MEK targeting in N-RAS mutated metastatic melanoma

Structural characterization and AlphaFold modeling of human T cell receptor recognition of NRAS cancer neoantigens

T cell receptors (TCRs) that recognize cancer neoantigens are important for anticancer immune responses and immunotherapy. Understanding the structural basis of TCR recognition of neoantigens provides insights into their exquisite specificity and can enable design of optimized TCRs. We determined crystal structures of a human TCR in complex with NRAS Q61K and Q61R neoantigen peptides and HLA-A1 major histocompatibility complex (MHC), revealing the molecular underpinnings for dual recognition and specificity versus wild-type NRAS peptide. We then used multiple versions of AlphaFold to model the corresponding complex structures, given the challenge of immune recognition for such methods. One implementation of AlphaFold2 (TCRmodel2) with additional sampling was able to generate accurate models of the complexes, while AlphaFold3 also showed strong performance, although success was lower for other complexes. This study provides insights into TCR recognition of a shared cancer neoantigen as well as the utility and practical considerations for using AlphaFold to model TCR-peptide-MHC complexes.

Structural characterization and AlphaFold modeling of human T cell receptor recognition of NRAS cancer neoantigens

T cell receptors (TCRs) that recognize cancer neoantigens are important for anti-cancer immune responses and immunotherapy. Understanding the structural basis of TCR recognition of neoantigens provides insights into their exquisite specificity and can enable design of optimized TCRs. We determined crystal structures of a human TCR in complex with NRAS Q61K and Q61R neoantigen peptides and HLA-A1 MHC, revealing the molecular underpinnings for dual recognition and specificity versus wild-type NRAS peptide. We then used multiple versions of AlphaFold to model the corresponding complex structures, given the challenge of immune recognition for such methods. Interestingly, one implementation of AlphaFold2 (TCRmodel2) was able to generate accurate models of the complexes, while AlphaFold3 also showed strong performance, although success was lower for other complexes. This study provides insights into TCR recognition of a shared cancer neoantigen, as well as the utility and practical considerations for using AlphaFold to model TCR-peptide-MHC complexes.

Targeted DNA Sequencing of Cutaneous Melanoma Identifies Prognostic and Predictive Alterations

BACKGROUND

Cutaneous melanoma (CM) can be molecularly classified into four groups: BRAF mutant, NRAS mutant, NF1 mutant and triple wild-type (TWT) tumors lacking any of these three alterations. In the era of immune checkpoint inhibition (ICI) and targeted molecular therapy, the clinical significance of these groups remains unclear. Here, we integrate targeted DNA sequencing with comprehensive clinical follow-up in CM patients.

METHODS

This was a retrospective cohort study that assessed clinical and molecular features from patients with localized or metastatic CM who underwent targeted next-generation sequencing as part of routine clinical care. A total of 254 patients with CM who had a CLIA-certified targeted sequencing assay performed on their tumor tissue were included.

RESULTS

Of the 254 patients with cutaneous melanoma, 77 were BRAF mutant (30.3%), 77 were NRAS mutant (30.3%), 47 were NF1 mutant (18.5%), 33 were TWT (13.0%) and the remaining 20 (7.9%) carried mutations in multiple driver genes (BRAF/NRAS/NF1 co-mutated). The majority of this co-mutation group carried mutations in NF1 (n = 19 or 90%) with co-occurring mutations in BRAF or NRAS, often with a weaker oncogenic variant. Consistently, NF1 mutant tumors harbored numerous significantly co-altered genes compared to BRAF or NRAS mutant tumors. The majority of TWT tumors (n = 29, 87.9%) harbor a pathogenic mutation within a known Ras/MAPK signaling pathway component. Of the 154 cases with available TMB data, the median TMB was 20 (range 0.7-266 mutations/Mb). A total of 14 cases (9.1%) were classified as having a low TMB (≤5 mutations/Mb), 64 of 154 (41.6%) had an intermediate TMB (>5 and ≤20 mutations/Mb), 40 of 154 (26.0%) had a high TMB (>20 and ≤50 mutations/Mb) and 36 of 154 (23.4%) were classified as having a very high TMB (>50 mutations/Mb). NRAS mutant melanoma demonstrated significantly decreased overall survival on multivariable analysis (HR for death 2.95, 95% CI 1.13-7.69, p = 0.027, log-rank test) compared with other TCGA molecular subgroups. Of the 116 patients in our cohort with available treatment data, 36 received a combination of dual ICI with anti-CTLA4 and anti-PD1 inhibition as first-line therapy. Elevated TMB was associated with significantly longer progression-free survival following dual-agent ICI (HR 0.26, 95% CI 0.07-0.90, p = 0.033, log-rank test).

CONCLUSIONS

NRAS mutation in CMs correlated with significantly worse overall survival. Elevated TMB was associated with increased progression-free survival for patients treated with a combination of dual ICI, supporting the potential utility of TMB as a predictive biomarker for ICI response in melanoma.

BRAF and MEK inhibitor combinations induce potent molecular and immunological effects in NRAS-mutant melanoma cells: Insights into mode of action and resistance mechanisms

About 25% of melanoma harbor activating NRAS mutations, which are associated with aggressive disease therefore requiring a rapid antitumor intervention. However, no efficient targeted therapy options are currently available for patients with NRAS-mutant melanoma. MEK inhibitors (MEKi) appear to display a moderate antitumor activity and also immunological effects in NRAS-mutant melanoma, providing an ideal backbone for combination treatments. In our study, the MEKi binimetinib, cobimetinib and trametinib combined with the BRAF inhibitors (BRAFi) encorafenib, vemurafenib and dabrafenib were investigated for their ability to inhibit proliferation, induce apoptosis and alter the expression of immune modulatory molecules in sensitive NRAS-mutant melanoma cells using two- and three-dimensional cell culture models as well as RNA sequencing analyses. Furthermore, NRAS-mutant melanoma cells resistant to the three BRAFi/MEKi combinations were established to characterize the mechanisms contributing to their resistance. All BRAFi induced a stress response in the sensitive NRAS-mutant melanoma cells thereby significantly enhancing the antiproliferative and proapoptotic activity of the MEKi analyzed. Furthermore, BRAFi/MEKi combinations upregulated immune relevant molecules, such as ICOS-L, components of antigen-presenting machinery and the "don't eat me signal" molecule CD47 in the melanoma cells. The BRAFi/MEKi-resistant, NRAS-mutant melanoma cells counteracted the molecular and immunological effects of BRAFi/MEKi by upregulating downstream mitogen-activated protein kinase pathway molecules, inhibiting apoptosis and promoting immune escape mechanisms. Together, our study reveals potent molecular and immunological effects of BRAFi/MEKi in sensitive NRAS-mutant melanoma cells that may be exploited in new combinational treatment strategies for patients with NRAS-mutant melanoma.

