Abstract 187: Dipeptidyl peptidases abolish growth inhibitory effect of neuropeptide Y in Ewing's sarcoma family of tumors

Abstract

Abstract Ewing's sarcoma family of tumors (ESFT) is a group of aggressive pediatric malignancies which exhibit a variable degree of neuronal differentiation. Previously, we have shown that ESFT cells express a sympathetic neurotransmitter, neuropeptide Y (NPY), and its Y1 and Y5 receptors. We have shown that both endogenous and exogenous NPY can stimulate Y1/Y5R-mediated apoptosis in ESFT cells, which can lead to inhibition of ESFT tumor growth in vivo. However, our further studies suggested that the growth-inhibitory effect of NPY in ESFT cells can be abolished by dipeptidyl peptidase IV (DPPIV) – a membrane protease which cleaves the peptide to its shorter form, NPY3-36, that is inactive at Y1Rs. DPPIV, as well as its homologs with similar activities – membrane-bound fibroblast activation protein (FAP) and cytoplasmic DPP8 and DPP9, have been identified as therapeutic targets in a variety of other tumors. Moreover, numerous broad-spectrum and selective DPP inhibitors have been developed and tested in clinical trials for diabetes and cancer. Thus, the goal of this study was to elucidate the role of particular DPPs in the regulation of ESFT growth and their potential use as therapeutic targets. We have found that aside from expressing NPY and its receptors, all ESFT cells expressed variable levels of DPPIV and its homologs. Both exogenous and endogenous NPY significantly inhibited growth of ESFT cells with low DPP activities. This effect was blocked by Y1/Y5R antagonists and abolished by transfection with DPPIV mRNA. In contrast, cells with high DPP activities did not respond to exogenous NPY and the endogenous peptide had no effect on their growth, as shown by experiments with NPY siRNA. In these DPP-rich cells, the response to both exogenous and endogenous peptide was restored by DPP siRNAs or their selective inhibitors. Surprisingly, similar levels of growth reduction were achieved by blocking DPPIV, as with inhibiting cytoplasmic DPP8 and DPP9. Both effects were mediated by AIF, suggesting caspase-independent cell death, and blocked by Y1/Y5R antagonists, confirming that this was indeed NPY-mediated. In contrast, FAP did not affect the growth-inhibitory actions of NPY in ESFT cells, which is consistent with its low activity, while cleaving substrates with Tyrosine in the first position, such as NPY. In summary, DPPs are important regulators of the growth-inhibitory effect of NPY in ESFT cells, indicating their potential value as therapeutic targets in the treatment of these tumors. However, given the multiple functions of both DPPs and NPY itself, more studies are required to determine their effects on other functions of ESFT cells, such as migration and invasiveness. Moreover, the role of particular DPPs differ in vivo, since FAP and DPPIV are known to be highly expressed in tumor-associated fibroblasts and endothelial cells, and have been shown to modify interactions between tumor and stromal cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 187. doi:10.1158/1538-7445.AM2011-187