Genetic Layout of Melanoma Lesions Is Associated with BRAF/MEK-Targeted Therapy Resistance and Transcriptional Profiles.

The genetic landscape of melanoma resistance to targeted therapy with small molecules inhibiting BRAF and MEK kinases is still largely undefined. In this study, we portrayed in detail the somatic alterations of resistant melanoma and explored the associated biological processes and their integration with transcriptional profiles. By targeted next-generation sequencing and whole-exome sequencing analyses, a list of 101 genes showing imbalance in metastatic tumors from patients with a complete/durable response or disease progression during therapy with vemurafenib or with dabrafenib and trametinib was defined. Classification of altered genes in functional categories indicated that the mutational pattern of both resistant tumors and melanoma cell lines was enriched in gene families involved in oncogenic signaling pathways and in DNA repair. Integration of genomic and transcriptomic features showed that the enrichment of mutations in gene sets associated with anabolic processes, chromatin alterations, and IFN-α response determined a significant positive modulation of the same gene signatures at the transcriptional level. In particular, MTORC1 signaling was enriched in tumors from poorly responsive patients and in resistant tumors excised from treated patients. Results indicate that genetic patterns are associated with melanoma resistance to targeted therapy and disclose the underlying key molecular pathways to define drug combinations for improved personalized therapies.

Induction of lymphocyte apoptosis by tumor cell secretion of FasL-bearing microvesicles.

The hypothesis that FasL expression by tumor cells may impair the in vivo efficacy of antitumor immune responses, through a mechanism known as 'Fas tumor counterattack,' has been recently questioned, becoming the object of an intense debate based on conflicting results. Here we definitely show that FasL is indeed detectable in the cytoplasm of melanoma cells and its expression is confined to multivesicular bodies that contain melanosomes. In these structures FasL colocalizes with both melanosomal (i.e., gp100) and lysosomal (i.e., CD63) antigens. Isolated melanosomes express FasL, as detected by Western blot and cytofluorimetry, and they can exert Fas-mediated apoptosis in Jurkat cells. We additionally show that melanosome-containing multivesicular bodies degranulate extracellularly and release FasL-bearing microvesicles, that coexpress both gp100 and CD63 and retain their functional activity in triggering Fas-dependent apoptosis of lymphoid cells. Hence our data provide evidence for a novel mechanism potentially operating in Fas tumor counterattack through the secretion of subcellular particles expressing functional FasL. Such vesicles may form a sort of front line hindering lymphocytes and other immunocompetent cells from entering neoplastic lesions and exert their antitumor activity.

PTPRK negatively regulates transcriptional activity of wild type and mutated oncogenic beta-catenin and affects membrane distribution of beta-catenin/E-cadherin complexes in cancer cells.

Previous reports showed that receptor-type protein-tyrosine phosphatase PTPRK co-localizes with beta-catenin at adherens junctions, and in vitro experiments suggested that beta-catenin could be substrate of PTPRK-mediated phosphatase activity. beta-catenin is a molecule endowed with a dual function being involved both in cell adhesion and in Wnt signaling pathway. Here we provide evidence for the role of PTPRK in negatively regulating the beta-catenin transcriptional activity by modulating its intracellular and membrane distribution. Expression of PTPRK protein in HEK293 cells and in PTPRK-null melanoma cell lines, one of which harbors a mutated oncogenic beta-catenin, impairs nuclear accumulation of wild type and oncogenic forms of beta-catenin, limits cytosolic levels of tyrosine-phosphorylated beta-catenin, and leads to re-localization of E-cadherin/beta-catenin complexes in ordered membrane phase along cell-cell contacts. This re-modulation of beta-catenin cellular distribution results in the inhibition of cyclin D1 and c-myc protein expression, whose genes are targets of beta-catenin. Tumor cells upon re-expression of PTPRK have a reduced proliferative and migration capacity. Moreover we show that PTPRK is also active in negatively regulating the transactivating function of beta-catenin in normal melanocytes as confirmed by experiments with silenced PTPRK by specific siRNA. Our data show that PTPRK influences transactivating activity of beta-catenin in non-tumoral and neoplastic cells by regulating the balance between signaling and adhesive beta-catenin, thus providing biochemical basis for the hypothesis of PTPRK as a tumor suppressor gene.

