title: Effect of alternative temozolomide schedules on glioblastoma O(6)-methylguanine-DNA methyltransferase activity and survival.
abstract: BACKGROUND
  O(6)-methylguanine-DNA methyltransferase (MGMT) expression in glioblastoma correlates with temozolomide resistance. Dose-intense temozolomide schedules deplete MGMT activity in peripheral blood mononuclear cells; however, no published data exist evaluating the effect of temozolomide schedules on intracranial tumour MGMT activity.
  
  
  METHODS
  Human glioblastoma cells (GBM43) with an unmethylated MGMT promoter were implanted intracranially in immunodeficient rodents. Three weeks later, animals received temozolomide 200 mg m(-2) for 5 days (schedule A, standard dose) or 100 mg m(-2) for 21 days (schedule B, dose intense).
  
  
  RESULTS
  Tumour MGMT activity was depleted by day 6 in both treatment groups compared with baseline. O(6)-methylguanine-DNA methyltransferase activity returned to baseline by day 22 in the schedule A group, but remained suppressed in the schedule B group. By day 29, MGMT activity had returned to baseline in both groups. Mean tumour volume was significantly decreased compared with untreated controls with either schedule (P<0.01), although neither schedule was superior (P=0.60). Median survival was 64, 42, and 28 days for schedule A, schedule B, and no drug, respectively (P<0.001 A or B vs control, P=NS A vs B).
  
  
  CONCLUSIONS
  Dose-intense temozolomide prolongs tumour MGMT activity depletion compared with standard dosing, however, survival was not improved in this model.
authors.affiliation: Department of Radiation Oncology, Washington University in St Louis, 4921 Parkview Place, St Louis, MO 63110, USA.
authors.forename: C G
authors.initials: CG
authors.lastname: Robinson
authors.forename: J M
authors.initials: JM
authors.lastname: Palomo
authors.forename: G
authors.initials: G
authors.lastname: Rahmathulla
authors.forename: M
authors.initials: M
authors.lastname: McGraw
authors.forename: J
authors.initials: J
authors.lastname: Donze
authors.forename: L
authors.initials: L
authors.lastname: Liu
authors.forename: M A
authors.initials: MA
authors.lastname: Vogelbaum
mesh_terms: D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology / Q000627:therapeutic use*; D001932:Brain Neoplasms / Q000378:metabolism* / Q000401:mortality; D045744:Cell Line, Tumor; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D005909:Glioblastoma / Q000378:metabolism* / Q000401:mortality; D006801:Humans; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000096:biosynthesis*; D051381:Rats; D016019:Survival Analysis; D000077204:Temozolomide; D047368:Tumor Burden / Q000187:drug effects
chemical_list: D018906:Antineoplastic Agents, Alkylating; D003606:Dacarbazine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000077204:Temozolomide