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Biomedical subjects

J F Barrett

Publications and source records attributed to J F Barrett.

At least 73 records · Page 4Linked to original sources
PubMed1997

DNA gyrase inhibitory and antimicrobial activities of some diphenic acid monohydroxamides.

The synthesis and inhibitory activity against DNA gyrase of a series of diphenic acid monohydroxamides 4a-f are described. A protocol of two biological assays showed conclusively that inhibition occurs specifically at the DNA-DNA gyrase complex and is not attributable to nonspecific inhibition. In the enzyme assays, 4c was potent as the prototypical quinolone, nalidixic acid (1), with an IC50 value of 58.3 micrograms/mL compared to 52 micrograms/mL for 1. MIC activity against bacterial strains showed a systematic drop for all compounds relative to 1. For compounds 4c-e, the addition of PMBN produced dramatic increases in MIC activity indicating that activity is likely to be related to membrane transport. Molecular modeling of 4a indicates that the diphenic acid monohydroxamides can bind to the DNA-DNA gyrase complex in a similar fashion as that hypothesized for the quinolone series according to the hypothesis suggested by Shen et al. but may not self-associate by pi-pi stacking. In contrast to the quinolone series, as the diphenic acid monohydroxamides are shown by molecular mechanics minimizations to be nonplanar, they may present novel approaches for chemotherapeutic intervention with a potential for decreased side effects.

Anti-Bacterial Agents↗
PubMed1997

Assessment of the synergistic interactions of levofloxacin and ampicillin against Enterococcus faecium by the checkerboard agar dilution and time-kill methods.

Multidrug-resistant enterococci have become increasingly difficult to eradicate in a growing number of nosocomial infections. With the emergence of vancomycin-resistant enterococci, the use of synergistic antibiotic combinations has become one of the only remaining therapeutic options. Levofloxacin, the active l-isomer of ofloxacin, is a new oral and intravenous fluoroquinolone with a broad spectrum of activity against numerous Gram-positive, Gram-negative, and atypical organisms. The in vitro activity of levofloxacin, alone and in combination with ampicillin, against recent clinical isolates of Enterococcus faecium was assessed for synergistic interactions using the checkerboard agar dilution technique and time-kill methodology. Against all strains, the static technique of checkerboard agar dilution demonstrated indifferent or additive effects for the ampicillin + levofloxacin combination. With the dynamic time-kill technique, synergy was demonstrated for ampicillin (16 micrograms/ml) + levofloxacin (2 micrograms/ml) combination against three levofloxacin-sensitive, ampicillin-resistant isolates. At 24 h, the combination yielded a > or = 2-log10 decrease in CFU/ml compared to levofloxacin alone, while ampicillin had negligible effects. Against both a levofloxacin-intermediate, ampicillin-resistant isolate, and a highly levofloxacin-resistant, ampicillin-resistant isolate, none of the ampicillin+levofloxacin combinations tested demonstrated a synergistic interaction. The time-kill method suggested synergy for the ampicillin+levofloxacin combination against some strains of E. faecium.

Ampicillin↗
PubMed1997

Comparison of the postantibiotic and postantibiotic sub-MIC effects of levofloxacin and ciprofloxacin on Staphylococcus aureus and Streptococcus pneumoniae.

