiltration by T cells and enhances the antitumor activity of adoptive immunotherapy in mice

PURPOSE

Treatment of melanoma patients with selective BRAF inhibitors results in objective clinical responses in the majority of patients with BRAF-mutant tumors. However, resistance to these inhibitors develops within a few months. In this study, we test the hypothesis that BRAF inhibition in combination with adoptive T-cell transfer (ACT) will be more effective at inducing long-term clinical regressions of BRAF-mutant tumors.

EXPERIMENTAL DESIGN

BRAF-mutated human melanoma tumor cell lines transduced to express gp100 and H-2D(b) to allow recognition by gp100-specific pmel-1 T cells were used as xenograft models to assess melanocyte differentiation antigen-independent enhancement of immune responses by BRAF inhibitor PLX4720. Luciferase-expressing pmel-1 T cells were generated to monitor T-cell migration in vivo. The expression of VEGF was determined by ELISA, protein array, and immunohistochemistry. Importantly, VEGF expression after BRAF inhibition was tested in a set of patient samples.

RESULTS

We found that administration of PLX4720 significantly increased tumor infiltration of adoptively transferred T cells in vivo and enhanced the antitumor activity of ACT. This increased T-cell infiltration was primarily mediated by the ability of PLX4720 to inhibit melanoma tumor cell production of VEGF by reducing the binding of c-myc to the VEGF promoter. Furthermore, analysis of human melanoma patient tumor biopsies before and during BRAF inhibitor treatment showed downregulation of VEGF consistent with the preclinical murine model.

CONCLUSION

These findings provide a strong rationale to evaluate the potential clinical application of combining BRAF inhibition with T-cell-based immunotherapy for the treatment of patients with melanoma.

Targeting oncogenic drivers and the immune system in melanoma

Melanoma is one of the most common cancers in Western countries but has defied the trend of reductions in age-adjusted mortality observed in most other cancers in recent years. Biologically, melanoma is characterized by a high propensity to metastasize at low tumor volumes necessitating the need for effective drug therapies to support efforts in prevention and early detection for reducing mortality. Efforts to study the clinical biology of melanoma have led to a new understanding of the disease, with genomic studies identifying several targetable oncogenes, in particular the protein kinases BRAF and KIT. Biologic studies have also identified a variety of immunologic targets, including the programmed death 1 (PD-1) and cytotoxic T-cell lymphocyte-associated antigen 4 (CTLA-4) inhibitory molecules expressed on T lymphocytes. After several decades of clinical trials that failed to demonstrate improvement in overall survival in patients with advanced melanoma, small molecule inhibitors of BRAF or MEK and inhibition of CTLA-4 can improve survival in patients with advanced disease. These early clinical studies have provided a great opportunity to improve mortality in melanoma with the significant potential of combinations of signaling inhibitors or signaling inhibitors combined with immunologic agents, particularly when used in the adjuvant setting, and to transform the care of patients with this most challenging of cancers.

Targeted therapies for metastatic melanoma

The next few years may show that when the novel therapeutics reviewed in this article are used in thoughtful combinations, a new standard of care for the treatment of advanced melanoma will emerge. As more understanding is gained on the different signaling pathways for tumor cell growth and mechanisms of action of the different classes of drugs, the ability to identify different subsets of patients with differentially dysregulated oncogenic signaling pathways may allow for more individualized treatments of advanced melanoma in the near future, which will ultimately translate into improved survival.

BRAF inhibition increases tumor infiltration by T cells and enhances the antitumor activity of adoptive immunotherapy in mice

PURPOSE

Treatment of melanoma patients with selective BRAF inhibitors results in objective clinical responses in the majority of patients with BRAF-mutant tumors. However, resistance to these inhibitors develops within a few months. In this study, we test the hypothesis that BRAF inhibition in combination with adoptive T-cell transfer (ACT) will be more effective at inducing long-term clinical regressions of BRAF-mutant tumors.

