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 microM), 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.

Acyclic guanosine analogs inhibit DNA polymerases alpha, delta, and epsilon with very different potencies and have unique mechanisms of action.

Acyclovir triphosphate, ganciclovir triphosphate and penciclovir triphosphate inhibited DNA polymerases alpha, delta, and epsilon. Each triphosphate preferentially inhibited pol delta, although ganciclovir triphosphate was the most impressive of the three; the Ki for inhibition of pol delta was 2 microM (competitive with dGTP), while the Kis for inhibition of pol alpha and epsilon were 80 and 140 microM, respectively. Each of the compounds was polymerized by pol alpha, delta, and epsilon. Incorporation of acyclovir triphosphate resulted in immediate chain termination, whereas incorporation of ganciclovir triphosphate often allowed polymerization of additional dNTPs. Interestingly, chain termination most often occurred after polymerization of just one additional dNTP onto the ganciclovir monophosphate. All three compounds were very weak inhibitors of DNA primase. Acyclovir triphosphate, however, was a unique inhibitor of the pol alpha-catalyzed elongation of primase-synthesized primers. Immediately after DNA primase synthesized a primer, pol alpha frequently incorporated acyclovir triphosphate with consequent chain termination. If, however, pol alpha did not immediately polymerize acyclovir triphosphate onto the primase-synthesized primer, further dNTPs were readily added and acyclovir triphosphate was incorporated much less frequently.