Further evidence for a different mode of action of caffeine and benzamide on mammalian cells

Post-treatment with 2 mM caffeine or 2 mM benzamide increased the lethality of MNNG (N-methyl-N'-nitro-N-nitrosoguanidine) treated V79 cells; in the presence of 50 microM deoxycytidine, the caffeine effect was eliminated whereas the benzamide effect remained the same. Combined treatment with caffeine/benzamide alone produced a large amount of cell lethality which was eliminated by 50 microM deoxycytidine. Benzamide produced a strong inhibition of the poly(ADP-ribose)polymerase activity present in cell-free extracts prepared from V79 cells with greater than 90% inhibition at 2 mM concentration; caffeine on the other hand did not produce any substantial inhibition of this activity in the 2-5 mM range. These results further substantiate our earlier hypothesis that the mode of action of caffeine and benzamide on eukaryotic cells containing DNA damage are not identical S.K. Das, C.C. Lau and A.B. Pardee (1984) Mutation Res., 131, 71-79].