Cepharanthin enhances thermosensitivity without a resultant reduction in the thermotolerance of a murine mammary carcinoma.

Cepharanthin (Ce) is a biscoclaurine alkaloid extracted from Stephania cepharantha Hayata. The results of our previous in vitro study indicated that Ce reduces thermotolerance by enhancing thermosensitivity. In the present study, we investigated the in vitro and in vivo effects of Ce on thermosensitivity and thermotolerance using a murine mammary carcinoma, MCa, and C3H/HeN mice. Ce enhanced the thermosensitivity of MCa cells for heating at 44 degrees C not only in vitro but also in vivo. The in vivo enhancement ratio +/- SD of Ce at 100 mg/kg for heating at 44 degrees C was 1.3+/-0.3. The fractionated heat treatments at 44 degrees C for 30 and 60 min with an interval time of 0-6 days resulted in the development of remarkable thermotolerance and the expression of heat shock protein 70 in MCa tumors after the first heating. Ce at 100 mg/kg given immediately after the first heating increased the expression of heat shock protein 70 in MCa tumors, and did not reduce the development of thermotolerance. Ce given immediately before the first or second heating also did not inhibit the thermotolerance. The results of this study suggest that Ce enhances the thermosensitivity of MCa tumors as a thermosensitizer, but that this mild thermosensitizing property of Ce might be insufficient to conquer the remarkable thermotolerance in MCa tumors that develops after the first heating.