Reovirus infection of tumor cells reduces the expression of NKG2D ligands, leading to impaired NK-cell cytotoxicity and functionality

In recent years, reoviruses have been of major interest in immunotherapy because of their oncolytic properties. Preclinical and clinical trials, in which reovirus was used for the treatment of melanoma and glioblastoma, have paved the way for future clinical use of reovirus. However, little is known about how reovirus infection affects the tumor microenvironment and immune response towards infected tumor cells. Studies have shown that reovirus can directly stimulate natural killer (NK) cells, but how reovirus affects cellular ligands on tumor cells, which are ultimately key to tumor recognition and elimination by NK cells, has not been investigated. We tested how reovirus infection affects the binding of the NK Group-2 member D (NKG2D) receptor, which is a dominant mediator of NK cell anti-tumor activity. Using models of human-derived melanoma and glioblastoma tumors, we demonstrated that NKG2D ligands are downregulated in tumor cells post-reovirus-infection due to the impaired translation of these ligands in reovirus-infected cells. Moreover, we showed that downregulation of NKG2D ligands significantly impaired the binding of NKG2D to infected tumor cells. We further demonstrated that reduced recognition of NKG2D ligands significantly alters NK cell anti-tumor cytotoxicity in human primary NK cells and in the NK cell line NK-92. Thus, this study provides novel insights into reovirus-host interactions and could lead to the development of novel reovirus-based therapeutics that enhance the anti-tumor immune response.

Lenvatinib or anti-VEGF in combination with anti-PD-1 differentially augments antitumor activity in melanoma

Targeting tumor-associated blood vessels to increase immune infiltration may enhance treatment effectiveness, yet limited data exist regarding anti-angiogenesis effects on the tumor microenvironment (TME). We hypothesized that dual targeting of angiogenesis with immune checkpoints would improve both intracranial and extracranial disease. We used subcutaneous and left ventricle melanoma models to evaluate anti-PD-1/anti-VEGF and anti-PD-1/lenvatinib (pan-VEGFR inhibitor) combinations. Cytokine/chemokine profiling and flow cytometry were performed to assess signaling and immune-infiltrating populations. An in vitro blood-brain barrier (BBB) model was utilized to study intracranial treatment effects on endothelial integrity and leukocyte transmigration. Anti-PD-1 with either anti-VEGF or lenvatinib improved survival and decreased tumor growth in systemic melanoma murine models; treatment increased Th1 cytokine/chemokine signaling. Lenvatinib decreased tumor-associated macrophages but increased plasmacytoid DCs early in treatment; this effect was not evident with anti-VEGF. Both lenvatinib and anti-VEGF resulted in decreased intratumoral blood vessels. Although anti-VEGF promoted endothelial stabilization in an in vitro BBB model, while lenvatinib did not, both regimens enabled leukocyte transmigration. The combined targeting of PD-1 and VEGF or its receptors promotes enhanced melanoma antitumor activity, yet their effects on the TME are quite different. These studies provide insights into dual anti-PD-1 and anti-angiogenesis combinations.

Melanogenesis and the Targeted Therapy of Melanoma

Pigment production is a unique character of melanocytes. Numerous factors are linked with melanin production, including genetics, ultraviolet radiation (UVR) and inflammation. Understanding the mechanism of melanogenesis is crucial to identify new preventive and therapeutic strategies in the treatment of melanoma. Here, we reviewed the current available literatures on the mechanisms of melanogenesis, including the signaling pathways of UVR-induced pigment production, MC1R's central determinant roles and MITF as a master transcriptional regulator in melanogenesis. Moreover, we further highlighted the role of targeting BRAF, NRAS and MC1R in melanoma prevention and treatment. The combination therapeutics of immunotherapy and targeted kinase inhibitors are becoming the newest therapeutic option in advanced melanoma.

Clinical significance and immune landscape of KIR2DL4 and the senescence-based signature in cutaneous melanoma

Senescence is an effective barrier to tumor progression. Mutations that inhibit senescence and promote cell division are mandatory for the development of cancer. Therefore, it is particularly important to explore the differences between cutaneous melanoma (CM) patients with severe and mild degrees of senescence. We clustered all the patients with CM in the Cancer Genome Atlas (TCGA) database based on all the genes of the senescence pathway in the cellAge and MSigDB database. The prognosis, immunotherapy effect, tumor microenvironment score, NRAS mutation rate, expression of CD274, CTLA4, and PDCD1, and abundance of CD8+ T and NK cell infiltration in the younger group of patients (YG) were higher than those in the older group (OG). Compared with the American Joint Committee on Cancer (AJCC) stage, the risk scoring system stratified the risk of CM patients and guided immunotherapy more accurately. The nomogram model, which combined the AJCC stage and risk score, greatly improved the ability and accuracy of prognosis prediction. As KIR2DL4 is the core molecule in the risk scoring system (RSS), knocking down the KIR2DL4 of human NK cells in vitro can inhibit the cytotoxicity of NK cells and can also inhibit the secretion of tumor necrosis factor-α and interferon-γ by NK cells. In contrast, upregulation of KIR2DL4 can activate the MEK/ERK signaling pathway, which is the activation pathway of NK cells. OurRSS and nomogram model can accurately stratify the risk of CM patients and effectively predict the effect of immunotherapy and prognosis in CM patients.

Dihydroartemisinin regulates immune cell heterogeneity by triggering a cascade reaction of CDK and MAPK phosphorylation

Artemisinin (ART) and dihydroartemisinin (DHA), apart from their profound anti-malaria effect, can also beneficially modulate the host immune system; however, the underlying molecular mechanisms remain unclear. Here, we report that DHA selectively induced T-cell activation, with an increased proportion of Ki67⁺CD4⁺ T cells, CD25⁺CD4⁺ T cells, interferon (IFN)-γ-producing CD8⁺ T cells, Brdu⁺ CD8⁺ T cells and neutrophils, which was found to enhance cellular immunity to experimental malaria and overcome immunosuppression in mice. We further revealed that DHA upregulated the expression of cell proliferation-associated proteins by promoting the phosphorylation of mitogen-activated protein kinase (MAPK), cyclin-dependent kinases (CDKs), and activator protein 1 in the spleen. This study is the first to provide robust evidence that DHA selectively induced the expansion of subsets of splenic T cells through phosphorylated CDKs and MAPK to enhance cellular immune responses under non-pathological or pathological conditions. The data significantly deepened our knowledge in the mechanism underlying DHA-mediated immunomodulation.

Clinical Translation of Combined MAPK and Autophagy Inhibition in RAS Mutant Cancer

RAS (rat sarcoma virus) mutant cancers remain difficult to treat despite the advances in targeted therapy and immunotherapy. Targeted therapies against the components of mitogen-activated protein kinase (MAPK) pathways, including RAS, RAF, MEK, and ERK, have demonstrated activity in BRAF mutant and, in limited cases, RAS mutant cancer. RAS mutant cancers have been found to activate adaptive resistance mechanisms such as autophagy during MAPK inhibition. Here, we review the recent clinically relevant advances in the development of the MAPK pathway and autophagy inhibitors and focus on their application to RAS mutant cancers. We provide analysis of the preclinical rationale for combining the MAPK pathway and autophagy and highlight the most recent clinical trials that have been launched to capitalize on this potentially synthetic lethal approach to cancer therapy.

