[Synthesis of S-9-(2,3-dihydroxypropyl)adenine (DHPA) analogs and their inhibition of S-adenosyl-L-homocysteine (SAH) hydrolase]

In order to search for new antiviral agents with high potency and low toxicity, eleven new acyclonucleosides were synthesized. Nucleic-acid bases were condensed with 3-chloro-2-methylpropene to give 5-8a. b, which were oxidized by N-methylmorpholine-N-oxide in the presence of OsO4 to give vicinal dihydroxy acyclonucleosides 1-4a.b. Four DHPA analogs have been tested for the inhibitory activities on s-adenosyl-L-homocysteine hydrolase (SAH). Only compound 1 showed some enzyme inhibitory effect with IC50 of 1.1 mmol.L-1.

[Synthesis of optically active (R)- and (S)-tai-ding-an(TDA) and their anti-HSV activity evaluation]

Tai-Ding-An (3-phthalimido-2-oxo-n-butyraldehyde bisthiosemicarbazone, TDA) is an antiviral drug first synthesized in this institute. In order to clarify the difference between the two enantiomeric isomers of TDA, (R)- and (S)-TDA were synthesized from (R)- and (S)-alanine, respectively, via the following steps: fusing with phthalic anhydride gave 2-phthalimido alanine(2a or 2b). The resulting acid was reacted with thionyl chloride to offer the corresponding acid chloride(3a or 3b), which was treated with diazomethane to give the diazoketone(4a or 4b). Bromination of the ketone with hydrobromic acid gave the key intermediate 3-phthalimido-2-oxo-1-bromobutanone (5a or 5b). Compound 5a or 5b was oxidized with DMSO to give 6a or 6b, which was directly condensed with thiosemicarbazide to afford the desired (R)- or (S)-TDA. (R)-TDA, (S)-TDA and (RS)-TDA have been tested in cell culture for anti-Herpes simplex virus I (HSV-1) and HSV-2 activities by plaque reducing method. All of them showed inhibitory effects on HSV-1 and HSV-2 replication with IC50 of 0.0296 mmol.L-1, 0.0359 mmol.L-1 and 0.0418 mmol.L-1 for HSV-1 and 0.88 mmol.L-1, 1.04 mmol.L-1 and 1.06 mmol.L-1 for HSV-2. Not much difference was found among these compounds either on IC50 or on therapeutic indexes.

CD8+ T-cell-mediated suppression of HIV replication in the first year of life: association with lower viral load and favorable early survival

OBJECTIVE AND DESIGN

To study the role and development of non-cytotoxic CD8+ T-cell-mediated suppression of HIV replication in early perinatal HIV infection in a prospective study of vertically infected infants. CD8 T-cell-mediated HIV suppression was measured several times during the first year of life and correlated with viral load, cytotoxic T-cell (CTL) activity, in vitro antibody production (IVAP) and clinical outcome.

METHODS

CD8+ T-cell-mediated HIV suppression was measured by comparing the amount of p24 antigen produced by endogenously infected lymphocytes with cultures of the same number of autologous CD4+ T cells from which CD8+ cells were removed immunomagnetically. CD8 viral suppressive activity (VSA) was defined as a > or = 50% reduction in p24 antigen in the cultures containing CD8+ cells.

RESULTS

CD8+ T-cell-mediated HIV VSA was detected in 11/16 infants in the first year of life, including six/nine infants studied before 6 months and as early as 3 weeks of age. Infants who demonstrated CD8 VSA had a lower early peak and 6-month 'setpoint' plasma HIV RNA concentration than infants who lacked CD8 VSA [1.51 versus 4.94 and 0.094 versus 0.639 x 10(6) copies/ml, respectively, and higher CD4 percentage at 1 year of age. Survival of infants lacking CD8 VSA (four/six were rapid progressors) was shorter than for infants who demonstrated CD8 VSA (none out of 10 were rapid progressors). CD8 VSA was present before CTL and before or at the same time as IVAP in two of two and 11 of 14 infants studied, respectively.

CONCLUSIONS

CD8+ T-cell-mediated VSA can be demonstrated in a large proportion of HIV-infected infants early in the course of infection. This non-cytolytic HIV-suppressive immune response appears to play an important protective role in the early control of perinatal HIV infection at a time when other immune responses are either absent or deficient.

