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At least 1,405 records · Page 78Linked to original sources
PubMed2006

The K65R mutation in human immunodeficiency virus type 1 reverse transcriptase exhibits bidirectional phenotypic antagonism with thymidine analog mutations.

The K65R mutation in human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) is selected in vitro by many D-nucleoside analog RT inhibitors (NRTI) but has been rarely detected in treated patients. In recent clinical trials, the K65R mutation has emerged frequently in patients experiencing virologic failure on antiretroviral combinations that do not include 3'-azidothymidine (AZT). The reason for this change is uncertain. To gain insight, we examined trends in the frequency of K65R in a large genotype database, the association of K65R with thymidine analog mutations (TAMs) and other NRTI mutations, and the viral susceptibility profile of HIV-1 with K65R alone and in combination with TAMs. Among >60,000 clinical samples submitted for genotype analysis that contained one or more NRTI resistance mutations, the frequency of K65R increased from 0.4% in 1998 to 3.6% in 2003. Among samples with K65R, a strong negative association was evident with the TAMs M41L, D67N, L210W, T215Y/F, and K219Q/E (P<0.005) but not with other NRTI mutations, including the Q151M complex. This suggested that K65R and TAMs are antagonistic. To test this possibility, we generated recombinant HIV-1 encoding K65R in two different TAM backgrounds: M41L/L210W/T215Y and D67N/K70R/T215F/K219Q. K65R reduced AZT resistance from >50-fold to <2.5-fold in both backgrounds. In addition, TAMs antagonized the phenotypic effect of K65R, reducing resistance to tenofovir, abacavir, 2',3'-dideoxycytidine, dideoxyinosine, and stavudine. In conclusion, K65R and TAMs exhibit bidirectional phenotypic antagonism. This antagonism likely explains the negative association of these mutations in genotype databases, the rare emergence of K65R with antiretroviral therapies that contain AZT, and its more frequent emergence with combinations that exclude AZT.

Adenine↗
PubMed2000

Immortalization of human CD8+ T cell clones by ectopic expression of telomerase reverse transcriptase.

Replicative senescence of T cells is correlated with erosion of telomere ends. Telomerase plays a key role in maintaining telomere length. Therefore, it is thought that telomerase regulates the life span of T cells. To test this hypothesis, we have over-expressed human telomerase reverse transcriptase in human CD8(+) T cells. Ectopic expression of human telomerase reverse transcriptase led to immortalization of these T cells, without altering the phenotype and without loss of specificity or functionality. As the T cells remained dependent on cytokines and Ag stimulation for their in vitro expansion, we conclude that immortalization was achieved without malignant transformation.

Antigens↗
PubMed2001

The role of non-nucleoside reverse transcriptase inhibitors in children with HIV-1 infection.

Over 1.4 million of the worlds' children are infected with HIV-1, mostly acquired in the perinatal period. Antiviral therapeutic options for children with HIV-1 infection have lagged behind those for infected adults. However, we now know that prevention of perinatal HIV-1 transmission to children is possible and that combination therapy for the management of infected children is efficacious. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) are developing a more prominent role in combination therapy regimens, particularly as alternatives to protease inhibitors. They also have a role in preventing perinatal transmission, where it has been shown that only 2 doses of the NNRTI nevirapine can significantly reduce mother-to-child transmission of HIV-1. This has major therapeutic implications, particularly in areas where combination therapy is not readily available. Palatable paediatric formulations of NNRTIs are available or are being developed. Whilst pharmacokinetic data regarding the use of antiretrovirals in children remain scarce, published clinical trials have demonstrated the efficacy of NNRTIs when used as part of combination regimens in the management of HIV-1 infected children. The toxicity profile of NNRTIs is relatively favourable; however, severe skin rash, hepatotoxicity and central nervous system adverse effects with various NNRTIs can lead to treatment cessation. The development of class resistance with single step mutations in the reverse transcriptase gene remains a major therapeutic problem with this class of antiretrovirals. Novel NNRTIs under development are of interest either because of improved pharmacodynamics, reduced toxicity profiles or because of action against NNRTI-mutation containing resistant virus. There are no data available yet on the use of these drugs in the paediatric population.

