Melanoma biomarker expression in melanocytic tumor progression: a tissue microarray study

The Combination of Trametinib and Ganitumab is Effective in RAS-Mutated PAX-Fusion Negative Rhabdomyosarcoma Models

PURPOSE

PAX-fusion negative rhabdomyosarcoma (FN RMS) is driven by alterations in the RAS/MAP kinase pathway and is partially responsive to MEK inhibition. Overexpression of IGF1R and its ligands is also observed in FN RMS. Preclinical and clinical studies have suggested that IGF1R is itself an important target in FN RMS. Our previous studies revealed preclinical efficacy of the MEK1/2 inhibitor, trametinib, and an IGF1R inhibitor, BMS-754807, but this combination was not pursued clinically due to intolerability in preclinical murine models. Here, we sought to identify a combination of an MEK1/2 inhibitor and IGF1R inhibitor, which would be tolerated in murine models and effective in both cell line and patient-derived xenograft models of RAS-mutant FN RMS.

EXPERIMENTAL DESIGN

Using proliferation and apoptosis assays, we studied the factorial effects of trametinib and ganitumab (AMG 479), a mAb with specificity for human and murine IGF1R, in a panel of RAS-mutant FN RMS cell lines. The molecular mechanism of the observed synergy was determined using conventional and capillary immunoassays. The efficacy and tolerability of trametinib/ganitumab was assessed using a panel of RAS-mutated cell-line and patient-derived RMS xenograft models.

RESULTS

Treatment with trametinib and ganitumab resulted in synergistic cellular growth inhibition in all cell lines tested and inhibition of tumor growth in four of six models of RAS-mutant RMS. The combination had little effect on body weight and did not produce thrombocytopenia, neutropenia, or hyperinsulinemia in tumor-bearing SCID beige mice. Mechanistically, ganitumab treatment prevented the phosphorylation of AKT induced by MEK inhibition alone. Therapeutic response to the combination was observed in models without a mutation in the PI3K/PTEN axis.

CONCLUSIONS

We demonstrate that combined trametinib and ganitumab is effective in a genomically diverse panel of RAS-mutated FN RMS preclinical models. Our data also show that the trametinib/ganitumab combination likely has a favorable tolerability profile. These data support testing this combination in a phase I/II clinical trial for pediatric patients with relapsed or refractory RAS-mutated FN RMS.

Immunohistochemical expression of PAX8, PAX2, and cytokeratin in melanomas

BACKGROUND

Deviations from the classic melanocytic immunophenotype in melanoma can present a diagnostic challenge. PAX8 and PAX2 are common markers for renal or Müllerian differentiation. While most PAX8+ or PAX2+ carcinomas are seldom confused with melanoma, some cases may show a more ambiguous immunophenotype, especially when MiTF family altered renal cell carcinoma (MiTF-RCC) is in the differential diagnosis. Neither PAX8 nor PAX2 expression has been reported in melanoma to date. We aimed to better characterize PAX8, PAX2, and cytokeratin immunoreactivity in a large series of melanomas.

METHODS

Tissue microarrays consisting of 263 melanomas were immunostained for PAX8, PAX2, and cytokeratin and graded by an h-score.

RESULTS

PAX8 expression was seen in 7.9% of melanomas and was significantly associated with spindle cytomorphology. PAX2 was positive in one (0.4%) melanoma. Cytokeratin positivity was seen in three (1.2%) cases and was associated with metastases.

CONCLUSIONS

PAX8 is expressed in a subset of melanomas and may be strong/extensive. As PAX8 positivity does not exclude a diagnosis of melanoma, it should be used in conjunction with other immunohistochemical markers, such as cytokeratin and PAX2, when melanoma, MiTF-RCC, and other PAX8+ tumors are in the differential diagnosis.

New insights into the roles of antiapoptotic members of the Bcl-2 family in melanoma progression and therapy

Prosurvival and antiapoptotic B cell lymphoma-2 (Bcl-2) family proteins are often overexpressed in cutaneous melanoma, one of the most aggressive types of human cancer. They are also implicated in resistance to therapy and participate in melanoma progression by regulating various processes, including cell proliferation, migration, invasion, and crosstalk with the tumor microenvironment. In this review, we summarize recent findings related to prosurvival members of the Bcl-2 family beyond their canonical functions in the apoptotic pathway, mainly focusing on their potential roles as diagnostic and prognostic biomarkers in cutaneous melanoma. We also provide an overview of different approaches used to inhibit Bcl-2 proteins in preclinical and clinical studies, which are mainly based on the inhibition of protein expression or the disruption of their antiapoptotic functions.

An evaluation of encorafenib for the treatment of melanoma

Introduction: In the treatment of advanced BRAF-mutant melanoma, selective regulation of the MAPK pathway with BRAF and MEK inhibition has emerged as one of the mainstays of therapy.Areas covered: The authors present the current data on encorafenib as a compound, its pharmacokinetic and pharmacodynamics properties. This review includes current data on encorafenib therapy as a single agent as well as in combination with the MEK-inhibitor binimetinib and other systemic therapies.Expert opinion: BRAF inhibition with encorafenib exhibits substantial antitumor activity with less paradoxical MAPK pathway activation leading to treatment resistance. Combination therapy with MEK inhibitors improves response rate, progression-free survival, and overall survival in patients with BRAF-mutant metastatic melanoma compared to prior treatment regimens. Serious adverse events, including the development of cutaneous malignancies, are reported at lower rates with combination therapy, while less severe events such as pyrexia can be more common. Existing data is lacking for a recommendation of triplet therapy, although results from multiple ongoing trials are highly anticipated.

Transcriptional repression of the tyrosinase-related protein 2 gene by transforming growth factor-β and the Kruppel-like transcription factor GLI2

BACKGROUND

Tyrosinase-Related Protein 2 (TRP2) is an enzyme involved in melanogenesis, that also exerts proliferative, anti-apoptotic and immunogenic functions in melanoma cells. TRP2 transcription is regulated by the melanocytic master transcription factor MITF. GLI2, a transcription factor that acts downstream of Hedgehog signaling, is also a direct transcriptional target of the TGF-β/SMAD pathway that contributes to melanoma progression and exerts transcriptional antagonistic activities against MITF.

