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Resistance to current therapies still impacts a significant number of melanoma patients and can be regulated by epigenetic alterations. Analysis of global cytosine methylation in a cohort of primary melanomas revealed a pattern of early demethylation associated with overexpression of oncogenic transcripts. Loss of methylation and associated overexpression of the CSF 1 receptor (CSF1R) was seen in a majority of tumors and was driven by an alternative, endogenous viral promoter in a subset of samples. CSF1R was particularly elevated in melanomas with BRAF and other MAPK activating mutations. Furthermore, rebound ERK activation after BRAF inhibition was associated with RUNX1-mediated further upregulation of CSF-1R and its ligand IL-34. Importantly, increased CSF-1R and IL-34 overexpression were detected in an independent cohort of resistant melanomas. Inhibition of CSF-1R kinase or decreased CSF-1R expression by RNAi reduced 3-D growth and invasiveness of melanoma cells. Coinhibition of CSF-1R and BRAF resulted in synergistic efficacy in vivo. To our knowledge, our data unveil a previously unknown role for the autocrine-regulated CSF-1R in BRAF V600E resistance and provide a preclinical rationale for targeting this pathway in melanoma.

Epigenetic changes in cancer are thought to contribute to the regulation of invasion and metastasis. To study this at a genome-wide level in melanoma, we analyzed the methylome of 44 cases of malignant melanoma. We saw widespread demethylation occurring preferentially outside of CpG islands. Comparison of primary and metastatic lesions showed demethylation occurs early during carcinogenesis with few additional alterations in advanced tumors. The colony stimulating factor-1 receptor was aberrantly expressed and hypomethylated in nearly all cases. Its expression was validated by IHC and RNA-FISH on primary tumors and by qPCR, Western blotting and FACS in BRAF mutant and WT cell lines. CSF1R can be aberrantly expressed via an upstream LTR element in Hodgkin's lymphoma. After analyzing our patient samples and cell lines, we have found this aberrant transcript may be the dominant form in melanoma as well. Expression of one of its ligands IL34 was also shown in the cell lines by both ELISA and qPCR pointing to a potential autocrine regulatory loop. The effects of a small molecule inhibitor, PLX3397 as well as shRNA-mediated knockdown of the receptor were investigated in 2D and 3D cell culture. We saw inhibition of cell growth, smaller colony size, increased apoptosis and decreased invasiveness suggesting a functional role for CSF-1R in melanoma. Treatment of melanoma with BRAF-V600E inhibitors is effective for a time, but resistance invariably develops. The feedback activation of EGFR, BRAF amplification, BRAF splice variants and others are known to aid in the acquisition of resistance and the rebound activation of the MAPK-pathway. We are suggesting a role for CSF1R in this process. In Western experiments, the rebound of phospho-ERK after BRAF inhibitor treatment was accelerated with the addition of CSF1R ligands, or delayed with PLX3397, also attenuating AKT phosphorylation. Melanoma cells stably expressing shRNA against CSF1R recapitulated the effects of the inhibitor. Assaying the cells at different time points during a long-term V600E inhibitory experiment, we saw increasing levels of the transcription factor RUNX1, followed by increasing levels of IL34 and of the receptor, as well as its maturation, and presentation on the cell surface. shRNA-mediated knockdown of RUNX1 resulted in lower levels of the CSF1R and IL34 transcripts and delayed the rebound. Analysis of primary RNA-Seq data showed an increase in RUNX1, CSF1R and IL34 expression in resistant tumors. Co-inhibition of CSF1R and BRAF was also tested and resulted in synergistic blockade of cell growth in vitro and xenograft growth in vivo.The CSF1R inhibitor, PLX3397 is currently in clinical trials for glioblastoma, prostate, breast cancers and other cancers. These data present a preclinical rationale for its study in malignant melanoma. Citation Format: Orsolya Giricz, Yongkai Mo, Kimberly B. Dahlman, Xiomaris M. Cotto-Rios, Chiara Vardabasso, Hoa Nguyen, Bernice Matusow, Matthias Bartenstein, Veronika Polishchuck-Lee, Douglas B. Johnson, Tushar B. Bhagat, Rafe Shellooe, Elizabeth Burton, Gaston Habets, John M. Greally, Yiting Yu, Gideon Bollag, Paraic A. Kenny, Kith Pradhan, E. Richard Stanley, Emily Bernstein, Evripidis Gavathiotis, Brian L. West, Jeffrey A. Sosman, Amit Verma. Aberrant expression of CSF1R in melanoma is driven through an endogenous viral promoter and it contributes to malignant growth and BRAF-inhibitor resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2515.

