Uptake of Ozenoxacin and Other Quinolones in Gram-Positive Bacteria

The big problem of antimicrobial resistance is that it requires great efforts in the design of improved drugs which can quickly reach their target of action. Studies of antibiotic uptake and interaction with their target it is a key factor in this important challenge. We investigated the accumulation of ozenoxacin (OZN), moxifloxacin (MOX), levofloxacin (LVX), and ciprofloxacin (CIP) into the bacterial cells of 5 species, including Staphylococcus aureus (SA4-149), Staphylococcus epidermidis (SEP7602), Streptococcus pyogenes (SPY165), Streptococcus agalactiae (SAG146), and Enterococcus faecium (EF897) previously characterized.The concentration of quinolone uptake was estimated by agar disc-diffusion bioassay. Furthermore, we determined the inhibitory concentrations 50 (IC50) of OZN, MOX, LVX, and CIP against type II topoisomerases from S. aureus.The accumulation of OZN inside the bacterial cell was superior in comparison to MOX, LVX, and CIP in all tested species. The accumulation of OZN inside the bacterial cell was superior in comparison to MOX, LVX, and CIP in all tested species. The rapid penetration of OZN into the cell was reflected during the first minute of exposure with antibiotic values between 190 and 447 ng/mg (dry weight) of bacteria in all strains. Moreover, OZN showed the greatest inhibitory activity among the quinolones tested for both DNA gyrase and topoisomerase IV isolated from S. aureus with IC50 values of 10 and 0.5 mg/L, respectively. OZN intracellular concentration was significantly higher than that of MOX, LVX and CIP. All of these features may explain the higher in vitro activity of OZN compared to the other tested quinolones.

A novel class of fast-acting antimalarial agents: Substituted 15-membered azalides

Background and Purpose

Efficacy of current antimalarial treatments is declining as a result of increasing antimalarial drug resistance, so new and potent antimalarial drugs are urgently needed. Azithromycin, an azalide antibiotic, was found useful in malaria therapy, but its efficacy in humans is low.

Experimental Approach

Four compounds belonging to structurally different azalide classes were tested and their activities compared to azithromycin and chloroquine. in vitro evaluation included testing against sensitive and resistant Plasmodium falciparum, cytotoxicity against HepG2 cells, accumulation and retention in human erythrocytes, antibacterial activity, and mode of action studies (delayed death phenotype and haem polymerization). in vivo assessment enabled determination of pharmacokinetic profiles in mice, rats, dogs, and monkeys and in vivo efficacy in a humanized mouse model.

Key Results

Novel fast‐acting azalides were highly active in vitro against P. falciparum strains exhibiting various resistance patterns, including chloroquine‐resistant strains. Excellent antimalarial activity was confirmed in a P. falciparum murine model by strong inhibition of haemozoin‐containing trophozoites and quick clearance of parasites from the blood. Pharmacokinetic analysis revealed that compounds are metabolically stable and have moderate oral bioavailability, long half‐lives, low clearance, and substantial exposures, with blood cells as the preferred compartment, especially infected erythrocytes. Fast anti‐plasmodial action is achieved by the high accumulation into infected erythrocytes and interference with parasite haem polymerization, a mode of action different from slow‐acting azithromycin.

Conclusion and Implications

The hybrid derivatives described here represent excellent antimalarial drug candidates with the potential for clinical use in malaria therapy.

Mutant prevention concentration of ozenoxacin for quinolone-susceptible or -resistant Staphylococcus aureus and Staphylococcus epidermidis

Ozenoxacin (OZN) belongs to a new generation of non-fluorinated quinolones for the topical treatment of skin infections which has shown to be effective in the treatment of susceptible and resistant Gram-positive cocci. The mutant prevention concentration (MPC) of ozenoxacin, levofloxacin and ciprofloxacin was determined in quinolone-susceptible and -resistant strains including methicillin-susceptible S. aureus, methicillin-resistant S. aureus, methicillin-susceptible S. epidermidis and methicillin-resistant S. epidermidis with different profile of mutation in the quinolone resistance determining regions (QRDR). The MPC value of OZN for the methicillin-susceptible S. aureus strain susceptible to quinolones, without mutations in QRDR, was 0.05 mg/L, being 280-fold lower than that observed with ciprofloxacin and levofloxacin. In methicillin-susceptible and–resistant S. aureus strains with mutations in the gyrA or/and grlA genes the MPC of OZN went from 0.1 to 6 mg/L, whereas the MPC of levofloxacin and ciprofloxacin was > 50 mg/L for the same strains. For methicillin-susceptible and–resistant S. epidermidis the results were similar to those abovementioned for S. aureus. According to our results, the MPC of OZN was far below the quantity of ozenoxacin achieved in the epidermal layer, suggesting that the in vivo selection of mutants, if it occurs, will take place at low frequency. Ozenoxacin is an excellent candidate for the treatment of bacterial infections caused by susceptible and quinolone-resistant staphylococci isolated usually from skin infections.

Microbiological profile of ozenoxacin

Aim: To explore the antibacterial spectrum of ozenoxacin and compare its in vitro activity with that of other antibacterial agents. Materials & methods: In 2010, 10,054 isolates were collected from 128 centers worldwide. Minimum inhibitory concentrations against Gram-positive and Gram-negative isolates were determined for 23 and 13 antibacterial agents, respectively. Results: Ozenoxacin exhibited high in vitro activity against susceptible, and methicillin- or levofloxacin-resistant, Gram-positive bacteria. Ozenoxacin was one or two dilutions less active against Enterobacteriaceae isolates, except for Escherichia coli, than other quinolones. Conclusion: Ozenoxacin is a potent antimicrobial agent mainly against susceptible and resistant strains of Gram-positive isolates (staphylococci and streptococci), and shows activity against some Gram-negative isolates.

Studies on articular and general toxicity of orally administered ozenoxacin in juvenile rats and dogs

AIM

Ozenoxacin is a nonfluorinated quinolone antibacterial approved for topical treatment of impetigo. Because quinolones have known chondrotoxic effects in juvenile animals, the potential toxicity of ozenoxacin was assessed in preclinical studies.

MATERIALS & METHODS

Ozenoxacin or ofloxacin (300 mg/kg/day for 5 days, for each compound) was orally administered to juvenile rats, and oral ozenoxacin (10-100 mg/kg/day for 14 days) was administered to juvenile dogs.

RESULTS

In juvenile rats, ozenoxacin showed no chondrotoxicity, whereas ofloxacin produced typical quinolone-induced lesions in articular cartilage in three of ten rats. Oral ozenoxacin administration to juvenile dogs showed no chondrotoxicity or toxicologically relevant findings in selected target organs.

CONCLUSION

Ozenoxacin was generally well-tolerated in juvenile rats and dogs, with no evidence of quinolone-induced arthropathy.

Comparative in vitro antibacterial activity of ozenoxacin against Gram-positive clinical isolates

AIM

To compare the in vitro activity of the anti-impetigo agent, ozenoxacin, and other antimicrobial agents against Gram-positive clinical isolates from skin and soft tissue infections.

MATERIALS & METHODS

Isolates were collected in two studies: 1097 isolates from 49 centers during 2009-2010 and 1031 isolates from ten centers during 2014. Minimum inhibitory concentrations were determined for 18 and 11 antimicrobials in these studies, respectively, using standard broth microdilution methods. Isolates were stratified by species and methicillin susceptibility/resistance and/or levofloxacin susceptibility/nonsusceptibility status.

