Correlation of enhanced 6-mercaptopurine cytotoxicity with increased phosphoribosylpyrophosphate levels in Chinese hamster ovary cells treated with 3-aminobenzamide.
3-Aminobenzamide (3AB) has been used widely to inhibit the nuclear enzyme poly(ADP-ribose) polymerase (EC 2.4.2.30) and study the involvement of poly(ADP-ribose) synthesis in DNA repair and other cellular functions. 3AB (3 mM) potentiates the cytotoxicity of 6-mercaptopurine (MP) and azathioprine in CHO-K1 cells with dose enhancement factors at 10% survival of 30-fold. In synchronized cells, 3AB is required during G1 and early S phase to obtain potentiation of MP cytotoxicity. There is a small but significant depletion of cellular NAD in MP-treated cells. As demonstrated by flow cytometric analysis, 20-40 microM MP causes an accumulation of cells in early S phase of the cell cycle. 3AB (3 mM) has no effect on cell cycle distribution; however, in the presence of MP, a similar accumulation is seen by 2-5 microM MP. 3AB and MP per se have no effect on phosphoribosylpyrophosphate levels, but coincubation causes a 30-fold increase in phosphoribosylpyrophosphate levels, reaching a maximum by 1.5 microM MP and declining to basal levels by 10 microM MP. There was a good correlation between the 3AB dose-dependent increase in cell killing and rise in phosphoribosylpyrophosphate levels.
Cancer Research Unit, University of Newcastle upon Tyne, Medical School, United Kingdom.
K
K
Moses
E
E
Willmore
A L
AL
Harris
B W
BW
Durkacz
D000818:Animals; D001379:Azathioprine / Q000633:toxicity; D001549:Benzamides / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004357:Drug Synergism; D005434:Flow Cytometry; D066298:In Vitro Techniques; D015122:Mercaptopurine / Q000633:toxicity*; D009243:NAD / Q000378:metabolism; D010428:Pentosephosphates / Q000378:metabolism*; D010754:Phosphoribosyl Pyrophosphate / Q000378:metabolism*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors
D001549:Benzamides; D010428:Pentosephosphates; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D009243:NAD; D010754:Phosphoribosyl Pyrophosphate; C025160:3-aminobenzamide; D015122:Mercaptopurine; D001379:Azathioprine