MDS is characterized by ineffective hematopoiesis that leads to peripheral cytopenias. Development of effective treatments has been impeded by limited insight into pathogenic pathways governing dysplastic growth of hematopoietic progenitors. We demonstrate that smad2, a downstream mediator of transforming growth factor–β (TGF-β) receptor I kinase (TBRI) activation, is constitutively activated in MDS bone marrow (BM) precursors and is overexpressed in gene expression profiles of MDS CD34+ cells, providing direct evidence of overactivation of TGF-β pathway in this disease. Suppression of the TGF-β signaling by lentiviral shRNA-mediated down-regulation of TBRI leads to in vitro enhancement of hematopoiesis in MDS progenitors. Pharmacologic inhibition of TBRI (alk5) kinase by a small molecule inhibitor, SD-208, inhibits smad2 activation in hematopoietic progenitors, suppresses TGF-β–mediated gene activation in BM stromal cells, and reverses TGF-β–mediated cell-cycle arrest in BM CD34+ cells. Furthermore, SD-208 treatment alleviates anemia and stimulates hematopoiesis in vivo in a novel murine model of bone marrow failure generated by constitutive hepatic expression of TGF-β1. Moreover, in vitro pharmacologic inhibition of TBRI kinase leads to enhancement of hematopoiesis in varied morphologic MDS subtypes. These data directly implicate TGF-β signaling in the pathobiology of ineffective hematopoiesis and identify TBRI as a potential therapeutic target in low-risk MDS.

Epigenetic changes in cancer are thought to contribute to regulation of invasion and metastasis. To study this at a genome-wide level in melanoma we analyzed the methylome of 44 cases of malignant melanoma. We saw widespread demethylation in melanoma occurring preferentially outside of CpG islands. Comparison of primary and metastatic lesions showed demethylation occurs early during carcinogenesis with few additional alterations in advanced tumors. The colony stimulating factor-1 receptor was aberrantly expressed and hypomethylated in nearly all cases. The expression of CSF1R was validated by IHC on primary tumors and by qPCR and Western blotting in BRAF mutant and WT cell lines. CSF1R can be aberrantly expressed via an upstream LTR element in Hodgkin’s lymphoma. After analyzing our patient samples and the cell lines, we have found this aberrant transcript may be the dominant form in melanoma as well. Expression of one of its ligands IL34 was also shown in the cell lines by both ELISA and qPCR pointing to a potential autocrine regulatory loop. The effects of a small molecule inhibitor, PLX3397 as well as shRNA-mediated knockdown of the receptor were investigated in 2D and 3D cell culture. We saw inhibition of cell growth, smaller colony size, increased apoptosis and decreased invasiveness - suggesting a functional role for CSF1R in melanoma. Treatment of melanoma with small molecule inhibitors of BRAF V600E is effective for a time, but resistance invariably develops. The feedback activation of EGFR, BRAF amplification, BRAF splice variants and others are known to aid in the acquisition of resistance and the rebound activation of the MAPK-pathway. We are suggesting a role for CSF1R in this process. In Western experiments, the rebound of phospho-ERK after BRAF inhibitor treatment was accelerated with the addition of CSF1R ligands, or delayed with PLX3397, also attenuating AKT phosphorylation. Melanoma cells stably expressing shRNA against CSF1R recapitulated the effects of the inhibitor. Assaying the cells at different time points during a long-term V600E inhibitory experiment, we saw increasing levels of the transcription factor RUNX1, followed by increasing levels of IL34 and of the receptor, as well as its maturation, evidenced by the appearance of the high MW form. Utilizing shRNA-mediated knockdown of RUNX1 resulted in lower levels of the CSF1R and IL34 transcripts and delayed the rebound. Analysis of