The postantibiotic subminimum inhibitory concentration effect (PA SME) may simulate in vivo drug exposure more accurately than the postantibiotic effect (PAE) since subinhibitory concentrations of drug persist between antibiotic dosings. In this study, we compared the PAEs and PA SMEs of levofloxacin and ciprofloxacin for clinical isolates of fluoroquinolone-susceptible Staphylococcus aureus and Streptococcus pneumoniae. At two times the MIC, PAEs of levofloxacin were an average of 0.6 h longer than the PAEs obtained for ciprofloxacin for methicillin-susceptible and methicillin-resistant S. aureus strains. The PAEs of levofloxacin and ciprofloxacin ranged from 1.8 to 3.1 and 1.1 to 2.4 h, respectively. Continued exposure of the methicillin-resistant strain to 1/16, 1/8, and 1/4 the MIC resulted in PA SMEs of 6.5, 15.3, and >22.3 h, respectively, for levofloxacin and 3.8, 8.0, and 12.3 h, respectively, for ciprofloxacin. For isolates of S. pneumoniae, at two times the MIC of both fluoroquinolones, the average PAEs of levofloxacin and ciprofloxacin were equivalent: 1.3 h for the penicillin-susceptible isolate and 0.6 h for the penicillin-resistant isolate. Continued exposure of the penicillin-susceptible S. pneumoniae strain to 1/16, 1/8, and 1/4 the MIC resulted in average PA SMEs of 1.0, 1.4, and 2.8 h, respectively, for levofloxacin and 1.8, 2.0, and 2.5 h, respectively, for ciprofloxacin. Continued exposure of penicillin-resistant S. pneumoniae to 1/16, 1/8, and 1/4 the MIC of the same fluoroquinolones resulted in average PA SMEs of 0.6, 1.1, and 2.9 h, respectively, for levofloxacin and 0.6, 1.1, and 1.5 h, respectively, for ciprofloxacin. The PA SMEs observed demonstrate the superior activity of levofloxacin against methicillin-susceptible or methicillin-resistant S. aureus. Although PAEs were similar for the penicillin-susceptible and penicillin-resistant S. pneumoniae strains, the PA SME of levofloxacin at one-fourth the MIC was longer for penicillin-resistant S. pneumoniae.

Anti-Infective Agents↗
PubMed1997

Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

Over 10,000 research scientists attended the ICAAC meeting in Toronto, Canada. The continued increase in the rate of resistance in bacteria and fungi and the underlying mechanisms of resistance were the focus of many presentations this year. So, too, were the attempts to combat this emerging resistance crisis. Many papers described new modifications to older antimicrobials, novel classes of antimicrobials and the potential use of new antibacterial and antifungal targets.

Journal Article↗
PubMed1997

The 97th Annual Meeting of the American Society for Microbiology.

The Annual Meeting of the American Society for Microbiology took place in Miami Beach, Florida, from May 4-8, 1997. Over 9000 scientists attended this meeting, which covers all major aspects of prokaryotic research (basic, applied, medical, and diagnostic). Genomics discussions were a major part of the meeting agenda, with scientists detailing both basic and applied research effort using genomics and bioinformatics. New ideas for potential novel antimicrobials have also surfaced as the tools to pursue Drug Discovery have fallen into place and pharmaceutical companies have ;rediscovered' anti-infectives.

Journal Article↗
PubMed1996

Design, synthesis, and biological evaluation of ellipticine-estradiol conjugates.

Three ellipticine-estradiol conjugates were synthesized in an effort to target the cytotoxicity of ellipticine to estrogen-receptor positive cells. The three conjugates were prepared with linker chains extending from the 17 alpha position of the estradiol to N-2 (compound 3), N-6 (compound 4), and C-9 (compound 5) positions of ellipticine. The ellipticine-estradiol conjugates were evaluated for their abilities to bind to estrogen receptors, to inhibit topoisomerase II, and for their cytotoxicities in human cancer cell lines. Conjugates 3 and 5 displayed weak binding affinities of 0.132 and 0.303 for the estrogen receptor (relative to estradiol = 100), while conjugate 4 did not show any detectable binding to the estrogen receptor. Compound 3 was a moderate inhibitor of topoisomerase II (IC50 24.1 microM), while 4 and 5 were inactive. Conjugate 3 was consistently more cytotoxic (GI50 values 1-10 microM) than compounds 4 and 5 (GI50 values 10-100 microM) in a variety of human cancer cell lines. None of the compounds displayed any selectivity for estrogen-receptor positive cell lines, which probably reflects their weak affinities for estrogen receptors.

Antineoplastic Agents↗
PubMed1996

In vivo efficacies of levofloxacin and ciprofloxacin in acute murine hematogenous pyelonephritis induced by methicillin-susceptible and-resistant Staphylococcus aureus strains.

