The rapidly expanding catalogue of human oncogenic mutations, coupled with difficulties in identifying the cellular targets of active compounds in phenotypic screens, has refocused drug discovery efforts on inhibitors of specific cellular proteins. This new ‘target-based’ approach has enjoyed some spectacular successes in several types of tumours, including non-small-cell lung cancer (NSCLC). Epidermal growth factor receptor (EGFR) mutations occur in 17% of NSCLC patients, with notable response to single agent therapy. Unfortunately, all patients eventually develop acquired resistance to EGFR tyrosine kinase inhibitors (TKIs), while complete remission rate to EGFR TKIs monotherapy is low. Priming BIM, a proapoptotic signalling BH3-only protein, induces sensitivity to erlotinib [Tarceva®] in EGFR-mutant cell lines. Synthetic lethal approaches and pre-emptive therapies based on the initial expression of BIM may significantly improve treatment outcomes. EGFR mutations result in transient pro-death imbalance of survival and apoptotic signalling in response to EGFR inhibition. Src homology 2 domain-containing phosphatase 2 is essential to the balance between extracellular signal-regulated kinase, phosphoinositide- 3-kinase/protein kinase B and signal transducer and activator of transcription 3 activity. Furthermore, stromal hepatocyte growth factor confers EGFR TKI resistance and induces inter-receptor crosstalk with Ephrin Type-A receptor 2, CDCP1, AXL, and JAK1. A better understanding of the complex cancer molecular biology of EGFR mutant lung cancer is crucial for development of effective treatment and design of successful future clinical studies.
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