Influence of environmental pH on the interaction and repair of heat and radiation damage

Madcap-37 cells derived from a mouse mammary tumor were heated and/or irradiated in vitro at pH 7.4 to 7.5 or 6.5 to 6.7. An acidic medium increased cytotoxicty resulting from hyperthermic treatment, but only after extended heating (e.g., 100 min at 42.50C). Cell lethality resulting from treatment by the combined modalities was also increased when the environmental pH was decreased. The increase in lethality was a result of an acidic environment increasing hyperthermic radiosensitization. The recovery from heat (60 min at 42.50C) and radiation (500 rad) damage was independent of environmental pH if the irradiation preceded heating. However, an acidic environment prolonged the duration of hyperthermic radiosensitization when heat preceded radiation