Levofloxacin, the active L-isomer of ofloxacin, has demonstrated strong activity against Staphylococcus aureus both in vitro and in vivo. In a murine model of hematogenous pyelonephritis, the in vivo efficacies of levofloxacin and ciprofloxacin were evaluated against two methicillin-susceptible and two methicillin-resistant S. aureus strains. All four isolates had virtually identical susceptibilities to levofloxacin and ciprofloxacin. Pyelonephritis was induced in carrageenan-primed mice by an intravenous injection of 0.5 ml of 10(7) CFU of methicillin-susceptible S. aureus isolates per ml or 10(8) CFU of methicillin-resistant S. aureus isolates per ml. At 1 h postinfection, the mice were treated orally with levofloxacin or ciprofloxacin once a day or twice a day (total daily dose of 20 to 160 mg/kg of body weight) for 4 days. Mice were euthanized 24 h after the final treatment, and the kidneys were excised and weighed. The kidneys were prepared for histological examination or were homogenized to determine the numbers of CFU per gram of tissue quantitatively. The reduction in the mean log10 number of CFU per gram as a function of total daily dose was recorded. A dose-response analysis showed that levofloxacin was superior to ciprofloxacin for all four isolates at any dose or regimen tested, independent of the methicillin susceptibility of the isolates. By using an inverse prediction technique, the equivalent effective doses of levofloxacin (once a day) were less than those of ciprofloxacin (twice a day) by 5.2 and 3.2 times, respectively, for methicillin-susceptible S. aureus 9039 and 3087. For methicillin-resistant S. aureus 667 and 2878, the equivalent effective doses of levofloxacin (once a day) were less than those of ciprofloxacin (twice a day) by 4.1 and 6.4 times, respectively. In a separate study, histological examination of all infected, untreated mice showed moderate to marked hematogenous pyelonephritis. Levofloxacin-treated mice (40 mg/kg once a day) showed no evidence of pyelonephritis in the kidneys, whereas the kidneys of mice treated with the same dose of ciprofloxacin showed only a reduction in the severity of the lesions. Treatment with ciprofloxacin (80 mg/kg twice a day) demonstrated a histology comparable to that of treatment with levofloxacin (40 mg/kg once a day). Levofloxacin (40 mg/kg once a day) reduced the log10 numbers of CFU per gram by 5 log10; however, ciprofloxacin (80 mg/kg twice a day) reduced the numbers of CFU per gram by only 3 log10. In the present murine model of pyelonephritis, levofloxacin was superior to ciprofloxacin in preventing pyelonephritis and eradicating S. aureus.

Acute Disease↗
PubMed1996

In vivo oral efficacy of levofloxacin for treatment of systemic Pseudomonas aeruginosa infections in a murine model of septicemia.

The in vivo efficacies of levofloxacin and ciprofloxacin in lethal, systemic Pseudomonas aeruginosa infections in mice were compared. MICs of levofloxacin and ciprofloxacin ranged from 0.5 to 2.0 micrograms/ml and from 0.12 to 1.0 microgram/ml respectively. Infecting doses ranged from 5.0 x 10(1) to 3.2 x 10(3) CFU per mouse, depending on the isolate. Test fluoroquinolones were administered orally at 1 h (single dose) or at 1 and 3 h (divided dose) postinfection, with 10 infected mice used for each of six concentrations of each fluoroquinolone tested (1 to 40 mg/kg of body weight) in each dosing regimen. Whether given in a single or a divided dose, the total daily dose was the same for each fluoroquinolone. For mice treated 1 h postinfection with levofloxacin and ciprofloxacin, the effective doses for 50% of the infected mice ranged from 2.09 to 13.80 mg/kg and from 2.34 to 11.22 mg/kg, respectively, and for those treated 1 and 3 h postinfection, the effective doses for 50% of the infected mice ranged from 3.71 to 16.98 mg/kg and from 2.95 to 13.18 mg/kg, respectively. Although the potency varied for both levofloxacin and ciprofloxacin among all strains of P. aeruginosa tested, there were small differences within the same strain for levofloxacin and ciprofloxacin when given in the same dosing regimen. Levofloxacin proved nearly as effective as ciprofloxacin against a systemic P. aeruginosa infection in mice.

