Pifithrin-μ, an inhibitor of heat-shock protein 70, can increase the antitumor effects of hyperthermia against human prostate cancer cells.
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 p21(WAF1/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.
Department of Immunology, Shimane University Faculty of Medicine, Shimane, Japan ; Department of Radiation Oncology, Shimane University Faculty of Medicine, Shimane, Japan.
Kazumasa
K
Sekihara
Nanae
N
Harashima
Miki
M
Tongu
Yukihisa
Y
Tamaki
Nobue
N
Uchida
Taisuke
T
Inomata
Mamoru
M
Harada
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D019938:Cyclin D1 / Q000096:biosynthesis; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D018840:HSP70 Heat-Shock Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D006979:Hyperthermia, Induced; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000473:pathology / Q000628:therapy*; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis; D023041:Xenograft Model Antitumor Assays
D000970:Antineoplastic Agents; C530104:CCND1 protein, human; D018840:HSP70 Heat-Shock Proteins; C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; D019938:Cyclin D1