EXPLORING THE ROLE OF GAT1 AND GABA IN TEMOZOLOMIDE TREATED GLIOMA

Approximately 3000 Canadians a year are diagnosed with the most aggressive and fatal form of brain cancer called glioma. Even with surgical resection, chemotherapy, and radiotherapy these patients have an average survival of less than 20 months. Research in the past has primarily focused on identifying and targeting specific genetic mutations in the tumor. However, it is apparent that the environment surrounding the tumor can influence tumor growth, tumor spread into the brain, and drug resistance. The brain presents many challenges to glioma treatment, one of which is the unique environment in which gliomas grow, which contributes to poor patient outcomes. The interaction between tumor cells, surrounding normal brain tissue, and immune cells supports the aggressiveness of glioma. Using a model of chemosensitive and chemoresistant tumors, we have identified an increase in the GABA transporter GAT1 in the chemosensitive tumor treated with the standard chemotherapy temozolomide. GAT1 is primarily expressed on neurons, but has also been shown to be expressed on astrocytes and immune cells such as macrophages. Our lab has identified that macrophages tend to concentrate in the same region as GAT1 expressing cells within the tumor environment. In addition, multiple papers have shown that an increase in GABA promotes a glioma-promoting immune microenvironment. Thus, we believe that treatment with temozolomide causes an increase in environmental GAT1 expression, resulting in a reuptake of GABA, and promoting a glioma-inhibitory macrophage phenotype. We believe that understanding how the glioma-inhibitory macrophage phenotype occurs will help improve patient outcomes.