Administration, Oral↗
PubMed1996

Synthesis of a series of cytotoxic 2-acyl-1,2-dihydroellipticines which inhibit topoisomerase II.

An array of novel 2-acyl-1,2-dihydroellipticines was prepared and evaluated for in vitro cytotoxicity in a variety of human cancer cell lines. The ellipticine analogs were also tested for inhibition of topoisomerase II in both decatenation and cleavable complex formation assays. Some of the new ellipticine derivatives were prepared by acylation of ellipticine with acid chlorides in tetrahydrofuran, followed by reduction of the intermediate 2-acylellipticinium ions with sodium cyanoborohydride. Others were synthesized by acylation of ellipticine with p-nitrophenyl chloroformate, reduction of the 2-acylellipticinium ion with sodium cyanoborohydride, and displacement of the p-nitrophenoxide anion with a variety of oxygen and nitrogen nucleophiles. The cytotoxicities of the new 2-acyl-1,2-dihydroellipticines varied widely, and correlated well with their topoisomerase II inhibitory activities.

Antineoplastic Agents, Phytogenic↗
PubMed1995

Cyclin A links c-Myc to adhesion-independent cell proliferation.

Adhesion-independent growth is a neoplastic phenotype that is inducible in Rat 1a fibroblasts by enforced MYC expression. The c-Myc protein has been well characterized as a transcription factor, yet the molecular basis of c-Myc-induced neoplastic transformation has remained elusive. In this report, we demonstrate a link between ectopic MYC expression, deregulated cyclin A levels, and adhesion-independent growth.

Animals↗
PubMed1995

A comparison of active site binding of 4-quinolones and novel flavone gyrase inhibitors to DNA gyrase.

The activity of 4-quinolone antibacterials at the enzyme target level is based on the well known and reported observations that 4-quinolone antibacterials target the Gyr A subunit of the DNA gyrase holoenzyme, inhibiting supercoiling while facilitating the "cleavable complex". Such inhibition can be observed by running the in vitro DNA gyrase supercoiling inhibition assay or the "cleavable complex" DNA gyrase assay. Although potency of the gyrase inhibitor is dependent on many factors including permeability and pharmacokinetics, the inherent potency of a gyrase inhibitor lies in its activity against the target enzyme. We have examined the binding activity of novel flavones [Bioorganic & Med. Chem. Letters 3:225-230, 1993] to Escherichia coli DNA gyrase and have found differences in binding consistent with inhibition of DNA gyrase supercoiling and ability to facilitate the cleavable complex, but of different rank order. [3H]norfloxacin was used in vitro competition studies with test compounds, pBR322 and E. coli DNA gyrase. Binding affinity results indicate the rank order of greatest to weakest binding (ability to compete with [3H]norfloxacin) of test compounds: Levofloxacin = ciprofloxacin > ofloxacin > norfloxacin > flavone compounds (including ellagic acid, quercetin, and compounds 5a through 5n [Bioorganic & Med. Chem. Letters 3:225-230, 1993]). Such differences in binding ability of the 4-quinolones and flavones to the ternary complex of DNA.DNA gyrase.drug, as compared to the catalytic inhibition and "cleavable complex" data, suggests a more complex binding of flavones than the previously hypothesized models for 4-quinolone binding.

Anti-Infective Agents↗
PubMed1995

A link between increased transforming activity of lymphoma-derived MYC mutant alleles, their defective regulation by p107, and altered phosphorylation of the c-Myc transactivation domain.

