PADI-dependent mitochondrial adaptation drives resistance to KRAS inhibitors

KRAS(ON) and KRAS(OFF) inhibitors have improved the treatment of KRAS-driven tumors, yet resistance remains a major challenge. Here, we identify PADI1 and PADI3 as negative prognostic markers in KRAS-mutant colorectal and pancreatic cancers. KRAS-driven metabolic rewiring sustains their expression through an enhancer within the PADI1 locus. Although KRAS inhibition suppresses PADI1/3 expression in sensitive cells, resistant models maintain elevated PADI1/3 expression and accumulate intracellular calcium, sustaining PADI-dependent adaptive survival. Pharmacological inhibition of PADIs synergizes with KRAS(ON) and KRAS(OFF) inhibitors in two- and three-dimensional cancer models, restores sensitivity in resistant cells, and enhances antitumor activity in vivo. Integrated transcriptomic and proteomic analyses identify HSPA9/Mortalin as a critical citrullinated effector. PADI3-mediated citrullination enhances Mortalin ATPase activity and ATP/ADP cycling, whereas loss of citrullination correlates with apoptosis. Disruption of this adaptive circuitry triggers mitochondrial dysfunction, caspase activation, and non-lytic apoptosis without detectable DAMP release, revealing a therapeutic vulnerability of KRAS-driven tumors.