OBJECTIVES

To characterize the molecular events responsible for TGF-β and GLI2 repression of TRP2 expression.

METHODS

In silico promoter analysis, transient cell transfection experiments with 5'-end TRP2 promoter deletion constructs, chromatin immuno-precipitation, and site-directed promoter mutagenesis were used to dissect the molecular mechanisms of TRP2 gene regulation by TGF-β and GLI2.

RESULTS

We demonstrate that TGF-β and GLI2-specific TRP2 repression involves direct mechanisms that occur in addition to MITF downregulation by TGF-β and GLI2. We identify two functional GLI2 binding sites within the TRP2 promoter that are critical for TGF-β and GLI2 responsiveness, one of them overlapping a CREB binding site. GLI2 and CREB competing for the same cis-element is associated with opposite transcriptional outcome.

CONCLUSION

Our results further refine the understanding of how TGF-β and GLI2 control the phenotypic plasticity of melanoma cells. In particular, we identify critical GLI2-binding cis-elements within the TRP2 promoter region that allow for its transcriptional repression independently from MITF concomitant downregulation.

Loss of Phd2 cooperates with BRAFV600E to drive melanomagenesis

Prolyl hydroxylase domain protein 2 (PHD2) is a well-known master oxygen sensor. However, the role of PHD2 in tumor initiation remains controversial. We find that during the transition of human nevi to melanoma, the expression of PHD2 protein is significantly decreased and lower expression PHD2 in melanoma is associated with worse clinical outcome. Knockdown of PHD2 leads to elevated Akt phosphorylation in human melanocytes. Mice with conditional melanocyte-specific expression of Phd2^lox/lox (Tyr::CreER;Phd2^lox/lox) fail to develop pigmented lesions. However, deletion of Phd2 in combination with expression of BRaf^V600E in melanocytes (Tyr::CreER;Phd2^lox/lox;BRaf^CA) leads to the development of melanoma with 100% penetrance and frequent lymph node metastasis. Analysis of tumor tissues using reverse phase protein arrays demonstrates that Phd2 deletion activates the AKT-mTOR-S6 signaling axis in the recovered tumors. These data indicate that PHD2 is capable of suppressing tumor initiation largely mediated through inhibiting of the Akt-mTOR signaling pathway in the melanocyte lineage.

Prolyl hydroxylase domain protein 2 (PHD2) regulates cellular response to hypoxia. Here the authors show that PHD2 is downregulated in melanoma and that PHD2 depletion, in a mouse model, promotes the progression of benign melanocytic lesions into melanoma, via activation of the Akt/mTOR signaling cascade.

Loss of GCNT2/I-branched glycans enhances melanoma growth and survival

Cancer cells often display altered cell-surface glycans compared to their nontransformed counterparts. However, functional contributions of glycans to cancer initiation and progression remain poorly understood. Here, from expression-based analyses across cancer lineages, we found that melanomas exhibit significant transcriptional changes in glycosylation-related genes. This gene signature revealed that, compared to normal melanocytes, melanomas downregulate I-branching glycosyltransferase, GCNT2, leading to a loss of cell-surface I-branched glycans. We found that GCNT2 inversely correlated with clinical progression and that loss of GCNT2 increased melanoma xenograft growth, promoted colony formation, and enhanced cell survival. Conversely, overexpression of GCNT2 decreased melanoma xenograft growth, inhibited colony formation, and increased cell death. More focused analyses revealed reduced signaling responses of two representative glycoprotein families modified by GCNT2, insulin-like growth factor receptor and integrins. Overall, these studies reveal how subtle changes in glycan structure can regulate several malignancy-associated pathways and alter melanoma signaling, growth, and survival.

Mechanisms and prevention of UV-induced melanoma

Melanoma is the deadliest form of skin cancer and its incidence is rising, creating a costly and significant clinical problem. Exposure to ultraviolet (UV) radiation, namely UVA (315-400 nm) and UVB (280-315 nm), is a major risk factor for melanoma development. Cumulative UV radiation exposure from sunlight or tanning beds contributes to UV-induced DNA damage, oxidative stress, and inflammation in the skin. A number of factors, including hair color, skin type, genetic background, location, and history of tanning, determine the skin's response to UV radiation. In melanocytes, dysregulation of this UV radiation response can lead to melanoma. Given the complex origins of melanoma, it is difficult to develop curative therapies and universally effective preventative strategies. Here, we describe and discuss the mechanisms of UV-induced skin damage responsible for inducing melanomagenesis, and explore options for therapeutic and preventative interventions.

Ablation of CD44 induces glycolysis-to-oxidative phosphorylation transition via modulation of the c-Src–Akt–LKB1–AMPKα pathway

Cluster of differentiation 44 (CD44) is a transmembrane glycoprotein that has been identified as a cancer stem cell marker in various cancer cells. Although many studies have focused on CD44 as a cancer stem cell marker, its effect on cancer cell metabolism remains unclear. To investigate the role of CD44 on cancer cell metabolism, we established CD44 knock-down cells via retroviral delivery of shRNA against CD44 in human breast cancer cells. Silencing of CD44 decreased the glycolytic phenotype of cancer cells, affecting glucose uptake, ATP production, and lactate production. We also found that ablation of the CD44-induced lactate dehydrogenase (LDH) isoenzyme results in a shift to LDH1 due to LDHA down-regulation and LDHB up-regulation, implying the importance of LDH isoenzyme modulation on cancer metabolism. The expression of glycolysis-related proteins including hypoxia inducible factor-1α (HIF-1α) and LDHA was decreased by CD44 silencing. These effects were due to the up-regulation of liver kinase B1 (LKB1)/AMP-activated protein kinase (AMPK)α activity by reduction in c-Src and Akt activity in CD44 knock-down cells. Finally, induction of LKB1/AMPKα activity blocked the expression of HIF-1α and its target gene, LDHA. Inversely, LDHB expression was repressed by HIF-1α. Collectively, these results indicate that the CD44 silencing-induced metabolic shift is mediated by the regulation of c-Src/Akt/LKB1/AMPKα/HIF-1α signaling in human breast cancer cells.