The c-Myc protein is a transcription factor with an N-terminal transcriptional regulatory domain and C-terminal oligomerization and DNA-binding motifs. Previous studies have demonstrated that p107, a protein related to the retinoblastoma protein, binds to the c-Myc transcriptional activation domain and suppresses its activity. We sought to characterize the transforming activity and transcriptional properties of lymphoma-derived mutant MYC alleles. Alleles encoding c-Myc proteins with missense mutations in the transcriptional regulatory domain were more potent than wild-type c-Myc in transforming rodent fibroblasts. Although the mutant c-Myc proteins retained their binding to p107 in in vitro and in vivo assays, p107 failed to suppress their transcriptional activation activities. Many of the lymphoma-derived MYC alleles contain missense mutations that result in substitution for the threonine at codon 58 or affect sequences flanking this amino acid. We observed that in vivo phosphorylation of Thr-58 was absent in a lymphoma cell line with a mutant MYC allele containing a missense mutation flanking codon 58. Our in vitro studies suggest that phosphorylation of Thr-58 in wild-type c-Myc was dependent on cyclin A and required prior phosphorylation of Ser-62 by a p107-cyclin A-CDK complex. In contrast, Thr-58 remained unphosphorylated in two representative mutant c-Myc transactivation domains in vitro. Our studies suggest that missense mutations in MYC may be selected for during lymphomagenesis, because the mutant MYC proteins have altered functional interactions with p107 protein complexes and fail to be phosphorylated at Thr-58.

Alleles↗
PubMed1994

Participation of cyclin A in Myc-induced apoptosis.

The involvement of c-Myc in cellular proliferation or apoptosis has been linked to differential cyclin gene expression. We observed that in both proliferating cells and cells undergoing apoptosis, cyclin A (but not B, C, D1, and E) mRNA level was elevated in unsynchronized Myc-overexpressing cells when compared with parental Rat1a fibroblasts. We further demonstrated that Zn(2+)-inducible cyclin A expression was sufficient to cause apoptosis. When Myc-induced apoptosis was blocked by coexpression of Bcl-2, the levels of cyclin C, D1, and E mRNAs were also elevated. Thus, while apoptosis induced by c-Myc is associated with an elevated cyclin A mRNA level, protection from apoptosis by coexpressed Bcl-2 is associated with a complementary increase in cyclin C, D1, and E mRNAs.

Animals↗
PubMed1994

Absorption of non-haem iron from food during normal pregnancy.

OBJECTIVE: To determine whether the increased iron demands of pregnancy could be met by increased absorption from dietary sources. DESIGN AND SETTING: Longitudinal prospective study in the research unit of a maternity hospital. SUBJECTS: 12 normal pregnant women. INTERVENTIONS: At 12, 24, and 36 weeks' gestation (within one week) and 16-24 weeks after delivery women ate a breakfast of meat, bread, and orange juice (3.2 mg iron), extrinsically labelled with the stable isotope iron-54 (2.8 mg); the stable isotope iron-57 (200 micrograms) was given intravenously. MAIN OUTCOME MEASURES: Serum samples were taken for 10 hours after administration of the isotopes; ratios of the isotopes were measured by inductively coupled plasma mass spectrometry, and the absorption of oral iron was calculated. RESULTS: The geometric mean (95% confidence interval) absorption of iron at 12, 24, and 36 weeks' gestation was 7% (5% to 11%), 36% (28% to 47%), and 66% (57% to 76%) respectively. At 16-24 weeks after delivery the absorption was 11% (6% to 21%). The mean increase in absorption at 36 weeks (compared with that at 12 weeks) was 9.1 times (6.0 to 13.7). One pregnant woman developed iron deficiency anaemia but was otherwise indistinguishable from the others. CONCLUSIONS: An increase in the absorption of iron from food is a physiological consequence of normal pregnancy, not the result of developing anaemia during pregnancy, and such an increase is large enough to meet the increased requirements of pregnancy provided that the dietary intake is adequate.

Female↗
PubMed1994

Design and synthesis of ellipticinium salts and 1,2-dihydroellipticines with high selectivities against human CNS cancers in vitro.

