Molecular analysis of castration sensitivity in the prostate epithelium

Project Summary/Abstract Nearly all aspects of prostate development, homeostasis, and cancer progression are dependent on the activity of androgen receptor (AR). Consequently, inhibition of AR activity has represented the mainstay of prostate cancer treatment for the past 80 years. Due to its clinical significance, the mechanisms that result in resistance to androgen-deprivation therapy, or castration-resistance, have been intensively studied, yet the molecular basis of castration-sensitivity in normal prostate and hormonally-intact prostate tumors has been poorly understood. Uncovering the mechanisms that promote castration-sensitivity may provide fundamental insights into new therapeutic approaches to improve the response to androgen-deprivation therapy (ADT) and potentially overcome castration-resistance. Therefore, in preliminary studies for this proposal, we have used in vivo analyses of genetically-engineered mouse models to define key features of castration-response in the normal prostate. We have shown that death of prostate luminal epithelial cells in response to castration results from the combined inactivation of an intrinsic pathway downstream of androgen receptor (AR) in luminal cells, and an extrinsic pathway dependent on AR activity in the prostate stroma. Loss of both intrinsic and extrinsic pathways induces death of luminal cells through ferroptosis, a form of regulated cell death due to lipid peroxidation. In support of these findings, we have also obtained evidence of ferroptosis in benign human prostate and primary tumors following ADT, and in metastatic castration-resistant tumors that respond to treatment with the AR inhibitor enzalutamide. Based on these preliminary findings, we hypothesize that the integration of intrinsic and extrinsic pathways mediates castration-response and ferroptosis in the prostate epithelium, and that dual targeting of both pathways may provide a novel approach for overcoming castration-resistance. To investigate this hypothesis, we will pursue conceptually and technically innovative in vivo, molecular, biochemical, and bioinformatic studies using genetically-engineered mouse models and validation in human prostate tissue. We will pursue the following specific aims: (1) Investigation of intrinsic mechanisms of resistance to ferroptosis to understand how a subpopulation of luminal epithelial cells in the normal prostate survives castration; (2) Analysis of extrinsic signaling that mediates resistance to ferroptosis to investigate the stromal signal and cognate epithelial receptor that suppresses ferroptosis through the extrinsic pathway; and (3) Analysis of ferroptosis induction in prostate tumors to investigate pharmacological and dietary interventions that can promote ferroptosis in normal prostate and prostate tumors. In combination, our studies will have strong translational impact by elucidating the detailed molecular basis for castration-sensitivity, and thereby providing novel approaches for overcoming castration- resistance in prostate cancer.