Drug Delivery and Drug Resistance: EGFR-Tyrosine Kinase Inhibitors in Non-Small Cell Lung Cancer

The epidermal growth factor receptor (EGFR) pathway has emerged as an important target in the treatment of non-small cell lung cancer (NSCLC). Currently available EGFR inhibitors approved for the therapy of NSCLC include the small molecules erlotinib and gefitinib. They are administered orally and interfere with the intracellular tyrosine kinase domain. These agents appear most effective in patients with tumors which are highly dependent on the EGFR signaling pathway because of EGFR activating mutations or amplifications. The use of EGFR tyrosine kinase inhibitors prolongs survival in metastatic NSCLC. However, despite the dramatic initial responses to treatment in some cases, NSCLC eventually becomes resistant to EGFR-tyrosine kinase inhibitors (TKIs). Mechanisms of resistance include EGFR secondary mutations that interfere with drug binding. Besides, molecular cross-talk and redundancy between EGFR and other signaling pathways creates alternative pathways for tumor cell proliferation promoting resistance to EGFR inhibition such as the amplification of the receptor tyrosine kinases MET. Polymorphisms in EGFR and EGFR pathwayrelated genes, as well as in genes involved in drug metabolism and intake/efflux might also predict clinical outcome and