Abstract 4364: S1P generated by SphK1 is important not only for primary tumor growth but also for tumor-induced hemangiogenesis and lymphangiogenesis

Abstract

Abstract INTRODUCTION: Sphingosine-1-phosphate (S1P), a pleiotropic bioactive lipid mediator, regulates many cellular processes important for breast cancer progression. The aim of this study is to investigate a role for S1P produced by sphingosine kinase 1 (SphK1) in breast cancer progression and tumor-induced hemangiogenesis and lymphangiogenesis. METHODS: An isozyme-specific inhibitor of SphK1 (SK1-I) was used. Tumor burden were quantified using an in vivo imaging system (IVIS 2000). S1P and SK1-I levels were measured by LC-ESI-MS/MS. Hemangiogenesis and lymphangiogenesis are determined by morphological analysis of microvessel density as well as by flow cytometric analysis of endothelial cells. RESULTS: A significant dose dependent effect of SK1-I on inhibition of 4T1-luc2 murine breast cancer cell growth was observed. We confirmed that SK1-I decreased the enzymatic activity of SphK1 and that downregulation of SphK1 with specific siRNA also suppressed growth of these cells. We found that S1P levels increased in the tumor and in the circulation after orthotopic implantation of 4T1-luc2 cells. Similarly, serum S1P levels were significantly elevated in stage IIIA breast cancer patients who have lymph node metastases, compared to age/ethnicity-matched healthy volunteers. SK1-I blocked serum S1P increases in in vivo model and reduced lymph node and lung metastases and overall tumor burden in vivo as well. Importantly, SK1-I also decreased hem- and lymphangiogenesis not only in the primary tumor, but also in lymph nodes, the host tumor microenvironment. Whereas supernatants from 4T1-luc2 cells significantly stimulated tube formation of HUVECs and HLECs, shRNA knockdown of SphK1 markedly reduced them, indicating that S1P produced by SphK1 in 4T1-luc2 breast cancer cells is an important contributor to hem- and lymphangiogenesis. CONCLUSIONS: S1P generated by SphK1 is important for tumor progression, tumor-induced hemangiogenesis and lymphangiogenesis, and lymph node metastais. Therefore targeting SphK1 and its product S1P would be a multi-pronged attack against breast cancer. This work was supported by Sumitomo Life Social Welfare Services Foundation grant to MN, NIH (K12HD055881) and Susan G. Komen for the Cure (KG090510) to KT, and NCI (R01CA61774) to SS. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4364. doi:1538-7445.AM2012-4364