3'-AZIDOTHYMIDINE (ZIDOVUDINE) INHIBITS GLYCOSYLATION AND DRAMATICALLY ALTERS GLYCOSPHINGOLIPID SYNTHESIS IN WHOLE CELLS AT CLINICALLY RELEVANT CONCENTRATIONS

Recent in vitro work with Golgi-enriched membranes showed that 3'-azidothymidine-5'-monophosphate (AZTMP), the primary intracellular metabolite of 3'-azidothymidine (AZT), is a potent inhibitor of glycosylation reactions (Hall. et al, (1994) J. Biol, Chem. 269, 14355-14358) and predicted that AZT treatment of whole cells should cause similar inhibition. In this report, we verify this prediction by showing that treatment of K562 cells with AZT inhibits lipid and protein glycosylation. AZT treatment dramatically alters the pattern of glycosphingolipid biosynthesis, nearly abolishing ganglioside synthesis at clinically relevant concentrations (1-5 mu M), and suppresses the incorporation of both sialic acid and galactose into proteins. Control experiments demonstrate that these changes do not result from nonspecific effects on either the secretory apparatus or protein synthesis. On the other hand, studies using isolated nuclei as a model system for chromosomal DNA replication show that AZTTP is a very weak inhibitor of DNA synthesis, These observations strongly suggest that the myelosuppressive effects of AZT in vivo are due to inhibition of protein and/or lipid glycosylation and not to effects on chromosomal DNA replication.