Abstract 3653: Structure-based study to overcome cross-reactivity of novel androgen receptor inhibitors

The mutation-driven transformation of clinically used anti-androgens into agonists of human androgen receptor (AR) represents a major challenge in the current treatment of prostate cancer (PCa). To address this problem, we have developed a novel class of AR inhibitors targeting the DNA-binding domain (DBD) of the receptor, which is distanced from the mutations-prone androgen binding site (ABS) in the ligand-binding domain (LBD) of the AR, targeted by all conventional antiandrogens. While many members of the developed phenyl-thiazol-2-yl-morpholine series demonstrated potent sub-micromolar inhibition of the wild-type AR, some compounds also exhibited an undesired partial agonistic effect toward the T877A mutated form of the receptor, implying their cross-interaction with the AR ABS. To study the molecular basis of the cross-reactivity, we have solved the T877A mutated form of the AR LBD in complex with one developed compound exhibiting such unwanted partial agonism. Based on the resolved crystal structure, we have identified critical protein-ligand interactions and conformational changes in wild-type and T877A forms of AR that drive observed agonistic effects. The identified structural basis has further been used to modify the scaffold of developed AR DBD binders to eliminate their cross-reactivity toward T877A mutated AR LBD. In particular, the replacement of the phenyl ring with less hydrophobic heterocycles resulted in a series of inhibitors that did not demonstrate affinity toward ABS or exhibit an undesired agonistic effect on AR. This study provides insights into the development of AR inhibitors with high specificity, which may help overcome the mutation-driven resistance of anti-AR drugs in the treatment of PCa. Citation Format: Huifang Li, Nada Lallous, Kush Dalal, Eric Leblanc, Fuqiang Ban, Fabrice Ciesielski, Paul S. Rennie, Artem Cherkasov. Structure-based study to overcome cross-reactivity of novel androgen receptor inhibitors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3653. doi:10.1158/1538-7445.AM2015-3653