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)

Genotypes that confer drug resistance to reverse transcriptase inhibitors and protease inhibitors were evaluated in HIV-1 proviral DNA obtained from peripheral blood mononuclear cell samples. Fifty-three HIV-1-infected patients were studied, 19 of whom had not received antiretroviral treatment. In the other 34 patients, 9 had been treated with combinations of two reverse transcriptase inhibitors (AZT, ddI, d4T, 3TC) and 25 had been treated with triple antiretroviral therapy including a protease inhibitor (nelfinavir, indinavir, saquinavir, ritonavir). To determine the presence of mutations involved in the development of resistance to reverse transcriptase inhibitors a hybridization Microtiter assay was carried out. Mutations were detected in treated patients as well as in those without previous antiretroviral treatment, with the most frequent mutations being those that confer resistance to AZT, followed by those that develop cross-resistance to ddI/ddC and 3TC, which are the most commonly used drugs to date. No mutations were detected to any nucleoside analog in only 13 cases. To analyze the presence of mutations in the protease gene a dot-blot hybridization was carried out which included the mutations in codons 36, 82 and 90. Mutation 82 was detected in one case. Therefore, with the aim of determining the pattern of genotypic mutations in patients infected with HIV-1 and in order to make the best therapeutic choice, it would be recommended to consider carrying out genotypic resistance assays in clinical practice.
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PMID:[Evaluation of mutations that confer resistance to nucleoside analogs and protease inhibitors in HIV-1-infected patients. Study Group on Resistance to Antiretroviral Agents]. 1085 10

The therapeutic goals in chronic hepatitis B are to prevent or decrease cirrhosis and hepatocellular carcinoma in patients with pre-cirrhotic or early cirrhotic disease and to stabilise patients with end-stage cirrhosis. Lamivudine is an oral nucleoside analogue that suppresses hepatitis B virus (HBV) replication, and so may achieve both these treatment objectives. The active 5'-triphosphate metabolite of lamivudine has two modes of viral suppression. First, it mimics deoxycytidine triphosphate and is incorporated into newly synthesised HBV DNA to cause chain termination. Second, it demonstrates competitive inhibition of viral DNA-dependent and RNA-dependent DNA polymerase activity (i.e., reverse transcriptase activity). Lamivudine may, therefore, act at four possible stages during HBV replication: reverse transcription of pre-genomic mRNA into nascent minus-strand DNA; formation of plus strand DNA from nascent minus-strand DNA; completion of double-stranded DNA; and formation of covalently closed circular DNA. In clinical studies, lamivudine therapy reduced serum HBV DNA and this was associated with significant improvements in liver histology and significant and sustained enhancement of the proliferative CD4-mediated response to HBeAg and hepatitis B core antigen (HBcAg), and an increased frequency of HBeAg-specific T cells. HBV DNA concentrations often returned to pre-treatment values when therapy ended prior to the loss of hepatitis B e antigen (HBeAg). Although the emergence of HBV variants with a mutation in the YMDD (tyrosine-methionine-aspartate-aspartate) motif has been observed, such variants show reduced susceptibility to lamivudine due to limited replication competence, and their emergence is not a signal to cease lamivudine therapy. In conclusion, viral suppression with lamivudine offers a means of disease improvement and immunological control in chronic hepatitis B.
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PMID:Profound suppression of hepatitis B virus replication with lamivudine. 1086 48

Treating HIV infections with drugs that block viral replication selects for drug-resistant strains of the virus. Particular inhibitors select characteristic resistance mutations. In the case of the nucleoside analogs 3TC and FTC, resistant viruses are selected with mutations at amino acid residue 184 of reverse transcriptase (RT). The initial change is usually to M184I; this virus is rapidly replaced by a variant carrying the mutation M184V. 3TC and FTC are taken up by cells and converted into 3TCTP and FTCTP. The triphosphate forms of these nucleoside analogs are incorporated into DNA by HIV-1 RT and act as chain terminators. Both of the mutations, M184I and M184V, provide very high levels of resistance in vivo; purified HIV-1 RT carrying M184V and M184I also shows resistance to 3TCTP and FTCTP in in vitro polymerase assays. Amino acid M184 is part of the dNTP binding site of HIV-1 RT. Structural studies suggest that the mechanism of resistance of HIV-1 RTs carrying the M184V or M184I mutation involves steric hindrance, which could either completely block the binding of 3TCTP and FTCTP or allow binding of these nucleoside triphosphate molecules but only in a configuration that would prevent incorporation. The available kinetic data are ambiguous: one group has reported that the primary effect of the mutations is at the level of 3TCTP binding; another, at the level of incorporation. We have approached this problem using assays that monitor the ability of HIV-1 RT to undergo a conformational change upon binding a dNTP. These studies show that both wild-type RT and the drug-resistant variants can bind 3TCTP at the polymerase active site; however, the binding to M184V and M184I is somewhat weaker and is sensitive to salt. We propose that the drug-resistant variants bind 3TCTP in a strained configuration that is salt-sensitive and is not catalytically competent.
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PMID:The role of steric hindrance in 3TC resistance of human immunodeficiency virus type-1 reverse transcriptase. 1087 73

