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: UMLS:C0021051 (immunodeficiency)
71,517 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Inophyllums are novel non-nucleoside inhibitors of human immunodeficiency virus (HIV) type 1 reverse transcriptase identified through an enzyme screening program and isolated from the plant Calophyllum inophyllum. The kinetics of reverse transcriptase inhibition by inophyllum B were characterized using recombinant purified enzyme, a heteropolymeric RNA template, and a scintillation proximity assay. Preincubation of inhibitor with the enzyme-template-primer complex for 11 min was required for maximal inhibition of reverse transcriptase to occur, suggesting that inophyllum B had a slow on-rate and that template-primer must bind to reverse transcriptase prior to inhibitor binding. Inhibition of reverse transcriptase by inophyllums was shown to be reversible. When thymidine triphosphate was the variable substrate, inophyllum B inhibited reverse transcriptase noncompetitively with a Ki of 42 nM. Enzyme inhibition with respect to template-primer was uncompetitive with a Ki of 26 nM. Reverse transcriptase enzymes containing point mutations in which tyrosine 181 was changed to either cysteine or isoleucine exhibited marginal resistance to inophyllums but were resistant to (+)-(5S)-4,5,6,7-tetrahydro-9-chloro-5-methyl-6- (3-methyl-2-butenyl)-imidazo[4,5,1-j,k][1,4]benzodiazepin-2-(1H)-t hione (TIBO R82913). A mutant enzyme in which tyrosine 188 was changed to leucine was cross-resistant to both inophyllum B and TIBO R82913, as was HIV type 2 reverse transcriptase. These studies suggest that inophyllum B and TIBO R82913 bind to distinct but overlapping sites. Inhibition of avian myeloblastosis virus reverse transcriptase and Moloney murine leukemia virus reverse transcriptase by inophyllum B was detectible, suggesting that these inhibitors may be more promiscuous than other previously described non-nucleoside inhibitors. Inophyllums were active against HIV type 1 in cell culture with IC50 values of approximately 1.5 microM. These studies imply that the inophyllums have a novel mechanism of interaction with reverse transcriptase and as such could conceivably play a role in combination therapy.
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PMID:Kinetic and mutational analysis of human immunodeficiency virus type 1 reverse transcriptase inhibition by inophyllums, a novel class of non-nucleoside inhibitors. 750

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

Studies presented here show that altering the intracellular redox balance by decreasing glutathione levels profoundly affects early signal transduction events in human T cells. In a T-cell receptor (TCR) signaling model, short-term pretreatment with buthionine sulfoximine, which specifically decreases intracellular glutathione, essentially abrogates the stimulation of calcium influx by anti-CD3 antibodies without significantly impairing other aspects of TCR-initiated signal transduction, such as overall levels of TCR-stimulated tyrosine phosphorylation. In an inflammatory-cytokine signaling model, the failure of tumor necrosis factor alpha to stimulate more than minimal tyrosine phosphorylation in lymphocytes is overcome by buthionine sulfoximine pretreatment--i.e., tumor necrosis factor alpha stimulates extensive tyrosine phosphorylation in glutathione-depleted lymphocytes. These redox-dependent changes in T-cell responsiveness suggest that the glutathione deficiency that we and others have demonstrated in human immunodeficiency virus-infected individuals may contribute significantly to the immunodeficiency and the increased inflammatory reactions in these individuals.
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PMID:Redox regulation of signal transduction: tyrosine phosphorylation and calcium influx. 751 25

The dipyridodiazepinone Nevirapine is a potent and highly specific inhibitor of the reverse transcriptase (RT) from human immunodeficiency virus type 1 (HIV-1). It is a member of an important class of nonnucleoside drugs that appear to share part or all of the same binding site on the enzyme but are susceptible to a variety of spontaneous drug-resistance mutations. The co-crystal-structure of HIV-1 RT and Nevirapine has been solved previously at 3.5-A resolution and now is partially refined against data extending to 2.9-A spacing. The drug is bound in a hydrophobic pocket and in contact with some 38 protein atoms from the p66 palm and thumb subdomains. Most, but not all, nonnucleoside drug-resistance mutations map to residues in close contact with Nevirapine. The major effects of these mutations are to introduce steric clashes with the drug molecule or to remove favorable protein-drug contacts. Additionally, four residues (Phe-227, Trp-229, Leu-234, and Tyr-319) in contact with Nevirapine have not been selected as sites of drug-resistance mutations, implying that there may be limitations on the number and types of resistance mutations that yield viable virus. Strategies of inhibitor design that target interactions with these conserved residues may yield drugs that are less vulnerable to escape mutations.
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PMID:Structure of the binding site for nonnucleoside inhibitors of the reverse transcriptase of human immunodeficiency virus type 1. 751 27

