title: Pharmacokinetics of O6-benzylguanine and its active metabolite 8-oxo-O6-benzylguanine in plasma and cerebrospinal fluid after intrathecal administration of O6-benzylguanine in the nonhuman primate.
abstract: O6-Benzylguanine (O6BG) irreversibly inactivates the single-turnover DNA repair protein alkylguanine-alkyltransferase. Thus, O6BG increases tumor-cell sensitivity to alkylating agents such as carmustine, lomustine, procarbazine, and temozolomide. We investigated the pharmacokinetic behavior of O6BG and O6-benzyl-8-oxoguanine (8-oxo-O6BG) in cerebrospinal fluid (CSF) and plasma after intraventricular administration of O6BG in a nonhuman primate model. In our study, three animals received a single 1-mg dose of O6BG into the lateral ventricle. CSF from the 4th ventricle and plasma samples were collected after administration, and O6BG and 8-oxo-O6BG concentrations were measured by high-performance liquid chromatography. Four additional animals received 1 mg of O6BG via the intralumbar route weekly for 6 weeks to assess the feasibility and toxicity of this route of administration. The peak O6BG CSF concentration was 412+/-86 microM, the t1/2 was 0.52+/-0.02 h, the clearance was 0.22+/-0.01 ml/min, and the area under the concentration-time curve was 319+/-15 microM x h in 4th ventricular CSF. The peak CSF concentration of 8-oxo-O6BG in CSF was 1.9+/-0.4 microM, the t1/2 was 0.76+/-0.03 h, and the area under the concentration-time curve was 5.0+/-1.1 microM x h. Both O6BG and 8-oxo-O6BG were detected in the plasma 0.5-3 h after intraventricular O6BG administration. The plasma peak concentration of O6BG was 0.4 microM at 30 min, and the concentration was <0.1 microM by 3 h. The plasma concentration of 8-oxo-O6BG was 0.2 microM at 30 min and 0.6 microM at 3 h. The animals tolerated the single intraventricular dose and 6 weekly intralumbar doses of O6BG without toxicity. We concluded that intrathecal administration of O6BG is well tolerated in the nonhuman primate and seems to have a substantial pharmacokinetic advantage over systemic administration for meningeal tumors.
authors.affiliation: Texas Children's Cancer Center, Texas Children's Hospital, Baylor College of Medicine, Houston 77030, USA. sberg@bcm.tmc.edu
authors.forename: S L
authors.initials: SL
authors.lastname: Berg
authors.forename: D J
authors.initials: DJ
authors.lastname: Murry
authors.forename: C L
authors.initials: CL
authors.lastname: McCully
authors.forename: K
authors.initials: K
authors.lastname: Godwin
authors.forename: F M
authors.initials: FM
authors.lastname: Balis
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism / Q000493:pharmacokinetics* / Q000633:toxicity; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics / Q000633:toxicity; D007278:Injections, Spinal; D008253:Macaca mulatta; D008297:Male
chemical_list: C110997:8-oxo-O(6)-benzylguanine; D000970:Antineoplastic Agents; C064976:O(6)-benzylguanine; D006147:Guanine