Duplications in the G3 domain or switch II region in HRAS identified in patients with Costello syndrome

Costello syndrome (CS) is an autosomal-dominant disorder characterized by distinctive facial features, hypertrophic cardiomyopathy, skeletal abnormalities, intellectual disability, and predisposition to cancers. Germline variants in HRAS have been identified in patients with CS. Intragenic HRAS duplications have been reported in three patients with a milder phenotype of CS. In this study, we identified two known HRAS variants, p.(Glu63_Asp69dup), p.(Glu62_Arg68dup), and one novel HRAS variant, p.(Ile55_Asp57dup), in patients with CS, including a patient with craniosynostosis. These intragenic duplications are located in the G3 domain and the switch II region. Cells expressing cDNA with these three intragenic duplications showed an increase in ELK-1 transactivation. Injection of wild-type or mutant HRAS mRNAs with intragenic duplications in zebrafish embryos showed significant elongation of the yolk at 11 h postfertilization, which was improved by MEK inhibitor treatment, and a variety of developmental abnormalities at 3 days post fertilization was observed. These results indicate that small in-frame duplications affecting the G3 domain and switch II region of HRAS increase the activation of the ERK pathway, resulting in developmental abnormalities in zebrafish or patients with CS.

Epidemiology of brain metastases and leptomeningeal disease

Brain metastases affect a significant percentage of patients with advanced extracranial malignancies. Yet, the incidence of brain metastases remains poorly described, largely due to limitations of population-based registries, a lack of mandated reporting of brain metastases to federal agencies, and historical difficulties with delineation of metastatic involvement of individual organs using claims data. However, in 2016, the Surveillance Epidemiology and End Results (SEER) program released data relating to the presence vs absence of brain metastases at diagnosis of oncologic disease. In 2020, studies demonstrating the viability of utilizing claims data for identifying the presence of brain metastases, date of diagnosis of intracranial involvement, and initial treatment approach for brain metastases were published, facilitating epidemiologic investigations of brain metastases on a population-based level. Accordingly, in this review, we discuss the incidence, clinical presentation, prognosis, and management patterns of patients with brain metastases. Leptomeningeal disease is also discussed. Considerations regarding individual tumor types that commonly metastasize to the brain are provided.

Unraveling the Wide Spectrum of Melanoma Biomarkers

The use of biomarkers in medicine has become essential in clinical practice in order to help with diagnosis, prognostication and prediction of treatment response. Since Alexander Breslow’s original report on “melanoma and prognostic values of thickness”, providing the first biomarker for melanoma, many promising new biomarkers have followed. These include serum markers, such as lactate dehydrogenase and S100 calcium-binding protein B. However, as our understanding of the DNA mutational profile progresses, new gene targets and proteins have been identified. These include point mutations, such as mutations of the BRAF gene and tumour suppressor gene tP53. At present, only a small number of the available biomarkers are being utilised, but this may soon change as more studies are published. The aim of this article is to provide a comprehensive review of melanoma biomarkers and their utility for current and, potentially, future clinical practice.

Reprogramming of bivalent chromatin states in NRAS mutant melanoma suggests PRC2 inhibition as a therapeutic strategy

The dynamic evolution of chromatin state patterns during metastasis, their relationship with bona fide genetic drivers, and their therapeutic vulnerabilities are not completely understood. Combinatorial chromatin state profiling of 46 melanoma samples reveals an association of NRAS mutants with bivalent histone H3 lysine 27 trimethylation (H3K27me3) and Polycomb repressive complex 2. Reprogramming of bivalent domains during metastasis occurs on master transcription factors of a mesenchymal phenotype, including ZEB1, TWIST1, and CDH1. Resolution of bivalency using pharmacological inhibition of EZH2 decreases invasive capacity of melanoma cells and markedly reduces tumor burden in vivo, specifically in NRAS mutants. Coincident with bivalent reprogramming, the increased expression of pro-metastatic and melanocyte-specific cell-identity genes is associated with exceptionally wide H3K4me3 domains, suggesting a role for this epigenetic element. Overall, we demonstrate that reprogramming of bivalent and broad domains represents key epigenetic alterations in metastatic melanoma and that EZH2 plus MEK inhibition may provide a promising therapeutic strategy for NRAS mutant melanoma patients.

Current Perspectives and Novel Strategies of NRAS-Mutant Melanoma

Melanoma is the deadliest cutaneous cancer. Activating mutations in NRAS are found in 20% of melanomas. NRAS-mutant melanoma is more aggressive and, therefore, has poorer outcomes, compared to non-NRAS-mutant melanoma. Despite promising preclinical data, to date immune checkpoint inhibitors remain the standard of care for locally advanced unresectable or metastatic NRAS melanoma. Data for efficacy of immunotherapy for NRAS melanoma mainly come from retrospective cohorts with divergent conclusions. MEK inhibitors have been the most developed targeted therapy approach. Although associated with an increase in progression-free survival, MEK inhibitors do not provide any benefit in terms of overall survival. Combination strategies with PI3K-AKT-mTOR pathway and CDK4/6 inhibitors seem to increase MEK inhibitors' benefit. Nevertheless, results from clinical trials are still prelaminar. A greater comprehension of the biology and intracellular interactions of NRAS-mutant melanoma will outline novel impactful strategies which could improve prognosis of these subgroup of patients.

NRAS mutant melanoma: Towards better therapies

Genetic alterations affecting RAS proteins are commonly found in human cancers. Roughly a fourth of melanoma patients carry activating NRAS mutations, rendering this malignancy particularly challenging to treat. Although the development of targeted as well as immunotherapies led to a substantial improvement in the overall survival of non-NRAS^mut melanoma patients (e.g. BRAF^mut), patients with NRAS^mut melanomas have an overall poorer prognosis due to the high aggressiveness of RAS^mut tumors, lack of efficient targeted therapies or rapidly emerging resistance to existing treatments. Understanding how NRAS-driven melanomas develop therapy resistance by maintaining cell cycle progression and survival is crucial to develop more effective and specific treatments for this group of melanoma patients. In this review, we provide an updated summary of currently available therapeutic options for NRAS^mut melanoma patients with a focus on combined inhibition of MAPK signaling and CDK4/6-driven cell cycle progression and mechanisms of the inevitably developing resistance to these treatments. We conclude with an outlook on the most promising novel therapeutic approaches for melanoma patients with constitutively active NRAS. STATEMENT OF SIGNIFICANCE: An estimated 75000 patients are affected by NRAS^mut melanoma each year and these patients still have a shorter progression-free survival than BRAF^mut melanomas. Both intrinsic and acquired resistance occur in NRAS-driven melanomas once treated with single or combined targeted therapies involving MAPK and CDK4/6 inhibitors and/or checkpoint inhibiting immunotherapy. Oncolytic viruses, mRNA-based vaccinations, as well as targeted triple-agent therapy are promising alternatives, which could soon contribute to improved progression-free survival of the NRAS^mut melanoma patient group.

Melanoma brain metastases in Ireland: surgical and systemic considerations

BACKGROUND

Cerebral metastases is a common complication in patients with melanoma. There is a paucity of information in the Republic of Ireland regarding the factors associated with melanoma brain metastases (MBM).

METHODS

Patients diagnosed with melanoma brain metastases in Ireland were retrospectively identified in Beaumont Hospital between 1999 and 2018. Patient demographics; age at diagnosis of primary melanoma, age at detection of MBM, year of detection of MBM, anatomical location of primary melanoma, BRAF mutation analysis and the number of metastases were investigated. Follow-up data were also derived, including overall survival.

RESULTS

There has being a 158% increase in the incidence of primary melanoma from 1999 compared to 2016. Over the same time period 128 patients with melanoma brain metastases were diagnosed. There was a significant male predominance (n = 77/128; 60%; p < 0.0001). BRAF mutation and leptomeningeal disease were independent prognostic factors in our cohort with a median survival 8 months and 0.5 months, respectively.

