H. Aoki1,2, M. Aoki1,2, P. Mukhopadhyay1,2, C. C. Barnett3, S. Spiegel1,2, K. Takabe1,2 1Virginia Commonwealth University,Division Of Surgical Oncology, Department Of Surgery,Richmond, VA, USA 2Virginia Commonwealth University,Department Of Biochemistry & Molecular Biology,Richmond, VA, USA 3University Of Colorado Denver,Department Of Surgery,Aurora, CO, USA
Introduction: In the U.S., pancreatic cancer is the 4th leading cause of cancer death in both gender. The 5-year relative survival rate is approximaly 6% for all stages. Up to 60% of the patients are found to have distant metastatic disease at the time of diagnosis, at which median survival is around 6 months. The most common sites for distant metastases are the liver (80%), peritoneum (60%), lung and pleura (50-70%), and adrenal glands (25%). Prognosis of patients with peritoneal carcinomatosis (PC), dissemination of cancer cells throughout the abdominal cavity, are particularly poor with median survival of only 6 weeks. This poor overall 5-year survival rate has not significantly changed over the past 5 decades, which reflects the fact that there is no effective treatment available for this condition. Sphingosine-1-phosphate (S1P), a bioactive lipid mediator produced by sphingosine kinase 1 (SphK1) and sphingosine kinase 2 (SphK2), plays critical roles in many aspects of cancer progression, such as cell proliferation, migration, angiogenesis and lymphangiogenesis. We have recently published that S1P link inflammation and cancer in colitis-associated cancer progression (Cancer Cell 2013). Given the fact that inflammation is known to be essential for establishment and progression of PC, where cancer cells need to adhere to the peritoneum and form a nodule, we hypothesized that S1P levels regulated by SphK1 and SphK2 in the host animal may have different mechanism in promoting progression of pancreatic cancer PC depending upon its levels.
Methods: Murine pancreatic adenocarcinoma panc02-luc cells were intraperitoneally injected into SphK1 wild type (WT) or knockout (KO), or SphK2 WT or KO mice to generate PC model. Tumor burden was quantified using bioluminescence imaging. Survival was assessed by Kaplan-Meier analysis. PC nodules were harvested 14 days after injection and analyzed. The proliferation was assessed by Ki-67 staining and apoptosis was evaluated by TUNEL assay. We also compared mRNA expression by RT-PCR.
Results: Circulating S1P levels were lower in SphK1 KO mice and higher in SphK2 KO mice compared with respective littermate WTs probably due to compensatory elevation of SphK1. Panc02-luc cells developed significantly less tumor burden, less inflammatory cell infiltration, and less cancer cell proliferation, but with no difference in apoptosis in PC of SphK1 KO mice. These results suggest that host S1P promotes PC progression by stimulation of proliferation of cancer cells. Interestingly, SphK2 KO mice developed less tumor burden, longer survival with elevated CD4 and CD8 lymphocyte infiltrates in PC.
Conclusion: Our results implicate an intriguing possibility that S1P levels in the host may have different mechanisms in promoting progression of pancreatic cancer PC depending upon its levels.