Phenotypic plasticity in a novel set of EGFR tyrosine kinase inhibitor‐adapted non‐small cell lung cancer cell lines

Here, we introduce novel sublines of the EGFR-mutant non-small cell lung cancer (NSCLC) cell lines HCC827 and HCC4006 adapted to the EGFR kinase inhibitors gefitinib (HCC827rGEFI2μm, HCC4006rGEFI1μm), erlotinib (HCC827rERLO2μm, HCC4006rERLO1μm) and afatinib (HCC827rAFA50nm, HCC4006rAFA100nm). All sublines displayed resistance to gefitinib, erlotinib, afatinib and the third-generation EGFR kinase inhibitor osimertinib that overcomes T790M-mediated resistance. HCC4006rERLO1μm displayed a spindle-like morphology in agreement with previous findings that had detected epithelial–mesenchymal transition (EMT) in its precursor cell line HCC4006rERLO0.5μm. EMT had also been reported for the HCC4006rGEFI1μm precursor cell line HCC4006rGEFI0.5μm and for HCC4006rAFA100nm, but the morphologies of HCC4006rGEFI1μm or HCC4006rAFA100nm did not support this, suggesting plasticity in EMT regulation during the drug adaptation process and in established resistant cell lines. Accordingly, HCC4006rERLO1μm displayed resistance to MEK and AKT inhibitors in contrast to its precursor HCC4006rERLO0.5μm. We also detected metabolic plasticity, that is a temporary Warburg metabolism, in HCC4006 and HCC827rGEFI2μm. Response profiles to cytotoxic anticancer drugs, kinase inhibitors and HDAC inhibitors resulted in complex patterns that were specific for each individual subline, indicating individual resistance phenotypes. All resistant sublines remained sensitive or displayed collateral sensitivity to at least one of the investigated drugs. In conclusion, the comparison of EGFR kinase-resistant NSCLC sublines with their precursor cell lines that had been previously characterised at a lower resistance level and metabolic investigations indicated phenotypic plasticity during the resistance formation process and in established cell lines. This plasticity may contribute to the well-known variability in cell line phenotypes observed between different laboratories and in intra-laboratory experiments.