Potentiation of temozolomide-induced cytotoxicity: a comparative study of the biological effects of poly(ADP-ribose) polymerase inhibitors

Abstract

Summary Four poly(ADP-ribose) polymerase (PADPRP) inhibitors [3-aminobenzamide, benzamide, 3,4-dihydro-5-methoxyisoquinolin-1(2H)-one (PD 128763) and 8-hydroxy-2-methylquinazolin-4(3H)-one (NU1025)] were compared with respect to their effects on a number of biological end points. The following parameters were assessed: their ability to inhibit the enzyme in permeabilised L1210 cells; their ability to potentiate the cytotoxicity of temozolomide (including the cytotoxicity of the compounds per se); their ability to increase net levels of temozolomide-induced DNA strand breaks and inhibit temozolomide-induced NAD depletion. PD 128763 and NU1025 were equipotent as PADPRP inhibitors, and 40-and 50-fold more potent than benzamide and 3-aminobenzamide respectively. All the compounds acted in a concentration-dependent manner to potentiate the cytotoxicity and increase DNA strand break levels in cells treated with temozolomide. There was an excellent correlation between the potency of the compounds as PADPRP inhibitors and their effects on cell survival and DNA repair. Temozolomide treatment caused a decrease in cellular NAD levels, and this was abolished by the PADPRP inhibitors. In conclusion, the new generation of PADPRP inhibitors are at least 50-fold more effective than 3-aminobenzamide as chemopotentiators, and can be used at micromolar rather than millimolar concentrations in intact cells.

Differential effects of the poly (ADP-ribose) polymerase (PARP) inhibitor NU1025 on topoisomerase I and II inhibitor cytotoxicity in L1210 cells in vitro

“…NU1025 was not cytotoxic per se at 200 µM (% survival for a 16-h exposure was 100 ± 12%), consistent with the results from the previous study by Boulton et al (1995). Exposure to the topoisomerase I and II inhibitors camptothecin and etoposide for 16 h induced a concentration-dependent decrease in L1210 cell survival ( Figure 1A and 1B).…”

“…Data, expressed as rad equivalents, from three independent experiments are given in Table 2. No DNA strand breakage was detected following exposure to 200 µM NU1025 alone (Figure 2A and 2B), consistent with the observation that exposure of cells to 1 mM NU1025 for 24 h had no effect on DNA strand-break levels (Boulton et al, 1995). Although exposure to an LC 50 concentration of camptothecin (15 nM) did not induce significant levels of DNA strand breaks, compared to control cells, treatment with 40 nM camptothecin (an LC 90 concentration) did produce a significant level of breaks ( Figure 2A, Table 2).…”

3-aminobenzamide and/or O6-benzylguanine evaluated as an adjuvant to temozolomide or BCNU treatment in cell lines of variable mismatch repair status and O6-alkylguanine-DNA alkyltransferase activity

“…While AGT depletion has been widely shown to potentiate the cytotoxicity of both methylating and bifunctional chloroethylating agents, studies investigating PARP inhibition and cytotoxicity have predominantly focused upon methylating agents such as dimethyl sulphate (Durkacz et al, 1980), N-methyl-N'-nitro-N-nitrosoguanidine (Nduka et al, 1980) and temozolomide (Boulton et al, 1995). Although it has been suggested that the enhancement of BCNU cytotoxicity by the nucleoside analogue tiazofurin is related to the inhibition of PARP activity , an additional study has indicated that the cytotoxicity of the bifunctional nitrosoureas is unaffected by PARP inhibition (Sebolt-Leopold and Scavone, 1992).…”

“…An effect on ADP(ribose) metabolism is most probable, given that 3-AB (1 mM) can completely inhibit a Potentiation of temozolomide by O6-BG and 3-AB SR Wedge et al 1034 50% reduction in cellular NAD produced by treatment with 2 mM temozolomide (Boulton et al, 1995). The association between DNA strand breakage and the inhibition of PARP with 3-AB, however, remains controversial (Boulton et al, 1995), and it is possible that the enhancement of temozolomide cytotoxicity by 3-AB could be related to the inhibition of acceptor protein ADP-(ribosyl)ation, particularly if such proteins regulate cell cycle progression or apoptosis in response to DNA damage (Kastan et al, 1991;Nosseri et al, 1994;Malcomson et al, 1995). The magnitude by which methylation and chloroethylation cytotoxicity was enhanced by 06-BG did not clearly correlate with AGT activity, although resistance to both agents can be multifactorial and dependent on factors other than at the level of DNA repair.…”

Potentiation of anti-cancer agent cytotoxicity by the potent poly(ADP-ribose) polymerase inhibitors NU1025 and NU1064

“…most of which has-e investigated the potentiation of monofunctional alkylatina agents and ionizing, radiation as these therapies are the most potent actixators of PARP. althoug!h some other agents have also been evaluated (reviewed in Griffin et al 1995).…”