title: Mismatch repair deficiency: a temozolomide resistance factor in medulloblastoma cell lines that is uncommon in primary medulloblastoma tumours.
abstract: BACKGROUND
  Tumours are responsive to temozolomide (TMZ) if they are deficient in O(6)-methylguanine-DNA methyltransferase (MGMT), and mismatch repair (MMR) proficient.
  
  
  METHODS
  The effect of TMZ on medulloblastoma (MB) cell killing was analysed with clonogenic survival assays. Expression of DNA repair genes and enzymes was investigated using microarrays, western blot, and immunohistochemistry. DNA sequencing and promoter methylation analysis were employed to investigate the cause of loss of the expression of MMR gene MLH1.
  
  
  RESULTS
  Temozolomide exhibited potent cytotoxic activity in D425Med (MGMT deficient, MLH1 proficient; IC(50)=1.7 μM), moderate activity against D341Med (MGMT proficient, MLH1 deficient), and DAOY MB cells (MGMT proficient, MLH1 proficient). MGMT inhibitor O(6)-benzylguanine sensitised DAOY, but not D341Med cells to TMZ. Of 12 MB cell lines, D341Med, D283Med, and 1580WÜ cells exhibited MMR deficiency due to MLH1 promoter hypermethylation. DNA sequencing of these cells provided no evidence for somatic genetic alterations in MLH1. Expression analyses of MMR and MGMT in MB revealed that all patient specimens (n=74; expression array, n=61; immunostaining, n=13) are most likely MMR proficient, whereas some tumours had low MGMT expression levels (according to expression array) or were totally MGMT deficient (3 out of 13 according to immunohistochemistry).
  
  
  CONCLUSIONS
  A subset of MB may respond to TMZ as some patient specimens are MGMT deficient, and tumours appear to be MMR proficient.
authors.affiliation: Department of Pediatric Hematology and Oncology, University Medical Center Hamburg-Eppendorf, Germany. a.von-bueren@uke.de
authors.forename: A O
authors.initials: AO
authors.lastname: von Bueren
authors.forename: M D
authors.initials: MD
authors.lastname: Bacolod
authors.forename: C
authors.initials: C
authors.lastname: Hagel
authors.forename: K
authors.initials: K
authors.lastname: Heinimann
authors.forename: A
authors.initials: A
authors.lastname: Fedier
authors.forename: U
authors.initials: U
authors.lastname: Kordes
authors.forename: T
authors.initials: T
authors.lastname: Pietsch
authors.forename: J
authors.initials: J
authors.lastname: Koster
authors.forename: M A
authors.initials: MA
authors.lastname: Grotzer
authors.forename: H S
authors.initials: HS
authors.lastname: Friedman
authors.forename: G
authors.initials: G
authors.lastname: Marra
authors.forename: M
authors.initials: M
authors.lastname: Kool
authors.forename: S
authors.initials: S
authors.lastname: Rutkowski
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000096:biosynthesis / Q000235:genetics*; D018906:Antineoplastic Agents, Alkylating / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D002528:Cerebellar Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D053843:DNA Mismatch Repair / Q000235:genetics*; D015254:DNA Modification Methylases / Q000096:biosynthesis / Q000235:genetics; D045643:DNA Repair Enzymes / Q000096:biosynthesis / Q000235:genetics; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000627:therapeutic use; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D008527:Medulloblastoma / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics*; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000378:metabolism; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018906:Antineoplastic Agents, Alkylating; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D025521:Tumor Suppressor Proteins; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000070957:MutL Protein Homolog 1; D045643:DNA Repair Enzymes; D000077204:Temozolomide