The Roles of Neutrophil Elastase in Lung Cancer

Lung cancer is the leading cause of cancer death in Hong Kong. Lung adenocarcinomas is the most common type, accounting for 70% of lung cancer and the molecular target of epidermal growth factor receptor (EGFR) gene mutation at exons 18 - 21 is present in about 50% of lung adenocarcinomas. The v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (K-ras) mutations are commonly present in the other 50% that are EGFR wildtype. EGFR and K-ras mutations are found to be mutually exclusive in the same tumor. EGFR-tyrosine kinase inhibitor (TKI) can be used as treatment for EGFR mutated tumors while no specific targeted therapy can be recommended for EGFR wildtype tumors and these patients often receive chemoirradiation, which is toxic and clinical response is suboptimal. There is a need to find alternative molecular pathways/targets in EGFR wildtype lung adenocarcinomas. Even with EGFR mutations, good clinical response to EGFR-TKI is achieved in about 70% of these patients. This would mean suboptimal targeting of the EGFR gene or the presence of alternative pathways mediating tumor progression and susceptibility to therapy. Exploration of molecular pathways in lung cancer may allow for discovery of new molecular targets for therapeutic development. Neutrophil infiltration is frequently observed in lung cancer. Recognized similarities between neutrophils and cancer cells include (i) ability to circulate as single cells; (ii) target attachment via vascular system; (iii) target invasion. The major difference is that migrated neutrophils will undergo apoptosis while cancer cells can escape apoptosis. This led to the postulation that neutrophils and cancer cells may share similar inflammatory cascades by secreting a similar panel of proteases, and one of these could be neutrophil elastase (NE). Animal studies demonstrated that NE from neutrophils moves into lung tumor cells and mediates lung tumor growth via degradation of Insulin receptor substrate-1 (IRS-1), leading to act