A PP2A molecular glue overcomes RAS/MAPK inhibitor resistance in KRAS-mutant non–small cell lung cancer

The effectiveness of RAS/MAPK inhibitors in treating metastatic KRAS-mutant non-small cell lung cancer (NSCLC) is often hindered by the development of resistance driven by disrupted negative feedback mechanisms led by phosphatases like PP2A. PP2A is frequently suppressed in lung cancer to maintain elevated RAS/MAPK activity. Despite its established role in regulating oncogenic signaling, targeting PP2A with RAS/MAPK to prevent resistance has not been previously demonstrated. In this study, we aimed to establish a treatment paradigm by combining a PP2A molecular glue with a RAS/MAPK inhibitor to restore PP2A activity and counteract resistance. We demonstrated that KRASG12C and MEK1/2 inhibitors disrupted PP2A carboxymethylation and destabilized critical heterotrimeric complexes. Furthermore, genetic disruption of PP2A carboxymethylation enhanced intrinsic resistance to MEK1/2 inhibition both in vitro and in vivo. We developed RPT04402, a PP2A molecular glue that selectively stabilizes PP2A-B56α heterotrimers. In commercial cell lines and in a patient-derived model, combining RPT04402 with a RAS/MAPK inhibitor slowed proliferation and enhanced apoptosis. In mouse xenografts, this combination induced tumor regressions, extended median survival, and delayed the onset of treatment resistance. These findings highlight that promoting PP2A stabilization and RAS/MAPK inhibition presents a promising therapeutic strategy to improve treatment outcomes and overcome resistance in metastatic KRAS-mutant NSCLC.