EFFECTS OF TUNICAMYCIN ON B16-METASTATIC MELANOMA CELL-SURFACE GLYCOPROTEINS AND BLOOD-BORNE ARREST AND SURVIVAL PROPERTIES

Abstract

The role of cell surface glycoproteins in determining in vivo blood-borne arrest and survival characteristics of murine melanoma sublines of low (B16-F1) or high (B16-F10) potential to form experimental lung metastases after injection i.v. was assessed after inhibiting tumor cell protein glycosylation with tunicamycin. Incubation of B16-F1 or B16-F10 cells with 0.5 .mu.g (or above) tunicamycin per ml for 12-36 h inhibited significantly lung tumor colony formation. Examination of B16 cells in the presence of 0.5 .mu.g drug/ml indicated that complex oligosaccharide synthesis was inhibited > 90%, while protein synthesis remained at about 50% of the control levels. Tunicamycin induced morphological changes in B16-F1 and B16-F10 cells such as cellular rounding. Cell growth was also inhibited by tunicamycin. These effects were reversible, and B16 cells recovered their normal morphologies and growth rates within 24 h after removal of the drug. Exposed cell surface protein analyzed by lactoperoxidase-catalyzed 125I iodination-sodium dodecyl sulfate-polyacrylamide gel electrophoresis-autoradiography showed few changes after tunicamycin treatment; sialogalactoproteins (detected by the binding of 125I-labeled Ricinus communis agglutinin I to polyacrylamide gels containing desialized B16 cell surface components) were reduced dramatically by the drug. The adhesive properties of untreated and tunicamycin-treated B16 cells were assessed by the binding of 51Cr-labeled B16 cells to endothelial cell monolayers. Tunicamycin-treated B16-F1 and B16-F10 cells adhered at lower rates to endothelial cells, so that after 24-36 h of drug (0.5 .mu.g/ml) treatment adhesion was almost completely blocked; this suggests that tunicamycin-induced cell surface glycoprotein changes in B16 melanoma cells may interfere with tumor cell-host cell interactions that lead to arrest and survival of blood-borne malignant cells.