primary RNA-Seq data showed an increase in RUNX1, CSF1R and IL34 expression in resistant tumors. Co-inhibition of CSF1R and BRAF was also tested and resulted in synergistic blockade of cell growth in vitro and xenograft growth in vivo. The CSF1R inhibitor, PLX3397 is currently in clinical trials for glioblastoma, prostate, breast cancers and other cancers. These data present a preclinical rationale for its study in malignant melanoma. Citation Format: Orsolya Giricz, Yongkai Mo, Caroline Y. Hu, Yiting Yu, Kith Pradhan, Matthias Bartenstein, Nandini Ramachandra, Veronika Polishchuck, Kimberly B. Dahlman, Tushar Bhagat, Hoa Nguyen, Bernice Matusow, Rafe Shellooe, Elizabeth Burton, Paraic Kenny, John Greally, Jeffrey Sosman, Gideon Bollag, Brian West, Amit Verma. Aberrant expression of CSF1R in melanoma is driven through an endogenous viral promoter and it contributes to malignant growth and the acquisition of resistance against BRAF inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3332. doi:10.1158/1538-7445.AM2017-3332

Acute myeloid leukemia (AML) is characterized by disruption of HSC and progenitor cell differentiation. Frequently, AML is associated with mutations in genes encoding epigenetic modifiers. We hypothesized that analysis of alterations in DNA methylation patterns during healthy HSC commitment and differentiation would yield epigenetic signatures that could be used to identify stage-specific prognostic subgroups of AML. We performed a nano HpaII-tiny-fragment-enrichment-by-ligation-mediated-PCR (nanoHELP) assay to compare genome-wide cytosine methylation profiles between highly purified human long-term HSC, short-term HSC, common myeloid progenitors, and megakaryocyte-erythrocyte progenitors. We observed that the most striking epigenetic changes occurred during the commitment of short-term HSC to common myeloid progenitors and these alterations were predominantly characterized by loss of methylation. We developed a metric of the HSC commitment–associated methylation pattern that proved to be highly prognostic of overall survival in 3 independent large AML patient cohorts, regardless of patient treatment and epigenetic mutations. Application of the epigenetic signature metric for AML prognosis was superior to evaluation of commitment-based gene expression signatures. Together, our data define a stem cell commitment–associated methylome that is independently prognostic of poorer overall survival in AML.

Epigenetic changes in cancer are thought to contribute to regulation of invasion and metastasis. To study this at a genome-wide level in melanoma we analyzed the methylome of 44 cases of malignant melanoma with the HELP (HpaII tiny fragment enriched by LM-PCR) assay and compared it to melanocyte controls. We saw widespread demethylation in melanoma occurring preferentially outside of CpG islands. Comparison of primary and metastatic lesions demonstrated that demethylation occurs early during carcinogenesis with few additional alterations in advanced tumors. Parallel transcriptomic analysis revealed many known and novel oncogenic pathways aberrantly expressed and regulated by loss of DNA methylation. The colony stimulating factor-1 receptor (CSF1R) was aberrantly expressed and hypomethylated in nearly all cases. The expression of CSF1R was validated by immunohistochemistry on primary tumors and by Western blotting in BRAF V600E mutant and WT melanoma cell lines. Expression of its ligand IL34, but not of CSF1 was also shown in the melanoma cells by both ELISA and qPCR. The effects of a small molecule inhibitor, PLX3397 as well as shRNA-mediated knockdown of the receptor were investigated in traditional and 3D cell culture. We saw inhibition of cell growth, smaller colony size, increased apoptosis and decreased invasiveness - suggesting a functional role for CSF1R in melanoma. Treatment of melanoma with small molecule inhibitors of BRAF V600E is effective for