Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.49 (reverse transcriptase)
 31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Phosphonoformate (PFA) inhibits multiplication of visna virus in sheep choroid plexus cells; a 50% reduction of virus yield was obtained by 20 to 80 microM PFA. Morphological changes, such as syncytial formation and cell degeneration, could be reversibly prevented by PFA. Cell growth was not significantly affected at 500 microM PFA, although prolonged treatment with 2 mM PFA did arrest cell growth. Cell-free reverse transcriptase activity primed with various synthetic template-primers was inhibited about 90% in the presence of 100 microM PFA. The results from kinetic experiments suggested that reverse transcriptase was utilized early but not late in the infection cycle. A structurally related substance, phosphonoacetate, did not inhibit visna virus multiplication and had no inhibitory effect on reverse transcriptase activity at a concentration of 500 microM.
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PMID:Phosphonoformate inhibition of visna virus replication. 9 Jan 68

The new antiviral substance phosphonoformate (PFA) has been tested in a cell-free system for its effect on reverse transcriptases from an avian retrovirus (avian myeloblastosis virus, AMV) and from mammalian retroviruses (Rauscher leukaemia virus, RMuLV; bovine leukaemia virus; baboon endogenous virus; simian sarcoma virus; visna virus). The observed inhibitory effect of PFA has been compared with that of a structurally related substance, phosphonoacetate (PAA). Phosphonoformate, at a concentration of 100 microM, reduced the activities of all the above mentioned polymerases by 90% when (rA)n.(dT)10 was used as a template/primer. The dose-response curves for AMV and RMuLV polymerases primed with (rA)n.(dT)10 showed PFA to be a 1000-fold more active than PAA; the RMuLV polymerase activity was reduced to 50% after incubation with 0.7 microM-PFA and 0.7 mM-PAA, respectively. There was no difference in PFA inhibition of virus-associated and purified reverse transcriptase activity. Results with various synthetic templates showed that both the RNA- and the DNA-dependent polymerase activities of reverse transcriptase were inhibited by PFA. The endogenous polymerase activity of AMV was inhibited to 50% at 100 microM-PFA, while PAA had no effect. The PFA inhibition was dependent on whether Mg2+ or Mn2+ was used as divalent cation in the assay. Phosphonoformate arrested DNA synthesis immediately after being added to the assay system. The mechanism of inhibition of the AMV polymerase was non-competitive with respect to substrate and template and the apparent inhibition constants were 16 microM and 9 microM, respectively.
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PMID:Phosphonoformate inhibits reverse transcriptase. 9 44

A Glu-89-->Gly alteration in the human immunodeficiency virus type 1 reverse transcriptase (RT) was previously shown to result in resistance to several dideoxynucleoside analogs and to phosphonoformic acid (PFA; foscarnet). This residue was altered to Ala, Val, Ser, Thr, Gln, Asp, Asn, or Lys, and the ddGTP and PFA sensitivities of the mutant RTs were measured. Replacements with Ala, Gly, Val, and Thr led to resistance to inhibition by ddGTP, while mutants with amino acid Ser, Gln, Asn, Asp, or Lys displayed only moderate or no resistance. A similar result was obtained with inhibition by PFA, except that the Asp-89 mutant also displayed resistance. Furthermore, the introduction of Glu-89-->Gly alteration into the RT of human immunodeficiency virus type 2 likewise rendered it resistant to both ddGTP and PFA.
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PMID:Mutagenesis of the Glu-89 residue in human immunodeficiency virus type 1 (HIV-1) and HIV-2 reverse transcriptases: effects on nucleoside analog resistance. 127 7

