Open Access Highly Accessed Research article

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

Jeffery D Eskew2, Takrima Sadikot2, Pedro Morales2, Alicia Duren1, Irene Dunwiddie2, Megan Swink2, Xiaoying Zhang2, Stacey Hembruff2, Alison Donnelly4, Roger A Rajewski3, Brian SJ Blagg4, Jacob R Manjarrez5, Robert L Matts5, Jeffrey M Holzbeierlein1 and George A Vielhauer12*

Author Affiliations

1 Department of Urology, The University of Kansas Medical Center, 3901 Rainbow Blvd, Kansas City, KS, 66160, USA

2 The University of Kansas Cancer Center, The University of Kansas Medical Center, 3901 Rainbow Blvd, Kansas City, KS, 66160, USA

3 Department of Pharmaceutical Chemistry, The University of Kansas, 2095 Constant Ave, Lawrence, KS, 66047, USA

4 Department of Medicinal Chemistry, The University of Kansas, 1251 Wescoe Hall Drive, Lawrence, KS, 66045, USA

5 Department of Biochemistry and Molecular Biology, Oklahoma State University, 246C Noble Research Center, Stillwater, OK, 74078, USA

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BMC Cancer 2011, 11:468  doi:10.1186/1471-2407-11-468

Published: 31 October 2011

Abstract

Background

The molecular chaperone, heat shock protein 90 (Hsp90) has been shown to be overexpressed in a number of cancers, including prostate cancer, making it an important target for drug discovery. Unfortunately, results with N-terminal inhibitors from initial clinical trials have been disappointing, as toxicity and resistance resulting from induction of the heat shock response (HSR) has led to both scheduling and administration concerns. Therefore, Hsp90 inhibitors that do not induce the heat shock response represent a promising new direction for the treatment of prostate cancer. Herein, the development of a C-terminal Hsp90 inhibitor, KU174, is described, which demonstrates anti-cancer activity in prostate cancer cells in the absence of a HSR and describe a novel approach to characterize Hsp90 inhibition in cancer cells.

Methods

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.

Results

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.

Conclusions

Overall, these findings suggest C-terminal Hsp90 inhibitors have potential as therapeutic agents for the treatment of prostate cancer.

Keywords:
Hsp90; prostate cancer; novobiocin; C-terminal inhibitors; N-terminal inhibitors