Potential therapeutic impact of CD13 expression in non-small cell lung cancer

BACKGROUND Aminopeptidase N (CD13) is a zinc-binding protease that has functional effects on both cancerogenesis and tumor angiogenesis. Since CD13 is an antigen suitable for molecular targeted therapies (e.g. tTF-NGR induced tumor vascular infarction), we evaluated its impact in NSCLC patients, and tested the effects of the CD13-targeted fusion protein tTF-NGR (truncated tissue factor (tTF) containing the NGR motif: asparagine-glycine-arginine) in vivo in nude mice. METHODS Expression of both CD13 and CD31 was studied in 270 NSCLC patients by immunohistochemistry. Clinical correlations and prognostic effects of the expression profiles were analyzed using univariate and multivariate analyses. In addition, a microarray-based analysis on the basis of the KM plotter database was performed. The in vivo effects of the CD13-targeted fusion protein tTF-NGR on tumor growth were tested in CD1 nude mice carrying A549 lung carcinoma xenotransplants. RESULTS CD13 expression in tumor endothelial and vessel associated stromal cells was found in 15% of the investigated samples, while expression in tumor cells was observed in 7%. Although no significant prognostic impact was observed in the full NSCLC study cohort, both univariate and multivariate models identified vascular CD13 protein expression to correlate with poor overall survival in stage III and pN2+ NSCLC patients. Microarray-based mRNA analysis for either adenocarcinomas or squamous cell carcinomas did not reveal any significant effect. However, the analysis of CD13 mRNA expression for all lung cancer histologies demonstrated a positive prognostic effect. In vivo, systemic application of CD13-targeted tissue factor tTF-NGR significantly reduced CD13+ A549 tumor growth in nude mice. CONCLUSIONS Our results contribute a data basis for prioritizing clinical testing of tTF-NGR and other antitumor molecules targeted by NGR-peptides in NSCLC. Because CD13 expression in NSCLC tissues was found only in a specific subset of NSCLC patients, rigorous pre-therapeutic testing will help to select patients for these studies.