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1.  Inhibitory activities of quinolones against DNA gyrase and topoisomerase IV purified from Staphylococcus aureus. 
Antimicrobial Agents and Chemotherapy  1997;41(11):2362-2366.
In order to clarify the mechanism of action of quinolones against Staphylococcus aureus, GrlA and GrlB proteins of topoisomerase IV encoded by genes with or without mutations were purified separately as fusion proteins with maltose-binding protein in Escherichia coli. The reconstituted enzymes showed ATP-dependent decatenation and relaxing activities but had no supercoiling activity. The inhibitory effects of quinolones on the decatenation activity of topoisomerase IV were determined by quantitative electrophoresis with kinetoplast DNA as a substrate. The 50% inhibitory concentrations (IC50s) of levofloxacin, DR-3354, DU-6859a, DV-7751a, ciprofloxacin, sparfloxacin, and tosufloxacin against topoisomerase IV of S. aureus FDA 209-P were 2.3, 97, 0.45, 1.5, 2.5, 7.4, and 1.8 microg/ml, respectively, and were correlated well with their MICs. The IC50s of these drugs were from 2 to 20 times lower than those for the DNA gyrase. These results support genetic evidence that the primary target of new quinolones is topoisomerase IV in quinolone-susceptible strains of S. aureus. Three altered proteins of topoisomerase IV containing Ser-->Phe changes at codon 80 or Glu-->Lys changes at codon 84 of grlA, or both, were also purified. The inhibitory activities of quinolones against the topoisomerase IV which contained a single amino acid change were from 8 to 95 times weaker than those against the nonaltered enzyme. These results suggest that the mutations in the corresponding genes confer quinolone resistance.
PMCID: PMC164129  PMID: 9371334
2.  Antimicrobial activity of DU-6681a, a parent compound of novel oral carbapenem DZ-2640. 
The in vitro antibacterial activity of DU-6681a, a parent compound of DZ-2640, against gram-positive and -negative bacteria was compared with those of penems and cephalosporins currently available. MICs at which 90% of the isolates are inhibited (MIC90s) of the compound for clinical isolates of methicillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis, including methicillin-susceptible and -resistant strains, were 0.10, 25, and 12.5 microg/ml, respectively. DU-6681a inhibited the growth of all strains of Streptococcus pyogenes and of penicillin-susceptible and -insusceptible Streptococcus pneumoniae at 0.006, 0.025, and 0.20 microg/ml, respectively, and MIC90s of the compound were 6.25 and >100 microg/ml for Enterococcus faecalis and Enterococcus faecium, respectively. MIC90s of DU-6681a were 0.20, 0.10, and 0.025 microg/ml for Haemophilus influenzae, Moraxella catarrhalis, and Neisseria gonorrhoeae, respectively. For Pseudomonas aeruginosa, the MIC50 and MIC90 of DU-6681a were 25 and 50 microg/ml, respectively. DU-6681a activity was not affected by different media, varied inoculum size (10(4) to 10(7) CFU), or the addition of human serum but was decreased under acidic conditions against gram-negative bacteria, under alkaline conditions against gram-positive bacteria, and in human urine, as was the activity of the other antibiotics tested. The frequency of spontaneous resistance to DU-6681a was less than or equal to those of the reference compounds. Time-kill curve studies demonstrated the bactericidal action of DU-6681a against S. aureus, S. pneumoniae, Escherichia coli, and H. influenzae.
PMCID: PMC163897  PMID: 9174181
3.  Effects of benzoxazinorifamycin KRM-1648 on cytokine production at sites of Mycobacterium avium complex infection induced in mice. 
Although various antimicrobial agents exhibit appreciable microbicidal activity in the early phase (weeks 2 t0 4) of Mycobacterium avium complex (MAC) infection induced in mice, progressive bacterial regrowth subsequently occurs. To clarify the reason for this pattern of changes, we studied changes in the levels of various cytokines in tissue at sites of infection (spleens and lungs) of MAC-infected mice which were or were not given a benzoxazinorifamycin, KRM-1648 (KRM). Levels of the proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) in tissues temporarily increased at around weeks 2 to 4 after infection, rapidly decreased thereafter, and returned to normal by week 8. Similar but somewhat delayed changes were noted for levels of interleukin 10 (IL-10) and transforming growth factor beta (TGF-beta), immunosuppressive cytokines with macrophage (M phi)-deactivating activity, in tissue, except that TGF-beta levels in the spleen remained high during weeks 4 to 8. KRM treatment blocked the increase in the levels of all of those cytokines in tissue in the early phase of infection, most strongly at week 4. IL-6 levels were beneath the limit of detection throughout the observation period. Bacterial loads in the visceral organs decreased during the first 2 weeks, and KRM treatment markedly promoted this decrease. However, regrowth of MAC organisms began at weeks 2 to 4 and continued thereafter, even in KRM-treated mice. Splenocytes and splenic M phi s of MAC-infected mice (week 2) produced and/or released into the culture fluid significant amounts of TNF-alpha (in a cell-bound form), IFN-gamma, and IL-10, but not TGF-beta, during 3 days of cultivation. A substantial amount of TGF-beta was produced during 2 weeks of cultivation of peritoneal M phi s. KRM itself did not significantly affect the IL-10- and TGF-beta-producing ability of cultured M phi s. These findings suggest that IL-10 and TGF-beta play important roles in the regrowth of MAC organisms seen during the course of KRM treatment.
