Abstract 3036: Sensitivity of ONC201/TIC10 cancer therapeutic on neuroendocrine prostate cancer (NEPC) and neuroendocrine differentiation (NED)
Authors: Ding Elizabeth C. , Pinho-Schwermann Maximilian , Zhang Shengliang , Purcell Connor , El-Deiry Wafik S. 
Published: March 2024

Abstract
Although androgen deprivation therapy and androgen receptor (AR) blockade are highly effective therapies for metastatic prostate cancer (PCa), most patients develop resistance, leading to castration-resistant prostate cancer (CRPC). A subset of CRPC shows neuroendocrine prostate cancer (NEPC) features, which are associated with poor prognosis and limited therapeutic strategies. NEPC is characterized by oncogenic driver activation and epigenetic changes, partly controlled by transcription factors like BRN2 and SOX2. AR has been shown to suppress BRN2 transcription, which is required for NEPC, and BRN2-dependent regulation of the NEPC marker SOX2 (Bishop et al., 2017). Dordaviprone (ONC201/TIC10) is a first-in-class small molecule that antagonizes DRD2, induces tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), and activates the integrated stress response (ISR). Neuroendocrine tumors express significant DRD2 levels, suggesting ONC201 as a potential therapeutic strategy in NEPC or when drivers for disease progression are overexpressed (OE). PCa cell lines PC3, DU145, LNCaP, and 22RV1 are ONC201 sensitive, with IC50=2.87 μM, 3.18 μM, 1.31 μM, and 1.16 μM, respectively (Ding et al., 2023). To characterize the association of BRN2/SOX2 dysregulation with ONC201 sensitivity, we transiently OE BRN2/SOX2 in PCa. We hypothesized that markers of neuroendocrine differentiation (NED), activation of the ISR, TRAIL, and ClpP and dopamine receptor expression contribute to NEPC cell death and sensitivity to ONC201. We performed CellTiter-Glo experiments to assess viability after 96 hours ± BRN2 OE. DU145 cells with BRN2 OE increased their sensitivity to ONC201 (IC50=2.75 µM) compared to empty vector (IC50=3.03 µM). Colony formation assays were conducted in PCa and analyzed 7 days after ONC201 treatment to show ONC201 effect on PCa cell lines. DU145 was treated at 0.5, 1, and 2 µM of ONC201. There were 95 ± 3.22 colonies for the control group, 83 ± 5.22 colonies with 0.5 µM, 74 ± 3.64 colonies with 1 µM, and 8 ± 2.03 colonies with 2 µM ONC201. DU145 showed a significant reduction in colony-forming ability when treated with 1 and 2 uM ONC201 compared to the control, with P values of &lt;0.05 and &lt;0.0001, respectively. We OE BRN2 and observed changes in NED markers and ISR pathway. In PC3, FoxO1 and ATF4 levels increased. In DU145, FoxO1, ENO2, PGP9.5, CgA, and ATF4 levels decreased. We reveal that DU145 OE at 48 hours does not result in greater expression of NEPC markers. BRN2 OE significantly increased PCa cell sensitivity to ONC201 and was evident without an increase in common phenotypical markers used for NEPC assessment (FoxO1, ENO2, PGP9.5, CgA). Expression change was not shown when PCa had an integral AR pathway. Ongoing efforts are observing ONC201 treatment effects on NED markers and the TRAIL pathway due to BRN2 OE and showing increased sensitivity of PCa to ONC201 with BRN2 OE.
Citation Format: Elizabeth C. Ding, Maximilian Pinho-Schwermann, Shengliang Zhang, Connor Purcell, Wafik S. El-Deiry. Sensitivity of ONC201/TIC10 cancer therapeutic on neuroendocrine prostate cancer (NEPC) and neuroendocrine differentiation (NED) [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(6_Suppl):Abstract nr 3036.