The effects of combined treatments with low hyperthermia and bleomycin on survivals of murine L cells.

ABSTRACT

Modification effects of low hyperthermia (40 degrees C) on cellular chemosensitivity to bleomycin (BLM), and of BLM on thermosensitivity (40 degrees C) were investigated in cultured murine L cells with simultaneous or sequential treatments of these two agents. The heating of L cells at 40 degrees C up to 6 hours resulted in no remarkable lethal damage. Treatment with low hyperthermia followed by BLM for 4 hours showed no more than additive effect. However, a significant chemical (BLM) enhancement effect on the cellular thermosensitivity was observed by the treatment with BLM for 4 hours prior to the low hyperthermia at 40 degrees C. No appreciable thermal enhancement effect on the cellular chemosensitivity to BLM was shown by preheating at 40 degrees C for 3 hours, while post-heating at 40 degrees C showed a significant thermal enhancement effect as well as in the simultaneous treatments. The cell phase response to BLM was levelled in the clinical range of the doses. It is possible that the repair of sublethal damage (SLDR) from treatment with BLM was inhibited by 40 degrees C post-heating and this SLDR was completed at 3 hours of the interval at 37 degrees C between BLM and 40 degrees C heating.