Abstract B011: Identifying druggable lipid synthesis targets as novel therapeutics for pancreatic cancer

Lipid metabolic reprogramming is a hallmark of cancer that contributes to tumorigenesis by supporting energy metabolism and the synthesis of signaling molecules, cellular membranes, and protein modifications. Cells modulate lipid metabolic genes through the regulation of sterol regulatory element-binding proteins (SREBPs), which serve as transcriptional activators of genes responsible for fatty acid and cholesterol synthesis and uptake. Despite efforts demonstrating that the SREBP pathway is an attractive chemotherapeutic target, a potent bioavailable inhibitor of the pathway has not yet been discovered. Here, we identify druggable SREBP target genes as potential targets in pancreatic ductal adenocarcinoma (PDAC). Results: To discover candidate genes, we constructed a CRISPR knockout library containing 148 known SREBP target genes. We used a patient-derived PDAC cell line to conduct the knockout screens in vivo (n = 7 tumors) by injecting library-infected cells into the pancreas of nude mice. After 4 weeks of growth, mouse PDAC tumors showed a statistically significant depletion of guide RNAs targeting 8 genes within the mevalonate pathway, which is responsible for synthesizing cholesterol and isoprenoids such as farnesyl-diphosphate and geranyl-diphosphate. One of the most significant hits was HMG-CoA reductase (HMGCR), which catalyzes the formation of mevalonate. We chose to investigate statins, which are a well-characterized class of FDA-approved drugs that inhibit HMGCR. Using flow cytometry, we stained for annexin-V as a marker for apoptosis and found minimal cell death induced by Fluvastatin alone. Given that inhibiting HMGCR would disrupt lipid homeostasis and in turn activate the SREBP pathway, we hypothesized that a combination therapy with an SREBP inhibitor, TMDP, would potentiate statin-induced cell death. We observed minimal cell death with TMDP alone, but striking synergy between Fluvastatin and TMDP, showing a five-fold increase in annexin-V staining after 48 hours. Mevalonate and geranylgeranyl-diphosphate both fully rescued this cell death to basal levels. Conclusions: In vivo CRISPR screening is a powerful tool for the identification of novel therapeutic targets for cancer. We found that the mevalonate pathway plays a significant role in pancreatic tumor growth in vivo and that existing FDA-approved drugs can be used in combination with an SREBP inhibitor to dramatically enhance cell killing in vitro. Citation Format: Casie S. Kubota, Chiaki T. Ishida, Stephanie Myers, Peter J. Espenshade. Identifying druggable lipid synthesis targets as novel therapeutics for pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B011.