DESCRIPTION: There is increasing evidence that growth factors may have multiple effects. In addition to stimulating mitogenesis, growth factors may promote differentiation or act as survival factors during development, or as survival factors to cells undergoing stress due to changed in trophic support or damage due to anticancer drug treatments. In neuroblastoma (NB) expression of TRK, the receptor for nerve growth factor (NGF), has been correlated with a good prognosis. In contrast, data presented in this application demonstrates that expression of TRKB, the receptor for BDNF, is associated with resistance to cisplatin. This application proposes to test the hypothesis that brain derived growth factor (BDNF), which is a ligand for TRKB, induces resistance to cisplatin in a human neuroblastoma (NB) cell line and that this resistance is mediated through one of three potential pathways. Three specific aims have been presented. Specific Aim 1 proposes to determine whether NGF or BDNF protect NB cells from cytotoxic drugs or serum withdrawal. This specific aim will also test compounds etoposide, vincristine, cyclophosphamide and doxorubicin. It will also test whether these compounds cause cell death by apoptosis or necrosis. Additional cell lines will also be tested for these receptors and ligands to determine how relevant these findings are to NB. Specific Aim 2 will define the signaling pathways involved in TRK and TRKB mediated protection of cells from either cytotoxic agents or serum starvation. Three potential pathways of signal transduction have been proposed to investigate: 1) RAS, phosphatidyl inositol-3 kinase, 2) P13K pathway, and 3) phospholipase C-g1(PLC-g1). They also propose to use site specific mutagenesis of the tyrosines in the kinase domain of TRKB which form the binding site for the SHC, P13K or PLC-g1. Additional studies will include specific inhibitors of the TRK and TRKB ,P13K, RAS and PLC-g1, and dominant negative constructs against RAS. In Specific Aim 3 they propose to determine if TRKB or TRK increases drug resistance in vivo using mouse xenograft models.