Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Drug susceptibility and mutations in the reverse transcriptase (RT) gene were analyzed with 167 virus isolates from 38 patients treated with nevirapine, a potent nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) RT. Resistant isolates emerged quickly and uniformly in all patients administered nevirapine either as monotherapy or in combination with zidovudine (AZT). Resistance developed as early as 1 week, indicating rapid turnover of the virus population. The development of resistance was associated with the loss of antiviral drug activity as measured by CD4 lymphocyte counts and levels of HIV p24 antigen and RNA in serum. In addition to mutations at amino acid residues 103, 106, and 181 that had been identified by selection in cell culture, mutations at residues 108, 188, and 190 were also found in the patient isolates. Sequences from patient clones documented cocirculating mixtures of populations of different mutants. The most common mutation with monotherapy, tyrosine to cysteine at residue 181, was prevented from emerging by coadministration of AZT, which resulted in the selection of alternative mutations. The observations documented that, under selective drug pressure, the circulating virus population can change rapidly, and many alternative mutants can emerge, often in complex mixtures. The addition of a second RT inhibitor, AZT, significantly altered the pattern of mutations in the circulating population of HIV.
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PMID:Nevirapine resistance mutations of human immunodeficiency virus type 1 selected during therapy. 750

High level resistance to 3'-azido-3'-deoxythymidine (AZT, zidovudine or Retrovir) is conferred by the presence of four or five mutations (Met-41-->Leu; Asp-67-->Asn; Lys-70-->Arg; Thr-215-->Tyr or Phe; Lys-219-->Gln) in the human immunodeficiency virus (HIV) reverse transcriptase. The order of appearance of these five mutations in asymptomatic patients during therapy has been studied. This has enabled us to propose a model for the acquisition of zidovudine resistance mutations during the treatment of high-risk asymptomatic HIV-infected individuals. A consistent acquisition pattern of mutations at codons 41, 70 and 215 was observed in 17 individuals. Complex mixtures of HIV species containing different combinations of single and linked double resistance mutations were present early in zidovudine therapy in isolates from two patients studied in detail. From these mixtures the linked Leu-41/Tyr-215 genotype outgrew all others initially. The development of each new virus population is likely to be mediated primarily by the increase in the level of drug resistance rather than changes in the growth kinetics of the virus. This leads us to conclude that one major driving force in the outgrowth of different mutant viruses is the selective advantage conferred by higher levels of drug resistance.
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PMID:Zidovudine treatment results in the selection of human immunodeficiency virus type 1 variants whose genotypes confer increasing levels of drug resistance. 750 70

HIV-1 reverse transcriptase can catalyze the addition of either azidothymidine monophosphate (AZTMP) or thymidine monophosphate (dTMP) to a primer strand opposite template adenosine bases. The ratio of incorporation of AZTMP to dTMP as catalyzed by HIV-1 reverse transcriptase has been determined to be 0.4 using an RNA-DNA duplex substrate prepared from oligonucleotides with sequences taken from the HIV-1 genome sequence. Slight variations are found for the incorporation ratio of the two nucleotides on other substrates. Substrates containing more than one adenosine in the single-stranded part of the template allow for more chances to incorporate AZTMP and less full-length product. Variations in the intensity of bands on an autoradiograph of a DNA sequencing gel corresponding to different positions of incorporation of AZTMP suggest that not all template adenosine positions offer the same level of discrimination against incorporation of AZTMP. A reverse transcriptase containing a set of four mutations (D67N, K70R, T215Y, K219Q) known to cause resistance to AZT in cell culture assays has a ratio of incorporation that is 0.77 +/- 0.03 times the ratio for the wild-type reverse transcriptase opposite one specific template adenosine. In contrast, a hybrid mutant containing the same four mutations that cause resistance to AZT and an additional mutation, Y181C, which by itself causes resistance to the non-nucleoside inhibitor L-697,661 [Sardana et al. (1992), J. Biol. Chem. 267, 17526-17530], has a ratio of incorporation that is 1.34 +/- 0.01 times that of the wild-type, indicating that the hybrid mutant enzyme is more susceptible to inhibition by AZTTP than the wild-type reverse transcriptase.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Sensitivity of HIV-1 reverse transcriptase and its mutants to inhibition by azidothymidine triphosphate. 750 34