RESULTS

Ozenoxacin exhibited high in vitro activity against Staphylococcus aureus and coagulase-negative staphylococci isolates in both studies. Ozenoxacin was also highly active against Streptococcus pyogenes and Streptococcus agalactiae isolates.

CONCLUSION

Ozenoxacin is a potent antimicrobial agent against staphylococci and streptococci.

In vitro selection of mutants resistant to ozenoxacin compared with levofloxacin and ciprofloxacin in Gram-positive cocci

OBJECTIVES

To determine the frequency of selecting mutants resistant to ozenoxacin, a des-fluoro-(6)-quinolone active against pathogens involved in skin and skin structure infections, compared with levofloxacin and ciprofloxacin in quinolone-susceptible and -resistant Gram-positive cocci.

METHODS

Forty-nine quinolone-susceptible and -resistant Gram-positive cocci strains with different profiles of mutations in the quinolone resistance-determining region (QRDR) were examined to determine the frequency of selecting mutants resistant to ozenoxacin compared with levofloxacin and ciprofloxacin. MICs and mutations in the QRDR were determined by standard broth microdilution and PCR amplification and sequencing, respectively.

RESULTS

The mean resistance rates were 3.8 × 10(-9) (range <9 × 10(-11)-1 × 10(-8)) for ozenoxacin, 9.7 × 10(-9) (range <1.1 × 10(-11)-4.2 × 10(-8)) for levofloxacin and 1.2 × 10(-8) (range <1.6 × 10(-10)-2.6 × 10(-7)) for ciprofloxacin. Spontaneous mutants resistant to ozenoxacin showed lower MICs (≤ 16 mg/L) than mutants resistant to levofloxacin and ciprofloxacin (≤ 512 mg/L). Additional mutations were observed only in ParC at Ser-80 in Staphylococcus spp., Ser-79 in Streptococcus agalactiae and Asp-83 and Ser-89 in Streptococcus pyogenes.

CONCLUSIONS

The probability of ozenoxacin selecting spontaneous resistant mutants in quinolone-susceptible and -resistant strains with pre-existing mutations in the QRDR is low, supporting the potential utility of ozenoxacin as a therapeutic alternative in the treatment of skin infections caused by strains highly resistant to quinolones.

Characterization of variables that may influence ozenoxacin in susceptibility testing, including MIC and MBC values

Ozenoxacin is a new des-fluoro-(6)-quinolone active against pathogens involved in skin and skin structure infections, including Gram-positives resistant to fluoroquinolones. The in vitro bacteriostatic and bactericidal activity of ozenoxacin, ciprofloxacin, and levofloxacin was studied against 40 clinical isolates and 16 ATCC quality control strains under different test conditions, including cation supplementation, pH, inoculum size, inoculum preparation, incubation time, human serum, and CO2 incubation. The activity of ozenoxacin was unaffected by cation test medium supplementation, inoculum preparation, incubation time, and the increasing CO2 environment. On the contrary, ozenoxacin activity decreased by high inoculum (10(7) CFU/mL), increased presence of human serum in the medium, and increased pH. The last effect was different for ciprofloxacin and levofloxacin, which decreased activity when pH decreased. The bactericidal mode of action of ozenoxacin and control drugs was consistently maintained (MBC/MIC ratios ≤4) in spite of variations of their activity under different test conditions.

Thermodynamic concepts in the study of microbial populations: age structure in Plasmodium falciparum infected red blood cells

Variability is a hallmark of microbial systems. On the one hand, microbes are subject to environmental heterogeneity and undergo changeable conditions in their immediate surroundings. On the other hand, microbial populations exhibit high cellular diversity. The relation between microbial diversity and variability of population dynamics is difficult to assess. This connection can be quantitatively studied from a perspective that combines in silico models and thermodynamic methods and interpretations. The infection process of Plasmodium falciparum parasitizing human red blood cells under laboratory cultivation conditions is used to illustrate the potential of Individual-based models in the context of predictive microbiology and parasitology. Experimental data from several in vitro cultures are compared to the outcome of an individual-based model and analysed from a thermodynamic perspective. This approach allows distinguishing between intrinsic and external constraints that give rise to the diversity in the infection forms, and it provides a criterion to quantitatively define transient and stationary regimes in the culture. Increasing the ability of models to discriminate between different states of microbial populations enhances their predictive capability which finally leads to a better the control over culture systems. The strategy here presented is of general application and it can substantially improve modelling of other types of microbial communities.

Potent antimalarial 4-pyridones with improved physico-chemical properties

Antimalarial 4-pyridones are a novel class of inhibitors of the plasmodial mitochondrial electron transport chain targeting Cytochrome bc1 (complex III). In general, the most potent 4-pyridones are lipophilic molecules with poor solubility in aqueous media and low oral bioavailability in pre-clinical species from the solid dosage form. The strategy of introducing polar hydroxymethyl groups has enabled us to maintain the high levels of antimalarial potency observed for other more lipophilic analogues whilst improving the solubility and the oral bioavailability in pre-clinical species.

Improved murine model of malaria using Plasmodium falciparum competent strains and non-myelodepleted NOD-scid IL2Rgammanull mice engrafted with human erythrocytes

Murine models of Plasmodium falciparum malaria may become crucial tools in drug discovery. Here we show that non-myelodepleted NOD-scid IL2Rgamma(null) mice engrafted with human erythrocytes support an infectious burden up to tenfold higher than that supported by engrafted NOD-scid beta2microglobulin(null) mice. The new model was validated for drug discovery and was used to assess the therapeutic efficacy of 4-pyridones, selective inhibitors of P. falciparum cytochrome bc1.

Quantitative measurement of Plasmodium-infected erythrocytes in murine models of malaria by flow cytometry using bidimensional assessment of SYTO-16 fluorescence

Flow cytometry is a powerful tool for measuring parasitemias in murine malaria models used to test new antimalarials. Measurement of the emission of the nonpermeable nucleic acid dye YOYO-1 (at 530 and 585 nm after excitation at 488 nm) allowed the unambiguous detection of low parasitemias (> or =0.01%) but required prolonged fixation and permeabilization of the sample. Thus, we tested whether this issue could be overcome by use of the cell-permeant dye SYTO-16 with this same bidimensional method. Blood samples from CD1 mice infected with Plasmodium yoelii, Plasmodium vinckei, or Plasmodium chabaudi or from NOD(scidbeta2m-/-) engrafted with human erythrocytes and infected with P. falciparum were stained with SYTO-16 in the presence or absence of TER-119 mAb (for engrafted mice) in 96-well plate format and acquired in Trucount tubes. Bidimensional analysis with SYTO-16 was quantitatively equivalent to YOYO-1. Moreover, by combining SYTO-16 with the use of TER-119-PE antimouse erythrocyte mAb and Trucount tubes, the measurement of the concentration of P. falciparum-infected erythrocytes over a range of five orders of magnitude was achieved. Bidimensional analysis using SYTO-16 can be used to accurately measure the concentration of Plasmodium spp.-infected erythrocytes in mice without complex sample preparation.

