Small cell neuroendocrine transdifferentiation in EGFR-mutant lung cancer evolving from mesenchymal drug-tolerant state

Small-cell neuroendocrine (SCN) transdifferentiation and epithelial-mesenchymal transition (EMT) are recognized as two kinds of lineage plasticity and they emerged as a model of targeted therapy evasion in a subset of EGFR-mutated NSCLC. Whether SCN transdifferentiation could phenocopy in isogenic acquired resistant clinically relevant cells and the association between EMT and SCN transdifferentiation remain unknown. 　We established several mesenchymal gefitinib-acquired resistant cells from HCC827 and showed SCN transdifferentiation could evolve from mesenchymal drug-tolerant state. The SCN property and the mesenchymal property in cancer cells are negatively correlated. Dynamic IL-6, correlated with mesenchymal property, could reflect this process and it might be a ready-to-use biomarker to monitor this process. By long term step-wise treatment with gefitinib, we established serial gefitinib-acquired resistant sublines (HCC827GRs) from HCC827 lung adenocarcinoma cells, harboring EGFR exon 19 deletion. HCC827GR was a parental resistant subline with unstable gefitinib-resistant ability while it was cultured in drug-free medium by passages. To obtain stable gefitinib-resistant sublines, we maintained HCC827GR in culture medium with or without gefitinib (1 μM) over 6 months to obtain two different sublines, HCC827GR+ and HCC827GR.M6, respectively.