Showing papers on "Quinolone published in 1998"
TL;DR: The results suggested that clinafloxacin displays comparable if unequal targeting of gyrase and topoisomerase IV and its first- and second-step mutants are desirable features in limiting the emergence of bacterial resistance.
Abstract: We examined the response of Streptococcus pneumoniae 7785 to clinafloxacin, a novel C-8-substituted fluoroquinolone which is being developed as an antipneumococcal agent. Clinafloxacin was highly active against S. pneumoniae 7785 (MIC, 0.125 μg/ml), and neither gyrA nor parC quinolone resistance mutations alone had much effect on this activity. A combination of both mutations was needed to register resistance, suggesting that both gyrase and topoisomerase IV are clinafloxacin targets in vivo. The sparfloxacin and ciprofloxacin MICs for the parC-gyrA mutants were 16 to 32 and 32 to 64 μg/ml, respectively, but the clinafloxacin MIC was 1 μg/ml, i.e., within clinafloxacin levels achievable in human serum. S. pneumoniae 7785 mutants could be selected stepwise with clinafloxacin at a low frequency, yielding first-, second-, third-, and fourth-step mutants for which clinafloxacin MICs were 0.25, 1, 6, and 32 to 64 μg/ml, respectively. Thus, high-level resistance to clinafloxacin required four steps. Characterization of the quinolone resistance-determining regions of the gyrA , parC , gyrB , and parE genes by PCR, Hin fI restriction fragment length polymorphism, and DNA sequence analysis revealed an invariant resistance pathway involving sequential mutations in gyrA or gyrB , in parC , in gyrA , and finally in parC or parE . No evidence was found for other resistance mechanisms. The gyrA mutations in first- and third-step mutants altered GyrA hot spots Ser-83 to Phe or Tyr ( Escherichia coli coordinates) and Glu-87 to Gln or Lys; second- and fourth-step parC mutations changed equivalent hot spots Ser-79 to Phe or Tyr and Asp-83 to Ala. gyrB and parE changes produced novel alterations of GyrB Glu-474 to Lys and of Pro-454 to Ser in the ParE PLRGK motif. Difficulty in selecting first-step gyrase mutants (isolated with 0.125 [but not 0.25] μg of clinafloxacin per ml at a frequency of 5.0 × 10 −10 to 8.5 × 10 −10 ) accompanied by the small (twofold) MIC increase suggested only a modest drug preference for gyrase. Given the susceptibility of defined gyrA or parC mutants, the results suggested that clinafloxacin displays comparable if unequal targeting of gyrase and topoisomerase IV. Dual targeting and the intrinsic potency of clinafloxacin against S. pneumoniae and its first- and second-step mutants are desirable features in limiting the emergence of bacterial resistance.
205 citations
TL;DR: This work demonstrates that norfloxacin, a model quinolone, converts Escherichia coliTopo IV into a poisonous adduct on DNA as opposed to inhibiting topoisomerase activity, and interprets results in terms of distinct but complementary roles of Topo IV and gyrase in DNA replication.
168 citations
TL;DR: The data indicate that gyrA mutation is the most important component of quinolone resistance, and simultaneous presence of parC mutations is associated with high-level resistance.
Abstract: Principal mechanisms of bacterial resistance to quinolones are modification of target enzymes, DNA gyrase (gyrA) and topoisomerase IV (parC), or reduction of intracellular concentration due to mutations in the regulatory genes for efflux systems, such as mexR and nfxB. We have examined gyrA, parC, mexR, and nfxB genes from 16 quinolone-resistant clinical isolates of Pseudomonas aeruginosa to determine the relation between mutations in DNA replicating enzymes or regulatory genes for efflux systems and to correlate the mutations with minimal inhibitory concentrations (MICs). The quinolone resistance-determining regions (QRDR) of these genes were amplified by PCR and sequenced by capillary electrophoresis. Fourteen of 16 isolates had mutations in gyrA, and 13/14 strains with MIC to norfloxacin > or = 8 mg/L had threonine at position 83 changed to isoleucine. Seven of 8 strains with MIC > or = 32 mg/L had mutations in parC. One of these strains showed a parC mutation at position 74 without any mutation in gyrA. Four strains had mexR and two strains nfxB mutations. The data indicate that gyrA mutation is the most important component of quinolone resistance, and simultaneous presence of parC mutations is associated with high-level resistance. parC mutation alone may contribute to resistance, and gyrA mutation may not be a prerequisite for parC mutation to express resistance. mexR and nfxB mutations were found mostly in strains with high-level resistance.
