PI3K Regulates Wild-type RAS Signaling to Confer Resistance to KRAS Inhibition

Despite the availability of RAS inhibitors and the dependence of >90% of pancreatic ductal adenocarcinomas (PDAC) on oncogenic KRAS mutations, resistance to KRAS inhibition remains a serious obstacle. We showed here that phosphoinositide 3-kinase (PI3K) plays a major role in this resistance through upstream activation of wild-type (WT) RAS signaling-beyond its known KRAS effector function. The combination of proximity labeling, CRISPR screening, live-cell imaging, and functional assays revealed that PI3K orchestrates phosphoinositide-mediated GAB1 recruitment to the plasma membrane, nucleating assembly of RAS signaling complexes that activate mitogen-activated protein kinase (MAPK) in an EGFR/SHP2/SOS1-dependent manner. Inhibiting PI3K enhanced sensitivity to mutant-specific KRAS inhibitors in PDAC cells, including in cells with clinically identified PIK3CA mutations. These findings refine RAS-PI3K signaling paradigms, reveal that PI3K-driven WT RAS activation drives resistance to KRAS inhibition, and illuminate avenues for augmenting KRAS-targeted therapies in PDAC. SIGNIFICANCE: PI3K plays a functional upstream role in assembling wild-type RAS signaling complexes that confer KRAS inhibitor resistance, providing a rationale for combined targeting of PI3K and KRAS in pancreatic cancer.