EXTH-35. SYNERGISTIC EFFECT OF TARGETING THIOREDOXIN REDUCTASE (TRX1) AND DEPLETION OF GLUTATHIONE SYSTEM (GSH) IN GLIOBLASTOMA STEM CELLS

Abstract

Abstract Glioblastoma (GBM), the most common and advanced malignant primary brain tumor in adults remains incurable. GBM tumor recurrence occurs within a short time reflecting the failure to eradicate chemo-radioresistant GBM stem cells (GSCs). GSCs alter the redox system including Thioredoxin (Trx) and glutathione (GSH) systems to counteract increased reactive oxygen species (ROS). We previously showed the role of O6-methylguanine-DNA methyltransferase (MGMT) in response to PRIMAMET, a drug that targets the TP53 tumor suppressor gene and decrease Thioredoxin reductase1 (TRxR1) levels and further identified a positive relationship between MGMT and TrxR1 in established GBM cell lines isogenic for MGMT. Auranofin (Au), an orally available ROS-inducing FDA-approved drug is a potent irreversible inhibitor of TrxR1. The effect of Au on GSCs and the potential relationship between TrXR1, MGMT and p53 specifically in GSCs remain unknown. We hypothesized that increased ROS levels in GSCs might affect their drug resistant phenotype. we investigated the cytotoxic effects of Au on GSCs with known MGMT and P53 status and the mechanisms underlying these effects. Our results suggest that Au exerts strong cytotoxic effects in GSCs within a micromolar range. These effects were associated with increased ROS levels, decreased TrXR1, MGMT, phosphorylation of ERk1/2, activation of p53 and increased apoptosis, we also used a knockdown strategy to assess the role of p53 and showed that increased sensitivity to Au for p53-knockdown. We showed the role of ROS in response to Au using ROS inducer L-Buthionine Sulfoxamine (L-BSO), a GSH inhibitor, and ROS scavenger N-Acetylcysteine (NAc). L-BSO combined with Au drastically decreased the IC50 within a nanomolar range suggesting the crucial role of both Trx and GSH systems in GSCs redox balance. Increased ROS with concomitant GSH depletion using L-BSO might circumvent drug-induced oxidative stress and overcome drug resistance in MGMT-positive and negative GSCs