142 citations
TL;DR: The quinolone antimicrobials are the class of inhibitors of bacterial topoisomerases that has been developed most fully for clinical use in human medicine as discussed by the authors, and they have a broad spectrum of potency.
140 citations
TL;DR: The quinolones, a synthetic class of antibacterials that act on both DNA gyrase and topoisomerase IV, have had the broadest clinical applications as discussed by the authors.
Abstract: Topoisomerases are ubiquitous enzymes necessary for controlling the interlinking and twisting of DNA molecules. Among the four topoisomerases identified in eubacteria, two, DNA gyrase and topoisomerase IV have been exploited by nature and the pharmaceutical industry as antibacterial targets. Natural products that are inhibitors of one or both of these topoisomerases include the coumarin and cyclothialidine classes, which interfere with adenosine triphosphate hydrolysis, cinodine, flavones, and terpenoid derivatives. The plasmid-encoded bacterial peptides micron B17 and CcdB also inhibit DNA gyrase. The quinolones, a synthetic class of antibacterials that act on both DNA gyrase and topoisomerase IV have had the broadest clinical applications, however. Quinolone congeners differ in their relative potencies for DNA gyrase and topoisomerase IV Studies of an expanding set of resistant mutant enzymes and the crystal structure of the homologous enzyme in yeast have contributed to our understanding of interactions of these drugs with topoisomerase-DNA complexes and the ways in which mutations effect resistance.
138 citations
Journal Article•
TL;DR: Study of an expanding set of resistant mutant enzymes and the crystal structure of the homologous enzyme in yeast have contributed to the understanding of interactions of these drugs with topoisomerase-DNA complexes and the ways in which mutations effect resistance.
Abstract: Topoisomerases are ubiquitous enzymes necessary for controlling the interlinking and twisting of DNA molecules. Among the four topoisomerases identified in eubacteria, two, DNA gyrase and topoisomerase IV, have been exploited by nature and the pharmaceutical industry as antibacterial targets. Natural products that are inhibitors of one or both of these topoisomerases include the coumarin and cyclothialidine classes, which interfere with adenosine triphosphate hydrolysis, cinodine, flavones, and terpenoid derivatives. The plasmid-encoded bacterial peptides microcin B17 and CcdB also inhibit DNA gyrase. The quinolones, a synthetic class of antibacterials that act on both DNA gyrase and topoisomerase IV, have had the broadest clinical applications, however. Quinolone congeners differ in their relative potencies for DNA gyrase and topoisomerase IV. Studies of an expanding set of resistant mutant enzymes and the crystal structure of the homologous enzyme in yeast have contributed to our understanding of interactions of these drugs with topoisomerase-DNA complexes and the ways in which mutations effect resistance.
133 citations
TL;DR: This study clearly shows that a mutation in Thr‐86 to Ile or Lys is a frequent mechanism associated with the acquisition of a high level of resistance to quinolones in clinical isolates of C. jejuni.
Abstract: Campylobacter jejuni is a frequent cause of enteritis and sometimes it requires antimicrobial therapy. We have studied the evolution of resistance to nine antibiotics from 1990 to 1994 and investigated how frequently gyrA mutations are involved in the acquisition of quinolone resistance. The percentage of chloramphenicol-, clindamycin-, tertracycline- and amoxicillin plus clavulanic acid-resistant strains has remained practically unchanged and erythromycin and gentamicin resistance has decreased, whereas the percentage of ampicillin-, nalidixic acid- or ciprofloxacin-resistant strains has almost doubled in the follow-up period, from 56 to 76% for ampicillin- and from 47.5 to 88% for quinolone-resistant strains. This study clearly shows that a mutation in Thr-86 to Ile or Lys is a frequent mechanism associated with the acquisition of a high level of resistance to quinolones in clinical isolates of C. jejuni.
