Effect of Combination of Anticancer Agents and Nitroimidazoles on the Survival of Human Hepatocellular Carcinoma Cells under Hypoxic Conditions

Purpose: In a previous study, we have shown that anticancer agents inhibiting topoisomerases improve survival of tumor cells under hypoxic condition. In the present study, we evaluated whether and how cell survival effect of the anticancer agents under hypoxic conditions could be eliminated by the addition of nitroimidazoles, a class of bioreductive agents. Methods: Human hepatocellular carcinoma cells (HepG2) were incubated with different combinations of pimonidazole(1∼1,000μg/ml) and doxorubicin (0.1 or 1μg/ml) concentrations under different O₂ concentrations [1, 3, 5, 10 and 21 O₂]. Then cell numbers, glucose concentrations and lactic acid concentrations in the medium were measured, and DNA fragmentation assay was performed. Finally, different combinations of nitroimidazoles, such as pimonidazole, misonidazole, etanidazole, tinidazole, metronidazole, ornidazole or dimetridazole, and anticancer agents, such as doxorubicin, campothecin, epirubicin, dactinomycin, etoposide or mitomycin C was added to the cell culture medium under hypoxic conditions (1% O₂). Results: Pimonidazole at a concentration of 100μg/ml eliminated cell survival effect of doxorubicin at the concentrations of 0.1 and 1μg/ml under hypoxic condition (1% O₂) by promoting apoptosis. Almost all the cells died even after 24 hours of incubation for all the oxygen concentrations at a combination of 100μg/ml pimonidazole and 1μg/ml doxorubicin. Finally, pimonidazole at a concentration of 100μg/ml, and misonidazole or etanidazole at a concentration of 1,000μg/ml eliminated cell survival effect of all the anticancer agents tested under hypoxic condition. Conclusion: Combination therapy of doxorubicin (adriamycin) with pimonidazole can maximize dororubicin efficacy by eliminating cell survival effect of doxorubicin under hypoxic conditions in treating solid tumors, such as breast cancer.