CONCLUSIONS

Male predominance, leptomeningeal disease and BRAF mutation represent important considerations in this population group. The results of this study add to our knowledge concerning outcomes in melanoma brain metastases and may be useful in clinical planning and future treatments.

Exploring Dysregulated Signaling Pathways in Cancer

Cancer cell biology takes advantage of identifying diverse cellular signaling pathways that are disrupted in cancer. Signaling pathways are an important means of communication from the exterior of cell to intracellular mediators, as well as intracellular interactions that govern diverse cellular processes. Oncogenic mutations or abnormal expression of signaling components disrupt the regulatory networks that govern cell function, thus enabling tumor cells to undergo dysregulated mitogenesis, to resist apoptosis, and to promote invasion to neighboring tissues. Unraveling of dysregulated signaling pathways may advance the understanding of tumor pathophysiology and lead to the improvement of targeted tumor therapy. In this review article, different signaling pathways and how their dysregulation contributes to the development of tumors have been discussed.

Baicalein and Baicalin Promote Melanoma Apoptosis and Senescence via Metabolic Inhibition

Malignant melanoma is one of the most common and dangerous skin cancers with a high rate of death every year. Furthermore, N-RAS and B-RAF mutations in melanoma cells increase the difficulties for clinical treatment in patients. Therefore, development of effective and universal drugs against melanoma is urgently needed. Here we demonstrate that baicalein and baicalin, the active components of the Chinese traditional medicinal plant Scutellaria baicalensis Georgi, can significantly inhibit melanoma cell growth and proliferation, suppress tumor cell colony formation and migration, as well as induce apoptosis and senescence in melanoma cells. The anti-tumor effects mediated by baicalein and baicalin are independent of N-RAS and B-RAF mutation statuses in melanoma cells. Mechanistically, we identify that the suppression of baicalein and baicalin on melanoma cells is due to inhibition of tumor cell glucose uptake and metabolism by affecting the mTOR-HIF-1α signaling pathway. In addition, we demonstrated that baicalein and baicalin can suppress tumorigenesis and tumor growth in vivo in the melanoma model. These studies clearly indicate that baicalein and baicalin can control tumor growth and development metabolically and have great potential as novel and universal drugs for melanoma therapy.

Primary tumor characteristics and next-generation sequencing mutations as biomarkers for melanoma immunotherapy response

INTRODUCTION

Considerable advances in melanoma have been realized through immunotherapy. The principal aim was to determine whether primary tumor characteristics or next-generation sequencing (NGS) could serve as markers of immunotherapy response.

METHODS AND RESULTS

The study cohort consisted of 67 patients who received immunotherapy for recurrent or metastatic melanoma and for whom primary tumor biopsies and pathology reports were available. A subset of 59 patient tumors were profiled using an NGS panel of 50 cancer-related genes. Objective response rate to immunotherapy was assessed using RECIST v1.1 criteria. Progression-free survival (PFS) and overall survival (OS) were used as endpoints. Lymphovascular invasion (LVI) strongly correlated with an increased proportion of immunotherapy responders (p = .002). PFS interval (p = .003) and OS (p = .036) were significantly higher in patients with LVI. NRAS mutation was more strongly correlated with an increased proportion of immunotherapy responders (p =.050). PFS was significantly higher in patients with NRAS mutation (p = .042); no difference in OS (p = .111).

DISCUSSION

This analysis demonstrates an association between lymphovascular invasion and immunotherapy response. Additionally, NGS mutation analysis demonstrated a potential association between NRAS mutations and immunotherapy response.

The protein kinase MAP3K19 phosphorylates MAP2Ks and thereby activates ERK and JNK kinases and increases viability of KRAS-mutant lung cancer cells

Identifying additional mitogen-activated protein kinase (MAPK) pathway regulators is invaluable in aiding our understanding of the complex signaling networks that regulate cellular processes, including cell proliferation and survival. Here, using in vitro kinase assays and by expressing WT or kinase-dead MAPK kinase kinase 19 (MAP3K19) in the HEK293T cell line and assessing activation of the extracellular signal-regulated kinase (ERK) and JUN N-terminal kinase (JNK) signaling pathways, we defined MAP3K19 as a novel regulator of MAPK signaling. We also observed that overexpression of WT MAP3K19 activates both the ERK and JNK pathways in a panel of cancer cell lines. Furthermore, MAP3K19 sustained ERK pathway activation in the presence of inhibitors targeting the RAF proto-oncogene Ser/Thr protein kinase (RAF) and MAPK/ERK kinase, indicating that MAP3K19 activates ERK via a RAF-independent mechanism. Findings from in vitro and in-cell kinase assays demonstrate that MAP3K19 is a kinase that directly phosphorylates both MAPK/ERK kinase (MEK) and MAPK kinase 7 (MKK7). Results from an short-hairpin RNA screen indicated that MAP3K19 is essential for maintaining survival in KRAS-mutant cancers; therefore, we depleted or inhibited MAP3K19 in KRAS-mutant cancer cell lines and observed that this reduces viability and decreases ERK and JNK pathway activation. In summary, our results reveal that MAP3K19 directly activates the ERK and JNK cascades and highlight a role for this kinase in maintaining survival of KRAS-mutant lung cancer cells.

A genome-wide CRISPR screen identifies FBXO42 involvement in resistance toward MEK inhibition in NRAS-mutant melanoma

NRAS mutations are the most common alterations among RAS isoforms in cutaneous melanoma, with patients harboring these aggressive tumors having a poor prognosis and low survival rate. The main line of treatment for these patients is MAPK pathway‐targeted therapies, such as MEK inhibitors, but, unfortunately, the response to these inhibitors is variable due to tumor resistance. Identifying genetic modifiers involved in resistance toward MEK‐targeted therapy may assist in the development of new therapeutic strategies, enhancing treatment response and patient survival. Our whole‐genome CRISPR‐Cas9 knockout screen identified the target Kelch domain‐containing F‐Box protein 42 (FBXO42) as a factor involved in NRAS‐mutant melanoma‐acquired resistance to the MEK1/2 inhibitor trametinib. We further show that FBXO42, an E3 ubiquitin ligase, is involved in the TAK1 signaling pathway, possibly prompting an increase in active P38. In addition, we demonstrate that combining trametinib with the TAK1 inhibitor, takinib, is a far more efficient treatment than trametinib alone in NRAS‐mutant melanoma cells. Our findings thus show a new pathway involved in NRAS‐mutant melanoma resistance and provide new opportunities for novel therapeutic options.

Binimetinib, a novel MEK1/2 inhibitor, exerts anti-leukemic effects under inactive status of PI3Kinase/Akt pathway

A MEK1/2 inhibitor, binimetinib is promising as a therapeutic agent for malignant melanoma with N-RAS mutation. We examined in vitro effects of binimetinib on 10 human myeloid/lymphoid leukemia cell lines, and found that three of five cell lines with N-RAS mutation and one of five without N-RAS mutation were responsive to treatment with binimetinib. Binimetinib inhibited cell growth mainly by inducing G₁ arrest and this action mechanism was assisted by gene set enrichment analysis. To identify signaling pathways associated with binimetinib response, we examined the status of MAP kinase/ERK and PI3Kinase/Akt pathways. The basal levels of phosphorylated ERK and Akt varied between the cell lines, and the amounts of phosphorylated ERK and Akt appeared to be reciprocal of each other. Interestingly, most of the binimetinib-resistant cell lines revealed strong Akt phosphorylation compared with binimetinib-sensitive ones. The effect of binimetinib may not be predicted by the presence/absence of N-RAS mutation, but rather by Akt phosphorylation status. Moreover, combination of binimetinib with a PI3K/Akt inhibitor showed additive growth-suppressive effects. These results suggest that binimetinib shows potential anti-leukemic effects and the basal level of phosphorylated Akt might serve as a biomarker predictive of therapeutic effect.

