Differential effect of benzamide on NAD+ content and the frequency of chromatid aberrations in X-irradiated L5178Y-R and L5178Y-S cells.

The effect of treatment with benzamide, an inhibitor of adenosine diphosphate (ADP) ribosyl polymerase (ADPRP) was studied in cells of two strains of L5178Y (LY) murine lymphoma exposed to ionizing radiation. Continuous 2 mmol/l benzamide (Bz) treatment increased the frequency of chromatid aberrations in the radiation sensitive LY-S strain, but not in the resistant LY-R strain. This result is in agreement with the previously found, enhanced by Bz, killing effect of roentgen irradiation in LY-S cells. Also, the decrease in the cellular NAD+ content in these cells after irradiation was more pronounced than in LY-R cells; this may indicate an increased ADPRP activity upon infliction of DNA damage, or a difference in poly(ADP-ribose) turnover.