BRAIN-DERIVED NEUROTROPHIC FACTOR PROTECTS NEUROBLASTOMA-CELLS FROM VINBLASTINE TOXICITY

Brain-derived neurotrophic factor (BDNF) and its receptors are necessa ry for the survival and development of many neuronal cells, Because BD NF and TrkB are expressed in many poor-prognosis neuroblastoma (NB) tu mors, we evaluated the role of BDNF in affecting sensitivity to chemot herapeutic agents. We investigated the effects of activation of the BD NF-TrkB signal transduction pathway in two NB cell lines, 15N and SY5Y , 15N cells lack the high-affinity receptor p145TrkB and express BDNF; 15N cells were used along with 15N-TrkB cells, a subline transfected with a TrkB expression vector. In cytotoxicity assays, 15N-TrkB cells were consistently 1.4-2-fold more resistant to vinblastine than 15N ce lls, Drug accumulation assays showed a 50% reduction in [H-3]vinblasti ne accumulation in 15N-TrkB cells compared with control 15N cells. Add ition of 30 ng/ml BDNF resulted in a reduction to 46% of control in 15 N cells and a reduction to 28% of control in 15N-TrkB cells. SY5Y cell s were chosen as a second model because they lack both endogenous BDNF and TrkB expression, p145TrkB expression is induced by 1 nm retinoic acid, Vinblastine accumulation was not significantly affected by 1 nM retinoic acid in SY5Y cells. Addition of 30 ng/ml BDNF decreased [H-3] vinblastine accumulation to 58% of control in SY5Y cells and decreased [H-3]vinblastine accumulation to 62% of control in TrkB-expressing SY 5Y cells. Although an increase in BDNF expression is seen in multidrug -resistant sublines of SY5Y and BE(2)-C NE cells, the protective effec t of BDNF in vinblastine toxicity may be unrelated to mdr-1, because t he activity of other agents transported by P-glycoprotein was not affe cted. There was no increase in mdr-1 expression in 1 nM RA SY5Y cells and 15N-TrkB cells, as assessed by Northern blot analysis. In addition to the effects of BDNF on vinblastine cytotoxicity and accumulation, there was an inhibition in the ability of vinblastine to depolymerize tubulin in BDNF-treated cells, Thus, BDNF and TrkB may partially rescu e NE cells from vinblastine toxicity and thereby may contribute to a m ore chemoresistant phenotype.