Phosphoprotein patterns predict trametinib responsiveness and optimal trametinib sensitisation strategies in melanoma

Malignant melanoma is a highly aggressive form of skin cancer responsible for the majority of skin cancer-related deaths. Recent insight into the heterogeneous nature of melanoma suggests more personalised treatments may be necessary to overcome drug resistance and improve patient care. To this end, reliable molecular signatures that can accurately predict treatment responsiveness need to be identified. In this study, we applied multiplex phosphoproteomic profiling across a panel of 24 melanoma cell lines with different disease-relevant mutations, to predict responsiveness to MEK inhibitor trametinib. Supported by multivariate statistical analysis and multidimensional pattern recognition algorithms, the responsiveness of individual cell lines to trametinib could be predicted with high accuracy (83% correct predictions), independent of mutation status. We also successfully employed this approach to case specifically predict whether individual melanoma cell lines could be sensitised to trametinib. Our predictions identified that combining MEK inhibition with selective targeting of c-JUN and/or FAK, using siRNA-based depletion or pharmacological inhibitors, sensitised resistant cell lines and significantly enhanced treatment efficacy. Our study indicates that multiplex proteomic analyses coupled with pattern recognition approaches could assist in personalising trametinib-based treatment decisions in the future.

MAPK pathway inhibition induces MET and GAB1 levels, priming BRAF mutant melanoma for rescue by hepatocyte growth factor

Therapeutic resistance is a major obstacle to achieving durable clinical responses with targeted therapies, highlighting a need to elucidate the underlying mechanisms responsible for resistance and identify strategies to overcome this challenge. An emerging body of data implicates the tyrosine kinase MET in mediating resistance to BRAF inhibitors in BRAF^V600E mutant melanoma. In this study we observed a dominant role for the HGF/MET axis in mediating resistance to BRAF and MEK inhibitors in models of BRAF^V600E and NRAS mutant melanoma. In addition, we showed that MAPK pathway inhibition induced rapid increases in MET and GAB1 levels, providing novel mechanistic insight into how BRAF^V600E mutant melanoma is primed for HGF-mediated rescue. We also determined that tumor-derived HGF, not systemic HGF, may be required to convey resistance to BRAF inhibition in vivo and that resistance could be reversed following treatment with AMG 337, a selective MET inhibitor. In summary, these findings support the clinical evaluation of MET-directed targeted therapy to circumvent resistance to BRAF and MEK inhibitors in BRAF^V600E mutant melanoma. In addition, the induction of MET following treatment with BRAF and MEK inhibitors has the potential to serve as a predictive biomarker for identifying patients best suited for MET inhibitor combination therapy.

NRAS-mutant melanoma: current challenges and future prospect

Melanoma is one of the most common cutaneous cancers worldwide. Activating mutations in RAS oncogenes are found in a third of all human cancers and NRAS mutations are found in 15%–20% of melanomas. The NRAS-mutant subset of melanoma is more aggressive and associated with poorer outcomes, compared to non-NRAS-mutant melanoma. Although immune checkpoint inhibitors and targeted therapies for BRAF-mutant melanoma are transforming the treatment of metastatic melanoma, the ideal treatment for NRAS-mutant melanoma remains unknown. Despite promising preclinical data, current therapies for NRAS-mutant melanoma remain limited, showing a modest increase in progression-free survival but without any benefit in overall survival. Combining MEK inhibitors with agents inhibiting cell cycling and the PI3K–AKT pathway appears to provide additional benefit; in particular, a strategy of MEK inhibition and CDK4/6 inhibition is likely to be a viable treatment option in the future. Patients whose tumors had NRAS mutations had better response to immunotherapy and better outcomes than patients whose tumors had other genetic subtypes, suggesting that immune therapies – especially immune checkpoint inhibitors – may be particularly effective as treatment options for NRAS-mutant melanoma. Improved understanding of NRAS-mutant melanoma will be essential to develop new treatment strategies for this subset of patients with melanoma.

BRAF Inhibitors Amplify the Proapoptotic Activity of MEK Inhibitors by Inducing ER Stress in NRAS-Mutant Melanoma

Purpose: NRAS mutations in malignant melanoma are associated with aggressive disease requiring rapid antitumor intervention, but there is no approved targeted therapy for this subset of patients. In clinical trials, the MEK inhibitor (MEKi) binimetinib displayed modest antitumor activity, making combinations a requisite. In a previous study, the BRAF inhibitor (BRAFi) vemurafenib was shown to induce endoplasmic reticulum (ER) stress that together with inhibition of the RAF-MEK-ERK (MAPK) pathway amplified its proapoptotic activity in BRAF-mutant melanoma. The present study investigated whether this effect might extent to NRAS-mutant melanoma, in which MAPK activation would be expected.Experimental Design and Results: BRAFi increased pERK, but also significantly increased growth inhibition and apoptosis induced by the MEKi in monolayer, spheroids, organotypic, and patient-derived tissue slice cultures of NRAS-mutant melanoma. BRAFi such as encorafenib induced an ER stress response via the PERK pathway, as detected by phosphorylation of eIF2α and upregulation of the ER stress-related factors ATF4, CHOP, and NUPR1 and the proapoptotic protein PUMA. MEKi such as binimetinib induced the expression of the proapoptotic protein BIM and activation of the mitochondrial pathway of apoptosis, the latter of which was enhanced by combination with encorafenib. The increased apoptotic rates caused by the combination treatment were significantly reduced through siRNA knockdown of ATF4 and BIM, confirming its critical roles in this process.Conclusions: The data presented herein encourage further advanced in vivo and clinical studies to evaluate MEKi in combination with ER stress inducing BRAFi as a strategy to treat rapidly progressing NRAS-mutant melanoma. Clin Cancer Res; 23(20); 6203-14. ©2017 AACR.

Immunoregulatory protein B7-H3 promotes growth and decreases sensitivity to therapy in metastatic melanoma cells

B7-H3 (CD276) belongs to the B7 family of immunoregulatory proteins and has been implicated in cancer progression and metastasis. In this study, we found that metastatic melanoma cells with knockdown expression of B7-H3 showed modest decrease in proliferation and glycolytic capacity and were more sensitive to dacarbazine (DTIC) chemotherapy and small-molecule inhibitors targeting MAP kinase (MAPK) and AKT/mTOR pathways: vemurafenib (PLX4032; BRAF inhibitor), binimetinib (MEK-162; MEK inhibitor), everolimus (RAD001; mTOR inhibitor), and triciribidine (API-2; AKT inhibitor). Similar effects were observed in melanoma cells in the presence of an inhibitory B7-H3 monoclonal antibody, while the opposite was seen in B7-H3-overexpressing cells. Further, combining B7-H3 inhibition with small-molecule inhibitors resulted in significantly increased antiproliferative effect in melanoma cells, as well as in BRAF^V600E mutated cell lines derived from patient biopsies. Our findings indicate that targeting B7-H3 may be a novel alternative to improve current therapy of metastatic melanoma.

