Purpose: To elucidate the relationship between p53 functions and the interactive effects of the combined treatment with mild hyperthermia and mitomycin C.
Methods and materials: p53-deficient human non-small-cell lung cancer H1299 cells were transfected with a vector carrying a neomycin-resistant gene (neo) or together with a wild-type or mutant p53 gene. Sensitivities of these transfectants to mild hyperthermia at 42 degrees C, mitomycin C (0.05 microg/mL) at 37 degrees C, or the combination treatment were determined by colony formation assay. After these treatments, the induction of apoptosis, the changes in cell cycle distribution, and the accumulation of Hsp72 were examined.
Results: The combined treatment resulted in an enhanced cell killing effect in H1299 cells in a p53-independent manner, which was partially the result of an enhancement of heat-induced apoptosis. The treatment also caused a marked G(2)/M arrest in the neo and the mutant p53 cells, but not in the wild-type p53 cells. The subsequent release of G(2)/M arrest was accompanied with an increase in the sub-G(1) fractions. Mitomycin C did not affect the accumulation of Hsp72 induced by hyperthermia in H1299 cells regardless of their p53 gene status.
Conclusion: Our findings demonstrate a p53-independent mechanism for an interactively cytotoxic enhancement by combined treatment with mild hyperthermia and mitomycin C.