The effect of 3-aminobenzamide on the frequency of X-ray- or neutron-induced chromosome aberrations in cycling or non-cycling human lymphocytes.

3-Aminobenzamide (3-AB) is a potent inhibitor of poly(ADP-ribose) synthesis in mammalian cells. It was found to cause a 2-fold increase in dicentric frequency following X-irradiation of 9-18 h PHA-stimulated human lymphocytes, while 3-AB by itself had no effect on aberration frequency. In contrast to previously reported data, however, our results indicate that 3-AB does not increase the frequency of aberrations following either neutron or X-ray exposure of unstimulated (G0) human lymphocytes. Although 3-AB incubation after X-ray exposure in G1 caused a large increase in dicentrics, there was no effect of 3-AB incubation following neutron exposure in G1. The implications of these experiments are presently uncertain, but they do, however, suggest the importance of cycling cells for 3-AB to exert its enhancement effect, presumably on some step of DNA repair. Furthermore, these data support the hypothesis that there are different mechanisms of chromosome aberration induction with fission neutrons and X-rays (at X-ray doses above 50 rad).