Synergistic effects of irradiation and hyperthermia on established cell lines derived from maxillary carcinoma. Report II.

We studied in vitro the capability of radiation, hyperthermia, and their combination to inhibit growth of cell strains isolated from maxillary carcinoma and their radiation tolerant strains. Synergic effects of the combination were studied by investigating effects of hyperthermia and radiation on cell cycles with BrdU pulse labelling to establish optimal conditions for the combination. Growth of cell strains from maxillary carcinoma was remarkably inhibited by thermal treatment because of retarded cellular cycles. Cells at the S-phase were so sensitive to heat that their intake of BrdU was debilitated. Radiation increased the proportion of cells at the S-phase that poorly synthesized DNA. When combining radiation with hyperthermia, the heat killed cells at the S-phase, which was prolonged by radiation, and survivors showed retarded cellular cycles; that is, synergism was found.