P2.01-076 Drebrin: A New Targetable Molecular Marker of Lung Adenocarcinoma

Abstract

Embryonic antigens, such as carcinoembryonic antigen (CEA) and alfa-fetoprotein (AFP), are routinely employed as serum and immunohistochemical tumor markers in clinical medicine. Since they are not expressed in adult human tissues, it is reasonable to conclude that embryonic antigens are extremely specific tumor markers. However, no systematic studies have yet identified clinically useful embryonic antigens for tumor diagnosis. In the present study, we developed a strategy for systematic identification of lung adenocarcinoma markers using monoclonal antibodies generated from embryonic swine tissue. Swine mRNA shows more than 80% homology with human mRNA, and embryonic swine tissue is thought to be a useful material for detection of human embryonic markers. In order to produce mouse monoclonal antibodies, we immunized BALB/c mice by injection of fetal swine lung nuclear fraction into the hock, and used a human lung adenocarcinoma nuclear fraction for the second immunization. We recovered lymph nodes from the mice, and fused mouse B lymphocytes with the murine myeloma cell line SP2/0 using polyethylene glycol. The resulting hybridomas were then selectively cultured. For selection of interesting hybridoma clones, we performed immunohistochemical staining using the supernatant from each one, with tissue microarray loading swine fetal and adult lung, human lung cancer and normal lung tissue. Immunohistochemical screening of 284-clones showed that the antibodies derived from four of them were strongly reactive with the cytoplasm and cytomembrane of fetal swine lung and human lung cancer. We then focused on one clone (B246) whose antibody reacted most clearly with human lung adenocarcinoma cells. Protein microarray analysis confirmed that B246 reacted specifically with “drebrin”, one of the actin binding proteins, originally identified in neuronal cells. There are two drebrin isoforms in human tissue: drebrin E (embryonic) is abundant in the developing neurons, and drebrin A (adult) is expressed in adult brain. We then examined the association of the drebrin expression pattern with the pathological features and prognosis of lung adenocarcinoma using 200 selected cases for which formalin-fixed and paraffin-embedded samples were available. Drebrin immunohistochemistry delineated the samples into those with strong (n=85) and weak (n=115) drebrin expression. Kaplan-Meier analysis demonstrated a significant difference in disease-free survival (DFS) between the groups with strong and weak drebrin expression (p=0.033). Drebrin is expressed specifically in lung adenocarcinoma and is associated with outcome. The present findings indicate that drebrin is a new marker of lung adenocarcinoma and indicative of prognosis.