Biomarkers in Melanoma: Lessons from Translational Medicine

The treatment landscape for advanced melanoma has been rapidly evolving. As new therapies become available, there is a need for better biomarkers to detect disease, guide patient selection, and monitor for response. The use of tumor genetics has been able to predict responses to targeted therapy in melanoma. However, the role of biomarkers in melanoma detection, monitoring, and immunotherapy has been less successful and is still being defined. Translational studies in many areas of melanoma are being performed to identify biomarkers and validate their clinical role. In this review, we examine the status of biomarkers in melanoma and areas of future development.

Microsomal PGE2 synthase-1 regulates melanoma cell survival and associates with melanoma disease progression

COX-2 and its product PGE2 enhance carcinogenesis and tumor progression, which has been previously reported in melanoma. As most COX inhibitors cause much toxicity, the downstream microsomal PGE2 synthase-1 (mPGES1) is a consideration for targeting. Human melanoma TMAs were employed for testing mPGES1 protein staining intensity and percentage levels, and both increased with clinical stage; employing a different Stage III TMA, mPGES1 intensity (not percentage) associated with reduced patient survival. Our results further show that iNOS was also highly expressed in melanoma tissues with high mPGES1 levels, and iNOS-mediated NO promoted mPGES1 expression and PGE2 production. An mPGES1-specific inhibitor (CAY10526) as well as siRNA attenuated cell survival and increased apoptosis. CAY10526 significantly suppressed tumor growth and increased apoptosis in melanoma xenografts. Our findings support the value of a prognostic and predictive role for mPGES1, and suggest targeting this molecule in the PGE2 pathway as another avenue toward improving melanoma therapy.

Cell Surface CD74-MIF Interactions Drive Melanoma Survival in Response to Interferon-γ

Melanoma is believed to be a highly immunogenic tumor and recent developments in immunotherapies are promising. IFN-γ produced by immune cells has a crucial role in tumor immune surveillance; however, it has also been reported to be pro-tumorigenic. In the current study, we found that IFN-γ enhances the expression of CD74, which interacts with its ligand, macrophage migration inhibitory factor (MIF), and thereby activates the PI3K/AKT pathway in melanoma, promoting tumor survival. IFN-γ increased phosphorylation of AKT Ser473 and upregulated total cell surface expression of CD74 in human melanoma cell lines tested. CD74 was highly expressed in melanoma tissues. Moreover, the expression of CD74 on tumor cells correlated with plasma IFN-γ levels in melanoma patient samples. In our analysis of melanoma cell lines, all produced MIF constitutively. Blockade of CD74-MIF interaction reduced AKT phosphorylation and expression of pro-tumorigenic molecules, including IL-6, IL-8, and BCL-2. Inhibition of CD74-MIF interaction significantly suppressed tumor growth in the presence of IFN-γ in our xenograft mouse model. Thus, we conclude that IFN-γ promotes melanoma cell survival by regulating CD74-MIF signaling, suggesting that targeting the CD74-MIF interaction under IFN-γ-stimulatory conditions would be an effective therapeutic approach for melanoma.

The role of thioredoxin reductase 1 in melanoma metabolism and metastasis

Although significant progress has been made in targeted and immunologic therapeutics for melanoma, many tumors fail to respond, and most eventually progress when treated with the most efficacious targeted combination therapies thus far identified. Therefore, alternative approaches that exploit distinct melanoma phenotypes are necessary to develop new approaches for therapeutic intervention. Tissue microarrays containing human nevi and melanomas were used to evaluate levels of the antioxidant protein thioredoxin reductase 1 (TR1), which was found to increase as a function of disease progression. Melanoma cell lines revealed metabolic differences that correlated with TR1 levels. We used this new insight to design a model treatment strategy that creates a synthetic lethal interaction wherein targeting TR1 sensitizes melanoma to inhibition of glycolytic metabolism, resulting in a decrease in metastases in vivo. This approach holds the promise of a new clinical therapeutic strategy, distinct from oncoprotein inhibition.

A review of sentinel lymph node biopsy for thin melanoma

INTRODUCTION

Although there is a lack of established survival benefit of sentinel lymph node biopsy (SLNB), this technique has been increasingly applied in the staging of patients with thin (≤1.00 mm) melanoma (T1Nx), without clear supportive evidence.

METHODS

We review the guidelines and available literature on the indications and rationale for performing SLNB in thin melanoma.

RESULTS

As a consequence of the paucity of evidence of SLNB in thin melanoma, there is considerable variability in the guidelines. It is difficult to define clinicopathologic factors that reliably predict the presence of nodal metastasis. SLNB does not yet inform management in thin melanoma to improve survival outcome.

CONCLUSION

Based on available evidence, high risk patients with melanomas between 0.75 and 1.00 mm may be appropriate candidates to be considered for SLN biopsy after discussing the likelihood of finding evidence of nodal progression, the risks of sentinel node biopsy, and the lack of proven survival benefit from any form of surgical nodal staging.