PMCID: PMC163714  PMID: 9021192
4.  Mechanism of differential activities of ofloxacin enantiomers. 
Ofloxacin, a potent quinolone antibacterial agent, has a tricyclic ring structure with a methyl group attached to the asymmetric carbon at the C-3 position on the oxazine ring. The S isomer (DR-3355) of ofloxacin has antibacterial activity up to 2 orders of magnitude greater than that of the R isomer (DR-3354). This differential antibacterial activity was not due to different drug transport mechanisms of the two isomers but was found to be derived from the inhibitory activity against the target enzyme, DNA gyrase. Previous mechanistic studies have suggested that the bactericidal effect of the drug is mediated through the stabilization of a cleavable complex via a cooperative drug binding process to a partially denatured DNA pocket created by DNA gyrase. The drug binds to supercoiled DNA in a manner similar to that to which it binds to the enzyme-DNA complex. In the present studies, we first examined the binding of the two radiolabeled ofloxacin enantiomers to supercoiled pUC9 plasmid DNA. Surprisingly, the two enantiomers possessed similar apparent binding affinities and binding cooperatives. The major difference in binding between the two stereoisomers was the molar binding ratio: 4 for the more active S isomer versus 2 for the less active R isomer. We next examined the relative binding potencies of the stereoisomers to the DNA-DNA gyrase complex. The results of a competition assay showed that (S)-ofloxacin binds 12-fold better to the complex than (R)-ofloxacin. The binding potencies of the two enantiomers and two other quinolones correlated well with their respective concentrations causing 50% inhibition against DNA gyrase. The results are interpreted by a stacking model by using the concept of the cooperative drug-DNA binding mechanism, indicating that the potencies of quinolones cannot be determined solely by the DNA binding affinity and cooperativity but can also be determined by their capability in maximally saturating the binding site. The capability of the drug in saturating the binding pocket manifests itself in an increased efficacy at inhibiting the enzyme through a direct interaction between the drug and the enzyme. The results augment the previous suggestion that the binding pocket in the enzyme-DNA complex involves multiple receptor groups including not only DNA bases but also a gyrase subunit. The higher level of potency of (S)-ofloxacin is proposed to derive from the fact that a greater number of molecules are assembled in the pocket. This greater number of molecules optimizes the interaction between the drug and the enzyme, possibly through a contact between the C-7 substituent and the quinolone pocket on the B subunit of DNA gyrase.
PMCID: PMC163416  PMID: 8843280
5.  Quinolone-resistant mutants of escherichia coli DNA topoisomerase IV parC gene. 
Escherichia coli quinolone-resistant strains with mutations of the parC gene, which codes for a subunit of topoisomerase IV, were isolated from a quinolone-resistant gyrA mutant of DNA gyrase. Quinolone-resistant parC mutants were also identified among the quinolone-resistant clinical strains. The parC mutants became susceptible to quinolones by introduction of a parC+ plasmid. Introduction of the multicopy plasmids carrying the quinolone-resistant parC mutant gene resulted in an increase in MICs of quinolones for the parC+ and quinolone-resistant gyrA strain. Nucleotide sequences of the quinolone-resistant parC mutant genes were determined, and missense mutations at position Gly-78, Ser-80, or Glu-84, corresponding to those in the quinolone-resistance-determining region of DNA gyrase, were identified. These results indicate that topoisomerase IV is a target of quinolones in E. coli and suggest that the susceptibility of E. coli cells to quinolones is determined by sensitivity of the targets, DNA gyrase and topoisomerase IV.
PMCID: PMC163185  PMID: 8851598
6.  In vitro antibacterial activity of DU-6859a, a new fluoroquinolone. 
Antimicrobial Agents and Chemotherapy  1995;39(12):2822-2826.
