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)

Ten subjects received 600 to 1,200 mg of the human immunodeficiency virus type 1 (HIV-1) protease inhibitor ritonavir per day. Following 2 weeks of therapy, plasma HIV RNA levels decreased by a mean of 1. 57 (range, 0.89 to 1.96) log units. With continued therapy, HIV RNA levels began to rise in eight subjects. The initial rise in plasma RNA levels was temporally associated with the development and quantitative increase in the V82 resistance mutation. Doubling times of the V82A mutant virus were estimated to be 2.4 to 4.8 days. An L63P/A mutation was commonly present at baseline even in subjects with a durable virologic response. The concomitant acquisition of an L63P/A mutation with the V82A/F mutation at the time when plasma RNA levels rebounded suggests a role for the L63P/A mutation in improving the fitness of the V82A/F mutation. Subsequent additional genotypic changes at codons 54 and 84 were often associated with further increases in plasma RNA levels. Ongoing viral replication in the presence of drugs resulted in the appearance of additional genotypic changes, including the L90M saquinavir resistance mutation, and decreased phenotypic susceptibility. The relative fitness of the protease V82A ritonavir resistance mutation and reverse transcriptase T215Y/F zidovudine resistance mutation following drug withdrawal were estimated to be 96 to 98% that of the wild type. Durability of the virologic response was associated with plasma RNA levels at the nadir. A virologic response beyond 60 days was not observed unless plasma HIV RNA levels were suppressed below 2,000 copies/ml, consistent with estimates from V82A doubling times for selection of a single resistance mutation to dominate the replicating population.
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PMID:Genotypic changes in human immunodeficiency virus type 1 associated with loss of suppression of plasma viral RNA levels in subjects treated with ritonavir (Norvir) monotherapy. 957 87

A novel L-nucleoside analog of deoxycytidine, 2',3'-dideoxy-2', 3'-didehydro-beta-L-5-fluorocytidine (beta-L-Fd4C), was recently shown to strongly inhibit hepatitis B virus (HBV) replication in the 2.2.15 cell line. Therefore, its antiviral activity was evaluated in the duck HBV (DHBV) infection model. Using a cell-free system for the expression of the DHBV polymerase, beta-L-Fd4C-TP exhibited a concentration-dependent inhibition of dCTP incorporation into viral minus-strand DNA with a 50% inhibitory concentration of 0.2 microM which was lower than that of other tested deoxycytidine analogs, i.e. , lamivudine-TP, ddC-TP, and beta-L-FddC-TP. Further analysis showed that beta-L-Fd4C-TP is likely to be a competitive inhibitor of dCTP incorporation and to cause premature DNA chain termination. In primary duck hepatocyte cultures infected in vitro, beta-L-Fd4C administration exhibited a long-lasting inhibitory effect on viral DNA synthesis but could not clear viral covalently closed circular DNA (CCC DNA). Results of short-term antiviral treatment in experimentally infected ducklings showed that beta-L-Fd4C exhibited the most potent antiviral effect, followed by beta-L-FddC, lamivudine, and ddC. Longer administration of beta-L-Fd4C induced a sustained suppression of viremia (>95% of controls) and of viral DNA synthesis within the liver. However, the persistence of trace amounts of viral CCC DNA detected only by PCR was associated with a recurrence of viral replication after drug withdrawal. In parallel, beta-L-Fd4C treatment suppressed viral antigen expression within the liver and decreased intrahepatic inflammation and was not associated with any sign of toxicity. Our data, therefore, demonstrate that in the duck model of HBV infection, beta-L-Fd4C is a potent inhibitor of DHBV reverse transcriptase activity in vitro and suppresses viral replication in the liver in vivo.
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PMID:Characterization of the antiviral effect of 2',3'-dideoxy-2', 3'-didehydro-beta-L-5-fluorocytidine in the duck hepatitis B virus infection model. 1060 31

The consequences of zidovudine (ZDV) replacement by other nucleoside reverse transcriptase inhibitors on the expression of resistance mutations at codons 215 and 41 of the reverse transcriptase (RT) gene was investigated prospectively in 66 patients harboring mutant genotypes who were changed to an effective two- or three-drug combination antiretroviral regimen. Quantitation of mutant (MUT) viral populations at codon 215 by means of RT-PCR with differential hybridization of amplicons specific for MUT and wild (WT) variants revealed no difference in the proportion of 215 MUT variants prior to (93.5 +/- 2.4%) and 12 to 20 months after (96.9 +/- 1.9%) ZDV replacement, independently of a therapeutic change for stavudine. The fitness of the variants harboring the ZDV-resistant MUT 215 genotype following drug withdrawal was calculated to be 96 to 99% of that of the variants harboring the WT 215 genotype. The apparent stability of ZDV-resistant variants in the study population may have two main complementary explanations: persistent selective pressure secondary to partial cross-resistance due to the new regimens given after the therapeutic alteration and suppression of viral replication after the therapeutic alteration that could have hampered the replacement of less fit variants by fitter variants. These findings indicate that, at least within 15 months following discontinuation of ZDV, an effective antiretroviral therapy is insufficient to allow for ZDV-resistant strains to disappear, and thus to allow for the safe re-introduction of the drug.
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PMID:Sustained high proportion of zidovudine-resistant HIV variants despite prolonged substitution of zidovudine by other nucleoside reverse transcriptase inhibitors. 1221 Apr 23