a time, but resistance invariably develops. The feedback activation of EGFR, BRAF amplification, BRAF splice variants and others are known to aid in the acquisition of resistance and lead to rebound activation of the MAPK-pathway. In Western blotting experiments, the rebound of ERK phosphorylation after BRAF inhibitor treatment was accelerated with the addition of the CSF1R ligands CSF1 and IL34, or delayed with PLX3397, also attenuating AKT phosphorylation. Melanoma cells stably expressing CSF1R shRNA recapitulated the effects of the inhibitor. Assaying the cells at different time points during a long-term V600E inhibitory experiment, we saw increasing levels of the transcription factor RUNX1, followed by increasing levels of IL34 and of the CSF1R protein, as well as its maturation, evidenced by the appearance of the high MW form. Utilizing shRNA-mediated knockdown of RUNX1 resulted in lower levels of the CSF1R and IL34 transcripts and delayed the rebound. Analysis of primary RNA-Seq data showed an increase in RUNX1, CSF1R and IL34 expression as resistance was acquired. Co-inhibition of CSF1R and BRAF was also tested and resulted in synergistic blockade of cell growth in vitro and xenograft growth in vivo. The CSF1R inhibitor, PLX3397, is in clinical trials for breast and other cancers, and these data present a preclinical rationale for its study in malignant melanoma. Citation Format: Orsolya Giricz, Yongkai Mo, Caroline H. Hu, Kimberly Dahlman, Nandini Ramachandra, Matthias Bartenstein, Kith Pradhan, Tushar Bhagat, Yiting Yu, Hoa Nguyen, Elizabeth Burton, Bernice Matusow, Gaston Habets, Rafe Shellooe, Gideon Bollag, Brian West, John Greally, Jeffrey Sosman, Paraic Kenny, Amit Verma. Integrated epigenomic profiling reveals widespread demethylation in melanoma and points to the role of CSF1R-RUNX1 axis in resistance against BRAF inhibition. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1885.

Even though mutations in epigenetic regulators frequently occur in myeloproliferative neoplasms, their effects on the epigenome have not been well studied. Furthermore, even though primary myelofibrosis (PMF) has a markedly worse prognosis than essential thrombocytosis or polycythemia vera, the molecular distinctions between these subgroups are not well elucidated. We conducted the HELP (HpaII tiny fragment enriched by LM-PCR) assay to study genome-wide methylation in polycythemia vera, essential thrombocytosis, and PMF samples compared with healthy controls. We determined that polycythemia vera and essential thrombocytosis are characterized by aberrant promoter hypermethylation, whereas PMF is an epigenetically distinct subgroup characterized by both aberrant hyper- and hypomethylation. Aberrant hypomethylation in PMF was seen to occur in non-CpG island loci, showing further qualitative differences between the disease subgroups. The differentially methylated genes in polycythemia vera and essential thrombocytosis were involved predominantly in cell signaling pathways and were enriched for binding sites of GATA1 and other transcription factors. In contrast, aberrantly methylated genes in PMF were involved in inflammatory pathways and were enriched for NF1, LEF1, and other transcription factors. Within the PMF subgroup, cases with ASXL1 disruptions formed an epigenetically distinct subgroup with relatively increased methylation. Cases of myeloproliferative neoplasms (MPN) with TET2 mutations showed decreased levels of hydroxymethylation and distinct set of hypermethylated genes. In contrast, the JAK2V617F mutation did not drive epigenetic clustering within MPNs. Finally, the significance of aberrant methylation was shown by sensitivity of MPN-derived cell lines to decitabine. These results show epigenetic differences between PMF and polycythemia vera/essential thrombocytosis and reveal methylomic signatures of ASXL1 and TET2 mutations. Cancer Res; 73(3); 1076–85. ©2012 AACR.

