- Part I: Patients receive escalating doses of O6-benzylguanine (O6-BG) IV continuously for 49 hours until the dose that produces the target depletion of tumor O6-alkylguanine-DNA alkyltransferase (AGT) is determined. Patients undergo a craniotomy after completion of the O6-BG infusion. (closed to accrual 12/19/2000)