Synergistic antileukemic effect of 6-aminonicotinamide and 1,3-bis(2-chloroethyl)-1-nitrosourea on L1210 cells in vitro and in vivo.

A series of nicotinamide analogs were evaluated for their ability to inhibit L1210 cell poly(adenosine diphosphoribose) polymerase, and also for their ability to potentiate the cytocidal effects of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), nitrogen mustard, and gamma-irradiation. In L1210 cells growing in culture and in vivo. In vitro, nicotinamide, 5-methylnicotinamide, 6-aminonicotinamide, and benzamide effectively inhibited L1210 cell poly(adenosine diphosphoribose) polymerase; 1-methylnicotinamide, nicotinic acid, and benzoic acid did not. In culture, 6-aminonicotinamide potentiated the cytocidal effect of BCNU; however, it did not significantly potentiate the effects of nitrogen mustard or gamma-irradiation in vivo, both 6-aminonicotinamide and nicotinamide potentiated the cytocidal effect of BCNU; however, the concentrations of nicotinamide required for this effect were 10- to 20-fold higher than those of 6-aminonicotinamide. None of the analogs significantly potentiated the in vivo effect of nitrogen mustard or gamma-irradiation. Treatment of L1210-bearing mice with varying combinations of BCNU and 6-aminonicotinamide produced a synergistic increase in life span; in some cases, the combination led to the production of long term disease-free survivors.