Abstract 1408: PlexinD1 drives enzalutamide-resistant neuroendocrine prostate cancer development and progression

Background: Neuroendocrine prostate cancer (NEPC) is a lethal subtype of prostate cancer (PC) arising as a consequence of more potent targeting of the androgen receptor (AR) pathway in castration-resistant prostate cancer (CRPC). Recently, the transition from CRPC to NEPC occurs more frequently due to the widespread use of highly potent antiandrogens such as enzalutamide (ENZ). This study sought to investigate the functional role of PlexinD1 in ENZ-induced NEPC and dissect the underlying molecular mechanism. Methods: The PlexinD1 expression levels and its association with neuroendocrine differentiation were determined in publicly available multi-omics datasets and clinical specimens. Human PC stable cell lines with augmentation or silencing of PlexinD1 expression were established and assayed for cell proliferation, colony formation and neuroendocrine marker gene expression by Western blotting and RT-qPCR analyses. Results: PlexinD1 expression was elevated in hormone-refractory PC compared to hormone-sensitive PC and further in NEPC compared to CRPC, which was paralleled by a positive correlation between PlexinD1 expression and NEPC score and an inverse relationship of PlexinD1 levels with AR score, by a survey of multiple independent clinical datasets. The association of PlexinD1 with different subtypes and disease status of PC will also be explored in our own patient cohorts by quantitative immunohistochemical analysis. The PlexinD1 mRNA levels were induced in androgen-dependent LNCaP cells grown in hormone-depleted media for 3 days and in C4-2B cells treated with 10 µM ENZ for 5 days. PlexinD1 was also increased in ENZ-resistant C4-2B (C4-2BENZR) cells at both mRNA and protein levels. shRNA-mediated knockdown of PlexinD1 in neuroendocrine-like PC cells, including C4-2BENZR, 22Rv1, PC-3 and DU145, suppressed cell proliferation by up to more than 50%, which was corroborated by decreased colony formation. PlexinD1 silencing in C4-2BENZR and 22Rv1 cells led to reduced expression of the NE marker chromogranin A (CHGA). The effects of PlexinD1 on NEPC tumor growth and neuroendocrine marker expression will be further examined in xenograft mouse models. Collectively, our data indicate that PlexinD1 plays an essential role supporting the acquisition of a neuroendocrine phenotype in PC cells and driving NEPC cell survival and growth. Conclusion: Our study suggests that PlexinD1 promotes the progression of CRPC to NEPC under ENZ pressure and subsequent emergence of resistance to ENZR possibly through induction of neuroendocrine traits, which provides new insights into further developing PlexinD1 as a new biomarker and therapeutic target in NEPC. Funding provided by Department of Defense PCRP grant W81XWH-19-1-0279, NIH/NCI grant R37CA233658, and the WSU start-up fund (to B.W.) Citation Format: Jing Wang, Jingjing Li, Boyang Wu. PlexinD1 drives enzalutamide-resistant neuroendocrine prostate cancer development and progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1408.