Current mechanism of acquired resistance to epidermal growth factor receptor-tyrosine kinase inhibitors and updated therapy strategies in human nonsmall cell lung cancer

Lung cancer continues to be a major health problem and the most common cancer-related mortality worldwide with about 80%-85% patients suffering from nonsmall cell lung cancer (NSCLC). More than 80% of NSCLC cases are often diagnosed as advanced stage and harbor epidermal growth factor receptor (EGFR) activating mutation. Although great success in initial response to EGFR-tyrosine kinase inhibitors (EGFR-TKIs) are found in EGFR-mutant NSCLC patients, acquired resistance usually occurs on the continuous treatment. Here, we provide an overview on the mechanism of acquired resistance to EGFR-TKIs in NSCLC therapy as well as current preclinical and clinical evidence of new therapy strategies and inhibitors in the treatment of NSCLC. Many studies have shown that original or induced T790M mutation, human EGFR 2 amplification, and activated secondary signaling such as MET amplification or phosphatidylinositol 3-kinase mutation can lead to acquired resistance to EGFR-TKIs. In addition, transformation from NSCLC to SCLC or conferred epithelial to mesenchymal transition has also been identified as mechanisms of acquired resistance to EGFR-TKIs. Increasing evidence has proven that non-coding RNA including long noncoding RNAs and microRNAs or new EGFR mutation is involved in acquired resistance. Preclinical and clinical Phase 1-3 evidence on combination drug therapy or new generation inhibitors with different tumor-targeting approaches have made those strategies the promising options for EGFR-TKI-resistant NSCLC therapy. This review aims to get deep insight into providing a state-of-the-art overview of the recent advances in the mechanisms of acquired resistance and new strategies for targeted cancer therapy in EGFR-TKI-resistant NSCLC.