Abstract 1146: Enhancer of zeste homolog 2 (EZH2) inhibition in metastatic melanoma promotes tumor regression in vivo

Abstract

Abstract Melanoma is a deadly variety of skin cancer, which is responsible for three-fourths of skin cancer-related deaths, but constitutes less than 5% of all skin cancer cases. It has been estimated that in 2015, about 73,870 new cases of melanoma will be diagnosed in United States alone, of which 9,940 are expected to die. According to the ACS, melanoma is also the fastest growing cancer, which makes it essential to investigate the pathogenesis involved in the advanced stage of melanoma, and design effective therapeutics for its treatment. Drugs targeting epigenetic modifiers like EZH2 are becoming increasingly popular because of the fact that most epigenetic modifications and their effects can be reversed using these drugs. There has been no study till date investigating the role of EZH2 in melanoma. Our laboratory is investigating the role of EZH2 in the pathogenesis involved in the advanced stage of melanoma, to enable the design of effective therapeutic strategies for the treatment of melanoma. Here we investigate the relationship between EZH2 and tumor suppressors E-cadherin and RUNX3 in melanoma using matched melanoma cell lines (WM115 and WM266-4), formalin-fixed-paraffin-embedded (FFPE) patient tissue samples and in vivo xenograft model. The studies performed in cell lines and FFPE tissue samples suggested EZH2-mediated silencing of E-cadherin and RUNX3 by promoting H3K27-trimethylation of the E-CADHERIN and RUNX3 promoters in WM266-4 cells (metastatic; high EZH2; low E-cadherin) relative to WM115 cells (primary; low EZH2; high E-cadherin). Furthermore, we observed that EZH2 inhibition restores E-cadherin and RUNX3 expression in metastatic melanoma cells by reducing EZH2 and H3K27me3 occupancy at E-CADHERIN and RUNX3 promoters respectively. In addition, we found that inhibition of EZH2 besides inducing apoptosis and inhibiting cellular proliferation, also adversely affected invasion of metastatic melanoma. E-cadherin depletion had an opposite effect, suggesting that EZH2 mediated E-cadherin silencing promotes invasion in metastatic melanoma. In vivo, treatment of WM266-4 xenografts with EZH2 inhibitor resulted in significant reduction of tumor growth. In combination with Dabrafenib, this effect was highly synergistic. Analysis of harvested tumors indicated increased E-cadherin and RUNX3 levels in EZH2 inhibited group compared to vehicle, due to reduced H3K27me3 enrichment by EZH2 at E-cadherin and RUNX3 promoters, validating our in vitro finding. Tumor regression by combination therapy was also accompanied by significant increased pro-apoptotic proteins like Bak, Bax and decreased anti-apoptotic proteins Bcl-xL and Bcl-2. Hence, our findings suggest strong potential of EZH2 inhibitors as promising melanoma drugs either by itself (monotherapy), or in conjunction with other chemotherapeutics (combination therapy). Citation Format: Deepanwita Sengupta, Nathan Avaritt, Sara C. Shalin, Alan J. Tackett. Enhancer of zeste homolog 2 (EZH2) inhibition in metastatic melanoma promotes tumor regression in vivo. [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 1146.