Preclinical Profile Of Azd3514: A Small Molecule-Targeting Androgen Receptor Function With A Novel Mechanism Of Action And The Potential To Treat Castration-Resistant Prostate Cancer

The androgen receptor (AR), an important molecular target in the aetiology and progression of prostate cancer, has been found recently to drive key signalling responses in castration resistant prostate cancer (CRPC) after classical androgen ablation therapies have failed. Here we describe the biological characterisation of AZD3514 an oral drug that targets AR function, with a novel mechanism of action that can result in down-regulation of AR protein. AZD3514 binds to the AR ligand binding domain and has selectivity for binding to AR over other nuclear hormone receptors. In vitro AZD3514 inhibits cell growth in prostate cancer cells expressing wild-type (VCaP) and mutated (T877A) AR (LNCaP), but is inactive in AR-negative prostate cancer cells, indicating a dependency on AR for efficacy. In vivo, we assessed activity initially in the Hershberger castrated rat assay in which oral dosing of AZD3514 (100mg/kg once-daily for 7 days) significantly inhibited testosterone-induced growth of sexual accessory organs. Studies to investigate the mode of action of AZD3514 revealed a number of cellular events associated with loss of AR function. Consistent with an inhibition of AR signalling, AZD3514 caused a rapid reduction in PSA synthesis in vitro; with a significant decrease in PSA mRNA being evident in LNCaP cells within 2 - 3 h of compound treatment. Additional experiments in LNCaP cells and U2OS AR-transfected cells, demonstrated that AZD3514 inhibits an androgen-induced translocation of AR from the cytoplasm to the nucleus within a comparable time-frame. In addition to the effects on AR localisation and AR-dependent transcription, AZD3514 treatment also reduced AR protein in LNCaP cells maintained in steroid-depleted conditions; an effect which was evident within 6 - 8h, and maximal at 18 - 24h. The ability to down-regulate AR under such conditions differentiates AZD3514 from the AR antagonists bicalutamide and MDV3100, which do not reduce AR protein levels. Administration of AZD3514 (100 mg/kg/day orally) for 3 days to Copenhagen rats bearing R3327H Dunning prostate tumours, indicates that AZD3514 treatment also reduces tumour AR in vivo. AZD3514 has also been shown to reduce AR protein expression, PSA synthesis and cell growth in vitro in a subclone of cells serially maintained in the presence of bicalutamide (LNCaP-CR) and an androgen-independent subclone of cells that was serially maintained in steroid-depleted medium (LNCaP-AI), suggesting that this novel mechanism of AR inhibition can deliver activity in CRPC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3848. doi:1538-7445.AM2012-3848