Mentor Name: Tobey MacDonald

Children with medulloblastoma (MB) need new treatments that are safer and more effective than current therapy. Emory undergraduate Isabella Gershon has worked with Dr. MacDonald over the past two years to investigate ONC 206, an agent in single-drug clinical trials at multiple sites for the treatment of malignant pediatric brain tumors including medulloblastoma. In vitro and in vivo studies demonstrated efficacy in tumor growth suppression and prolonged survival in cell and mouse models. ONC206 is an agonist to the mitochondrial enzyme Caseinolytic peptidase P (ClpP), resulting in disturbed oxidative phosphorylation and MB cell death. However, based on our preliminary data it appears that in response to ONC206, some MB cells turn on a compensatory survival mechanism, whereby blocked self-renewal triggered by ClpP activation is rescued by PI3K-AKT-mTOR pathway secondary activation. We thus hypothesize that inhibiting PI3K-AKT-mTOR while activating ClpP will result in synthetic lethality. We will test this hypothesis by learning to subculture ONC206-resistant MB cells and treating both drug-sensitive and -resistant cells with ONC206 in conjunction with various combinations of specific inhibitors of PI3K, AKT, and mTOR to tease apart the most critical molecules of the pathway for mediating drug resistance. We will identify the best synergistic drug combination with ONC206. The MacDonald lab will then conduct in vivo studies on mouse models using this combination as a step towards clinical investigation. We will generate IC50 curves to evaluate drug efficacy. Our studies will elucidate the role of PI3K-AKT in MB survival in addition to investigating the pathway as a novel and viable therapeutic target when combined with ONC206 treatment. We will expand the investigation beyond in vitro therapeutic development to uncover the mechanisms of MB resistance and confirm on-target drug effects, involving Western Blot, PCR, flow cytometry, and single cell sequencing techniques. We will also involve gene knockdown to confirm drug-induced cell killing is a property of the expected targets. Our long-term goal is to to translate these preclinical studies into clinical implementation for children with MB.