title: A MDR1 (ABCB1) gene single nucleotide polymorphism predicts outcome of temozolomide treatment in glioblastoma patients.
abstract: BACKGROUND
  Some patients with glioblastoma multiform do not respond to temozolomide even though they have aberrant promoter methylation of the DNA repair enzyme O(6)-methylguanine methyltransferase (MGMT). This suggests that additional factors hamper temozolomide cytotoxicity. We aimed to confirm first that temozolomide is a target for the multidrug resistance transporter MDR1/ABCB1 and second to investigate whether genetic variants of the MDR1 gene are associated with the survival of glioblastoma patients treated with temozolomide.
  
  
  METHODS
  Temozolomide-mediated cytotoxicity was determined by the colorimetric methyl-thiazol-tetrazolium assay in MDR-expressing and MDR-nonexpressing cell lines. Genotypes of three single nucleotide polymorphisms (SNPs) of the MDR1 gene (C1236T, G2677T, and C3435T), MDR1 mRNA expression levels, and the MGMT promoter methylation status were analyzed in 112 glioblastoma patients who had been treated either by surgery plus radiotherapy alone or by additional temozolomide chemotherapy.
  
  
  RESULTS
  In vitro analysis revealed that temozolomide-mediated cytotoxicity is dependent on MDR1 expression. Multivariate analysis of MDR1 genotypes showed that the C/C variant of the exon12 C1236T SNP is predictive for survival of patients treated with temozolomide. This effect was independent of the MGMT methylation status. Patients with the C/C genotype had a 2-year overall survival of 37% compared with 8% and 10% for patients with C/T and T/T genotypes, respectively (P=0.02). No influence was seen in the group of patients with radiotherapy only.
  
  
  CONCLUSIONS
  The genotype of the MDR1 exon12 C1236T SNP is a novel independent predictive factor for outcome of temozolomide treatment in glioblastoma patients.
authors.affiliation: Department of Medicine I, University Hospital C. G. Carus, Dresden, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Schaich
authors.forename: L
authors.initials: L
authors.lastname: Kestel
authors.forename: M
authors.initials: M
authors.lastname: Pfirrmann
authors.forename: K
authors.initials: K
authors.lastname: Robel
authors.forename: T
authors.initials: T
authors.lastname: Illmer
authors.forename: M
authors.initials: M
authors.lastname: Kramer
authors.forename: C
authors.initials: C
authors.lastname: Dill
authors.forename: G
authors.initials: G
authors.lastname: Ehninger
authors.forename: G
authors.initials: G
authors.lastname: Schackert
authors.forename: D
authors.initials: D
authors.lastname: Krex
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018906:Antineoplastic Agents, Alkylating / Q000627:therapeutic use; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000188:drug therapy* / Q000235:genetics / Q000401:mortality; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000627:therapeutic use; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D005787:Gene Frequency; D005838:Genotype; D005909:Glioblastoma / Q000175:diagnosis* / Q000188:drug therapy* / Q000235:genetics / Q000401:mortality; D006801:Humans; D020014:K562 Cells; D008297:Male; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide / Q000502:physiology; D011379:Prognosis; D000077204:Temozolomide; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018906:Antineoplastic Agents, Alkylating; D003606:Dacarbazine; D000077204:Temozolomide