Preclinical pharmacology of the antitumor agent O-6-methylguanine in CDF1 mice.
O-6-methylguanine (O6-mG), a guanine analog recently shown to be a potent inhibitor of alkylguanine-DNA alkyltransferase, has been found to potentiate the antitumor activity of nitrosoureas, in particular, carmustine (BCNU), in resistant cell lines (HT-29 mer+) and is targeted for development as a modulating agent with chloroethyl nitrosoureas. A high-performance liquid chromatography (HPLC) assay of O6-mG in plasma has been developed using a microC18 reverse-phase column. O6-mG and the internal standard deoxyguanosine (dGuo) were eluted with a linear gradient of from 15% to 35% methanol in 0.5 M ammonium acetate (pH 6.5) at a flow rate of 1 ml/min. The assay was linear over a 4-log concentration range with a detection limit of 0.1 microgram/ml. The within-run and between-run coefficients of variation (CV) were found to be 8.1% and 9.3%, respectively. The pharmacokinetics (PK) of O6-mG were investigated in healthy CDF1 mice following separate i.v. and i.p. administrations. At 20 mg/kg i.v., plasma O6-mG gave a biexponential profile with a terminal half-life (t1/2) of 24 min and a total clearance (CLT) of 23.7 ml min-1 kg-1. Higher doses (40-80 mg/kg) revealed a fluctuating third phase, probably due to enterohepatic cycling. Dose-dependent kinetics as measured by CLT and area under the plasma-concentration curve (AUC) values were also seen. Following i.p. dosing, O6-mG was completely absorbed and available to the circulation. No acute toxicity was observed in the animals, except for mild sedation, a possible side effect of the 10% ethanol used in the formulation. Studies on the cellular metabolism of highly purified [3H]-O6-mG have shown that the compound is not anabolized by a human lymphoblastoid cell line (CEM). Biochemistry studies have shown that the parent molecule is inactivating the alkylguanine-DNA alkyltransferase (AGT), thus exerting its pharmacological effect.
Avramis
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VI
School of Pharmacy, University of Southern California, Childrens Hospital, Los Angeles 90027.
Chan
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KK
Solorzano
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MM
Chen
Z L
ZL
D000818:Animals; D001798:Blood Proteins / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004353:Drug Evaluation, Preclinical; D006147:Guanine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics; D006207:Half-Life; D006801:Humans; D007274:Injections, Intraperitoneal; D007275:Injections, Intravenous; D007945:Leukemia, Lymphoid / Q000378:metabolism / Q000473:pathology; D051379:Mice; D011485:Protein Binding; D051381:Rats; D014407:Tumor Cells, Cultured
D001798:Blood Proteins; D006147:Guanine; C008449:O-(6)-methylguanine