A murine model of falciparum-malaria by in vivo selection of competent strains in non-myelodepleted mice engrafted with human erythrocytes

To counter the global threat caused by Plasmodium falciparum malaria, new drugs and vaccines are urgently needed. However, there are no practical animal models because P. falciparum infects human erythrocytes almost exclusively. Here we describe a reliable falciparum murine model of malaria by generating strains of P. falciparum in vivo that can infect immunodeficient mice engrafted with human erythrocytes. We infected NOD(scid/beta2m-/-) mice engrafted with human erythrocytes with P. falciparum obtained from in vitro cultures. After apparent clearance, we obtained isolates of P. falciparum able to grow in peripheral blood of engrafted NOD(scid/beta2m-/-) mice. Of the isolates obtained, we expanded in vivo and established the isolate Pf3D7(0087/N9) as a reference strain for model development. Pf3D7(0087/N9) caused productive persistent infections in 100% of engrafted mice infected intravenously. The infection caused a relative anemia due to selective elimination of human erythrocytes by a mechanism dependent on parasite density in peripheral blood. Using this model, we implemented and validated a reproducible assay of antimalarial activity useful for drug discovery. Thus, our results demonstrate that P. falciparum contains clones able to grow reproducibly in mice engrafted with human erythrocytes without the use of myeloablative methods.

Synthesis and structure-activity relationships of 4-pyridones as potential antimalarials

A series of diaryl ether substituted 4-pyridones have been identified as having potent antimalarial activity superior to that of chloroquine against Plasmodium falciparum in vitro and murine Plasmodium yoelii in vivo. These were derived from the anticoccidial drug clopidol through a systematic study of the effects of varying the side chain on activity. Relative to clopidol the most active compounds show >500-fold improvement in IC50 for inhibition of P. falciparum in vitro and about 100-fold improvement with respect to ED50 against P. yoelii in mice. These compounds have been shown elsewhere to act selectively by inhibition of mitochondrial electron transport at the cytochrome bc1 complex.

Improvement of detection specificity of Plasmodium-infected murine erythrocytes by flow cytometry using autofluorescence and YOYO-1

BACKGROUND

Microscopic analysis of blood smears is currently the most frequently used method to measure parasitemias in experiments of drug efficacy in murine models of malaria. However, it is subjective and labour intensive, which preclude its utilization in large-scale evaluation programs. Flow cytometry is an alternative method, but due to the limited specificity achieved with the currently available techniques, it has not been widely used in murine models of malaria during preclinical evaluation. We describe a new flow cytometric method based on the differences of autofluorescence and DNA content measured after staining with YOYO-1 that are observed in infected erythrocytes compared with noninfected erythrocytes.

METHODS

Samples of blood from Plasmodium yoelii-infected animals were fixed with glutaraldehyde, incubated with RNAase, and stained with YOYO-1 in 96-well plate format. After acquisition, erythrocytes gated in logarithmic side/scatter plots were analyzed in bidimensional FL-2/YOYO-1 plots in comparison with unidimensional YOYO-1 analysis.

RESULTS

The infected erythrocytes showed a characteristic pattern of staining different from that of noninfected erythrocytes. In routine evaluation, the limit of sensitivity was 0.01% and the measurements of parasitemia were linear at parasitemias above 0.1%. Interestingly, using this approach, infected reticulocytes could be differentiated from infected normocytes.

CONCLUSIONS

The method described is robust, increases the specificity and sensitivity of detection in routine testing, and is especially well suited for detection of low parasitemias in murine models of malaria.

High seroprevalence of Pneumocystis infection in Spanish children

Pneumocystis infection occurs worldwide, and most individuals test seropositive for Pneumocystis early in childhood. Little is known about the epidemiology of this infection in western Europe. The seroprevalence of Pneumocystis infection in 233 Spanish children was determined in a community study by immunoblot analysis of sera. The overall seroprevalence was 73%, with an age-related increase from 52% at 6 years to 66% at 10 years and 80% at 13 years. The data indicated a high seroprevalence of Pneumocystis infection in healthy Spanish children, thereby demonstrating that this pathogen is widespread in southern Spain.

Therapeutic efficacies of GW471552 and GW471558, two new azasordarin derivatives, against pneumocystosis in two immunosuppressed-rat models

Two new azasordarins, GW471552 and GW471558, were studied in vivo for treatment of Pneumocystis carinii pneumonia. In the Wistar rat spontaneous pneumonia model, both azasordarins significantly reduced the number of P. carinii cysts per gram of lung homogenate when administered at 1 mg/kg of body weight twice a day for 10 days. In a nude rat inoculation model, both compounds showed therapeutic efficacy at 0.25 mg/kg twice a day for 10 days.

Antifungal activities of two new azasordarins, GW471552 and GW471558, in experimental models of oral and vulvovaginal candidiasis in immunosuppressed rats

Sordarins constitute a new class of antifungal agents with a novel mechanism of action involving the selective inhibition of fungal protein synthesis. A further evolution of this class of antifungals has led to a new family of sordarin derivatives called azasordarins. The therapeutic efficacies of two new azasordarins, GW471552 and GW471558, were studied in experimental models of oral and vulvovaginal candidiasis in immunosuppressed rats. In all cases rats were immunosuppressed with dexamethasone in the drinking water. Oral candidiasis was established by inoculating 0.1 ml of a yeast suspension containing 5 x 10(8) cells of Candida albicans 4711E with a cotton swab on three alternate days. Vulvovaginal candidiasis was established in ovariectomized and estrus-induced rats by intravaginal inoculation of 10(7) CFU of C. albicans 4711E in 0.1 ml of saline. GW471552 and GW471558 were administered at 1, 5, and 10 mg/kg of body weight via the subcutaneous route. In oral candidiasis, azasordarins were administered each 8 h for 7 consecutive days, while in vaginal candidiasis the compounds were given each 4 h for 3 consecutive days. Antifungal activity of azasordarins was assessed by colony counts and by histological examination 1 day after treatment. In the oral infection model, GW471552 and GW471558 administered at 5 mg/kg significantly reduced (P < 0.05) the number of CFU of C. albicans compared with untreated controls. In addition, GW471552 and GW471558 given at 10 mg/kg eradicated C. albicans from the oral cavities of 100% of infected animals. Against vulvovaginal infection, both compounds showed significant therapeutic efficacy. GW471552 was able to eradicate the vaginal fungal burden at a dose of 10 mg/kg, and it significantly reduced the number of CFU of C. albicans in vaginas of rats treated with a dose of 5 mg/kg (P < 0.05). GW471558 showed greater efficacy, eradicating the fungal burden of 100% of infected rats at a dose of 5 mg/kg and significantly reducing (P < 0.05) the C. albicans vaginal counts even at a dose of 1 mg/kg. In both therapeutic efficacy studies, the histological findings confirmed the microbiological results. The experimental results presented show that the tested azasordarins are effective against oral and vulvovaginal candidiasis in immunosuppressed rats and could be promising antifungal agents for use in humans.

