Abstract 1326: Second generation androgen receptor signaling inhibitor resistant neuroendocrine like prostate cancer: A mechanistic study

Background:Failure of castration resistant prostate cancer patients to Androgen Receptor Signaling Inhibitor (ARSI) poses a major challenge in terms of therapeutic development. The heterogeneous nature of prostate cancer makes it difficult to stratify the treatment modalities. A multitude of variable pathological and genetic alterations induced by systemic treatment adds further to the therapeutic complexity. Upon continued exposure to enzalutamide (ARSI), nearly 15-20% of castration resistant patients advance towards a highly aggressive neuroendocrine like phenotype with concomitant functional loss of RB1 and TP53 and persistent AR expression in some. Elucidation of the underlying mechanism of resistance among this aggressive subset of patients is of utmost importance to clinically stratify the treatment options and target these advanced neuroendocrine like patients, who currently lack specific treatment approaches. The following study aims to identify the molecular signature responsible for driving this enzalutamide resistant neuroendocrine like development. Objective:The primary objective of the study is to identify the molecular mechanism behind ARSI induced neuroendocrine like Prostate cancer development. Methods:We have developed two cell line model systems. C4-2 has been genetically modified to develop a simultaneous genetic loss of RB1 and TP53 (DKD). C4-2B has been kept on continued exposure to Enzalutamide to develop Enzalutamide Resistant (C4-2BER). C4-2BER maintains AR expression while DKD loses AR expression, resembling different stages in neuroendocrine like development. Using Western Blot and RT PCR analysis the neuroendocrine like background of these resistant cell line models has been characterized. We performed an RNA-Seq with C4-2B and its resistant model C4-2BER and further downstream analysis through gene ontology and GSEA were performed. Results:Model system characterization study revealed neuroendocrine like characteristics and gene expression. Genetic analysis revealed an upregulation of multiple genes in C4-2BER in comparison to its parental C4-2B, which is comparable to patient dataset available online. GSEA analysis revealed several neuronal biology related pathways to be prominently upregulated among C4-2BER. Further analysis revealed that expression of WT1, which binds near most of these upregulated genes, is downregulated in C4-2BER. Conclusions:The downregulation of WT1 is noted during progression from CRPC towards enzalutamide resistant neuroendocrine development in C4-2BER, which is in turn accompanied with various epigenetic changes. Understanding such pattern of changes and identifying the underlying molecular signature would help elucidate the targets behind treatment induced neuroendocrine characteristics from a therapeutic point of view. Citation Format: Sreyashi Bhattacharya, Ridwan Islam, Sanika Bodas, Navatha Polavaram, Kaustubh Datta, Samikshan Dutta. Second generation androgen receptor signaling inhibitor resistant neuroendocrine like prostate cancer: A mechanistic study [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 1326.