Effects of g Radiation and Hyperthermia on DNA Repair Synthesis and the Level of NAD + in Cultured Human Mononuclear Leukocytes

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Abstract
DNA repair was investigated, estimated by unscheduled DNA synthesis(UDS) and the cellular NAD+ pool, after exposing human mononuclear leukocytes to hyperthermia and .gamma. radiation separately and in combination. Apparently, .gamma. radiation induced a decline in UDS with increasing temperature through the temperature region studied (37-45.degree. C). At 42.5.degree. C the .gamma.-ray-induced UDS was reduced to about 70% of that at 37.degree. C. Following .gamma.-ray damage the NAD+ pool dropped to about 20% of control values. Without hyperthermic treatment the cells completely recovered to the original level within 5 h. Moderate hyperthermia (42.5.degree. C for 45 min) followed by .gamma.-ray damage altered the kinetics so that even after 8 h the NAD+ pool had recovered to only 70% of the original level. After heat treatment at 44.degree. C for 45 min prior to .gamma. radiation the cells did not recover at all, presumably because of the cytotoxic effects from the combined treatment. [Combined treatment with hyperthermia and ionizing radiation is becoming a useful tool in cancer therapy.].