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 7

RPT04402 enhances trametinib-induced apoptosis in vivo.

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RPT04402 enhances trametinib-induced apoptosis in vivo. (A) Schematic of...
(A) Schematic of the A549 pharmacodynamic study. Mice were treated daily for 7 days with vehicle, trametinib (1 mg/kg), RPT04402 (30 mg/kg), or the combination. Mice were euthanized 3, 6, 24, or 48 hours after the final dose for analysis. (B) Waterfall plots displaying the percentage change in tumor volume for each treatment arm 3, 6, 24, and 48 hours after the final dose. The plot indicates responses based on RECIST criteria: PD, progressive disease; SD, stable disease; PR, partial response; CR, complete response. (C) Western blot analysis of mePP2ACα in tumors from A549 CDX. Blot quantifications are located in Supplemental Figure 21. (D) Representative images of TUNEL staining (green) from histological sections of A549 CDX tumors harvested 3, 6, 24, and 48 hours after the final dose. Between 5 and 15 images per tumor slice were captured to calculate the average percentage of TUNEL-positive cells. (E) Representative images of Ki67 staining (green) from A549 CDX pharmacodynamics as described in D. Nuclei are stained with DAPI. Scale bar: 75 μm. Graphs and quantifications are in Supplemental Figure 21. Raw values are in the Supporting Data Values file.