Activation mutations in EGF receptor kinase have the advantages of cell physiology in the bronchiolar region : Implication of anti-apoptotic signals and lung tumorigenesis and metastasis.

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Backgrounds : The evolving concept of molecular targeting drugs has revolutionized the treatment of cancer. The first success of imatinib targeting the chimera protein of Bcr-abl in hematologic malignancies is followed by drugs for solid tumors, gefitinib or erlotinib, targeting the activation form of EGFR kinase (either deletion or L858R mutation). The latter is unique in facts that (1)Rthe mutation is specific for lung adenocarcinoma, (2)resulting in high affinity for ATP and anti-apoptosis, and (3) somatic but high incidence in far-east Orientals. We hypothesized that this specific EGFR mutation is selected because of the advantages in the respiratory bronchiolar regions.Methods : We used PC9 (EGFR deletion type), 11-18 (EGFR L858R) and A549 (EGFR wild type) cell lines and prepared COS-7 cells with EGFR/wt, EGFR/del, EGFR/L858R. Western blot analysis for in vitro signaling, and in vivo metastatic model using nude mice were performed. Expression microarray (Affymetrix U133 plus 2.0) … More analysis were conducted using 3 cell lines.Results : 1. In vitro signaling revealed that (1) while PC9 is constitutively active in usual FCS medium, 11-18 or COS-7 showed phosphorylation in Tyr1068 only after the addition of EGF after overnight starvation. (2) The pEGFR/Tyr1068 was detected in the order of COS-7/EGFR wt> COS-7/EGFR del>COS-7.2. PC9 (1O'6 cells) administered in the cervical vein resulted in tumors only in the lung in 2 months. Micro-metastatic lesions in the bronchiolar region were found using PC9 labeled with Cell Tracker 1 week after administration.3. Microarray expression analysis of PC9, 11-18, and A549 cell lines revealed two characteristic patterns: (1) PC9=11-18 > A549 (ARHGAP29 etc) or PC9=11-18 < A549 (DKK1 etc). (2) PC9 > 11-18=A549 (FOX03A etc) or PC9 < 11-18=A549 (catenin α 1 etc).Conclusion : Specific EGFR activation mutation showed distinct patterns of phosphrylation signaling. In vivo micro-metastasis was seen in the bronchiolar regions. Two characteristic patterns in the microarray expression analysis using PC9, 11-18, and A549 indicated the possible difference in the EGFR signaling and biological outcome. Less