Abstract PO-027: Investigating unfolded protein responses in pancreatic ductal adenocarcinoma under lipid imbalance

Pancreatic ductal adenocarcinoma (PDAC) is the 4th leading cause of cancer-related death with a five-year survival rate of only 10%. A major feature of PDAC tumor microenvironment (TME) is desmoplasia, which are dense fibrotic and inflammatory stromal regions constituting the PDAC TME. This desmoplastic reaction results in poor intratumoral perfusion and elevated interstitial fluid pressure, creating regions with severe oxygen and nutrient deprivation. One result is a significant deficiency in unsaturated fatty acids (UFAs) because the de novo synthesis of UFAs requires molecular oxygen. Our data indicate that PDAC cells experience endoplasmic reticulum (ER) stress and trigger a subsequent unfolded protein response (UPR) under tumor-like stress, which can be mitigated by UFAs. The UPR regulates an intricate signaling network mediated by three major stress sensors: Inositol-requiring enzyme 1a (IRE1a), PKR-like ER kinase (PERK) and activating transcription factor 6a (ATF6a). UPR output can be either cytoprotective or cytotoxic depending on tumor types and the severity of stress. Our data suggest that B-I09, a selective IRE1 RNase inhibitor, impairs PDAC cell viability under stress conditions, indicating a pro-survival role for IRE1a. Previous studies showed that MYC-driven cancer cells are highly reliant on UPR pathways. Therefore, we hypothesize that the two major PDAC transcriptional subtypes “Classical” and “Basal-like” may have distinct dependencies on UPR pathways, with the Basal-like subtype being more dependent due to an enrichment of MYC gene signatures. Overall, we hypothesize that IRE1a, PERK and/or ATF6a play(s) an oncogenic role in PDAC tumorigenesis due to lipid saturation abnormalities, and the Basal-like PDAC subtype is more sensitive to inhibition of UPR pathway(s). We are evaluating the role of IRE1a, PERK and ATF6a using pharmacologic inhibition and genetic knockdown in vitro and in vivo under UFA deprived conditions. We will also evaluate PDAC intracellular and interstitial fluid lipidomics using LC-MS. In addition, we will assess whether hypoxic PDAC cells experience ER stress in vivo due to UFA deprivation using Stimulated Raman scattering (SRS) microscopy. To explore the subtype-specific dependency on the UPR pathways, we are querying a UPR gene signature in different tumor cell clusters using single cell RNA-seq datasets of patient samples. In addition, we will employ an isogenic system for PDAC subtypes and examine subtype-specific responses to UPR inhibition in vitro and in vivo. Our goal is to better understand UPR pathways in PDAC cells as a survival mechanism in response to the “lipotoxicity” induced by ER membrane saturation, with a consideration of intratumoral heterogeneity of PDAC cell subtype. Citation Format: Yanqing (Christine) Jiang, Xu Han, Michelle Burrows, Carson Poltorack, Celeste Simon, Brian Keith. Investigating unfolded protein responses in pancreatic ductal adenocarcinoma under lipid imbalance [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 PO-027.