Effects of hyperthermia and radiation in two L5178Y cell lines with different efficiencies of DNA repair

L5178Y-R and L5178Y-S cells show inverse cross-sensitivity to X-rays and UV light. Recovery of cells after exposure to X-rays, DNA single-strand break rejoining, and excision repair are more efficient in L5178Y-R than in L5178Y-S cells. Caffeine-inhibitable, postreplication repair of UV-induced damage is present in L5178Y-S but not in L5178Y-R cells. Exposure to heat (41 degrees C) for up to 300 minutes did not affect survival of either cell line. Heating time-survival relationship for 43 degrees C was exponential for L5178Y-R cells (D0.9.1 min), whereas that for L5178Y-S was sigmoid (D0.7.8 min, n.2.5). Sparing effect due to heating fractionation (2X15 min at 43 degrees C separated by different intervals at 37 degrees C, vs. 30 min at 43 degrees C) was much more pronounced in L5178Y-S than in L5178Y-R cells (relative survival 8 and 2, for a 30-min interval, respectively). Preheating at 41 degrees C (120 min) had little effect on X-ray sensitivity of either cell line. Preheating at 43 degrees C (30 min) increased X-ray sensitivity of both cell lines (thermal enhancement ratios: 2.1 and 1.8 for L5178Y-R and L5178Y-S cells, respectively)