The in vitro antibacterial activity of DU-6859a, a new fluoroquinolone, against a wide variety of clinical isolates was evaluated and compared with those of tosufloxacin, ofloxacin, ciprofloxacin, and sparfloxacin. DU-6859a showed potent broad-spectrum activity against gram-positive, gram-negative, and anaerobic bacteria, and its activity was greater than those of the control quinolones. By comparison of MICs at which 90% of strains are inhibited, DU-6859a had potent activity against bacteria resistant to the control quinolones. The time-killing curves of quinolones showed that the number of viable cells decreased rapidly during 2 to 4 of incubation, and regrowth was not seen even after 8 h incubation. At a concentration of four times the MIC, the frequencies of appearance of spontaneous mutants of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa resistant to DU-6859a were < or = 4.0 x 10(-9) to 1.9 x 10(-8). The 50% inhibitory concentrations of DU-6859a were 0.86 and 1.05 micrograms/ml for the supercoiling activities of DNA gyrases isolated from E. coli and P. aeruginosa, respectively. The rank order of the 50% inhibitory concentrations observed for both DNA gyrases roughly paralleled the MICs.
PMCID: PMC163041  PMID: 8593031
7.  In vitro and in vivo activities of the benzoxazinorifamycin KRM-1648 against Mycobacterium tuberculosis. 
Antimicrobial Agents and Chemotherapy  1995;39(10):2295-2303.
The in vitro and in vivo activities of a new benzoxazinorifamycin, KRM-1648 (KRM), against Mycobacterium tuberculosis were studied. The MIC at which 50% of the isolates are inhibited (MIC50) and the MIC90 of KRM for 30 fresh isolates of M. tuberculosis measured by the BACTEC 460 TB System were 0.016 and 2 micrograms/ml, respectively. These values were much lower than those for rifampin (RMP), which were 4 and >128 micrograms/ml, respectively, and considerably lower than those for rifabutin (RBT), which were 0.125 and 8 micrograms/ml, respectively. A correlational analysis of the MICs of these drugs for the clinical isolates revealed the presence of cross-resistance of the organisms to KRM and either RMP or RBT although the MICs of KRM were distributed over a much lower range than were those of the other two drugs. KRM and RMP at concentrations of 1 to 10 micrograms/ml almost completely inhibited the bacterial growth of RMP-sensitive strains (H37Rv, Kurono, and Fujii) of M. tuberculosis phagocytosed in macrophage-derived J774.1 cells. KRM was more active than RMP in inhibiting the growth of the RMP-resistant (MIC = 8 micrograms/ml) Kurata strain but failed to show such an effect against the RMP-resistant (MIC >128 micrograms/ml) Watanabe stain. When KRM was given to M. tuberculosis-infected mice at dosages of 5 to 20 mg/kg of body weight by gavage, one daily six times per week from day 1 after infection, it was much more efficacious than RMP against infections induced in mice by the RMP-sensitive Kurono strain, as measured by a reduction of rates of mortality, a reduction of the frequency and extent of gross lung lesions, histopathological changes in lung tissues, and a decrease in the bacterial loads in the lungs and spleens of infected mice. KRM also displayed significant therapeutic efficacy against infection induced by the RMP-resistant Kurata strain, while neither KRM nor RMP was efficacious against infection by the RMP-resistant Watanabe strain. In the case of infection with the Kurono strain, the efficacy of the drugs in prolonging the time of survival was in the order KRM, RBT, RMP. KRM was much more efficacious than RMP, when given at 1- to 4-week intervals. These findings suggest that KRM may be useful for the clinical treatment of tuberculosis contracted through RMP-sensitive strains, even when it is administered at long intervals.
PMCID: PMC162932  PMID: 8619585
8.  Timing of penicillin treatment influences the course of Streptococcus pneumoniae-induced middle ear inflammation. 
Penicillin treatment timing, using the chinchilla pneumococcal otitis media model, was investigated. Early treatment (when approximately 10(3) pneumococcal CFU/ml was present in middle ear fluid) significantly accelerated inflammatory-cell influx, whereas late treatment (with approximately 10(7) pneumococcal CFU/ml present in middle ear fluid) did not. Therefore, antiinflammatory interventions will be needed early in the course of inflammation.
PMCID: PMC162851  PMID: 7486944
9.  Contribution of the C-8 substituent of DU-6859a, a new potent fluoroquinolone, to its activity against DNA gyrase mutants of Pseudomonas aeruginosa. 
Inhibitory effects of five quinolones against DNA gyrases purified from four quinolone-resistant clinical isolates of Pseudomonas aeruginosa and the quinolone-susceptible strain PAO1 were examined. All of the quinolone-resistant strains tested were found to be DNA gyrase mutants. The 50% inhibitory concentrations (IC50s) of the quinolones for these DNA gyrases roughly correlated with their MICs. Interestingly, gyrase inhibition by DU-6859a was found to be significantly less affected by these mutations that inhibition by other currently available quinolones. To assess the enhanced activity shown by DU-6859a, the effects of quinolones with altered substituents at the N-1, C-7, and C-8 positions of the quinolone ring of DU-6859a were tested. Measurement of MICs for four DNA gyrase mutants and IC50s for their purified DNA gyrases showed that removal of the C-8 chlorine of DU-6859a significantly increased MICs and IC50s for DNA gyrase mutants. However, no deleterious effects were observed when either the fluorine on the cyclopropyl substituent at the N-1 position or the cyclopropyl ring at the C-7 substituent was removed. Moreover, removal of the C-8 chlorine also increased the MIC for 19 of 20 quinolone-resistant clinical isolates. Our results led to the conclusion that DU-6859a is much more active against quinolone-resistant clinical isolates of P. aeruginosa than other currently available quinolones, probably because of its strong inhibitory effects against mutant quinolone-resistant DNA gyrases, and that the C-8 chlorine is necessary for these potent effects.
