Relationship between androgen biosynthesis linked to 3βHSD1 and resistance to radiotherapy: A germline biomarker for combined androgen blockade with radiation in high-risk 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

The Maverick trial: A phase 2 study of abivertinib in patients (pts) with metastatic castration resistant prostate cancer (mCRPC)

TPS5106 Background: Abivertinib is a potent, small molecule third-generation tyrosine kinase inhibitor (TKI) of epidermal growth factor receptor (EGFR), Bruton tyrosine kinase (BTK) receptor, and bone marrow tyrosine kinase gene on chromosome X (BMX). Abivertinib irreversibly binds to the BTK receptor, preventing the phosphorylation of the receptor, and also BMX. The adrenal-permissive HSD3B1(1245C) allele, which is present in upwards of 50% of men with prostate cancer, encodes a 3βHSD1 enzyme missense that up-regulates the rate-limiting step of androgen biosynthesis from extragonadal precursor steroids and promotes poor clinical outcomes. 3βHSD1 must be phosphorylated by BMX for androgen biosynthesis. Preclinical studies suggest BMX inhibition blocks 3βHSD1, androgen biosynthesis and CRPC in xenograft models. These provide the rationale for use of the combination of abivertinib and abiraterone to block residual androgen synthesis that escapes abiraterone inhibition. Methods: The Maverick Trial is a multicenter, open-label phase 2 study within the US Dept of Defense Prostate Cancer Clinical Trials Consortium (DOD PCCTC) of abivertinib with abiraterone in pts with mCRPC harboring the adrenal-permissive HSD3B1(1245C) allele (germline heterozygous or homozygous). HSD3B1 status will be confirmed centrally prior to enrollment via CLIA testing at the Cleveland Clinic. The study includes two cohorts: abiraterone-naïve and abiraterone-progressing. There will be cap of 50% of accrual in each cohort for pts heterozygous for the HSD3B1(1245C) allele. An interim futility analysis is embedded in each cohort, and toxicity rates will be continuously monitored for early stoppage according to predefined rules. Pts receive continuous treatment with abivertinib 200 mg BID with abiraterone 1000 mg QD + prednisone 5 mg BID until radiographic progression, unacceptable toxicity, intercurrent illness, or other reason, such as subject withdrawal. The primary endpoint is 6-month rPFS defined as percent of subjects alive and without progression by RECIST version 1.1 for measurable disease and PCWG3 criteria for bone metastases. Secondary and exploratory endpoints include objective response rate, duration of response, PSA progression, pharmacokinetics, pharmacodynamic tissue changes, and mechanisms of response and resistance to therapy via sequential tissue and blood sampling. The study is currently open at 1 site and will activate at 9 additional sites. It is sponsored by Sorrento Therapeutics, Inc, and managed by the Prostate Cancer Clinical Trials Consortium. Trial Registration: NCT05361915 Funding Source: Sorrento Therapeutics, Inc, the trial’s sponsor who is funding the trial. Clinical trial information: NCT05361915