EXPERIMENTAL DESIGN

BRAF-mutated human melanoma tumor cell lines transduced to express gp100 and H-2D(b) to allow recognition by gp100-specific pmel-1 T cells were used as xenograft models to assess melanocyte differentiation antigen-independent enhancement of immune responses by BRAF inhibitor PLX4720. Luciferase-expressing pmel-1 T cells were generated to monitor T-cell migration in vivo. The expression of VEGF was determined by ELISA, protein array, and immunohistochemistry. Importantly, VEGF expression after BRAF inhibition was tested in a set of patient samples.

RESULTS

We found that administration of PLX4720 significantly increased tumor infiltration of adoptively transferred T cells in vivo and enhanced the antitumor activity of ACT. This increased T-cell infiltration was primarily mediated by the ability of PLX4720 to inhibit melanoma tumor cell production of VEGF by reducing the binding of c-myc to the VEGF promoter. Furthermore, analysis of human melanoma patient tumor biopsies before and during BRAF inhibitor treatment showed downregulation of VEGF consistent with the preclinical murine model.

CONCLUSION

These findings provide a strong rationale to evaluate the potential clinical application of combining BRAF inhibition with T-cell-based immunotherapy for the treatment of patients with melanoma.

What is new in the treatment of advanced melanoma? State of the art

The incidence of melanoma is increasing steadily both in Poland and worldwide. Until 2010 three drugs were approved for the treatment of metastatic melanoma – dacarbazine (DTIC) in Europe and USA, fotemustine in Europe and interleukin-2 (IL-2) in USA. Approval of ipilimumab and vemurafenib in Europe and USA has changed the standard of care, while the next candidates such as dabrafenib and trametinib have improved survival in phase III studies in metastatic melanoma patients. An encouraging treatment strategy is the combination of dabrafenib and trametinib, evaluated in a phase I/II study with an ongoing phase III trial. Another promising new immune modulating monoclonal antibody (mAb) is anti-PD1 (BMS-936558), tested in an early phase trial in monotherapy or in combination with a multipeptide vaccine in metastatic melanoma patients. Ipilimumab or BRAF inhibitors (vemurafenib, dabrafenib) seem to be active in patients with brain metastases. Intensive research of melanoma vaccines is currently being carried out in a number of countries worldwide. However, no vaccine in the treatment of melanoma has been approved by regulatory authorities so far. Lack of effective therapy in patients with high-risk resected melanoma led to a number of clinical studies of adjuvant treatment. Interferon-α (INF-α) therapy in this setting is still controversial. A dendritic cell-based vaccine in a randomized phase II trial showed a survival benefit over the control group in patients with high-risk resected melanoma. Promising results of long-term survival of advanced resected melanoma patients in a phase II study evaluating the genetically modified tumour vaccine (GMTV) AGI-101 were reported.

This review provides an update on clinical strategies used or tested in patients with metastatic melanoma.

Inhibition of melanoma development in the Nras((Q61K)) ::Ink4a(-/-) mouse model by the small molecule BI-69A11

To date, there are no effective therapies for tumors bearing NRAS mutations, which are present in 15-20% of human melanomas. Here we extend our earlier studies where we demonstrated that the small molecule BI-69A11 inhibits the growth of melanoma cell lines. Gene expression analysis revealed the induction of interferon- and cell death-related genes that were associated with responsiveness of melanoma cell lines to BI-69A11. Strikingly, the administration of BI-69A11 inhibited melanoma development in genetically modified mice bearing an inducible form of activated Nras and a deletion of the Ink4a gene (Nras((Q61K)) ::Ink4a(-/-) ). Biweekly administration of BI-69A11 starting at 10 weeks or as late as 24 weeks after the induction of mutant Nras expression inhibited melanoma development (100 and 36%, respectively). BI-69A11 treatment did not inhibit the development of histiocytic sarcomas, which constitute about 50% of the tumors in this model. BI-69A11-resistant Nras((Q61K)) ::Ink4a(-/-) tumors exhibited increased CD45 expression, reflective of immune cell infiltration and upregulation of gene networks associated with the cytoskeleton, DNA damage response, and small molecule transport. The ability to attenuate the development of NRAS mutant melanomas supports further development of BI-69A11 for clinical assessment.

