Effects of 3-aminobenzamide on DNA synthesis and cell cycle progression in Chinese hamster ovary cells

3-Aminobenzamide (3AB), an inhibitor of poly(ADP-ribose) polymerase, is a potent inducer of sister chromatid exchanges (SCEs). Because of the possible relation between SCEs and DNA synthesis, the effects of 3AB on DNA synthesis and cell cycle progression in Chinese hamster ovary (CHO) cells were examined. Unlike all other SCE-inducing agents whose effects on DNA synthesis have been studied, short term exposures (30–120 min) of 3AB did not inhibit the overall rate of DNA synthesis and this result was independent of the amount of bromodeoxyuridine (BrdU) in the DNA. Longer exposure times (>24 h) did result in an extended S phase, but this was not due to an effect on the rate of DNA chain elongation. 3AB also delayed the entry of cells into S phase. The overall cell cycle delay was dose dependent, approaching 9 h after a 54 h exposure to 10 mM 3AB. Earlier reports that 3AB is neither mutagenic nor cytotoxic were confirmed. Thus 3AB acts to increase SCE frequency by a mechanism distinct from that which causes cytotoxicity and mutagenicity, and does not involve any inhibition in the rate of DNA chain growth.