123 citations
TL;DR: Peptide sequences of the QRDR of GyrA were identical in all the species, except for the amino acid at position 83, suggesting that this amino acid is involved in the observed differences of quinolone susceptibility within theMycobacterium genus.
Abstract: The in vitro activities of seven quinolones and the sequences of the quinolone resistance-determining regions (QRDR) in the A and B subunits of DNA gyrase were determined for 14 mycobacterial species. On the basis of quinolone activity, quinolones were arranged from that with the greatest to that with the least activity as follows: sparfloxacin, levofloxacin, ciprofloxacin, ofloxacin, pefloxacin, flumequine, and nalidixic acid. Based on MICs, the species could be organized into three groups: resistant (Mycobacterium avium, M. intracellulare, M. marinum, M. chelonae, M. abscessus [ofloxacin MICs, >/=8 microg/ml]), moderately susceptible (M. tuberculosis, M. bovis BCG, M. kansasii, M. leprae, M. fortuitum third biovariant, M. smegmatis [ofloxacin MICs, 0.5 to 1 microg/ml]), and susceptible (M. fortuitum, M. peregrinum, M. aurum [ofloxacin MICs,
112 citations
TL;DR: Results suggest that in C. trachomatis, DNA gyrase is the primary target of ofloxacin and sparfloxac in the selection of fluoroquinolone-resistant mutants.
Abstract: The L2 reference strain of Chlamydia trachomatis was exposed to subinhibitory concentrations of ofloxacin (0.5 μg/ml) and sparfloxacin (0.015 μg/ml) to select fluoroquinolone-resistant mutants. In this study, two resistant strains were isolated after four rounds of selection. The C. trachomatis mutants presented with high-level resistance to various fluoroquinolones, particularly to sparfloxacin, for which a 1,000-fold increase in the MICs for the mutant strains compared to the MIC for the susceptible strain was found. The MICs of unrelated antibiotics (doxycycline and erythromycin) for the mutant strains were identical to those for the reference strain. The gyrase (gyrA, gyrB) and topoisomerase IV (parC, parE) genes of the susceptible and resistant strains of C. trachomatis were partially sequenced. A point mutation was found in the gyrA quinolone-resistance-determining region (QRDR) of both resistant strains, leading to a Ser83→Ile substitution (Escherichia coli numbering) in the corresponding protein. The gyrB, parC, and parE QRDRs of the resistant strains were identical to those of the reference strain. These results suggest that in C. trachomatis, DNA gyrase is the primary target of ofloxacin and sparfloxacin.
108 citations
TL;DR: The findings indicate that alterations in topoisomerases may have pleiotropic effects on different classes of inhibitors as well as on inhibitors within the same class.
Abstract: Previous studies have shown that topoisomerase IV and DNA gyrase interact with quinolones and coumarins in different ways. The MICs of coumarins (novobiocin and coumermycin) for MT5, a Staphylococcus aureus nov mutant, are higher than those for wild-type strains. Sequencing the gyrB gene encoding one subunit of the DNA gyrase revealed the presence of a double mutation likely to be responsible for this resistance: at codon 102 (Ile to Ser) and at codon 144 (Arg to Ile). For single-step flqA mutant MT5224c9, previously selected on ciprofloxacin, the fluoroquinolone MIC was higher and the coumarin MIC was lower than those for its parent, MT5. Sequencing the grlB and grlA genes of topoisomerase IV of MT5224c9 showed a single Asn-470-to-Asp mutation in GrlB. Genetic outcrosses by transformation with chromosomal DNA and introduction of plasmids carrying either the wild-type or the mutated grlB gene indicated that this mutation causes both increased MICs of fluoroquinolones and decreased MICs of coumarins and that the mutant grlB allele is codominant for both phenotypes with multicopy alleles. Integration of these plasmids into the chromosome confirmed the codominance of fluoroquinolone resistance, but grlB+ appeared dominant over grlB (Asp-470) for coumarin resistance. Finally, the gyrA (Leu-84) mutation previously described as silent for fluoroquinolone resistance increased the MIC of nalidixic acid, a nonfluorinated quinolone. Combining the grlA (Phe-80) and grlB (Asp-470) mutations with this gyrA mutation also had differing effects. The findings indicate that alterations in topoisomerases may have pleiotropic effects on different classes of inhibitors as well as on inhibitors within the same class. A full understanding of drug action and resistance at the molecular level must take into account both inhibitor structure-activity relationships and the effects of different classes of topoisomerase mutants.