PMCID: PMC162764  PMID: 7492087
10.  In vitro and in vivo antifungal activities of DU-6859a, a fluoroquinolone, in combination with amphotericin B and fluconazole against pathogenic fungi. 
DU-6859a is an investigational fluoroquinolone agent with potent bactericidal activity, but by itself it has no antifungal activity. When combined with amphotericin B (AmB), however, DU-6859a clearly enhanced the in vitro antifungal activity of AmB against Candida albicans, Candida tropicalis, Candida krusei, Candida glabrata, and Cryptococcus neoformans in microdilution checkerboard studies. Positive interactions of DU-6859a with AmB against Aspergillus fumigatus were dependent on the medium used; yeast nitrogen base supplemented with amino acids, ammonium sulfate, and 1% glucose was better for demonstrating synergism, while in RPMI 1640 medium, unexpected antagonism between the drugs occurred against three of the strains tested. In combination with fluconazole (Flu), DU-6859a increased the activity of Flu against C. albicans both in synthetic amino acid medium fungal and in supplemented yeast nitrogen base. An in vitro time-kill study revealed that DU-6859a combined with AmB significantly suppressed the regrowth of C. albicans compared with the suppression brought about by AmB used alone in a concentration-dependent fashion. Furthermore, in a model of C. albicans infection in mice, the fungal load in infected kidneys was significantly less in mice given the combination treatment of DU-6859a plus either AmB or Flu, and thus, the combination treatment resulted in prolonged survival of infected mice compared with treatment with either antifungal alone. The prolonged survival in mice given the combined treatment was also observed in mice with A. fumigatus infection, indicating that DU-6859a potentiated the actions of the antifungal agents in vivo as well as in vitro.
PMCID: PMC162773  PMID: 7492096
11.  Cloning of multidrug resistance gene pqrA from Proteus vulgaris. 
The multiple antibiotic resistance gene pqrA was cloned from the chromosomal DNA of a clinical isolate of Proteus vulgaris 881051 into Escherichia coli KY2563. The MICs of quinolones tetracycline, cephalosporin, and chloramphenicol for transformant strain DNS7020 were from 8 to 32 times higher than those for the parent strain, KY2563. The level of expression of outer membrane protein F (OmpF) by DNS7020 was lower than that of KY2563 but not as low as that of an OmpF-deficient control strain. The 1.4-kb fragment containing the pqrA gene had an open reading frame encoding a polypeptide of 122 amino acid residues with a molecular weight of about 14,000, which was consistent with the experimental value identified by the Maxicell method. The putative PqrA polypeptide showed significant amino acid sequence similarity to the E. coli proteins SoxS and MarA. These polypeptides are strongly conserved in predicted helix-turn-helix DNA binding domains. The MarA protein, which is responsible for multiple antibiotic resistance in E. coli, also decreases OmpF expression. Moreover, the SoxS protein, which is characterized as a superoxide response regulon of E. coli, has also been shown to increase resistance to many structurally unrelated antibiotics. The soxS gene increases superoxide dismutase levels in addition to decreasing OmpF expression. The expression level of superoxide dismutase with DNS7020 was about 1.5 times higher than that with KY2563. These findings suggest that the pqrA gene in P. vulgaris confers multidrug resistance in a way similar to that of the soxS and marA genes in E. coli.
PMCID: PMC162559  PMID: 7726514
12.  In vitro and in vivo antimycobacterial activities of a new quinolone, DU-6859a. 
Antimicrobial Agents and Chemotherapy  1994;38(12):2877-2882.