Acquired Immunodeficiency Syndrome↗
PubMed1977

Inhibition of the reverse transcriptase of bovine leukemia virus by antibody in sera from leukemic cattle and immunological characterization of the enzyme.

Sera from some leukemic cattle contain an antibody that inhibits the reverse transcriptase activity of the bovine leukemia virus. The antibody is not directed against the synthetic template or the major internal and envelope viral antigens. The antibody failed to inhibit the DNA polymerases of the murine leukemia virus, simian sarcoma-associated virus, avian myeloblastosis virus, or Escherichia coli. Conversely, the bovine leukemia virus enzyme was not inhibited by antibody against the reverse transcriptases of other C-type viruses. These findings agree with previous results showing that the major internal bovine leukemia virus protein lacks the known interspecies- and intraspecies-specific antigenic determinants indentified in the homologous proteins of other oncornaviruses.

Animals↗
PubMed2005

Ty1-copia group retrotransposon families in cultivated cottons G. barbadense L. identified by reverse transcriptase domain analysis.

The objective of the current study was to analyze Ty1-copia group retrotransposons in cultivated G. barbadense L. cottons. DNA sequence analysis of 27 partial reverse transcriptase sequences revealed that these elements are heterogeneous and this heterogeneity is resolved into 11 distinct families. Phylogenetic analyses provided strong bootstrap support for a monophyletic origin of plant Ty1-copia group retrotransposons, yet showed high diversity within and between Gossypium species. Furthermore, G. Barbadense element topologies are incongruent with Gossypium phylogeny. The high ratio of synonymous to nonsynonymous changes indicates that the reverse transcriptase domain of these families is evolving under purifying selection. The antiquity and wide distribution of Ty1-copia group retrotransposons illustrate their active role in shaping and evolution of the Gossypium genome.

Amino Acid Sequence↗
PubMed2006

A modified single-tube one-step product-enhanced reverse transcriptase (mSTOS-PERT) assay with heparin as DNA polymerase inhibitor for specific detection of RTase activity.

BACKGROUND: Current regulations and recommendations proposed for the production of vaccines in continuous cell lines of any origin demand that these be free of exogenous viruses, particularly retroviruses. Recently, the ultra-sensitive product-enhanced reverse transcriptase (PERT) assay can be used to detect minute of reverse transcriptase (RTase) in single retroviral particle and is 10(6) times more sensitive than the conventional RTase assays. However, coincidental with this increase in sensitivity is an increase in false-positive reactions derived from contaminating cellular DNA polymerases, which are known to have RTase-like activities. OBJECTIVES: To develop a modified single-tube one-step PERT (mSTOS-PERT) assay with improvements on decreasing significantly the level of false-positive reactions, and to evaluate the mSTOS-PERT assay for sensitivity and specificity. STUDY DESIGN: Ampliwaxtrade mark was used to compartmentalize the reverse transcription (RT) and PCR step in the same micro-tube with more efficiency and reproducibility, while maintaining the high sensitivity. The DNA amplification products were separated by 2% agarose gel electrophoresis, and then analyzed by non-isotopic Southern blot hybridization. A wide variety of cell lines used in biologicals production were detected to validate the improved mSTOS-PERT assay. RESULTS: The detection limit for the mSTOS-PERT assay was at least 10(-9)U, when using AMV-RTase as a positive control. Furthermore, heparin involvement in the RT step can eliminate completely the false-positive PERT signals which are exhibited by cellular polymerases such as DNA-dependent DNA polymerase alpha, gamma released by cell death. Most mammalian cells (MRC-5, Vero, WISH, 2BS, RK-13, MDCK, etc.) are PERT-negative in cell supernatants. Some PERT-positive signals in cell lysates were found to be introduced by the cellular DNA polymerases and could be inhibited specifically by heparin. Chick cells derived from either chick embryo fibroblasts (CEF) or allantoic fluid from SPF embryonated eggs, murine hybridoma cell SP2/0, etc., contained authentic RTase activities, which could not be inactivated by heparin. CONCLUSIONS: The improved mSTOS-PERT assay described here may distinguish the genuine RTase activity from cellular polymerases with high sensitivity and specificity, and is rapid and easy to perform to screen for the possible contamination of minute retroviruses in the cell substrates used in vaccine production.

