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Therapeutic Targeting of BET Bromodomain Proteins in Castration-Resistant Prostate Cancer (microarray)

ABSTRACT: Men who develop metastatic castration-resistant prostate cancer (CRPC) invariably succumb to the disease. The development and progression to CRPC following androgen ablation therapy is predominantly driven by unregulated androgen receptor (AR) signaling1-3. Despite the success of recently approved therapies targeting AR signaling such as abiraterone4-6 and second generation anti-androgens MDV3100 (enzalutamide)7,8, durable responses are limited, presumably due to acquired resistance. Recently JQ1 and I-BET, two selective small molecule inhibitors that target the amino-terminal bromodomains of BRD4, have been shown to exhibit antiproliferative effects in a range of malignancies9-12. Here we show that AR signaling-competent CRPC cell lines are preferentially sensitive to BET bromodomain inhibition. BRD4 physically interacts with the N-terminal domain of AR and can be disrupted by JQ111,13. Like the direct AR antagonist, MDV3100, JQ1 disrupted AR recruitment to target gene loci. In contrast to MDV3100, JQ1 functions downstream of AR, and more potently abrogated BRD4 localization to AR target loci and AR mediated gene transcription including induction of TMPRSS2-ERG and its oncogenic activity. In vivo, BET bromodomain inhibition was more efficacious than direct AR antagonism in CRPC xenograft models. Taken together, these studies provide a novel epigenetic approach for the concerted blockade of oncogenic drivers in advanced prostate cancer.

ORGANISM(S): Homo sapiens

PROVIDER: GSE55063 | GEO | 2014/04/25

SECONDARY ACCESSION(S): PRJNA238360

REPOSITORIES: GEO

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Project description:Continued androgen receptor (AR) signaling is an established mechanism underlying castration-resistant prostate cancer (CRPC), and suppression of AR signaling remains a therapeutic goal of CRPC therapy. Constitutively active androgen receptor splicing variants (AR-Vs) lack the AR ligand-binding domain (AR-LBD), the intended target of androgen deprivation therapies (ADT) including new CRPC therapies such as abiraterone and MDV3100. While the canonical full-length AR (AR-FL) and AR-Vs are both increased in CRPC, their expression regulation, associated transcriptional programs, functional relationships, and respective roles in mediating responses to endocrine therapies have not been dissected. In this study, we show that suppression of canonical AR-FL signaling by targeting AR-LBD leads to increased AR-V expression in two cell line models of CRPC. Importantly, treatment-induced AR-Vs activate a distinct expression signature enriched for cell cycle genes without requiring the presence of AR-FL. Conversely, activation of AR-FL signaling suppresses the AR-V signature but activates expression programs mainly associated with macromolecular synthesis, metabolism, and differentiation. In prostate cancer cells and CRPC xenografts treated with MDV3100 and abiraterone, increased expression of two constitutively active AR-Vs, AR-V7 and ARV567ES, but not AR-FL, parallels increased expression of the AR-driven cell cycle gene UBE2C. In addition, protein expression of AR-V7, but not AR-FL, is positively correlated with UBE2C in clinical CRPC specimens. The cumulative in vitro and in vivo evidence support an adaptive shift toward AR-V-mediated signaling in at least a subset of CRPC tumors as the AR-LBD is rendered inactive, suggesting an important mechanism contributing to drug resistance to CRPC therapies. LNCaP cells lacking AR-V were transfected with AR-V7 with or without androgen stimulation of AR-FL (4 conditions); LNCaP95 cells expressing AR-Vs were treated with control siRNA or siRNA trageting AR-LBD or AR-DBD, with or without androgen stimulation of AR-FL (6 conditions); VCaP cells expressing AR-Vs in the presence of androgen were treated with control siRNA, siRNA trageting AR-LBD, DMSO or MDV3100 to inhibit AR-FL (4 conditions). Total 14 arrays with no replicates.

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Therapeutic Targeting of BET Bromodomain Proteins in Castration-Resistant Prostate Cancer (microarray)

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