Abstract P1-03-03: Obesity increases the lipid mediator, sphingosine-1-phosphate in the tumor and tumor microenvironment, and promotes tumor progression

INTRODUCTION: While obesity is an established independent prognostic factor for breast cancer patients, the underlying mechanisms how obesity promotes breast cancer progression are not well understood. Sphingosine-1-phosphate (S1P) is a pleiotropic bioactive lipid mediator produced by sphingosine kinases (SphKs) that plays critical roles in inflammation and cancer progression. Our hypothesis is that obesity increases levels of S1P in both tumor and its microenvironment, which promotes obesity-induced inflammation and breast cancer progression. The aim of this study is to test the hypothesis. METHODS: A high fat diet (HFD) was fed C57Bl/6 mice, which is the most commonly used murine diet-induced obesity model. E0771 cells derived from C57Bl/6 mice were implanted into mammary fat pads of mice that were fed with HFD or normal diet (ND) for 12 weeks prior to the implantation. Western blot, immunofluorescent staining, RT-qPCR and LC-ESI-MS/MS assays were used. RESULTS: Mice fed with HFD for 20 weeks developed severe obesity with an almost 2 fold increase of body weight compared with ND fed mice. E0771 mouse breast cancer cells were implanted into mammary fat pad of C57Bl/6 mice, and the mice fed with HFD developed significantly larger tumors within 30 days than those fed with ND. Expression of pro-inflammatory cytokines, IL-6 and TNF-α, was increased in the tumors of HFD fed mice, compared to those fed with ND. Furthermore, immunofluorescent analysis with anti-F4/80 antibody showed that tumors from HFD fed animals recruited significantly more tumor associated macrophages than those from ND fed animals. Expression of SphK1 and S1PR1, but not SphK2, was increased in the tumors from mice fed HFD. Mass spectrometry analysis revealed that while S1P levels in the normal breast mammary fat pad were increased with HFD feeding, S1P levels were even higher in breast tumors. Consistent with increased SphK1 and S1P in tumors, S1P was also significantly increased in the tumor interstitial fluid, which is a component of the tumor microenvironment and bathes cancer cells in the tumor. S1P levels were also increased in the serum of the tumor-implanted animals fed with HFD compared with those fed with ND, while minimal changes in S1P were evident in the serum of non-tumor bearing mice fed with HFD. Furthermore, S1P levels in the lungs of tumor-implanted animals fed with HFD were significantly higher than those fed with ND. CONCLUSION: S1P is increased not only in tumor, but also in tumor microenvironment such as tumor interstitial fluid by obesity. Our results suggest that S1P has a role in obesity-induced inflammation and the cancer progression. This work was supported by the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research Grant Number 15H05676 and 15K15471 for M.N and 15H04927 for W.T. M.N. is supported by the Uehara Memorial Foundation, Nakayama Cancer Research Institute, and Tsukada Medical Foundation. K.T. is supported by NIH/NCI grant R01CA160688 and Susan G. Komen Investigator Initiated Research Grant IIR12222224. Citation Format: Tsuchida J, Nagahashi M, Moro K, Tatsuda K, Koyama Y, Takabe K, Wakai T. Obesity increases the lipid mediator, sphingosine-1-phosphate in the tumor and tumor microenvironment, and promotes tumor progression. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-03-03.