Dabrafenib in BRAF-mutated metastatic melanoma: a multicentre, open-label, phase 3 randomised controlled trial

Immunotherapy and the concept of a clinical cure

Immunotherapy has entered a new phase in its history, i.e. the phase of being broadly accepted as a key component of therapeutic strategies to control and cure cancer. Immune-modulation by checkpoint inhibitors have demonstrated to be capable of inducing long lasting tumour responses. Breaking tolerance by ipilimumab has been a crucial event in the past recent years, but PD-1/PD-L1 antibodies have forever changed the landscape in oncology in 2013. The most mature results have been obtained in advanced melanoma patients. High response rates of high quality with prolonged duration have been demonstrated in melanoma, renal cancer and in lung cancer. The broad potential is now being explored across a wide range of tumours. Importantly, synergy with ipilimumab has been demonstrated in melanoma, indicating a bright further future. Long term tumour control now seems achievable and thus the concept of a "clinical cure" is emerging. These antibodies bring immunotherapy to the forefront and indicate that immune-modulation will be a key component of therapeutic strategies from now on. All these observations indicate that "clinical cures" can only be achieved when the immune system is involved, and so the true renaissance of immunotherapy has arrived.

Paradoxical oncogenesis: are all BRAF inhibitors equal?

Cutaneous squamous cell carcinoma (cSCC) is a concerning toxicity with BRAF inhibitors in the treatment for melanoma. While the two drugs shown to improve survival, vemurafenib, and dabrafenib, have similar efficacy, the reported rates of cSCC are quite different. Drawing upon preclinical and clinical trial data, this article discusses the potential factors behind the different cSCC incidences reported with the two BRAF inhibitors and provides a strategic approach to understand this issue further.

Recent advances in melanoma systemic therapy. BRAF inhibitors, CTLA4 antibodies and beyond

Metastatic melanoma has a poor prognosis and until recently systemic therapy was ineffective. Advances in the understanding of tumour biology and immune regulation have led to the development of targeted agents that have changed clinical practice, with further improvements expected with new compounds and combinations. The first major advance was the development of selective mitogen-activated protein (MAP) kinase inhibitors (BRAF and MEK inhibitors) and immune checkpoint blockade with a CTLA4 antibody (ipilimumab). These drugs proved vastly superior to conventional chemotherapy, however response, resistance and toxicity were limitations. The second major advance is the development of other immune checkpoint blocking agents, including PD-1 and PD-L1 antibodies, and the use of BRAF and MEK inhibitors in combination, with a higher proportion of durable responses coupled with less toxicity. In an effort to improve outcomes for patients with melanoma further, trials are underway examining the combination of MAPK inhibitors, immunotherapies and other pathway inhibitors and adjuvant studies of many of these agents have commenced.

New developments in biomarkers for melanoma

PURPOSE OF REVIEW

Therapy of malignant melanoma recently experienced remarkable advances with the introduction of two treatment regimens, gene mutation-based therapies with signaling pathway inhibitors (kinase inhibitors) and treatments with immune modulators. Both strategies prolong patients' survival but still have specific limitations, demanding the identification of additional genetic and immunological biomarkers as predictors of treatment response and prognosis. New developments in that field are summarized in this review.

RECENT FINDINGS

Activating oncogene mutations are important melanoma biomarkers. They predict responsiveness to kinase inhibitor therapies and have therapy independent prognostic relevance. Epigenetic alterations (DNA methylation, chromatin remodeling, and noncoding RNA) in melanoma are emerging as potentially valuable biomarkers. With the successful introduction of immunotherapies for melanoma, interest in immunological biomarkers has grown. Tumor-reactive cytotoxic T cells from patients' peripheral blood were recently proposed to predict prognosis and response to immunotherapy. A superior immune profile assessment could be achieved by combining a detailed characterization of a tumor's immune cell infiltrate with its (immune) gene signature.

SUMMARY

Genetic melanoma markers have already become clinically relevant. We expect both their role and that of immunological biomarkers to increase significantly in the next few years, enabling personalized therapy with optimal treatment selection for individual tumors.

