We conducted a two-phase clinical trial in patients with progressive malignant glioma (MG). The first phase of this trial was designed to determine the dose of O⁶-BG effective in producing complete depletion of tumor AGT activity for 48 hours. The second phase of the trial was designed to define the maximum tolerated dose (MTD) of a single dose of temozolomide when combined with O⁶-BG. In addition, plasma concentrations of O⁶-BG and O⁶-benzyl-8-oxoguanine were evaluated after O⁶-BG.

For our first phase of the clinical trial, patients were scheduled to undergo craniotomy for AGT determination after receiving a 1-hour O⁶-BG infusion at 120 mg/m² followed by a continuous infusion at an initial dose of 30 mg/m²/d for 48 hours. The dose of the continuous infusion of O⁶-BG escalated until tumor AGT was depleted. Once the O⁶-BG dose was established a separate group of patients was enrolled in the second phase of clinical trial, in which temozolomide, administered as a single dose at the end of the 1-hour O⁶-BG infusion, was escalated until the MTD was determined.

The O⁶-BG dose found to be effective in depleting tumor AGT activity at 48 hours was an IV bolus of 120 mg/m² over 1 hour followed by a continuous infusion of 30 mg/m²/d for 48 hours. On enrolling 38 patients in six dose levels of temozolomide, the MTD was established at 472 mg/m² with dose-limiting toxicities limited to myelosuppression.

This study provides the foundation for a phase II trial of O⁶-BG plus temozolomide in temozolomide-resistant MG.