Cell Line↗
PubMed2000

Phosphorylation of AZT-resistant human immunodeficiency virus type 1 reverse transcriptase by casein kinase II in vitro: effects on inhibitor sensitivity.

Casein kinase II (CKII) phosphorylates wild-type (WT) recombinant reverse transcriptase (RT) mainly in the p66 subunit in vitro. Phosphorylation of T215F RT and D67N/K70R/T215F/K219Q RT (AZT-resistant RT) in vitro increases discrimination against AZTTP 2. 5- and 3.6-fold, respectively. This in vitro resistance can be reversed by treatment of phosphorylated AZT-resistant RT with phosphatase. Phosphorylation has no effect on WT RT. Terminal transferase activity of RT is selectively suppressed on phosphorylated AZT-resistant RT. Resistance to phosphonoformic acid (PFA, foscarnet) increases 3-fold upon phosphorylation of AZT-resistant RT. Although T215, the most important residue for AZT-resistance, is part of a CKII consensus target site, serines are primarily phosphorylated relative to threonines. Mutational analysis shows that phosphorylation can be reduced to 10% that of WT when amino-acid changes are introduced both in the "fingers" subdomain and motif D. These results suggest that phosphorylation of RT might be one factor involved in drug resistance in vivo.

Amino Acid Motifs↗
PubMed1997

Synthesis and biological activity of novel nonnucleoside inhibitors of HIV-1 reverse transcriptase. 2-Aryl-substituted benzimidazoles.

The development of new nonnucleoside inhibitors of human immunodeficiency virus type-1 (HIV-1) reverse transcriptase (RT) active against the drug-induced mutations in RT continues to be a very important goal of AIDS research. We used a known inhibitor of HIV-1 RT, 1-(2,6-difluorophenyl)-1H,3H-thiazolo[3,4-alpha]benzimidazole (TZB), as the lead structure for drug design with the objective of making more potent inhibitors against both wild-type (WT) and variant RTs. A series of structurally related 1,2-substituted benzimidazoles was synthesized and evaluated for their ability to inhibit in vitro polymerization by HIV-1 WT RT. A structure-activity study was carried out for the series of compounds to determine the optimum groups for substitution of the benzimidazole ring at the N1 and C2 positions. The best inhibitor, 1-(2,6-difluorobenzyl)-2-(2,6-difluorophenyl)-4-methylbenzimida zole (35), has an IC50 = 200 nM against HIV-1 WT RT in an in vitro enzyme assay. Cytoprotection assays utilizing HIV-infected MT-4 cells revealed that 35 had strong antiviral activity (EC50 = 440 nM) against wild-type virus while retaining broad activity against many clinically observed HIV-1 strains resistant to nonnucleoside inhibitors. Overall, the activity of 35 against wild-type and resistant strains with amino acid substitution in RT is 4-fold or greater than that of TZB and is comparable to that of other nonnucleoside inhibitors currently undergoing clinical trials, most of which do not have the capacity to inhibit the variant forms of the enzyme.

Anti-HIV Agents↗
PubMed2003

Effects of dipeptide insertions between codons 69 and 70 of human immunodeficiency virus type 1 reverse transcriptase on primer unblocking, deoxynucleoside triphosphate inhibition, and DNA chain elongation.

