Potentiation of the cytotoxicity of carboquone by flavone acetic acid combined with hyperthermia.

Flavone acetic acid (FAA) has shown the effectiveness of vasoactive drugs in the selective reduction of tumor blood flow. A FAA-mediated decrease in tumor blood flow may produce sufficient hypoxic conditions within the tumor. Carboquone (CQ), a naturally occurring prototype bioreductive alkylating agent like mitomycin C (MMC), has been shown to be selectively more cytotoxic toward hypoxic tumor cells. We have reported enhancement of the combined antitumor effects of MMC plus FAA and hyperthermia (HT). In this study, we examined the combined effects of FAA, CQ and HT. In vitro, although HT (43 degrees C, 60 min) reduced the colonogenicity to 0.58 in CQ (0.01 microg/ml) alone, the combined cytotoxicity of CQ and HT was not enhanced with exposure to FAA at a concentration of 100 microg/ml. In vivo, the tumor growth time, calculated as the time required to reach twice the initial tumor volume, for CQ (2 mg/kg) alone, FAA (150 mg/kg) alone, CQ+FAA, CQ+HT (43 degrees C, 15 min), FAA+HT and FAA+CQ+HT was 6.1, 5.1, 7.1, 8.0, 7.6 and 13.4 days, respectively. A significant enhancement of antitumor effects by trimodality therapy with CQ, FAA and HT was observed, when compared to the treatment with CQ and FAA (p < 0.05). The possible mechanisms of an increased antitumor response achieved with the combination of CQ, FAA and HT may be explained in the following way: the FAA-mediated decrease in tumor blood flow produced sufficient hypoxic conditions within the tumor, and these resulted in a significant increase of the antitumor effects of CQ and HT.