Combined BRAF and MEK inhibition in melanoma with BRAF V600 mutations

BACKGROUND

Resistance to therapy with BRAF kinase inhibitors is associated with reactivation of the mitogen-activated protein kinase (MAPK) pathway. To address this problem, we conducted a phase 1 and 2 trial of combined treatment with dabrafenib, a selective BRAF inhibitor, and trametinib, a selective MAPK kinase (MEK) inhibitor.

METHODS

In this open-label study involving 247 patients with metastatic melanoma and BRAF V600 mutations, we evaluated the pharmacokinetic activity and safety of oral dabrafenib (75 or 150 mg twice daily) and trametinib (1, 1.5, or 2 mg daily) in 85 patients and then randomly assigned 162 patients to receive combination therapy with dabrafenib (150 mg) plus trametinib (1 or 2 mg) or dabrafenib monotherapy. The primary end points were the incidence of cutaneous squamous-cell carcinoma, survival free of melanoma progression, and response. Secondary end points were overall survival and pharmacokinetic activity.

RESULTS

Dose-limiting toxic effects were infrequently observed in patients receiving combination therapy with 150 mg of dabrafenib and 2 mg of trametinib (combination 150/2). Cutaneous squamous-cell carcinoma was seen in 7% of patients receiving combination 150/2 and in 19% receiving monotherapy (P=0.09), whereas pyrexia was more common in the combination 150/2 group than in the monotherapy group (71% vs. 26%). Median progression-free survival in the combination 150/2 group was 9.4 months, as compared with 5.8 months in the monotherapy group (hazard ratio for progression or death, 0.39; 95% confidence interval, 0.25 to 0.62; P<0.001). The rate of complete or partial response with combination 150/2 therapy was 76%, as compared with 54% with monotherapy (P=0.03).

CONCLUSIONS

Dabrafenib and trametinib were safely combined at full monotherapy doses. The rate of pyrexia was increased with combination therapy, whereas the rate of proliferative skin lesions was nonsignificantly reduced. Progression-free survival was significantly improved. (Funded by GlaxoSmithKline; ClinicalTrials.gov number, NCT01072175.).

The activation of MAPK in melanoma cells resistant to BRAF inhibition promotes PD-L1 expression that is reversible by MEK and PI3K inhibition

PURPOSE

Selective BRAF inhibition (BRAFi) provides a paradigm shift for melanoma treatment. The duration of benefit is typically limited before resistance develops. Interest remains in combining targeted and immune therapies to overcome resistance and improve durability of clinical benefit. One mechanism of evading immune destruction is programmed death-1-ligand 1 (PD-L1) expression by tumors that results in potent antitumor immune suppression.

EXPERIMENTAL DESIGN

BRAFi-resistant melanoma cells were examined for changes in PD-L1 expression by immunoblot and flow cytometry. Signaling pathways involved in altering PD-L1 expression were examined. Strategies to maximize the effect of the BRAFi therapy were studied including MEKi, MEKi combinations, and additional pathways including phosphoinositide-3 kinase (PI3K).

RESULTS

Melanoma cells resistant to BRAFi exhibit increased MAPK signaling and promotion of PD-L1 expression. PD-L1 expression is transcriptionally modulated by c-Jun and augmented by STAT3. MEK inhibition (MEKi) regains downregulation of MAPK signaling and suppresses the production of PD-L1. MEKi in melanoma cells shows dual therapeutic effects with simultaneous suppression of PD-L1 expression and induction of apoptosis. By combining MEKi with BRAFi, an additive effect on the inhibition of PD-L1 expression results.

CONCLUSIONS

We report a novel mechanism that suppresses preexisting immune responses in patients with melanoma receiving BRAFi therapy. BRAFi resistance leads to increased expression of PD-L1 in melanoma cells, mediated by c-Jun and STAT3. MEKi may be feasible to counteract BRAFi resistance of MAPK reactivation and also for the additive effect of PD-L1 suppression. Potential therapeutic benefits of combining targeted inhibitors and immune modulation to improve patient outcomes should be investigated.

