Abstract 6203: An altered profile of ribosomal proteins and ERK-eIF4E translational control in an inflammatory breast cancer model of acquired resistance and reversal is associated with pathological complete response in patients
Authors: Devi Gayathri R. , PAI Pritha , Foster Matthew W. , Sannareddy Dorababu S. , Lee Seayoung , Laere Steven V. 
Published: March 2024

Abstract
Background: Drug resistance is a major challenge in inflammatory breast cancer (IBC), a hyperproliferative subtype characterized by the presence of diffuse tumor cell clusters that show high level of heterogeneity. As the degree of tumor heterogeneity during cancer progression can cause evolution of cell states that can either compete or co-operate resulting in therapeutic failure, the study objective was to identify drug resistance networks that can serve as biomarkers or therapeutic targets.
Methods: Integrated transcriptomic and proteomic profiling approach was conducted in a progression model of acquired drug resistance and its reversal comprised of a treatment-naïve patient-derived SUM149 cell line, along with two isogenic derivatives and representing drug-resistant (rSUM149) and resistance-reversal states (rrSUM149). Global gene expression analysis in IBC patients (n=87) recorded responses to neoadjuvant chemotherapy. Based on the data, targeted multikinase inhibitors were evaluated in viability and signaling assays.
Results: We identified specific ribosomal proteins associated with resistance acquisition, which correlated with high levels of pERK, CDK1, XIAP, and SOD2. Conversely, the resistance reversal in rrSUM149 showed almost complete normalization to the profile of SUM149. However, VIPER analysis revealed proteins related to ribosomal processes (AGO2, Exportin 1, RPL5) that did not revert in rrSUM149, suggesting this pathway may have pleiotropic effects in governing drug resistance. Notably, genes linked to ribosomal processes were significantly enriched (P&lt;0.001) among the overexpressed genes in IBC patients (n=87) who exhibited pCR to neoadjuvant chemotherapy. This is crucial as IBC tumors, including rSUM149, exhibit MAPK hyperactivation including in the presence of EGFR tyrosine kinase inhibitors. Treatment with Merestinib, a multikinase inhibitor, suppressed pERK, peIF4E, downstream targets like CDK1, and ribosomal protein IMP3 underscoring the impact on protein synthesis signaling crucial for countering translational dependence in cancer cells. Additionally, Merestinib synergized with EGFR-TKI (lapatinib) in increasing cell death in all three states.
Conclusion: Overall, our study describes adaptive changes in response to both therapeutic stress and therapy break that have the potential to serve as biomarkers or extended for pharmacological interrogation toward precision medicine for this rare, understudied cancer. Furthermore, the ability of Merestinib, in clinical trials, to target translational dependence is attractive as cancer cells often appropriate these signaling pathways to gain tolerance to various stress stimuli. Support: NIH-R01CA264529; DoD Breast Cancer Breakthrough level 2 Award W81XWH2010153
Citation Format: Gayathri R. Devi, Pritha PAI, Matthew W. Foster, Dorababu S. Sannareddy, Seayoung Lee, Steven V. Laere. An altered profile of ribosomal proteins and ERK-eIF4E translational control in an inflammatory breast cancer model of acquired resistance and reversal is associated with pathological complete response in patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6203.