We demonstrated previously that prolonged tenofovir treatment of infant macaques, starting early during infection with virulent simian immunodeficiency virus (SIVmac251), can lead to persistently low or undetectable viremia even after the emergence of mutants with reduced in vitro susceptibility to tenofovir as a result of a K65R mutation in reverse transcriptase; this control of viremia was demonstrated to be mediated by the generation of effective antiviral immune responses. To determine whether structured treatment interruptions (STI) can induce similar immunologic control of viremia, eight newborn macaques were infected with highly virulent SIVmac251 and started on a tenofovir STI regimen 5 days later. Treatment was withdrawn permanently at 33 weeks of age. All animals receiving STI fared much better than 22 untreated SIVmac251-infected infant macaques. However, there was a high variability among animals in the viral RNA set point after complete drug withdrawal, and none of the animals was able to achieve long-term immunologic suppression of viremia to persistently low levels. Early immunologic and viral markers in blood (including the detection of the K65R mutation) were not predictive of the viral RNA set point after drug withdrawal. These results, which reflect the complex interactions between drug resistance mutations, viral virulence, and drug- and immune-mediated inhibition of virus replication, highlight the difficulties associated with trying to develop STI regimens with predictable efficacy for clinical practice.
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PMID:Structured treatment interruptions with tenofovir monotherapy for simian immunodeficiency virus-infected newborn macaques. 1677 28

This study sought to investigate the impacts of the antiretroviral (ARV) therapy regimens currently used in Chinese HIV-1-infected individuals. Seven hundred eighteen ARV-treated and treatment-naive HIV-1-infected individuals living in seven provinces were enrolled in 2005 by a multistage sampling approach according to a national cross-sectional survey program on HIV-1 drug resistance. All patients were investigated clinically, and CD4+ T cell counts and HIV-1 viral loads were measured while genotyping for drug resistance was determined by a home brew nested PCR. Viral inhibition in ARV-treated individuals was higher than that in ARV treatment-naive individuals. The overall prevalence of drug-resistant mutations was 37.8%. Higher frequencies of mutations in ARV-treated and drug withdrawal groups were found than in the ARV treatment-naive group (P<0.01). Of the four regimens currently used, the D4T/3TC/NVP regimen showed a higher-level viral inhibition. No statistical significance was found among the four regimens in drug-resistant mutations. The rate of resistance-associated mutations to non-nucleotide reverse transcriptase inhibitors (NNRTIs) was higher than that to nucleotide reverse transcriptase inhibitors (NRTIs) (P<0.01). The most common mutations conferring resistance to NNRTIs were K103N, Y181C and G190A, representing 56.5, 30.4 and 14.5%, respectively. Furthermore, higher viral inhibition and a lower rate of drug-resistant mutations were achieved in the good compliance group. This study revealed an efficient viral inhibition achieved with the current first-line regimens in China. Most of these regimens could rapidly result in emergence of drug-resistant mutations, suggesting that a second-line ARV therapy is urgently needed and that the compliance with treatment must be emphasized during long-term treatment.
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PMID:The impacts of current antiretroviral therapy regimens on Chinese AIDS patients and their implications for HIV-1 drug resistance mutation. 1880 42

Etravirine (ETR) is the first representative of a new generation of non-nucleoside reverse transcriptase inhibitors (NNRTI) and is indicated in patients with HIV infection and virological failure. The recommended dose is 200 mg (two tablets) every 12 hours after a meal. ETR has good tolerability and the tablets can be dissolved in water, which can aid swallowing in some patients. This drug has a plasma half-life of 30-40 hours and consequently is a candidate for once-daily regimens. The most frequent adverse effect is rash (affecting 19% of patients), which is usually mild (grades 1 or 2) and does not lead to drug withdrawal. The DUET 1 and 2 studies, which compared ETR versus placebo, with both groups receiving boosted darunavir and an optimized background regimen, did not demonstrate a higher incidence of liver toxicity, neuropsychiatric symptoms, gastrointestinal disturbances or atherogenic dyslipidemia in patients receiving ETR. The safety profile of ETR suggests that it could be used as a substitute drug in patients with toxicity induced by first-generation NNRTIs or other antiretroviral drugs.
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PMID:[Safety and tolerability of etravirine]. 2011 24

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