99 citations
TL;DR: Results suggest that DNA topoisomerase IV is a primary target of ciprofloxacin in viridans group streptococci, DNA gyrase being a secondary target.
Abstract: The nucleotide sequences of the quinolone resistance-determining regions (QRDRs) of the parC and gyrA genes from seven ciprofloxacin-resistant (Cpr) isolates of viridans group streptococci (two high-level Cpr Streptococcus oralis and five low-level Cpr Streptococcus mitis isolates) were determined and compared with those obtained from susceptible isolates. The nucleotide sequences of the QRDRs of the parE and gyrB genes from the five low-level Cpr S. mitis isolates and from the NCTC 12261 type strain were also analyzed. Four of these low-level Cpr isolates had changes affecting the subunits of DNA topoisomerase IV: three in Ser-79 (to Phe or Ile) of ParC and one in ParE at a position not previously described to be involved in quinolone resistance (Pro-424). One isolate did not show any mutation. The two high-level Cpr S. oralis isolates showed mutations affecting equivalent residue positions of ParC and GyrA, namely, Ser-79 to Phe and Ser-81 to Phe or Tyr, respectively. The parC mutations were able to transform Streptococcus pneumoniae to ciprofloxacin resistance, while the gyrA mutations transformed S. pneumoniae only when mutations in parC were present. These results suggest that DNA topoisomerase IV is a primary target of ciprofloxacin in viridans group streptococci, DNA gyrase being a secondary target.
TL;DR: The preference of topoisomerase IV for catalyzing DNA decatenation over relaxation reflects increased rates of strand passage and enzyme recycling rather than a heightened recognition of intermolecular DNA helices.
TL;DR: Gatifloxacin possessed potent activity against the NorA-overproducing strain S. aureus NY12, thenorA transformant, which was slightly lower than that against the parent strain SA113, and the increases in the MICs of the quinolones tested against NY12 were negatively correlated with the hydrophobicity of thequinolones (correlation coefficient, −0.93;P < 0.01).
Abstract: Alternate mutations in the grlA and gyrA genes were observed through the first- to fourth-step mutants which were obtained from four Staphylococcus aureus strains by sequential selection with several fluoroquinolones. The increases in the MICs of gatifloxacin accompanying those mutational steps suggest that primary targets of gatifloxacin in the wild type and the first-, second-, and third-step mutants are wild-type topoisomerase IV (topo IV), wild-type DNA gyrase, singly mutated topo IV, and singly mutated DNA gyrase, respectively. Gatifloxacin had activity equal to that of tosufloxacin and activity more potent than those of norfloxacin, ofloxacin, ciprofloxacin, and sparfloxacin against the second-step mutants (grlA gyrA; gatifloxacin MIC range, 1.56 to 3.13 microg/ml) and had the most potent activity against the third-step mutants (grlA gyrA grlA; gatifloxacin MIC range, 1.56 to 6.25 microg/ml), suggesting that gatifloxacin possesses the most potent inhibitory activity against singly mutated topo IV and singly mutated DNA gyrase among the quinolones tested. Moreover, gatifloxacin selected resistant mutants from wild-type and the second-step mutants at a low frequency. Gatifloxacin possessed potent activity (MIC, 0.39 microg/ml) against the NorA-overproducing strain S. aureus NY12, the norA transformant, which was slightly lower than that against the parent strain SA113. The increases in the MICs of the quinolones tested against NY12 were negatively correlated with the hydrophobicity of the quinolones (correlation coefficient, -0.93; P < 0.01). Therefore, this slight decrease in the activity of gatifloxacin is attributable to its high hydrophobicity. Those properties of gatifloxacin likely explain its good activity against quinolone-resistant clinical isolates of S. aureus harboring the grlA, gyrA, and/or norA mutations.
