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 1

Inhibition of RAS/MAPK signaling in NSCLC reduces methylated PP2ACα and alters PP2A heterotrimer composition in vitro.

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Inhibition of RAS/MAPK signaling in NSCLC reduces methylated PP2ACα and ...
(A and B) Western blot and quantification of pERK, ERK, mePP2ACα, and total PP2ACα in A549 cells treated with trametinib (30 nM) and NCI-H358 cells treated with adagrasib (300 nM) for the indicated time points. pERK was normalized to ERK; mePP2ACα and total PP2ACα were normalized to vinculin, and all targets are expressed relative to DMSO, 0 hours. Vinculin blots are shown in Supplemental Figure 2. Significance determined by 1-way ANOVA with Dunnett’s correction: *P ≤ 0.05, **P ≤ 0.01, ****P ≤ 0.0001. MS I, methylation-insensitive; MS, methylation-sensitive. (C and D) Heatmaps summarizing mePP2ACα and total PP2ACα levels in the indicated cell lines after trametinib or adagrasib treatment. Associated Western blots and quantification data are in Supplemental Figures 6 and 7 and the Supporting Data Values file. (E and F). Co-IP from A549 and H358 expressing V5-tagged PP2A-Aα showing altered holoenzyme composition 2 and 96 hours after trametinib or adagrasib treatment. Input controls are in Supplemental Figure 4; quantification is in Supplemental Figures 4 and 5. All data are presented as mean ± SEM (n ≥ 3).