Molecular diagnostics and personalized medicine in oncology: challenges and opportunities

Increasing evidence demonstrates that target-based agents are active only in molecularly selected populations of patients. Therefore, the identification of predictive biomarkers has become mandatory to improve the clinical development of these novel drugs. Mutations of the epidermal growth factor receptor (EGFR) or rearrangements of the ALK gene in non-small-cell lung cancer, and BRAF mutations in melanoma are clear examples of driver mutations and predictive biomarkers of response to treatment with specific inhibitors. Predictive biomarkers might also identify subgroups of patients that are not likely to respond to specific drugs, as shown for KRAS mutations and anti-EGFR monoclonal antibodies in colorectal carcinoma. The discovery of novel driver molecular alterations and the availability of drugs capable to selectively block such oncogenic mechanisms are leading to a rapid increase in the number of putative biomarkers that need to be assessed in each single patient. In this respect, two different approaches are being developed to introduce a comprehensive molecular characterization in clinical practice: high throughput genotyping platforms, which allow the detection of recognized genetic aberrations in clinical samples, and next generation sequencing that can provide information on all the different types of cancer-causing alterations. The introduction of these techniques in clinical practice will increase the possibility to identify molecular targets in each individual patient, and will also allow to follow the molecular evolution of the disease during the treatment. By using these approaches, the development of personalized medicine for patients with cancer will finally become possible.

The use of systemic therapies for the treatment of brain metastases in metastatic melanoma: opportunities and unanswered questions

The development of brain metastases is common in patients with metastatic melanoma and heralds a particularly poor prognosis. The development of the immunological agent ipilimumab and targeted treatments such as the selective BRAF inhibitor vemurafenib have revolutionised the treatment of metastatic disease. Evidence from clinical trials suggest these drugs may be effective in the treatment of brain metastases from melanoma. However efficacy may be limited by a lack of penetration of the blood brain barrier (BBB) and by multi substrate efflux pumps expressed on the BBB. The role and sequencing of radiotherapy, both whole brain and stereotactic radiotherapy, is yet to be determined but combinations of radiotherapy and systemic therapies may further increase the effects of these drugs on brain metastases. Considering the impact of brain metastases on morbidity and mortality in metastatic melanoma, future research into systemic drug therapy for the treatment of brain metastases and improvements in BBB penetrance should be a priority.

NRAS and BRAF mutations in melanoma-associated nevi and uninvolved nevi

According to the prevailing multistep model of melanoma development, oncogenic BRAF or NRAS mutations are crucial initial events in melanoma development. It is not known whether melanocytic nevi that are found in association with a melanoma are more likely to carry BRAF or NRAS mutations than uninvolved nevi. By laser microdissection we were able to selectively dissect and genotype cells either from the nevus or from the melanoma part of 46 melanomas that developed in association with a nevus. In 25 cases we also genotyped a control nevus of the same patients. Available tissue was also immunostained using the BRAF^V600E-mutation specific antibody VE1. The BRAF^V600E mutation was found in 63.0% of melanomas, 65.2% of associated nevi and 50.0% of control nevi. No significant differences in the distribution of BRAF or NRAS mutations could be found between melanoma and associated nevi or between melanoma associated nevi and control nevi. In concordant cases immunohistochemistry showed a higher expression (intensity of immunohistochemistry) of the mutated BRAF^V600E-protein in melanomas compared to their associated nevi. In this series the presence of a BRAF- or NRAS mutation in a nevus was not associated with the risk of malignant transformation. Our findings do not support the current traditional model of stepwise tumor progression.

Tumor genetic analyses of patients with metastatic melanoma treated with the BRAF inhibitor dabrafenib (GSK2118436)

PURPOSE

Dabrafenib is a selective inhibitor of V600-mutant BRAF kinase, which recently showed improved progression-free survival (PFS) as compared with dacarbazine, in metastatic melanoma patients. This study examined potential genetic markers associated with response and PFS in the phase I study of dabrafenib.

EXPERIMENTAL DESIGN

Baseline (pretreatment or archival) melanoma samples were evaluated in 41 patients using a custom genotyping melanoma-specific assay, sequencing of PTEN, and copy number analysis using multiplex ligation amplification and array-based comparative genomic hybridization. Nine patients had on-treatment and/or progression samples available.

RESULTS

All baseline patient samples had BRAF(V600E/K) confirmed. Baseline PTEN loss/mutation was not associated with best overall response to dabrafenib, but it showed a trend for shorter median PFS [18.3 (95% confidence interval, CI, 9.1-24.3) vs. 32.1 weeks (95% CI, 24.1-33), P=0.059]. Higher copy number of CCND1 (P=0.009) and lower copy number of CDKN2A (P=0.012) at baseline were significantly associated with decreased PFS. Although no melanomas had high-level amplification of BRAF, the two patients with progressive disease as their best response had BRAF copy gain in their tumors.

CONCLUSIONS

Copy number changes in CDKN2A, CCND1, and mutation/copy number changes in PTEN correlated with the duration of PFS in patients treated with dabrafenib. The results suggest that these markers should be considered in the design and interpretation of future trials with selective BRAF inhibitors in advanced melanoma patients.

