Abstract C047: Phospholipid scramblase TMEM16F in cancer associated fibroblasts regulates trogocytosis to sustain critical dependency of pancreatic cancer cells on exogenous lipids
Authors: Ogier Charline , Klochkova Alena , Gabitova-Cornell Linara , Bayarmagnai Battuya , Restifo Diana , Surumbayeva Aizhan , Vendramini-Costa Debora Barbosa , Francescone Ralph , Franco-Barraza Janusz , Gardiner Jaye , Nicolas Emmanuelle , Efimov Andrei , Handorf Elizabeth A. , Cai Kathy Q. , Gligorijevic Bojana , Cukierman Edna , Astsaturov Igor 
Published: November 2022

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). Trogocytosis is a process of “nibbling” of plasma membranes between two living cells. Here, we demonstrate CAFs are the primary recipients of exogenous lipids which they transfer to metabolically “parasitic” PDAC cells via a contact-mediated trogocytosis. Whereas trogocytosis has been described in immune system and in normal development, the biochemical and signaling regulators of trogocytosis between CAFs and PDAC cells have not been defined. Results: We determine that trogocytosis occurs through heterotypic CAF-PDAC cell contacts: membrane blebbing (readily observed in activated CAFs and exaggerated by release of Ca2+ from the ER stores) results in the blebs uptake by the PDAC cells. The CAF blebs express externalized phosphatidylserine (PtdSer), and blockade of PtdSer in vitro transiently deters trogocytic uptake of CAF membranes. Probing a short list of candidate targets involved in regulation of cholesterol trafficking, membrane fusion and membrane protrusions using CRISPRi, has shown that CAFs deficient in CD81, ARF6 or TMEM16F exhibit 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 PtdSer on the outer leaflet of the plasma membrane. 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, and do not support the growth of PDAC cells in orthotopic co-implantation model. Furthermore, several clinically available antibiotics used to treat tapeworms are selective TMEM16F inhibitors. One of the widely available TMEM16F inhibitors, niclozamide, is effective in blocking cholesterol transfer from CAFs to PDAC cells in vivo. Conclusion: Our overall model is that activated CAFs initiate trogocytosis by expressing PtdSer as “eat me” signals on the surfaces of their membrane blebs. This process is regulated by Ca2+-dependent phospholipid scramblase TMEM16F which is an attractive drug-amenable target to dismantle the critical metabolic dependency in PDAC on the exogenous lipids. 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-Cornell, Battuya Bayarmagnai, Diana Restifo, Aizhan Surumbayeva, Debora Barbosa Vendramini-Costa, Ralph Francescone, Janusz Franco-Barraza, Jaye Gardiner, Emmanuelle Nicolas, Andrei Efimov, Elizabeth A. Handorf, Kathy Q. Cai, Bojana Gligorijevic, Edna Cukierman, Igor Astsaturov. Phospholipid scramblase TMEM16F in cancer associated fibroblasts regulates trogocytosis to sustain critical dependency of pancreatic cancer cells on exogenous lipids [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 C047.