TL;DR: The results confirm that mitochondria represent a biological target of fluoroquinolones and modification of decorin seems to be an early event (before mitochondrion alteration) which may contribute to the explanation of tendon rupture.
Abstract: Tendinitis and tendon rupture complicating fluoroquinolone therapy have been reported recently, especially affecting men over 60 years. These new quinolones are more potent antimicrobial agents than older nonfluorinated compounds like nalidixic acid. We compared the effects of one quinolone (nalidixic acid) and two fluoroquinolones (norfloxacin and pefloxacin) on cultured rabbit Achilles tendon cells. First, we examined their effects on cell viability, mitochondrial succinate dehydrogenase and global activity, mitochondrial activity using microtitration methods. Pefloxacin and norfloxacin were more cytotoxic than nalidixic acid according to IC50 values. These results confirm that mitochondria represent a biological target of fluoroquinolones. Moreover, the extracellular matrix was studied by molecular hybridization. After a 72 h treatment, the level of type I collagen transcripts was not modified with any of the three antimicrobial agents, whereas mRNA encoding decorin was decreased with 10-4 mol/L pefloxacin only. The decrease of transcripts encoding decorin suggests that this matrix component is another target of pefloxacin and modification of decorin seems to be an early event (before mitochondrion alteration) which may contribute to the explanation of tendon rupture.
TL;DR: Eight novel quinolones with anti-Helicobacter pylori activity were isolated from the actinomycete Pseudonocardia sp.
Abstract: Eight novel quinolones with anti-Helicobacter pylori activity were isolated from the actinomycete Pseudonocardia sp. CL38489. The quinolones were very potent against H. pylori with MICs up to 0.1 ng/ml. The quinolones appear to be specific for H. pylori, since they did not show antimicrobial activity when tested against a panel of other microorganisms.
TL;DR: Analysis of eight multistep-selected mutants of M. hominis revealed that in M.hominis DNA gyrase is the primary target of sparfloxacin whereas topoisomerase IV is theprimary target of pefloxACin, ofloxac in, and ciprofloxAcin, respectively.
Abstract: Mycoplasma hominis mutants were selected stepwise for resistance to ofloxacin and sparfloxacin, and their gyrA, gyrB, parC, and parE quinolone resistance-determining regions were characterized. For ofloxacin, four rounds of selection yielded six first-, six second-, five third-, and two fourth-step mutants. The first-step mutants harbored a single Asp426-->Asn substitution in ParE. GyrA changes (Ser83-->Leu or Trp) were found only from the third round of selection. With sparfloxacin, three rounds of selection generated 4 first-, 7 second-, and 10 third-step mutants. In contrast to ofloxacin resistance, GyrA mutations (Ser83-->Leu or Ser84-->Trp) were detected in the first-step mutants prior to ParC changes (Glu84-->Lys), which appeared only after the second round of selection. Further analysis of eight multistep-selected mutants of M. hominis that were previously described (2) revealed that they carried mutations in ParE (Asp426-->Asn), GyrA (Ser83-->Leu) and ParE (Asp426-->Asn), GyrA (Ser83-->Leu) and ParC (Ser80-->Ile), or ParC (Ser80-->Ile) alone, depending on the fluoroquinolone used for selection, i.e., ciprofloxacin, norfloxacin, ofloxacin, or pefloxacin, respectively. These data indicate that in M. hominis DNA gyrase is the primary target of sparfloxacin whereas topoisomerase IV is the primary target of pefloxacin, ofloxacin, and ciprofloxacin.
