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Biomedical subjects

I B Duncan

Publications and source records attributed to I B Duncan.

At least 19 recordsLinked to original sources
PubMed1998

HIV protease genotype and viral sensitivity to HIV protease inhibitors following saquinavir therapy.

OBJECTIVE: To examine the relationship between HIV protease genotype and altered protease inhibitor sensitivity of isolates from patients after therapy with saquinavir (SQV) in its hard gelatin formulation. DESIGN: Forty-one post-therapy isolates and corresponding baseline samples were obtained from 37 patients in four different clinical trials after therapy with SQV for 16-147 weeks. Post-therapy isolates were selected on the basis of preliminary sequence or drug sensitivity data. RESULTS: Fifteen out of 17 isolates without detectable Val-48 or Met-90 mutations retained sensitivity to SQV. (The remaining isolates showed only a marginal increase in median inhibitory concentration.) In addition, three out of 15 isolates with Met-90 retained sensitivity to all other protease inhibitors tested (indinavir, ritonavir, amprenavir, nelfinavir). Of the isolates showing reduced sensitivity to SQV, six out of 22 retained sensitivity to all other protease inhibitors, whereas only four out of 22 showed broad cross-resistance to all protease inhibitors tested. The reduction in sensitivity correlated closely with the presence of Val-48 or Met-90. Subsequent accessory substitutions were also linked to reduced sensitivity. However, significant linkage was observed only between mutations at residues 48 and 82 and between those at residues 82 and 74. CONCLUSIONS: Recruitment of Val-48/Met-90 mutations was not found to be synonymous with cross-resistance. Indeed, the majority of isolates with these mutations retained sensitivity to at least one protease inhibitor (Val-48, 86%; Met-90, 77%). The recruitment of accessory mutations may occur only after the selection of key resistance mutations. Furthermore, Met-90 was found to be a poor marker of cross-resistance in SQV-treated patients.

Amino Acid Substitution↗
PubMed1998

Correlation of response to treatment and HIV genotypic changes during phase III trials with saquinavir and reverse transcriptase inhibitor combination therapy.

OBJECTIVES: Assessment of genotypic change in HIV protease during treatment with saquinavir (SQV) in combination with zidovudine (ZDV) and/or zalcitabine (ddC), to determine the influence of such changes on viral phenotype and response to treatment. DESIGN: Virologic substudies of Phase III clinical trials NV14256 and SV14604. METHODS: Population sequencing of HIV protease genes amplified from pre- and post-treatment plasma. Phenotyping of peripheral blood mononuclear cell (PBMC)-derived virus isolates, and genotyping of proviral DNA clones amplified from PBMC used in the expansion of virus isolates. RESULTS: In both trials the incidence of Met90 remained at < or = 20% in subjects receiving SQV in combination with ddC (with or without ZDV) for 1 year. A Val48 substitution was observed in two out of 81 subjects after 24 weeks and in two out of 75 subjects after 48 weeks. In 12 out of 13 NV14256 subjects with viral load rebound during SQV monotherapy these substitutions were associated with the rebound. In subjects treated with SQV plus ddC, rebound was associated with SQV resistance in six out of 22 cases and ddC resistance in five out of 22 cases. The incidences of non-BRU residues at positions 10, 63 and 71 were increased significantly (P < 0.05, Fisher's exact test) after SQV treatment with or without ZDV. However, comparison of genotypic and phenotypic data showed that these changes were not associated with reduced sensitivity to SQV. CONCLUSIONS: Virological failure during combination therapy can be due to resistance to either treatment drug, emphasising the need to change both the reverse transcriptase inhibitor and the protease inhibitor. Only Val48 and Met90 correlated directly with the development of reduced drug sensitivity during treatment with SQV in vivo.

Amino Acid Sequence↗
PubMed1996

Reduced sensitivity to saquinavir: an update on genotyping from phase I/II trials.

A genotypic analysis of the HIV-1 proteinase was performed on clinical specimen obtained from patients after different periods of Saquinavir (SQV) treatment. Proteinase genes of integrated proviral DNA from PBMC were isolated by PCR, cloned and individual sequences were obtained. Genotypic resistance was defined by the Gly48-->Val and Leu90-->Met exchanges. Frequencies and kinetics of resistance development will be reported for phase I/II trials V13330. V13329, O13328 and ACTG229 in patients on monotherapy or combination therapy with RT inhibitors. Data from V13330 have been analysed in more detail for correspondence of genotypic and phenotypic resistance and any correlation between resistance and changes in plasma viral RNA load. Furthermore, we will discuss the data from our extensive proteinase gene sequence collection with respect to mutational changes which would be indicative of resistance to other inhibitors of HIV-1 proteinase.

