Cancer associated fibroblasts sustain critical dependency of pancreatic cancer cells on exogenous lipids

Abstract Pancreatic ductal adenocarcinoma (PDAC) cells derive their resistance to therapy and aggressive clinical course from the symbiotic signaling and metabolic interactions with cancer-associated fibroblasts (CAFs). CAFs have been shown to provide to metabolically “parasitic” PDAC cells with water-soluble metabolites such as glucose and amino acids, or bulk protein via micropinocytosis. To meet the elevated demands for cellular membrane lipids, cancer cells rely on uptake of the exogenous lipids. However, the mechanism by which PDAC cells obtain water-insoluble essential lipids, such as cholesterol, remains poorly understood. Here, we define CAFs as a main source of lipids for PDAC cells by direct “feeding” of the CAF plasma membrane (PM) to cancer cells via heterotypic cellular contacts, a phenomenon known as trogocytosis. To gain insights into the mechanisms of regulation of CAF trogocytosis, we engineered cholesterol-auxotrophic human and mouse PDAC cells. In the absence of exogenously provided cholesterol, these cancer cells undergo apoptosis, which is completely rescued in CAF co-cultures. Using CRISPRi-mediated depletion in CAFs of select genes involved in cholesterol trafficking, membrane fusion and membrane protrusions, we found that CAFs deficient in CD81, TMEM16F, or ARF6 exhibited markedly reduced ability to support the viability of cholesterol-auxotrophic PDAC cells in lipid-poor media. As a promising therapy target, TMEM16F is a Ca2+-regulated scramblase increasing phosphatidylserine (PtdSer) on the outer leaflet of the PM. TMEM16F protein is highly expressed in human PDAC CAFs compared to fibroblasts isolated from the adjacent non-malignant pancreatic tissues. The TMEM16F-null CAFs are unable to sustain of cholesterol-auxotrophic PDAC cells in lipid-poor co-cultures. Our overall model is that, to initiate trogocytosis, PDAC cells release paracrine “feed me” signals activating Ca2+-dependent phospholipid scramblase TMEM16F. As the result, increased outward expression of PtdSer on CAF PM is a hallmark “eat me” signal that is recognized by the trogocytic PDAC cells. We conclude that trogocytosis is the critical metabolic dependency in PDAC, and nominated TMEM16F as a plausible PDAC therapy target. Re-purposing of clinically available TMEM16 inhibitors will make a tangible impact on treatment of PDAC patients in the near term. Citation Format: Charline Ogier, Alena Klochkova, Linara Gabitova, Battuya Bayarmagnai, Diana Restifo, Aizhan Surumbayeva, Janusz Franco-Barraza, Ralph Francescone, Debora B. Barbosa Vendramini-Costa, Jaye Gardiner, Emmanuelle Nicolas, Elizabeth A. Handorf, Kathy Q. Cai, Edna Cukierman, Igor Astsaturov. Cancer-associated fibroblasts sustain critical dependency of pancreatic cancer cells on exogenous lipids [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PR-015.