Abstract B013: PP2A regulated macropinocytosis and therapeutic vulnerabilities in pancreatic cancer

Abstract Pancreatic Ductal Adenocarcinoma (PDAC) is the fourth leading cause of cancer related deaths in the US, with the lowest five-year survival rate of all cancers. Nutrients in the PDAC microenvironment are commonly depleted, with the vital amino acid glutamine among the most deficient metabolites. In an attempt to circumvent this deprivation, PDAC cells initiate KRAS dependent macropinocytosis, an actin-driven nutrient scavenging pathway. Macropinocytosis allows cells to replenish the nutrients required for proliferation and survival. As glutamine is essential for PDAC cell survival, therapeutic inhibition of macropinocytosis represents a novel strategy to suppress nutrient acquisition and drive cell death in PDAC. Protein phosphatase 2A (PP2A) is a heterotrimeric Serine/Threonine phosphatase known to inhibit downstream targets of the KRAS signaling cascade and is implicated in macropinocytosis regulation. We demonstrate that pharmacological activation of PDAC cell lines with the small molecule activator of PP2A, DT061, leads to significant accumulation of intracellular vesicles. Therefore, we hypothesize that PP2A activation results in methuosis, a non-apoptotic cell death process driven by aberrant macropinocytosis. Using high molecular weight TMR-Dextran, we confirmed that these vesicles are macropinosomes. PP2A activation prevented the colocalization of macropinosomes with lysosomes, likely limiting the nutrients supply to PDAC cells. RNA sequencing analysis showed that glutamine deprivation genes are significantly enriched with acute activation of PP2A, and the oxidative phosphorylation pathway was observed to be significantly inhibited. Further, combination of DT061 with Glutamine transport inhibitor V-9302 significantly inhibits the survival of PDAC cells. Together, these findings indicate that activation of PP2A in late stage PDAC promotes aberrant macropinocytosis and establishes a novel role of PP2A in nutrient scavenging and cell death. These pathways can be further exploited to identify potential therapeutics in PDAC. Citation Format: Garima Baral, Claire M. Pfeffer, Brittany L. Allen-Petersen, Indiraa Doraivel. PP2A regulated macropinocytosis and therapeutic vulnerabilities in 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 B013.