Abstract 1576: Chemotherapy induced cellular cannibalism is mediated by phosphoinositide species and clathrin

Abstract Cancer cells can survive chemotherapy and drive lethal relapse if they avoid cell death in conditions of 1) DNA damage and/or mitotic stress caused by treatment; 2) nutrient depletion. We and others have previously shown that the breast cancers most likely to survive chemotherapy are TP53 wild-type, and these are among the most lethal breast cancers. For instance, chemotherapy treated TNBC patients with TP53 wild-type tumors have a median overall survival of 45 months, contrasting with 263 months for TP53 mutant tumors. TP53 wild type cells survive stress by entering a state of arrest and cellular senescence. But to persist in senescence, cells must survive in limited access to vasculature and nutrient sources while also supporting a high metabolic burden that includes production of cytokines and chemokines that drive pro-tumorigenic phenotypes and relapse. We previously showed a novel cannibalism phenotype of chemotherapy induced senescent cells. Engulfment occurred after exposure to different chemotherapy drugs in vitro, in 9 different cell lines, and in vivo in syngeneic mouse mammary tumor models. Engulfed prey cells were processed to the lysosomes of predator cells and broken down. While we showed the phenotype was unrelated to entosis, and senescent cells expressed many phagocytosis/macrophage related genes, the basic mechanisms of the engulfment are unknown. Here, we use biosensors and live cell imaging to delineate the steps of whole cell engulfment in cells that have entered senescence to survive chemotherapy. We show predator cell filamentous actin was localized to the prey cell throughout the process of engulfment. Biosensors to various phosphoinositide (PI) species showed increased concentration and localization of predator PI(4)P and PI(4,5)P2 at the prey cell during early stages of engulfment, followed by a burst of PI(3)P before internalization. PIK3C2B, an enzyme responsible for generating PI(3)P, was required for complete engulfment. Inhibition or knockdown of Clathrin, known to associate with PIK3C2B and PI(4,5)P2, severely impaired engulfment. In sum, these data demonstrate the mechanism of cellular cannibalism used by breast cancer cells to survive chemotherapy. Citation Format: Wesley D. Frey, Ashlyn Anderson, Julie Nguyen, Emma Cowles, James Jackson. Chemotherapy induced cellular cannibalism is mediated by phosphoinositide species and clathrin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1576.