Understanding, recognizing, and managing toxicities of targeted anticancer therapies

Answer questions and earn CME/CNE Advances in genomics and molecular biology have identified aberrant proteins in cancer cells that are attractive targets for cancer therapy. Because these proteins are overexpressed or dysregulated in cancer cells compared with normal cells, it was assumed that their inhibitors will be narrowly targeted and relatively nontoxic. However, this hope has not been achieved. Current targeted agents exhibit the same frequency and severity of toxicities as traditional cytotoxic agents, with the main difference being the nature of the toxic effects. Thus, the classical chemotherapy toxicities of alopecia, myelosuppression, mucositis, nausea, and vomiting have been generally replaced by vascular, dermatologic, endocrine, coagulation, immunologic, ocular, and pulmonary toxicities. These toxicities need to be recognized, prevented, and optimally managed.

Liver resection for metastatic melanoma: equivalent survival for cutaneous and ocular primaries

BACKGROUND

The value of surgical resection in patients with hepatic metastases from melanoma is poorly documented in the literature. This study sought to determine the clinicopathologic and surgical factors predictive of outcome for melanoma patients who underwent resection of hepatic metastases.

METHODS

Thirty-three patients who underwent liver resection for melanoma metastases were identified from the Melanoma Institute Australia research database. Univariate and multivariate analyses were performed to identity factors predictive of recurrence and survival following liver resection for melanoma metastasis.

RESULTS

The actuarial 2- and 5-year survival rates were 59% and 42%, respectively, with a median survival of 29 months (range 1-139). The 5-year survival rates for cutaneous and ocular primary melanoma were 44% and 39%, respectively. Improved post-hepatic metastasectomy survival was observed in patients with microscopically clear resection margins (R0, 44 months; R1/2, 12 months; P = 0.04). Although major hepatic resection was associated with improved survival (major, 70 months; minor, 23 months; P = 0.07), major hepatectomies were performed almost exclusively in patients with isolated liver metastases.

CONCLUSIONS

Hepatic resection for metastatic melanoma is associated with improved survival in selected patients with both primary ocular and cutaneous melanoma. Surgical treatment of hepatic melanoma metastases should be considered when complete resection is feasible.

TERT promoter mutations in ocular melanoma distinguish between conjunctival and uveal tumours

BACKGROUND

Recently, activating mutations in the TERT promoter were identified in cutaneous melanoma. We tested a cohort of ocular melanoma samples for similar mutations.

METHODS

The TERT promoter region was analysed by Sanger sequencing in 47 uveal (ciliary body or choroidal) melanomas and 38 conjunctival melanomas.

RESULTS

Mutations of the TERT promoter were not identified in uveal melanomas, but were detected in 12 (32%) conjunctival melanomas. Mutations had a UV signature and were identical to those found in cutaneous melanoma.

CONCLUSION

Mutations of TERT promoter with UV signatures are frequent in conjunctival melanomas and favour a pathogenetic kinship with cutaneous melanomas. Absence of these mutations in uveal melanomas emphasises their genetic distinction from cutaneous and conjunctival melanomas.

Effective activity of cytokine-induced killer cells against autologous metastatic melanoma including cells with stemness features

PURPOSE

We investigate the unknown tumor-killing activity of cytokine-induced killer (CIK) cells against autologous metastatic melanoma and the elusive subset of putative cancer stem cells (mCSC).

EXPERIMENTAL DESIGN

We developed a preclinical autologous model using same patient-generated CIK cells and tumor targets to consider the unique biology of each patient/tumor pairing. In primary tumor cell cultures, we visualized and immunophenotypically defined a putative mCSC subset using a novel gene transfer strategy that exploited their exclusive ability to activate the promoter of stemness gene Oct4.

RESULTS

The CIK cells from 10 patients with metastatic melanoma were successfully expanded (median, 23-fold; range, 11-117). Primary tumor cell cultures established and characterized from the same patients were used as autologous targets. Patient-derived CIK cells efficiently killed autologous metastatic melanoma [up to 71% specific killing (n = 26)]. CIK cells were active in vivo against autologous melanoma, resulting in delayed tumor growth, increased necrotic areas, and lymphocyte infiltration at tumor sites. The metastatic melanoma cultures presented an average of 11.5% ± 2.5% putative mCSCs, which was assessed by Oct4 promoter activity and stemness marker expression (Oct4, ABCG2, ALDH, MITF). Expression was confirmed on mCSC target molecules recognized by CIK cells (MIC A/B; ULBPs). CIK tumor killing activity against mCSCs was intense (up to 71%, n = 4) and comparable with results reported against differentiated metastatic melanoma cells (P = 0.8).

