Molecular changes in EGFR downstream signalling and intracellular calcium changes associated with the cisplatin-resistant phenotype of lung cancer cells

Introduction: Lung cancer is the most common cause of cancer-related death worldwide. Cisplatin remains the treatment of choice, despite clinical advances in medicine. However, resistance to these drugs limits their clinical efficacy. Different tumour cells have various mechanisms of drug resistance and different survival pathways, which makes it difficult to determine the underlying causes of resistance. Purpose: Identify molecular changes triggered by cisplatin resistance in the EGFR signalling pathways and intracellular calcium to identify potential targets for novel combination therapies that could improve patient survival. Experimental design and methods: An isogenic clinical model was used to generate a cisplatin-resistant phenotype (CRP) in mutant-EGFR non-small-cell lung cancer cells (H838, HCC827, H1975, and H1650) and small-cell lung cancer cells (H1339). The effect of cisplatin on cell survival, proliferation, colony formation, and apoptosis was characterised in CRP cells and age-matched naïve cells. EGFR phosphorylation and signalling were analysed using an EGFR signalling antibody array. We measured the efficacy of third-generation EGFR tyrosine kinase inhibitors (erlotinib, gefitinib, afatinib, and rociletinib) at clinical concentrations. Results: Cisplatin decreased proliferation, increased resistance to cell death, and enhanced the clonogenic survival of CRP cells. Cisplatin resistance altered EGFR expression, EGFR phosphorylation, and EGFR downstream signalling molecules in CRP cells, but this varied between cell lines. The effect of EGFR TKIs was similar in CRP cells and their precursors. There no significant difference in calcium levels between cisplatin-resistant and naïve cells. Conclusion: EGFR signalling was altered in CRP lung cancer cells, and these effects were cell-specific. In addition, cisplatin resistance induced chemosensitisation to erlotinib but not to other TKIs in EGFR-wild-type cells. These results provide a deeper understanding of the EGFR downstream cellular events involved in cisplatin resistance. Cisplatin resistance did not change intracellular calcium levels