The BH3-mimetic ABT-737 sensitizes human melanoma cells to apoptosis induced by selective BRAF inhibitors but does not reverse acquired resistance

Although the introduction of selective v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) inhibitors has been a major advance in treatment of metastatic melanoma, approximately 50% of patients have limited responses including stabilization of disease or no response at all. This study aims to identify a novel means of overcoming resistance of melanoma to killing by BRAF inhibitors. We examined the influence of the BH3-mimetic ABT-737 on induction of apoptosis by the selective BRAF inhibitor PLX4720 in melanoma cells with or without BRAF V600E mutation. Included were cell lines established from four patients before and during treatment with selective BRAF inhibitors and 3D spheroids derived from these cell lines. Cell lines with no or low sensitivity to PLX4720 underwent synergistic increases and increased rates of apoptosis when combined with ABT-737. This degree of synergism was not seen in cell lines without BRAF V600E mutations. Apoptosis was mediated through the mitochondrial pathway and was due in part to upregulation of Bim as shown by inhibition of apoptosis following small interfering RNA knockdown of Bim. Similar effects were seen in cell lines established from patients prior to treatment but not in lines from patients clinically resistant to the selective BRAF inhibitors and in 3D spheroids derived from these cell lines. These results suggest that combination of selective BRAF inhibitors with ABT-737 or the related orally available compound ABT-263 may increase the degree and rate of responses in previously untreated patients with V600E melanoma but not in those with acquired resistance to these agents.

Vemurafenib: the first drug approved for BRAF-mutant cancer

The identification of driver oncogenes has provided important targets for drugs that can change the landscape of cancer therapies. One such example is the BRAF oncogene, which is found in about half of all melanomas as well as several other cancers. As a druggable kinase, oncogenic BRAF has become a crucial target of small-molecule drug discovery efforts. Following a rapid clinical development path, vemurafenib (Zelboraf; Plexxikon/Roche) was approved for the treatment of BRAF-mutated metastatic melanoma in the United States in August 2011 and the European Union in February 2012. This Review describes the underlying biology of BRAF, the technology used to identify vemurafenib and its clinical development milestones, along with future prospects based on lessons learned during its development.

MEK and RAF inhibitors for BRAF-mutated cancers

The mitogen-activated protein kinase (MAPK) pathway has been implicated in the pathophysiology of many cancers. Under normal physiologic conditions, the RAS-RAF-mitogen-activated protein kinase kinase (MEK)-mitogen-activated protein kinase (ERK) signalling cascade interaction is initiated by ligation of a receptor-linked tyrosine kinase by its cognate growth factor. It has been demonstrated in many systems that aberrant autocrine or paracrine stimulation of growth factor receptors is pathogenic in large part because of MAPK activation. As one of the key downstream effector pathways of mutated RAS (KRAS, NRAS and HRAS), pharmacologic inhibition of components of the MAPK pathway has been pursued as a means to indirectly inhibit RAS, which remains a technical challenge for direct pharmacologic inhibition. RAF and MEK are the two non-membrane-bound, serine-threonine and tyrosine-threonine kinases, within the pathway that have been most extensively explored as drug targets. The discovery of activating BRAF mutations in cancer clarified which cancer types and subsets of certain cancers are most dependent on activation of the MAPK pathway for growth and survival. Now, with the successful translation of selective BRAF and MEK inhibitors into validated therapies for BRAF mutant melanoma, the field seeks to resolve the role for these agents in cancers harbouring RAS mutations or those driven by aberrant growth factor receptor activation.

The prognostic value of BRAF mutation in colorectal cancer and melanoma: a systematic review and meta-analysis

BACKGROUND

Mutation of BRAF is a predominant event in cancers with poor prognosis such as melanoma and colorectal cancer. BRAF mutation leads to a constitutive activation of mitogen activated protein kinase pathway which is essential for cell proliferation and tumor progression. Despite tremendous efforts made to target BRAF for cancer treatment, the correlation between BRAF mutation and patient survival is still a matter of controversy.

