American Association for Cancer Research
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Supplementary Methods from Targeting Bromodomain and Extra-Terminal (BET) Family Proteins in Castration-Resistant Prostate Cancer (CRPC)

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posted on 2023-03-31, 20:43 authored by Jonathan Welti, Adam Sharp, Wei Yuan, David Dolling, Daniel Nava Rodrigues, Ines Figueiredo, Veronica Gil, Antje Neeb, Matthew Clarke, George Seed, Mateus Crespo, Semini Sumanasuriya, Jian Ning, Eleanor Knight, Jeffrey C. Francis, Ashley Hughes, Wendy S. Halsey, Alec Paschalis, Ram S. Mani, Ganesh V. Raj, Stephen R. Plymate, Suzanne Carreira, Gunther Boysen, Arul M. Chinnaiyan, Amanda Swain, Johann S. de Bono

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ARTICLE ABSTRACT

Purpose: Persistent androgen receptor (AR) signaling drives castration-resistant prostate cancer (CRPC) and confers resistance to AR-targeting therapies. Novel therapeutic strategies to overcome this are urgently required. We evaluated how bromodomain and extra-terminal (BET) protein inhibitors (BETi) abrogate aberrant AR signaling in CRPC.Experimental Design: We determined associations between BET expression, AR-driven transcription, and patient outcome; and the effect and mechanism by which chemical BETi (JQ1 and GSK1210151A; I-BET151) and BET family protein knockdown regulates AR-V7 expression and AR signaling in prostate cancer models.Results: Nuclear BRD4 protein expression increases significantly (P ≤ 0.01) with castration resistance in same patient treatment-naïve (median H-score; interquartile range: 100; 100–170) and CRPC (150; 110–200) biopsies, with higher expression at diagnosis associating with worse outcome (HR, 3.25; 95% CI, 1.50–7.01; P ≤ 0.001). BRD2, BRD3, and BRD4 RNA expression in CRPC biopsies correlates with AR-driven transcription (all P ≤ 0.001). Chemical BETi, and combined BET family protein knockdown, reduce AR-V7 expression and AR signaling. This was not recapitulated by C-MYC knockdown. In addition, we show that BETi regulates RNA processing thereby reducing alternative splicing and AR-V7 expression. Furthermore, BETi reduce growth of prostate cancer cells and patient-derived organoids with known AR mutations, AR amplification and AR-V7 expression. Finally, BETi, unlike enzalutamide, decreases persistent AR signaling and growth (P ≤ 0.001) of a patient-derived xenograft model of CRPC with AR amplification and AR-V7 expression.Conclusions: BETi merit clinical evaluation as inhibitors of AR splicing and function, with trials demonstrating their blockade in proof-of-mechanism pharmacodynamic studies. Clin Cancer Res; 24(13); 3149–62. ©2018 AACR.

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