Homing zirkulierender HCC-Zellen in die Leber - ein Chemokinrezeptor vermittelter Prozess? Homing of circulating HCC-cells to the liver - a chemokine receptor mediated process?

Introduction: Haematogenous homing of circulating tumor cells frequently accounts for intrahepatic recurrence of hepatocellular carcinoma after liver resection or transplantation for hepatocellular carcinoma. Understanding the molecular basis of this phenomenon is of crucial interest for the development of modern therapeutic strategies preventing tumor recurrence. Due to chemokine receptor expression, metastasing cancer cells can mimic leukocyte like behaviour like homing to different organs. In this study we evaluated the role of the chemokinereceptor CXCR4 for the homing of HCC cells to the liver in a rat model in vivo. Materials and methods: The hepatitis negative cell line HEP G2, derived from a human hepatocellular carcinoma was used. The chemokine receptor expression was determined by flowcytometry (FACS). Tumor cell adhesion and migration in vitro were determined in collagen and fibronectin coated static adhesion assays and trans well-chambers respectively. Tumor cell adhesion and migration in vivo were quantified by intravital fluorescence microscopy of the rat liver as described earlier. Localisation of the CXCR4 ligand CXCL12 in human livers was achieved by immunhistochemistry. After testing for normal distribution, mean values were compared by the T-test. Results: CXCR4 is expressed in 97 % of HEP G2 cells determined by FACS. The corresponding ligand CXCL12 exhibits chemotactic activity on HEP G2 cells seeded on collagen or fibronectin in a dose dependend manner at concentrations from 25 ng/ml to 100 ng/ml. Chemotaxis can be inhibited by anti-CXCR4 treatment of the cells. Adhesion of HEP G2 to collagen or fibronectin is not significantly influenced by anti-CXCR4 treatment. Immunhistochemical analysis of human livers without signs of cirrhosis or hepatitis showed significant CXCL12 expression in Kupffer cells and along the endothelial lining of the liver sinusoids. After intraarterial injection of fluorescene marked HEP G2 cells in rats, we observed adhesion of tumor cells within the hepatic sinusoids that was obviously not due to mechanical size restriction but specific adhesive interactions. When unspecific IgG control treated cells were used (n = 10), after 30 minutes 44,2 ± 3,4 cells/30 MF were arrested within the liver, while 22 % ± 4 % of these cells were extravadated into the liver parenchyma. After treatment of the cells with anti-CXCR4 IgG (n = 12) prior to injection, 49,4 ± 2,4 cells/30 MF were arrested in the liver after 30 minutes (n. s.), but the rate of extravadated cells was significantly reduced to 6 % ± 5 % (p < 0,05). Conclusions: Chemokine receptors, especially CXCR4, are expressed on human hepatocellular carcinoma. The only known Ligand for CXCR4, CXCL12, is expressed by sinusoidal endothelial cells and Kupffer cells and thereby perfedtly positioned within the hepatic microcirculation to support the homing of circulating tumor cells to the hepatic parenchyma.