ABSTRACT
It has been hypothesized that the metastatic capacity of tumors may be correlated with hypersialylation of the cell surface. We used a novel inhibitor of sialic acid incorporation, KI-8110, to determine the effect of depletion of cell surface sialic acid on the metastatic behavior of three human colorectal cancer cell lines, in which hepatic seeding was related to tumor cell differentiation. Treatment of tumor cells with KI-8110 prior to intrasplenic injection prevented liver colonization. Total cellular sialic acid was reduced, as was that of the cell surface. Secreted forms of carcinoembryonic antigen also were depleted of sialic acid by this treatment. These data show that depletion of sialic acid from cell surface glycoconjugates reduces the incidence of hepatic metastases from human colorectal primary tumors and adds to the mounting evidence of the importance of sialic acid in determining the biological behavior of tumor cells.
Subject(s)
Liver Neoplasms, Experimental/secondary , Sialic Acids/antagonists & inhibitors , Animals , Carcinoembryonic Antigen/analysis , Cell Line/drug effects , Cell Line/metabolism , Colorectal Neoplasms/metabolism , Glycosides/pharmacology , Humans , Liver Neoplasms, Experimental/metabolism , Liver Neoplasms, Experimental/prevention & control , Male , Membrane Glycoproteins/analysis , Membrane Glycoproteins/drug effects , Mice , Mice, Nude , Neoplasm Transplantation , Sialic Acids/analysis , Sialic Acids/metabolism , Tumor Cells, Cultured/drug effects , Tumor Cells, Cultured/metabolism , Uridine/analogs & derivatives , Uridine/pharmacologyABSTRACT
Uptake of carcinoembryonic antigen (CEA) by isolated rat alveolar cells was time, temperature, and concentration dependent (Kuptake = 2.4 x 10(-7) M). Pretreatment of the alveolar cells with colchicine inhibited internalization of CEA. Uptake of 125I-labeled CEA by alveolar cells required divalent cations and was inhibited by cold CEA and nonspecific cross-reacting antigen (NCA). The carbohydrate portion of CEA was modified by neuraminidase treatment and Smith degradation. The modified glycoproteins inhibited endocytosis by the alveolar macrophages, thus excluding nonreducing terminal carbohydrate residues as the recognition site of the receptor. Endocytosis of CEA was independent of native protein conformation since performic acid oxidized CEA and glycopeptides produced by pepsin digestion were inhibitory. Rat alveolar macrophages bound CEA with similar specificity to that of rat Kupffer cells. Alveolar macrophages, unlike Kupffer cells, did not rapidly exocytose the internalized CEA. Neither P388D1, a macrophage-like murine cell line, nor murine peritoneal exudate cells were capable of endocytosing CEA in vitro.
