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.

An open study of remoxipride, a benzamide derivative, in schizophrenia.

Remoxipride is a novel substituted benzamide derivative with specific dopamine-(D2)-receptor blocking properties and selective action on brain mesolimbic functions. Ten inpatients with a DSM-III diagnosis of schizophrenia were treated with the drug in a 6-week open-label study. After 1 week placebo washout, the patients were given stepwise increased doses from 20 to 100 mg t.i.d. Most patients showed a clinically significant improvement; the mean scores in the Brief Psychiatric Rating Scale decreased from 25.8 at baseline to 11.3 at endpoint. Few adverse events were recorded and the rated extrapyramidal symptoms were lower at endpoint than at baseline. No abnormalities in clinical chemistry, haematology, cardiovascular assessments or EEG recordings were seen.

9-(3,4-dihydroxybutyl)guanine, a new inhibitor of herpesvirus multiplication.

A new compound, 9-(3,4-dihydroxybutyl)guanine, has been synthesized and its antiherpes activity determined. 9-(3,4-Dihydroxybutyl)guanine was selectively phosphorylated by herpes simplex virus thymidine kinase and had a high affinity for this enzyme, with an inhibition constant of 1.5 microM. In cell culture, replication of different strains of herpes simplex virus types 1 and 2 was inhibited to the extent of 50% by 4 to 18 microM (RS)-9-(3,4-dihydroxybutyl)guanine. The (R)-enantiomer of this compound was more inhibitory than the (S)-enantiomer. Herpesvirus DNA synthesis was selectively inhibited by (RS)-9-(3,4-dihydroxybutyl)guanine in infected cells, and a low cellular toxicity was observed. (RS)-9-(3,4-Dihydroxybutyl)guanine had a therapeutic effect when applied topically to guinea pigs with cutaneous herpes simplex type 1 infections and to rabbits with herpes keratitis. Oral treatment of a generalized herpes simplex type 2 infection in mice had a therapeutic effect.

Synthesis of esters of phosphonoformic acid and their antiherpes activity.

Aliphatic and aromatic mono-, di-, and triesters of phosphonoformic acid (foscarnet) were synthesized. The triesters were prepared by the Michaelis-Arbuzov reaction and were hydrolyzed to di- and monoesters. The compounds were tested for antiviral activity on isolated herpes simplex virus type 1 (HSV-1) DNA polymerase, in a HSV-1 plaque reduction assay, and on a cutaneous HSV-1 infection in guinea pigs. None of the esters inhibited the activity of isolated HSV-1 polymerases. Monoesters with a free carboxylic group and diesters with an aromatic carboxylic ester function were active against the cutaneous herpes infection. Mono- and diesters with an aromatic phosphonic ester group also showed activity in the plaque-reduction assay. However, mono- and diesters with an aromatic phosphonic ester group also showed activity in the plaque-reduction assay. However, mono- and diesters with aliphatic carboxylic ester groups were inactive in all test systems. The results show that all three acidic groups of phosphonoformic acid must be free in order to get antiviral activity at the enzyme level. However, certain esters of this acid may be biotransformed to the acid itself to give antiherpes activity.

Inhibition of reverse transcriptase activity of avian myeloblastosis virus by pyrophosphate analogues.

Several pyrophosphate analogues have been studied for their effects on avian myeloblastosis virus reverse transcriptase and on cellular DNA polymerase alpha. Examination of structure-activity relationships for these compounds revealed that two acidic groups connected by a short bridge were necessary, but not sufficient, for inhibition of the enzyme activities. Foscarnet sodium (trisodium phosphonoformate) was the most potent inhibitor of reverse transcriptase, giving non-competitive inhibition of reactions primed by (rA)n . (dT)12-18, (rC)n . (dG)12-18, (dC)n . (dG)12-18, and activated DNA. Carbonyldiphosphonate and 2-hydroxyphosphonoacetate also caused non-competitive inhibition patterns, whereas hypophosphate and imidodiphosphonate inhibited AMV reverse transcriptase in a competitive, non-linear manner. The reverse transcriptase reactions directed by (rA)n . (dT)12-18 and activated DNA were most affected by the non-competitive inhibitors. Hypophosphate and imidodiphosphonate inhibited preferentially reactions primed by (dC)n . (dG)12-18 and activated DNA. In all cases the (rC)n . (dG)12-18 directed reaction was the least affected.

Antiherpes activity of [E]-5-(1-propenyl)-2'-deoxyuridine and 5-(1-propenyl)-1-beta-D-arabinofuranosyluracil.

5-(1-Propenyl)-1-beta-D-arabinofuranosyluracil has been synthesized, and this compound and [E]-5-(-propenyl)-2'-deoxyuridine have been tested for inhibition of herpes virus multiplication. Only [E]-5-(1-propenyl)-2'-deoxyuridine was found to be an active inhibitor reducing by 50% the plaque formation of herpes simplex virus type 1 (HSV-1) at about 1 muM. A comparison to the bromovinyl derivatives showed the following order of descending activity; [E]-5-(2-bromovinyl)-2'-deoxyuridine greater than 5-(2-bromovinyl)-1-beta-D-arabinofuranosyluracil greater than or equal to [E]-5-(1-propenyl)-2'-deoxyuridine greater than 5-(1-propenyl)-1-beta-arabinofuranosyluracil. HSV-1 mutants lacking thymidine kinase or resistant against acycloguanosine were resistant against [E]-5-(1-propenyl)-2'-deoxyuridine. All compounds seemed to be phosphorylated by HSV-1 thymidine kinase in a cell-free assay. The compounds were phosphorylated to a lower extent by cellular or HSV-2 thymidine kinase, and the HSV-2 strains tested were inhibited by less than 50% at 100 muM in plaque assays. A selective inhibition of HAV-1 DNA synthesis by [E]-5-(1-propenyl)-2'-deoxyuridine was observed in infected cells indicating an effect on viral DNA polymerase. [E]-5-(1-Propenyl)-2'-deoxyuridine had a low cellular toxicity and a therapeutic effect when applied topically to HSV-1-infected guinea pig skin.

The effect of pyrophosphate analogues on influenza virus RNA polymerase and influenza virus multiplication.

Analogues of pyrophosphate have been tested as inhibitors of influenza virus-RNA polymerase activity in cell-free assays. The most active compound, phosphonoformic acid (PFA), reduced the polymerase activity to 50 per cent at a concentration of 20 muM. The inhibition was dependent on the type of divalent cation present in the assay. PFA at a concentration of 400 muM also inhibited the influenza virus plaque formation by 90 per cent.

Trisodium phosphonoformate, a new antiviral compound.

Trisodium phosphonoformate selectively inhibits cell-free DNA polymerase activity induced by herpesvirus. The new inhibitor has an antiviral effect on herpes simplex virus types 1 and 2, pseudorables virus, and infectious bovine rhinotracheitis virus in cell culture. It has a good therapeutic activity against cutaneous herpes simplex virus infection in guinea pigs.

Inhibition of influenza virus ribonucleic acid polymerase by ribavirin triphosphate.

Ribavirin 5'-triphosphate (RTP), derived from the broad-spectrum antiviral compound ribavirin (Virazole), can selectively inhibit influenza virus ribonucleic acid polymerase in a cell-free assay. Ribavirin and its 5'-monophosphate have no effect on the polymerase. The inhibition is competitive with respect to adenosine 5'-triphosphate and guanosine 5'-triphosphate. RTP also inhibits ApG- and GpC-stimulated influenza virus ribonucleic acid polymerase. Since ribavirin is phosphorylated in the cell, the inhibition of influenza multiplication in the cell may also be caused by RTP.