To evaluate the potential that multiply resistant human immunodeficiency virus type 1 variants may arise during combination nucleoside and nonnucleoside reverse transcriptase inhibitor therapy, we constructed a series of mutant reverse transcriptase enzymes and viruses that coexpressed various combinations of resistance-associated amino acid substitutions. Substitutions at residues 100 (Leu-->Ile) and 181 (Tyr-->Cys), which mediate resistance to the nonnucleosides, suppressed resistance to 3'-azido-3'-deoxythymidine (AZT) when coexpressed with AZT-specific substitutions. However, a number of viral variants that exhibited significantly reduced susceptibilities to both classes of inhibitors were constructed.
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PMID:Susceptibilities of human immunodeficiency virus type 1 enzyme and viral variants expressing multiple resistance-engendering amino acid substitutions to reserve transcriptase inhibitors. 752 28

We have studied selected mutants of human immunodeficiency virus type 2 (HIV-2) reverse transcriptase (RT) in a cell-free system in order to assess whether the mutant proteins exhibit a reduction in the sensitivity to nucleoside analog inhibitors similar to that of HIV-1 RT. We have modified, by site-directed mutagenesis, several of those amino acid residues so that their equivalent substitutions in HIV-1 RT have led to the formation of HIV-1 RT variants with the highest degree of resistance to dideoxynucleoside triphosphates (i.e., Glu-89-->Gly, Leu-74-->Val, and Ser-215-->Tyr [which is comparable to the Thr-215-->Tyr mutation of HIV-1 RT] and the double mutations Glu-89-->Gly/Ser-215-->Tyr and and Leu-74-->Val/Ser-215-->Tyr). The similarity found between resistance of the newly generated HIV-2 RT mutants to nucleoside analogs and that of the comparable mutants of HIV-1 RT can support the notion that the overall protein folding around the DNA polymerase active site in HIV-2 RT is quite similar to that of HIV-1 RT.
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PMID:Resistance to nucleoside analogs of selective mutants of human immunodeficiency virus type 2 reverse transcriptase. 752 86

A number of structurally diverse compounds have been shown to be potent inhibitors of the DNA polymerase activity of human immunodeficiency virus (HIV-1) reverse transcriptase (RT). The compounds can be grouped into two broad classes: nucleoside analogs and nonnucleoside inhibitors. The nonnucleoside inhibitors are quite specific for the polymerase activity of HIV-1 RT; they do not affect the polymerase activity of HIV-2 RT or the ribonuclease H (RNase H) activity of either HIV-1 RT or HIV-2 RT. Structural, biochemical, and genetic analyses showed that this group of inhibitors binds in a hydrophobic pocket near the polymerase active site. Mutations in amino acids that line this hydrophobic pocket, for example at tyrosine 181, tyrosine 188, or lysine 103, lead to enzymes that are resistant to the nonnucleoside inhibitors. We have investigated the enzymatic properties of two mutants of HIV-1 RT in which residues 181 and 188 were replaced by the corresponding amino acids in HIV-2 RT (tyrosine 181-->isoleucine and tyrosine 188-->leucine). The two tyrosine mutants closely resemble the wild-type HIV-1 RT in almost all the catalytic functions tested, including the heat stability, sensitivity of the DNA polymerase activity to inhibition by deoxynucleoside analogs, inhibition by the zinc chelator o-phenanthroline, and the Km values calculated for the DNA polymerase activity. There is, however, a slight difference in the effect of orthophenanthroline on the RNase H activity. In addition, there is a subtle disparity in the fidelity of DNA synthesis (analyzed by a mispair extension assay), thus indicating that these mutant RTs are not likely to confer any selective advantages or disadvantages to the variant virions over wild-type virus.
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PMID:Enzymatic properties of two mutants of reverse transcriptase of human immunodeficiency virus type 1 (tyrosine 181-->isoleucine and tyrosine 188-->leucine), resistant to nonnucleoside inhibitors. 752 32