Antifungal activities and cytotoxicity studies of six new azasordarins

GW 471552, GW 471558, GW 479821, GW 515716, GW 570009, and GW 587270 are members of a new family of sordarin derivatives called azasordarins. The in vitro activities of these compounds were evaluated against clinical isolates of yeasts, including Candida albicans, Candida non-albicans, and Cryptococcus neoformans strains. Activities against Pneumocystis carinii, Aspergillus spp., less common molds, and dermatophytes were also investigated. Azasordarin derivatives displayed significant activities against the most clinically important Candida species, with the exception of C. krusei. Against C. albicans, including fluconazole-resistant strains, MICs at which 90% of the isolates tested are inhibited (MIC(90)s) were 0.002 microg/ml with GW 479821, 0.015 microg/ml with GW 515716 and GW 587270, and 0.06 microg/ml with GW 471552, GW 471558, and GW 570009. The MIC(90)s of GW 471552, GW 471558, GW 479821, GW 515716, GW 570009, and GW 587270 were 0.12, 0.12, 0.03, 0.06, 0.12, and 0.06 microg/ml, respectively, against C. tropicalis and 4, 0.25, 0.06, 0.25, 0.5, and 0.5 microg/ml, respectively, against C. glabrata. In addition, some azasordarin derivatives (GW 479821, GW 515716, GW 570009, and GW 58720) were active against C. parapsilosis, with MIC(90)s of 2, 4, 4, and 1 microg/ml, respectively. The compounds were extremely potent against P. carinii, showing 50% inhibitory concentrations of <or=0.001 microg/ml. However Cryptococcus neoformans was resistant to all compounds tested (MIC > 16 microg/ml). These azasordarin derivatives also showed significant activity against emerging fungal pathogens, which affect immunocompromised patients, such as Rhizopus arrhizus, Blastoschizomyces capitatus, and Geotrichum clavatum. Against these organisms, the MICs of GW 587270 ranged from 0.12 to 1 microg/ml, those of GW 479821 and GW 515716 ranged from 0.12 to 2 microg/ml, and those of GW 570009 ranged from 0.12 to 4 microg/ml. Against Fusarium oxysporum, Scedosporium apiospermum, Absidia corymbifera, Cunninghamella bertholletiae, and dermatophytes, GW 587270 was the most active compound, with MICs ranging from 4 to 16 microg/ml. Against Aspergillus spp., the MICs of the compounds tested were higher than 16 microg/ml. The in vitro selectivity of azasordarins was investigated by cytotoxicity studies performed with five cell lines and primary hepatocytes. Concentrations of compound required to achieve 50% inhibition of the parameter considered (Tox(50)s) of GW 570009, GW 587270, GW 479281, and GW 515716 in the cell lines ranged from 60 to 96, 49 to 62, 24 to 36, and 16 to 38 microg/ml, respectively. The cytotoxicity values of GW 471552 and GW 471558 were >100 microg/ml for all cell lines tested. Tox(50)s on hepatocytes were in the following order: GW 471558 > GW 471552 > GW 570009 > GW 587270 > GW 515716 > GW 479821, with values ranging from higher than 100 microg/ml to 23 microg/ml. The cytotoxicity results obtained with fully metabolizing rat hepatocytes were in total agreement with those obtained with cell lines. In summary, the in vitro activities against important pathogenic fungi and the selectivity demonstrated in mammalian cell lines justify additional studies to determine the clinical usefulness of azasordarins.

Antibacterial activities and pharmacokinetics of E-4767 and E-5065, two new 8-chlorofluoroquinolones with a 7-azetidin ring substituent

E-4767 [(-)-7-[3-(R)-amino-2-(S)-methyl-1-azetidinyl]-8-chloro-1-cyclopropyl-1,4-dihydro-6-fluoro-4-oxo-3-quinolinecarboxylic acid] and E-5065 [(-)-7-(3-amino-1-azetidinyl)-8-chloro-1-cyclopropyl-1,4-dihydro-6-fluoro-4-oxo-3-quinolinecarboxylic acid] are two new chlorofluoroquinolones with an azetidine moiety at position 7. Their in vitro activities were evaluated in comparison with those of ciprofloxacin, ofloxacin, fleroxacin, and tosufloxacin, while ciprofloxacin was used as a reference for in vivo studies. Against gram-positive organisms, E-4767 and E-5065 were, in general, eight- and fourfold more active than tosufloxacin, which is the most potent of the reference compounds. E-4767 and E-5065 were also more potent than the reference compounds against all species of enteric bacteria tested. The MICs of E-4767 and E-5065 at which 90% of the isolates tested were inhibited (MIC(90)s) were 0.007 to 0.5 microg/ml and 0.03 to 2 microg/ml, respectively, for gram-positive organisms and <or=0.003 to 0.06 microg/ml and 0.007 to 0.12 microg/ml, respectively, for members of the family Enterobacteriaceae except Serratia marcescens and Providencia spp. (MIC(90)s of E-4767 and E-5065 for these species were <or=0.5 microg/ml and <or=2 microg/ml, respectively). For Pseudomonas aeruginosa both compounds had a MIC(90) of 0.5 microg/ml. E-4767 and E-5065 were 356- and 32-fold more potent than ciprofloxacin against Bacteroides spp., and their MIC(90)s for Clostridium spp. were 0.25 and 0.5 microg/ml, respectively. Both products showed a remarkable reduction of activity when the pH was below 4.8 and, in general, were less active in the presence of 5 or 10 mM Mg(2+). The presence of horse serum or human urine (pH 7.2) decreased the activity of E-4767 and E-5065 only two- to fourfold more than the activity observed in broth. After an oral dose of 50 mg/kg of body weight, the maximum levels in serum (the maximum concentration of drug in serum was reached 30 min postadministration) of E-4767 and E-5065 were approximately threefold higher than that of ciprofloxacin. The area under the concentration-time curve from 0 to 4 h for ciprofloxacin was about two- and fourfold lower than that for E-4767 and E-5065, respectively. These two new chlorofluoroquinolones were as effective as or more effective than ciprofloxacin against all experimental infections evaluated, not only against gram-negative bacteria, such as Escherichia coli or P. aeruginosa, but also against gram-positive pathogens, such as Staphylococcus aureus or Streptococcus pneumoniae. E-4767 was the most effective compound, with a 50% effective dose (ED(50)) of <or=17 mg/kg for all strains tested except ciprofloxacin-resistant S. aureus strains. The ED(50) of E-4767 for these strains was <or=47.5 mg/kg. Against gram-positive experimental infections, the ED(50) values of E-4767 were 3- to 14-fold lower than those of E-5065 and up to 25 times lower than those of ciprofloxacin.

Animal pharmacokinetics and interspecies scaling of sordarin derivatives following intravenous administration

Sordarin derivatives constitute a new group of synthetic antifungal agents that selectively inhibit fungal protein synthesis. They have demonstrated in vitro activity against the most important fungal pathogens, both yeast and filamentous. This new family of compounds has also shown in vivo activity against murine Candida albicans, Histoplasma capsulatum, and Coccidioides immitis experimental infections, as well as against Pneumocystis carinii pneumonia in rats. After intravenous dosing in animals, both the area under the concentration-time curve and the elimination half-life were highest in Cynomolgus monkeys, followed by those in rats, mice, and rabbits. The volume of distribution at steady state for sordarin derivatives was similar in all species tested. The clearance in rats and mice was higher than for other species. GM 237354, a sordarin derivative, was characterized by high serum protein binding in mouse, rat, and monkey serum (unbound fraction, < or =5%). An indirect evaluation of the effect of liver function upon the metabolism of this class of compounds has been made in animals with impaired liver function such as Gunn rats, as well as in allometric studies that showed better correlations of half-life to liver blood flow than to animal body weight. Linearity of the main pharmacokinetic parameters was demonstrated after intravenous dosing of the representative compound GM 193663 at 10 and 20 mg/kg of body weight in rats. Allometry was used to determine whether human pharmacokinetic parameters can be predicted from animal data by regression analysis against body weight and liver blood flow. All these results have demonstrated that the human pharmacokinetics of sordarin derivatives can be forecast from animal data.

