Abstract 3864: Targeting IL-6/STAT3 signaling in EGFR-mutant drug tolerant persister cells
Authors: Patel Sonia A. , Nilsson Monique , Yang Yan , Shen Li , Wang Jing , Poteete Alissa , Yu Xiaoxing , Ren Xiaoyang , Le Xiuning , Heymach John 
Published: June 2023

Abstract
While the majority of epidermal growth factor receptor (EGFR) mutant non-small cell lung cancer (NSCLC) patients initially respond to treatment with an EGFR tyrosine kinase inhibitor (TKI), most will eventually develop acquired resistance to these agents. The evolution of tumor cells with acquired resistance to targeted agents initially involves the persistence of a drug-tolerant subpopulation of tumor cells which display a transient and flexible resistant state. These persister cells can remain quiescent for prolonged periods of time, but eventually give rise to fully drug resistant tumor cells that resume growth and metastatic spread. The signaling pathways that allow persister cells to remain viable or to re-activate expansive growth are poorly understood. We and others have reported that EGFR TKI resistance that occurs independent of secondary EGFR mutations or MET amplification is associated with an epithelial to mesenchymal transition (EMT). Our analysis of tumor cells that had undergone EMT-mediated resistance to the EGFR TKI osimertinib revealed that interleukin-6 (IL-6) was highly upregulated in resistant cells as compared to parental cells. We find that in the setting of EGFR mutant NSCLC, IL-6 suppresses the anti-tumor cell activity of T cells and NK cells. To assess the role of IL-6 in the early events of EGFR TKI resistance, we generated drug-tolerant persister cells by treating EGFR mutant HCC4006 and HCC827 NSCLC cells with the EGFR TKI osimertinib for 10 days and then assessed IL-6 expression. We observed that IL-6 was upregulated at both the RNA and protein levels in EGFR-TKI persister cells as compared to parental cells. While the cell surface expression of IL6R was not significantly increased in EGFR-TKI persister cells as compared to parental cells, we observed increased secretion of soluble IL6R in persister cells by ELISA assay. We next assessed changes in protein expression and activation in drug tolerant persister cells by reverse phase protein array (RPPA) and observed that p-STAT3, a key component of the IL-6 signaling pathway, was significantly elevated in persister cells as compared parental cells or cells treated with osimertinib for 24 hours. Using genetically engineered mouse models (GEMM) of EGFRL858R mutant lung cancer, we also observed a similar upregulation of both IL-6 and p-STAT3 expression at the RNA and protein levels in EGFR-mutant tumors treated with osimertinib for 2 or 4 weeks. Additionally, circulating levels of IL-6 also are elevated in EGFRL858R GEMMs treated with osimertinib for 2 or 4 weeks. Collectively, our data indicates that upregulation of IL-6 is an early event in the evolution of drug resistance. Given the role of IL-6 in promoting EGFR TKI resistance, further studies investigating whether targeting of IL-6 signaling may impair the survival or outgrowth of persister populations are warranted.
Citation Format: Sonia A. Patel, Monique Nilsson, Yan Yang, Li Shen, Jing Wang, Alissa Poteete, Xiaoxing Yu, Xiaoyang Ren, Xiuning Le, John Heymach. Targeting IL-6/STAT3 signaling in EGFR-mutant drug tolerant persister cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3864.