Estramustine phosphate enhances the effects of hyperthermia and induces the small heat shock protein HSP27 in the human prostate carcinoma cell line PC-3

The antimicrotubule drug estramustine phosphate (EMP) has been shown to sensitize prostate carcinoma cells to radiation via synchronization at the G2/M phase of the cell cycle. This synchronization may also render cells more sensitive to hyperthermia, providing a rationale for multimodal treatment approaches. We have investigated the effects of EMP and hyperthermia, as well as the regulation of heat shock proteins (HSP) in the PC-3 prostatic carcinoma cell line. Cells were incubated with four doses of EMP for 48 h followed by a 1-h hyperthermia treatment ranging from 41 degrees C to 44 degrees C. Cell cycle distribution at the end of the EMP incubation was investigated by flow cytometry. Cytotoxicity was assessed by colony formation assays. HSP accumulation was investigated by Western immunoblotting. Doses of 1, 5, 10 and 15 microM EMP synchronized 27, 28, 46, and 68% of PC-3 cells at G2/M. With 5, 10 and 15 microM, a sensitizing effect of EMP was assessed at hyperthermic temperatures of 42, 43 and 44 degrees C. EMP did not alter the expression of HSP72, but substantially induced the synthesis of HSP27 in PC-3 cells. Our data show that EMP sensitizes PC-3 cells to hyperthermia induced cytotoxicity. This observation supports the rationale for multimodal treatment approaches in locally advanced prostate cancer.