All current clinically approved androgen deprivation therapies for prostate cancer target the C-terminal ligand-binding domain of the androgen receptor (AR). However, the main transactivation function of the receptor is localized at the AR Nterminal domain (NTD). Targeting the AR NTD directly is a challenge because of its intrinsically disordered structure and the lack of pockets for drugs to bind. Here, we have taken an alternative approach using the cochaperone BAG1L, which interacts with the NTD, to develop a novel AR inhibitor. We describe the identification of 2-(4-fluorophenyl)-5-(trifluoromethyl)-1,3-benzothiazole (A4B17), a small molecule that inhibits BAG1L−AR NTD interaction, attenuates BAG1L-mediated AR NTD activity, downregulates AR target gene expression, and inhibits proliferation of AR-positive prostate cancer cells. This compound represents a prototype of AR antagonists that could be key in the development of future prostate cancer therapeutics.

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<p>Crystallographic data and structure refinement information for X15695, X15696 and X19168.</p>

<p>X15695 alters the cellular localization of wild-type p53 but not mutant p53.</p>

<div>Abstract<p>The pro-oncogenic activities of estrogen receptor alpha (ER) drive breast cancer pathogenesis. Endocrine therapies that impair the production of estrogen or the action of the ER are therefore used to prevent primary disease metastasis. Although recent successes with ER degraders have been reported, there is still the need to develop further ER antagonists with additional properties for breast cancer therapy. We have previously described a benzothiazole compound A4B17 that inhibits the proliferation of androgen receptor positive (AR+) prostate cancer cells by disrupting the interaction of the cochaperone BAG1 with the AR. A4B17 was also found to inhibit the proliferation of ER+ breast cancer cells. Using a scaffold hopping approach, we report here a group of small molecules with imidazopyridine scaffolds that are more potent and efficacious than A4B17. The prototype molecule X15695 efficiently degraded ER and attenuated estrogen-mediated target gene expression as well as transactivation by the AR. X15695 also disrupted key cellular protein-protein interactions such as BAG1-mortalin (GRP75) interaction as well as wild-type p53-mortalin or mutant p53-BAG2 interactions. These activities together reactivated p53 and resulted in cell cycle block and the induction of apoptosis. When administered orally to in vivo tumor xenograft models, X15695 potently inhibited the growth of breast tumor cells but less efficiently the growth of prostate tumor cells. We therefore identify X15695 as an oral selective ER degrader and propose further development of this compound for therapy of ER+ breast cancers.</p></div>

<p>Potency of inhibition of colony formation by different imidazopyridines in breast and prostate cancer cells.</p>

<p>X15695-mediated regulation of expression and cellular localization of p53 in prostate cancer cells.</p>

<p>Volcano plots and Hallmark gene set analyses showing pathways targeted by X15695.</p>