Sublethal radiation damage repair and its inhibition by hyperthermia in two human melanoma cell lines of different radiosensitivities.

Two human melanoma tumour cell lines, one radiation resistant and one radiation sensitive, were studied for their capacity for repair of sublethal radiation damage (SLDR) and for hyperthermia inhibition of radiation damage. The most resistant cell line demonstrated a survival curve with a large shoulder and a large SLDR capacity. The sensitive cell line was characterized by an exponential survival curve and had less SLDR capacity than the resistant line. Hyperthermia could inhibit SLDR in both cell lines and complete inhibition was achieved at 43 degrees C for 30 min. Hyperthermia was more effective after than before irradiation. The SLDR inhibition was greater in the resistant cell line, showing that hyperthermia may be an effective way to overcome resistance in melanoma, especially when such resistance stems from an increased SLDR capacity. In addition, relatively mild thermal treatments, easily achievable clinically, were sufficient to inhibit SLDR in melanoma cells.