TL;DR: The results obtained with different 6-substituted compounds supports the idea that position 6 of the drug, besides playing a pharmacokinetic role, is involved in recognition of the enzyme pocket, but does not support a mechanism of action based upon quinolone intercalation into B-DNA.
TL;DR: Similar mutations to quinolone resistance, predominantly at codons 82--83 of gyrA, are occurring independently in genotypically distinct isolates of Acinetobacter spp.
TL;DR: The simultaneous presence of GyrA and ParC alterations was associated with a high level of fluoroquinolone resistance in the clinical isolates of S. epidermidis.
Abstract: We examined 22 clinical isolates of Staphylococcus epidermidis to analyze the association of alterations in GyrA and ParC with fluoroquinolone resistance. The simultaneous presence of GyrA and ParC alterations was associated with a high level of fluoroquinolone resistance in the clinical isolates of S. epidermidis.
TL;DR: Analysis of drug-resistance mutations in the T4 topoisomerase have implicated certain regions of the protein in drug interaction and provided a strong link between the mechanism of action of the antibacterial quinolones, which inhibit DNA gyrase, and the various antitumor agents, who inhibit mammalian type II topoisomersase.
Journal Article•
TL;DR: Following the discovery of nalidixic acid in 1962, numerous structural modifications have been made to the quinolone nucleus to increase antimicrobial activity and improve pharmacokinetic performance.
Abstract: Following the discovery of nalidixic acid in 1962, numerous structural modifications have been made to the quinolone nucleus to increase antimicrobial activity and improve pharmacokinetic performance. A major advance occurred during the 1980's with the discovery that a fluorine at position-6 conferred broad and potent antimicrobial activity, (e.g. norfloxacin) but still with relatively less activity for Gram-positive and antiaerobic organisms than Gram-negative bacteria. Subsequent developments produced quinolones with further improvements, predominantly in either solubility (e.g. ofloxacin), antimicrobial activity (e.g. ciprofloxacin) or prolonged serum half-life (e.g. pefloxacin). Recent modifications have attempted to achieve an optimal blend of favourable properties together with minimal potential for undesirable side-effects. The mode of action of quinolones is by blocking of the bacterial enzyme gyrase. This enzyme is responsible for the coiling and supercoiling of the DNA within the cell. When this enzyme is inhibited, DNA transcription, which results in protein synthesis, and DNA replication, which results in cell division, are inhibited. Improvements in antimicrobial activity combined with adequate blood and tissue concentrations do offer expectancy of enhanced therapeutic efficacy for new derivatives in those infections by organisms which are 'marginally' sensitive to currently used quinolones. The possibility of resistance emerging in these organisms during treatment should also be reduced.
TL;DR: The encoded ParE and ParC proteins exhibit higher homologies with the topoisomerase IV subunits of the gram-positive bacteria Staphylococcus aureus and Streptococcus pneumoniae than with their Escherichia colicounterparts.
Abstract: The topoisomerase IV parC and parE genes from the wall-less organism Mycoplasma hominis PG21 were cloned and sequenced. The coupled genes are located far from the DNA gyrase genes gyrA and gyrB. They encode proteins of 639 and 866 amino acids, respectively. As expected, the encoded ParE and ParC proteins exhibit higher homologies with the topoisomerase IV subunits of the gram-positive bacteria Staphylococcus aureus and Streptococcus pneumoniae than with their Escherichia coli counterparts. The conserved regions include the Tyr residue of the active site and the region involved in quinolone resistance (quinolone resistance-determining region [QRDR]) in ParC and the ATP-binding site and the QRDR in ParE.
TL;DR: This study indicated that Du-6859a is more potent than the comparator quinolones, is less affected by the mechanisms responsible for high-level quinOLone resistance and may be less likely to select resistant mutants if it has a susceptible breakpoint of 1 mg/L.