Genotypes that confer drug resistance to reverse transcriptase inhibitors and protease inhibitors were evaluated in HIV-1 proviral DNA obtained from peripheral blood mononuclear cell samples. Fifty-three HIV-1-infected patients were studied, 19 of whom had not received antiretroviral treatment. In the other 34 patients, 9 had been treated with combinations of two reverse transcriptase inhibitors (AZT, ddI, d4T, 3TC) and 25 had been treated with triple antiretroviral therapy including a protease inhibitor (nelfinavir, indinavir, saquinavir, ritonavir). To determine the presence of mutations involved in the development of resistance to reverse transcriptase inhibitors a hybridization Microtiter assay was carried out. Mutations were detected in treated patients as well as in those without previous antiretroviral treatment, with the most frequent mutations being those that confer resistance to AZT, followed by those that develop cross-resistance to ddI/ddC and 3TC, which are the most commonly used drugs to date. No mutations were detected to any nucleoside analog in only 13 cases. To analyze the presence of mutations in the protease gene a dot-blot hybridization was carried out which included the mutations in codons 36, 82 and 90. Mutation 82 was detected in one case. Therefore, with the aim of determining the pattern of genotypic mutations in patients infected with HIV-1 and in order to make the best therapeutic choice, it would be recommended to consider carrying out genotypic resistance assays in clinical practice.
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PMID:[Evaluation of mutations that confer resistance to nucleoside analogs and protease inhibitors in HIV-1-infected patients] 1087 23

Several first-generation nucleoside analogues have been tested against chronic hepatitis B virus (HBV) infection, but trials were unsuccessful or accompanied by toxicity. Recently, oral second-generation nucleoside analogues have been developed that have potent activity against HBV. The best-studied compound so far is lamivudine ((-)2'-deoxy-3'-thiacytidine; 3TC). Lamivudine is an inhibitor of reverse transcriptase (RT) activity and is in clinical use in human immunodeficiency virus (HIV)-infected individuals. As several studies on the use of lamivudine for hepatitis B show, the development of resistance in the viral polymerase under lamivudine treatment, however, causes a significant clinical problem. All other drugs in advanced clinical development for HBV are nucleosides; cross-resistance is therefore expected in most cases. The history of HIV treatment demonstrates that new classes of drugs, the protease inhibitors and non-nucleosidic inhibitors of RT, allowed for a longer-term clinical benefit when used in combination with nucleoside analogues. The development of non-nucleosidic compounds with different modes of action therefore appears very important for the treatment of chronic hepatitis B as well.
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PMID:Development of resistance and perspectives for future therapies against hepatitis B infections: lessons to be learned from HIV. 1088 29

Antiretrovirals, particularly nucleoside analogue reverse transcriptase inhibitors (RTIs) - DDI, 3TC and D4T, are widely used to effectively control human immunodeficiency virus (HIV) infection. These drugs have several adverse effects including anemia, peripheral neuropathy, pancreatitis and, on rare occasions, lactic acidosis. We describe the case of a 39 year old patient who had severe lactic acidosis after receiving stavudine (D4T) and didanosine (DDI) for an 8 month period. She had never manifested an opportunistic infection and presented a CD4 count of 378 cells/mm3 and an undetectable viral load (< 400 copies/ml). The purpose of the following report is to alert clinicians and infectious diseases specialists to the occurrence of lactic acidosis in asymptomatic HIV patients receiving antiretrovirals for long periods of time.
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PMID:Lactic acidosis and antiretroviral therapy: a case report and literature review. 1093 99

Recently, d4T/ddI combination has been associated with the selection of thymidine analogue mutations (TAMs) in 50% of patients with a detectable viral load after 6 to 12 months of this bi-therapy (ALBI, STADI and BMS A1460 tests). We evaluated the rate of selection of the TAMs in naive patients with a viral load of > 200 copies/mL after: 6 months to 1 year of d4T/3TC bi-therapy (group 1); 1 year or more of a treatment including d4T/3TC (group 2); and more than 6 months of tri-therapy including d4T/ddI (group 3). The reverse transcriptase gene has ben studied in 33 patients in group 1, 17 patients in group 2 and ten patients in group 3. For the latter patients, the tri-therapies were as follows: d4T/ddI/PI (n = 5), d4T/ddI/NNRTI (n = 4), d4T/ddI/NRTI (n = 1). For the group 1 patients, at baseline, two patients already had TAMs. At M6, all the patients acquired the 3TC-associated mutations, M184V. Only one patient selected a MDR mutation profile (F116Y, Q151M). At M12, 26 of 33 plasmas were analysed. Only one patient selected one TAM (T215Y). For the group 2 patients, only three patients selected TAMs after more than 30 months of treatment. For the group 3 patients, at baseline, only one patient already harbored TAMs. None of the other patients had selected TAMs. In patients who received d4T/ddI/3TC, only the M184V, the 3TC-associated mutation, was selected. In conclusion, stavudine in association with 3TC selected a low rate of TAMs; in patients receiving a treatment including d4T/3TC, time of exposure to stavudine seemed to be an important parameter for the selection of TAMs; and in contrast to results obtained on d4T/ddI, tri-therapies including d4T/ddI did not select any TAMs, whatever the combination (NRTI, NNRTI, PI).
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PMID:[Conditions of "thymidine analog mutations" (TAMs) in naive patients treated with different combinations of d4T]. 1094 50