Bench to bedside: mechanistic principles of targeting the RAF kinase in melanoma

Melanoma, in its advanced form, is an aggressive cancer with a poor prognosis. To date, no therapeutic modality has afforded a high likelihood of curative outcome, with the exception of early surgical resection in patients diagnosed with local disease. However, recent advances in our understanding of the molecular mechanisms and pathophysiology of melanoma have paved the way towards the development of targeted therapeutics. A central player in melanomagenesis is the RAF family of kinases. Key mechanistic details regarding the regulation of RAF kinases have now begun to emerge. Already, vemurafenib, a tailored kinase inhibitor of aberrant RAF function in melanoma, has led to clinical benefit. Despite vemurafenib's success, acquired resistance to the drug warrants the need for further drug development. In this review, we discuss the critical role of RAF dimerization in both melanomagenesis and resistance to RAF inhibitors such as vemurafenib. We also highlight the potential for inhibitors of RAF dimerization to lead to improved outcomes in patients with advanced melanoma.

Relationships between signaling pathway usage and sensitivity to a pathway inhibitor: examination of trametinib responses in cultured breast cancer lines

Cellular signaling pathways involving mTOR, PI3K and ERK have dominated recent studies of breast cancer biology, and inhibitors of these pathways have formed a focus of numerous clinical trials. We have chosen trametinib, a drug targeting MEK in the ERK pathway, to address two questions. Firstly, does inhibition of a signaling pathway, as measured by protein phosphorylation, predict the antiproliferative activity of trametinib? Secondly, do inhibitors of the mTOR and PI3K pathways synergize with trametinib in their effects on cell proliferation? A panel of 30 human breast cancer cell lines was chosen to include lines that could be classified according to whether they were ER and PR positive, HER2 over-expressing, and “triple negative”. Everolimus (targeting mTOR), NVP-BEZ235 and GSK2126458 (both targeting PI3K/mTOR) were chosen for combination experiments. Inhibition of cell proliferation was measured by IC₅₀ values and pathway utilization was measured by phosphorylation of signaling kinases. Overall, no correlation was found between trametinib IC₅₀ values and inhibition of ERK signaling. Inhibition of ERK phosphorylation was observed at trametinib concentrations not affecting proliferation, and sensitivity of cell proliferation to trametinib was found in cell lines with low ERK phosphorylation. Evidence was found for synergy between trametinib and either everolimus, NVP-BEZ235 or GSK2126458, but this was cell line specific. The results have implications for the clinical application of PI3K/mTOR and MEK inhibitors.

Neuropilin-2 gene expression correlates with malignant progression in cutaneous melanoma

BACKGROUND

It is currently not possible to predict the metastatic potential of early-stage melanoma lesions by histological examination alone; however, a significant number of thin melanomas will progress over time to advanced disease. Molecular biomarkers that could identify patients with melanoma at high risk at the time of original diagnosis would contribute significantly to improved patient outcomes and increased survival. Neuropilin-2 (NRP2), a cell surface receptor involved in tumour-associated angiogenesis and lymphangiogenesis, has recently been shown to be expressed in melanoma.

OBJECTIVES

To evaluate the potential value of NRP2 gene transcript levels as biomarkers for malignant melanoma progression.

METHODS

We measured NRP2 gene expression in a panel of formalin-fixed paraffin-embedded tissue specimens consisting of naevi, primary melanomas and metastatic melanomas using quantitative reverse transcriptase-polymerase chain reaction technique.

RESULTS

NRP2 levels are clearly segregated among the groups of naevi, primary and metastatic melanoma samples with a statistical trend towards increasing NRP2 gene expression correlating with disease progression. Logistic regression analysis reveals that the probability of malignant progression increases with elevated levels of NRP2 (odds ratio of 2·60 with confidence interval 1·29-5·21). Within the group of primary melanomas, there is a positive correlation (r = 0·823) between NRP2 expression and Breslow depth. This correlation was validated in an independent sample set of patients with melanoma.

CONCLUSIONS

This preliminary study strongly supports the significance of NRP2 as a useful biomarker for malignant progression of melanoma, which may be useful for early identification of patients with melanoma at high risk.

Identification of a ZEB2-MITF-ZEB1 transcriptional network that controls melanogenesis and melanoma progression

Deregulation of signaling pathways that control differentiation, expansion and migration of neural crest-derived melanoblasts during normal development contributes also to melanoma progression and metastasis. Although several epithelial-to-mesenchymal (EMT) transcription factors, such as zinc finger E-box binding protein 1 (ZEB1) and ZEB2, have been implicated in neural crest cell biology, little is known about their role in melanocyte homeostasis and melanoma. Here we show that mice lacking Zeb2 in the melanocyte lineage exhibit a melanoblast migration defect and, unexpectedly, a severe melanocyte differentiation defect. Loss of Zeb2 in the melanocyte lineage results in a downregulation of the Microphthalmia-associated transcription factor (Mitf) and melanocyte differentiation markers concomitant with an upregulation of Zeb1. We identify a transcriptional signaling network in which the EMT transcription factor ZEB2 regulates MITF levels to control melanocyte differentiation. Moreover, our data are also relevant for human melanomagenesis as loss of ZEB2 expression is associated with reduced patient survival.

Platelet-derived growth factor C and calpain-3 are modulators of human melanoma cell invasiveness

The molecular mechanisms responsible for the elevated metastatic potential of malignant melanoma are still not fully understood. In order to shed light on the molecules involved in the acquisition by melanoma of a highly aggressive phenotype, we compared the gene expression profiles of two cell clones derived from the human cutaneous metastatic melanoma cell line M14: a highly invasive clone (M14C2/MK18) and a clone (M14C2/C4) with low ability to invade the extracellular matrix (ECM). The highly invasive phenotype of M14C2/MK18 cells was correlated with overexpression of neuropilin-1, activation of a vascular endothelial growth factor (VEGF)-A/VEGFR-2 autocrine loop and secretion of matrix metalloprotease-2. Moreover, in an in vivo murine model, M14C2/MK18 cells displayed a higher growth rate as compared with M14C2/C4 cells, even though in vitro both clones possessed comparable proliferative potential. Microarray analysis in M14C2/MK18 cells showed a strong upregulation of platelet-derived growth factor (PDGF)-C, a cytokine that contributes to angiogenesis, and downregulation of calpain-3, a calcium-dependent thiol-protease that regulates specific signalling cascade components. Inhibition of PDGF-C with a specific antibody resulted in a significant decrease in ECM invasion by M14C2/MK18 cells, confirming the involvement of PDGF-C in melanoma cell invasiveness. Moreover, the PDGF-C transcript was found to be upregulated in a high percentage of human melanoma cell lines (17/20), whereas only low PDGF-C levels were detected in a few melanocytic cultures (2/6). By contrast, inhibition of calpain-3 activity in M14C2/C4 control cells, using a specific chemical inhibitor, markedly increased ECM invasion, strongly suggesting that downregulation of calpain-3 plays a role in the acquisition of a highly invasive phenotype. The results indicate that PDGF-C upregulation and calpain-3 downregulation are involved in the aggressiveness of malignant melanoma and suggest that modulators of these proteins or their downstream effectors may synergise with VEGF‑A therapies in combating tumour-associated angiogenesis and melanoma spread.