Variation of mutant allele frequency in NRAS Q61 mutated melanomas

BACKGROUND

Somatic mutations of BRAF or NRAS activating the MAP kinase cell signaling pathway are present in 70% of cutaneous melanomas. The mutant allele frequency of BRAF V600E (M%BRAF) was recently shown to be highly heterogeneous in melanomas. The present study focuses on the NRAS Q61 mutant allele frequency (M%NRAS).

METHODS

Retrospective quantitative analyze of 104 NRAS mutated melanomas was performed using pyrosequencing. Mechanisms of M%NRAS imbalance were studied by fluorescence in situ hybridization (FISH) and microsatellite analysis.

RESULTS

M%NRAS was increased in 27.9% of cases. FISH revealed that chromosome 1 instability was the predominant mechanism of M%NRAS increase, with chromosome 1 polysomy observed in 28.6% of cases and intra-tumor cellular heterogeneity with copy number variations of chromosome 1/NRAS in 23.8%. Acquired copy-neutral loss of heterozygosity (LOH) was less frequent (19%). However, most samples with high M%NRAS had only one copy of NRAS locus surrounding regions suggesting a WT allele loss. Clinical characteristics and survival of patients with either <60% or ≥60% of M%NRAS were not different.

CONCLUSION

As recently shown for M%BRAF, M%NRAS is highly heterogeneous. The clinical impacts of high M%NRAS should be investigated in a larger series of patients.

ERK inhibition sensitizes CZ415-induced anti-osteosarcoma activity in vitro and in vivo

mTOR is a valuable oncotarget for osteosarcoma. The anti-osteosarcoma activity by a novel mTOR kinase inhibitor, CZ415, was evaluated. We demonstrated that CZ415 potently inhibited survival and proliferation of known osteosarcoma cell lines (U2OS, MG-63 and SaOs2), and primary human osteosarcoma cells. Further, CZ415 provoked apoptosis and disrupted cell cycle progression in osteosarcoma cells. CZ415 treatment in osteosarcoma cells concurrently blocked mTORC1 and mTORC2 activation. Intriguingly, ERK-MAPK activation could be a major resistance factor of CZ415. ERK inhibition (by MEK162/U0126) or knockdown (by targeted ERK1/2 shRNAs) dramatically sensitized CZ415-induced osteosarcoma cell apoptosis. In vivo, CZ415 oral administration efficiently inhibited U2OS tumor growth in mice. Its activity was further potentiated with co-administration of MEK162. Collectively, we demonstrate that ERK inhibition sensitizes CZ415-induced anti-osteosarcoma activity in vitro and in vivo. CZ415 could be further tested as a promising anti-osteosarcoma agent, alone or in combination of ERK inhibition.

Can binimetinib, encorafenib and masitinib be more efficacious than currently available mutation-based targeted therapies for melanoma treatment?

INTRODUCTION

Historically, there were few effective and durable treatments for metastatic melanoma. Recently, mutation based targeted therapies have revolutionized treatment and outcomes for patients with metastatic melanoma. Specifically, inhibitors aimed at BRAF, NRAS, and C-KIT mutations are now commonly used in treatment for patients harboring the specific mutations. Areas covered: A brief review of current BRAF, NRAS, and C-KIT inhibitors provides background for a thorough review of newly developed agents namely binimetinib, a MEK inhibitor, encorafenib a BRAF inhibitor, and masitinib which inhibits C-KIT. Expert opinion: While the 3 novel agents reviewed here have potential for use in melanoma, optimal utilization will occur once a more personalized approach incorporating genomic, proteomic, and immunologic data guides therapeutic decisions.

Acyl protein thioesterase 1 and 2 (APT-1, APT-2) inhibitors palmostatin B, ML348 and ML349 have different effects on NRAS mutant melanoma cells

Oncogenic NRAS mutations are frequent in melanoma and lead to increased downstream signaling and uncontrolled cell proliferation. Since the direct inhibition of NRAS is not possible yet, modulators of NRAS posttranslational modifications have become an area of interest. Specifically, interfering with NRAS posttranslational palmitoylation/depalmitoylation cycle could disturb proper NRAS localization, and therefore decrease cell proliferation and downstream signaling. Here, we investigate the expression and function of NRAS depalmitoylating acyl protein thioesterases 1 and 2 (APT-1, APT-2) in a panel of NRAS mutant melanoma cells. First, we show that all melanoma cell lines examined express APT-1 and APT-2. Next, we show that siRNA mediated APT-1 and APT-2 knock down and that the specific APT-1 and -2 inhibitors ML348 and ML349 have no biologically significant effects in NRAS mutant melanoma cells. Finally, we test the dual APT-1 and APT-2 inhibitor palmostatin B and conclude that palmostatin B has effects on NRAS downstream signaling and cell viability in NRAS mutant melanoma cells, offering an interesting starting point for future studies.

Molecular characterization of a selected cohort of patients affected by pulmonary metastases of malignant melanoma: Hints from BRAF, NRAS and EGFR evaluation

Background

Melanoma is highly curable in early stages but holds devastating consequences in advanced phases with a median survival of 6–10 months. Lungs are a common metastasis target, but despite this, limited data are available on the molecular status of pulmonary lesions.

Materials and Methods

25 patients with surgically resected melanoma lung metastases were screened for BRAF, NRAS, CKIT and EGFR alterations. The results were correlated with time to lung metastasis (TLM), relapse-free survival after metastasectomy (RFS) and overall survival (OS).

Results

BRAF or NRAS were mutated in 52% and 20% of cases while CKIT was unaffected. Chromosome 7 polysomy was detected in 47% of cases with 17.5% showing EGFR amplification and concomitant BRAF mutation. NRAS mutated patients developed LM within 5 yrs from primary melanoma with larger lesions compared with BRAF (mean diameter 3.3 ± 2.2cm vs 1.9 ± 1.1cm, p = 0.2). NRAS was also associated with a shorter median RFS and OS after metastasectomy. Moreover, Cox regression analysis revealed that NRAS mutation was the only predictive factor of shorter survival from primary melanoma (p = 0.039, OR = 5.5 (1.1–27.6)).

Conclusions

Molecular characterization identifies advanced melanoma subgroups with distinct prognosis and therapeutic options. The presence of NRAS mutation was associated to a worse disease evolution.

Cutaneous Melanoma with Brain Metastasis: Report of 193 Patients with New Observations

BACKGROUND

Brain metastasis is a common endpoint in patients suffering from malignant melanoma. However, little is known about factors that predispose to brain metastases.

OBJECTIVE

We performed a retrospective clinical and pathological investigation of melanoma patients with brain metastases in order to better characterise this patient population.

METHODS

193 melanoma patients with brain metastasis histologically diagnosed between 1990 and 2015 at the University Hospital Zurich were retrospectively identified and further specified for sex, age at diagnosis and detection of brain metastasis, and localisation. In addition, data were extracted regarding the subtype of primary melanoma, Breslow tumour thickness, Clark Level, mutation status, extent of metastatic spread and history of a second melanoma.

