title: O6-methylguanine-DNA methyltransferase, O6-benzylguanine, and resistance to clinical alkylators in pediatric primary brain tumor cell lines.
abstract: OBJECTIVE
  Primary brain tumors are the leading cause of cancer death in children. Our purpose is (a) to assess the contribution of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) to the resistance of pediatric brain tumor cell lines to clinical alkylating agents and (b) to evaluate variables for maximal potentiation of cell killing by the MGMT inhibitor O6-benzylguanine, currently in clinical trials. Few such data for pediatric glioma lines, particularly those from low-grade tumors, are currently available.
  
  
  METHODS
  We used clonogenic assays of proliferative survival to quantitate cytoxicity of the chloroethylating agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and the methylating agent temozolomide in 11 glioma and five medulloblastoma lines. Twelve lines are newly established and characterized here, nine of them from low-grade gliomas including pilocytic astrocytomas.
  
  
  RESULTS
  (a) MGMT is a major determinant of BCNU resistance and the predominant determinant of temozolomide resistance in both our glioma and medulloblastoma lines. On average, O(6)-benzylguanine reduced LD10 for BCNU and temozolomide, 2.6- and 26-fold, respectively, in 15 MGMT-expressing lines. (b) O6-Benzylguanine reduced DT (the threshold dose for killing) for BCNU and temozolomide, 3.3- and 138-fold, respectively. DT was decreased from levels higher than, to levels below, clinically achievable plasma doses for both alkylators. (c) Maximal potentiation by O6-benzylguanine required complete and prolonged suppression of MGMT.
  
  
  CONCLUSIONS
  Our results support the use of O6-benzylguanine to achieve full benefit of alkylating agents, particularly temozolomide, in the chemotherapy of pediatric brain tumors.
authors.affiliation: Division of Neurosurgery, Department of Surgery and Hematology/Oncology, Children's Hospital and Regional Medical Center, Seattle, Washington 98105, USA. michael.bobola@seattlechildrens.org
authors.forename: Michael S
authors.initials: MS
authors.lastname: Bobola
authors.forename: John R
authors.initials: JR
authors.lastname: Silber
authors.forename: Richard G
authors.initials: RG
authors.lastname: Ellenbogen
authors.forename: J Russell
authors.initials: JR
authors.lastname: Geyer
authors.forename: A
authors.initials: A
authors.lastname: Blank
authors.forename: Ryan D
authors.initials: RD
authors.lastname: Goff
mesh_terms: D000293:Adolescent; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D001921:Brain / Q000201:enzymology / Q000473:pathology; D002330:Carmustine / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D002648:Child; D002675:Child, Preschool; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D006801:Humans; D008297:Male; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000077204:Temozolomide; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D018906:Antineoplastic Agents, Alkylating; D004791:Enzyme Inhibitors; C064976:O(6)-benzylguanine; D006147:Guanine; D003606:Dacarbazine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D002330:Carmustine; D000077204:Temozolomide