Inhibition of Protein Glycosylation and Selective Cytotoxicity toward Virally Transformed Fibroblasts Caused by B3‐Tunicamycin

The biological effect of B3-tunicamycin, the only known homologue of tunicamycin which contains a saturated fatty-acid side chain, was examined using chick embryo fibroblasts, a mouse fibroblastic line (3T3) and a virally transformed mouse fibroblastic line (SV40–3T3). This homologue inhibited the transfer of N-acetylglucosamine 1-phosphate from UDP-N-acetylglucosamine to dolichyl phosphate, catalyzed by microsomes from chick liver or from cultured mouse fibroblasts. B3-tunicamycin also inhibited the incorporation of mannose into glycoproteins synthesized by chick or mouse fibroblasts. Incorporation of the amino acids proline and tyrosine was inhibited by B3-tunicamycin to a lesser extent than the incorporation of mannose. The mannose incorporation into glycoproteins synthesized by virally transformed cells was inhibited by B3-tunicamycin to a higher degree than what was achieved in the nontransformed lines or in the chick primary fibroblats. When the activity of B3-tunicamycin as an inhibitor of protein glycosylation was compared to other homologues of tunicamycin, it was found to be the most active. This homologue caused complete (more than 95%) inhibition of protein glycosylation at a concentration of 50 ng/ml in chick and in mouse fibroblasts and at a concentration of 10 ng/ml in transformed mouse fibroblasts. When the cytotoxic activities of tunicamycin homologues were examined on nontransformed and virally transformed 3T3 cells, it was found that B3-tunicamycin displayed the highest selective cytotoxicity toward the transformed cells. When transformed fibroblasts (105 cells/plate) were treated with B3-tunicamycin (100 ng/ml) for 48 h, complete cell death was observed. The viability and the proliferative activity of the nontransformed fibroblast were normal even when treated with concentrations up to 500 ng/ml of B3-tunicamycin. This suggests that B3-tunicamycin may be a suitable candidate for studies of tumor growth in animals.