ABSTRACT
PURPOSE: Autocrine growth stimulation by IGF-II and BDNF is frequently observed in neuroblastoma. The signals of the receptors of these growth factors are transduced to the nucleus via the Ras-MAP-kinase pathway where they induce proliferation. Inactivation of Ras-proteins by farnesyltransferase inhibitors such as FTI-277 disrupts growth stimulation of ras-transformed cells. We investigated whether FTI-277 is also active against tumor cells with constitutively activated growth factor receptors but lacking ras-mutations. METHOD: We analyzed eight different neuroblastoma cell lines for the expression of BDNF and its receptor trkB. Two of these cell lines with a complete autocrine BDNF loop were treated with FTI-277, and the effects of Ras-inactivation on the signal transduction of BDNF were analyzed. RESULTS: Treatment of neuroblastoma cells with 10 microM FTI-277 for 4 days reduced the amount of membrane-bound Ras-protein to almost 50%. Activation of MAP-kinase, induction of N-myc expression, and proliferation were clearly reduced in the treated cells. In addition, we observed some cytotoxic effects of FTI-277 accompanied by morphological changes of the neuroblastoma cells and a delayed induction of apoptosis. CONCLUSION: Farnesyltransferase inhibitors are active against neuroblastoma cells but the mechanism of action is not limited to inactivation of Ras. Further investigations on the targets of FTI-277 are recommended.
Subject(s)
Alkyl and Aryl Transferases/antagonists & inhibitors , Brain-Derived Neurotrophic Factor/physiology , Enzyme Inhibitors/pharmacology , Methionine/analogs & derivatives , Methionine/pharmacology , Neuroblastoma/pathology , Brain-Derived Neurotrophic Factor/genetics , Cell Division/drug effects , Farnesyltranstransferase , Genes, myc , Humans , Neuroblastoma/drug therapy , Neuroblastoma/metabolism , RNA, Messenger/analysis , Receptor, trkB/genetics , Signal Transduction , Tumor Cells, Cultured , ras Proteins/metabolismABSTRACT
Genetic aberrations are the primary events leading to carcinogenesis in various tissues and are characteristic for certain tumor types. Amplification of N-myc and deletion of 1p significantly correlate with poor prognosis of neuroblastoma patients. Very little informations is available on the regulation of N-myc expression by external factors. Insulin-like growth factor-II (IGF-II) has been identified as an autocrine growth factor in neuroblastoma. Four neuroblastoma cell lines were examined for their expression of IGF-II and IGF-receptor. Stimulation of neuroblastoma cells with IGF-II leads to an increased activity of the MAP-kinase Erk1, an induction of N-myc expression and an enhanced proliferation rate. In order to disrupt the signal transduction of the IGF-receptor, we inactivated the Ras-proteins in neuroblastoma cells by inhibition of the farnesyl-protein transferase by FTI-277. This inactivation prevented activation of MAP-kinase Erk1 and induction of N-myc expression by IGF-II. Inactivation of Ras by farnesyltransferase inhibitors might become a promising new approach in future treatments of neuroblastoma tumors.