Efavirenz is a potent and selective nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). Nucleotide sequence analyses of the protease and RT genes (coding region for amino acids 1 to 229) of multiple cloned HIV-1 genomes from virus found in the plasma of patients in phase II clinical studies of efavirenz combination therapy were undertaken in order to identify the spectrum of mutations in plasma-borne HIV-1 associated with virological treatment failure. A K103N substitution was the HIV-1 RT gene mutation most frequently observed among plasma samples from patients for whom combination therapy including efavirenz failed, occurring in at least 90% of cases of efavirenz-indinavir or efavirenz-zidovudine (ZDV)-lamivudine (3TC) treatment failure. V108I and P225H mutations were observed frequently, predominantly in viral genomes that also contained other nonnucleoside RT inhibitor (NNRTI) resistance mutations. L100I, K101E, K101Q, Y188H, Y188L, G190S, G190A, and G190E mutations were also observed. V106A, Y181C, and Y188C mutations, which have been associated with high levels of resistance to other NNRTIs, were rare in the patient samples in this study, both before and after exposure to efavirenz. The spectrum of mutations observed in cases of virological treatment failure was similar for patients initially dosed with efavirenz at 200, 400, or 600 mg once a day and for patients treated with efavirenz in combination with indinavir, stavudine, or ZDV-3TC. The proportion of patients carrying NNRTI resistance mutations, usually K103N, increased dramatically at the time of initial viral load rebound in cases of treatment failure after exposure to efavirenz. Viruses with multiple, linked NNRTI mutations, especially K103N-V108I and K103N-P225H double mutants, accumulated more slowly following the emergence of K103N mutant viruses.
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PMID:Human immunodeficiency virus type 1 mutations selected in patients failing efavirenz combination therapy. 1095 98

Our objective was to describe clinical features and predisposing factors attributed to lactic acidosis in 4 HIV-infected patients on long-term nucleoside reverse transcriptase inhibitor (NRTI) therapy. All patients had received at least 6-20 months of NRTI-containing antiretroviral therapy: all used stavudine (d4T), in one combined with lamivudine (3TC), in the other 3 with didanosine (ddI); in one hydroxyurea was added. In all, the initial symptoms were gastrointestinal (nausea and vomiting), followed by tachypnoea preceding the lactic acidosis; death followed 6-22 days after admission (liver failure and uncontrollable arrhythmias). Treatment with riboflavin was unsuccessful in one patient. The only definite risk factor in all cases was NRTI-induced mitochondrial toxicity; one patient was concomitantly treated for Kaposi's sarcoma (with bleomycin and vinblastine) and one just recovered from pneumococcal sepsis. None of the patients had a history of chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) infection. In all patients, some sort of toxicity to other previously used NRTIs had occurred earlier. Lactic acidosis occurred after months of NRTI therapy in patients who had already suffered other forms of NRTI toxicity. Concomitant diseases or comedication might have aggravated the mitochondrial toxicity of the NRTIs. Screening methods to detect mitochondrial toxicity are necessary, since lactic acidosis occurs rather unexpectedly, with a rapid, fatal course.
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PMID:Clinical features and risk factors of lactic acidosis following long-term antiretroviral therapy: 4 fatal cases. 1099 8

Currently seven viruses, A, B, C, D, E, G and transfusion transmitted virus (TTV), are recognised in the hepatitis virus alphabet. Hepatitis G virus and TTV probably do not cause liver disease in humans. Hepatitis A and E usually cause a self-limiting hepatitis followed by complete recovery but occasionally cause fulminant hepatic failure. Hepatitis B and C are major public health problems worldwide due to their sequelae of chronic hepatitis, cirrhosis and primary liver cancer. Chronic hepatitis C is a particular health issue for Western Europe already, accounting for 40% of end-stage cirrhosis and 30% of liver transplants. The contribution of hepatitis C to chronic liver disease is predicted to rise in the future. Vaccines can prevent hepatitis A and B. Interferon alpha is effective treatment in 25-30% of patients with chronic hepatitis B or C. The prospects for treating chronic hepatitis B have been improved by the introduction of reverse transcriptase inhibitors. Lamivudine is the first drug of this class to be licensed. The optimal use of these new drugs is currently being studied. The success rate for treating chronic hepatitis C can be raised to about 40% with combination therapy of interferon alpha and ribavirin. A large research effort to discover new antiviral agents against hepatitis C is already giving the prospect of more effective therapies in the next few years.
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PMID:Virus hepatitis update. 1119 85


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