The effect of tumor microenvironment on autophagy and sensitivity to targeted therapy in EGFR-mutated lung adenocarcinoma

Abstract

Purpose: Lung cancer is the top cancer killer worldwide. Tyrosine kinase inhibitors (TKIs), for example erlotinib, are commonly used to target epidermal growth factor receptor (EGFR)-mutated lung adenocarcinoma (ADC). Autophagy is a cellular response to stress, serving as a protective mechanism during anticancer therapy. The tumor microenvironment (TME) is composed of non-tumor cells that include fibroblasts. Our study aimed to investigate the effect of TME on autophagy and TKI sensitivity. Methods: A model of TME was established by direct or indirect (transwell system) co-culture of HCC827 (EGFR exon 19-deleted lung ADC) and MRC-5 (human lung fibroblast) cells. Cell viability, apoptosis, autophagic proteins, epithelial-to-mesenchymal transition and cytokine (interleukin (IL)-6 and IL-8) expression were investigated. The effect of combined erlotinib/chloroquine treatment was studied in both a co-cultured in vitro model and HCC827 xenografts in nude mice. Results: Activation of MRC-5 cells with actin over-expression was evident when co-culturing with HCC827 cells. Direct co-culturing resulted in autophagy (p62 degradation) and cytokine storm (IL-6 and IL-8 production). Following cell sorting, autophagy and cytokine production were observed in both HCC827 and MRC-5 cells, with epithelial-to-mesenchymal transition (EMT) in HCC827 cells. Human recombinant IL-6 and IL-8 induced autophagy in homotypical HCC827 and MRC-5 cells. HCC827 cells became more sensitive to erlotinib upon co-culturing with MRC-5 cells, while the synergistic combination of erlotinib and chloroquine (autophagy inhibitor) was more pronounced in the presence of TME. Tumor growth was significantly suppressed with combined erlotinib/chloroquine compared with erlotinib in HCC827 xenografts. Conclusions: A model of TME with MRC-5 fibroblasts induced autophagy, cytokine production and EMT in HCC827 lung ADC. Combined erlotinib/chloroquine remained synergistic in the presence of TME, with enhanced tumor suppression compared with erlotinib alone in a HCC827 xenograft model.