Novel MSH6 Mutations in Treatment-Naïve Glioblastoma and Anaplastic Oligodendroglioma Contribute to Temozolomide Resistance Independently of MGMT Promoter Methylation

Abstract

Purpose: The current standard of care for glioblastoma (GBM) involves a combination of surgery, radiotherapy, and temozolomide chemotherapy, but this regimen fails to achieve long-term tumor control. Resistance to temozolomide is largely mediated by expression of the DNA repair enzyme MGMT; however, emerging evidence suggests that inactivation of MSH6 and other mismatch repair proteins plays an important role in temozolomide resistance. Here, we investigate endogenous MSH6 mutations in GBM, anaplastic oligodendroglial tumor tissue, and corresponding brain tumor-initiating cell lines (BTIC).Experimental Design: MSH6 sequence and MGMT promoter methylation were determined in human tumor samples and BTICs. Sensitivity to temozolomide was evaluated in vitro using BTICs in the absence and presence of O 6 -benzylguanine to deplete MGMT. The influence of MGMT and MSH6 status on in vivo sensitivity to temozolomide was evaluated using intracranial BTIC xenografts. Results: We identified 11 previously unreported mutations in MSH6 in nine different glioma samples and six paired BTIC lines from adult patients. In addition, MSH6 mutations were documented in three oligodendrogliomas and two treatment-na€ ve gliomas, both previously unreported findings. These mutations were found to influence the sensitivity of BTICs to temozolomide both in vitro and in vivo, independent of MGMT promoter methylation status.Conclusions: These data demonstrate that endogenous MSH6 mutations may be present before alkylator therapy and occur in at least two histologic subtypes of adult glial neoplasms, with this report serving as the first to note these mutations in oligodendroglioma. These findings broaden our understanding of the clinical response to temozolomide in gliomas. Clin Cancer Res; 20(18); 4894-903. Ó2014 AACR.

Disulfiram when Combined with Copper Enhances the Therapeutic Effects of Temozolomide for the Treatment of Glioblastoma

“…In recent years, there has been considerable attention to the presence of a stem-like population of glioma cells (4,5,46,47), termed as BTICs, that have been shown to re-populate a tumor (recurrence) and confer resistance to conventional therapies, including temozolomide and radiation (4,6,11,13,48). In this study, we focused on this population of cells as a model and platform to develop new therapeutic strategies to improve the therapeutic efficacy of standard of care (temozolomide) in the adjuvant setting.…”

“…Surgical samples from patients with newly diagnosed and recurrent glioblastoma were obtained from the Tumor Tissue Bank within the Arnie Charbonneau Cancer Institute (Calgary, Alberta, Canada), transported to the BTIC Core Facility (Calgary, Alberta, Canada) and established as described previously (2,3,13). All established cell lines used within this study were validated for identity by short tandem repeat analysis performed by Calgary Laboratory Services (CLS) after each thaw and for each experiment that involved intracranial xenografts.…”

“…DSF-Cu combined with temozolomide significantly inhibited tumor growth and prolonged survival in patient-derived BTIC intracranial models As the in vitro data indicated that DSF-Cu is cytotoxic in a wide range of patient-derived BTICs and had the ability to enhance the cytotoxic effects of temozolomide in vitro, we assessed the clinical applicability of this treatment regime in our well-defined preclinical in vivo models (2,3,13,32). For these studies, we chose genetically distinct patient-derived BTICs established from a newly diagnosed (BT134: P53WT, PTENWT, EGFR WT, MGMT unmethylated), recurrent (BT147: P53mut, PTEN À/À , EGFRVIII, MGMT unmethylated), and temozolomide-resistant (BT73R) tumors.…”

“…To improve the survival of glioblastoma patients, new therapeutic strategies including combination-based therapies are desperately needed. We have been investigating the treatments that are adjunctive to current standard-of-care and enhance the cytotoxicity of temozolomide using BTICs established from newly diagnosed and recurrent glioblastoma patients (2,3,(11)(12)(13) as the screening platform. These cells retain cardinal features of stem cells including the ability to self-renew and differentiate into multiple neural cell lineages (2,3).…”

Association of MSH6 mutation with glioma susceptibility, drug resistance and progression

“…MSH6 mutations may arise in GBM prior to alkylating therapy, as well as in glioma subtypes other than GBM (31). Considering that such exceptions are rare, they should be considered as accidental mutations.…”