Effects of hyperthermia at 42.DEG.C on DNA lesion and cell inactivation caused by X-ray.

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Abstract
The hyperthermic modification of radiation effect on cell inactivation should be important role for cancer therapy. This work has been done to obtain the DNA-scision and -repair relevant to the cell death and to recovery of clonogenesity after preirradiation heating at 42°C where heat effect on cell death has not been severe. Radiation inactivation of human melanoma cultured cells (HMV-I) has been synergetically enhanced by the preirradiation heating at 42°C. The DNA lesion has been detected by the alkaline elution method. The amount of initial lesion for cells heated before irradiation seemed to be less than those for X-ray alone irradiated cells. This result may be relevant to the crosslinking or aggregation introduced in DNA strand after the heat treatment. Recovery capacity of cell clonogenic damage after irradiation was considerably reduced by post-irradiation heat treatment. Time course of DNA damage repair after irradiation was similar to that of recovery of clonogenesity. These results indicate that mild hyperthermic treatment inhibit the repair of DNA damage caused by irradiation.