Correlation between in vitro and in vivo activities of GM 237354, a new sordarin derivative, against Candida albicans in an in vitro pharmacokinetic-pharmacodynamic model and influence of protein binding

The antifungal effect of GM 237354, a sordarin derivative, was studied in an in vitro pharmacokinetic (PK)-pharmacodynamic dynamic system (bioreactor) which reproduces PK profiles observed in a previously described model of drug efficacy against murine systemic candidiasis. Immunocompetent mice infected intravenously with 10(5) CFU of Candida albicans were treated with GM 237354 at 2.5, 10, and 40 mg/kg of body weight every 8 h subcutaneously for 7 days. Free concentrations in serum were calculated by multiplying total concentrations measured in vivo by 0.05, the free fraction determined in vitro by equilibrium dialysis. In the bioreactor the inoculum was approximately 10(6) CFU/ml; and a one-compartment PK model was used to reproduce the PK profiles of free and total GM 237354 in serum obtained in mice, and clearance of C. albicans was measured over 48 h. A good correlation was observed when the in vivo fungal kidney burden and the area under the survival time curve were compared with the in vitro broth "burden," although only when free in vivo levels in serum were reproduced in vitro. GM 237354 displayed a 3-log decrease effect both in vivo and in vitro. The very few reports available on in vitro-in vivo correlations have been obtained with antibiotics. The good in vitro-in vivo correlation obtained with an antifungal agent shows that the in vitro dynamic system could constitute a powerful investigational tool prior to assessment of the efficacy of an anti-infective agent in animals and humans.

Antifungal efficacy of GM237354, a sordarin derivative, in experimental oral candidiasis in immunosuppressed rats

GM237354 is a novel sordarin derivative with a broad spectrum of potent activity against a wide range of fungi. The members of this new class of antifungal agents act as potent inhibitors of fungal protein synthesis. In this study, the therapeutic effects of GM237354 were investigated in a novel experimental oral Candida albicans infection model in immunosuppressed rats. The animals were immunosuppressed with dexamethasone in their drinking water and infected on three alternate days. GM237354 was given three times per day for seven consecutive days at 1.25, 2.5, 5, or 10 mg/kg of body weight per dose. In addition, to provide a preliminary idea of the correlation between regimen administration and therapeutic efficacy, GM237354 was administered to two additional groups of rats at 5 mg/kg once or twice a day for 7 days. The drug efficacy was assessed microbiologically, histologically, and by a morphometric study of lesions. Evident agreement was observed among results obtained by the different methods in all of the animals studied. Microbiologically, the efficacy of GM237354 was determined by measuring the number of C. albicans organisms in the oral cavities of rats in the middle (day 4) and at the end (day 7) of the treatment. GM237354 administered at 5, 7.5, 10, 15, or 30 mg/kg/day for 7 days significantly reduced the number of CFU in the oral cavities of treated rats compared with the number of CFU in the oral cavities of the untreated controls. A significant reduction was also observed when GM237354 was administered at 7.5, 10, 15, or 30 mg/kg/day for 4 days. Furthermore, C. albicans was not detected in oral swabs from any infected rats after 1 week of treatment when GM237354 was administered at 15 or 30 mg/kg/day or after 4 days of treatment at 30 mg/kg/day. Histologically, untreated control animals showed extensive colonization of the epithelium of the dorsal tongue by numerous hyphae. Animals treated with GM237354 at 7.5 mg/kg/day showed small areas with superficial hyphal penetration into the epithelium that produced intraepithelial microabscesses. However, animals treated with GM237354 at 15 mg/kg/day showed multiple regenerative areas of the covering epithelium, and only focalized zones of the tongue surface were occupied by hyphae. No hyphal colonization of the epithelium was seen in rats treated with GM237354 at 30 mg/kg/day and which showed extensive areas of epithelial regeneration of the tongue. The histopathology findings were confirmed by morphometry studies, and the percentage of epithelium occupied by C. albicans hyphae decreased from 17.5% in the control group to 4.8 and 0.1% in animals treated with GM237354 at 7.5 and 15 mg/kg/day, respectively. These results demonstrated that the sordarin derivative GM237354 was effective against experimental oral candidiasis in immunosuppressed rats, and further studies are needed to determine the potential of GM237354 for use in the treatment of this infection in humans.

Activities of sordarins in experimental models of candidiasis, aspergillosis, and pneumocystosis

Sordarin derivatives represent a new class of antifungal agents that act as potent inhibitors of fungal protein synthesis and possess a broad spectrum of activity. The in vivo activity of GM193663 and GM237354 was studied in mouse models of disseminated candidiasis and aspergillosis and in a rat model of pneumocystosis. The pharmacokinetic behavior of both sordarin derivatives was studied in mice and rats. In all studies, compounds were administered by the subcutaneous route. After a subcutaneous dose of 50 mg/kg of body weight to mice, the maximum level in serum, area under the concentration-time curve, half-life, and clearance for GM193663 and GM237354 were 51.8 and 23 microg/ml, 79.5 and 46 microg. h/ml, 0.8 and 0.85 h, and 21 and 25 ml/h, respectively. Systemic candidiasis and aspergillosis were established in CD-1 male mice infected with Candida albicans or Aspergillus fumigatus. For systemic candidiasis, compounds were given three times per day for seven consecutive days at 15, 30, 60, or 120 mg/kg/day. GM193663 and GM237354 showed dose-related efficacy against C. albicans, with 50% effective doses, 1 month after infection, of 25.2 and 10.7 mg/kg/dose, respectively. In experimental infections with A. fumigatus, GM237354 was given three times per day at 30, 60, or 120 mg/kg/day for five consecutive days. Animals treated with GM237354 demonstrated irregular responses. The survival of animals treated with GM237354 was 0, 30, and 0% at 30, 60, and 120 mg/kg/day, respectively. The therapeutic efficacy of GM193663 and GM237354 against Pneumocystis carinii was studied in an experimental P. carinii pneumonia (PCP) rat model. After a subcutaneous dose of 10 mg/kg given to rats, the maximum level in serum, area under the concentration-time curve, half-life, and clearance for GM193663 and GM237354 were 6.6 and 7.2 microg/ml, 8.5 and 11.8 microg. h/ml, 0.7 and 0.8 h, and 230 and 133 ml/h, respectively. To induce spontaneous PCP, rats were chronically immunosuppressed with dexamethasone. Infected animals were treated twice daily for 10 days at 0.2, 2, or 10 mg/kg/day. The therapeutic effect was estimated by the reduction in the number of cysts in the lungs of treated versus untreated animals. GM193663 and GM237354 significantly reduced the mean (+/- standard deviation) log number of cysts from 7.6 +/- 0.2 in the untreated group to 4.7 +/- 0.2 and 4.6 +/- 0.1, respectively, when the drugs were administered at a dose of 2 mg/kg/day. The log number of cysts was also reduced in infected animals given lower doses of the compounds (0.2 mg/kg/day). In summary, GM193663 and GM237354 are new sordarin derivatives that may potentially play a major role in the treatment of candidiasis and PCP. Further testing with Aspergillus in other animal models is warranted.