9-Methoxy-2-methylellipticinium acetate (6), along with the 9-methyl and 9-chloro derivatives (7, and 8, respectively) have shown remarkable selectivities in vitro against the NCI human CNS cancer subpanel. In order to target these types of compounds to the CNS in vivo, a series of 1,2-dihydroellipticines was synthesized. 9-Methoxy-2-methyl-1,2-dihydroellipticine (9) retained the potency and selectivity of the parent compound 6 but was unstable toward oxidation to 6. In order to improve the stability of 9, it was converted to the vinylogous amide 33 by introduction of a formyl group in the 4-position. Compound 33 proved to be much more stable than 9, but it was also less potent than 9 by about 1 order of magnitude, and it was less selective for the CNS subpanel than 9. To overcome the limited water solubilities of the ellipticines and dihydroellipticines, several ellipticine analogues incorporating polar groups on the N-2 nitrogen were prepared. The 2-(methoxymethyl)ellipticinium salts 24 and 25, as well as the (methylthio)methyl congener 26, were relatively potent anticancer agents which displayed cytotoxicity selectivity profiles similar to compound 6. The cytotoxic dihydroellipticines 9 and 10 exhibited potencies approaching that of ellipticine itself in facilitating the formation of a "cleavable complex", while the least cytotoxic ellipticine derivatives exhibited no cleavage above background.

Brain Neoplasms↗
PubMed1994

Comparison of stable isotopes and radioisotopes in the measurement of iron absorption in healthy women.

1. Stable isotope methods are being used to investigate the absorption of dietary iron. In order to be certain that this new methodology is accurate, we have compared results obtained using stable isotopes and inductively coupled plasma mass spectrometry with those determined using a radioisotope and whole body counting. 2. The stable isotope 54Fe (2.8 mg) was given to 10 healthy non-pregnant women. Six women received the isotope in aqueous form, and four took it with a meat meal. The 54Fe served as a carrier for 10 ng of the radioisotope 59Fe. An ampoule (200 micrograms) of the isotope 57Fe or 58Fe was then given intravenously, and in serum samples taken over the next 10 h the ratios of the stable iron isotopes were measured by inductively coupled plasma mass spectrometry and the oral iron absorption was calculated. This was then compared with the results obtained by using a whole body counter to measure (on day 0 and day 14) the gamma-activity emitted by the radioisotope. 3. The mean iron absorption measured by both methods ranged from 8% to 45%. Measurement of the post-absorptive serum enrichment of the stable isotopes provided estimates of absorption from both aqueous and food iron which were similar to that yielded by whole body counting, the mean difference being -1.5% (95% confidence interval -5.2 to 2.1%). Absorption estimated by stable isotopes exhibited the same inverse relationship with the serum ferritin level (body iron stores) to that known to exist with whole body counting.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Testing potential gyrase inhibitors of bacterial DNA gyrase: a comparison of the supercoiling inhibition assay and "cleavable complex" assay.

Inhibitory activity of test compounds against Escherichia coli DNA gyrase in a "cleavable complex" assay, readily observed in vitro at the enzyme level by the artificial addition of a denaturing agent, is found to be an excellent indicator of 4-quinolone inhibition of DNA gyrase, and as accurate a predictor of target enzyme inhibitory activity as the measurement of the inhibition of DNA gyrase supercoiling. This study was designed to examine the specificity of DNA gyrase inhibitors of various chemical classes in these two DNA gyrase assays, and define the use of these two assays in understanding the nature of inhibition by experimental compounds. Supercoiling inhibition was detected by determination of the 50% inhibition level, and cleavable complex inhibition measured by the determination of the drug concentration at which 50% of the maximal (of control) formation of linear, cleaved DNA was obtained. Results indicate that these two assays can serve several different functions in microbiological research, among them: (1) quantitation of enzyme inhibitory activity at the target level; and (2) distinguishing between nonspecific inhibition or artifactual inhibition of DNA gyrase and true, mechanism-based inhibition of the catalytic activity of DNA gyrase.

Anti-Bacterial Agents↗