Mer or Axl receptor tyrosine kinase inhibition promotes apoptosis, blocks growth and enhances chemosensitivity of human non-small cell lung cancer

• Published in: Oncogene Vol. 32; no. 29; pp. 3420 - 3431
• Main Authors: Linger, R M A, Cohen, R A, Cummings, C T, Sather, S, Migdall-Wilson, J, Middleton, D H G, Lu, X, Barón, A E, Franklin, W A, Merrick, D T, Jedlicka, P, DeRyckere, D, Heasley, L E, Graham, D K
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18-07-2013; Nature Publishing Group
• Subjects: 631/67/1059/602; 631/80/82/23; 631/80/86; 692/699/67/1612/1350; AKT protein; Animals; Apoptosis; Apoptosis - physiology; Axl protein; Bcl-2 protein; Bcl-x protein; Blotting, Western; Breast; c-Mer Tyrosine Kinase; Carcinoma, Non-Small-Cell Lung - metabolism; Carcinoma, Non-Small-Cell Lung - pathology; Care and treatment; Cell Biology; Cell Proliferation; Chemotherapy; Cyclic AMP response element-binding protein; Development and progression; Drug Resistance, Neoplasm - physiology; Female; Gene Knockdown Techniques; Gene therapy; Genetic aspects; Human Genetics; Humans; Immunoprecipitation; Internal Medicine; Kinases; Lung cancer; Lung cancer, Non-small cell; Lung Neoplasms - metabolism; Lung Neoplasms - pathology; Male; MAP kinase; Medicine; Medicine & Public Health; Mice; Middle Aged; Non-small cell lung carcinoma; Oncology; original-article; Pancreatic cancer; Physiological aspects; Prostate; Protein tyrosine kinase; Protein-tyrosine kinase receptors; Proto-Oncogene Proteins - metabolism; Receptor Protein-Tyrosine Kinases - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Signal transduction; Signal Transduction - physiology; Small cell lung carcinoma; Survivin; Therapeutic targets; Tissue Array Analysis; Tumors; Xenograft Model Antitumor Assays; Xenografts; United States; United States > US; targeted therapy; receptor tyrosine kinase; xenograft; chemosensitivity; signal transduction; MerTK
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/onc.2012.355

Non-small cell lung cancer (NSCLC) is a prevalent and devastating disease that claims more lives than breast, prostate, colon and pancreatic cancers combined. Current research suggests that standard chemotherapy regimens have been optimized to maximal efficiency. Promising new treatment strategies involve novel agents targeting molecular aberrations present in subsets of NSCLC. We evaluated 88 human NSCLC tumors of diverse histology and identified Mer and Axl as receptor tyrosine kinases (RTKs) overexpressed in 69% and 93%, respectively, of tumors relative to surrounding normal lung tissue. Mer and Axl were also frequently overexpressed and activated in NSCLC cell lines. Ligand-dependent Mer or Axl activation stimulated MAPK, AKT and FAK signaling pathways indicating roles for these RTKs in multiple oncogenic processes. In addition, we identified a novel pro-survival pathway—involving AKT, CREB, Bcl-xL, survivin, and Bcl-2—downstream of Mer, which is differentially modulated by Axl signaling. We demonstrated that short hairpin RNA (shRNA) knockdown of Mer or Axl significantly reduced NSCLC colony formation and growth of subcutaneous xenografts in nude mice. Mer or Axl knockdown also improved
in vitro
NSCLC sensitivity to chemotherapeutic agents by promoting apoptosis. When comparing the effects of Mer and Axl knockdown, Mer inhibition exhibited more complete blockade of tumor growth while Axl knockdown more robustly improved chemosensitivity. These results indicate that Mer and Axl have complementary and overlapping roles in NSCLC and suggest that treatment strategies targeting both RTKs may be more effective than singly-targeted agents. Our findings validate Mer and Axl as potential therapeutic targets in NSCLC and provide justification for development of novel therapeutic compounds that selectively inhibit Mer and/or Axl.