Resistance mechanisms to treatment with temozolomide in glioma cells

Abstract

Patients with glioblastoma, the most common type of malignant neoplasm of the brain in adults, still show poor prognoses with the available therapeutic protocols, and Temozolomide (TMZ) is the main drug used to treat this type of tumor. TMZ is an alkylating agent that causes DNA methylation and a wide range of DNA damage (genomic and mitochondrial), leading to cell death. However, tumors treated with TMZ presents several mechanisms of resistance. One of the main mechanisms is the ability of MGMT (Methyl Guanine Methyl Transferase) to directly reverse the lesions (methylation) in the DNA molecule. Additionally, MGMT loss of expression is associated with better prognosis and survival in patients treated with TMZ. The increase in the level of reactive oxygen species (ROS) has also been associated with resistance to TMZ. Our group showed that gluthathione (GSH), a peptide that plays a crucial role in the maintenance of redox cell homeostasis, prevents cell death by TMZ, a mechanism mediated by the transcription factor NRF2. However, it is unclear how this mechanism is involved directly in the reduction of methylation of genomic DNA (and therefore subject to the action of MGMT) or damage generated by oxidative stress. Thus, the initial idea of this project is to verify, by over-expression of MGMT in glioma cells, the role of DNA methylation lesions, in relation to oxidatively generated damage, on TMZ induced cell death, in conditions where the levels of GSH are modulated.Other mechanisms of resistance to TMZ have been reported. Through the generation of libraries using the CRISPR system (clustered regurlaly interspaced short palindrome repeats)-Cas9 (CRISPR-associated nuclease 9) (CRISPR-Cas9), our group identified a list of potential genes associated with TMZ resistance. Among these genes, the Fanconi anemia pathway has caught our attention because of its role in DNA repair. Thus, we expect that this project will help us not only to a better understanding in the protection of tumor cells to TMZ therapy, but also will provide us data to allow the development of alternatives that can potentiate the chemotherapeutic action of this drug. (AU)