title: Temozolomide Resistance in Glioblastoma Cell Lines: Implication of MGMT, MMR, P-Glycoprotein and CD133 Expression.
abstract: BACKGROUND
  The use of temozolomide (TMZ) has improved the prognosis for glioblastoma multiforme patients. However, TMZ resistance may be one of the main reasons why treatment fails. Although this resistance has frequently been linked to the expression of O6-methylguanine-DNA methyltransferase (MGMT) it seems that this enzyme is not the only molecular mechanism that may account for the appearance of drug resistance in glioblastoma multiforme patients as the mismatch repair (MMR) complex, P-glycoprotein, and/or the presence of cancer stem cells may also be implicated.
  
  
  METHODS
  Four nervous system tumor cell lines were used to analyze the modulation of MGMT expression and MGMT promoter methylation by TMZ treatment. Furthermore, 5-aza-2'-deoxycytidine was used to demethylate the MGMT promoter and O(6)-benzylguanine to block GMT activity. In addition, MMR complex and P-glycoprotein expression were studied before and after TMZ exposure and correlated with MGMT expression. Finally, the effect of TMZ exposure on CD133 expression was analyzed.
  
  
  RESULTS
  Our results showed two clearly differentiated groups of tumor cells characterized by low (A172 and LN229) and high (SF268 and SK-N-SH) basal MGMT expression. Interestingly, cell lines with no MGMT expression and low TMZ IC50 showed a high MMR complex expression, whereas cell lines with high MGMT expression and high TMZ IC50 did not express the MMR complex. In addition, modulation of MGMT expression in A172 and LN229 cell lines was accompanied by a significant increase in the TMZ IC50, whereas no differences were observed in SF268 and SK-N-SH cell lines. In contrast, P-glycoprotein and CD133 was found to be unrelated to TMZ resistance in these cell lines.
  
  
  CONCLUSIONS
  These results may be relevant in understanding the phenomenon of TMZ resistance, especially in glioblastoma multiforme patients laking MGMT expression, and may also aid in the design of new therapeutic strategies to improve the efficacy of TMZ in glioblastoma multiforme patients.
authors.affiliation: Institute of Biopathology and Regenerative Medicine (IBIMER), Granada, Spain.
authors.forename: Gloria
authors.initials: G
authors.lastname: Perazzoli
authors.affiliation: Institute of Biopathology and Regenerative Medicine (IBIMER), Granada, Spain; Biosanitary Institute of Granada (ibs.GRANADA), SAS-Universidad de Granada, Granada, Spain.
authors.forename: Jose
authors.initials: J
authors.lastname: Prados
authors.affiliation: Department of Health Science, University of Jaén, Jaén, Spain.
authors.forename: Raul
authors.initials: R
authors.lastname: Ortiz
authors.affiliation: Department of Health Science, University of Jaén, Jaén, Spain.
authors.forename: Octavio
authors.initials: O
authors.lastname: Caba
authors.affiliation: Institute of Biopathology and Regenerative Medicine (IBIMER), Granada, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Cabeza
authors.affiliation: Cancer Epigenetics and Biology Program, Bellvitge Biomedical Research Institute, L'Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Maria
authors.initials: M
authors.lastname: Berdasco
authors.affiliation: Service of Medical Oncology, San Cecilio Hospital, Granada, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Gónzalez
authors.affiliation: Institute of Biopathology and Regenerative Medicine (IBIMER), Granada, Spain; Biosanitary Institute of Granada (ibs.GRANADA), SAS-Universidad de Granada, Granada, Spain.
authors.forename: Consolación
authors.initials: C
authors.lastname: Melguizo
mesh_terms: D000071916:AC133 Antigen; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D045744:Cell Line, Tumor; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics / Q000378:metabolism*; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000077209:Decitabine; D019008:Drug Resistance, Neoplasm; D044127:Epigenesis, Genetic; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005909:Glioblastoma / Q000188:drug therapy / Q000201:enzymology*; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism; D006147:Guanine / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D020128:Inhibitory Concentration 50; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000071916:AC133 Antigen; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D015703:Antigens, CD; D018906:Antineoplastic Agents, Alkylating; D006023:Glycoproteins; C097065:O(6)-benzyl-8-oxoguanine; C000606023:PROM1 protein, human; D010455:Peptides; D025521:Tumor Suppressor Proteins; D006147:Guanine; D000077209:Decitabine; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes; D001374:Azacitidine; D000077204:Temozolomide