COMPARISON OF THERMORADIOSENSITIZATION IN 2 HUMAN-MELANOMA CELL-LINESAND ONE FIBROBLAST CELL-LINE BY CONCURRENT MILD HYPERTHERMIA AND LOW-DOSE-RATE IRRADIATION

Two human melanoma cell lines, one radioresistant (SK-MEL-3) and one r adiosensitive (HT-144), and a normal human fibroblast line (AG1522) we re evaluated for thermoradiosensitization of low-dose-rate irradiation by concurrent mild hyperthermia (39-41 degrees C). None of the cell l ines expressed chronic thermotolerance during heating at 39-41 degrees C. The SK-MEL-3 cells were the most heat sensitive, while AG1522 and HT-144 cells had the same sensitivity at 39 and 40 degrees C but HT-14 4 cells were more sensitive at 41 degrees C. All cell lines expressed thermal enhancement of radiosensitivity with heating during irradiatio n which increased with heating temperature. The SK-MEL-3 cells, which were the most resistant to radiation and demonstrated the greatest rep air of sublethal damage (SLD) during low-dose-rate irradiation, had th e greatest thermal enhancement of radiosensitivity, while the HT144 ce lls, which were the most sensitive and expressed little repair of SLD during low-dose-rate irradiation, had the smallest thermal enhancement of radiosensitivity. These data show that concurrent mild hyperthermi a during low-dose-rate irradiation may be most efficacious in radiatio n-resistant tumor cells which express resistance through an enhanced c apacity for repair of SLD.