Transmission of Pneumocystis carinii disease from immunocompetent contacts of infected hosts to susceptible hosts

Pneumocystis carinii organisms constitute a large group of heterogeneous atypical microscopic fungi that are able to infect immunocompromised mammals by an airborne route and to proliferate in their lungs, inducing Pneumocystis carinii pneumonia. This pneumonia remains a crucial epidemiological challenge, since neither the source of Pneumocystis carinii infection in humans nor the process by which humans become infected has been clearly established. Polymerase chain reaction (PCR) assays have shown that profoundly immunosuppressed patients without pneumocystosis can be subclinically infected with Pneumocystis. Other PCR-based studies have suggested that healthy immunocompetent hosts are not latent carriers of the parasite. However, recent reports have indicated that Pneumocystis carinii can persist for limited periods in the lungs of convalescent rats after recovery from corticosteroid-induced pneumocystosis, and also that immunocompetent mammals can be transiently parasitized by Pneumocystis carinii after close contact with hosts with Pneumocystis carinii pneumonia. Can transiently parasitized hosts be a source of infection for immunosuppressed hosts? In order to investigate this important clinical question, the ability of immunocompetent BALB/c mice, which were carrying subclinical levels of Pneumocystis carinii, to transmit the infection by the airborne route to highly susceptible, uninfected mice with severe combined immunodeficiency was studied. The results indicated that the immunocompetent mice, transiently parasitized by Pneumocystis carinii organisms after close contact with Pneumocystis carinii-infected mice, were able to transmit the infection to Pneumocystis carinii-free mice with severe combined immunodeficiency.

Pharmacokinetics-pharmacodynamics of a sordarin derivative (GM 237354) in a murine model of lethal candidiasis

Sordarins are a new class of antifungal agents which selectively inhibit fungal protein synthesis (FPS) by impairing the function of elongation factor 2. The present study investigates possible correlations between sordarin pharmacokinetic (PK) properties and therapeutic efficacy, based on a murine model of invasive systemic candidiasis, and provides a rationale for dose selection in the first study of efficacy in humans. A significant correlation between PK parameters and the in vivo activity of GM 237354, taken as a representative FPS inhibitor, was demonstrated in a murine model of lethal systemic candidiasis. Area under the concentration-time curve (AUC) and maximum concentration of drug in serum (C(max)) over 24 h were determined after a single GM 237354 subcutaneous (s.c.) dose (50 mg/kg of body weight) in healthy animals (no significant PK changes with infection were observed for other sordarin derivatives). These results have been used to simulate PK profiles obtained after several doses and/or schedules in animal therapy. A PK-pharmacodynamic (PD) parameter such as the time that serum drug concentrations remain above the MIC (t > MIC) was also determined. Treatment efficacies were evaluated in terms of the area under the survival time curve (AUSTC), using Kaplan-Meier survival analysis and in terms of kidney fungal burden (log CFU/gram) after s.c. doses of 2.5, 5, 10, 20, and 40 mg/kg every 4, 8, or 12 h (corresponding to total daily doses of 5 to 240 mg/kg). The results show all treatments to significantly prolong survival versus that of infected and nontreated controls (P < 0.05). Relationships between simulated PK and PK-PD parameters and efficacy were explored. A good correlation independent of the dosing interval was observed with AUC (but not C(max) or t > MIC) and both AUSTC and kidney burden. Following repeated dosing every 8 h, AUC(50) (AUC at which 50% of the maximum therapeutic efficacy is obtained) was estimated as 21.7 and 37.1 microg. h/ml (total concentrations) for AUSTC and kidney burden using a sigmoid E(max) and an inhibitory sigmoid E(max) PK-PD model, respectively. For an efficacy target of 90% survival, AUC was predicted as 67 microg. h/ml. We conclude that the PK-PD approach is useful for evaluating relationships between PK parameters and efficacy in antifungal research. Moreover, the results obtained with this approach could be successfully applied to clinical studies.

In vitro pharmacodynamic parameters of sordarin derivatives in comparison with those of marketed compounds against Pneumocystis carinii isolated from rats

Pneumocystis carinii pneumonia remains one of the most serious complications of immunosuppressed patients. In this study, the in vitro pharmacodynamic parameters of four sordarin derivatives (GM 191519, GM 237354, GM 193663, and GM 219771) have been evaluated by a new quantitative approach and compared with the commercially available drugs pentamidine, atovaquone, and trimethoprim-sulfamethoxazole (TMP-SMX). In vitro activities and in vivo therapeutic efficacies of sordarin derivatives against P. carinii were also evaluated. In vitro activity was determined by the broth microdilution technique, comparing the total number of microorganisms in treated and drug-free cultures by using Giemsa staining. The in vitro maximum effect (E(max)), the drug concentrations to reach 50% of E(max) (EC(50)), and the slope of the dose-response curve were then estimated by the Hill equation (E(max) sigmoid model). Sordarin derivatives were the most potent agents against P. carinii, with EC(50)s of 0.00025, 0.0007, 0.0043, and 0. 025 microg/ml for GM 191519, GM 237354, GM 193663, and GM 219771, respectively. The EC(50)s of pentamidine, atovaquone, and TMP-SMX were 0.025, 0.16, and 26.7/133.5 microg/ml, respectively. The results obtained with this approach showed GM 237354 and GM 191519 to be approximately 35- and 100-fold more active in vitro than pentamidine, the most active marketed compound. All sordarin derivatives tested were at least 5,000-fold more active in vitro than TMP-SMX. The three sordarin derivatives tested in vivo-GM 191519, GM 237354, and GM 219771-showed a marked therapeutic efficacy, defined as reduction of cyst forms per gram of lung. GM 191519 was the most potent (daily dose reducing 50% of the P. carinii burden in the lungs [ED(50)], 0.05 mg/kg/day) followed by GM 237354 and GM 219771 (ED(50)s, 0.30 and 0.49 mg/kg/day, respectively). Good agreement between in vitro parameters and in vivo outcome was obtained when P. carinii pneumonia in rats was treated with sordarin derivatives.

Magnetic resonance imaging in the evaluation of inflammatory lesions in muscular and soft tissues: an experimental infection model induced by Candida albicans

We have developed an experimental model to monitor inflammatory lesions in muscle and soft-tissues during the different stages of the disease by means of Magnetic Resonance Imaging (MRI). MRI of mice legs infected with Candida albicans was performed by standard two-dimensional spin echo and fast spin echo (RARE) using customized coils. The MRI findings were compared with pathologic examinations at the initial acute and established acute inflammatory stages, which provided accurate and detailed information on the evolution of the processes involved. The yeast caused inflammation within the first hours post-inoculation, appearing on T2-weighted images as an inhomogeneous mass with increased signal intensity. The presence of fungal hyphae was observed as hypointense signal areas in both T2 and T1 weighted images, with histologic confirmation. Areas of decreased signal intensity on T2 weighted images were apparent on the last experimental day and were attributed to the granulation tissue located within the capsule surrounding the abscess. The close correlation found between MRI and histopathology suggests that MRI is an ideal radiologic technique for monitoring the clinical and therapeutic follow-up of fungal infections in muscle and soft tissues.