Abstract: A panel of 266 clinically isolated Gram-positive cocci and Gram-negative bacilli with varying levels of resistance to ciprofloxacin were analysed for susceptibility to Du-6859a, ciprofloxacin, ofloxacin, temafloxacin and nalidixic acid. Staphylococci were divided into ciprofloxacin-susceptible, moderately resistant and highly resistant subgroups. Du-6859a was the most potent quinolone against all taxa. As ciprofloxacin resistance increased to high levels, MICs of all quinolones increased but Du-6859a MICs increased least, and ciprofloxacin MICs increased most. Less susceptible single-step mutants were selected from 80% of 15 representative clinical isolates exposed to ciprofloxacin, 71% of isolates exposed to temafloxacin, 67% of isolates exposed to Du-6859a and 53% of isolates exposed to ofloxacin. Du-6859a inhibited more mutants (67%) at a concentration of 1 mg/L than did the other quinolones (26-43%) at their susceptible breakpoints. Du-6859a was the most rapidly bactericidal quinolone in time-kill studies with Enterococcus faecalis and Enterococcus faecium. This study indicated that Du-6859a is more potent than the comparator quinolones, is less affected by the mechanisms responsible for high-level quinolone resistance and may be less likely to select resistant mutants if it has a susceptible breakpoint of 1 mg/L.
TL;DR: Y-688 failed in vivo and its use carried the risk of resistance selection, which suggests that the treatment of ciprofloxacin-resistant MRSA with new quinolones might be more problematic than expected.
Abstract: Ever since their introduction into the armamentarium of antimicrobial agents, fluorinated quinolones have emerged as major antibacterial compounds against gram-negative microorganisms. In the late 1980s, relatively new drugs such as ciprofloxacin also emerged, and it was hoped that these drugs could solve the increasing problem posed by multidrug-resistant gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) in hospitals. However, extensive use of such quinolones very rapidly selected for quinolone-resistant MRSA (14, 21, 22). More than 90% of these organisms are now resistant to ciprofloxacin in certain places (21).
Quinolone-resistant staphylococci can readily be selected for in vitro by exposure to stepwise increasing concentrations of these agents (9, 21). In vivo, this phenomenon may have been accentuated by the relatively low therapeutic margin of the earlier quinolones against these bacteria. For example, the MIC of ciprofloxacin for susceptible S. aureus ranges between 0.25 and 1 mg/liter (3, 25). In comparison, therapeutic doses of this drug produce peak and trough concentrations in the serum of humans of 2.5 and 0.5 mg/liter, respectively (2, 18), i.e., not much greater than the ciprofloxacin MIC for the most susceptible staphylococci. This is an ideal situation for resistance selection in test tubes (9, 21) and thus may have provided the perfect conditions for the emergence of quinolone-resistant MRSA in the clinical environment.
The resistance of S. aureus to fluoroquinolones involves at least three different mechanisms, which are often combined in highly resistant organisms. One mechanism is the active efflux of the drugs by the NorA transporter (27). The two other mechanisms result from modifications of the quinolone molecular targets of the bacterium, i.e., the DNA gyrase (gyrA mutants) (13) and/or the topoisomerase IV (grlA mutants) (10). Newer quinolones, including sparfloxacin and others, have lower levels of susceptibility to NorA-mediated efflux and may have higher affinities for bacterial gyrases and topoisomerases (16, 20, 27). Therefore, they are more potent, in a weight-to-weight ratio, than older quinolones against staphylococci and other gram-positive pathogens. Some of these molecules are active even against MRSA strains showing low-level resistance to ciprofloxacin. However, these compounds may fail against high-level ciprofloxacin-resistant MRSA encountered in the clinical environment (5, 12, 23). Therefore, quinolones with increased activity against ciprofloxacin-resistant MRSA are still needed.
Y-688 (17) is a novel molecule of this family demonstrating in vitro activity against both ciprofloxacin-susceptible and ciprofloxacin-resistant S. aureus (26). If this activity is preserved in vivo, the drug could become extremely important owing to its effectiveness against multidrug-resistant MRSA. To investigate this question, the therapeutic efficacy of Y-688 was tested in rats with experimental aortic endocarditis due to ciprofloxacin-resistant MRSA. The new compound was administered to mimic the anticipated pharmacokinetics in the serum of humans. Control drugs included vancomycin, which is the sole drug uniformly proposed for the treatment of severe MRSA infections, and ciprofloxacin, which was used as a negative control.