Genetic recombination between viral genomes has been shown to contribute to the generation of genetic diversity during retrovirus infections. The role of recombination in the development of human immunodeficiency virus type 1 (HIV-1) zidovudine resistance was investigated as a possible cause of the formation of the linked Leu-41/Tyr-215 resistance genotype. Zidovudine resistance is conferred by the presence of subsets of four or five amino acid substitutions in the HIV-1 reverse transcriptase. Zidovudine therapy of asymptomatic HIV-1-infected individuals results in the selection of drug-resistant variants that posses defined combinations of the five zidovudine resistance mutations. The linked Leu-41/Tyr-215 resistance genotype appears central to the continued development of high-level zidovudine resistance. By using genetically tagged mutant viruses, it was possible readily to select recombinant viruses from mixed infections of Leu-41 and Tyr-215 single mutants in the presence of zidovudine drup pressure. After three passages of a mixed infection in the presence of drug, 38% of clones screened were recombinant double mutants. In the absence of zidovudine selection, little change in the mixed virus populations was noted. No evidence of de novo generation of mutations at codons 41 and 215 was seen during any in vitro passage. This provides the first example of the role of retroviral recombination in the development of HIV-1 variants with increased drug resistance.
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PMID:Retroviral recombination can lead to linkage of reverse transcriptase mutations that confer increased zidovudine resistance. 752 34

We investigated a T-cell activation deficiency in a 3-month-old boy with protracted diarrhea, serious cytomegalovirus pneumonia, and a family history (in a brother) of cytomegalovirus infection and toxoplasmosis. In spite of detection of normal number of peripheral lymphocytes, T cells did not proliferate after activation by anti-CD3 and anti-CD2 antibodies, although proliferation induced by antigens was detectable. We sought to determine the origin of this defect as it potentially represented a valuable tool to analyze T-cell physiology. T-cell activation by anti-CD3 antibody or phytohemagglutinin (PHA) led to reduced interleukin-2 (IL-2) production and abnormal nuclear factor-activated T cell (NF-AT; a complex regulating the IL-2 gene transcription) binding activity to a specific oligonucleotide. T-cell proliferation was restored by IL-2. Early events of T-cell activation, such as anti-CD3 antibody-induced cellular protein tyrosine phosphorylation, p59fyn and p56lck kinase activities, and phosphoinositide turnover, were found to be normal. In contrast, anti-CD3 antibody-induced Ca2+ flux was grossly abnormal. Release from endoplasmic reticulum stores was detectable as tested in the presence of anti-CD3 antibody or thapsigargin after cell membrane depolarization in a K+ rich medium, whereas extracellular entry of Ca2+ was defective. The latter abnormality was not secondary to defective K+ channel function, which was found to be normal. A similar defect was found in other hematopoietic cell lineages and in fibroblasts as evaluated by both cytometry and digital video imaging experiments at a single-cell level. This primary T-cell immunodeficiency appears, thus, to be due to defective Ca2+ entry through the plasma membrane. The same abnormality did not alter B-cell proliferation, platelet function, and polymorphonuclear neutrophil (PMN) function. Elucidation of the mechanism underlying this defect would help to understand the physiology of Ca2+ mobilization in T cells.
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PMID:A primary T-cell immunodeficiency associated with defective transmembrane calcium influx. 753 12

Tetrahydro-imidazo[4,5,1-jk][1,4]-benzodiazepin-2(1H)-one and -thione (TIBO) derivatives were shown to specifically block human immunodeficiency virus type 1 (HIV-1) replication through a unique interaction with the HIV-1 reverse transcriptase (RT). Through further modification of the lead compounds and structure-activity relationship analysis several new TIBO derivatives that show high potency, selectivity, and specificity against HIV-1 have been obtained. A new TIBO derivative, R86183, inhibits the replication of HIV-1, but not HIV-2, in a variety of CD4+ T-cell lines and peripheral blood lymphocytes, at a concentration of 0.3 to 30 nM, which is at least 4 orders of magnitude lower than the 50% cytotoxic concentration. Whereas an HIV-1 strain containing the Leu-100-->Ile mutation in the RT gene is about 400-fold less susceptible, R86183 still inhibits the replication of an HIV-1 strain containing the Tyr-181-->Cys RT mutation by 50% at a concentration of 130 nM. R86183 inhibits the poly(C).oligo(dG)12-18-directed HIV-1 RT reaction by 50% at a concentration of 57 nM. The antiviral activity of 22 TIBO derivatives in cell culture correlated well with their activity against HIV-1 RT. No such correlation was found for their cytotoxicity. The combination of R86183 with either zidovudine or didanosine resulted in a synergistic inhibition of HIV-1 (strain IIIB) replication. Combination of R86183 with the protease inhibitor Ro31-8959 was found to be additive. Also described is a dilution protocol circumventing overestimation and underestimation of antiviral activity due to adherence to plastic surfaces.
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PMID:New tetrahydroimidazo[4,5,1-jk][1,4]-benzodiazepin-2(1H)-one and -thione derivatives are potent inhibitors of human immunodeficiency virus type 1 replication and are synergistic with 2',3'-dideoxynucleoside analogs. 753 37


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