PANCREATIC DUCTAL ADENOCARCINOMAS RESISTANT TO KRAS INHIBITION ARE DRUGGABLE WITH AN ANTI-MUC1-C ADC
Treatment of pancreatic ductal carcinomas (PDACs) has been advanced by the development of KRAS mutant inhibitors. Despite this progress, PDACs invariably develop resistance to these agents by mechanisms that largely remain unclear. The MUC1 gene, which encodes an oncogenic MUC1-C protein, is upregulated in PDAC KRAS G12D tumors. We report that treatment of PDAC cells with the selective KRAS G12D MRTX1133 inhibitor is associated with induction of MUC1-C expression. We show that KRAS G12D inhibition activates a MUC1-C/NF-?B p65 auto-inductive pathway. Our results further demonstrate that MUC1-C drives resistance to MRTX1133 by activating the inflammatory IFN type I and II pathways. Of clinical relevance, targeting MUC1-C genetically and pharmacologically reverses MRTX1133 resistance and is synergistic in combination with MRTX1133 treatment. In leveraging MRTX1133-induced upregulation of MUC1-C expression, an anti-MUC1-C (M1C) antibody-drug conjugate (ADC) is highly effective against MRTX1133-resistant PDAC KRAS G12D cell lines, patient-derived organoids and PDX tumor xenograft models. These findings demonstrate that MUC1-C confers resistance of PDAC KRAS G12D mutant cells to MRTX1133 and identify MUC1-C as a target for M1C ADC treatment of PDAC patients who are refractory to MRTX1133 treatment. Overall design: RNA Seq in PDAC Cell line with MUC1-C shRNA silencing. We conpared DMSO and DOX treatment cells for differential gene expression analysis. MUC1shRNA (MISSION shRNA TRCN0000122938; Sigma, St. Louis, MO, USA)  was inserted into the pLKO-tet-puro vector (Plasmid #21915; Addgene, Cambridge, MA, USA) . Vector-transduced cells were selected for growth in 1–2 µg/ml puromycin. Cells were treated with 0.1% DMSO as the vehicle control or 500 ng/ml doxycycline (DOX; Millipore Sigma).