Melanoma-associated leukoderma - immunology in black and white?

Melanoma is an 'immunogenic tumor', often highly infiltrated with lymphocytes, which are capable of inducing regression of the primary tumor. The commonly observed phenomenon of regression suggests substantial cross-talk between immune cells and transformed melanocytes. An immune response to melanocyte differentiation antigens common to transformed and normal melanocytes manifests clinically at distant sites as melanoma-associated vitiligo or halo nevi. Despite similar antigenic targets, the pathogenesis and prognosis differ between the different melanoma-associated leukodermas. Understanding immunologic cross-talk between melanocytes and the immune system will aid the development of approaches to combat melanoma.

Melanoma metastasis: new concepts and evolving paradigms

Melanoma progression is typically depicted as a linear and stepwise process in which metastasis occurs relatively late in disease progression. Significant evidence suggests that in a subset of melanomas, progression is much more complex and less linear in nature. Epidemiologic and experimental observations in melanoma metastasis are reviewed here and are incorporated into a comprehensive model for melanoma metastasis, which takes into account the varied natural history of melanoma formation and progression.

MERTK receptor tyrosine kinase is a therapeutic target in melanoma

Metastatic melanoma is one of the most aggressive forms of cutaneous cancers. Although recent therapeutic advances have prolonged patient survival, the prognosis remains dismal. C-MER proto-oncogene tyrosine kinase (MERTK) is a receptor tyrosine kinase with oncogenic properties that is often overexpressed or activated in various malignancies. Using both protein immunohistochemistry and microarray analyses, we demonstrate that MERTK expression correlates with disease progression. MERTK expression was highest in metastatic melanomas, followed by primary melanomas, while the lowest expression was observed in nevi. Additionally, over half of melanoma cell lines overexpressed MERTK compared with normal human melanocytes; however, overexpression did not correlate with mutations in BRAF or RAS. Stimulation of melanoma cells with the MERTK ligand GAS6 resulted in the activation of several downstream signaling pathways including MAPK/ERK, PI3K/AKT, and JAK/STAT. MERTK inhibition via shRNA reduced MERTK-mediated downstream signaling, reduced colony formation by up to 59%, and diminished tumor volume by 60% in a human melanoma murine xenograft model. Treatment of melanoma cells with UNC1062, a novel MERTK-selective small-molecule tyrosine kinase inhibitor, reduced activation of MERTK-mediated downstream signaling, induced apoptosis in culture, reduced colony formation in soft agar, and inhibited invasion of melanoma cells. This work establishes MERTK as a therapeutic target in melanoma and provides a rationale for the continued development of MERTK-targeted therapies.

HIF1α and HIF2α independently activate SRC to promote melanoma metastases

Malignant melanoma is characterized by a propensity for early lymphatic and hematogenous spread. The hypoxia-inducible factor (HIF) family of transcription factors is upregulated in melanoma by key oncogenic drivers. HIFs promote the activation of genes involved in cancer initiation, progression, and metastases. Hypoxia has been shown to enhance the invasiveness and metastatic potential of tumor cells by regulating the genes involved in the breakdown of the ECM as well as genes that control motility and adhesion of tumor cells. Using a Pten-deficient, Braf-mutant genetically engineered mouse model of melanoma, we demonstrated that inactivation of HIF1α or HIF2α abrogates metastasis without affecting primary tumor formation. HIF1α and HIF2α drive melanoma invasion and invadopodia formation through PDGFRα and focal adhesion kinase-mediated (FAK-mediated) activation of SRC and by coordinating ECM degradation via MT1-MMP and MMP2 expression. These results establish the importance of HIFs in melanoma progression and demonstrate that HIF1α and HIF2α activate independent transcriptional programs that promote metastasis by coordinately regulating cell invasion and ECM remodeling.

Tumor profiling using protein biomarker panels in malignant melanoma: application of tissue microarrays and beyond

Despite advances in our knowledge of the disease, malignant melanoma remains an unpredictable entity. The revolution in molecular biological techniques, such as DNA sequencing and gene-expression profiling, has uncovered many potential protein targets and biomarkers relevant to melanoma progression. Successful clinical application would be aided significantly by downstream proteomic validation of those candidate markers using a combination of immunohistochemistry and tissue microarrays. Yet, research in this context seems to lag behind the output of genomic data relating to melanoma. In this article, we look at the strengths and pitfalls of tissue microarrays in malignant melanoma. We will show how tissue microarrays have become a vital step in the transition from molecular techniques to useful clinical assays and interventions and look at likely future developments for advances in this field.

