PT - JOURNAL ARTICLE AU - Weiya Liu AU - George A. Vielhauer AU - Jeffrey M. Holzbeierlein AU - Huiping Zhao AU - Suman Ghosh AU - Douglas Brown AU - Eugene Lee AU - Brian S. J. Blagg TI - KU675, a Concomitant Heat-Shock Protein Inhibitor of Hsp90 and Hsc70 that Manifests Isoform Selectivity for Hsp90<em>α</em> in Prostate Cancer Cells AID - 10.1124/mol.114.097303 DP - 2015 Jul 01 TA - Molecular Pharmacology PG - 121--130 VI - 88 IP - 1 4099 - http://molpharm.aspetjournals.org/content/88/1/121.short 4100 - http://molpharm.aspetjournals.org/content/88/1/121.full SO - Mol Pharmacol2015 Jul 01; 88 AB - The 90-kDa heat-shock protein (Hsp90) assists in the proper folding of numerous mutated or overexpressed signal transduction proteins that are involved in cancer. Inhibiting Hsp90 consequently is an attractive strategy for cancer therapy as the concomitant degradation of multiple oncoproteins may lead to effective antineoplastic agents. Here we report a novel C-terminal Hsp90 inhibitor, designated KU675, that exhibits potent antiproliferative and cytotoxic activity along with client protein degradation without induction of the heat-shock response in both androgen-dependent and -independent prostate cancer cell lines. In addition, KU675 demonstrates direct inhibition of Hsp90 complexes as measured by the inhibition of luciferase refolding in prostate cancer cells. In direct binding studies, the internal fluorescence signal of KU675 was used to determine the binding affinity of KU675 to recombinant Hsp90α, Hsp90β, and Hsc70 proteins. The binding affinity (Kd) for Hsp90α was determined to be 191 μM, whereas the Kd for Hsp90β was 726 μM, demonstrating a preference for Hsp90α. Western blot experiments with four different prostate cancer cell lines treated with KU675 supported this selectivity by inducing the degradation of Hsp90α-dependent client proteins. KU675 also displayed binding to Hsc70 with a Kd value at 76.3 μM, which was supported in cellular by lower levels of Hsc70-specific client proteins on Western blot analyses. Overall, these findings suggest that KU675 is an Hsp90 C-terminal inhibitor, as well as a dual inhibitor of Hsc70, and may have potential use for the treatment of cancer.