Wang, Chenyao

Abstract Background: Prostate cancer is the second leading cause of cancer-related death in men in the United States and is dependent on androgens and androgen receptor (AR) activation. Androgen deprivation therapy (ADT) is the mainstay treatment, but it as well as next-generation treatments eventually fail. Disease then progresses as castration-resistant prostate cancer (CRPC), which is driven by reactivation of the androgen-AR axis. 3β-hydroxysteroid dehydrogenase-1 (3βHSD1) catalyzes the rate-limiting step for potent androgen synthesis from adrenal-derived precursors, thereby stimulating CRPC. HSD3B1, which encodes for 3βHSD1, has a common missense-encoding germline variation that enhances conversion from adrenal DHEA to potent androgens. Clinical studies demonstrate that this “adrenal-permissive” HSD3B1 genotype confers more rapid progression on ADT, and recent studies show that overall survival is shorter in patients with the adrenal-permissive genotype who are treated with ADT + enzalutamide. The Etk/BMX kinase may be involved in the development and progression of CRPC. We sought to determine whether phosphorylation of 3βHSD1 is required for its activation and that the necessary kinase could be a potential target. Methods: In prostate cancer lines, mouse xenograft models, and fresh patient prostatectomy tissues, mass spectrometry and HPLC were used to identify steroid metabolites. Genetic and pharmacological methods were used to identify inhibition of BMX-mediated 3βHSD1 phosphorylation in CRPC. Results: BMX inhibition suppressed castration-resistant prostate cancer through targeting 3βHSD1 phosphorylation. 3βHSD1 transcription level and enzyme activity were induced in enzalutamide-resistant prostate cancer cell lines. 3βHSD1 and SF-1 transcription levels were positively correlated in prostate adenocarcinoma (TCGA database). BMX inhibition by zanubrutinib suppressed enzalutamide resistance induced 3βHSD1 enzyme activity. Conclusions: BMX promotes CRPC by regulating 3βHSD1 phosphorylation. BMX inhibition has potential as a new therapy to optimize CRPC treatment. Citation Format: Xiuxiu Li, Michael Berk, Christopher Goins, Mohammad Alyamani, Yoon-Mi Chung, Chenyao Wang, Monaben Patel, Nityam Rathi, Ziqi Zhu, Belinda Willard, Shaun Stauffer, Eric Klein, Nima Sharifi. BMX inhibition reverses HSD3B1-driven resistance in prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A026.

In cancer cells, endogenous or therapy-induced DNA damage leads to the abnormal presence of DNA in the cytoplasm, which triggers the activation of cGAS (cyclic GMP–AMP synthase) and STING (stimulator of interferon genes). STAT2 suppresses the cGAMP-induced expression of IRF3-dependent genes by binding to STING, blocking its intracellular trafficking, which is essential for the full response to STING activation. STAT2 reshapes STING signaling by inhibiting the induction of IRF3-dependent, but not NF-κB–dependent genes. This noncanonical activity of STAT2 is regulated independently of its tyrosine phosphorylation but does depend on the phosphorylation of threonine 404, which promotes the formation of a STAT2:STING complex that keeps STING bound to the endoplasmic reticulum (ER) and increases resistance to DNA damage. We conclude that STAT2 is a key negative intracellular regulator of STING, a function that is quite distinct from its function as a transcription factor.

144 Background: Kinase inhibitors have been ineffective in prostate cancer and have no known role in androgen biosynthesis. Inheritance of the adrenal-permissive HSD3B1(1245C) allele encodes a 3βHSD1 enzyme missense that up-regulates the rate-limiting step of androgen biosynthesis from non-gonadal precursor steroids and confers poor clinical outcomes in castration-resistant prostate cancer (CRPC). About half of all men with prostate cancer inherit the adrenal-permissive HSD3B1 allele. Multiple clinical studies demonstrate that adrenal-permissive HSD3B1 allele inheritance confers more rapid progression on ADT and others also suggest worse CRPC outcomes even after treatment with abiraterone or enzalutamide. However, there is no known method to clinically block 3βHSD1. Furthermore, 3βHSD1 is not known to be phosphorylated. Methods: Mass spectrometry was used to identify protein phosphorylation sites and steroid metabolites, genetic and pharmacologic methods were used to identify the kinase required for 3βHSD1 phosphorylation and mouse xenograft studies were performed with BMX inhibition. The identified mechanism was used to design and launch a multicenter phase 2 study of the BMX inhibitor abivertinib in combination with abiraterone in men with metastatic CRPC. Results: 3βHSD1 enzyme activity requires tyrosine phosphorylation at Y344 by the BMX kinase. Androgen biosynthesis is blocked by a phosphorylation-defective 3βHSD1 344F, or BMX genetic knockdown, or BMX pharmacologic inhibition. BMX inhibition using zanubrutinib suppresses CRPC growth in the C4-2 and VCaP xenograft models by blocking intratumoral androgen synthesis and tumor androgen receptor (AR) signaling. Discovery of this mechanism provides the rationale for the phase 2 Maverick trial of abivertinib, a BMX inhibitor, combined with abiraterone, in men with CRPC with adrenal-permissive HSD3B1 allele inheritance (NCT05361915). Eligibility includes 1) presence of metastatic CRPC, 2) measurable and/or non-measurable disease, and 3) confirmed positivity of adrenal-permissive HSD3B1(1245C) allele inheritance via central testing (cap heterozygosity at 50%). Patients will be enrolled in 2 arms: 1) abiraterone naïve (n=45) and 2) abiraterone progressing (n=55). All patients will receive treatment with abivertinib 200mg twice daily with abiraterone 1000mg daily and prednisone 5mg by mouth twice daily. The primary outcome is 6-month radiographic progression-free survival. On-treatment biopsies will be used to inform mechanisms of response and resistance in patients. Conclusions: BMX is required for 3βHSD1 phosphorylation, androgen biosynthesis and CRPC progression with the adrenal-permissive HSD3B1(1245C) allele. The Maverick trial will test clinical proof-of-concept of BMX inhibition in men with adrenal-permissive HSD3B1(1245C) inheritance. Clinical trial information: NCT05361915 .