RESULTS

We found a significant male predominance (n = 126/193; 65%; p < 0.001). Breslow tumour thickness showed a wide range from 0.2 to 12.0 mm (n = 99; median 2.3 mm). 14 of 101 melanomas (14%) were classified as T1, thereof 11 (79%) were found in men. In 32 of 193 patients (17%), the primary melanoma was unknown.

CONCLUSIONS

Of special interest in our series is the high incidence of male predominance (79%) in cases of thin metastasing melanoma (14%), implicating genetic or epigenetic (hormonal) gender differences underlying tumour progression. Additionally, the high percentage of unknown primary melanoma (17%), at least partly representing completely regressed melanomas, indicates the importance of immune surveillance in melanoma progression.

Recurrent NRAS mutations in pulmonary Langerhans cell histiocytosis

The mitogen-activated protein kinase (MAPK) pathway is constantly activated in Langerhans cell histiocytosis (LCH). Mutations of the downstream kinases BRAF and MAP2K1 mediate this activation in a subset of LCH lesions. In this study, we attempted to identify other mutations which may explain the MAPK activation in nonmutated BRAF and MAP2K1 LCH lesions.We analysed 26 pulmonary and 37 nonpulmonary LCH lesions for the presence of BRAF, MAP2K1, NRAS and KRAS mutations. Grossly normal lung tissue from 10 smoker patients was used as control. Patient spontaneous outcomes were concurrently assessed.BRAF(V600E) mutations were observed in 50% and 38% of the pulmonary and nonpulmonary LCH lesions, respectively. 40% of pulmonary LCH lesions harboured NRAS(Q61K) (/R) mutations, whereas no NRAS mutations were identified in nonpulmonary LCH biopsies or in lung tissue control. In seven out of 11 NRAS(Q61K) (/R)-mutated pulmonary LCH lesions, BRAF(V600) (E) mutations were also present. Separately genotyping each CD1a-positive area from the same pulmonary LCH lesion demonstrated that these concurrent BRAF and NRAS mutations were carried by different cell clones. NRAS(Q61K) (/R) mutations activated both the MAPK and AKT (protein kinase B) pathways. In the univariate analysis, the presence of concurrent BRAF(V600E) and NRAS(Q61K) (/R) mutations was significantly associated with patient outcome.These findings highlight the importance of NRAS genotyping of pulmonary LCH lesions because the use of BRAF inhibitors in this context may lead to paradoxical disease progression. These patients might benefit from MAPK kinase inhibitor-based treatments.

Targeting mutant NRAS signaling pathways in melanoma

Cutaneous melanoma is a devastating form of skin cancer and its incidence is increasing faster than any other preventable cancer in the United States. The mutant NRAS subset of melanoma is more aggressive and associated with poorer outcomes compared to non-NRAS mutant melanoma. The aggressive nature and complex molecular signaling conferred by this transformation has evaded clinically effective treatment options. This review examines the major downstream effectors of NRAS relevant in melanoma and the associated advances made in targeted therapies that focus on these effector pathways. We outline the history of MEK inhibition in mutant NRAS melanoma and recent advances with newer MEK inhibitors. Since MEK inhibitors will likely be optimized when combined with other targeted therapies, we focus on recently identified targets that can be used in combination with MEK inhibitors.

Comparison of the Conformations of KRAS Isoforms, K-Ras4A and K-Ras4B, Points to Similarities and Significant Differences

Human HRAS, KRAS, and NRAS genes encode four isoforms of Ras, a p21 GTPase. Mutations in KRAS account for the majority of RAS-driven cancers. The KRAS has two splice variants, K-Ras4A and K-Ras4B. Due to their reversible palmitoylation, K-Ras4A and N-Ras have bimodal signaling states. K-Ras4A and K-Ras4B differ in four catalytic domain residues (G151R/D153E/K165Q/H166Y) and in their disordered C-terminal hypervariable region (HVR). In K-Ras4A, the HVR is not as strongly positively charged as in K-Ras4B (+6e vs +9e). Here, we performed all-atom molecular dynamics simulations to elucidate isoform-specific differences between the two splice variants. We observe that the catalytic domain of GDP-bound K-Ras4A has a more exposed nucleotide binding pocket than K-Ras4B, and the dynamic fluctuations in switch I and II regions also differ; both factors may influence guanine-nucleotide exchange. We further observe that like K-Kas4B, full-length K-Ras4A exhibits nucleotide-dependent HVR fluctuations; however, these fluctuations differ between the GDP-bound forms of K-Ras4A and K-Ras4B. Unlike K-Ras4B where the HVR tends to cover the effector binding region, in K-Ras4A, autoinhibited states are unstable. With lesser charge, the K-Ras4A HVR collapses on itself, making it less available for binding the catalytic domain. Since the HVRs of N- and H-Ras are weakly charged (+1e and +2e, respectively), autoinhibition may be a unique feature of K-Ras4B.

Clinically relevant genes and regulatory pathways associated with NRASQ61 mutations in melanoma through an integrative genomics approach

Therapies such as BRAF inhibitors have become standard treatment for melanoma patients whose tumors harbor activating BRAFV600 mutations. However, analogous therapies for inhibiting NRAS mutant signaling have not yet been well established. In this study, we performed an integrative analysis of DNA methylation, gene expression, and microRNA expression data to identify potential regulatory pathways associated with the most common driver mutations in NRAS (Q61K/L/R) through comparison of NRASQ61-mutated melanomas with pan-negative melanomas. Surprisingly, we found dominant hypomethylation (98.03%) in NRASQ61-mutated melanomas. We identified 1,150 and 49 differentially expressed genes and microRNAs, respectively. Integrated functional analyses of alterations in all three data types revealed important signaling pathways associated with NRASQ61 mutations, such as the MAPK pathway, as well as other novel cellular processes, such as axon guidance. Further analysis of the relationship between DNA methylation and gene expression changes revealed 9 hypermethylated and down-regulated genes and 112 hypomethylated and up-regulated genes in NRASQ61 melanomas. Finally, we identified 52 downstream regulatory cascades of three hypomethylated and up-regulated genes (PDGFD, ZEB1, and THRB). Collectively, our observation of predominant gene hypomethylation in NRASQ61 melanomas and the identification of NRASQ61-linked pathways will be useful for the development of targeted therapies against melanomas harboring NRASQ61 mutations.

Demonstration of differential radiosensitivity based upon mutation profile in metastatic melanoma treated with stereotactic radiosurgery

BACKGROUND

Metastatic melanoma often involves the brain. Radiotherapy is an important treatment of melanoma brain metastases, although melanoma radiosensitivity is considered heterogeneous. Thus, identifying subsets with differential radiosensitivity is essential.

MATERIALS AND METHODS

Patients with metastatic melanoma were identified in a prospective stereotactic radiosurgery (SRS) database. Tumor were tested for alterations in B-RAF, N-RAS, and c-KIT. Standardized imaging following SRS was reviewed for recurrence. Differences in local and distant failure were determined using modified Cox proportional hazards models.

RESULTS

102 patients and 1,028 brain metastases were included. N-RAS mutated patients were significantly less likely to develop local recurrence after SRS than wild type patients (HR 0.17, 95% CI 0.04-0.72, p=0.017). B-RAF and c-KIT mutations were not associated with altered rates of local recurrence. Lower local recurrence rates for N-RAS mutated tumors persisted on multivariate analysis (HR 0.18, 95% CI 0.04-0.84p=0.029).

