Poly(ADP-ribose) polymerase-independent potentiation of nitrosourea cytotoxicity by 3-aminobenzamide in human malignant glioma cells

Poly(ADP-ribose) polymerase is a zinc-finger DNA-binding protein that detec ts specifically DNA strand breaks generated by genotoxic agents and is thou ght to be involved in DNA repair. Here, we examined the effects of 3-aminob enzamide, a poly(ADP-ribose) polymerase inhibitor, on the chemosensitivity of human malignant glioma cells. 3-Aminobenzamide selectively potentiated t he cytotoxicity of the nitrosoureas, nimustine, carmustine and lomustine in 10 of 12 human malignant glioma cell lines. In contrast, 3-aminobenzamide did not modulate the cytotoxic effects of doxorubicine, teniposide, vincris tine, camptothecin or cytarabine. The nitrosoureas did not induce poly(ADP- ribose) polymerase activity in the glioma cells. Ectopic expression of trun cated poly(ADP-ribose) polymerase containing the poly(ADP-ribose) polymeras e DNA-binding domain, which acts as a dominant-negative mutant, in LN-18 or LN-229 cells did not alter the 3-aminobenzamide effect on nitrosourea-medi ated cytotoxicity. Thus, 3-aminobenzamide may target another nicotinamide a denine dinucleotide (NAD)-requiring enzyme, but not poly(ADP-ribose) polyme rase, when enhancing nitrosourea cytotoxicity in human malignant glioma cel ls. Carmustine cytotoxicity was associated with a G2/M arrest. Coexposure t o carmustine and 3-aminobenzamide overcame this G2/M arrest in T98G cells, which are sensitized to carmustine by 3-aminobenzamide, but not in U251MG c ells, which are refractory to 3-aminobenzamide-mediated sensitization to ca rmustine. Thus, 3-aminobenzamide-mediated sensitization to carmustine cytot oxicity may result from interference with the stable G2/M arrest response t o carmustine in human glioma cells. (C) 2000 Elsevier Science B.V. All righ ts reserved.