Drug Resistance, Microbial↗
PubMed1996

In vivo resistance to a human immunodeficiency virus type 1 proteinase inhibitor: mutations, kinetics, and frequencies.

Resistance to saquinavir (Ro 31-8959), an inhibitor of human immunodeficiency virus type I proteinase, was studied in peripheral blood mononuclear cell-derived proviral DNA from patients undergoing prolonged treatment. A Leu90-->Met exchange was the predominant resistance mutation in vivo; Gly48-->Val or doubly mutant virus was rarely observed. After 8-12 months of treatment with saquinavir alone (600 mg, 3 times/day) or in combination with zidovudine (200 mg, 3 times/day), approximately 45% of all patients carried provirus with mutant proteinase; the incidence was lower (22%) in patients treated with a combination of saquinavir, zidovudine, and dideoxycytidine. There was a good relationship between genotypic analysis of saquinavir resistance and data from virus assays, confirming that Leu90-->Met and Gly48-->Val are the essential exchanges in the proteinase that determine loss of sensitivity to this inhibitor. Absence of genotypic resistance correlated with a sustained decrease in plasma viral RNA. There was a positive correlation between a Met90 mutation and some residues at natural polymorphic sites (positions 10, 36, 63, and 71).

Antiviral Agents↗
PubMed1996

Efficiency of nanoparticles as a carrier system for antiviral agents in human immunodeficiency virus-infected human monocytes/macrophages in vitro.

Polyhexylcyanoacrylate nanoparticles loaded with either the human immunodeficiency virus (HIV) protease inhibitor saquinavir (Ro 31-8959) or the nucleoside analog zalcitabine (2',3'-dideoxycytidine) were prepared by emulsion polymerization and tested for antiviral activity in primary human monocytes/macrophages in vitro. Both nanoparticulate formulations led to a dose-dependent reduction of HIV type 1 antigen production. While nanoparticle-bound zalcitabine showed no superiority to an aqueous solution of the drug, a significantly higher efficacy was observed with saquinavir-loaded nanoparticles. In acutely infected cells, an aqueous solution of saquinavir showed little antiviral activity at concentrations below 10 nM, whereas the nanoparticulate formulation exhibited a good antiviral effect at a concentration of 1 nM and a still-significant antigen reduction at 0.1 nM (50% inhibitory concentrations = 4.23 nM for the free drug and 0.39 nM for the nanoparticle-bound drug). At a concentration of 100 nM, saquinavir was completely inactive in chronically HIV-infected macrophages, but when bound to nanoparticles it caused a 35% decrease in antigen production. Using nanoparticles as a drug carrier system could improve the delivery of antiviral agents to the mononuclear phagocyte system in vivo, overcoming pharmacokinetic problems and enhancing the activities of drugs for the treatment of HIV infection and AIDS.

Antiviral Agents↗
PubMed1995

Safety and activity of saquinavir in HIV infection.

We evaluated saquinavir, an orally active, selective inhibitor of HIV proteinase, in a randomised, double-blind, dose-ranging study in 49 zidovudine-naive HIV-positive patients with few or no symptoms and CD4 cell counts of 500 or less. The study was designed to assess the antiviral activity and tolerability of saquinavir. Patients were randomised to receive 25, 75, 200, or 600 mg of saquinavir three times daily for 16 weeks. No serious adverse events occurred. CD4 cell counts showed a trend indicative of a dose response in favour of the 600 mg dosage, the maximum increase being seen around week 4. In none of the 8 patients with positive plasma viraemia at baseline did cultures become negative after treatment; peripheral blood mononuclear cell and plasma-viral load by culture and DNA and RNA PCR all showed a trend towards reduction at higher doses of saquinovir. Saquinavir was well tolerated in this group of previously untreated patients with few or no symptoms; this study shows that an HIV-proteinase inhibitor is active in HIV-infected patients.

CD4 Lymphocyte Count↗
PubMed1995

Characterization of human immunodeficiency virus type 1 mutants with decreased sensitivity to proteinase inhibitor Ro 31-8959.

A human immunodeficiency virus type 1 (HIV-1) variant with highly reduced susceptibility to Ro 31-8959, an inhibitor of the viral proteinase, has been selected by repeated passage of wild-type virus in CEM cells in the presence of increasing concentrations of the inhibitor. Peptide sequences of the proteinase of selected virus were obtained from proviral DNA. Sequence comparison to wild-type (wt) proteinase demonstrated two amino acid substitutions in the resistant virus, a Gly to Val exchange at position 48 and a Leu to Met exchange at position 90. Furthermore, sequences of intermediate passage virus suggest contributions from positions 12, 36, 57, and 63 in early steps of resistance development. The selected virus showed a ca. 40-fold increase in 50% inhibitory concentration of Ro 31-8959. Growth kinetics of resistant virus were comparable to wild-type virus and the resistant genotype proved to be stable in the absence of inhibitor. Directed mutagenesis of the HIV-1 HXB2 proteinase at positions 48 and 90 suggested that each mutation alone led to a moderate decrease in sensitivity of the recombinant virus to proteinase inhibitor. However, a recombinant virus carrying both mutations in the proteinase gene showed a significant reduction in its sensitivity to Ro 31-8959 thus proving the importance of these exchanges for the resistance phenotype.