Myelodysplastic syndromes (MDS) are characterized by abnormal and dysplastic maturation of all blood lineages. Even though epigenetic alterations have been seen in MDS marrow progenitors, very little is known about the molecular alterations in dysplastic peripheral blood cells. We analyzed the methylome of MDS leukocytes by the HELP assay and determined that it was globally distinct from age-matched controls and was characterized by numerous novel, aberrant hypermethylated marks that were located mainly outside of CpG islands and preferentially affected GTPase regulators and other cancer-related pathways. Additionally, array comparative genomic hybridization revealed that novel as well as previously characterized deletions and amplifications could also be visualized in peripheral blood leukocytes, thus potentially reducing the need for bone marrow samples for future studies. Using integrative analysis, potentially pathogenic genes silenced by genetic deletions and aberrant hypermethylation in different patients were identified. DOCK4, a GTPase regulator located in the commonly deleted 7q31 region, was identified by this unbiased approach. Significant hypermethylation and reduced expression of DOCK4 in MDS bone marrow stem cells was observed in two large independent datasets, providing further validation of our findings. Finally, DOCK4 knockdown in primary marrow CD34(+) stem cells led to decreased erythroid colony formation and increased apoptosis, thus recapitulating the bone marrow failure seen in MDS. These findings reveal widespread novel epigenetic alterations in myelodysplastic leukocytes and implicate DOCK4 as a pathogenic gene located on the 7q chromosomal region.

The binding of all-trans retinoic acid (ATRA) to retinoid receptor-alpha (RAR-alpha) relieves transcriptional repression induced by the promyelocytic leukemia-retinoic acid receptor (PML-RAR) oncoprotein. The ATRA molecule contains a cyclohexenyl ring, a polyene chain containing conjugated double alkene bonds, and a terminal carboxyl group. To determine the contributions of these structural components of ATRA to its clinical efficacy, we synthesized three novel retinoids. These consisted of either a modified conjugated alkene backbone with an intact acid moiety (13a) or a modified conjugated alkene backbone and conversion of the acid group to either an ester (13b) or an aromatic amide (13c). Reporter assays demonstrated that compound 13a successfully relieved transcriptional repression by RAR-alpha, while 13b and 13c could not, demonstrating the critical role of the acid moiety in this binding. However, only ATRA was able to significantly inhibit the proliferation of APL cells while 13a, 13b, or 13c was not. Furthermore, only 13a led to partial non-significant differentiation of NB4 cells, demonstrating the importance of C9-C10 double bonds in differentiation induced CD11 expression. Our results demonstrate that both the acid moiety and conjugated double bonds present in the ATRA molecule are important for its biological activity in APL and have important implications for the design of future novel retinoids.

Malignant melanoma remains one of the most deadly human cancers with no effective cures for metastatic disease. The poor efficacy of current therapy in advanced melanoma highlights the need for better understanding of molecular mechanisms contributing to the disease. Recent work has shown that epigenetic changes, including aberrant DNA methylation, lead to alterations in gene expression and are as important in the development of malignant melanoma as the specific and well-characterized genetic events. Reversion of these methylation patterns could thus lead to a more targeted therapy and are currently under clinical investigation. The purpose of this review is to compile recent information on aberrant DNA methylation of melanoma, to highlight key genes and molecular pathways in melanoma development, which have been found to be epigenetically altered and to provide insight as to how DNA methylation might serve as targeted treatment option as well as a molecular and prognostic marker in malignant melanoma.

