Prognosis of lung cancer remains poor despite the recent development of new chemotherapeutic agents. Novel therapeutic strategies therefore need to be developed. The search for factors inhibiting tumor growth in a paracrine/autocrine fashion might result in a well-tolerated adjuvant tumor therapy. In this study we aimed to identify candidate genes for such inhibitors of tumor cell growth. Native and heat-inactivated supernatants of confluent, slow growing H460 tumor cell cultures and of sparse (non-confluent), fast growing H460 tumor cell cultures were tested in proliferation assays. We observed that native supernatant of confluent H460 and A549 cells contain proteins inhibiting tumor cell growth of NSCLC cell lines. Microarray gene expression analysis of sparse and confluent H460 cells exhibited overexpression of 7 candidate genes in confluent, slow growing cells. The products of these genes possess cell growth inhibitory function and also exist in the extracellular compartment. The increased expression level of these genes was verified using real-time RT-PCR analysis. Our results show that especially components of IGF pathway appear to be involved in exogenous growth inhibition of confluent cells. Further investigations of these factors may result in the identification of autocrine/paracrine tumor cell growth inhibitory proteins for future use in clinical applications.

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