Finger insertion mutations of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) (T69S mutations followed by various dipeptide insertions) have a multinucleoside resistance phenotype that can be explained by decreased sensitivity to deoxynucleoside triphosphate (dNTP) inhibition of the nucleotide-dependent unblocking activity of RT. We show that RTs with SG or AG (but not SS) insertions have three- to fourfold-increased unblocking activity and that all three finger insertion mutations have threefold-decreased sensitivity to dNTP inhibition. The additional presence of M41L and T215Y mutations increased unblocking activity for all three insertions, greatly reduced the sensitivity to dNTP inhibition, and resulted in defects in in vitro DNA chain elongation. The DNA chain elongation defects were partially repaired by additional mutations at positions 210, 211, and 214. These results suggest that structural communication between the regions of RT defined by these mutations plays a role in the multinucleoside resistance phenotype.

Adenosine Triphosphate↗
PubMed2002

Broad nucleoside-analogue resistance implications for human immunodeficiency virus type 1 reverse-transcriptase mutations at codons 44 and 118.

Two large, independent human immunodeficiency virus type 1 resistance databases containing >7700 reverse-transcriptase (RT) sequences were used to analyze the epidemiology of amino acid substitutions at codons 44 and 118, which confer moderate lamivudine resistance in the presence of zidovudine resistance. As expected, E44A/D and V118I mutations were strongly associated with M41L, D67N, L210W, and T215Y but also with other mutations, including K43E/N/Q, T69D, V75M, H208Y, R211K, and K219R. Both E44D and V118I were more frequently associated with stavudine and didanosine than with zidovudine and lamivudine treatment. However, selection of E44A/D and V118I was also detected in association with a switch to other nucleoside RT inhibitors, including zalcitabine and abacavir. Site-directed mutagenesis confirmed that 44D and 118I can decrease phenotypic susceptibility not only to lamivudine but also to most other nucleoside analogues, particularly stavudine and abacavir. Thus, substitutions at RT codons 44 and 118 have broad implications in nucleoside RT inhibitor resistance in the setting of several nucleoside-associated mutations.

Amino Acid Substitution↗
PubMed1989

Phosphorothioate and cordycepin analogues of 2',5'-oligoadenylate: inhibition of human immunodeficiency virus type 1 reverse transcriptase and infection in vitro.

Natural antiviral activity can be mediated by the interferon-induced synthesis of 2',5'-oligoadenylates (2-5As) and subsequent RNase L activation by these molecules. Analogues of 2-5A that are biologically active and metabolically stable were synthesized and analyzed for antiviral activity against the human immunodeficiency virus type 1 (HIV-1). Replacement of the 3' hydroxyl group of the adenosine moieties of 2-5A with hydrogen atoms (i.e., cordycepin analogues of 2-5A) converted authentic 2-5A trimer into anti-HIV-1 agents in vitro. These cordycepin analogues of 2-5A also inhibited partially purified HIV-1 reverse transcriptase. Introduction of chirality into the 2',5'-phosphodiester internucleotide linkages or 5'-phosphate moieties of the 2-5A molecule (i.e., phosphorothioate analogues of 2-5A) converted authentic 2-5A into more potent inhibitors of HIV-1 reverse transcriptase. However, these phosphorothioate 2-5As demonstrated little or no anti-HIV-1 activity in vitro. Thus, some analogues of 2-5A may form a class of anti-HIV-1 drugs with possible pleiotropic activities that include activation of latent RNase L and inhibition of reverse transcription.

Adenine Nucleotides↗
PubMed2005

In vitro activity of structurally diverse nucleoside analogs against human immunodeficiency virus type 1 with the K65R mutation in reverse transcriptase.

Human immunodeficiency virus type 1 (HIV-1) with a lysine-to-arginine substitution at codon 65 (HIV-1(65R)) of reverse transcriptase (RT) can rapidly emerge in patients being treated with specific combinations of nucleoside analog RT inhibitors (NRTIs). A better understanding of the activity of approved and investigational NRTIs against HIV-1(65R) is needed to select optimal therapy for patients infected with this mutant and to devise strategies to prevent its emergence. Therefore, we tested a broad panel of NRTIs that differed by enantiomer, pseudosugar, and base component against HIV-1(65R) to determine how NRTI structure affects activity. Drug susceptibilities of recombinant wild-type (HIV-1(65K)) or mutant HIV-1(65R) were determined using a single-replication-cycle susceptibility assay with P4/R5 cells and/or a multiple-replication-cycle susceptibility assay with MT-2 cells. All D, L, and acyclic NRTIs were significantly less active against HIV-1(65R) than against HIV-1(65K) except for analogs containing a 3'-azido moiety. Pseudosugar structure and base component but not enantiomer influenced NRTI activity against HIV-1(65R). These findings support the inclusion of 3'-azido-3'-deoxythymidine in drug combinations to treat patients having HIV-1(65R) and to prevent its emergence.

