Homotypic Adhesion through Carcinoembryonic Antigen Plays a Role in Hepatic Metastasis Development

We established a cell line with high metastatic potential to the liver (LS‐LM4) after four successive repetitions of splenic injection of liver‐metastatic cells in SCID mice. This cell line strongly expressed CEA and showed increased homotypic adhesion as compared with the parent cell line (LS174T). To examine the role of CEA in the increased homotypic adhesion, LS‐LM4 cells were treated with anti‐CEA antibody and subjected to an in vitro adhesion and aggregation assay. Further, to study the role of CEA in the hepatic metastasis of cells with high metastatic potential, LS‐LM4 cells were treated with anti‐CEA antibody, and the inhibition of hepatic metastasis after splenic injection in vivo was examined. There was a 62% decrease in the homotypic adhesion of anti‐CEA antibody‐treated (100 μg/ml) LS‐LM4 cells under a Ca(2+)‐free condition as compared with the control (P<0.01). Anti‐CEA antibody (100 μg/ml) inhibited cell aggregation under a Ca(2+)‐free condition (P<0.05). Treatment with anti‐E‐cadherin antibody (60 μ/ml) plus anti‐CEA antibody (100 μg/ml) inhibited cell aggregation more potently than anti‐E‐cadherin antibody treatment alone in the presence of Ca(2+). In vivo, there was a 75% decrease in the number of hepatic metastatic nodules in the G125 anti‐CEA antibody‐treated group as compared with the control group (P<0.01). Similarly, there was a 40% decrease in the diameter of metastatic nodules and there was a 90% decrease in total tumor volume of hepatic metastasis in the G125 anti‐CEA antibody‐treated group as compared with the control (P<0.01). These results suggest that increased metastatic potential to the liver is at least partly due to increased homotypic binding mediated by CEA.