Relationship between androgen biosynthesis linked to 3bHSD1 and resistance to radiotherapy: A germline biomarker for combined androgen blockade with radiation in highrisk prostate cancer.

e17084 Background: Around 50% of men with advanced prostate cancer (PCa) have at least one germline copy of the adrenal-permissive (1245C) HSD3B1 allele. This allele leads to higher levels of the steroid biosynthesis enzyme, 3β-hydroxysteroid dehydrogenase (3βHSD1). Inheriting this allele is linked to worse outcomes in men with advanced PCa. To determine if (1245C) HSD3B1 could be causing early resistance to combined androgen deprivation and radiotherapy in localized PCa, we studied its role in modulating radioresistance. Methods: PCa cell lines were used to investigate the reciprocal effects of 3βHSD1 knockdown and overexpression in intrinsically high and low 3βHSD1 lines, respectively. PCa xenografts were used to confirm the results in vivo. The connection between androgen receptor (AR) expression and elevated DNA Damage Response (DDR) gene expression was validated using transcriptomic data from 680 radical prostatectomy specimens The ability of enzalutamide, a non-steroidal anti-androgen, to restore radiosensitivity in 1245C expressing lines was interrogated in vitro and in vivo. Results: 1245C HSD3B1 expressing PCa lines displayed increased clonogenic survival after ionizing radiation. Effects were dependent on the 3βHSD1 substrate, DHEA, confirming intratumoral androgen metabolism was required for radioresistance. Resistant lines showed enhanced DNA double-strand break (DSB) repair and heightened DDR gene expression. PCa xenografts with 1245C HSD3B1 were similarly more resistant to radiation using murine models that faithfully mimic human adrenal physiology. A correlation between AR expression and increased DDR gene expression was confirmed in 680 patient samples. Enzalutamide pretreatment resulted in a decrease in DSB repair ability and re-sensitized 1245C HSD3B1 PCa cells to radiation. Conclusions: 1245C HSD3B1 fuels prostate cancer treatment resistance by elevating regional androgen biosynthesis from adrenal steroid precursors, leading to DDR gene overexpression and enhanced DNA DSB repair kinetics. This work supports clinical validation of biomarker informed selective intensification strategies, e.g., combined androgen blockade, for high-risk men with the 1245C HSD3B1 allele receiving curative intent radiotherapy.