The apoptosis inhibitor protein survivin induces tumor-specific CD8+ and CD4+ T cells in colorectal cancer patients.

The identification of tumor-associated antigens expressed by colorectal carcinoma remains one of the major goals for designing novel immunological treatments for this tumor. By using a reverse-immunology approach, we show here that the inhibitor of apoptosis protein, survivin, is immunogenic in colorectal cancer patients. In particular, we found that survivin elicited CD8(+) T cell-mediated responses in peripheral blood or in tumor-associated lymphocytes from patients at different disease stage. Colorectal carcinoma cells were recognized by survivin-specific T lymphocytes, and the survivin-specific, class-I HLA-restricted T lymphocytes were fully activated and released interleukin-2 in response to HLA/survivin-peptide complexes expressed by tumor cells. In addition to CD8-mediated responses, survivin specifically stimulated CD4+ T-cell reactivity in peripheral blood lymphocytes from the same patients, thus suggesting that a complete activation of the immune system may occur in response to this antiapoptotic protein. These findings indicate that survivin could be considered a valuable tumor-associated antigen for immune-based clinical approaches in colorectal cancer.

microRNA Expression in Sentinel Nodes from Progressing Melanoma Patients Identifies Networks Associated with Dysfunctional Immune Response.

Sentinel node biopsy (SNB) is a main staging biomarker in melanoma and is the first lymph node to drain the tumor, thus representing the immunological site where anti-tumor immune dysfunction is established and where potential prognostic immune markers can be identified. Here we analyzed microRNA (miR) profiles in archival tumor-positive SNBs derived from melanoma patients with different outcomes and performed an integrated analysis of transcriptional data to identify deregulated immune signaling networks. Twenty-six miRs were differentially expressed in melanoma-positive SNB samples between patients with disease progression and non-progressing patients, the majority being previously reported in the regulation of immune responses. A significant variation in miR expression levels was confirmed in an independent set of SNB samples. Integrated information from genome-wide transcriptional profiles and in vitro assessment in immune cells led to the identification of miRs associated with the regulation of the TNF receptor superfamily member 8 (TNFRSF8) gene encoding the CD30 receptor, a marker increased in lymphocytes of melanoma patients with progressive disease. These findings indicate that miRs are involved in the regulation of pathways leading to immune dysfunction in the sentinel node and may provide valuable markers for developing prognostic molecular signatures for the identification of stage III melanoma patients at risk of recurrence.

Overcoming melanoma resistance to vemurafenib by targeting CCL2-induced miR-34a, miR-100 and miR-125b.

In melanoma, the adaptative cell response to BRAF inhibitors includes altered patterns of cytokine production contributing to tumor progression and drug resistance. Among the factors produced by PLX4032-resistant melanoma cell lines, CCL2 was higher compared to the sensitive parental cell lines and increased upon drug treatment. CCL2 acted as an autocrine growth factor for melanoma cells, stimulating the proliferation and resistance to apoptosis. In patients, CCL2 is detected in melanoma cells in tumors and in plasma at levels that correlate with tumor burden and lactate dehydrogenase. Vemurafenib treatment increased the CCL2 levels in plasma, whereas the long-term clinical response was associated with low CCL2 levels.Increased CCL2 production was associated with miRNA deregulation in the resistant cells. miR-34a, miR-100 and miR-125b showed high expression in both resistant cells and in tumor biopsies that were obtained from treated patients, and they were involved in the control of cell proliferation and apoptosis. Inhibition of CCL2 and of the selected miRNAs restored both the cell apoptosis and the drug efficacy in resistant melanoma cells. Therefore, CCL2 and miRNAs are potential prognostic factors and attractive targets for counteracting treatment resistance in metastatic melanoma.

