Abstract 1628: Neuropeptide Y (NPY) and its receptor expression in neuroblastoma patients - associations with disease prognosis and patients’ survival

Neuropeptide Y (NPY) is a sympathetic neurotransmitter, abundantly expressed in neuroblastoma (NB). Previously, we have shown that NPY, acting via its Y2 receptor (Y2R), stimulates proliferation of NB cells and tumor vascularization, while inducible Y5 receptor (Y5R) promotes tumor cell survival and chemoresistance. The aim of the current study was to assess the prognostic value of NPY and its receptor expression in NB. We have tested corresponding samples of RNA, tissue sections and serum from 87 NB patients at various stages of the disease, obtained from the Children's Oncology Group. Samples were analyzed in terms of NPY system expression (NPY, Y2R and Y5R). Protein levels and mRNA in tumor tissue were quantified by immunohistochemistry (IHC) and real time-PCR, respectively, while NPY concentration in serum was measured by ELISA. The expression of other factors implicated in NB development and progression (MYCN, ALK, TrkA III, TrkB and BDNF) were detected on mRNA levels by real time-PCR. For each of the categorical prognostic variables, a Wilcoxon rank-sum or Fisher's exact test were administered to compare NPY and receptor values between groups, and a log-rank test was performed to compare the event-free survival and overall survival between groups. 1) NPY mRNA was detectable in 100% of analyzed tumors. IHC staining revealed that NPY accumulated intracellularly in differentiating and maturing cells, while in undifferentiated NBs a significant amount of the peptide was observed in extracellular spaces, suggesting its free release. In line with this observation, serum concentrations of NPY were higher in the subset of NB patients with undifferentiated and poorly differentiated tumors, as compared to those with differentiating NBs (p-value = 0.03). High serum concentrations of NPY strongly correlated with several adverse prognostic factors (Stage 4, high risk, diploidy, and unfavorable histology) (p-value