Alkylpurine–DNA–N-glycosylase confers resistance to temozolomide in xenograft models of glioblastoma multiforme and is associated with poor survival in patients
Sameer Agnihotri, … , Monika Hegi, Abhijit Guha
Sameer Agnihotri, … , Monika Hegi, Abhijit Guha
Published December 12, 2011
Citation Information: J Clin Invest. 2012;122(1):253-266. https://doi.org/10.1172/JCI59334.
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Research Article Oncology

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

Sameer Agnihotri, Aaron S. Gajadhar, Christian Ternamian, Thierry Gorlia, Kristin L. Diefes, Paul S. Mischel, Joanna Kelly, Gail McGown, Mary Thorncroft, Brett L. Carlson, Jann N. Sarkaria, Geoffrey P. Margison, Kenneth Aldape, Cynthia Hawkins, Monika Hegi, Abhijit Guha

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Figure 9

In large clinical trial datasets, APNG expression predicts poorer overall survival.

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In large clinical trial datasets, APNG expression predicts poorer overal...
Patient samples were analyzed on TMAs by IHC for APNG expression. (A) There was no statistical difference in overall survival with respect to APNG expression in a GBM patient cohort treated with surgery and RT only (pre-TMZ era). (B) In patients treated within the EORTC-NCIC clinical trial, there was a statistically significant decrease in overall survival in patients whose tumor exhibited nuclear APNG. (C) In the EORTC-NCIC subgroup containing patients with a methylated MGMT promoter, APNG-positive patients had poorer survival than did their APNG-negative counterparts, but the difference was not significant. (D) In the EORTC-NCIC subgroup with an unmethylated MGMT, there was a significant decrease in overall survival in APNG-positive patients.