Epigenetic changes in cancer are thought to contribute to regulation of tumor invasion and metastasis, but this previously has not been studied at a genome wide level in melanoma. We analyzed the methylome of 44 cases of malignant melanoma with the HELP (HpaII tiny fragment enriched by LM-PCR) assay and compared it with healthy melanocyte controls. We observed widespread demethylation in malignant melanoma, preferentially outside of CpG islands. The epigenomic loss of methylation was independent of mutational status of BRAF, RAS and Kit. Comparison of primary and metastatic lesions demonstrated that demethylation occurs early during carcinogenesis with very few additional alterations in advanced tumors. Parallel transcriptomic analysis revealed many known and novel oncogenic pathways that were aberrantly expressed and regulated by loss of DNA methylation. Strikingly, the colony stimulating factor-1 receptor (CSF1R, c-fms) was aberrantly expressed and hypomethylated in nearly all cases. CSF1R is a transmembrane tyrosine kinase receptor that predominantly regulates macrophages, osteoclasts, and microglia, but is known to sometimes be aberrantly expressed by malignant cells in Hodgkins lymphoma. The expression of CSF1R on malignant melanocytes was validated by immunohistochemical analysis of primary tumors. In several melanoma cell lines (A2058, WM-266-4, SK-MEL-2, M14c#5) we found through PCR sequencing of the cDNA 5′ untranslated region that the CSF1R can be expressed through an aberrant promoter, as has been described for Hodgkin lymphoma. A custom Taqman assay was developed for this unique transcript, and then used to detect the transcript in 4 of 40 samples in a panel of melanoma biopsies, suggesting that aberrant CSF1R expression in melanoma is not uncommon. Expression of CSF1R protein in the cell lines was confirmed by FACS using anti-CD115 antibodies, and by Western blot using antibodies directed to the C-terminus. Expression of the ligand CSF-1 was also found in the melanoma cells by both ELISA and Taqman assays. Inhibition of in vitro cell growth by PLX3397, a clinically relevant small molecule inhibitor of CSF1R kinase, could be observed in 3D cell culture, indicating that under some conditions an autocrine stimulation of growth occurs. shRNA mediated knockdown of CSF1R also demonstrated decreased colony size and increased apoptosis in 3D culture conditions. The invasiveness of melanoma cells was decreased after treatment with PLX3397 or anti-CSF1 antibodies, suggesting a role for melanoma cancer cell expression of CSF1R in metastasis. Since three of cell lines possess an oncogenic BRAF mutation, co-inhibition of CSF1R and BRAF was tested and resulted in synergistic blockade of cell growth in vitro and A2058 xenograft growth in vivo. The CSF1R inhibitor, PLX3397, is under investigation in clinical trials for breast, glioma, and other cancers, and these data present a preclinical rationale for its study in malignant melanoma. This abstract is also being presented as Poster A06. Citation Format: Orsolya Giricz, Yongkai Mo, Caroline Hu, Kimberly Dahlman, Sanchari Bhattacharyya, Hoa Nguyen, Bernice Matusow, Tushar Bhagat, Yiting Yu, Rafe Shellooe, Elizabeth Burton, Gaston Habets, John Greally, Kenny Paraic, Jeffrey Sosman, Gideon Bollag, Brian West, Amit Verma. Integrated epigenomic profiling reveals widespread demethylation in melanoma and reveals CSF-1 Receptor as an aberrant regulator of malignant growth and invasion. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Melanoma: From Biology to Therapy; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(14 Suppl):Abstract nr PR06.

