Search

Zidovudine (ZDV or AZT) is the only drug approved for use in treating infection with the human immunodeficiency virus (HIV), the agent that causes AIDS. This drug works by entering infected cells and being incorporated into the viral genetic material, blocking replication of the virus. AZT treatment has helped prolong the lives of patients with AIDS. However, it can have a number of severe side effects which can inhibit its use, and its effectiveness diminishes over time. This decreased effectiveness may be caused by the development of resistant strains of the virus or by dormant virus becoming partially or fully active, or both. When AZT is initially given, signs of HIV infection decrease for about the first six months, then begin to reappear. One indication of HIV replication is increased p24 production. This is a protein produced by the virus that can be detected using antigen tests. This study examined p24 production in an HIV-infected patient who received long-term treatment with AZT, and compared it with reverse transcriptase (RT) activity. RT is an enzyme necessary for full replication of HIV, whereas p24 may be produced without fully infectious viruses being produced. Infected cells were obtained from the patient and cultured. RT activity and p24 production were measured with and without AZT. Results showed that p24 production was high when AZT was present, but the RT activity remained low when AZT was present. These findings indicate that p24 production and full viral replication, as indicated by RT activity, can be independent of each other. This could mean that AZT is still effective in preventing replication of HIV while p24 production is high, and thus p24 production may not always indicate that AZT is no longer effective. (Consumer Summary produced by Reliance Medical Information, Inc.)

Several 4-benzyl analogues of 5-ethyl-6-methyl-4-(phenylthio)pyridin-2(1H)-ones were synthesized and evaluated for their anti-HIV-l activities. Key transformations include metalation at the 4-C-position of 5-ethyl-2-methoxy-6-methyl-3-pivaloylaminopyridine (5) and its coupling with benzyl bromide or benzaldehyde derivatives. Biological studies revealed that some of the new 4-benzylpyridinones show potent HIV-1 specific reverse transcriptase inhibitory properties. Compounds 14, 19, and 27, which inhibit the replication of HIV-1 in CEM-SS cells, with IC50 values ranging from 0.2 to 6 nM are the most active compounds in this series. Biochemical studies showed that compound 27 strongly inhibited the activity of a recombinant HIV-1 RT. Moreover, the infectivity of isolated HIV-1 particles was severely decreased after exposure to compound 27. Although cross resistance is frequently observed between non-nucleoside reverse transcriptase inhibitors, compound 27 was capable of inhibiting a virus resistant to nevirapine with an IC50 of 40 nM.

Three DNA polymerases (A, B and C) have been purified from the soluble cytoplasm of ungerminated embryos. Mainly on the basis of chromatographic, template-specificity and salt-inhibition evidence, we have characterized the three enzymes. Other physico-chemical and enzymic properties are described. From purified mitochondria we have purified a DNA polymerase that behaves like DNA polymerase B on chromatographic and template-specificity criteria. Only highly purified enzyme B from the soluble cytoplasm showed an exonuclease activity able to degrade 3′- or 5′-labelled polydeoxyribonucleotides, as well as a ‘proof-reading’ capacity.

A series of 22 derivatives of AZT substituted at the N-3 position of the thymine base were prepared and evaluated for anti-HIV activity in cell culture (Lai strain of HIV-1 in CEM-c113 cells). The AZT analogs bearing a N-3 amino group (7), a hydroxyalkyl chain (12f), and a phosphonomethyl (12k) substituent displayed activities in the 0.045−0.082 μM range. The analogs 12d, 12e, 12q, 15, and 19 were active at <0.5 μM concentration. Compound 18 in which two molecules of AZT are connected at N-3 via a two-carbon link and “dimer” 11 also displayed significant activity. To obtain information concerning the mechanism of RT inhibition by these AZT analogs, compounds 7, 12d, 12e, and 12q were incubated with recombinant HIV-1 RT in the presence of poly(A)-oligo[dT(12-18)] and poly(C)-oligo[dG(12-18)] template−primers. In contrast to AZT−TP (control), none of these nucleosides displayed any significant inhibition of RT in the recombinant enzyme assay, indicating that phosphorylation is a necessary prerequisite for activity.

Turnip yellow mosaic virus (TYMV) RNA treated with snake venom phosphodiesterase accepts cytidine 5'-monophosphate and adenosine 5'-monophosphate (AMP) when it is incubated in the presence of cytidine 5'-triphosphate (CTP), adenosine 5'-triphosphate, and Escherichia colitransfer RNA nucleotidyltransferase; untreated TYMV RNA accepts only AMP. When a 32PCTP was used for terminal labeling, the nearest neighbor analyses and the anallyses after action of various nucleases showed that the sequence of five nucleotides at the 3' end of TYMV RNA is: pGpCpApCpC. A nuclease present in commerical preparations of snake venom phosphodiesterase leads to the fragmentation of TYMV RNA, the 3' end of which is found in a fragment having a sedimentation constant close to 5s.