The bisheteroarylpiperazines (BHAPs) are potent inhibitors of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) and specifically block HIV-1 replication (Romero, D. L., Busso, M., Tan, C.-K., Reusser, F., Palmer, J. R., Poppe, S. M., Aristoff, P. A., Downey, K. M., So, A. G., Resnick, L., and Tarpley, W. G. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 8806-8810). Here we show that the radiolabeled BHAP [3H]U-88204 binds specifically to HIV-1 RT with high affinity (KD of 50 nM) and a stoichiometry of 1 mol of U-88204 per 1 mol of p66/p51 RT heterodimer. Binding of [3H]U-88204 to RT is unaffected by the presence of saturating poly(rC).oligo (dG)12-18 template-primer. Direct measurement of competition between [3H]U-88204 and other RT inhibitors for binding to RT reveals mutually exclusive competition between [3H]U-88204 and the non-nucleoside RT inhibitor BI-RG-587 (Kopp, E. B., Miglietta, J. J., Shrutkowski, A. G., Shih, C.-K., Grob, P. M. and Skoog, M.T. (1991) Nucleic Acids Res. 19, 3035-3039), indicating that both share the same binding site. Phosphonoformate in concentrations up to 50 microM shows no competition with [3H]U-88204 for binding to RT either alone or in the presence of template-primer. Dideoxynucleotide RT inhibitors affect the binding of [3H]U-88204 to RT when complementary template-primer is present. [3H]U-88204 and the dideoxynucleotide ddGTP can bind RT simultaneously, but the presence of one ligand decreases the affinity of RT for the second. Inasmuch as ddGTP approximates the nucleotide substrate of RT, the direct demonstration of an RT-dideoxynucleotide-[3H]U-88204 complex validates the use of indirect kinetic methods to assess the strength of BHAP interaction with RT and suggests that RT inhibition by U-88204 is achieved via effects on nucleotide substrate binding.
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PMID:The binding of a novel bisheteroarylpiperazine mediates inhibition of human immunodeficiency virus type 1 reverse transcriptase. 137 Apr 45

Foscarnet is a pyrophosphate analogue with activity against herpesviruses, human immunodeficiency virus (HIV), and other RNA and DNA viruses. Foscarnet and its analogues achieve their antiviral effects via inhibition of viral polymerases, with such inhibition not being dependent on activation or phosphorylation of the compounds by viral or cellular proteins. Current evidence indicates that foscarnet interferes with exchange of pyrophosphate from deoxynucleoside triphosphate during viral replication by binding to a site on the herpesvirus DNA polymerase or HIV reverse transcriptase. Reviewed herein are basic findings regarding the mechanism of action and antiviral activity of foscarnet and the related compound phosphonoacetic acid (PAA), as well as findings regarding potential mechanisms of viral resistance and interactions with other antiviral agents.
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PMID:Mechanism of action of foscarnet against viral polymerases. 137 Oct 38

The pharmacokinetics of thiophosphonoformate (TPFA) and phosphonoformate (foscarnet, PFA) were studied in normal adult cats, a species susceptible to feline immunodeficiency virus (FIV) infection. Parent drugs and metabolites were quantitated by high-performance liquid chromatography (HPLC). TPFA had a mean terminal plasma half-life of 42 min, a total clearance of 4.58 ml/min/kg, and a renal clearance of 1.24 ml/min/kg (N = 4). TPFA underwent in vivo metabolism to PFA and thiophosphonic acid (TPA); the latter was inactive against HIV reverse transcriptase. The 6-h cumulative urinary excretion was 42.3% of the intravenous administered dose of TPFA, consisting of 23.5% unchanged TPFA, 13.8% PFA, and 5.0% TPA. In comparison, PFA had a mean (N = 5) terminal half-life of 172 min and a total clearance of 1.88 ml/min/kg, approximating its renal clearance. There was no evidence of PFA metabolism. Oral doses of TPFA were administered either in enteric-coated capsules or in solution by gavage. The mean oral bioavailability of encapsulated TPFA and PFA was 22 and 8%, respectively. When given by gavage, TPFA had a higher mean bioavailability (33%), but with a greater variability. Based on the 6-h cumulative urinary excretion of TPFA, the mean oral bioavailability of TPFA was 44%, similar to that based on plasma data. The TPFA appears to be superior to PFA because of its greater oral bioavailability and its ability to deliver an active metabolite, PFA, to the systemic circulation after oral dosing.
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PMID:Pharmacokinetics of potential anti-AIDS agents thiofoscarnet and foscarnet in the cat. 138 17

A characterization of equine infectious anemia virus reverse transcriptase (EIAV RT) and its inhibition by 5'-triphosphate analogs was undertaken to explore the possibility of using EIAV RT as an in vitro model for studying human immunodeficiency virus (HIV). EIAV RT activity was found to be dependent on the bivalent cations Mg++ and Mn++. The optimal pH for enzyme reaction was pH 8.2. EIAV RT preferred a 70 mmol/L concentration of monovalent salts. Phosphonoformic acid (PFA) was an active inhibitor of EIAV RT, but phosphonoacetic acid (PAA) and N-ethylmaleimide (NEM) were not. The inhibition of EIAV RT activity by 5'-triphosphates of nucleoside derivatives was in the following decreasing order: FLTTP greater than AZTTP greater than nPrearaUTP greater than nPredUTP = CEdUTP greater than EtdUTP greater than nPrdUTP greater than HMdUTP. nPrearaUTP was a linear competitive and PFA a linear noncompetitive inhibitor of EIAV RT with respect to dTTP. Apparent Kis and Kii were 1.5 and 2.2 mumol/L respectively. The susceptibility pattern of EIAV RT to inhibitors was similar to that of HIV RT.
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PMID:The characterization of EIAV reverse transcriptase and its inhibition by 5'-triphosphates of 2'-deoxyuridine analogs, PFA and PAA. 171 94

