Effect of a combination of mild-temperature hyperthermia and nicotinamide on the radiation response of experimental tumors

The effect of mild-temperature hyperthermia and nicotinamide individually o r combined on tumor radiosensitivity was investigated with SCK tumors grown s.c. in the right hind limbs of A/J mice. An i.p. injection of nicotinamid e at 50-250 mg/kg slightly enhanced the cell killing caused by 10-20 Gy of ionizing radiation as determined by the in vivo/in vitro tumor excision ass ay, Treatment of tumors with mild-temperature hyperthermia at 41.5 degrees C for 60 min prior to tumor irradiation was significantly more effective th an nicotinamide and the combination of nicotinamide and hyperthermia was fa r more effective than nicotinamide or hyperthermia alone in enhancing radia tion-induced cell killing. Radiation-induced tumor growth delay was enhance d by a factor of 1.2 by 50 mg/kg nicotinamide, 2.1 by hyperthermia, and 3.6 by the combination of nicotinamide and hyperthermia. Taking these results and those of our previous studies together, we conclude that mild-temperatu re hyperthermia increases tumor blood flow and oxygenation and that combini ng mild-temperature hyperthermia and nicotinamide is more effective than ei ther of these alone in increasing tumor radiosensitivity, (C) 2000 by Radia tion Research Society.