Mechanisms of Biguanide Sensitivity in GBM

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Project Summary/Abstract The biguanide drug metformin that is widely used for the management of Type 2 diabetes is being evaluated as an anti- neoplastic agent in cancer trials including GBM (NCT02780024, NCT03243851). The various mechanisms of action of metformin as an anti-neoplastic agent is still being investigated, but recent studies have unequivocally demonstrated that its therapeutic effects in tumor cell growth, cell death, gene expression, and signaling are dependent on inhibition of mitochondrial complex I. Based on the success of metformin in combination therapy in some cancers, new generation of mitochondrial complex I inhibitors (MCI-i) are currently under investigation. Diffusion of metformin across the plasma membrane occurs slowly. Its entry is facilitated by two transporters OCT1 and OCT2 that are not well expressed outside the liver and kidney. This presents a problem due its lack of accumulation in other tissues at therapeutic concentrations. Therefore, identification of tumor subtypes that respond better to lower concentrations of metformin may be leveraged for targeted metformin therapy. Metformin GBM trials may be unsatisfactory since there are no molecular markers to distinguish metformin responders from non-responders. Identification of molecular markers may greatly improve metformin and other MCI-i-based therapy in GBM. We identified that a pyruvate dehydrogenase subunit (PDHA1) is a possible molecular beacon for MCI-i therapy in GBM. We will test this in vitro and in vivo. We also found that the cellular energy sensor AMPK provides resistance to MCI-i therapy in a subset of GBM. We will test if a brain-penetrating AMPK inhibitor restores MCI-i sensitivity in vivo. Lastly, our molecular analysis showed that ErbB activation is a likely mechanism of resistance to AMPK inhibition. In mouse models we will test if a brain-penetrating ErbB inhibitor overcomes AMPK inhibitor resistance in vivo.