Pifithrin-μ, an Inhibitor of Heat-Shock Protein 70, Can Increase the Antitumor Effects of Hyperthermia Against Human Prostate Cancer Cells

Abstract

Hyperthermia (HT) improves the efficacy of anti-cancer radiotherapy and chemotherapy. However, HT also inevitably evokes stress responses and increases the expression of heat-shock proteins (HSPs) in cancer cells. Among the HSPs, HSP70 is known as a pro-survival protein. In this study, we investigated the sensitizing effect of pifithrin (PFT)-μ, a small molecule inhibitor of HSP70, when three human prostate cancer cell lines (LNCaP, PC-3, and DU-145) were treated with HT (43°C for 2 h). All cell lines constitutively expressed HSP70, and HT further increased its expression in LNCaP and DU-145. Knockdown of HSP70 with RNA interference decreased the viability and colony-forming ability of cancer cells. PFT-μ decreased the viabilities of all cell lines at one-tenth the dose of Quercetin, a well-known HSP inhibitor. The combination therapy with suboptimal doses of PFT-μ and HT decreased the viability of cancer cells most effectively when PFT-μ was added immediately before HT, and this combination effect was abolished by pre-knockdown of HSP70, suggesting that the effect was mediated via HSP70 inhibition. The combination therapy induced cell death, partially caspase-dependent, and decreased proliferating cancer cells, with decreased expression of c-Myc and cyclin D1 and increased expression of p21WAF1/Cip, indicating arrest of cell growth. Additionally, the combination therapy significantly decreased the colony-forming ability of cancer cells compared to therapy with either alone. Furthermore, in a xenograft mouse model, the combination therapy significantly inhibited PC-3 tumor growth. These findings suggest that PFT-μ can effectively enhance HT-induced antitumor effects via HSP70 inhibition by inducing cell death and arrest of cell growth, and that PFT-μ is a promising agent for use in combination with HT to treat prostate cancer.

Sensitizing tumor cells to radiation by targeting the heat shock response

“…One possible mechanism might be a decrease of the radioresistant S-phase. In line with our data, the Hsp70 inhibitors, VER-155008 and pifithrin-μ have been found to exert identical effects on the cell cycle distribution [27,29,30].…”

Novel Improved Synthesis of HSP70 Inhibitor, Pifithrin-μ. In Vitro Synergy Quantification of Pifithrin-μ Combined with Pt Drugs in Prostate and Colorectal Cancer Cells

“…There are no previous reports in the literature of pifithrin-μ in combination with cisplatin against prostate cancer cells. Interestingly, the HSP70 inhibitor pifithrin-μ has been previously shown to increase the antitumor effects of hyperthermia against LNCaP, PC-3, and DU-145 prostate cancer cells [16].…”

Mechanism of dihydroartemisinin-induced apoptosis in prostate cancer PC3 cells: An iTRAQ-based proteomic analysis

“…In the present study, DHA significantly decreased HSP70 expression and induced apoptosis in PC3 cells. Although the mechanism of apoptosis induced by DHA is poorly understood, several lines of evidence have shown inhibition of HSP70 expression results in apoptosis of cancer cells, and/or sensitizes cells to anticancer therapy in prostate cancer lines PC3, PC3M, DU145, LNCaP, JCA-1, and 22RV1 [87][88][89][90][91][92][93][94][95]. Our protein interaction network analysis suggests that HSP70 should function as both a chaperone and a modulator of cell signaling to participate in several biological processes in response to the cytotoxicity of DHA in PC3 cells.…”