METHODS/PRINCIPAL FINDINGS

Clinical studies on the correlation between BRAF mutation and patient survival were retrieved from MEDLINE and EMBASE databases between June 2002 and December 2011. One hundred twenty relevant full text studies were categorized based on study design and cancer type. Publication bias was evaluated for each category and pooled hazard ratio (HR) with 95% confidence interval (CI) was calculated using random or fixed effect meta-analysis based on the percentage of heterogeneity. Twenty six studies on colorectal cancer (11,773 patients) and four studies on melanoma (674 patients) were included in our final meta-analysis. The average prevalence of BRAF mutation was 9.6% in colorectal cancer, and 47.8% in melanoma reports. We found that BRAF mutation increases the risk of mortality in colorectal cancer patients for more than two times; HR = 2.25 (95% CI, 1.82-2.83). In addition, we revealed that BRAF mutation also increases the risk of mortality in melanoma patients by 1.7 times (95% CI, 1.37-2.12).

CONCLUSIONS

We revealed that BRAF mutation is an absolute risk factor for patient survival in colorectal cancer and melanoma.

Making sense of MEK1 mutations in intrinsic and acquired BRAF inhibitor resistance

In this issue of Cancer Discovery, Shi and colleagues add further insight into the role of exon 3 MEK1 mutations in BRAF inhibitor resistance by demonstrating the presence of P124SMEK1 and I111SMEK1 mutations concurrently with V600E/KBRAF mutations at baseline in 16% of melanoma specimens. Although the presence of P124SMEK1 or I111SMEK1 mutations did not predict for resistance, and these alleles were not selected for upon BRAF inhibition, other exon 3 MEK1 mutations, such as C121S, did convey resistance, suggesting a role for defined exon 3 MEK1 mutations in acquired BRAF inhibitor resistance.

Oncogenic NRAS signaling differentially regulates survival and proliferation in melanoma

The discovery of potent inhibitors of the BRAF proto-oncogene has revolutionized therapy for melanoma harboring mutations in BRAF, yet NRAS-mutant melanoma remains without an effective therapy. Because direct pharmacological inhibition of the RAS proto-oncogene has thus far been unsuccessful, we explored systems biology approaches to identify synergistic drug combination(s) that can mimic RAS inhibition. Here, leveraging an inducible mouse model of NRAS-mutant melanoma, we show that pharmacological inhibition of mitogen-activated protein kinase kinase (MEK) activates apoptosis but not cell-cycle arrest, which is in contrast to complete genetic neuroblastoma RAS homolog (NRAS) extinction, which triggers both of these effects. Network modeling pinpointed cyclin-dependent kinase 4 (CDK4) as a key driver of this differential phenotype. Accordingly, combined pharmacological inhibition of MEK and CDK4 in vivo led to substantial synergy in therapeutic efficacy. We suggest a gradient model of oncogenic NRAS signaling in which the output is gated, resulting in the decoupling of discrete downstream biological phenotypes as a result of incomplete inhibition. Such a gated signaling model offers a new framework to identify nonobvious coextinction target(s) for combined pharmacological inhibition in NRAS-mutant melanomas.

Molecular testing in malignant melanoma

Molecular testing of cancers to determine therapeutic eligibility is now standard of care and has changed the practice of pathology. Recent advances in the treatment of metastatic melanoma with BRAF and KIT inhibitors have increased the demand for molecular testing in melanoma. Furthermore, rapid progress is being made in determining potential new targets, mechanisms of resistance, and developing additional rationally designed therapies. The likely consequence will be a significant expansion of molecular testing for melanoma to include an array of multiple signaling intermediates. Currently, routine testing is mostly limited to BRAF and KIT. Mutations in these genes generally occur in a distinct group of melanoma subsets though, and with the numerous techniques available for mutation analysis, decisions about testing can be complex. The purpose of this review is to provide an overview of clinically relevant mutations which currently guide systemic therapy in Stage IV melanoma, how these molecular events vary with melanoma subtype and primary site of origin, and practical recommendations for testing.

