CBIO-14. ELUCIDATING THE MECHANISM OF TEMOZOLOMIDE-INDUCED ATR ACTIVATION IN MGMT-METHYLATED GLIOBLASTOMA MULTIFORME

Abstract

Abstract Glioblastoma multiforme (GBM) is an aggressive, malignant brain tumor in adults. The current standard of care for GBM is surgical resection, radiation therapy and chemotherapy with temozolomide (TMZ). It is well established that GBM patients with a methylated MGMT promoter (MGMT-) who are treated with TMZ have a better overall survival than patients with an unmethylated MGMT promoter (MGMT+). The enzyme produced by the MGMT gene is responsible for removing cytotoxic O6-methylguanine (O6-meG) lesions formed by TMZ. In the MGMT- setting, the O6-meG lesion activates the mismatch repair (MMR) pathway which functions to remove the damage. Published work from our group reported differential activation of the ataxia telangiectasia and RAD3 related protein (ATR) in MGMT- and MGMT+ GBM cells in response to TMZ treatment, as demonstrated through the phosphorylation of CHK1. It is known that MMR proteins are involved in ATR activation, however, this project aims to unravel the specific MMR proteins required for ATR activation by TMZ-induced alkyl lesions. To accomplish this, we treated an shMSH2 MGMT- GBM cell line with TMZ and an ATR inhibitor (ATRi) compared to treatment in an MSH2-proficient MGMT- GBM cell line. We observed decreased cell death in the shMSH2 setting compared to the MSH2-proficient cells, suggesting that MSH2 is integral in the activation of ATR upon TMZ treatment in the MGMT- setting. This study elucidates a potential role for MSH2 in ATR activation. Mechanistic understanding of how the MMR system is involved in ATR activation by TMZ can ultimately be exploited for therapeutic gain in the treatment of patients with GBM.