New HSP90 selective inhibitors as therapeutic agents for prostate and bladder cancer.

285 Background: Hsp90 is a molecular chaperone responsible for folding many of the proteins directly associated with cancer progression and consequently, inhibition of the Hsp90 protein folding machinery results in a combinatorial attack on numerous oncogenic pathways. Hsp90 family consist of four isoforms; Hsp90α, Hsp90β, Grp94 and Trap-1. The development of Hsp90 isoform-selective inhibitors represent an alternative approach towards the treatment of cancer that may limit some of the detriments. We demonstrate novel Hsp90 inhibitors, on prostate and bladder cancer cells, which shows both potent antiproliferative effects and specific selectivity for Hsp90β. Methods: PC3MM2, LNCap-LN3, C4-2b, LAPC4 (prostate cancer) and T24, UC3 (bladder cancer) cancer cells were utilized. Cell Titer-Glo luminescent anti-proliferative assay was used to determine the IC50 numbers after 72h treatment. Trypan Blue Cytotoxicity assay was performed for 24h treatment with increasing concentrations of KUNB inhibitors. Effects of KUNB inhibitors on Hsp90’s client protein degradation were investigated by Western Blot. Results: KUNB31 manifested an IC50 of 3.00 µM against UC3 bladder cancer cells, UC3 cells were then evaluated via western blot analyses of known Hsp90α- and Hsp90β-dependent client proteins following treatment with KUNB31 for 24 hours. The data showed that, KUNB31 would not induce the heat shock response like 17AAG, and did cause Hsp90β related protein degradation (CXCR4). Moreover, Hsp27, PKM2, Her2, Hsf-1and Akt all showed degradation to different extent. KUNB105 exhibited potent anti-proliferative in both prostate and bladder cancer cells. IC50 number was determined as 1.24 µM for PC3MM2, 1.18 µM for LNCap-LN3, 1.03 µM for C4-2b, 2.56 µM for LAPC4, 0.20 µM for T24, and 0.30 µM for UC3 cancer cells. Conclusions: KUNB novel Hsp90β selective inhibitors, exhibit potent anti-proliferative and cytotoxic activity along with client protein degradation, without induction of HSR in prostate and bladder cancer cell lines. KUNB compound’s selective inhibition on Hsp90β isomers supports the development of Hsp90-selective inhibitors as a method to overcome the detriments associated with pan-inhibition in cancer treatment.