A new fluoroquinolone, DU-6859a, was studied for its in vitro and in vivo antimycobacterial activities. MIC determination by the agar dilution method with 7H11 medium revealed that DU-6859a had MICs at which 90% of M. kansasii (0.78 microgram/ml), M. marinum (1.56 micrograms/ml), M. scrofulaceum (1.56 micrograms/ml), M. fortuitum (0.39 microgram/ml), M. chelonae subsp. abscessus (6.25 micrograms/ml), and M. chelonae subsp. chelonae (1.56 micrograms/ml) were inhibited were 4 to 32 times lower than those of ofloxacin and sparfloxacin. The MICs of DU-6859a at which 90% of M. tuberculosis (0.2 microgram/ml) and M. avium-M. intracellulare complex (12.5 micrograms/ml each) were inhibited were comparable to those of sparfloxacin but were four- to eightfold lower than those of ofloxacin. Thus, DU-6859a possessed more potent in vitro activity than sparfloxacin and ofloxacin against most mycobacterial species. DU-6859a exerted significant efficacy against infections caused by M. intracellulare and M. chelonae subsp. abscessus induced in mice when it was given at a dose of 1 mg per mouse (ca. 50 mg/kg of body weight) in terms of reducing the frequency of occurrence and the degree of gross pulmonary or renal lesions and bacterial loads in the lungs, spleens, or kidneys. The efficacy of DU-6859a was greater than that of ofloxacin and was more pronounced against M. chelonae infections than against M. intracellulare infections.
PMCID: PMC188300  PMID: 7695276
13.  Comparison of inhibition of Escherichia coli topoisomerase IV by quinolones with DNA gyrase inhibition. 
Antimicrobial Agents and Chemotherapy  1994;38(11):2623-2627.
In order to examine the inhibitory activities of quinolones against topoisomerase IV, both subunits of this enzyme, ParC and ParE, were purified from Escherichia coli. The specific activity of topoisomerase IV decatenation was found to be more than five times greater than that of topoisomerase IV relaxation. Thus, the decatenation activity of topoisomerase IV seems the most relevant activity for use in studies of drug inhibition of this enzyme. Although topoisomerase IV was less sensitive to quinolones than DNA gyrase, the 50% inhibitory concentrations for decatenation were significantly lower than those for type I topoisomerases. Moreover, there was a positive correlation between the inhibitory activity against topoisomerase IV decatenation and that for DNA gyrase supercoiling. These results imply that topoisomerase IV could be a target for the quinolones in intact bacteria and that quinolones could inhibit not only supercoiling of DNA gyrase but also decatenation of topoisomerase IV when high concentrations of drug exist in bacterial cells.
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PMCID: PMC188252  PMID: 7872758
14.  Antimicrobial activity of DV-7751a, a new fluoroquinolone. 
Antimicrobial Agents and Chemotherapy  1993;37(10):2112-2118.
We compared the in vitro antibacterial activity of DV-7751a against gram-positive and -negative bacteria with those of quinolones currently available. MICs for 90% of the strains tested (MIC90s) against clinical isolates of methicillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis were 0.20, 0.39, 0.20, and 0.78 micrograms/ml, respectively. Moreover, MIC50s for DV-7751a against ofloxacin-resistant methicillin-resistant S. aureus were 4-, 8-, 16-, 32-, and 64-fold lower than those for tosufloxacin and sparfloxacin, levofloxacin, ofloxacin and fleroxacin, ciprofloxacin, and lomefloxacin, respectively. DV-7751a inhibited the growth of all strains of Streptococcus pneumoniae, Streptococcus pyogenes, and Peptostreptococcus spp. at 0.39, 0.39, and 0.78 micrograms/ml, respectively, and was 4- to > 16-fold more active against enterococci at the MIC90 level than the other quinolones tested. The activity of DV-7751a against Pseudomonas aeruginosa was roughly comparable to those of levofloxacin and sparfloxacin at the MIC90 level and was two- to fourfold less than that of ciprofloxacin. DV-7751a showed activity comparable to those of levofloxacin and ciprofloxacin against the other glucose-nonfermenting bacteria Haemophilus influenzae, Neisseria gonorrhoeae, and Moraxella catarrhalis (MIC90s of 0.025, 0.20, and 0.10 micrograms/ml, respectively). DV-7751a activity was not affected by medium, inoculum size, or the addition of human serum but was decreased under acidic conditions and in human urine, as were the other quinolones tested. Time-kill curve studies demonstrated the rapid bactericidal action of DV-7751a against S. aureus, S. pneumoniae, Escherichia coli, and P. aeruginosa. The frequency of spontaneous resistance to DV-7751a was less than or equal to those of the reference drugs. DV-7751a inhibited the supercoiling activity of DNA gyrases from S. aureus, E. coli, and P. aeruginosa at concentrations comparable to those of levofloxacin and sparfloxacin.
