ABSTRACT
A novel fluoropyrazole ribonucleoside has been shown to have significant anti-influenza activity in vitro. The compound is compared and contrasted with the structurally-related compound ribavirin in attempts to identify factors having significant bearing on the mode of action of both compounds.
Subject(s)
Antiviral Agents/chemical synthesis , Nucleosides/chemical synthesis , Ribavirin/analogs & derivatives , Antiviral Agents/pharmacology , DNA-Directed RNA Polymerases/antagonists & inhibitors , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/pharmacology , Fluorine Compounds/chemical synthesis , IMP Dehydrogenase/antagonists & inhibitors , Influenza A virus/drug effects , Influenza B virus/drug effects , Intestinal Absorption , Molecular Structure , Pyrazoles/chemical synthesis , Ribavirin/chemical synthesis , Ribose/analogs & derivativesABSTRACT
(-)-2'-deoxy-3'-thiacytidine (3TC) has been shown to be a potent, selective inhibitor of HIV replication in vitro, which requires phosphorylation to its 5'-triphosphate for antiviral activity. The intracellular concentration of 3TC 5'-triphosphate in phytohaemagglutinin (PHA)-stimulated peripheral blood lymphocytes (PBL) shows a linear dependence on the extracellular concentration of 3TC up to an extracellular 3TC concentration of 10 microM. At this extracellular concentration of 3TC, the resulting intracellular concentration of 3TC 5'-triphosphate is 5 microM. This value is similar to the inhibition constant (Ki) values for the competitive inhibition of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase and human DNA polymerases (10-16 microM) by 3TC 5'-triphosphate. Since the concentration of 3TC producing 90% inhibition (IC90) of HIV replication in PBLs has been reported to be 76 nM, the antiviral activity of 3TC requires intracellular concentrations of 3TC 5'-triphosphate, which would result in very little inhibition of reverse transcriptase if its sole mode of action was competitive inhibition. This apparent discrepency may be explained by the ability of 3TC 5'-triphosphate to act as a substrate for reverse transcriptase. Primer extension assays have shown that 3TC 5'-triphosphate is a substrate for HIV-1 reverse transcriptase and DNA polymerase gamma, resulting in the incorporation of 3TC 5'-monophosphate into DNA. In the case of DNA polymerase gamma, the product of this reaction (i.e. double-stranded DNA with 3TC 5'-monophosphate incorporated at the 3'-terminus of the primer strand) is also a substrate for the 3'-5' exonuclease activity of this enzyme. This may explain the low levels of mitochondrial toxicity observed with 3TC.
Subject(s)
DNA Polymerase III/metabolism , DNA/metabolism , Deoxycytidine Monophosphate/analogs & derivatives , Lymphocytes/metabolism , RNA-Directed DNA Polymerase/metabolism , Reverse Transcriptase Inhibitors/metabolism , Zalcitabine/analogs & derivatives , Base Sequence , Deoxycytidine Monophosphate/metabolism , HIV Reverse Transcriptase , HeLa Cells , Humans , Kinetics , Lamivudine , Lymphocytes/drug effects , Molecular Sequence Data , Phosphorylation , Phytohemagglutinins , Stereoisomerism , Zalcitabine/metabolism , Zalcitabine/pharmacologyABSTRACT
The metabolism of (-) enantiomeric 2'-deoxy-3'-thiacytidine (3TC) was examined in human immunodeficiency virus type 1 (HIV-1)-infected and mock-infected human cells. 3TC 5'-triphosphate levels accumulated comparably in HIV-1-infected and mock-infected phytohaemagglutinin-stimulated peripheral blood lymphocytes (PBL) and reached 40% or more of total intracellular 3TC metabolites after 4 hr. The rate of decay of 3TC triphosphate in HIV-1-infected and mock-infected PBL measured as a half-life (T1/2) ranged from 10.5 to 15.5 hr. 3TC did not significantly affect metabolism of deoxynucleotides in the U937 cell line, and was shown to be resistant to the action of human platelet pyrimidine nucleoside phosphorylase.