Mutation in the human immunodeficiency virus type 1 reverse transcriptase (RT) at codon 215 has been shown to play a significant role in resistance to zidovudine (AZT). Substitution of threonine with tyrosine or phenylalanine alone confers decreased susceptibility to the inhibitor. In this study we constructed a panel of 10 viruses with different amino acids at this codon, including 7 novel mutants, and assessed their susceptibilities to AZT. The majority of the new mutants were AZT sensitive, whereas the Thr-215-->Trp mutant was partially resistant (threefold less susceptible). A combination of the Thr-215-->Trp with the other AZT resistance mutations Lys-70-->Arg and Met-41-->Leu gave additive resistance. The Thr-215-->Phe virus was less AZT resistant than the Thr-215-->Tyr mutant, both on its own and when each was combined with the Met-41-->Leu mutant. These observations confirm the general hypothesis that increased bulk of the amino acid side chains at this position confers decreased AZT sensitivity. A leucine-to-valine substitution at codon 74 has previously been found to confer dideoxynucleoside resistance. We constructed mutants with five novel amino acid substitutions (Ala, Gly, Glu, Met, and Asp) at codon 74. Of these, only one (that with the Met substitution) retained enough RT activity to yield viable virus. It thus appears that there are severe structure-function constraints on the amino acid side chains at this position in the enzyme. The activities of the Leu-74-->Ala and Leu-74-->Met RT enzymes expressed in Escherichia coli appeared to have reduced susceptibility to ddGTP compared with the wild-type enzyme. The mutants described in this work may prove useful for correlation with structural studies of the human immunodeficiency virus type 1 RT.
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PMID:Mutagenic study of codons 74 and 215 of the human immunodeficiency virus type 1 reverse transcriptase, which are significant in nucleoside analog resistance. 751 65

Combinations of the human immunodeficiency virus (HIV) Tat protein antagonist Ro 24-7429 with either the HIV protease inhibitor Ro 31-8959 or the HIV reverse transcriptase inhibitors AZT (3'-azido-3'-deoxythymidine), ddC (2',3'-dideoxycytidine), ddI (2',3'-dideoxyinosine), and nevirapine were synergistic or additive in reducing HIV type 1 p24 antigen production in CEM cells or inhibiting HIV type 1-induced syncytium formation in HT4-6C cells.
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PMID:Combinative interactions of a human immunodeficiency virus (HIV) Tat antagonist with HIV reverse transcriptase inhibitors and an HIV protease inhibitor. 751 58

Of the different steps of the HIV replicative cycle, the reverse transcription step has received most attention as a target for chemotherapeutic intervention. The reverse transcriptase (RT) can be blocked by both nucleoside (nucleotide) and non-nucleoside type of inhibitors. Whereas the former act as competitive inhibitors with respect to the natural substrates or alternate substrates (chain terminators), the latter act allosterically with a non-substrate binding site of the enzyme. Several non-nucleoside types of RT inhibitors have proved to inhibit HIV-1 replication at nanomolar concentrations that are 10(4)- to 10(5)-fold lower than the cytotoxic concentrations. Although a non-nucleoside HIV-1-specific RT inhibitor may rapidly select for virus-drug resistance in cell culture, the resulting mutant strain may or may not show cross-resistance, and in some instances even hypersensitivity, to other HIV-specific RT inhibitors. When used at the appropriate concentrations, HIV-1-specific RT inhibitors are able to completely shut off ("knock-out") virus replication in vitro, under conditions where dideoxynucleoside analogues such as AZT fail to do so. This apparent "sterilizing effect" achieved by the non-nucleoside type of HIV-1-specific RT inhibitors opens new perspectives for the treatment of HIV infections in patients.
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PMID:New developments in the chemotherapy of lentivirus (human immunodeficiency virus) infections: sensitivity/resistance of HIV-1 to non-nucleoside HIV-1-specific inhibitors. 751 7

