Abstract B056: Wild-type RAS/MAPK signaling complexes mediate adaptive resistance to KRAS inhibition in PDAC

Abstract

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy and predicted to be the second most common cause of death in the US within the next decade. A striking hallmark of PDAC is the presence of activating KRAS mutations in >90% of all cases. Studies in animal models and cell lines have suggested that oncogenic KRAS is important for both the initiation and progression of PDAC, making KRAS an attractive target for therapy. Recent FDA approvals of KRAS mutant-specific inhibitors has advanced the clinical treatment of patients with cancers harboring mutant KRAS, yet resistance inevitably occurs through both genetic (second-site mutations, bypass pathways) and non-genetic (adaptive) mechanisms. Elucidating the adaptive mechanisms by which cancers evade KRAS inhibition in PDAC will enable the development of more efficacious and durable combinatorial therapeutic strategies with emerging KRAS inhibitors. To address this gap in knowledge, we used CRISPR/Cas-mediated gene knockout technology to model KRAS inhibition in PDAC and found that KRAS is dispensable in a subset of human and mouse PDAC cells, arguing that KRAS is not absolutely required for tumor maintenance. KRAS-deficient cells showed enhanced sensitivity to phosphoinositide 3-kinase (PI3K) inhibitors (PI3Ki), which functioned not only to block canonical AKT signaling but also, unexpectedly, to suppress mitogen-activated protein kinase (MAPK) signaling through rapid attenuation of wild-type RAS/MAPK activity in single cells. Importantly, we confirmed this novel regulatory role of PI3K in mediating RAS/MAPK activity across multiple wild-type KRAS-expressing malignant and non-malignant cell lines, supporting the generalizability of this signaling axis. Furthermore, unbiased proximity protein labeling (BioID) revealed that PI3K inhibition reduces the interaction of KRAS with canonical regulators, effectors, and scaffolds in RAS/MAPK signaling. Parallel genome-wide CRISPR screens comparing KRAS intact and isogenic KRAS-deficient PDAC cells revealed specific RAS/MAPK scaffold/docking proteins as essential for PDAC cell fitness following KRAS ablation. Together, our work sheds new light into the regulatory role of PI3K in wild-type RAS/MAPK signaling, highlights the importance of functional wild-type RAS/MAPK signaling complexes in adaptive resistance to KRAS inhibition, and nominates potential therapeutic targets to overcome resistance to KRAS inhibition in PDAC and possibly other KRAS mutant cancers. Citation Format: Xiangyu Ge, Christian F. Ruiz, Wenxue Li, Yanixa Quiñones-Avilés, Mandar Deepak Muzumdar. Wild-type RAS/MAPK signaling complexes mediate adaptive resistance to KRAS inhibition in PDAC [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 B056.