A PP2A molecular glue overcomes RAS/MAPK inhibitor resistance in KRAS-mutant non–small cell lung cancer
Brynne Raines, Stephanie Tseng-Rogenski, Amanda C. Dowdican, Irene Peris, Matthew Hinderman, Kaitlin P. Zawacki, Kelsey Barrie, Gabrielle Hodges Onishi, Alexander M. Dymond, Tahra K. Luther, Sydney Musser, Behirda Karaj Majchrowski, J. Chad Brenner, Aqila Ahmed, Derek J. Taylor, Caitlin M. O’Connor, Goutham Narla
Brynne Raines, Stephanie Tseng-Rogenski, Amanda C. Dowdican, Irene Peris, Matthew Hinderman, Kaitlin P. Zawacki, Kelsey Barrie, Gabrielle Hodges Onishi, Alexander M. Dymond, Tahra K. Luther, Sydney Musser, Behirda Karaj Majchrowski, J. Chad Brenner, Aqila Ahmed, Derek J. Taylor, Caitlin M. O’Connor, Goutham Narla
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Research Article Cell biology Oncology

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

Abstract

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.

Authors

Brynne Raines, Stephanie Tseng-Rogenski, Amanda C. Dowdican, Irene Peris, Matthew Hinderman, Kaitlin P. Zawacki, Kelsey Barrie, Gabrielle Hodges Onishi, Alexander M. Dymond, Tahra K. Luther, Sydney Musser, Behirda Karaj Majchrowski, J. Chad Brenner, Aqila Ahmed, Derek J. Taylor, Caitlin M. O’Connor, Goutham Narla

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Figure 2

Demethylation of PP2ACα drives intrinsic resistance to RAS/MAPK inhibition in vitro and MEK1/2 inhibition in vivo.

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Demethylation of PP2ACα drives intrinsic resistance to RAS/MAPK inhibiti...
(A and B) Western blot of LCMT1, mePP2ACα, and PP2ACα in A549 and NCI-H358 cells expressing empty vector (EV) or LCMT1–/– using 2 gRNAs. (C and D) Cell viability of A549 and NCI-H358 EV or LCMT1–/– cells treated with trametinib or adagrasib (0–10 μM, 72 hours). (E) Western blot of A549 EV, LCMT1–/–, and V5-tagged LCMT1 (reconstitution) cells. (F) Corresponding trametinib cell viability (CTG) assay (0–10 μM, 72 hours). (G and H) Clonogenic assay of A549 EV, LCMT1–/–, and V5-tagged LCMT1 cells treated with trametinib (0–10 μM, 1.5 weeks), with growth inhibition (%) calculated in H. (I) Tumor growth curves for A549 EV and LCMT1–/– CDXs treated with vehicle or trametinib (1 mg/kg, QD). TGI was assessed at day 34. (J) Waterfall plot showing tumor response by RECIST: PD, progressive disease; SD, stable disease; PR, partial response; CR, complete response. All Western blot quantifications are in Supplemental Figure 8, and raw data are in Supporting Data Values file. One-way ANOVA with Tukey’s multiple-comparison test was used to calculate statistical significance in I: ****P ≤ 0.0001.