Transcriptional profiling of melanoma sentinel nodes identify patients with poor outcome and reveal an association of CD30(+) T lymphocytes with progression.

Sentinel lymph nodes set the stance of the immune system to a localized tumor and are often the first site to be colonized by neoplastic cells that metastasize. To investigate how the presence of neoplastic cells in sentinel lymph nodes may trigger pathways associated with metastatic progression, we analyzed the transcriptional profiles of archival sentinel node biopsy specimens obtained from melanoma patients. Biopsies from positive nodes were selected for comparable tumor infiltration, presence or absence of further regional node metastases, and relapse at 5-year follow-up. Unsupervised analysis of gene expression profiles revealed immune response to be a major gene ontogeny represented. Among genes upregulated in patients with progressing disease, the TNF receptor family member CD30/TNFRSF8 was confirmed in biopsy specimens from an independent group of patients. Immunohistochemical analysis revealed higher numbers of CD30(+) lymphocytes in nodes from progressing patients compared with nonprogressing patients. Phenotypic profiling demonstrated that CD30(+) lymphocytes comprised a broad population of suppressive or exhausted immune cells, such as CD4(+)Foxp3(+) or PD1(+) subpopulations and CD4(-)CD8(-) T cells. CD30(+) T lymphocytes were increased in peripheral blood lymphocytes of melanoma patients at advanced disease stages. Our findings reinforce the concept that sentinel nodes act as pivotal sites for determining progression patterns, revealing that the presence of CD30(+) lymphocytes at those sites associate positively with melanoma progression.

Identification of MET and SRC activation in melanoma cell lines showing primary resistance to PLX4032.

PLX4032/vemurafenib is a first-in-class small-molecule BRAF(V600E) inhibitor with clinical activity in patients with BRAF mutant melanoma. Nevertheless, drug resistance develops in treated patients, and strategies to overcome primary and acquired resistance are required. To explore the molecular mechanisms involved in primary resistance to PLX4032, we investigated its effects on cell proliferation and signaling in a panel of 27 genetically characterized patient-derived melanoma cell lines. Cell sensitivity to PLX4032 was dependent on BRAF(V600E) and independent from other gene alterations that commonly occur in melanoma such as PTEN loss, BRAF, and MITF gene amplification. Two cell lines lacking sensitivity to PLX4032 and harboring a different set of genetic alterations were studied as models of primary resistance. Treatment with the MEK inhibitor UO126 but not with PLX4032 inhibited cell growth and ERK activation. Resistance to PLX4032 was maintained after CRAF down-regulation by siRNA indicating alternative activation of MEK-ERK signaling. Genetic characterization by multiplex ligation-dependent probe amplification and analysis of phosphotyrosine signaling by MALDI-TOF mass spectrometry analysis revealed the activation of MET and SRC signaling, associated with the amplification of MET and of CTNNB1 and CCND1 genes, respectively. The combination of PLX4032 with drugs or siRNA targeting MET was effective in inhibiting cell growth and reducing cell invasion and migration in melanoma cells with MET amplification; similar effects were observed after targeting SRC in the other cell line, indicating a role for MET and SRC signaling in primary resistance to PLX4032. Our results support the development of classification of melanoma in molecular subtypes for more effective therapies.

Heterogeneous phenotype of human melanoma cells with in vitro and in vivo features of tumor-initiating cells.

