Abstract 2639: Combined therapy targeting AR and EZH2 restrains the growth of castration resistant prostate cancer by enhancing antitumor T cell response

Abstract Castration resistant prostate cancer (CRPC) is a fatal disease. Androgen receptor pathway inhibitors, like enzalutamide, are initially effective but resistance eventually occurs, often associated to the emergence of aggressive neuroendocrine variants (NEPC). Even immunotherapy induced limited results in prostate cancer, governed by an immunosuppressive microenvironment. Therefore, effective therapies are needed. We here investigate in preclinical models a new approach aimed to revert castration resistance and simultaneously turn the immune milieu from “cold” to “hot”, through the combination between enzalutamide and the drug GSK-126, which inhibits the epigenetic modulator EZH2. We show that enzalutamide and GSK-126 can synergize to restrain the growth of CRPC in vitro and in vivo. Moreover, this therapeutic combination efficiently reduced NEPC differentiation, in both subcutaneous and autochthonous in vivo models, increasing the rate of cured mice with regressed lesions. The antitumor efficacy observed in immunocompetent mice bearing subcutaneous syngeneic CRPC tumors was lost in immunodeficient mice, indicating a contribution of immune cells. Additional experiments in the TRAMP spontaneous mouse model revealed that the combination of enzalutamide and GSK-126 significantly induced cytotoxic activity and IFNγ production by tumor-specific CD8+ T cells, otherwise tolerant, and increased IL-17 production by CD4+ T cells. The two drugs did not directly modulate T cell activity in vitro, suggesting the importance of microenvironment accomplices in triggering these effects. These results promote the combined use of enzalutamide and GSK-126 to restrain CRPC growth and NEPC differentiation, and, simultaneously, to awake antitumor T cell response, opening new possibilities for immunotherapy in prostate cancer. Citation Format: Irene Fischetti, Botti Laura, Roberta Sulsenti, Valeria Cancila, Claudia Enriquez, Renata Ferri, Marco Bregni, Filippo Crivelli, Claudio Tripodo, Mario P. Colombo, Elena Jachetti. Combined therapy targeting AR and EZH2 restrains the growth of castration resistant prostate cancer by enhancing antitumor T cell response abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2639.