The preliminary results of the Concorde trial demonstrated the transient clinical benefit of monotherapy with zidovudine (AZT) in asymptomatic persons infected with human immunodeficiency virus type 1 (HIV-1). This result, which has been widely disseminated and discussed, was predictable given the previous demonstration of the development of resistance to AZT in isolates from individuals receiving prolonged treatment with the drug and given the finding that didanosine (ddI) is more efficacious than continued therapy with AZT in individuals who have received > or = 6 months of AZT monotherapy. On the basis of these findings, interest in combinations of antiretroviral agents has continued to grow. Many in vitro studies of nucleoside and nonnucleoside inhibitors of reverse transcriptase combined with interferon-alpha or inhibitors of protease have been published. In addition, numerous clinical trials of various combinations have been completed or are under way. Dr. Martin Hirsch and his colleagues at the Massachusetts General Hospital have been among the leaders of this effort. He and Dr. Angela Caliendo review, in this AIDS Commentary, the current state of our knowledge regarding the potential utility of combination therapy for infection with HIV-1.
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PMID:Combination therapy for infection due to human immunodeficiency virus type 1. 751 1

A Human immunodeficiency virus type-1 endogenous reverse transcriptase reaction was developed as an in vitro assay to study the inhibition of reverse transcription by antiviral compounds. Conditions were established for producing genomic length (-) strand DNA in high yields and measuring the inhibition of this transcript as the assay endpoint. In addition to genomic length (-) strand DNA, a novel segmented (-) strand product composed of a 6.0 kb reverse transcript of the 5' 2/3 of the viral RNA genome and a 3.5 kb reverse transcript of the 3' 1/3 was observed. The most prominent (+) strand product was the size expected for plus-strong stop DNA. Additional minor (+) strand species were also observed. The triphosphate form of the nucleoside analog inhibitor 3'-azido-3'-deoxythymidine (RETROVIR, Zidovudine, AZT) and BI-RG-587 (nevirapine), a non nucleoside inhibitor, were used to demonstrate the utility of the endogenous system for the analysis of reverse transcriptase inhibitors. In a standard reaction, synthesis of genomic length DNA was 50% inhibited by 0.1 microM AZTTP and 0.1 microM nevirapine.
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PMID:Development of a human immunodeficiency virus-1 in vitro DNA synthesis system to study reverse transcriptase inhibitors. 751 3

Artificial neural networks were used to analyze and predict the human immunodeficiency virus type 1 reverse transcriptase inhibitors. The training and control sets included 44 molecules (most of them are well-known substances such as AZT, dde, etc.). The activities of the molecules were taken from literature. Topological indices were calculated and used as molecular parameters. The four most informative parameters were chosen and applied to predict activities of both new and control molecules. We used a network pruning algorithm and network ensembles to obtain the final classifier. Increasing of neural network generalization of the new data was observed, when using the aforementioned methods. The prognosis of new molecules revealed one molecule as possibly very active. It was confirmed by further biological tests.
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PMID:HIV-1 reverse transcriptase inhibitor design using artificial neural networks. 752 81

During DNA synthesis, the binding of human immunodeficiency virus (HIV) reverse transcriptase (RT) to the template-primer precedes its binding to nucleotide triphosphates. The interaction of oligonucleotide DNA with HIV-1 RT was investigated by using a gel retardation assay. Both homodimeric (p66/p66) and heterodimeric (p66/p51) isoforms of HIV-1 RT were capable of binding the DNA oligomers. Thus, all further studies on the interaction of HIV-1 RT with DNA were done with heterodimeric RT. We have studied the conditions for optimal binding. The formation of the RT-DNA complex was primer-independent, and the extent of DNA binding was indistinguishable for both single-stranded and double-stranded DNA (either blunt-ended or recessed). The DNA binding activity of the RT was found to be dependent on oligonucleotide length. HIV-1 RT binds DNA with no apparent sequence specificity. Hence, this enzyme belongs to the sequence nonspecific DNA binding proteins. The interaction was found to be independent of DNA synthesis. The formation of the RT-DNA complex was not influenced by the presence of either template-complementary or noncomplementary dNTPs, indicating that neither DNA polymerization nor binding of the RT to the dNTP affects the stability of the complex. The gel retardation assay was utilized to examine also the effect of various HIV-1 RT inhibitors (i.e., AZT-TP, ddTTP, TIBO, and 3,5,8-trihydroxy-4-quinolone) on the enzyme-DNA interaction. The results indicate differences in the modes of action of these compounds.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Interaction of the reverse transcriptase of human immunodeficiency virus type 1 with DNA. 752 56


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