HIV Reverse Transcriptase↗
PubMed2003

Design, synthesis, SAR, and molecular modeling studies of acylthiocarbamates: a novel series of potent non-nucleoside HIV-1 reverse transcriptase inhibitors structurally related to phenethylthiazolylthiourea derivatives.

A novel series of potent, selective HIV-1 N-acylthiocarbamate (ATC) nonnucleoside reverse transcriptase inhibitors (NNRTIs) is described. The title compounds were synthesized through a highly convergent, one-pot procedure. In cell-based assays, the lead compound (17c) prevented the HIV-1 multiplication with an EC(50) of 8 microM. The lead optimization strategy was developed by single or multiple modifications of the three molecular portions, in which 17c was notionally divided. Molecular modeling studies led to the synthesis of O-(2-phthalimidoethyl)-N-(p-substituted phenyl)-N-acylthiocarbamates, which showed in vitro activities against HIV-1 in the low nanomolar range. Nevertheless, the title compounds retained low potency against HIV-1 strains carrying mutations (K103R, Y181C, and K103N/Y181C) responsible for NNRTI resistance. The hypothetical docking model of RT/17c and RT/25c, derived from X-ray crystallographic structure of a PETT derivative in complex with HIV-1 RT, revealed that the model structures of ATCs do not approximate the NNRTI butterfly-like conformation. Analysis of these hypotetical complexes helps to rationalize some SARs and resistance data.

Cell Line↗
PubMed2006

Antiretroviral activity of didanosine in patients with different clusters of reverse transcriptase mutations.

Patterns of mutations associated with didanosine (ddI) resistance are still a controversial issue. The correlation between different clusters of reverse transcriptase mutations with the short-term virological activity of ddI when added to a failing regimen was examined in 40 patients. The median fall in plasma viral load at week 4 was 0.67 log10 copies/ml. There was good correlation between the median fall in plasma HIV RNA levels and the number of nucleoside-associated (P = 0.0152) or thymidine-associated (P = 0.0142) mutations. In conclusion, ddI retained substantial antiretroviral activity when the number of nucleoside-associated or thymidine-associated mutations was less than four.

Didanosine↗
PubMed1989

Differential inhibitory effects of several pyrimidine 2',3'-dideoxynucleoside 5'-triphosphates on the activities of reverse transcriptase and various cellular DNA polymerases.

Several analogues of 2',3'-dideoxythymidine 5'-triphosphate [i.e., 3'-azido-2', 3'-dideoxythymidine 5'-triphosphate(Azdd TTP), 2',3'-didehydro-2',3'-dideoxythymidine 5'-triphosphate (ddeTTP), alpha, beta-methylene 3'-azido-2',3'-dideoxythymidine 5'-diphosphate, alpha, beta-methylene 3'-azido-2',3'-dideoxythymidine 5'-triphosphate, and beta, gamma-methylene 3'-azido-2',3'-dideoxythymidine 5'-triphosphate] and 2',3'-didehydro-2',3'-dideoxycytidine 5'-triphosphate (ddeCTP) have been evaluated for their inhibitory effects on murine retroviral reverse transcriptase and various other DNA polymerases, including DNA polymerases alpha, beta, and gamma, terminal deoxynucleotidyl transferase, and DNA polymerase I. None of the compounds inhibited the activity of DNA polymerase alpha under the reaction conditions employed. When Mg2+ was replaced by Mn2+, however, DNA polymerase alpha was strongly inhibited only by ddeTTP. DNA polymerase beta activity was inhibited only by ddeTTP and ddeCTP. All the compounds, except for ddeCTP, inhibited DNA polymerase gamma activity, ddeTTP being a particularly strong inhibitor of gamma-polymerase (Ki = 3.5 nM). Terminal deoxynucleotidyl transferase was only slightly inhibited by any of the compounds. AzddTTP was a potent inhibitor of reverse transcriptase (Ki = 42 nM), but it also inhibited the activities of DNA polymerase gamma and DNA polymerase I.