Epigenetic alterations can direct carcinogenesis by leading to transcriptional changes and inducing genomic instability. We analyzed the methylome of malignant melanoma and observed widespread loss of DNA methylation that was found to preferentially occur outside of CpG islands. Demethylation was seen to occur early during carcinogenesis, was independent of mutational status and correlated with genomic instability. Parallel transcriptomic analyses revealed that various immune and cancer associated pathways were overexpressed and were associated with promoter demethylation. The CSF1-receptor (CSF1R) was aberrantly overexpressed and hypomethylated in nearly all cases and was strikingly expressed via an aberrant upstream promoter in 10% of melanomas. shRNA mediated knockdown and inhibition of CSF1R kinase via a clinically relevant inhibitor, PLX3397, led to decreased 3D growth and invasiveness. Co-inhibition of CSF1R and BRAF resulted in synergistic blockade of BRAF-mutant melanoma xenograft growth. Thus, widespread epigenetic changes are seen in melanoma and CSF1R is a potential therapeutic target in this disease. Citation Format: Yongkai Mo, Orsolya Giricz, Caroline H. Hu, Kimberly B. Dahlman, Sanchari Bhattacharyya, Hoa Nguyen, Bernice Matusow, Tushar Bhagat, Rafe Shellooe, Elizabeth Burton, James Tsai, Chao Zhang, Gaston Habets, Yu Shyr, John Greally, Yiting Yu, Gideon E. Bollag, Richard Stanley, Jeffrey Trent, Paraic A. Kenny, Brian L. West, Jeffrey Sosman, Amit K. Verma. Integrated epigenomic profiling reveals widespread demethylation in melanoma and reveals CSF-1 receptor as an aberrant regulator of malignant growth and invasion. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4781. doi:10.1158/1538-7445.AM2014-4781

Epigenetic changes in cancer are thought to contribute to regulation of tumor invasion and metastasis, but this previously has not been studied at a genome wide level in melanoma. We analyzed the methylome of 44 cases of malignant melanoma with the HELP (HpaII tiny fragment enriched by LM-PCR) assay and compared it with healthy melanocyte controls. We observed widespread demethylation in malignant melanoma, preferentially outside of CpG islands. The epigenomic loss of methylation was independent of mutational status of BRAF, RAS and Kit. Comparison of primary and metastatic lesions demonstrated that demethylation occurs early during carcinogenesis with very few additional alterations in advanced tumors. Parallel transcriptomic analysis revealed many known and novel oncogenic pathways that were aberrantly expressed and regulated by loss of DNA methylation. Strikingly, the colony stimulating factor-1 receptor (CSF1R, c-fms) was aberrantly expressed and hypomethylated in nearly all cases. CSF1R is a transmembrane tyrosine kinase receptor that predominantly regulates macrophages, osteoclasts, and microglia, but is known to sometimes be aberrantly expressed by malignant cells in Hodgkins lymphoma. The expression of CSF1R on malignant melanocytes was validated by immunohistochemical analysis of primary tumors. In a melanoma cell line (A2058) we found through PCR sequencing of the cDNA 5' untranslated region that the CSF1R can be expressed through an aberrant promoter, as has been described for Hodgkin lymphoma. A custom Taqman assay was developed for this unique transcript, and then used to detect the transcript in 4 of 40 samples in a panel of melanoma biopsies, suggesting that aberrant CSF1R expression in melanoma is not uncommon. Expression of CSF1R protein in A2058 cells was confirmed by FACS using anti-CD115 antibodies, and by Western blot using antibodies directed to the C-terminus. Expression of the ligand CSF-1 was also found in A2058 cells by both ELISA and Taqman assays. Inhibition of A2058 cell growth by PLX3397, a clinically relevant small molecule inhibitor of CSF1R kinase, could be observed in 3D cell culture, indicating that under some conditions an autocrine stimulation of growth occurs. shRNA mediated knockdown of CSF1R also demonstrated decreased colony size and increased apoptosis in 3D culture conditions. The invasiveness of A2058 cells was decreased after treatment with PLX3397 or anti-CSF1 antibodies, suggesting a role for melanoma cancer cell expression of CSF1R in metastasis. Since A2058 cells possess an oncogenic BRAF mutation, co-inhibition of CSF1R and BRAF was tested and resulted in synergistic blockade of xenograft growth. The CSF1R inhibitor, PLX3397, is under investigation in clinical trials for breast, glioma, and other cancers, and these data present a preclinical rationale for its study in malignant melanoma. Citation Format: Yongkai Mo, Orsolya Giricz, Caroline Hu, Kimberly Dahlman, Sanchari Bhattacharyya, Hoa Nguyen, Bernice Matusow, Tushar Bhagat, Yiting Yu, Rafe Shellooe, Elizabeth Burton, Gaston Habets, John Greally, Paraic Kenny, Jeffrey Sosman, Gideon Bollag, Brian L. West, Amit Verma. Integrated epigenomic profiling reveals widespread demethylation in melanoma, and reveals aberrant CSF-1 receptor expression as a regulator of malignant growth and invasion inhibited by PLX3397. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr A26.