MODL-02. DEVELOPMENT OF RODENT GLIOBLASTOMA MODELS OF MGMT-MEDIATED TEMOZOLOMIDE RESISTANCE

Abstract

Abstract O6-methylguanine-DNA methyltransferase (MGMT) is an enzyme that repairs O6-methylguanine DNA damage lesions generated by alkylators such as temozolomide (TMZ), the standard chemotherapeutic for glioblastoma (GBM) treatment. High MGMT expression leads to TMZ resistance and is correlated with lower survival, making it an important prognostic biomarker and potential therapeutic target. Xenograft models with human GBM cell lines require implantation into immunodeficient animals, precluding the study of MGMT-dependent alkylator sensitivity in the setting of an intact tumor immune microenvironment. In this study, we developed rat and mouse glioma models of MGMT overexpression and characterized response to alkylator therapy. RG2 rat glioma and SB28 mouse glioma cells, which have low endogenous MGMT levels, were transduced with cDNA expressing FLAG-tagged MGMT to generate an isogenic pair. RG2 MGMT+ and SB28 MGMT+ cells showed robust expression of MGMT, which was effectively abrogated by MGMT inhibitors. In vitro cell viability assays showed that MGMT overexpression resulted in increased resistance to TMZ compared to parental cells, and this resistance was reversed when cells were concurrently treated with the MGMT inhibitor lomeguatrib. To model MGMT overexpression in vivo, luciferase-expressing RG2 MGMT+ cells were implanted into the brains of syngeneic Fischer 344 rats. Rats were treated with TMZ at 50mg/kg daily x 5 days via intraperitoneal injection. Tumor growth was measured by bioluminescence imaging and rats were monitored for survival and toxicity. RG2 MGMT+ tumors were highly resistant to TMZ, as treatment did not improve survival or delay tumor growth. Overall, our newly developed isogenic rat and mouse glioma models recapitulate MGMT-dependent TMZ sensitivity and provide useful preclinical tools for studying MGMT as a biomarker and potential therapeutic target in GBM. In addition, these syngeneic models facilitate studies on the immune modulation of chemotherapeutic agents in the context of MGMT expression and allows for testing of chemoimmunotherapy combinations.