TL;DR: This review summarises patents claiming novel DNA gyrase inhibitors (quinolone and non-quinolones) published from January 1995 to date, which claimed to provide improved physical stability or improved therapeutic efficacy.
Abstract: This review summarises patents claiming novel DNA gyrase inhibitors (quinolones and non-quinolones) published from January 1995 to date. The majority of these patents describe the synthesis and biological evaluation of new fluoroquinolone analogues with modified substituents on N-1, C-5, C-7 or C-8 of the quinolone ring system. A series of quinolizinones were reported as potent broad-spectrum antibacterial agents with activity against several resistant bacterial strains. Two interesting non-quinolone inhibitors with new chemotypes were reported. However, no detailed reports on biological profiles were described. Several patents relating to the improved synthesis of quinolone intermediates were also published. The last group of patents reported new formulation methods for known quinolones, which claimed to provide improved physical stability or improved therapeutic efficacy. New applications of known fluoroquinolones against aphthous ulcers and human immunodeficiency virus (HIV) were also claimed.
Journal Article•
TL;DR: The results support models in which both quinolones and antitumor agents bind to a conserved site that overlaps the active site of the enzyme, and support a new class of topoisomerase mutants.
Abstract: Various antitumor and antibacterial agents target type II DNA topoisomerases, stabilizing a cleaved DNA reaction intermediate and thereby converting topoisomerase into a cellular poison. Two 4′-(9-acridinylamino)methanesulfon- m -anisidide ( m -AMSA)-resistant bacteriophage T4 topoisomerases have previously been characterized biochemically, and we have now determined the sequence of the causative mutations. In one case, a mutation (E457K) in a conserved domain of gp39 (ATPase subunit) causes resistance to antitumor agent m -AMSA but hypersensitivity to the quinolone oxolinic acid. In the second case, a combination of two amino acid substitutions (S79F and G269V) in gp52 (DNA-cleaving subunit) causes resistance to both m -AMSA and oxolinic acid. The S79F mutation is responsible for drug resistance, whereas the G269V mutation suppresses a topoisomerase deficiency caused by S79F. Surprisingly, the G269V mutation by itself causes a dramatic hypersensitivity to both inhibitors, defining a new class of topoisomerase mutants. Because S79 and the adjacent N78 are homologous to two key residues of DNA gyrase that affect quinolone sensitivity, we generated additional amino acid substitutions at these two positions. The substitutions alter sensitivity to m -AMSA and to oxolinic acid, sometimes in opposite directions. Furthermore, the quinolone sensitivities of the various mutants paralleled those of corresponding gyrase mutants. These results support models in which both quinolones and antitumor agents bind to a conserved site that overlaps the active site of the enzyme.
Journal Article•
TL;DR: Results suggest that the risk of oxygen-free radical generation from quinolones should be considered, and Pipemidic acid and norfloxacin are suggested to be considered.
TL;DR: The quinolones, similar to the sulfonamides and nitrofurans, are totally synthetic chemical compounds used to combat infections (Albrecht 1977); they are derived by substitution of 1,4-dihydro-4-oxo-quinoline-3-carboxylic acids (structural formula 1) at the nitrogen atom of position 1 as discussed by the authors.
Abstract: The quinolones, similar to the sulfonamides and nitrofurans, are totally synthetic chemical compounds used to combat infections (Albrecht 1977). They are derived by substitution of 1,4-dihydro-4-oxo-quinoline-3-carboxylic acids (structural formula 1) at the nitrogen atom of position 1.
TL;DR: 5-Amino-7-(3R,4R-N,N'-dimethyldiamino-6,8-difluoro-1,4-dihydro-1-c yclopropyl -4-oxoquinoline-3-carboxylic acid was found to have potent antibacterial activity against gram +ve organisms.