Plasma and cerebrospinal fluid pharmacokinetics of O-6-benzylguanine and analogues in nonhuman primates

O-6-Benzylguanine (BG) is a potent, specific inactivator of the DNA repair protein, O-6-alkylguanine-DNA alkyltransferase, that enhances the sensitivi ty of tumor cell lines and tumor xenografts to chloroethylnitrosoureas. To search for BG analogues with greater penetration into the cerebrospinal flu id (CSF), we evaluated plasma and CSF pharmacokinetics of BG, 8-aza-O-6-ben zylguanine (8-azaBG), O-6-benzyl-8-bromoguanine (8-BrBG), O-6-benzyl-8-oxog uanine (8-oxoBG), O-6-benzyl-8-trifluoromethylguanine (8-tfmBG), and O-6-be nzyl-2'-deoxyguanosine (B2dG) after i.v. administration of 200 mg/m(2) of d rug through an indwelling Ommaya reservoir in a nonhuman primate model. BG and its analogues were quantified in plasma and CSF using reverse-phase hig h-performance liquid chromatography assays. The plasma clearances of the fo ur 8-substituted BG analogues were similar (0.04-0.06 1h/kg), but half-live s ranged from <2 to >24 h, BG was converted to g-oxoBG, an equally potent O -6-alkylguanine-DNA alkyltransferase inactivator, and the elimination of 8- oxoBG was much slower than that of BG, As a result, the plasma area under t he curve of 8-oxoBG was 3.5-fold greater than that of BG, B2dG was metaboli zed to BG and 8-oxoBG, but this pathway accounted for only 20% of B2dG elim ination. The CSF penetration percentages (based on the ratio of AUG,,,: AUC (plasma)) for BG, 8-azaBG, 8-oxoBG, 8-tfmBG, 8-BrBG, and B2dG were 3.2, 0.1 8, 4.1, 1.4, <0.3, and 2.0%, respectively. The CSF penetration of BG and it s active metabolite 8-oxoBG is greater than the penetration of 8-azaBG, 8-B rBG, 8-tfmBG, and B2dG.