Amino Acid Sequence↗
PubMed1993

Assessment of the effectiveness of body substance precautions as the infection control system of a large teaching hospital.

BACKGROUND: Body substance precautions was the name given to the body substance isolation-based infection control system that was introduced in January 1990 at a Canadian university hospital with 650 acute care beds and 570 long-term care beds. When the body substance precautions system was begun, traditional category-specific isolation was discontinued. METHODS: After 2 years, we reviewed the incidence of several types of nosocomial infections and the frequency of isolation of hospital strains of bacteria before and after the introduction of body substance precautions to find out whether this system was as effective as the previous system of infection control. RESULTS: Most nosocomial infections did not increase. There was another likely cause for the only one that did. For many years, we had isolated patients infected or colonized by hospital bacteria, limiting their spread throughout the institution. Body substance precautions proved equally effective in doing this. CONCLUSION: Our results to date therefore indicate that the body substance precautions system was as successful as category-specific isolation used with other standard infection control techniques in maintaining low rates of nosocomial infections and in controlling the dissemination of hospital strains of bacteria in our institution. Body substance precautions provided a satisfactory alternative to universal precautions and traditional isolation categories for the protection of health care workers against the risk of infection by blood-borne viruses.

Body Fluids↗
PubMed1991

Antiviral properties of Ro 31-8959, an inhibitor of human immunodeficiency virus (HIV) proteinase.

Ro 31-8959 inhibits the spread of HIV infection and the production of cytopathic effects in cultures of acutely infected cells. IC50 values for these effects are in the range 0.5-6.0 nM and IC90 values are in the range 6.0-30.0 nM. This inhibitor is effective even when added to cultures at a late stage of infection, after syncytia have started to form. Virus antigen, virus particles and virus cytopathic effects can largely be cleared from cultures treated with compound from 3 days until 6 days post infection. In chronically-infected cells, inhibition of virus maturation can be detected after 24 hours' treatment with 10 nM Ro 31-8959. In addition, a significant reduction of the proteolytic processing of p56 to p24 can be demonstrated in these cells with compound at picomolar concentrations. These properties indicate that Ro 31-8959 is highly effective against HIV with the potential to inhibit acute, established acute and chronic infections.

Antiviral Agents↗
PubMed1990

Rational design of peptide-based HIV proteinase inhibitors.

A series of peptide derivatives based on the transition-state mimetic concept has been designed that inhibit the proteinase from the human immunodeficiency virus (HIV). The more active compounds inhibit both HIV-1 and HIV-2 proteinases in the nanomolar range with little effect at 10 micromolar against the structurally related human aspartic proteinases. Proteolytic cleavage of the HIV-1 gag polyprotein (p55) to the viral structural protein p24 was inhibited in chronically infected CEM cells. Antiviral activity was observed in the nanomolar range (with one compound active below 10 nanomolar) in three different cell systems, as assessed by p24 antigen and syncytium formation. Cytotoxicity was not detected at 10 and 5 micromolar in C8166 and JM cells, respectively, indicating a high therapeutic index for this new class of HIV proteinase inhibitors.

Amino Acid Sequence↗
PubMed1990

Synthesis and antiviral activity of monofluoro and difluoro analogues of pyrimidine deoxyribonucleosides against human immunodeficiency virus (HIV-1).

A range of 2'-fluoro and 2',3'-difluoro analogues of pyrimidine deoxyribonucleosides have been synthesized and evaluated against human immunodeficiency virus (HIV-1) in a human lymphoblastoid cell line. Among these compounds, 1-(2,3-dideoxy-2-fluoro-beta-D-threopentofuranosyl)cytosine (12), 2',3'-didehydro-2',3'-dideoxy-2'-fluorocytidine (35), 1-(2,3-dideoxy-2,3-difluoro-beta-D-arabinofuranosyl)cytosine (41), and 3'-deoxy-2',3'-didehydro-2'-fluorothymidine (45) were found to have significant antiviral activity, with IC50 values of 0.65, 10, 10, and 100 microM, respectively. The structure-activity relationships are discussed.