CONCLUSIONS

N-RAS mutation is associated with improved local control following SRS. Local recurrence is more common in wild type patients and those with B-RAF or c-KIT mutations. Further research is needed to validate these findings and integrate into practice.

Metastatic melanoma treatment: Combining old and new therapies

Metastatic melanoma is an aggressive form of cancer characterised by poor prognosis and a complex etiology. Until 2010, the treatment options for metastatic melanoma were very limited. Largely ineffective dacarbazine, temozolamide or fotemustine were the only agents in use for 35 years. In recent years, the development of molecularly targeted inhibitors in parallel with the development of checkpoint inhibition immunotherapies has rapidly improved the outcomes for metastatic melanoma patients. Despite these new therapies showing initial promise; resistance and poor duration of response have limited their effectiveness as monotherapies. Here we provide an overview of the history of melanoma treatment, as well as the current treatments in development. We also discuss the future of melanoma treatment as we go beyond monotherapies to a combinatorial approach. Combining older therapies with the new molecular and immunotherapies will be the most promising way forward for treatment of metastatic melanoma.

MEK1/2 Inhibitors: Molecular Activity and Resistance Mechanisms

Aberrant activation of the three-layered protein kinase cascade, Raf/MEK/ERK, is often detected in human cancer, which is mainly attributed to the oncogenic alterations of RAF, or its upstream activators RAS or cell surface receptor tyrosine kinases. Deregulated activity of the Raf/MEK/ERK pathway drives uncontrolled tumor cell proliferation and survival, thus providing a rational therapeutic target for the treatment of many cancers. While Raf, MEK1/2, and ERK1/2 are equally important targets for the design of therapeutic small molecular weight inhibitors, the effort to develop MEK1/2-specific inhibitors has been greatly successful. Particularly, MEK1/2 have been relatively advantageous for the design of highly selective adenosine triphosphate (ATP)-noncompetitive inhibitors. Indeed, a plethora of highly selective and potent MEK1/2 inhibitors are now available and many of those inhibitors have been evaluated for their therapeutic potential. Herein, we review different MEK1/2 inhibitors that have been studied for their inhibitory mechanisms and therapeutic potential in cancer. Some of the key structural features of MEK1/2 that are important for the efficacy of these inhibitors are also discussed. In addition, we discuss current challenges and future prospective in using these advanced MEK1/2 inhibitors for cancer therapy.

Vertical Targeting of AKT and mTOR as Well as Dual Targeting of AKT and MEK Signaling Is Synergistic in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common cancer, and the third most common cause of cancer related death worldwide. The multi-kinase inhibitor Sorafenib represents the only systemic treatment option until today, and results from clinical trials with allosteric mTOR inhibitors were sobering. Since the PI3K/AKT/mTOR and RAF/MEK/ERK signaling pathways are frequently upregulated in HCC, we have analyzed the effects of AKT inhibitor MK-2206, MEK inhibitor AZD6244 (ARRY 142886) and mTOR kinase inhibitor AZD8055, given as single drugs or in combination, on proliferation and apoptosis of three HCC cell lines in vitro. We show that all three inhibitor combinations synergistically inhibit proliferation of the three HCC cell lines, with the strongest synergistic effect observed after vertical inhibition of AKT and mTORC1/2. We demonstrate that AKT kinase activity is restored 24h after blockade of mTORC1/2 by increased phosphorylation of T308, providing a rationale for combined targeting of AKT and mTOR inhibition in HCC. Our data suggest that a combination of inhibitors targeting those respective pathways may be a viable approach for future application in patients with hepatocellular carcinoma.

Nevospheres from neurocutaneous melanocytosis cells show reduced viability when treated with specific inhibitors of NRAS signaling pathway

BACKGROUND

Neurocutaneous melanocytosis (NCM) is characterized by clonal nevomelanocytic proliferations in the CNS and skin. Given the scarcity of effective therapeutic targets, testing new drugs requires a reliable and reproducible in vitro cellular model of the disease.

METHODS

We generated nevomelanocytic spheroids in vitro from lesions of the spinal cord, brain, and skin from 4 NCM patients. Nevomelanocytic cells were grown as monolayers or spheroids and their growth characteristics were evaluated. Cultured cell identity was confirmed by demonstration of the same NRAS mutation found in the original lesions and by immunophenotyping. Nevomelanocytic spheroids were treated with inhibitors of specific mediators of the NRAS signaling pathway (vemurafenib, MEK162, GDC0941, and GSK2126458). Drug sensitivity and cell viability were assessed.

RESULTS

Cultured cells were growth-factor dependent, grew as spheroids on Geltrex matrix, and maintained their clonogenicity in vitro over passages. Skin-derived cells formed more colonies than CNS-derived cells. Inhibitors of specific mediators of the NRAS signaling pathway reduced viability of NRAS mutated cells. The highest effect was obtained with GSK2126458, showing a viability reduction below 50%.

CONCLUSIONS

NRAS mutated cells derived from clinical NCM samples are capable of continuous growth as spheroid colonies in vitro and retain their genetic identity. Drugs targeting the NRAS signaling pathway reduce in vitro viability of NCM cells. NCM lesional spheroids represent a new and reliable experimental model of NCM for use in drug testing and mechanistic studies.

The broad-spectrum receptor tyrosine kinase inhibitor dovitinib suppresses growth of BRAF-mutant melanoma cells in combination with other signaling pathway inhibitors

BRAF inhibitors have revolutionized treatment of mutant BRAF metastatic melanomas. However, resistance develops rapidly following BRAF inhibitor treatment. We have found that BRAF-mutant melanoma cell lines are more sensitive than wild-type BRAF cells to the small molecule tyrosine kinase inhibitor dovitinib. Sensitivity is associated with inhibition of a series of known dovitinib targets. Dovitinib in combination with several agents inhibits growth more effectively than either agent alone. These combinations inhibit BRAF-mutant melanoma and colorectal carcinoma cell lines, including cell lines with intrinsic or selected BRAF inhibitor resistance. Hence, combinations of dovitinib with second agents are potentially effective therapies for BRAF-mutant melanomas, regardless of their sensitivity to BRAF inhibitors.

Enhancing therapeutic efficacy of the MEK inhibitor, MEK162, by blocking autophagy or inhibiting PI3K/Akt signaling in human lung cancer cells

Human non-small cell lung cancer (NSCLC) displays activated MEK/ERK signaling due to a high frequency of K-Ras mutation and is thus a potential candidate for MEK-targeted therapy. The current study focuses on demonstrating the activity of MEK162 (binimetinib), a MEK inhibitor under clinical testing, against NSCLC and exploring possible mechanism-driven strategies to enhance its therapeutic efficacy. MEK162 inhibits the growth of human NSCLC cell lines with varied potencies through induction of G1 cell cycle arrest and apoptosis. Moreover, it induces autophagy and accordingly the combination of MEK162 with the autophagy inhibitor, chloroquine, synergistically inhibits the growth of NSCLC cells and enhances apoptosis. MEK162 activates Akt signaling while effectively inhibiting MEK/ERK signaling. Accordingly, the combination of MEK162 and BKM120 (buparlisib), a pan-PI3K inhibitor, abrogates induced Akt activation and significantly augments therapeutic efficacy against the growth of NSCLC cells both in vitro and in vivo. Hence our findings warrant further evaluation of these rational combinations in the clinic.