Enhancement of N-methyl-N'-nitro-N-nitrosoguanidine-induced DNA amplification in a Simian virus 40-transformed Chinese hamster cell line by 3-aminobenzamide.

A Simian virus 40-transformed Chinese hamster cell line (CO 60) amplifies integrated viral DNA sequences as a response to treatment with a variety of carcinogens. To study a possible involvement of poly(ADP-ribose) synthesis, DNA amplification was induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), an alkylating carcinogen that strongly stimulates poly(ADP-ribose) synthesis. In the presence of 3-aminobenzamide (3AB) (2 mM), a competitive inhibitor of poly(ADP-ribose) polymerase, MNNG-induced amplification was increased two to six times the level induced by MNNG alone. Concomitantly, 3AB reduced cellular poly(ADP-ribose) levels and increased MNNG-induced cytotoxicity, as expected. The effect of 3AB on MNNG-induced amplification depended both on the concentration of 3AB and the duration of its presence after MNNG treatment. By contrast, 3-aminobenzoic acid, a noninhibitory structural analogue of 3AB, had no influence on amplification induced by MNNG. These data strongly suggest an involvement of poly(ADP-ribose) in the process of DNA amplification, as it is shown that inhibition of carcinogen-stimulated poly(ADP-ribose) synthesis by 3AB is correlated with an enhancement of inducible DNA amplification in this cell line.