Comparison of single- versus double-bolus treatments of O(6)-benzylguanine for depletion of O(6)-methylguanine DNA methyltransferase (MGMT) activity in vivo: development of a novel fluorometric oligonucleotide assay for measurement of MGMT activity.
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 O(6)-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 O(6)-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.
Kreklau
E L
EL
Indiana University Cancer Center, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
Liu
N
N
Li
Z
Z
Cornetta
K
K
Erickson
L C
LC
D000818:Animals; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D005470:Fluorometry; D006147:Guanine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology*; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008297:Male; D051379:Mice; D016513:Mice, SCID; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009841:Oligonucleotides; D012038:Regeneration / Q000187:drug effects; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
D004791:Enzyme Inhibitors; D009841:Oligonucleotides; C064976:O(6)-benzylguanine; D006147:Guanine; D019853:O(6)-Methylguanine-DNA Methyltransferase