Abstract 1671: Exploring the mechanism of PP2A regulated cell death via macropinocytosis in pancreatic cancer

Abstract Pancreatic Ductal Adenocarcinoma (PDAC) is the 4th leading cause of cancer-related death in the United States. KRAS is an oncogene mutated in 90% of PDAC patients. Oncogenic KRAS leads to aberrant cell proliferation and survival. KRAS is considered hard to target because resistance mechanisms to KRAS inhibitors are common highlighting the need to understand alternative strategies. PDAC tumor microenvironment evolves with cancer cell progression leading to vascular remodeling and blood vessel collapse. This makes the tumors nutrient deplete. To circumvent this, cells employ KRAS-dependent macropinocytosis- a nutrient scavenging pathway. Macropinocytosis is the process by which cells take up extracellular material by membrane ruffling to form vesicles which then fuse with lysosomes to release nutrients. Targeting KRAS-driven macropinocytosis can be crucial to limiting nutrients to the cell to prevent tumor growth. Protein Phosphatase 2A (PP2A), a heterotrimeric Serine/Threonine phosphatase, is a downstream regulator of KRAS. Its activity is repressed by mutated KRAS. We have seen that the activation of PP2A with small molecular activator, DT061, prevents macropinosomes from fusing with lysosomes which leads to cell death. But how DT061 regulated PP2A activity affects the macropinocytosis pathway is still unknown. The purpose of this study is to understand the mechanism of cell death brough upon by the activation of PP2A with DT061. Membrane ruffling is critical for the initiation of macropinocytosis. Rac is a GTPase usually involved with membrane ruffling. To show that Rac is needed for DT061 mediated macropinocytosis, we used EHT 1864, a Rac family inhibitor. Cells were treated with EHT 1864 before being treated with DT061 and stained with crystal violet. The inhibition of Rac prevented DT061 driven cell death, indicating that Rac is crucial to DT061 driven cell death. High molecular weight TMR-Dextran can only be taken up by the cells through macropinocytosis. Cells were treated with TMR-Dextran and EHT 1864. Cells with Rac inhibition showed lower uptake of TMR-Dextran than cells that were treated with DT061. Together these findings indicate to us that Rac plays a crucial role in the initiation of macropinocytosis and the regulation of cell death caused by the activation of PP2A. Understanding the pathway of DT061 mediated cell death can be vital to developing this concept as a therapeutic method of treatment for PDAC patients who currently have the lowest 5-year survival rate (12%) of all cancers. Citation Format: Indiraa Doraivel, Garima Baral, Claire M. Pfeffer, Brittany L. Allen-Petersen. Exploring the mechanism of PP2A regulated cell death via macropinocytosis in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1671.