Abstract 396: Role of PHF8 in resistance to melanoma targeted therapies

Abstract

Abstract Melanoma is a highly prevalent cancer with increasing incidence worldwide. While immune checkpoint inhibitors have drastically improved outcomes for about half of metastatic melanoma patients, many are still resistant to these treatments or develop life-threatening toxicities. Around 50% of melanomas carry BRAF mutations that result in constitutive activation of the MAPK pathway. Therapeutic combinations of BRAF and MEK inhibitors (MAPKi) have proven very efficient against these tumors, but responses are not durable and treatment-resistant recurrence almost inevitably occurs. Our group recently uncovered a role for the histone demethylase PHF8 in melanoma metastasis, and demonstrated that PHF8 directly controls the expression of key components of the TGFβ pathway. Given that TGFβ signaling crosstalks with the MAPK pathway and contributes to resistance to therapy in various tumors, we decided to investigate a potential role for PHF8 in response and resistance to MAPKi therapy in melanoma. To test our hypothesis, we assessed the effect of modulating PHF8 expression in BRAFV600E-mutant cells and their matched MAPKi-resistant derivatives. PHF8 silencing did not affect cell survival or proliferation of parental, MAPKi-sensitive melanoma cell lines, but it re-sensitized resistant cells to MAPKi treatment. Conversely, PHF8 overexpression in melanoma cell lines did not affect their proliferation rate but increased the emergence of resistant clones in BRAFV600E-mutant melanoma cells treated with BRAFi (Dabrafenib) and MEKi (Trametinib) combinations. Next, we assessed the dynamics of PHF8 expression and TGFβ signaling in melanoma cells exposed to MAPKi. Treatment of MAPKi-sensitive cells leads to a fast and complete downregulation of PHF8 protein expression without a change in mRNA levels, paralleled by reduced TGFβ signaling, as evidenced by decreased SMAD2 phosphorylation. However, PHF8 protein expression is restored in MAPKi resistant clones. Therefore, based on our preliminary data, we postulate that PHF8 suppression by the MAPK pathway plays a critical role in melanoma response to targeted therapy and that its restoration contributes to acquisition of resistance. We are currently investigating MAPK-dependent mechanisms controlling PHF8 stability, and testing novel PHF8 inhibitors for their ability to bypass or overcome melanoma resistance to MAPKi. Our studies might provide basis for a novel epigenetic therapy as a strategy to maximize the potential of MAPKi therapy in melanoma treatment. Citation Format: María de los Ángeles Gómez-Muñoz, Nicole Eskow, Ines Delclaux, Rana Moubarak, Eva Hernando-Monge. Role of PHF8 in resistance to melanoma targeted therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 396.