Vol. 297, Issue 2, 524-530, May 2001

Comparison of Single- Versus Double-Bolus Treatments of O⁶-Benzylguanine for Depletion of O⁶-Methylguanine DNA Methyltransferase (MGMT) Activity in Vivo: Development of a Novel Fluorometric Oligonucleotide Assay for Measurement of Mgmt Activity

Emiko L. Kreklau , Naili Liu , Zhaohua Li, Kenneth Cornetta and Leonard C. Erickson

Indiana University Cancer Center (E.L.K., N.L., K.C., L.C.E.), Department of Pharmacology and Toxicology (E.L.K., N.L., L.C.E.), Herman B Wells Center for Pediatric Research, Department of Pediatrics (Z.L.), and Department of Medicine (K.C.), Indiana University School of Medicine, Indianapolis, Indiana

Previous studies have demonstrated that optimal reversal of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) resistance requires complete inactivation of the DNA repair protein O⁶-methylguanine DNA methyltransferase (MGMT) for at least 24 h following BCNU administration. In preparation for clinical trials at this institution, this study was undertaken to compare the efficacy of a conventional single-bolus dose versus double-bolus dose treatments with O⁶-benzylguanine (BG) in depleting MGMT activity in vivo. In xenograft human glioma SF767 tumors, a single 30-mg/kg bolus dose of BG completely inhibited MGMT activity for at least 8 h, but approximately 50% of the basal MGMT activity recovered within 24 h. To sustain the MGMT depletion for 24 h, a second bolus injection of BG at escalating doses was administered 8 h after the first dose. Second bolus doses of 5, 10, and 15 mg/kg BG attenuated the MGMT recovery in a dose-dependent manner compared with the single 30-mg/kg BG dose alone. When the 15-mg/kg BG dose was administered 8 h after the 30-mg/kg initial dose, MGMT activity was completely inactivated in the tumor xenografts for 24 h. This double-bolus BG treatment also depleted MGMT activity in normal murine tissues, including the liver, kidney, lung, brain, spleen, and bone marrow; and the kinetics of MGMT recovery varied among these tissues. When combined with BCNU treatment, the double-bolus BG treatment would be expected to produce greater antitumor activity in future trials than the conventional single-bolus BG treatment.