BH3-only protein silencing contributes to acquired resistance to PLX4720 in human melanoma

B-RAF is mutated to a constitutively active form in 8% of human cancers including 50% of melanomas. In clinical trials, the RAF inhibitor, PLX4032 (vemurafenib), caused partial or complete responses in 48-81% of mutant B-RAF harboring melanoma patients. However, the average duration of response was 6-7 months before tumor regrowth, indicating the acquisition of resistance to PLX4032. To understand the mechanisms of resistance, we developed mutant B-RAF melanoma cells that displayed resistance to RAF inhibition through continuous culture with PLX4720 (the tool compound for PLX4032). Resistance was associated with a partial reactivation of extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, recovery of G1/S cell-cycle events, and suppression of the pro-apoptotic B-cell leukemia/lymphoma 2 (Bcl-2) homology domain 3 (BH3)-only proteins, Bcl-2-interacting mediator of cell death-extra large (Bim-EL) and Bcl-2 modifying factor (Bmf). Preventing ERK1/2 reactivation with MEK (mitogen-activated protein/extracellular signal-regulated kinase kinase) inhibitors blocked G1-S cell-cycle progression but failed to induce apoptosis or upregulate Bim-EL and Bmf. Treatment with the histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid, led to de-repression of Bim-EL and enhanced cell death in the presence of PLX4720 or AZD6244 in resistant cells. These data indicate that acquired resistance to PLX4032/4720 likely involves ERK1/2 pathway reactivation as well as ERK1/2-independent silencing of BH3-only proteins. Furthermore, combined treatment of HDAC inhibitors and MEK inhibitors may contribute to overcoming PLX4032 resistance.

The current state of targeted therapy in melanoma: this time it's personal

Treatment of metastatic melanoma has long been a challenge. Over the past 8 years significant advances have been made in understanding the genetic changes that drive melanoma development and progression. These studies have shown melanoma to be a heterogeneous group of tumors, driven by a diverse array of oncogenic mutations. There is now good evidence that activating mutations in the serine/threonine kinase BRAF and the receptor tyrosine kinase KIT constitute good therapeutic targets for restricted subgroups of melanoma. In this article, we discuss the genetics and etiology of cutaneous and noncutaneous melanoma and review some of the latest preclinical and clinical data on the new targeted therapy agents that are beginning to make an impact on the lives of melanoma patients.

GSK3β inhibition blocks melanoma cell/host interactions by downregulating N-cadherin expression and decreasing FAK phosphorylation

This study addresses the role of glycogen synthase kinase (GSK)-3β signaling in the tumorigenic behavior of melanoma. Immunohistochemical staining revealed GSK3β to be focally expressed in the invasive portions of 12 and 33% of primary and metastatic melanomas, respectively. GSK3 inhibitors and small interfering RNA (siRNA) knockdown of GSK3β were found to inhibit the motile behavior of melanoma cells in scratch wound, three-dimensional collagen-implanted spheroid, and modified Boyden chamber assays. Functionally, inhibition of GSK3β signaling was found to suppress N-cadherin expression at the messenger RNA and protein levels, and was associated with decreased expression of the transcription factor Slug. Pharmacological and genetic ablation of GSK3β signaling inhibited the adhesion of melanoma cells to both endothelial cells and fibroblasts and prevented transendothelial migration, an effect rescued by the forced overexpression of N-cadherin. A further role for GSK3β signaling in invasion was suggested by the ability of GSK3β inhibitors and siRNA knockdown to block phosphorylation of focal adhesion kinase (FAK) and increase the size of focal adhesions. In summary, we have, to our knowledge, demonstrated a previously unreported role for GSK3β in modulating the motile and invasive behavior of melanoma cells through N-cadherin and FAK. These studies suggest the potential therapeutic utility of inhibiting GSK3β in defined subsets of melanoma.