Melanospheres, the melanoma cells that grow as nonadherent colonies and that show in vitro self-renewing capacity and multipotency, were selected from melanoma specimens or from melanoma cell lines. Melanospheres were highly tumorigenic, and intradermal injections in severe combined immunodeficient (SCID) mice of as few as 100 cells generated tumors that maintained tumorigenic potential into subsequent recipients. Primary and serially transplanted xenografts recapitulated the phenotypic features of the original melanoma of the patient. Melanoma cells cultured in the presence of fetal calf serum (FCS) were also tumorigenic in SCID mice, although with lower efficiency; these xenografts showed a homogeneous phenotype for the expression of melanoma-associated markers, Melan-A/Mart-1, HMB45, and MITF, and contained cells with features of fully differentiated cells. Melanospheres were heterogeneous for the expression of stem cell markers and showed a significantly enhanced expression of the Nanog and Oct3/4 transcription factors when compared with adherent melanoma cells. No direct and unique correlation between any of the examined stem cell markers and in vivo tumorigenicity was found. Taken together, our data provide further evidence on the heterogeneous nature of human melanomas and show that melanospheres and their corresponding tumors, which are generated in vivo in immunocompromised mice, represent a model to investigate melanoma biology.

CCN3/nephroblastoma overexpressed matricellular protein regulates integrin expression, adhesion, and dissemination in melanoma.

CCN3/nephroblastoma overexpressed belongs to the CCN family of genes that encode secreted proteins associated with the extracellular matrix (ECM) and exert regulatory effects at the cellular level. Overexpression of CCN3 was shown in metastatic melanoma cells compared with cells of the primary tumor from the same patient. Analysis of short-term cultures from 50 primary and metastatic melanomas revealed a heterogeneous expression pattern of both the 46-kDa full-length cytoplasmic/secreted protein and the 32-kDa nuclear-truncated form. The different protein expression patterns were not associated with gene alterations or polymorphisms. Like the metastatic cells expressing high levels of the 46-kDa CCN3, cells transfected to overexpress CCN3 showed increased adhesion to ECM proteins, whereas inhibition of CCN3 expression by small interfering RNA decreased adhesion to laminin and vitronectin. CCN3 overexpression induced increased expression of laminin and vitronectin integrin receptors alpha 7 beta 1 and alpha v beta 5 by increasing their mRNA production. Moreover, CCN3 secreted by melanoma cells acted as an adhesion matrix protein for melanoma cells themselves. Analysis of CCN3 protein expression with respect to melanoma progression detected the protein in all visceral metastases tested and in most nodal metastases from relapsing patients but in only a few nodal metastases from nonrelapsing patients and cutaneous metastases. Consistently, xenotransplantation in immunodeficient mice showed a higher metastatic potential of melanoma cells overexpressing CCN3. Together, these data indicate a role for CCN3 in melanoma cell interaction with the ECM by regulating integrin expression, resulting in altered cell adhesion and leading melanoma progression to aggressive disease.

Identification of a mutated receptor-like protein tyrosine phosphatase kappa as a novel, class II HLA-restricted melanoma antigen.

Recent studies increasingly point to a pivotal role of CD4(+) T cells in human anti-tumor immune response. Here we show that lymphocytes purified from a tumor-infiltrated lymph node of a melanoma patient that had remained disease free for 10 years after surgical resection of a lymph node metastasis comprised oligoclonal class II HLA-restricted CD4(+) T cells recognizing the autologous tumor cells in vitro. In fact, the CD4(+) T cell clones isolated from these lymphocytes displayed a tumor-specific, cytotoxic activity in addition to a Th1-like cytokine profile. By a genetic approach, a peptide derived from a mutated receptor-like protein tyrosine phosphatase kappa was identified as a novel HLA-DR10-restricted epitope for all the melanoma-specific CD4(+) T cell clones. The immunogenic peptide was shown to contain the mutated residue that was crucial for T cell recognition and activation. Moreover, a systemic immunity against the mutated peptide was detectable in the patient's peripheral blood T lymphocytes obtained during the disease-free period of follow-up. These findings further support the relevance of CD4(+) T cells directed against mutated epitopes in tumor immunity and provide the rationale for a possible usage of mutated, tumor-specific Ags for immunotherapy of human cancer.