Various combinations of inhibitors of HIV reverse transcriptase were tested for inhibition of HIV replication in order to reveal any potential synergism or antagonism. PFA, a pyrophosphate analogue, gave synergistic inhibition of HIV replication in combination with both of the thymidine analogues AZT and FLT. The combination of PFA and AZT-TP gave only additive or weakly synergistic inhibition in a reverse transcriptase enzyme assay. The combination of AZT and FLT also gave synergistic inhibition of HIV replication, whilst the combination of AZT-TP and FLT-TP gave only additive or weakly synergistic inhibition of reverse transcriptase. Thus, the synergy does not arise from effects on reverse transcriptase alone but must be owing to other, cellular factors, such as effects on nucleoside metabolism or metabolism of the analogues. The results are consistent with the hypothesis that AZT may have an alternative mechanism of inhibition other than inhibition of reverse transcriptase. The diminished cytotoxicity observed in addition to the synergistic inhibition makes these combinations attractive from the point of view of combination chemotherapy. The inhibition of HIV replication by peptides from various parts of the V3 region of gp120 whose sequences were homologous with the tryptase inhibitor trypstatin was tested. Inhibitory activity was displayed by two peptides containing cysteine in their sequence. Antibodies to two peptides containing the two conserved cysteine residues from opposite sides of the neutralizing loop of gp120 were previously associated with protection from vertical transmission of HIV. The V3 region thus seems to be important for the function of gp120 and the transmission of HIV.
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PMID:Synergistic combinations and peptides in the inhibition of human immunodeficiency virus. 171 18

Phosphonoformate (PFA), a noncompetitive inhibitor of reverse transcriptase (RT), inhibited feline leukemia virus (FeLV) infection of 2 feline cell lines and inhibited progeny virus RT activity in a chronically FeLV-infected cell line. Feline leukemia virus infection of 3201 cells, an FeLV-negative lymphoma cell line, was inhibited by greater than 70% at a concentration of only 1 microM PFA and by greater than 90% at concentrations of 64 to 256 microM PFA, as evidenced by RT activity. However, FeLV antigen expression by 3201 cells remained relatively constant over noncytotoxic concentrations of PFA. Because the persistence of viral antigen expression with concomitant suppression of RT activity appears to be unique and because 3201 cells express small amounts of an endogenous retrovirus (RD-114) and contain endogenous FeLV proviral sequences, a possible role of endogenous retroviruses acting as helper viruses was suggested. Feline leukemia virus infection of 81C cells, a sarcoma-positive, leukemia-negative fibroblast cell line, was inhibited by greater than 50% at a concentration of 64 microM PFA and by greater than 98% at concentrations of 256 to 512 microM PFA, as indicated by suppression of focus formation. The feline lymphoid cell line FL-74 is a large producer of FeLV. When FL-74 cells were cultured in the presence of 256 microM PFA, virus production (virus budding and viral antigen) was not affected, but progeny virus lost RT activity and infectivity. Direct addition of PFA (256 microM) to FeLV also reduced RT activity and infectivity. These data indicate that PFA can directly and rapidly inactivate retrovirus independent of cellular processing, presumably by inhibiting RT.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Prophylactic and therapeutic effects of phosphonoformate against feline leukemia virus in vitro. 172 22

Phosphonoformate (PFA) is a simple PPi analog which inhibits the activities of a variety of viral DNA polymerase, RNA polymerase, and reverse transcriptase enzymes. PFA is a topical and parenteral treatment for human herpesvirus infections and is currently in phase I trials for treatment of acquired immunodeficiency syndrome. Pharmacokinetic properties of PFA in young (growing) and adult specific-pathogen-free cats were compared. Mean PFA clearance from plasma was twofold higher in young cats (7.52 ml/min per kg of body weight) than in adult cats (3.70 ml/min per kg). Higher PFA clearance from plasma observed in young cats may result from higher renal clearance or enhanced accumulation of PFA in bone tissue of young versus adult cats. No plasma protein binding of PFA was observed. Mean oral bioavailability was 35% in young cats. These data indicate that age-related differences in PFA clearance from plasma occur in cats.
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PMID:Age-related differences in pharmacokinetics of phosphonoformate in cats. 214 79


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