CONCLUSIONS

For the first time, the intense killing activity of CIK cells against autologous metastatic melanoma, including mCSCs, has been shown. These findings move clinical investigation of a new immunotherapy for metastatic melanoma, including mCSCs, closer.

Evolving pharmacotherapies for the treatment of metastatic melanoma

Metastatic melanoma remains a difficult disease to treat, and long term survivors are rare. Over the past few years, however, breakthroughs in both immunotherapy as well as targeted agents have had a tremendous impact on patients diagnosed with this disease. This review summarizes recent advances in systemic therapies for melanoma, including immune modulators directed against cytotoxic T lymphocyte associated antigen-4 (CTLA-4) and programmed death-1 (PD-1), as well as a number of targeted agents. These approaches hold great promise as the landscape of therapeutic options for advanced melanoma continues to evolve.

Melanogenesis affects overall and disease-free survival in patients with stage III and IV melanoma

Because melanogenesis can affect immune responses to and chemotherapy and radiotherapy for melanoma, we analyzed overall survival and disease-free survival times in melanoma patients in relation to the degree of tumor pigmentation. Clinicopathologic data were obtained from the Oncology Centre, Prof Franciszek Łukaszczyk Memorial Hospital, Bydgoszcz, Poland. The overall survival and disease-free survival analyses were performed using the log-rank test, whereas differences between mean/median overall survival and disease-free survival (days) were analyzed using the Student t test. In patients with metastatic disease, those with melanotic melanomas exhibited significantly shorter disease-free survival and overall survival than those with amelanotic lesions. Similarly, melanin-producing lymph node metastases were linked to shorter overall survival and disease-free survival, which was confirmed by a significantly longer mean/median disease-free survival for amelanotic versus melanotic metastases. Melanogenesis shortens overall survival and disease-free survival in patients with metastatic melanoma. Inhibition of melanogenesis appears a rational adjuvant approach to the therapy of metastatic melanoma.

Mind the IQGAP

The scaffold protein IQGAP1 regulates cell signaling through the RAF/MEK/ERK pathway. Recent data show that cancer cells in which the RAF/MEK/ERK pathway is activated are particularly sensitive to the disruption of IQGAP1 function. IQGAP drugs may be particularly effective in tumors that develop resistance to existing pathway drugs.

Molecular targeted therapies in metastatic melanoma

The advent of personalized medicine has ushered in a new era for cancer therapy with a significant impact on the management of advanced melanoma. Molecular targeted therapies have shown promise in the management of various malignancies, including melanoma, with lower toxicity profiles and better overall survival as compared with conventional therapy. The discovery of BRAF mutations in melanoma led to the development of BRAF inhibitors for the treatment of advanced melanoma. However, growing concerns over drug resistance to molecular targeted therapies including BRAF inhibitors, have spurred efforts to elucidate additional molecular targets for the treatment of advanced melanoma. In this review, we discuss the known molecular aberrations in melanoma, current and novel targeted approaches in its treatment, and drug resistance patterns.

Future perspectives in melanoma research. Meeting report from the "Melanoma Bridge. Napoli, December 2nd-4th 2012"

Recent insights into the genetic and somatic aberrations have initiated a new era of rapidly evolving targeted and immune-based treatments for melanoma. After decades of unsuccessful attempts to finding a more effective cure in the treatment of melanoma now we have several drugs active in melanoma. The possibility to use these drugs in combination to improve responses to overcome the resistance, to potentiate the action of immune system with the new immunomodulating antibodies, and identification of biomarkers that can predict the response to a particular therapy represent new concepts and approaches in the clinical management of melanoma. The third "Melanoma Research: "A bridge from Naples to the World" meeting, shortened as "Bridge Melanoma Meeting" took place in Naples, December 2 to 4th, 2012. The four topics of discussion at this meeting were: advances in molecular profiling and novel biomarkers, combination therapies, novel concepts toward integrating biomarkers and therapies into contemporary clinical management of patients with melanoma across the entire spectrum of disease stage, and the knowledge gained from the biology of tumor microenvironment across different tumors as a bridge to impact on prognosis and response to therapy in melanoma. This international congress gathered more than 30 international faculty members who in an interactive atmosphere which stimulated discussion and exchange of their experience regarding the most recent advances in research and clinical management of melanoma patients.