The TWEAK receptor Fn14 is a therapeutic target in melanoma: immunotoxins targeting Fn14 receptor for malignant melanoma treatment

Fn14, the cell surface receptor for TWEAK, is over-expressed in various human solid tumor types and can be a negative prognostic indicator. We detected Fn14 expression in ~60% of the melanoma cell lines we tested, including both B-Raf WT and B-Raf^V600E lines. Tumor tissue microarray analysis indicated that Fn14 expression was low in normal skin but elevated in 173/190 (92%) of primary melanoma specimens and in 86/150 (58%) of melanoma metastases tested. We generated both a chemical conjugate composed of the rGel toxin and the anti-Fn14 antibody ITEM-4 (designated ITEM4-rGel) and a humanized, dimeric single-chain antibody of ITEM-4 fused to rGel (designated hSGZ). Both ITEM4-rGel and hSGZ were highly cytotoxic to a panel of different melanoma cell lines. Mechanistic studies showed that both immunotoxins induced melanoma cell necrosis. Also, these immunotoxins could up-regulate the cellular expression of Fn14 and trigger cell signaling events similar to the Fn14 ligand TWEAK. Finally, treatment of mice bearing human melanoma MDA-MB-435 xenografts with either ITEM4-rGel or hSGZ showed significant tumor growth inhibition compared to controls. We conclude that Fn14 is a novel therapeutic target in melanoma and the hSGZ construct appears to warrant further development as a novel therapeutic agent against Fn14-positive melanoma.

Importance of glycolysis and oxidative phosphorylation in advanced melanoma

Serum lactate dehydrogenase (LDH) is a prognostic factor for patients with stage IV melanoma. To gain insights into the biology underlying this prognostic factor, we analyzed total serum LDH, serum LDH isoenzymes, and serum lactate in up to 49 patients with metastatic melanoma. Our data demonstrate that high serum LDH is associated with a significant increase in LDH isoenzymes 3 and 4, and a decrease in LDH isoenzymes 1 and 2. Since LDH isoenzymes play a role in both glycolysis and oxidative phosphorylation (OXPHOS), we subsequently determined using tissue microarray (TMA) analysis that the levels of proteins associated with mitochondrial function, lactate metabolism, and regulators of glycolysis were all elevated in advanced melanomas compared with nevic melanocytes. To investigate whether in advanced melanoma, the glycolysis and OXPHOS pathways might be linked, we determined expression of the monocarboxylate transporters (MCT) 1 and 4. Analysis of a nevus-to-melanoma progression TMA revealed that MCT4, and to a lesser extend MCT1, were elevated with progression to advanced melanoma. Further analysis of human melanoma specimens using the Seahorse XF24 extracellular flux analyzer indicated that metastatic melanoma tumors derived a large fraction of energy from OXPHOS. Taken together, these findings suggest that in stage IV melanomas with normal serum LDH, glycolysis and OXPHOS may provide metabolic symbiosis within the same tumor, whereas in stage IV melanomas with high serum LDH glycolysis is the principle source of energy.

The immune system--a hidden treasure for biomarker discovery in cutaneous melanoma

This chapter describes how skin immune system (SIS) is specifically involved in the development of cutaneous melanoma. Local immune surveillance is presented as a complex process that comprises markers to be monitored in disease's evolution and in therapy. The ranking of tissue or soluble immune markers in a future panel of diagnostic/prognostic panel are evaluated. Taking into account the difficulties of cutaneous melanoma patients' management, this chapter shows the immune surveillance at the skin level, the conditions that favor the tumor escape from the immunological arm, the immune pattern of skin melanoma with diagnostic/prognostic relevance, the circulatory immune markers, and, last but not least, how immune markers are used in immune-therapy monitoring. The chapter cannot be exhaustive but will give the reader a glimpse of the complex immune network that lies within tumor escape and where to search for immune-therapeutical targets in skin melanoma.

Conserved expression signatures between medaka and human pigment cell tumors

Aberrations in gene expression are a hallmark of cancer cells. Differential tumor-specific transcript levels of single genes or whole sets of genes may be critical for the neoplastic phenotype and important for therapeutic considerations or useful as biomarkers. As an approach to filter out such relevant expression differences from the plethora of changes noted in global expression profiling studies, we searched for changes of gene expression levels that are conserved. Transcriptomes from massive parallel sequencing of different types of melanoma from medaka were generated and compared to microarray datasets from zebrafish and human melanoma. This revealed molecular conservation at various levels between fish models and human tumors providing a useful strategy for identifying expression signatures strongly associated with disease phenotypes and uncovering new melanoma molecules.

Lack of correlation between immunohistochemical expression of CKIT and KIT mutations in atypical acral nevi

BACKGROUND

Given the correlation between KIT mutations and immunohistochemical expression of CKIT in acral melanoma, our aim was to confirm the utility of CKIT detection as a screening tool for KIT genotyping in atypical acral nevi and to ascertain the frequency of KIT mutations in the same.

DESIGN

Immunohistochemical staining for CKIT was performed and staining criteria were the following: negative = <10%, 1 = 11%-49%, and 2 = >50% of cells. Intensity grading was as follows: negative = 0, weak = 1, moderate = 2, and strong = 3. Genomic amplification was performed on KIT exons commonly mutated in acral melanomas (11, 13, and 17) from atypical acral nevi (23) ranging in severity from mild (9), moderate (10), and severe (4). The control group included acral nevi without atypia (19). For purposes of statistical analyses, cases with 11% or more staining of cells were compared with negative cases and cases with a staining intensity of 1 or higher were compared with the negatives.

RESULTS

Immunohistochemical analyses revealed the following: positive staining with an intensity 1 or more in 18 of 22 (82%) of cases with atypia (5 mild; 9 moderate and 4 severe) and in 13 of 17 (76%) nevi without atypia with no statistically significant differences between both groups. Genomic analyses of exon regions revealed no abnormalities in "hotspots" frequently associated with point mutations in acral melanomas.

CONCLUSIONS

Our findings indicate a lack of correlation between immunohistochemical expression of CKIT and KIT mutations in atypical acral nevi. Atypical acral nevi do not exhibit genetic alterations in KIT associated with acral melanomas.

