Preferential tumor radiosensitization by analogs of nicotinamide and benzamide

The effects of a range of different analogs of nicotinamide and benzamide on the X ray response of the EMT-6 tumor in vivo was investigated. Using an in vivo/in vitro survival assay, sensitization was seen at a dose of 2 mmole/kg for all but one of the analogs tested. The enhancement ratios (ER's) ranged from 1.0 to 1.5. Of particular interest were nicotinamide and SR-4350 which gave large ER's (1.5 and 1.4 respectively) at doses which were only about 12% of the LD50 values. In one normal tissue studied (skin reaction) a large single dose of nicotinamide (8 mmole/kg) only gave an ER of 1.1. These results will be discussed with reference to the mechanisms involved and the clinical implications.