Development and characterization of a novel C-terminal inhibitor of Hsp90 in androgen dependent and independent prostate cancer cells

PC3-MM2 and LNCaP-LN3 cells were used in both direct and indirect in vitro Hsp90 inhibition assays (DARTS, Surface Plasmon Resonance, co-immunoprecipitation, luciferase, Western blot, anti-proliferative, cytotoxicity and size exclusion chromatography) to characterize the effects of KU174 in prostate cancer cells. Pilot in vivo efficacy studies were also conducted with KU174 in PC3-MM2 xenograft studies.KU174 exhibits robust anti-proliferative and cytotoxic activity along with client protein degradation and disruption of Hsp90 native complexes without induction of a HSR. Furthermore, KU174 demonstrates direct binding to the Hsp90 protein and Hsp90 complexes in cancer cells. In addition, in pilot in-vivo proof-of-concept studies KU174 demonstrates efficacy at 75 mg/kg in a PC3-MM2 rat tumor model.Overall, these findings suggest C-terminal Hsp90 inhibitors have potential as therapeutic agents for the treatment of prostate cancer.Prostate cancer is generally recognized as a relatively heterogeneous disease lacking strong biological evidence to implicate specific oncogenesis, mutations, signaling pathways, or risk factors in tumorigenesis and/or resistance to therapy across patients. In 1952, Huggins and Hodges first reported susceptibility of prostate cancer to androgen withdrawal. Since that time, hormonal therapy has become a mainstay for prostate cancer treatment; however, despite dramatic initial clinical responses, virtually all patients ultimately fail androgen-targeted ablation. Experimental therapies in prostate cancer such as targeted agents, immunotherapy, and vaccine therapy exhibit limited efficacy and no improvement in survival [1]. Thus, a critical need for novel therapies to treat prostate cancer remains.One such approach is based on the development of small molecules that inhibit Hsp90 chaperone function which leads to the degradation of Hsp90 dependent oncogenic proteins, many of which are involved in a multitude of signaling cascades. Inhibitors of Hsp