IL-8 confers resistance to EGFR inhibitors by inducing stem cell properties in lung cancer

Abstract

Epidermal growth factor receptor (EGFR)-targeted strategy is limited by resistance. We identify the potential genes involved in EGFR TKI (tyrosine kinase inhibitor) resistance and study the therapeutic mechanism in the non-small cell lung cancers. Potential genes involved in resistance were examined by analyzing datasets from a pair of EGFR TKI-sensitive (PC9) and TKI-resistant cells (PC9/gef). Blood specimens from patients taking EGFR TKI as first-line treatment were used to examine the correlation between drug's efficacy and IL-8 level. The effects of IL-8 on gefitinib-induced apoptosis, stemness, and in vivo tumorigenicity were investigated using established cell lines. We identified IL-8 was up-regulated in gefitinib-resistant cells, and high plasma IL-8 level was correlated with shorter progression-free-survival time. IL-8 overexpression suppressed gefitinib-induced apoptosis in gefitinib-sensitive cells. By contrast, suppression of IL-8 enhanced gefitinib-induced cell death in gefitinib-resistant cells. IL-8 also increased stem-like characteristics including aldehyde dehydrogenase activity, expression of stemness-related genes, clonogenic activity, side-population, and in vivo tumorigenicity. Consistently, knockdown of IL-8 leads to loss of stem cell-like characteristics in gefitinib-resistant cells. Our study demonstrates an important role for IL-8, and suggests IL-8 is a potential therapeutic target for overcoming EGFR TKI resistance.

IL-8 signaling is involved in resistance of lung carcinoma cells to erlotinib

“…As predicted, both A549 and HCC827 erlotinib-resistant cell lines exhibited greater percentage of ALDH bright cells (25.5 and 18.9%, respectively, Figure 6C), compared to their corresponding parental lines (14.7 and 9.9% for A549 and HCC827, respectively). This data was in agreement with previous reports demonstrating the enrichment of stem-like populations in tumor cells selected for resistance to EGFR inhibition in long-term culture [30]. To further investigate whether upregulation of the IL-8 axis could be related to the presence of higher percentage of cells bearing a stem-like phenotype, erlotinib-resistant A549 and HCC827 cells were separated into CXCR1 positive and negative fractions by using magnetic beads, and the levels of the stem cell marker OCT4 were evaluated by real time PCR analysis in each cell fraction.…”

“…These results indicated that mesenchymal-like cells generated in the context of erlotinib resistance have upregulated the IL-8/IL-8R signaling loop, which, in turn, could be responsible for the acquisition and/or maintenance of mesenchymal traits in those cells. The results are also in agreement with a recent report demonstrating the significant upregulation of IL-8 in gefitinib-resistant, EGFR mutated lung cancer cells [30]. …”

“…To further investigate whether upregulation of the IL-8 axis could be related to the presence of higher percentage of cells bearing a stem-like phenotype, erlotinib-resistant A549 and HCC827 cells were separated into CXCR1 positive and negative fractions by using magnetic beads, and the levels of the stem cell marker OCT4 were evaluated by real time PCR analysis in each cell fraction. As shown in Figure 6D, there was a significant increase of OCT4 mRNA levels in the CXCR1 positive vs. negative fraction, thus reinforcing the observations that IL-8 signaling is enhanced in stem-like cell populations enriched in the EGFR-resistant cell lines [30]. …”

Epithelial-mesenchymal transition and inflammation at the site of the primary tumor

“…In particular, multiple reports have now demonstrated that acquisition of lung cancer resistance to EGFR inhibition is associated, in a subset of patients, with the occurrence of EMT [97–100]. Furthermore, several recent reports have implicated the IL-8/IL-8R axis in the resistance of lung cancer to the widely used EGFR tyrosine kinase inhibitors gefitinib [101] and erlotinib [102]. Observed among various preclinical model systems, lung cancer cells resistant to EGFR inhibition have been shown to transition into a mesenchymal-like phenotype while simultaneously upregulating the expression of both IL-6 and IL-8.…”

“…Interestingly, blockade of IL-8 signaling was shown to effectively reduce the mesenchymal features of erlotinib-resistant cells, and more importantly, to markedly enhance their susceptibility to erlotinib or to chemotherapies [102]. Work from Liu and colleagues also revealed a central role for the chemokine IL-8 in tumor resistance to the EGFR inhibitor gefitinib [101]. In particular, this study demonstrated that IL-8 levels in the plasma inversely correlated with median progression-free survival of patients with stage IV lung adenocarcinoma with EGFR-mutation positive tumors who also received gefitinib or erlotinib as their first-line treatment.…”