Optimal management of metastatic melanoma: current strategies and future directions

Melanoma is increasing in incidence and remains a major public health threat. Although the disease may be curable when identified early, advanced melanoma is characterized by widespread metastatic disease and a median survival of less than 10 months. In recent years, however, major advances in our understanding of the molecular nature of melanoma and the interaction of melanoma cells with the immune system have resulted in several new therapeutic strategies that are showing significant clinical benefit. Current therapeutic approaches include surgical resection of metastatic disease, chemotherapy, immunotherapy, and targeted therapy. Dacarbazine, interleukin-2, ipilimumab, and vemurafenib are now approved for the treatment of advanced melanoma. In addition, new combination chemotherapy regimens, monoclonal antibodies blocking the programmed death-1 (PD-1)/PD-ligand 1 pathway, and targeted therapy against CKIT, mitogen-activated protein/extracellular signal-regulated kinase (MEK), and other putative signaling pathways in melanoma are beginning to show promise in early-phase clinical trials. Further research on these modalities alone and in combination will likely be the focus of future clinical investigation and may impact the outcomes for patients with advanced melanoma.

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.

Oncogenic B-Raf(V600E) abrogates the AKT/B-Raf/Mps1 interaction in melanoma cells

Activating B-Raf mutations that deregulate the mitogen-activated protein kinase (MAPK) pathway commonly occur in cancer. Although B-Raf(V600E) induces increased Mps1 protein contributing to centrosome amplification and chromosome instability, the regulatory mechanisms of Mps1 in melanoma cells is not fully understood. Here, we report that Mps1/AKT and B-Raf(WT)/ERK signaling form an auto-regulatory negative feedback loop in melanoma cells; notably, oncogenic B-Raf(V600E) abrogates the negative feedback loop, contributing the aberrant Mps1 functions and tumorigenesis. Our findings raise the possibility that targeting the oncogenic B-Raf and Mps1, especially when used in combination could potentially provide great therapeutic opportunities for cancer treatment.

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.

Pharmacotherapy of metastatic melanoma: emerging trends and opportunities for a cure

Metastatic melanoma is one of the most deadly forms of cancer and is poorly responsive to standard chemotherapeutics, such as Dacarbazine and Paclitaxel. Recently, the advent of Vemurafenib and Ipilimumab has broadened the spectrum of therapeutic options for advanced melanoma patients but the occurrence of resistance and of high-grade toxicities call for better and more effective treatments. This review focuses on approved and experimental therapies for metastatic melanoma. The mechanism of action and the reported efficacy data for small molecule drugs and biologics are discussed, outlining directions for future pharmaceutical research in this field.

Ipilimumab, vemurafenib, dabrafenib, and trametinib: synergistic competitors in the clinical management of BRAF mutant malignant melanoma

There have been significant advances in the treatment of malignant melanoma with the U.S. Food and Drug Administration approval of two drugs in 2011, the first drugs approved in 13 years. The developments of immune checkpoint modulation via cytotoxic T-lymphocyte antigen-4 blockade, with ipilimumab, and targeting of BRAF(V600), with vemurafenib or dabrafenib, as well as MEK, with trametinib, have been paradigm changing both for melanoma clinical practice and for oncology therapeutic development. These advancements, however, reveal new clinical questions regarding combinations and optimal sequencing of these agents in patients with BRAF mutant disease. We review the development of these agents, putative biomarkers, and resistance mechanisms relevant to their use, and possibilities for sequencing and combining these agents.

Low BRAF and NRAS expression levels are associated with clinical benefit from DTIC therapy and prognosis in metastatic melanoma

Metastatic melanoma is characterized by a poor response to chemotherapy. Furthermore, there is a lack of established predictive and prognostic markers. In this single institution study, we correlated mutation status and expression levels of BRAF and NRAS to dacarbazine (DTIC) treatment response as well as progression-free and overall survival in a cohort of 85 patients diagnosed with advanced melanoma. Neither BRAF nor NRAS mutation status correlated to treatment response. However, patients with tumors harboring NRAS mutations had a shorter overall survival (p < 0.001) compared to patients with tumors wild-type for NRAS. Patients having a clinical benefit (objective response or stable disease at 3 months) on DTIC therapy had lower BRAF and NRAS expression levels compared to patients progressing on therapy (p = 0.037 and 0.003, respectively). For BRAF expression, this association was stronger among patients with tumors wild-type for BRAF (p = 0.005). Further, low BRAF as well as NRAS expression levels were associated with a longer progression-free survival in the total population (p = 0.004 and <0.001, respectively). Contrasting low NRAS expression levels, which were associated with improved overall survival in the total population (p = 0.01), low BRAF levels were associated with improved overall survival only among patients with tumors wild-type for BRAF (p = 0.013). These findings indicate that BRAF and NRAS expression levels may influence responses to DTIC as well as prognosis in patients with advanced melanoma.