Slug expression during melanoma progression

Slug (Snai2), a member of the Snail family of zinc finger transcription factors, plays a role in the epithelial-to-mesenchymal transformation (EMT) that occurs during melanocyte emigration from the neural crest. A role for Slug in the EMT-like loss of cell adhesion and increased cell motility exhibited during melanoma progression has also been proposed. Our immunohistochemical studies of melanoma arrays, however, revealed that Slug expression was actually higher in nevi than in primary or metastatic melanomas. Moreover, Slug expression in melanomas was not associated with decreased expression of E-cadherin, the canonical Slug target in EMT. Comparisons of endogenous Slug and E-cadherin expression in cultured normal human melanocytes and melanoma cell lines supported our immunohistochemical findings. Expression of exogenous Slug in melanocytes and melanoma cells in vitro, however, suppressed E-cadherin expression, enhanced N-cadherin expression, and stimulated cell migration and invasion. Interestingly, both in tumors and cultured cell lines, there was a clear relationship between expression of Slug and MITF, a transcription factor known to regulate Slug expression during development. Taken together, our findings suggest that Slug expression during melanomagenesis is highest early in the process and that persistent Slug expression is not required for melanoma progression. The precise role of Slug in melanomagenesis remains to be elucidated and may be related to its interactions with other drivers of EMT, such as Snail.

β-catenin signaling controls metastasis in Braf-activated Pten-deficient melanomas

Malignant melanoma is characterized by frequent metastasis, however, specific changes that regulate this process have not been clearly delineated. Although it is well known that Wnt signaling is frequently dysregulated in melanoma, the functional implications of this observation are unclear. By modulating β-catenin levels in a mouse model of melanoma that is based on melanocyte-specific Pten loss and Braf(V600E) mutation, we demonstrate that β-catenin is a central mediator of melanoma metastasis to the lymph nodes and lungs. In addition to altering metastasis, β-catenin levels control tumor differentiation and regulate both MAPK/Erk and PI3K/Akt signaling. Highly metastatic tumors with β-catenin stabilization are very similar to a subset of human melanomas. Together these findings establish Wnt signaling as a metastasis regulator in melanoma.

In melanoma, beta-catenin is a suppressor of invasion

Cell-type-specific signalling determines cell fate under physiological conditions, but it is increasingly apparent that also in cancer development the impact of any given oncogenic pathway on the individual cancer pathology is dependent on cell-lineage-specific molecular traits. For instance in colon and liver cancer canonical Wnt signalling produces increased cytoplasmic and nuclear localised beta-catenin, which correlates with invasion and poor prognosis. In contrast, in melanoma increased cytoplasmic and nuclear beta-catenin is currently emerging as a marker for good prognosis, and thus seems to have a different function compared with other cancer types; however, this function is unknown. We discovered that in contrast to its function in other cancers, in melanoma, beta-catenin blocks invasion. We demonstrate that this opposing role of nuclear beta-catenin in melanoma is mediated through MITF, a melanoma-specific protein that defines the lineage background of this cancer type. Downstream of beta-catenin MITF not only suppresses the Rho-GTPase-regulated cell morphology of invading melanoma cells, but also interferes with beta-catenin-induced expression of the essential collagenase MT1-MMP, thus affecting all aspects of an invasive phenotype. Importantly, overexpression of MITF in invasive colon cancer cells modifies beta-catenin-directed signalling and induces a 'melanoma phenotype'. In summary, the cell-type-specific presence of MITF in melanoma affects beta-catenin's pro-invasive properties otherwise active in colon or liver cancer. Thus our study reveals the general importance of considering cell-type-specific signalling for the accurate interpretation of tumour markers and ultimately for the design of rational therapies.

Constitutive aberrant endogenous interleukin-1 facilitates inflammation and growth in human melanoma

Interleukin (IL)-1-mediated inflammation is proposed to contribute to the development and progression of some cancers. IL-1 family member proteins are known to be expressed constitutively in many melanoma tumor cells, and we hypothesize that these support molecular pathways of inflammation and facilitate tumor growth. To investigate the expression of IL-1α and IL-1β in melanoma patients, and their association with disease progression, immunohistochemical staining was carried out on tissues from 170 patients including benign nevi, primary melanomas, and metastatic melanomas. IL-1β levels were low (or zero) in benign nevi and higher in primary and metastatic melanomas (P < 0.0001). IL-1α was expressed in about 73% of nevi and 55% of metastatic melanomas, with levels significantly higher in primary tumors (P < 0.0001); most (98%) primary melanoma samples were positive for IL-1α. In vitro studies with seven human melanoma cell lines showed that five cell lines expressed IL-1α and IL-1β proteins and mRNA. We identified for the first time several important downstream signaling pathways affected by endogenous IL-1, including reactive oxygen and nitrogen species, COX-2, and phosphorylated NF-κB inhibitor (IκB) and stress-activated protein kinase/c-jun-NH(2)-kinase; all of which were decreased by siRNA to IL-1s. Downregulation of IL-1α, IL-1β, or MyD88 substantially increased p21 and p53 levels. Treatment with IL-1 receptor type I neutralizing antibody or IL-1 pathway-specific siRNAs led to growth arrest in IL-1-positive melanoma cells. Furthermore, blocking the IL-1 pathway increased autophagy in IL-1-positive melanoma cells. These results indicate that the endogenous IL-1 system is functional in most human melanoma and interrupting its signaling inhibits the growth of IL-1-positive melanoma cells.

Glutamatergic pathway targeting in melanoma: single-agent and combinatorial therapies

PURPOSE

Melanoma is a heterogeneous disease where monotherapies are likely to fail due to variations in genomic signatures. B-RAF inhibitors have been clinically inadequate but response might be augmented with combination therapies targeting multiple signaling pathways. We investigate the preclinical efficacy of combining the multikinase inhibitor sorafenib or the mutated B-RAF inhibitor PLX4720 with riluzole, an inhibitor of glutamate release that antagonizes metabotropic glutamate receptor 1 (GRM1) signaling in melanoma cells.

