title: Alkylpurine-DNA-N-glycosylase confers resistance to temozolomide in xenograft models of glioblastoma multiforme and is associated with poor survival in patients.
abstract: Glioblastoma multiforme (GBM) is the most common and lethal of all gliomas. The current standard of care includes surgery followed by concomitant radiation and chemotherapy with the DNA alkylating agent temozolomide (TMZ). O⁶-methylguanine-DNA methyltransferase (MGMT) repairs the most cytotoxic of lesions generated by TMZ, O⁶-methylguanine. Methylation of the MGMT promoter in GBM correlates with increased therapeutic sensitivity to alkylating agent therapy. However, several aspects of TMZ sensitivity are not explained by MGMT promoter methylation. Here, we investigated our hypothesis that the base excision repair enzyme alkylpurine-DNA-N-glycosylase (APNG), which repairs the cytotoxic lesions N³-methyladenine and N⁷-methylguanine, may contribute to TMZ resistance. Silencing of APNG in established and primary TMZ-resistant GBM cell lines endogenously expressing MGMT and APNG attenuated repair of TMZ-induced DNA damage and enhanced apoptosis. Reintroducing expression of APNG in TMZ-sensitive GBM lines conferred resistance to TMZ in vitro and in orthotopic xenograft mouse models. In addition, resistance was enhanced with coexpression of MGMT. Evaluation of APNG protein levels in several clinical datasets demonstrated that in patients, high nuclear APNG expression correlated with poorer overall survival compared with patients lacking APNG expression. Loss of APNG expression in a subset of patients was also associated with increased APNG promoter methylation. Collectively, our data demonstrate that APNG contributes to TMZ resistance in GBM and may be useful in the diagnosis and treatment of the disease.
authors.affiliation: Arthur and Sonia Labatt Brain Tumour Research Centre, Hospital for Sick Children Research Institute, University of Toronto, Toronto, Ontario, Canada. sameer.agnihotri@utoronto.ca
authors.forename: Sameer
authors.initials: S
authors.lastname: Agnihotri
authors.forename: Aaron S
authors.initials: AS
authors.lastname: Gajadhar
authors.forename: Christian
authors.initials: C
authors.lastname: Ternamian
authors.forename: Thierry
authors.initials: T
authors.lastname: Gorlia
authors.forename: Kristin L
authors.initials: KL
authors.lastname: Diefes
authors.forename: Paul S
authors.initials: PS
authors.lastname: Mischel
authors.forename: Joanna
authors.initials: J
authors.lastname: Kelly
authors.forename: Gail
authors.initials: G
authors.lastname: McGown
authors.forename: Mary
authors.initials: M
authors.lastname: Thorncroft
authors.forename: Brett L
authors.initials: BL
authors.lastname: Carlson
authors.forename: Jann N
authors.initials: JN
authors.lastname: Sarkaria
authors.forename: Geoffrey P
authors.initials: GP
authors.lastname: Margison
authors.forename: Kenneth
authors.initials: K
authors.lastname: Aldape
authors.forename: Cynthia
authors.initials: C
authors.lastname: Hawkins
authors.forename: Monika
authors.initials: M
authors.lastname: Hegi
authors.forename: Abhijit
authors.initials: A
authors.lastname: Guha
mesh_terms: D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D045744:Cell Line, Tumor; D045647:DNA Glycosylases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015254:DNA Modification Methylases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D005909:Glioblastoma / Q000188:drug therapy* / Q000201:enzymology*; D006801:Humans; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D034741:RNA, Small Interfering / Q000235:genetics; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D018906:Antineoplastic Agents, Alkylating; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045647:DNA Glycosylases; C076131:DNA-3-methyladenine glycosidase II; D045643:DNA Repair Enzymes; D000077204:Temozolomide