1,3-Disubstituted-1,2,4-triazin-6-ones with potent activity against androgen receptor-dependent prostate cancer cells.

Synthesis and biological evaluation of a small, focused library of 1,3-disubstituted-1,2,4-triazin-6-ones for in vitro inhibitory activity against androgen-receptor-dependent (22Rv1) and androgen-receptor independent (PC3) castration-resistant prostate cancer (CRPC) cells led to highly active compounds with in vitro IC50 values against 22Rv1 cells of <200 nM, and with apparent selectivity for this cell type over PC3 cells. From metabolic/PK evaluations of these compounds, a 3-benzyl-1-(2,4-dichlorobenzyl) derivative had superior properties and showed considerably stronger activity, by nearly an order of magnitude, against AR-dependent LNCaP and C4-2B cells compared to AR-independent DU145 cells. This lead compound decreased AR expression in a dose and time dependent manner and displayed promising therapeutic effects in a 22Rv1 CRPC xenograft mouse model. Computational target prediction and subsequent docking studies suggested three potential known prostate cancer targets: p38a MAPK, TGF-ß1, and HGFR/c-Met, with the latter case of c-Met appearing stronger, owing to close structural similarity of the lead compound to known pyridazin-3-one derivatives with potent c-Met inhibitory activity. RNA-seq analysis showed dramatic reduction of AR signalling pathway and/or target genes by the lead compound, subsequently confirmed by quantitative PCR analysis. The lead compound was highly inhibitory against HGF, the c-Met ligand, which fitted well with the computational target prediction and docking studies. These results suggest that this compound could be a promising starting point for the development of an effective therapy for the treatment of CRPC.

1-Benzyloxy-5-phenyltetrazole derivatives highly active against androgen receptor-dependent prostate cancer cells.

A series of 1-benzyloxy-5-phenyltetrazole derivatives and similar compounds were synthesized and evaluated for their in vitro inhibitory activity against androgen-receptor-dependent (22Rv1) and androgen-receptor independent (PC3) prostate cancer cells. The most active compounds had in vitro IC50 values against 22Rv1 cells of <50 nM and showed apparent selectivity for this cell type over PC3 cells; however, these active compounds had short half-lives when incubated with mouse liver microsomes and/or when plasma concentration was monitored during in vivo pharmacokinetic studies in mice or rats. Importantly, lead compound 1 exhibited promising inhibitory effects on cell proliferation, expression of AR and its splicing variant AR-v7 as well as AR regulated target genes in 22Rv1 cells, which are so called castration-resistant prostate cancer (CRPC) cells, and a 22Rv1 CRPC xenograft tumour model in mice. Structural changes which omitted the N-O-benzyl moiety led to dramatic or total loss of activity and S-benzylation of a cysteine derivative, as a surrogate for in vivo S-nucleophiles, by representative highly active compounds, suggested a possible chemical reactivity basis for this "activity cliff" and poor pharmacokinetic profile. However, representative highly active compounds did not inhibit a cysteine protease, indicating that the mode of activity is unlikely to be protein modification by S-benzylation. Despite our efforts to elucidate the mode of action, the mechanism remains unclear.