EXPERIMENTAL DESIGN

Melanoma cell lines that express GRM1 and either wild-type B-RAF or mutated B-RAF were treated with riluzole, sorafenib, PLX4720, or the combination of riluzole either with sorafenib or with PLX4720. Extracellular glutamate levels were determined by glutamate release assays. MTT assays and cell-cycle analysis show effects of the compounds on proliferation, viability, and cell-cycle profiles. Western immunoblotting and immunohistochemical staining showed apoptotic markers. Consequences on mitogen-activated protein kinase pathway were assessed by Western immunoblotting. Xenograft tumor models were used to determine the efficacy of the compounds in vivo.

RESULTS

The combination of riluzole with sorafenib exhibited enhanced antitumor activities in GRM1-expressing melanoma cells harboring either wild-type or mutated B-RAF. The combination of riluzole with PLX4720 showed lessened efficacy compared with the combination of riluzole and sorafenib in suppressing the growth of GRM1-expressing cells harboring the B-RAF(V600E) mutation.

CONCLUSIONS

The combination of riluzole with sorafenib seems potent in suppressing tumor proliferation in vitro and in vivo in GRM1-expressing melanoma cells regardless of B-RAF genotype and may be a viable therapeutic clinical combination.

Gastrointestinal stromal tumor markers in cutaneous melanomas: relationship to prognostic factors and outcome

Melanoma expresses c-kit, a gastrointestinal stromal tumor marker, but has not been extensively evaluated for protein kinase C θ (PKCθ) or DOG1, and these stains have not been correlated with prognostic factors. We immunostained 62 primary cutaneous and 15 metastatic melanomas for polyclonal c-kit (pc-kit), monoclonal c-kit (mc-kit), PKCθ, and DOG1 and correlated results with prognostic parameters and survival. Of the cutaneous melanomas, 34 (55%) stained for pc-kit, 30 (48%) for mc-kit, 11 (18%) for PKCθ, and 2 (3%) for DOG1. The Breslow depth was 1.00 mm or less in 21 (68%) of 31 pc-kit+ cutaneous melanomas compared with 7 (27%) of 26 pc-kit- melanomas (P = .002). The pc-kit+ melanomas had less nodal disease (1/31 [3%] vs 9/25 [36%]; P = .001) and local recurrence (1/33 [3%] vs 6/27 [22%]; P = .021) but no statistically significant difference in the rate of distant metastases (13/32 [41%] vs 14/27 [52%]; P = .388) or survival (10/34 [29%] vs 16/39 [41%]; P = .301). We found that pc-kit correlates better with prognostic parameters than does mc-kit.

Inflammatory signaling compromises cell responses to interferon alpha

Interferon alpha (IFNα) is widely used for treatment of melanoma and certain other malignancies. This cytokine as well as the related IFNβ exerts potent anti-tumorigenic effects; however, their efficacy in patients is often suboptimal. Here, we report that inflammatory signaling impedes the effects of IFNα/β. Melanoma cells can secrete pro-inflammatory cytokines that inhibit cellular responses to IFNα/β via activating the ligand-independent pathway for the phosphorylation and subsequent ubiquitination and accelerated degradation of the IFNAR1 chain of type I IFN receptor. Catalytic activity of the p38 protein kinase was required for IFNAR1 downregulation and inhibition of IFNα/β signaling induced by proinflammatory cytokines such as interleukin 1 (IL-1). Activation of p38 kinase inversely correlated with protein levels of IFNAR1 in clinical melanoma specimens. Inhibition of p38 kinase augmented the inhibitory effects of IFNα/β on cell viability and growth in vitro and in vivo. The roles of inflammation and p38 protein kinase in regulating cellular responses to IFNα/β in normal and tumor cells are discussed.

Biology and clinical relevance of the micropthalmia family of transcription factors in human cancer

Members of the micropthalmia (MiT) family of transcription factors (MITF, TFE3, TFEB, and TFEC) are physiologic regulators of cell growth, differentiation, and survival in several tissue types. Because their dysregulation can lead to melanoma, renal cell carcinoma, and some sarcomas, understanding why these genes are co-opted in carcinogenesis may be of general utility. Here we describe the structure of the MiT family of proteins, the ways in which they are aberrantly activated, and the molecular mechanisms by which they promote oncogenesis. We discuss how meaningful understanding of these mechanisms can be used to elucidate the oncogenic process. Because the expression of these proteins is essential for initiating and maintaining the oncogenic state in some cancer types, we propose ways that they can be exploited to prevent, diagnose, and rationally treat these malignancies.

Melanoma pathology: important issues for clinicians involved in the multidisciplinary care of melanoma patients

Histologic analysis remains the gold standard for diagnosis of melanoma. The pathology report should document those histologic features important for guiding patient management, including those characteristics on which the diagnosis was based and also prognostic factors. Pathologic examination of sentinel lymph nodes provides very important prognostic information. New techniques, such as comparative genomic hybridization and fluorescence in situ hybridization are currently being studied to determine their usefulness in the diagnosis of melanocytic lesions. Recent molecular studies have opened new avenues for the treatment of patients with metastatic melanoma (ie, targeted therapies) and molecular pathology is likely to play an important role in the emerging area of personalized melanoma therapy.

Advances in melanoma senescence and potential clinical application

Normal cells possess a limited proliferative life span, after which they enter a state of irreversible growth arrest, called replicative senescence, which acts as a potent barrier against transformation. Transformed cells have escaped the process of replicative senescence and theoretically can not re-enter senescence. However, recent observations showed that transformed cells, and particularly the melanoma cells, can still undergo oncogene or stress-induced senescence. This senescence state is accompanied by many of the markers associated with replicative senescence, such as flattened shape, increased acidic β-galactosidase activity, characteristic changes in gene expression and growth arrest. Interestingly, in some cancers, senescence induction following chemotherapy has been correlated with a favorable patient outcome. In this review, we gathered recent results describing senescence-like phenotype induction in melanoma cells and discuss why senescence may also be exploited as a therapeutic strategy in melanoma.