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Bypassing drug-resistance mechanisms of prostate cancer with small-molecules that target androgen receptor chromatin interactions

ABSTRACT: Human androgen receptor (AR) is a hormone-activated transcription factor that is an important drug-target in the treatment of prostate cancer. Current small molecule AR-antagonists (such as Enzalutamide) compete with male hormones that bind to the steroid binding pocket of the AR ligand binding domain (LBD). In castration-resistant prostate cancer (CRPC), drug-resistance can manifest through AR-LBD mutations that convert AR-antagonists into agonists, or by expression of AR-variants lacking the LBD. Such treatment resistance underscores the importance of novel ways of targeting the AR. In this study, we tested whether VPC14449, a small molecule inhibitor that was rationally designed to selectively target the AR DNA binding domain (DBD), could directly interfere with AR-DNA interactions. Using ChIP-seq in cell line models expressing AR or AR variants, we found that genome-wide chromatin binding of AR was dramatically impacted by VPC14449 (although with lesser effect on AR variants).

ORGANISM(S): Homo sapiens

PROVIDER: GSE96084 | GEO | 2018/02/16

REPOSITORIES: GEO

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Project description:Androgen receptor (AR)-targeting prostate cancer drugs, which are predominantly competitive ligand binding domain (LBD)-binding antagonists, are inactivated by common resistance -mechanisms. It is important to develop next-generation mechanistically-distinct drugs to treat castration- and drug- resistant prostate cancers. Here, we describe a second-generation AR pan-antagonist (UT-34) that degrades the AR and AR splice variants. UT-34 inhibits the wild-type and LBD mutant ARs comparably and inhibits the in vitro proliferation and in vivo growth of enzalutamide-sensitive and resistant prostate cancer xenografts. In preclinical models, UT-34 induced the regression of enzalutamide-resistant tumors at doses when the AR is degraded; but, at lower doses when the AR is just antagonized, it inhibits, without shrinking, the tumors. This indicates that degradation might be a prerequisite for tumor regression. Mechanistically, UT-34 promotes a conformation that is distinct from the LBD-binding competitive antagonist, enzalutamide, and degrades the AR through the ubiquitin proteasome mechanism. UT-34 has a broad safety margin and exhibits no cross-reactivity with G-Protein Coupled Receptor, kinase, and nuclear receptor family members. Collectively, UT-34 exhibits the properties necessary for a next-generation prostate cancer drug. MR49F cells (n=3-4/group) were maintained in charcoal-stripped serum containing medium for 48 hours and treated with vehicle, 0.1 nM R1881, or 10 uM of UT-34 in combination with 0.1 nM R1881. Twenty four hours after treatment, the cells were harvested, RNA was isolated and expression of genes was measured using microarray (Affymetrix Clarion S) UT-34 is a selective androgen receptor degrader that degrades and antagonizes the AR. UT-34 binds to the AF-1 domain of the AR and degrades the AR through ubiquitin proteasome pathways. The transcriptome study was performed to evaluate the ability of UT-34 to antagonize the enzalutamide-resistant AR function.

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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Bypassing drug-resistance mechanisms of prostate cancer with small-molecules that target androgen receptor chromatin interactions

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