Sordarins: in vitro activities of new antifungal derivatives against pathogenic yeasts, Pneumocystis carinii, and filamentous fungi

GM 193663, GM 211676, GM 222712, and GM 237354 are new semisynthetic derivatives of the sordarin class. The in vitro antifungal activities of GM 193663, GM 211676, GM 222712, and GM 237354 against 111 clinical yeast isolates of Candida albicans, Candida kefyr, Candida glabrata, Candida parapsilosis, Candida krusei, and Cryptococcus neoformans were compared. The in vitro activities of some of these compounds against Pneumocystis carinii, 20 isolates each of Aspergillus fumigatus and Aspergillus flavus, and 30 isolates of emerging less-common mold pathogens and dermatophytes were also compared. The MICs of GM 193663, GM 211676, GM 222712, and GM 237354 at which 90% of the isolates were inhibited (MIC90s) were 0.03, 0.03, 0.004, and 0.015 microg/ml, respectively, for C. albicans, including strains with decreased susceptibility to fluconazole; 0.5, 0.5, 0.06, and 0.12 microg/ml, respectively, for C. tropicalis; and 0.004, 0.015, 0.008, and 0.03 microg/ml, respectively, for C. kefyr. GM 222712 and GM 237354 were the most active compounds against C. glabrata, C. parapsilosis, and Cryptococcus neoformans. Against C. glabrata and C. parapsilosis, the MIC90s of GM 222712 and GM 237354 were 0.5 and 4 microg/ml and 1 and 16 microg/ml, respectively. The MIC90s of GM 222712 and GM 237354 against Cryptococcus neoformans were 0.5 and 0.25 microg/ml, respectively. GM 193663, GM 211676, GM 222712, and GM 237354 were extremely active against P. carinii. The efficacies of sordarin derivatives against this organism were determined by measuring the inhibition of the uptake and incorporation of radiolabelled methionine into newly synthesized proteins. All compounds tested showed 50% inhibitory concentrations of <0.008 microg/ml. Against A. flavus and A. fumigatus, the MIC90s of GM 222712 and GM 237354 were 1 and 32 microg/ml and 32 and >64 microg/ml, respectively. In addition, GM 237354 was tested against the most important emerging fungal pathogens which affect immunocompromised patients. Cladosporium carrioni, Pseudallescheria boydii, and the yeast-like fungi Blastoschizomyces capitatus and Geotrichum clavatum were the most susceptible of the fungi to GM 237354, with MICs ranging from </=0.25 to 2 microg/ml. The MICs of GM 237354 against Trichosporon beigelii and the zygomycetes Absidia corymbifera, Cunninghamella bertholletiae, and Rhizopus arrhizus ranged from </=0.25 to 8 microg/ml. Against dermatophytes, GM 237354 MICs were >/=2 microg/ml. In summary, we concluded that some sordarin derivatives, such as GM 222712 and GM 237354, showed excellent in vitro activities against a wide range of pathogenic fungi, including Candida spp., Cryptococcus neoformans, P. carinii, and some filamentous fungi and emerging invasive fungal pathogens.

Antibacterial activity and pharmacokinetics of four new 7-azetidinyl fluoroquinolones

The activity of E-4535, E-4534, E-4528, and E-4527, four new 7-azetidinyl-6-fluoroquinolones, was studied to evaluate the role played by the C-2' and C-3' substitutions of the azetidinyl group, together with a C-8 fluorine atom. In general, like other 6,8-difluoroquinolones, E-4534 and E-4527 showed higher levels of activity than the corresponding monofluorinated derivatives, E-4535 and E-4528. E-4535 and E-4534, having a 7-(2-methyl-3-aminoazetidinyl) substituent, demonstrated higher levels of activity in vitro than their corresponding structural analogs, E-4528 and E-4527, distinguished by a 3-methyl-3-methylaminoazetidinyl group at position 7 of the quinolone nucleus. In consequence, E-4534 was the most potent of the new agents tested.

E-4695, a new C-7 azetidinyl fluoronaphthyridine with enhanced activity against gram-positive and anaerobic pathogens

E-4695, (-)-7-[3-(R)-amino-2-(S)-methyl-1-azetidinyl]-1-cyclopropyl-1,4- dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid, is a new fluorinated naphthyridine with an azetidine moiety. The MICs of E-4695 at which 90% of the isolates were inhibited (MIC90s) were 0.06 to 0.5 microgram/ml for gram-positive cocci, including species of the genera Staphylococcus, Streptococcus, and Enterococcus, and the MIC90s against gram-negative pathogens such as members of the family Enterobacteriaceae (with the exception of Providencia spp. [MIC90, 8 micrograms/ml]) and Pseudomonas aeruginosa were 0.015 to 0.5 microgram/ml. E-4695 inhibited 90% of the Clostridium perfringens and Bacteroides fragilis isolates at 0.25 and 4 micrograms/ml, respectively. Against gram-positive cocci the potency of E-4695 was 2- to 8-fold higher than that of ciprofloxacin, 4- to 8-fold higher than that of ofloxacin, and 8- to 16-fold higher than that of fleroxacin. Against enteric bacteria and P. aeruginosa the potency of E-4695 was, in general, similar to that of ciprofloxacin and eightfold higher than those of ofloxacin and fleroxacin. E-4695 was four- and eightfold more potent than ciprofloxacin against C. perfringens and B. fragilis isolates, respectively. E-4695 and ciprofloxacin showed similar properties when the effects of pH or magnesium concentration were tested on them. E-4695 and ciprofloxacin had substantial reductions of activity only when pH decreased below 4.8. E-4695 and ciprofloxacin activities were not markedly affected by the presence of 5 or 10 mM Mg2+. The presence of serum and human urine at pH 7.2 decreased the activity of E-4695 between two- and fourfold. After an oral dose of 50 mg/kg of body weight, the maximum level in serum, the biological half-life, and the area under the concentration-time curve from 0 to 10 h for E-4695 were 13.2 microgram/ml, 3.3 h, and 45.6 microgram . h/ml, respectively. The area under the concentration-time curve from 0 to 4 h for ciprofloxacin was 2.3 microgram . h/ml at the same dose. Fifty-percent effective doses (ED50S) against Staphylococcus aureus HS-93 infections in mice were 4.5 mg/kg with E-4695 and 37.6 mg/kg with ciprofloxacin. Infection with Streptococcus pneumoniae 29206 was more effectively treated with E-4695 (ED50, 41,2 mg/kg) than with ciprofloxacin (ED50, 200 mg/kg). The ED50 of E-4695 for infections with Streptococcus pneumoniae 1625 was 132.2 mg/kg; ciprofloxacin was ineffective at 400 mg/kg against this strain. E-4695 was also more potent than ciprofloxacin in treatment of infections caused by gram-negative organisms such as Escherichia coli HM-42 (ED50S, 1.0 and 3.9 mg/kg, respectively). The ED50S of E-4695 and ciprofloxacin were 33.0 and 145.5 mg/kg against P. aeruginosa HS-116 and 9.6 and 18.9 mg/kg against P. aeruginosa B-120, respectively. The therapeutic efficacy of E-4695 may depend not only on its in vitro activity but also on its improved pharmacokinetic properties.

