Resistance to BET Inhibitor Leads to Alternative Therapeutic Vulnerabilities in Castration-Resistant Prostate Cancer.

BRD4 plays a major role in the transcription networks orchestrated by androgen receptor (AR) in castration-resistant prostate cancer (CRPC). Several BET inhibitors (BETi) that displace BRD4 from chromatin are being evaluated in clinical trials for CRPC. Here, we describe mechanisms of acquired resistance to BETi that are amenable to targeted therapies in CRPC. BETi-resistant CRPC cells displayed cross-resistance to a variety of BETi in the absence of gatekeeper mutations, exhibited reduced chromatin-bound BRD4, and were less sensitive to BRD4 degraders/knockdown, suggesting a BRD4-independent transcription program. Transcriptomic analysis revealed reactivation of AR signaling due to CDK9-mediated phosphorylation of AR, resulting in sensitivity to CDK9 inhibitors and enzalutamide. Additionally, increased DNA damage associated with PRC2-mediated transcriptional silencing of DDR genes was observed, leading to PARP inhibitor sensitivity. Collectively, our results identify the therapeutic limitation of BETi as a monotherapy; however, our BETi resistance data suggest unique opportunities for combination therapies in treating CRPC.

Pawar A ，Gollavilli PN ，Wang S ，Asangani IA ... -  《Cell Reports》

Targeting Bromodomain and Extra-Terminal (BET) Family Proteins in Castration-Resistant Prostate Cancer (CRPC).

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.

Welti J ，Sharp A ，Yuan W ，Dolling D ，Nava Rodrigues D ，Figueiredo I ，Gil V ，Neeb A ，Clarke M ，Seed G ，Crespo M ，Sumanasuriya S ，Ning J ，Knight E ，Francis JC ，Hughes A ，Halsey WS ，Paschalis A ，Mani RS ，Raj GV ，Plymate SR ，Carreira S ，Boysen G ，Chinnaiyan AM ，Swain A ，de Bono JS ，International SU2C/PCF Prostate Cancer Dream Team ... -  《-》

Exploitation of Castration-Resistant Prostate Cancer Transcription Factor Dependencies by the Novel BET Inhibitor ABBV-075.

Competitive inhibitors of acetyl-lysine binding to the bromodomains of the BET (bromodomain and extra terminal) family are being developed for the treatment of solid and hematologic malignancies. The function of BET family member BRD4 at enhancers/superenhancers has been shown to sustain signal-dependent or pathogenic gene expression programs. Here, the hypothesis was tested that the transcription factor drivers of castration-resistant prostate cancer (CRPC) clinical progression, including the androgen receptor (AR), are critically dependent on BRD4 and thus represent a sensitive solid tumor indication for the BET inhibitor ABBV-075. DHT-stimulated transcription of AR target genes was inhibited by ABBV-075 without significant effect on AR protein expression. Furthermore, ABBV-075 disrupted DHT-stimulated recruitment of BET family member BRD4 to gene-regulatory regions cooccupied by AR, including the well-established PSA and TMPRSS2 enhancers. Persistent BET inhibition disrupted the composition and function of AR-occupied enhancers as measured by a reduction in AR and H3K27Ac ChIP signal and inhibition of enhancer RNA transcription. ABBV-075 displayed potent antiproliferative activity in multiple models of resistance to second-generation antiandrogens and inhibited the activity of the AR splice variant AR-V7 and ligand-binding domain gain-of-function mutations, F877L and L702H. ABBV-075 was also a potent inhibitor of MYC and the TMPRSS2-ETS fusion protein, important parallel transcription factor drivers of CRPC. The ability of BET family inhibitor ABBV-075 to inhibit transcription activation downstream of the initiating events of transcription factors like AR and TMPRSS2:ETS fusion proteins provides a promising therapeutic option for CRPC patients who have developed resistance to second-generation antiandrogens. Mol Cancer Res; 15(1); 35-44. ©2016 AACR.

Faivre EJ ，Wilcox D ，Lin X ，Hessler P ，Torrent M ，He W ，Uziel T ，Albert DH ，McDaniel K ，Kati W ，Shen Y ... -  《-》

Selective targeting of PARP-2 inhibits androgen receptor signaling and prostate cancer growth through disruption of FOXA1 function.

Gui B ，Gui F ，Takai T ，Feng C ，Bai X ，Fazli L ，Dong X ，Liu S ，Zhang X ，Zhang W ，Kibel AS ，Jia L ... -  《-》

Role of BET proteins in castration-resistant prostate cancer.

Castration resistant prostate cancer (CRPC) is a deadly disease with few therapeutic options once patients become resistant to second generation drugs targeting the AR-transcriptional program. The BET-BRD readers of chromatin are key regulators of AR-, ERG-, and c-Myc-mediated transcription in CRPC. BET-BRD inhibitors have demonstrated pre-clinical efficacy in models of CRPC and are currently being evaluated in several clinical trials. These novel drugs have the potential to transform the way we treat CRPC in the near future.

Fernandez-Salas E ，Wang S ，Chinnaiyan AM 《-》