Abstract P1-01-06: Targeting the SphK1/S1P/S1PR1 axis that connects obesity, chronic inflammation, and breast cancer metastasis
Authors: Nagahashi M , Yamada A , Aoyagi T , Huang W-C , Terracina KP , Hait N , Allegood JC , Tsuchida J , Nakajima M , Katsuta E , Milstien S , Wakai T , Spiegel S , Takabe K 
Published: February 2018

Introduction: Obesity with associated inflammation is now recognized as a risk factor for breast cancer and increased incidence of distant metastases. However, the link between obesity and breast cancer progression remains poorly understood. There is growing evidence that sphingosine-1-phosphate (S1P), a pleiotropic bioactive sphingolipid metabolite enriched both in blood and lymphatic fluid is involved in inflammation, obesity, and breast cancer progression. Our hypothesis is that obesity increases levels of S1P in both tumor and its microenvironment, which play a role in obesity-induced inflammation and breast cancer metastasis. The aim of this study is to test this hypothesis in in vitro and in vivo as well as patient settings.

Methods: Levels of sphingolipids including S1P in serum from breast cancer patients were quantified. Orthotopically-implanted E0771 syngeneic breast cancer and MMTV-PyMT transgenic breast cancer mouse models were used. Mice were fed with normal or high-fat diet (HFD). FTY720 was administered orally (1 mg/kg/day). To examine pre-metastatic niche formation, a mouse model utilizing tail vein injection of E0771 cells was used. In this model, mice were treated with conditioned media from E0771 breast cancer cells overexpressing SphK1 (K1-CM) or that from E0771 cells cultured with the vector control (CT-CM), prior to tail vein injections of naive E0771 cells. S1P levels were determined by electrospray ionization-tandem mass spectrometry.

Results: We found that obesity significantly increased S1P levels in serum from breast cancer patients. In animal breast cancer models, HFD upregulated expression of sphingosine kinase 1 (SphK1), the enzyme that produces S1P, and its receptor S1PR1 in syngeneic and spontaneous breast tumors. HFD also significantly increased S1P in breast tumors and in the tumor interstitial fluid, which is a component of the tumor microenvironment and bathes cancer cells in the tumor. Targeting the SphK1/S1P/S1PR1 axis with FTY720/fingolimod attenuated obesity-induced key pro-inflammatory cytokines, macrophage infiltration, and tumor progression. In addition, S1P produced by tumor SphK1 primed lung pre-metastatic niches, increased macrophage recruitment into the lung, and induced IL-6 and signaling pathways important for lung metastatic colonization. FTY720 suppressed HFD-induced lung IL-6 and macrophage infiltration as well as S1P-mediated signaling pathways and dramatically reduced formation of metastatic foci. In tumor bearing mice, FTY720 also suppressed obesity-related inflammation, S1P signaling, pulmonary metastasis, and prolonged survival.

Conclusion: Our results highlight a critical role for circulating S1P produced by tumor and the SphK1/S1P/S1PR1 axis in obesity-related inflammation, metastatic niche formation and breast cancer metastasis and suggest that targeting the SphK1/S1P/S1PR1 axis would be a useful therapeutic for obesity promoted metastatic breast cancer.

Citation Format: Nagahashi M, Yamada A, Aoyagi T, Huang W-C, Terracina KP, Hait N, Allegood JC, Tsuchida J, Nakajima M, Katsuta E, Milstien S, Wakai T, Spiegel S, Takabe K. Targeting the SphK1/S1P/S1PR1 axis that connects obesity, chronic inflammation, and breast cancer metastasis [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-01-06.