In vitro and in vivo antibacterial activities of E-4868, a new fluoroquinolone with a 7-azetidin ring substituent

E-4868, (-)-7-[3-(R)-amino-2-(S)-methyl-1-azetidinyl]-1-(2,4- difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-3-quinolinecarboxylic acid, is a new fluoroquinolone with an azetidine moiety at the 7 position. The in vitro activity of E-4868 has been compared with those of ciprofloxacin, ofloxacin, and fleroxacin, while the activity of ciprofloxacin was used as reference for in vivo studies. The MICs of E-4868 for 90% of the isolates tested (MIC90s) were 0.06 to 0.5 microgram/ml against gram-positive organisms, including Staphylococcus, Streptococcus, and Enterococcus spp. In general, the in vitro potency of E-4868 against gram-positive bacteria was higher than those of all of the other fluoroquinolones tested. MIC90s against members of the family Enterobacteriaceae between 0.03 and 1 microgram/ml were observed, with the exception of those against Serratia marcescens and Providencia spp., and a MIC90 of 2 micrograms/ml against Pseudomonas aeruginosa was obtained. E-4868 inhibited 90% of the Clostridium spp. and Bacteroides spp. at 2 micrograms/ml and was twofold more active than ciprofloxacin. An increase in the Mg2+ concentration from 1 to 10 mM increased the MIC between two and three times. Human urine caused a significant decrease in activity of E-4868, which was more pronounced at pH 5.5 than at pH 7.2. The presence of serum also decreased the activity of E-4868. Fifty percent effective dose (ED50) values against experimental Escherichia coli HM-42 infections in mice were 3.9 mg/kg of body weight with E-4868 and 3.5 mg/kg of body weight with ciprofloxacin. Corresponding ED50 values against P. aeruginosa HS-116 were 93.2 and 107.8 mg/kg, respectively, and those against Staphylococcus aureus HS-93 were 6.5 and 44.6 mg/kg, respectively. In experimental infections with Streptococcus pneumoniae 84551, the ED50 value of E-4868 was 154.4 mg/kg, while ciprofloxacin proved totally inactive at a dose of 400 mg/kg. When E-4868 was administered orally at a dose of 50 mg/kg in mice, the area under the concentration-time curve (0 to 4 h) value was 28.4 microgram . h/ml, while an area under the concentration-time curve value of 2.3 microgram . h/ml was observed for ciprofloxacin at the same dose. In these studies, levels of the two agents in blood 1 h postadministration were 7.6 and 1.2 microgram/ml, respectively.

In vitro and in vivo antibacterial activities of E-4497, a new 3-amine-3-methyl-azetidinyl tricyclic fluoroquinolone

The in vitro and in vivo antibacterial activities of a new tricyclic fluoroquinolone, E-4497 [S(-)-9-fluoro-3-methyl-10-(3-amine-3-methyl-azetidin-1-yl)-7-oxo- 2,3-dihydro- 7H-pyrido-(1,2,3-de)-1,4-benzoxazine-6-carboxylic acid], were evaluated in comparison with those of DR-3355 [S-(-)-ofloxacin], norfloxacin, and ciprofloxacin. E-4497 was more potent than norfloxacin and as potent as or more potent than DR-3355 and ciprofloxacin against Staphylococcus spp., Streptococcus spp., and Enterococcus faecalis. With the exception of Providencia spp., E-4497 inhibited 90% of the Enterobacteriaceae at less than or equal to 0.25 micrograms/ml. Against enteric bacteria, E-4497 was similar in potency to norfloxacin but less potent than DR-3355 and ciprofloxacin. For Pseudomonas aeruginosa, the MICs of E-4497, DR-3355, norfloxacin, and ciprofloxacin for 90% of strains were 2, 2, 4, and 0.5 micrograms/ml, respectively. Against Clostridium perfringens and Bacteroides fragilis, E-4497 (MICs for 90% of strains, 2 and 8 micrograms/ml, respectively) was two- to fourfold more active than norfloxacin and ciprofloxacin. E-4497 activity decreased moderately in the presence of 10 mM Mg2+. Urine at pH 5.5 caused a significant decrease in activity compared with urine at pH 7.2. However, the presence of serum either had no effect or increased the activity of E-4497. In general, E-4497 was bactericidal at the MIC. In systemic infections with Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, and Pseudomonas aeruginosa in mice, the protective effect of E-4497 was generally greater than that of norfloxacin and comparable to those of DR-3355 and ciprofloxacin.

Comparative in vitro and in vivo activities of six new monofluoroquinolone and difluoroquinolone 3-carboxylic acids with a 7-azetidin ring substituent

E-4502, E-4501, E-4500, E-4480, E-4474, and E-4441 are new monofluorinated or difluorinated quinolone agents that are chemically characterized by the presence of an azetidin ring, with different C'-3 substituents, at position 7 of the molecular structure. The MICs of the difluorinated compounds E-4501, E-4474, and E-4441 for 90% of isolates were 0.06 to 1, 0.06 to 1, and 0.12 to 1 microgram/ml, respectively, against gram-positive organisms (staphylococci, streptococci, and Enterococcus faecalis); 0.0015 to 0.12, 0.015 to 0.12, and 0.03 to 0.12 microgram/ml, respectively, against members of the family Enterobacteriaceae except Providencia spp.; and 1, 1, and 2 micrograms/ml, respectively, against Pseudomonas aeruginosa. E-4501, E-4474, and E-4441 inhibited all anaerobic bacteria at concentrations of 1, 2, and 4 micrograms/ml, respectively. Difluorinated compounds were significantly more active than the corresponding monofluorinated analogs E-4502, E-4500, and E-4480 against aerobic and facultatively anaerobic organisms, as well as against anaerobes. Considering monofluorinated and difluorinated compounds, activity in moderate ascending order was observed in quinolones containing an amine and a methyl group (E-4441 and E-4480), an amine group (E-4474 and E-4500), and a methylamine group (E-4501 and E-4502) in the C'-3 position of the azetidin ring. E-4501, E-4474, and E-4441 were more active than norfloxacin and DR-3355 [S-(-)-ofloxacin], had activities comparable to or slightly lower than that of ciprofloxacin against gram-negative bacteria, and were more active than all the reference quinolones against gram-positive organisms and anaerobes. E-4502 and E-4501, which were used to determine the effect of pH, were less active in acidic medium. In general, E-4502, E-4501, E-4500, E-4480, E-4474, and E-4441 activities were not affected or increased in medium containing serum but decreased in the presence of 10 mM Mg2+ or in human urine at pH 5.5. The protective effect of E-4501, E-4474, and E-4441 after oral administration against systemic infections with Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa in mice was greater than that of ciprofloxacin.

Enzyme polymorphism, prodigiosin production, and plasmid fingerprints in clinical and naturally occurring isolates of Serratia marcescens

Enzyme polymorphism and genetic relationship among 99 Serratia marcescens isolates obtained from clinical and environmental sources were determined by analysis of electromorphs in nine enzyme loci encoded by chromosomal genes. Seven of the loci were polymorphic, and 33 distinctive electrophoretic types (ETs) representing multilocus genotypes were identified. Cluster analysis, based on the proportion of mismatches between multilocus genotypes, revealed two clearly differentiated groups of ETs in S. marcescens. One was represented exclusively by isolates with nonchromogenic biotypes recovered almost entirely (97.3%) from clinical samples. The other group comprised all isolates characterized by the production of prodigiosin or by belonging to a chromogenic biotype. Absolute correlation was found between the ability to produce prodigiosin and the absence of plasmids. In contrast, 24% of the nonchromogenic isolates contained plasmids. Results obtained by analysis of multilocus genotypes were related to those obtained by biotyping and plasmid fingerprinting. However, more groups could be distinguished by analysis of ETs than by biotyping. Plasmid fingerprinting was a limited typing system because many isolates lacked plasmids. Although the results of this study did not permit a definitive correlation between ETs and pathogenicity of the isolates, more detailed studies of these groups will help to understand the different clinical significances of the nonchromogenic and chromogenic isolates of S. marcescens.