Antiviral Agents↗
PubMed1989

Synthesis and antiviral activity of phosphonoacetic and phosphonoformic acid esters of 5-bromo-2'-deoxyuridine and related pyrimidine nucleosides and acyclonucleosides.

Phosphonoacetic acid (PAA, 1) was coupled with various acyclonucleosides, 2'-deoxyuridines, cytidines, and arabinosyluracils, with 2,4,6-triisopropylbenzenesulfonyl chloride (TPS) or dicyclohexylcarbodiimide (DCCI) as condensing agents, to give a range of phosphonate esters. The carboxylic ester linkage of PAA to the 5'-position of 5-bromo-2'-deoxyuridine (BUdR, 3) was achieved via the mixed anhydride formed from (diethylphosphono)acetic acid and trifluoroacetic anhydride. Phosphonoformic acid (PFA, 2) was coupled with BUdR by using the DCCI method to give the phosphonate ester. Of these compounds only phosphonate esters in the 2'-deoxyuridine series showed significant activity against herpes simplex virus types 1 and 2. The BUdR-PAA derivative and the BUdR-PFA derivative were highly active, especially the latter, which was more active than the parent nucleoside BUdR against the type 2 virus. The active compounds may exert their effects by extracellular or intracellular hydrolysis to the corresponding antiviral agents, but an intrinsic component of antiviral activity may also be involved.

Antiviral Agents↗
PubMed1986

Antiviral activity of 5'-PAA and 5'-PFA phosphate esters of 2'-deoxyuridines.

The 5'-PAA and 5'-PFA phosphate esters of 5-bromo-2'-deoxyuridine (BUdR) were synthesized and their antiherpes virus activity was evaluated in vitro. Both compounds showed activity of the same order as the parent nucleoside, BUdR, against HSV-2 but were 4 to 12 times less potent against HSV-1. The 5'-PAA phosphate ester of BUdR (Ro 21-9875) was also active against varicella-zoster virus (VZV) and human cytomegalovirus (HCMV). The 5'-PAA phosphate ester of 5-bromovinyl-2'-deoxyuridine (BVdU) was also synthesized and showed good antiviral activity against HSV-1 only (ID50 = 1.3 mg/l). Further evaluation against selected mutants (TK- or PAAr) indicated a requirement for the expression of the virus-coded thymidine kinase (TK) for the antiviral activity of Ro 21-9875. Kinetic studies revealed non-competitive mixed inhibition of the viral enzyme by this compound. This suggests that it may have some intrinsic TK mediated activity though breakdown to its component parts is undoubtedly a significant contributing factor.

Animals↗
PubMed1984

In-vitro activity of enoxacin against aminoglycoside-resistant gram-negative bacilli and other clinical isolates.

The in-vitro activity of enoxacin was tested against 500 clinical isolates of Gram-negative bacilli that were resistant to one or more of gentamicin, tobramycin and amikacin, and against 1060 recent consecutive clinical isolates of Gram-negative bacilli and Gram-positive cocci. Enoxacin was active against staphylococci (MICs less than or equal to 4 mg/l) but less active against Streptococcus faecalis (MICs mostly 8 mg/l). It was active against Pseudomonas aeruginosa (MICs 0.5-4 mg/l) and very active against Enterobacteriaceae. In the series of consecutive isolates 97% of Enterobacteriaceae had MICs less than or equal to 1 mg/l. The aminoglycoside-resistant series of Enterobacteriaceae included more strains with higher MICs (13% were 2-4 mg/l and 10% were greater than or equal to 8 mg/l); the majority of the isolates with MICs greater than or equal to 8 mg/l); the majority of the isolates with MICs greater than or equal to 8 mg/l were Serratia marcescens and Providencia spp. Among the non-fermenting species the least sensitive were Acinetobacter calcoaceticus and Ps. maltophilia. Enoxacin-resistant strains of Enterobacteriaceae were resistant to nalidixic acid, but nalidixic acid-resistant strains ranged from fully sensitive to highly resistant to enoxacin.

Aminoglycosides↗
PubMed1981

Resistance to aminoglycoside antibiotics of gram-negative bacilli isolated in Canadian hospitals.

A survey was made of the frequency of resistance to amikacin, gentamicin and tobramycin among aerobic gram-negative bacilli isolated over a 4-week period in 1979 at six large, geographically separated Canadian hospitals. In the entire series of 4407 isolates the frequency of resistance was 2.5% to amikacin, 8.1% to gentamicin, 5.9% to tobramycin and 1.7% to all three. Most (81%) of the resistant bacteria were acquired by the patients after admission to hospital. The frequency of resistance to the three aminoglycoside antibiotics in each hospital largely reflected the local rate of cross-infection by endemic strains of resistant bacteria.

Amikacin↗