Brain-derived neurotrophic factor (BDNF) and its receptors are necessary for the survival and development of many neuronal cells. Because BDNF and TrkB are expressed in many poor-prognosis neuroblastoma (NB) tumors, we evaluated the role of BDNF in affecting sensitivity to chemotherapeutic agents. We investigated the effects of activation of the BDNF-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 cells. Drug accumulation assays showed a 50% reduction in[3H]vinblastine accumulation in 15N-TrkB cells compared with control 15N cells. Addition of 30 ng/ml BDNF resulted in a reduction to 46% of control in 15N cells and a reduction to 28% of control in 15N-TrkB cells. SY5Y cells 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 [3H]vinblastine accumulation to 58% of control in SY5Y cells and decreased [3H]vinblastine accumulation to 62% of control in TrkB-expressing SY5Y cells. Although an increase in BDNF expression in seen in multidrug-resistant sublines of SY5Y and BE(2)-C NB cells, the protective effect of BDNF in vinblastine toxicity may be unrelated to mdr-1, because the activity of other agents transported by P-glycoprotein was not affected. 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 rescue NB cells from vinblastine toxicity and thereby may contribute to a more chemoresistant phenotype.