The combination of novel targeted molecular agents and radiation in the treatment of pediatric gliomas

Brain tumors are the most common solid pediatric malignancy. For high-grade, recurrent, or refractory pediatric brain tumors, radiation therapy (XRT) is an integral treatment modality. In the era of personalized cancer therapy, molecularly targeted agents have been designed to inhibit pathways critical to tumorigenesis. Our evolving knowledge of genetic aberrations in pediatric gliomas is being exploited with the use of specific targeted inhibitors. These agents are additionally being combined with XRT to increase the efficacy and duration of local control. In this review, we discuss novel agents targeting three different pathways in gliomas, and their potential combination with XRT. BRAF is a serine/threonine kinase in the RAS/RAF/MAPK kinase pathway, which is integral to cellular division, survival, and metabolism. Two-thirds of pilocytic astrocytomas, a low-grade pediatric glioma, contain a translocation within the BRAF gene called KIAA1549:BRAF that causes an overactivation of the MEK/MAPK signaling cascade. In vitro and in vivo data support the use of MEK or mammalian target of rapamycin (mTOR) inhibitors in low-grade gliomas expressing this translocation. Additionally, 15-20% of high-grade pediatric gliomas express BRAF V600E, an activating mutation of the BRAF gene. Pre-clinical in vivo and in vitro data in BRAF V600E gliomas demonstrate dramatic cooperation between XRT and small molecule inhibitors of BRAF V600E. Another major signaling cascade that plays a role in pediatric glioma pathogenesis is the PI3-kinase (PI3K)/mTOR pathway, known to be upregulated in the majority of high- and low-grade pediatric gliomas. Dual PI3K/mTOR inhibitors are in clinical trials for adult high-grade gliomas and are poised to enter studies of pediatric tumors. Finally, many brain tumors express potent stimulators of angiogenesis that render them refractory to treatment. An analog of thalidomide, CC-5103 increases the secretion of critical cytokines of the tumor microenvironment, including IL-2, IFN-γ, TNF-α, and IL-10, and is currently being evaluated in clinical trials for the treatment of recurrent or refractory pediatric central nervous system tumors. In summary, several targeted inhibitors with radiation are currently under investigation in both translational bench research and early clinical trials. This review article summarizes the molecular rationale for, and the pre-clinical data supporting the combinations of these targeted agents with other anti-cancer agents and XRT in pediatric gliomas. In many cases, parallels are drawn to molecular mechanisms and targeted inhibitors of adult gliomas. We additionally discuss the potential mechanisms underlying the efficacy of these agents.

Companion biomarkers: paving the pathway to personalized treatment for cancer

BACKGROUND

Companion biomarkers are biomarkers that are used in combination with specific therapies and that prospectively help predict likely response or severe toxicity. In this article we review the role of companion biomarkers in guiding treatment in patients with cancer.

CONTENT

In addition to the established companion biomarkers such as estrogen receptors and HER2 (human epidermal growth factor receptor 2) in breast cancer, several new companion biomarkers have become available in recent years. These include v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations for the selection of patients with advanced colorectal cancer who are unlikely to benefit from anti-epidermal growth factor receptor antibodies (cetuximab or panitumumab), epidermal growth factor receptor (EGFR) mutations for selecting patients with advanced non-small cell lung cancer (NSCLC) for treatment with tyrosine kinase inhibitors (gefitinib or erlotinib), v-raf murine sarcoma viral oncogene homolog B1 (BRAF) mutations for selecting patients with advanced melanoma for treatment with anti-BRAF agents (vemurafenib and dabrafenib), and anaplastic lymphoma receptor tyrosine kinase (ALK) translocations for identifying patients with NSCLC likely to benefit from crizotinib.

SUMMARY

The availability of companion biomarkers should improve drug efficacy, decrease toxicity, and lead to a more individualized approach to cancer treatment.

Phase I/II RAF kinase inhibitors in cancer therapy

INTRODUCTION

Aberrant activation of RAF signalling is a frequent finding in human cancers. BRAF is the only RAF family member that is commonly mutated, whilst CRAF and ARAF play important roles in the signal transduction from mutant RAS. BRAF-specific inhibitors have been more effective in the treatment of BRAF-mutant melanoma than BRAF-mutant thyroid and colorectal cancers.

AREAS COVERED

The review summarises the experience with RAF kinase inhibitors, including efficacy, modes of acquired resistance, and the mechanism behind the progression of pre-malignant RAS-mutant lesions observed with RAF kinase inhibitors. The authors review all the completed and ongoing Phase I or II clinical trials of RAF kinase inhibitors and discuss in detail the rationale behind the combinatorial approaches.