Antiviral Agents↗
PubMed1979

On the presence of reverse transcriptase in myelo- and lymphoproliferative disorders.

Buffy coats from 31 patients with a diagnosis of leukemia and 16 normal donors were tested for the presence of a viral-like reverse transcriptase. Eighty-five percent of fresh leukemic buffy coats were positive. Also tested were spleens from 16 patients with hematological disorders and 5 spleens from patients without history of hematological malignancy. The 5 normal spleens were negative. Also negative were 4 spleens from patients with Hairy cell leukemia. From the remaining 12 spleens 7 were positive. Reverse transcriptase measurements can be used to distinguish leukemic from normal buffy coats.

Deoxyguanine Nucleotides↗
PubMed2003

Peptides as new inhibitors of HIV-1 reverse transcriptase and integrase.

Current treatments of human immunodeficiency virus type 1 (HIV-1) infection consist in the combination of drugs targeting reverse transcriptase (RT) and protease (PR). Despite the multiple clinical benefits of this combination therapy, the emergence of resistance highlights the need for new anti-HIV agents. Agents able to interfere with additional steps of viral replication, such as integration of viral DNA in the host genome, would improve the antiviral potency of the treatment. In this regard, we have focused our interest on peptide-based compounds that have been shown to exhibit potential inhibition of RT and integrase (IN) activities in vitro and in vivo. Recently, the expansion of powerful technologies which allow the selection of peptides exhibiting high affinity for a target protein have provided a new approach to selecting potential anti-HIV drugs. Furthermore, efforts to characterize the protein-protein interactions involved in efficient reverse transcription and integration, as well as the determination of the enzyme structure, have generated a very useful source of data for the development of peptide inhibitors. Finally, while this class of compounds has long been considered as poor drug candidates, current knowledge on improving the stability and bioavailability of these agents would lead to the effective use of peptides in therapy.

Anti-HIV Agents↗
PubMed1991

Inhibition of HIV-reverse transcriptase activity by some phloroglucinol derivatives.

Four phloroglucinol derivatives, named mallotophenone (5-methylene-bis-2,6-dihydroxy-3-methyl-4-methoxyacetophenone), mallotochromene (8-acetyl-5,7-dihydroxy-6-(3-acetyl-2,4- dihydroxy-5-methyl-6-methoxybenzyl)-2,2-dimethylchromene), mallotojaponin (3-(3,3(dimethylallyl)5-(3(acetyl-2,4- dihydroxy-5-methyl-6-methoxybenzyl)-phloracetophenone) and mallotolerin (3-(3-methyl-2-hydroxybut-3-enyl)-5(3-acetyl-2,4- dihydroxy-5-methyl-6-methoxybenzyl)-phloracetophenone), have been tested for their ability to inhibit the activity of human immunodeficiency virus (HIV)-reverse transcriptase. Under the reaction conditions with (rA)n.(dT)12-18 as the template.primer, the enzyme activity was inhibited by approximately 70% in the presence of 10 micrograms/ml mallotochromene or mallotojaponin, whereas mallotophenone and mallotolerin were much less inhibitory to the enzyme. The enzyme activity was also inhibited, though to lesser extent, by these compounds under similar conditions with initiated MS-2 phage RNA as the template.primer. The mode of inhibition was, as analyzed with mallotojaponin, competivite with respect to the template.primer, (rA)n.(dT)12-18, and non-competitive with respect to the triphosphate substrate, dTTP. The Ki value of mallotojaponin for HIV-reverse transcriptase was determined to be 6.1 microM.

Base Sequence↗