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Genetic Predictors of MEK Dependence in Non–Small Cell Lung Cancer

Departments of ¹ Pediatrics, ² Medicine, and ³ Molecular Pharmacology and Chemistry, ⁴ Human Oncology and Pathogenesis Program, and ⁵ Computational Biology Center, Memorial Sloan-Kettering Cancer Center; Department of ⁶ Pharmacology and ⁷ Physiology and Biophysics, Weill Cornell Graduate School of Medical Science, New York, New York; ⁸ Hamon Center for Therapeutic Oncology Research and ⁹ Department of Pathology, University of Texas Southwestern Medical Center, Dallas, Texas; and ¹⁰ Department of Cancer and Thoracic Surgery, Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Okayama, Japan

Requests for reprints: David B. Solit, Department of Medicine and Human Oncology and Pathogenesis Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065. Phone: 646-888-2641; Fax: 646-888-2595; E-mail: solitd{at}mskcc.org.

Key Words: BRAF • non–small cell lung cancer • MEK inhibitor • PD0325901 • EGFR mutation • gefitinib • erlotinib

Hyperactivated extracellular signal-regulated kinase (ERK) signaling is common in human cancer and is often the result of activating mutations in BRAF, RAS, and upstream receptor tyrosine kinases. To characterize the mitogen-activated protein kinase/ERK kinase (MEK)/ERK dependence of lung cancers harboring BRAF kinase domain mutations, we screened a large panel of human lung cancer cell lines (n = 87) and tumors (n = 916) for BRAF mutations. We found that non–small cell lung cancers (NSCLC) cells with both V600E and non-V600E BRAF mutations were selectively sensitive to MEK inhibition compared with those harboring mutations in epidermal growth factor receptor (EGFR), KRAS, or ALK and ROS kinase fusions. Supporting its classification as a "driver" mutation in the cells in which it is expressed, MEK inhibition in ^V600EBRAF NSCLC cells led to substantial induction of apoptosis, comparable with that seen with EGFR kinase inhibition in EGFR mutant NSCLC models. Despite high basal ERK phosphorylation, EGFR mutant cells were uniformly resistant to MEK inhibition. Conversely, BRAF mutant cell lines were resistant to EGFR inhibition. These data, together with the nonoverlapping pattern of EGFR and BRAF mutations in human lung cancer, suggest that these lesions define distinct clinical entities whose treatment should be guided by prospective real-time genotyping. To facilitate such an effort, we developed a mass spectrometry-based genotyping method for the detection of hotspot mutations in BRAF, KRAS, and EGFR. Using this assay, we confirmed that BRAF mutations can be identified in a minority of NSCLC tumors and that patients whose tumors harbor BRAF mutations have a distinct clinical profile compared with those whose tumors harbor kinase domain mutations in EGFR. [Cancer Res 2008;68(22):9375–83]