EXPERT OPINION

The success of RAF kinase inhibitors has demonstrated the necessity of genotype-driven treatment selection for cancer patients. The spectrum of responses in different tumour types is explained by feedback events that are determined by cell lineage. Dissection of these events and the mechanisms of acquired resistance will determine the appropriate combination therapies. Ongoing characterisation of RAS-MAPK regulation in malignant cells may aid the development of novel agents that have greater potency for the inhibition of activated RAF kinase, and lesser propensity for promotion of RAS-mutant tumours.

Effects of BRAF inhibitors on human melanoma tissue before treatment, early during treatment, and on progression

Selective BRAF inhibitors (BRAFi) are a standard of care for the treatment of BRAF(V) (600) -mutant metastatic melanoma. We analyzed a unique set of serial triplicate human metastatic melanoma tumor biopsies to identify biomarkers of BRAFi response and resistance. Morphologic features and immunohistochemical biomarkers were analyzed in 37 metastatic melanoma biopsies at pretreatment (PRE), early during treatment (EDT), and on progression (PROG) from 15 patients treated with a BRAFi and correlated with response and outcome. At EDT, proliferative markers decreased regardless of response, whereas markers of cell death increased in responders. High expression of nuclear p27 at baseline was the strongest predictor of a poorer OS and predicted worse response. The results show that BRAFi are universally antiproliferative, regardless of clinical response, whereas markers of cell death increased only in responders. The addition of therapies targeting the cell cycle machinery may improve the response and duration of BRAFi, and investigation of the mechanisms of apoptosis may provide additional therapeutic targets.

Brain metastasis: opportunity for drug development?

PURPOSE OF REVIEW

Brain metastases are a common clinical problem, and only limited treatment options exist. We review recent advances in medical brain metastasis research with a focus on the most common tumor types associated with secondary brain colonization: melanoma, breast cancer and lung cancer. We speculate on opportunities for drug development in patients with brain metastases, both as a treatment of established disease and as an adjuvant and prophylactic strategy.

RECENT FINDINGS

BRAF inhibitors and the immunomodulatory anticytotoxic T-lymphocyte-associated antigen 4 antibody ipilimumab have shown clinically meaningful activity in melanoma patients with brain metastases. In breast cancer, current studies on drug treatment of brain metastases are mainly focusing on human epidermal growth factor receptor 2 targeting agents such as lapatinib. Emerging data seem to implicate a potential role of targeted agents including antiangiogenic compounds, pazopanib, and epithelial growth factor receptor inhibitors for prevention of brain metastasis formation in breast cancer or nonsmall cell lung cancer.

SUMMARY

Novel drugs are beginning to enter clinical practice for selected patients with brain metastases. The promising findings from recent studies may fuel more research on brain metastases and their optimal drug treatment.

Antiproliferative effects of continued mitogen-activated protein kinase pathway inhibition following acquired resistance to BRAF and/or MEK inhibition in melanoma

Inhibitors of the mitogen-activated protein kinases (MAPK), BRAF, and MAP-ERK kinase (MEK) induce tumor regression in the majority of patients with BRAF-mutant metastatic melanoma. The clinical benefit of MAPK inhibitors is restricted by the development of acquired resistance with half of those who benefit having progressed by 6 to 7 months and long-term responders uncommon. There remains no agreed treatment strategy on disease progression in these patients. Without published evidence, fears of accelerated disease progression on inhibitor withdrawal have led to the continuation of drugs beyond formal disease progression. We now show that treatment with MAPK inhibitors beyond disease progression can provide significant clinical benefit, and the withdrawal of these inhibitors led to a marked increase in the rate of disease progression in two patients. We also show that MAPK inhibitors retain partial activity in acquired resistant melanoma by examining drug-resistant clones generated to dabrafenib, trametinib, or the combination of these drugs. All resistant sublines displayed a markedly slower rate of proliferation when exposed to MAPK inhibitors, and this coincided with a reduction in MAPK signaling, decrease in bromodeoxyuridine incorporation, and S-phase inhibition. This cytostatic effect was also associated with diminished levels of cyclin D1 and p-pRb. Two short-term melanoma cultures generated from resistant tumor biopsies also responded to MAPK inhibition, with comparable inhibitory changes in proliferation and MAPK signaling. These data provide a rationale for the continuation of BRAF and MEK inhibitors after disease progression and support the development of clinical trials to examine this strategy.