PMCID: PMC192237  PMID: 8257132
15.  Comparative antimycobacterial activities of the newly synthesized quinolone AM-1155, sparfloxacin, and ofloxacin. 
AM-1155 is a newly synthesized 6-fluoro-8-methoxy quinolone. We assessed its in vitro antimycobacterial activity using sparfloxacin (SPFX) and ofloxacin (OFLX) as comparison drugs. The MICs of these agents for various mycobacterial strains were determined by the agar dilution method with 7H11 medium. AM-1155 had lower MICs for 50 and 90% of tested strains of Mycobacterium kansasii, M. marinum, and M. fortuitum-M. chelonae complex than SPFX and OFLX, and the values for M. tuberculosis, M. scrofulaceum, and the M. avium-M. intracellulare complex were similar to those of SPFX and considerably lower than those of OFLX. In addition, the antimicrobial activity of AM-1155 against M. tuberculosis and M. intracellulare phagocytosed into murine peritoneal macrophages was compared with that of OFLX. AM-1155 (1 microgram/ml) inhibited the intracellular growth of both M. tuberculosis and M. intracellulare, whereas OFLX at the same concentration failed to show any such effect. Moreover, AM-1155 (10 micrograms/ml) exhibited a steady bactericidal action against M. tuberculosis, whereas OFLX at the same concentration had only a weak effect. AM-1155 (10 micrograms/ml) also inhibited the growth of M. intracellulare more effectively than OFLX.
PMCID: PMC187950  PMID: 8392307
16.  Therapeutic efficacy of the benzoxazinorifamycin KRM-1648 against experimental Mycobacterium avium infection induced in rabbits. 
The therapeutic efficacy of the benzoxazinorifamycin KRM-1648 was studied in an experimental rabbit infection system with avian Mycobacterium avium. The infected rabbits died from Yersin type infections, a peculiar type of experimental bovine tuberculosis characterized by a very rapid course, enlargement of the spleen and liver, and septic infection, 14 to 20 days after bacterial challenge, as evidenced by bacteremia and severe bacterial loads in the visceral organs. Histopathologic studies of the visceral organs of the infected rabbits revealed the development of numerous typical granulomatous lesions. This experimental rabbit infection system, features of which resemble certain features of disseminated M. avium complex infections in AIDS patients, was used to evaluate the therapeutic efficacy of KRM-1648, a newly synthesized benzoxazinorifamycin. KRM-1648 given orally at 25 and 50 mg/kg of body weight reduced the incidence and degree of bacteremia in infected rabbits and protected against subsequent death. Moreover, the drug allowed almost complete recovery of infected rabbits by week 7. KRM-1648 cleared infections in the lungs, liver, spleen, and kidneys and restored histopathologic features of healthy tissue in the visceral organs. KRM-1648 exhibited a more potent therapeutic effect against M. avium infection than rifampin and clarithromycin.
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PMCID: PMC187742  PMID: 7684214
17.  In vitro antimicrobial activity of benzoxazinorifamycin, KRM-1648, against Mycobacterium avium complex, determined by the radiometric method. 
MICs of a newly developed benzoxazinorifamycin derivative, KRM-1648, for Mycobacterium avium complex (MAC) were determined by the BACTEC 460 TB system and compared with those of other known antimicrobial agents. The radiometric method gave a fast, accurate, and reproducible MIC for each antimicrobial agent. MICs of KRM-1648 for 30 strains of MAC (10 strains each of M. avium isolated from AIDS and non-AIDS patients and of Mycobacterium intracellulare isolated from non-AIDS patients) were measured. The MICs, ranging from 0.004 to 0.0625 microgram/ml, were the lowest of all tested drugs, including rifampin, rifabutin, streptomycin, kanamycin, isoniazid, ethambutol, ofloxacin, ciprofloxacin, sparfloxacin, and clarithromycin. The MICs were 2 to 512 and 1 to 32 times lower than those of rifampin and rifabutin, respectively. With rifampin and ethambutol, there were some differences between the MICs for M. avium isolated from AIDS patients (American) and those for M. avium from non-AIDS patients (Japanese). Moreover, appreciable differences between the MICs of some drugs against M. avium and M. intracellulare isolated from non-AIDS patients were found. Many strains of M. avium were more susceptible to ofloxacin than M. intracellulare, but, conversely, M. avium was more resistant to rifampin, streptomycin, ethambutol, and clarithromycin than M. intracellulare.
