Abstract 7228: In-vitro efficacy of Dordaviprone/GSK126 combination therapy on castration resistant and neuroendocrine prostate cancer

Abstract Neuroendocrine prostate cancer (NEPC) is an aggressive histologic subtype associated with poor prognosis that commonly arises in later stages as a mechanism of treatment resistance. Activation of oncogenic drivers, in combination with epigenetic changes (such as EZH2 overexpression and DNA methylation) further promotes tumor proliferation and expression of downstream neuroendocrine lineage pathways (in part controlled by transcription factors, including SOX2, ASCL1, and BRN2). Importantly, EZH2 inhibitors (EZH2i) can restore AR expression in CRPC (Ku et al. , 2017). Imipridones, including Dordaviprone (ONC201), show promise in treating neuroendocrine tumors by interacting with DRD2 and CLpP (Anderson et al. , 2022). These results warrant investigation into the potential for synergism in imipridone/EZH2i combination therapies. In the PCa cell lines LNCap, PC3, 22Rv1, and DU145 the combination of ONC201 and EZH2i GSK126 was assessed. Cell viability data after treatment with ONC201 and GSK126 reveals several dose ranges with potential synergistic activity after 72h. Preliminary western blots after 72 hours of GSK126 treatment indicate modulation of proteins relevant to the mechanism of action of imipridones, specifically DR5 and CLpP, in LNCap, PC3, and 22Rv1. Notably, the decrease in DR5 expression warrants investigation into the effects of EZH2i on TRAIL sensitivity and whether imipridones may rescue DR5 expression to maintain TRAIL sensitivity. Subsequent experiments will investigate dosing and time point-based effects on viability and protein expression, in addition to assessing the synergy of other imipridones and EZH2i’s. Further, while the cell lines PC3, 22Rv1, and DU145 are castration-resistant, the neuroendocrine prostate cell line NCI-H660 will be used as a positive control as it expresses higher neuroendocrine features, including DRD2. Additionally, the modulation in DR5 expression warrants inquiry into the effects of combination therapy on tumor-immune cell interactions. Further, we will manipulate the expression of neuroendocrine transcription factors to assess changes in therapy sensitivity. Citation Format: Connor Purcell, Praveen Srinivasan, Maximilian Pinho-Schwermann, William MacDonald, Elizabeth C. Ding, Vida Tajiknia, Wafik El-Deiry. In-vitro efficacy of Dordaviprone/GSK126 combination therapy on castration resistant and neuroendocrine prostate cancer 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 7228.