Effects of antiviral therapy on the production of anti-human immunodeficiency virus-specific immunoglobulin in infants and children

The effect of zidovudine therapy on human immunodeficiency virus (HIV)-specific antibody production was studied in 64 HIV-1-infected infants and children > 6 months old. HIV-specific in vitro antibody production (IVAP) was measured in cultures of peripheral blood mononuclear cells (PBMC). IVAP decreased in 85% of children after zidovudine was initiated (mean decline, 1 log within 2 months). Effects were seen as early as 1 week after starting zidovudine. No change in IVAP was seen in children not treated. In comparison, plasma core (p24) antigen levels declined and CD4+ lymphocytes increased in only 42% and 52%, respectively, of treated subjects. Thus, the production of antibody to HIV-1 decreases rapidly after the initiation of antiretroviral therapy. This response to therapy may provide a simple and sensitive method of monitoring antiretroviral therapy.

Inhibition of HIV-1 reverse transcriptase by 5'-triphosphates of 5-substituted uridine analogs

The 5'-triphosphates of some 5-substituted 2'-deoxyuridine analogs were investigated for their effects on purified recombinant reverse transcriptase of human immunodeficiency virus type 1 (HIV-1) as well as cellular DNA polymerase alpha. The triphosphates were competitive inhibitors of the viral enzyme with dTTP as the variable substrate and poly(rA)oligo(dT) as template, and preferentially inhibited the viral polymerase. Ordering the compounds according to their decreasing binding affinities, as reflected by their increasing inhibition constants for the reverse transcriptase, gave nPrearaUTP greater than nPrdUTP greater than EtdUTP greater than nPredUTP greater than HMdUTP greater than CEdUTP. Although nPredUTP was less inhibitory than nPrearaUTP under conditions of competitive inhibition, nPredUTP caused a time- and concentration-dependent inactivation of reverse transcriptase activity when preincubated with template. This inactivation was not reversed by excess dTTP. The decrease in template-primer activity did not occur with nPrearaUTP, but was shown with the chain-terminating 5'-triphosphates of 3'-fluoro- and 3'-azidothymidine. As nPredUTP, but not nPrearaUTP, was an alternative substrate, shown by the ability to support DNA synthesis in absence of competing substrate, the incorporation of nPredUTP into the primer-template apparently leads to increased inhibition of the enzyme.

Inhibition of human hepatitis B virus DNA polymerase and duck hepatitis B virus DNA polymerase by triphosphates of thymidine analogs and pharmacokinetic properties of the corresponding nucleosides

Replication of hepadnaviruses involves a viral DNA polymerase containing both a DNA-dependent and an RNA dependent activity. This polymerase is a potential target for chemotherapy against hepatitis B. We have used human hepatitis B virus DNA-dependent DNA polymerase from human serum and duck hepatitis B virus DNA-dependent DNA polymerase from duck serum as well as RNA-dependent DNA polymerase activity from duck hepatitis B-infected duck liver. Triphosphates of thymidine analogs have been synthesized and tested for their inhibitory activities against these enzymes with the intention both to explore differences between these enzymes and structural requirements for inhibitors. The results showed that with the inhibitors tested, hepatitis B virus DNA-dependent DNA polymerase was the most sensitive enzyme and the triphosphate of 5-propenyl-2'-deoxyuridine was the most active inhibitor. In addition, the 5'-triphosphate of 5-propenyl-arabinofuranosyluracil also inhibited the hepadnavirus DNA-dependent DNA polymerases, and was a competitive inhibitor with respect to 2'-deoxythymidine triphosphate as showed by kinetic studies with duck hepatitis B virus DNA-dependent DNA polymerase from serum. Pharmacokinetic analysis showed 5-propenyl-2'-deoxyuridine to be well absorbed orally, but rapidly cleared from plasma. The arabinofuranosyl analog was also well absorbed but cleared less rapidly. Hence, these results indicate the potential of 5-propenyl-2'-deoxyuridine and 5-propenyl-arabinofuransyluracil for chemotherapy of hepatitis B.

Phosphorylation of four acyclic guanosine analogs by herpes simplex virus type 2 thymidine kinase

Four acyclic guanosine analogs, the (R) and (S) enantiomers of 9-(3,4-dihydroxybutyl)guanine, 9-(4-hydroxybutyl)guanine, and acyclovir were compared in enzyme kinetic experiments, using purified herpes simplex virus type 2 thymidine kinase. All four analogs showed competitive patterns of inhibition in the phosphorylation of thymidine by the viral thymidine kinase, but different affinities and relative rates of phosphorylation were observed.