PMCID: PMC187606  PMID: 8431020
18.  Antimicrobial activity of DU-6859, a new potent fluoroquinolone, against clinical isolates. 
DU-6859, (-)-7-[(7S)-amino-5-azaspiro(2,4)heptan-5-yl]-8-chloro-6- fluoro-1-[(1R,2R)-cis-2-fluoro-1-cyclopropyl]-1,4-dihydro-4-oxoquinol one-3- carboxylic acid, is a new fluoroquinolone with antibacterial activity which is significantly better than those of currently available quinolones. The MICs for 90% of methicillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis clinical isolates (MIC90s) were 0.1, 3.13, 0.1, and 0.39 microgram/ml, respectively. MIC50s of DU-6859 against quinolone-resistant, methicillin-resistant S. aureus were 8-, 32-, 64-, and 128-fold lower than those of tosufloxacin and sparfloxacin, ofloxacin and fleroxacin, ciprofloxacin, and lomefloxacin, respectively. DU-6859 inhibited the growth of all strains of Streptococcus pneumoniae and Streptococcus pyogenes at 0.1 and 0.2 microgram/ml, respectively, and was more active against enterococci than the other quinolones tested. Although the activity of DU-6859 against Pseudomonas aeruginosa was roughly comparable to that of ciprofloxacin at the MIC50 level, it was fourfold more active than ciprofloxacin at the MIC90 level. DU-6859 was also more active against other glucose-nonfermenting bacteria, Haemophilus influenzae, Moraxella catarrhalis, and Neisseria gonorrhoeae, than the other drugs tested. Strains of Bacteroides fragilis and Peptostreptococcus spp. were susceptible to DU-6859; MIC90s were 0.39 and 0.2 microgram/ml, respectively. DU-6859 generally showed activities twofold or greater than those of ciprofloxacin and the other drugs against almost all members of the family Enterobacteriaceae. The action of DU-6859 against the clinical isolates was bactericidal at concentrations near the MICs. DU-6859 activity was not affected by different media, pH, inoculum size, or human serum but was decreased in human urine.
PMCID: PMC191610  PMID: 1324647
19.  Chemotherapeutic efficacy of a newly synthesized benzoxazinorifamycin, KRM-1648, against Mycobacterium avium complex infection induced in mice. 
Newly synthesized benzoxazinorifamycin, KRM-1648, was studied for its in vivo anti-Mycobacterium avium complex (MAC) activities. When the MICs were determined by the agar dilution method with Middlebrook 7H11 agar medium, KRM-1648 exhibited similarly potent in vitro antimicrobial activities against the MAC isolated from AIDS and non-AIDS patients, indicating possible usefulness of KRM-1648 against AIDS-associated MAC infections. KRM-1648 exhibited potent therapeutic activity against experimental murine infections induced by M. intracellulare N-260 (virulent strain) and N-478, which has much weaker virulence. Similarly, KRM-1648 exhibited an excellent therapeutic efficacy against M. intracellulare infection induced in NK-cell-deficient beige mice (as a plausible model for AIDS-associated MAC infection), in which a much more progressed state of gross lesions and bacterial loads at the sites of infection were observed. When the infected beige mice were killed at weeks 4 and 8, obvious therapeutic efficacy was seen on the basis of reduction in the incidence and degree of lung lesions and bacterial loads in the lungs and spleen with infections due to M. intracellulare N-241, N-256, and N-260. In this case, the efficacy was the highest in N-260 infection, followed by strain N-241. When mice were observed until infection-induced death, survival time of the infected beige mice was found to be prolonged by KRM treatment. However, KRM-1648 was not efficacious in suppressing the progression of pulmonary lesions and the increase in bacterial loads at the sites of infection, including lungs and spleen, at the late phase of infection. This may imply some difficulty with chemotherapy for AIDS-associated MAC infection, even with KRM-1648 treatment, which has excellent in vitro and in vivo anti-MAC activities, as shown in present study.
PMCID: PMC188446  PMID: 1605603
20.  Inhibition by quinolones of DNA gyrase from Staphylococcus aureus. 
In order to clarify the mechanism of action of quinolones against Staphylococcus aureus, the subunit A and B proteins of DNA gyrase were separately purified from a crude extract of S. aureus FDA 209-P. The reconstituted enzyme exhibited ATP-dependent DNA supercoiling activity. The inhibitory effects of quinolones on the supercoiling activity of the purified enzyme were measured by the quantitative electrophoresis method (17), using plasmid DNA, pBR322 or pUB110, as substrates and expressed as the 50% inhibitory concentrations (IC50s). The IC50s of ofloxacin, DR-3355 (l-ofloxacin), ciprofloxacin, tosufloxacin, sparfloxacin, and DS-4524, a new quinolone derivative, for pBR322 were 63.0, 37.8, 30.5, 46.0, 28.5, and 3.2 micrograms/ml, respectively. These values were closely correlated with antibacterial activity (MIC), with correlation coefficients of 0.953 for pBR322 and 0.938 for pUB110. These results indicate that, in S. aureus, as in gram-negative bacteria, DNA gyrase is likely to be a major target enzyme of quinolones.
