Genome-wide synthetic lethal screening for vulnerabilities in a cell model of succinate dehydrogenase-loss paraganglioma

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Abstract: Genome-wide synthetic lethal screening for vulnerabilities in a cell model of succinate dehydrogenase-loss paraganglioma This proposal focuses on the molecular pathology of familial paraganglioma (PGL). Paradoxically, this remarkable neuroendocrine cancer is caused by inherited mutations that inactivate succinate dehydrogenase (SDH), an enzyme of the mitochondrial tricarboxylic acid (TCA) cycle. A fundamental scientific understanding of the molecular basis of this tumor is lacking, limiting powerful approaches that might be identified to exploit unique vulnerabilities due to the fundamental metabolic defect in this cancer. The links between SDH loss and tissue-specific tumorigenesis remain unknown, and conventional preclinical models have been unavailable. The current hypothesis for PGL tumorigenesis invokes loss or inactivation of both parental copies of any of the four SDH subunit genes (A-D). The subsequent accumulation of succinate competitively inhibits the activities of several dioxygenase enzymes that normally suppress hypoxic signaling and demethylate histones and DNA. Despite this general mechanistic model, other mechanisms are possible and it is unclear what unique vulnerabilities may be present in SDH-loss cells that could permit targeted therapies. We hypothesize that an unbiased genome-wide lentiviral CRISPR screen will identify genes whose loss displays synthetic lethality with SDH loss. This hypothesis is supported by previous successful work in our labs identifying genes whose loss confers resistance to multiple forms of endocrine therapy in ERα+ and ERβ+ breast cancer cells. Important new PGL cell models have become available in the form of Sdhblox/lox and Sdhb-/- immortalized mouse chromaffin cells (imCC). This positions us ideally to conduct and analyze an unbiased genome-wide synthetic lethal screen using an available CRISPR single guide RNA (sgRNA) library. Aim 1 will undertake a paired unbiased lentiviral CRISPR screen in matched normal and SDH-loss imCC lines. Aim 2 will complete data analysis to identify candidate synthetic lethal genes. Aim 3 will complete independent validation of representative synthetic lethal genes and pathways. Finally, Aim 4 will implement a mouse allograft tumor model to monitor selective inhibitory effects of nominated target gene knockdown in Sdhb-/- vs. Sdhblox/lox imCC. This project is unique in being the first unbiased synthetic lethal screen addressing the unmet cancer needs of SDH-loss familial PGL patients. Because SDH genes are tumor suppressors in other cancers, including gastrointestinal stromal tumor (GIST) and some kidney cancers, identifying potential vulnerabilities in SDH-loss cells may be broadly applicable clinically.