FTY720 Suppresses Liver Tumor Metastasis by Reducing the Population of Circulating Endothelial Progenitor Cells

BACKGROUND: Surgical procedures such as liver resection and liver transplantation are the first-line treatments for hepatocellular carcinoma (HCC) patients. However, the high incidence of tumor recurrence and metastasis after liver surgery remains a major problem. Recent studies have shown that hepatic ischemia-reperfusion (I/R) injury and endothelial progenitor cells (EPCs) contribute to tumor growth and metastasis. We aim to investigate the mechanism of FTY720, which was originally applied as an immunomodulator, on suppression of liver tumor metastasis after liver resection and partial hepatic I/R injury. METHODOLOGY/PRINCIPAL FINDINGS: An orthotopic liver tumor model in Buffalo rat was established using the hepatocellular carcinoma cell line McA-RH7777. Two weeks after orthotopic liver tumor implantation, the rats underwent liver resection for tumor-bearing lobe and partial hepatic I/R injury. FTY720 (2 mg/kg) was administered through the inferior caval vein before and after I/R injury. Blood samples were taken at days 0, 1, 3, 7, 14, 21 and 28 for detection of circulating EPCs (CD133+CD34+). Our results showed that intrahepatic and lung metastases were significantly inhibited together with less tumor angiogenesis by FTY720 treatment. The number of circulating EPCs was also significantly decreased by FTY720 treatment from day 7 to day 28. Hepatic gene expressions of CXCL10, VEGF, CXCR3, CXCR4 induced by hepatic I/R injury were down-regulated in the treatment group. CONCLUSIONS/SIGNIFICANCE: FTY720 suppressed liver tumor metastasis after liver resection marred by hepatic I/R injury in a rat liver tumor model by attenuating hepatic I/R injury and reducing circulating EPCs.