PMCID: PMC245197  PMID: 1656864
21.  In vitro antimycobacterial activities of newly synthesized benzoxazinorifamycins. 
Newly synthesized rifamycin derivatives, KRM-1648, KRM-1657, KRM-1668, KRM-1686, and KRM-1687, having the chemical structures of 3'-hydroxy-5'-(4-alkylpiperazinyl)-benzoxazinorifamycins (alkyl residues: isobutyl, propyl, sec-butyl, sec-butyl [R configuration], and sec-butyl [S configuration], respectively), were studied for their in vitro antimycobacterial activities. Representative (KRM-1648) MICs for 90% of the strains tested, determined by the agar dilution method on 7H11 medium, of various pathogenic mycobacteria (9 species, 174 strains) were as follows (in micrograms per milliliter): Mycobacterium tuberculosis (rifampin [RMP]-susceptible strains), less than or equal to 0.0125; M. tuberculosis (RMP-resistant strains), 12.5; M. kansasii, 0.05; M. marinum, less than or equal to 0.0125; M. scrofulaceum, 0.1; M. avium, 1.56; M. intracellulare, 0.1; M. fortuitum, greater than 100; and M. chelonae subsp. abscessus and M. chelonae subsp. chelonae, greater than 100. These values are more than 64 times lower than those of RMP, except for the values against RMP-resistant M. tuberculosis (8 times lower) and those against rapid growers, including M. fortuitum and M. chelonae (the same as those of RMP). The other derivatives had similar levels of in vitro activity against these mycobacteria. When murine peritoneal macrophages in which M. intracellulare was phagocytosed in vitro were cultured in the presence of the benzoxazinorifamycins (1 microgram/ml), much more rapid killing of the organisms ingested in the macrophages was seen compared with when the same amount of RMP was added to the medium. The addition of benzoxazinorifamycins at the concentration of 0.05 micrograms/ml caused more marked suppression of intracellular growth of the organisms compared with addition of RMP. KRM-1648 and KRM-1657 inhibited intracellular growth of M. tuberculosis, and their efficacies were much greater than that of RMP.
PMCID: PMC245047  PMID: 2039206
22.  Significance of the methyl group on the oxazine ring of ofloxacin derivatives in the inhibition of bacterial and mammalian type II topoisomerases. 
A study was made of the correlation between the in vitro inhibitory effects of several quinolones, including four ofloxacin derivatives, on bacterial DNA gyrase from Escherichia coli KL-16 and on topoisomerase II from fetal calf thymus. No correlation was observed between the inhibitions of DNA gyrase activity and topoisomerase II activity. On the other hand, the inhibitory effects of these quinolones against topoisomerase II were closely correlated with their inhibition of cell growth. Furthermore, among the oxazine derivatives tested, the derivative with a methyl group at position 3 in an S configuration showed the highest activity against DNA gyrase and derivatives without a methyl group on the oxazine ring were more potent against topoisomerase II than those with a methyl group. Among these derivatives, DR-3355, the S isomer of ofloxacin, showed the highest activity against DNA gyrase and low activity against topoisomerase II. These results indicate that the methyl group on the oxazine ring plays an important role in the inhibitory activities of ofloxacin derivatives for these enzymes.
PMCID: PMC244997  PMID: 1850968
23.  Effect of ofloxacin combined with Lactobacillus casei against Mycobacterium fortuitum infection induced in mice. 
Multiple injections of ofloxacin (subcutaneous or oral) in combination with a Lactobacillus casei preparation, LC9018 (subcutaneous), in mice infected intravenously with Mycobacterium fortuitum led to a marked delay in the incidence of spinning disease, a lowered incidence of gross renal lesions, and an increase in the rate of elimination of organisms from the kidneys. This indicates synergism in the therapeutic efficacy of the two agents. When the antimicrobial ability of peritoneal macrophages (M phi s) against M. fortuitum was measured in medium with or without ofloxacin, growth of the organisms was more markedly inhibited by ofloxacin in LC9018-induced M phi s than in normal M phi s. Synergism in the therapeutic activity of oxfloxacin plus LC9018 is assumed to be mediated in part by host M phi s, that is, functional stimulation of host M phi s by LC9018 treatment results in the synergistic effects of the two agents.
PMCID: PMC171656  PMID: 2344170
24.  Inhibitory effects of quinolones on DNA gyrase of Escherichia coli and topoisomerase II of fetal calf thymus. 
Antimicrobial Agents and Chemotherapy  1989;33(10):1816-1818.
The in vitro inhibitory effects of quinolones on the bacterial DNA gyrase of Escherichia coli KL-16 and topoisomerase II of fetal calf thymus were compared. All the quinolones tested required higher concentrations to inhibit the topoisomerase II than to inhibit the DNA gyrase, and no correlation existed among their inhibitory activities against both enzymes. However, there was a large difference among the quinolones in their selectivities between the bacterial enzyme and its eucaryotic counterpart. The selectivity of ofloxacin was highest, and the selectivities of CI-934 and nalidixic acid were lowest.
PMCID: PMC172762  PMID: 2556080
25.  Quinolone resistance in clinical isolates of Serratia marcescens. 
The uptakes of norfloxacin by quinolone-resistant and -susceptible strains of Serratia marcescens were almost the same and 50% inhibitory concentrations for DNA gyrase and the MICs of quinolones were correlated, suggesting that DNA gyrase alterations are the basis of quinolone resistance.
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PMCID: PMC172536  PMID: 2546493

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