Hydroxylation of CYP11A1-derived products of vitamin D3 metabolism by human and mouse CYP27B1

CYP11A1 can hydroxylate vitamin D3 at carbons 17, 20, 22, and 23, producing a range of secosteroids which are biologically active with respect to their ability to inhibit proliferation and stimulate differentiation of various cell types, including cancer cells. As 1α-hydroxylation of the primary metabolite of CYP11A1 action, 20S-hydroxyvitamin D3 [20(OH)D3], greatly influences its properties, we examined the ability of both human and mouse CYP27B1 to 1α-hydroxylate six secosteroids generated by CYP11A1. Based on their kcat/Km values, all CYP11A1-derived metabolites are poor substrates for CYP27B1 from both species compared with 25-hydroxyvitamin D3. No hydroxylation of metabolites with a 17α-hydroxyl group was observed. 17α,20-Dihydroxyvitamin D3 acted as an inhibitor on human CYP27B1 but not the mouse enzyme. We also tested CYP27B1 activity on 20,24-, 20,25-, and 20,26-dihydroxyvitamin D3, which are products of CYP24A1 or CYP27A1 activity on 20(OH)D3. All three compounds were metabolized with higher catalytic efficiency (kcat/Km) by both mouse and human CYP27B1 than 25-hydroxyvitamin D3. CYP27B1 action on these new dihydroxy derivatives was confirmed to be 1α-hydroxylation by mass spectrometry and nuclear magnetic resonance analyses. Both 1,20,25- and 1,20,26- trihydroxyvitamin D3 were tested for their ability to inhibit melanoma (SKMEL-188) colony formation, and were significantly more active than 20(OH)D3. This study shows that CYP11A1-derived secosteroids are 1α-hydroxylated by both human and mouse CYP27B1 with low catalytic efficiency, and that the presence of a 17α-hydroxyl group completely blocks 1α-hydroxylation. In contrast, the secondary metabolites produced by subsequent hydroxylation of 20(OH)D3 at C24, C25, or C26 are very good substrates for CYP27B1.

Deja Vu: EGF receptors drive resistance to BRAF inhibitors

The promise of personalized medicine is upon us, and in some cancers, targeted therapies are rapidly becoming the mainstay of treatment for selected patients based on their molecular profile. The protein kinase BRAF is a driver oncogene in both thyroid cancer and melanoma, but while drugs that target BRAF and its downstream signaling pathway are effective in melanoma, they are ineffective in thyroid cancer. In this issue of Cancer Discovery, Montero-Conde and colleagues investigate why thyroid cancer is resistant to BRAF inhibitors despite the presence of BRAF mutation.

[Systemic therapy for malignant melanoma]

For decades dacarbazine was the standard in the therapy for metastatic melanoma even though response rates were low. In recent years multiple pharmacological approaches have led to new therapy options including immune modulators like anti-CTLA4 antibodies and kinase inhibitors of the MAPK signaling pathway that showed better response rates and increased overall survival. However, since immune modulators lead only in a small subgroup of patients to long-term responses and kinase inhibitors lose their function due to development of resistance after several months, continuation of clinical studies is strongly required. Classical chemotherapeutic drugs will remain a basic part of the therapy especially as combinations of different treatment options have to be focused on in order to achieve better long-term survival rates.

B-Raf and the inhibitors: from bench to bedside

The B-Raf protein is a key signaling molecule in the mitogen activated protein kinase (MAPK) signaling pathway and has been implicated in the pathogenesis of a variety of cancers. An important V600E mutation has been identified and can cause constitutive B-Raf activation. Recent studies have evaluated a variety of small molecule inhibitors targeting B-Raf, including PLX4032/vemurafenib, dabrafenib, LGX818, GDC0879, XL281, ARQ736, PLX3603 (RO5212054), and RAF265. Therapeutic resistance has been identified and various mechanisms described. This review also discussed the current understanding of B-Raf signaling mechanism, methods of mutation detection, treatment strategies as well as potential methods of overcoming therapeutic resistance.

Discovery of a novel ERK inhibitor with activity in models of acquired resistance to BRAF and MEK inhibitors

The high frequency of activating RAS or BRAF mutations in cancer provides strong rationale for targeting the mitogen-activated protein kinase (MAPK) pathway. Selective BRAF and MAP-ERK kinase (MEK) inhibitors have shown clinical efficacy in patients with melanoma. However, the majority of responses are transient, and resistance is often associated with pathway reactivation of the extracellular signal-regulated kinase (ERK) signaling pathway. Here, we describe the identification and characterization of SCH772984, a novel and selective inhibitor of ERK1/2 that displays behaviors of both type I and type II kinase inhibitors. SCH772984 has nanomolar cellular potency in tumor cells with mutations in BRAF, NRAS, or KRAS and induces tumor regressions in xenograft models at tolerated doses. Importantly, SCH772984 effectively inhibited MAPK signaling and cell proliferation in BRAF or MEK inhibitor-resistant models as well as in tumor cells resistant to concurrent treatment with BRAF and MEK inhibitors. These data support the clinical development of ERK inhibitors for tumors refractory to MAPK inhibitors.