Shogo Kuwahara

In vitro activities of a new lipopeptide antifungal agent, FK463, against a variety of clinically important fungi

ABSTRACT The in vitro antifungal activity and spectrum of FK463 were compared with those of amphotericin B, fluconazole, and itraconazole by using a broth microdilution method specified by National Committee for Clinical Laboratory Standards document M27-A (National Committee for Clinical Laboratory Standards, Wayne, Pa., 1997). FK463 exhibited broad-spectrum activity against clinically important pathogens including Candida species (MIC range, ≦0.0039 to 2 μg/ml) and Aspergillus species (MIC range, ≦0.0039 to 0.0313 μg/ml), and its MICs for such fungi were lower than those of the other antifungal agents tested. FK463 was also potently active against azole-resistant Candida albicans as well as azole-susceptible strains, and there was no cross-resistance with azoles. FK463 showed fungicidal activity against C. albicans, i.e., a 99% reduction in viability after a 24-h exposure at concentrations above 0.0156 μg/ml. The minimum fungicidal concentration (MFC) assays indicated that FK463 was fungicidal against most isolates of Candida species. In contrast, the MFCs of FK463 for A. fumigatus isolates were much higher than the MICs, indicating that its action is fungistatic against this species. FK463 had no activity against Cryptococcus neoformans,Trichosporon species, or Fusarium solani. Neither the test medium (kind and pH) nor the inoculum size greatly affected the MICs of FK463, while the addition of 4% human serum albumin increased the MICs for Candida species and A. fumigatus more than 32 times. Results from preclinical in vitro evaluations performed thus far indicate that FK463 should be a potent parenteral antifungal agent.

Efficacy of FK463, a New Lipopeptide Antifungal Agent, in Mouse Models of Disseminated Candidiasis and Aspergillosis

ABSTRACT The efficacy of intravenous injection of FK463, a novel water-soluble lipopeptide, was evaluated in mouse models of disseminated candidiasis and aspergillosis and was compared with those of fluconazole (FLCZ) and amphotericin B (AMPH-B). In the candidiasis model, FK463 significantly prolonged the survival of intravenously infected mice at doses of 0.125 mg/kg of body weight or higher. In disseminated candidiasis caused by Candida species, including FLCZ-resistant Candida albicans, FK463 exhibited an efficacy 1.4 to 18 times inferior to that of AMPH-B, with 50% effective doses (ED50s) ranging from 0.21 to 1.00 mg/kg and 0.06 to 0.26 mg/kg, respectively, and was much more active than FLCZ. The protective effect of FK463 was not obviously influenced by the fungal inoculum size, the starting time of the treatment, or the immunosuppressed status of the host. The reduction in efficacy was less than that observed with FLCZ or AMPH-B. The efficacy of FK463 was also evaluated in the disseminated candidiasis target organ assay and was compared with those of FLCZ and AMPH-B. Efficacies were evaluated on the basis of a comparison between the mean log10 CFU in kidneys in the groups treated with antifungal agents and that in control group. A single dose of FK463 at 0.5 mg/kg or higher significantly reduced the viable counts in kidneys compared with the numbers of yeast cells before treatment, and its efficacy was comparable to that of AMPH-B, while FLCZ at 4 mg/kg showed only a suppressive effect on the growth of C. albicans in the kidneys. In the disseminated aspergillosis model, FK463 given at doses of 0.5 mg/kg or higher significantly prolonged the survival of mice infected intravenously with Aspergillus fumigatus conidia. The efficacy of FK463 was about 2 times inferior to that of AMPH-B, with ED50s ranging from 0.25 to 0.50 mg/kg and 0.11 to 0.29 mg/kg, respectively. These results indicate that FK463 may be a potent parenterally administered therapeutic agent for disseminated candidiasis and aspergillosis.

Efficacy of FK463, a New Lipopeptide Antifungal Agent, in Mouse Models of Pulmonary Aspergillosis

ABSTRACT The efficacy of FK463, a novel water-soluble lipopeptide, was evaluated in mouse models of pulmonary aspergillosis and was compared with that of amphotericin B (AMPH-B). In the pulmonary aspergillosis models induced by intranasal inoculation, FK463 exhibited good efficacy, with 50% effective doses in the range of 0.26 to 0.51 mg/kg of body weight; these values were comparable to those of AMPH-B. In anAspergillus target organ assay with immunosuppressed mice, under conditions of constant plasma levels of FK463, using a subcutaneously implanted osmotic pressure pump, a significant reduction in viable fungal cells was observed at plasma FK463 levels of 0.55 to 0.80 μg/ml or higher. We conclude that FK463 is highly effective in the treatment of pulmonary aspergillosis in this animal model. These results indicate that FK463 may be a potent parenterally administered antifungal agent for pulmonary aspergillosis.

Ceftizoxime (FK 749), a new parenteral cephalosporin: in vitro and in vivo antibacterial activities.

FK 749 is a new parenteral cephalosporin derivative which is more active against various gram-negative bacilli, including the opportunistic pathogens such as Enterobacter, Citrobacter species, and Serratia marcescens, than cephalosporins and cephamycins such as cefotiam, cefamandole, cefuroxime, cefotaxime, and cefmetazole. FK 749 was especially active against gram-negative organisms resistant to these related antibiotics. FK 749 was more potent in bactericidal activity than the other antibiotics, and the activity was clearly enhanced in the presence of 90% defibrinated rabbit blood. The therapeutic effect of subcutaneously injected FK 749 in mice infected with various gram-negative bacilli was far superior to that of cefotiam, cefamandole, cefuroxime, and cefmetazole and was almost the same as that of cefmetazole in mice infected with Staphylococcus aureus and that of ticarcillin in mice infected with Pseudomonas aeruginosa. FK 749 has, in general, nearly the same in vitro and in vivo antibacterial activities as cefotaxime. The former had more potent bactericidal activity in the presence of the blood than the latter and showed more excellent therapeutic effect than cefotaxime against infections caused by large inoculum sizes.

In vitro and in vivo antibacterial properties of FK 027, a new orally active cephem antibiotic.

FK 027 was more active than cefaclor, cephalexin, and amoxicillin against stock strains of a wide variety of gram-negative bacteria, including such opportunistic pathogens as Citrobacter and Enterobacter species and Serratia marcescens. FK 027 was significantly more active than the three reference drugs against clinical isolates of Escherichia coli, Klebsiella pneumoniae, indole-positive and -negative Proteus species, Providencia species, Haemophilus influenzae, and Neisseria gonorrhoeae. It was less active than cefaclor, cephalexin, and amoxicillin against staphylococci, but it was similar to cefaclor in its activity against streptococci. With few exceptions, FK 027 was active against strains of E. coli, K. pneumoniae, and Proteus mirabilis that were resistant to the reference agents. The bactericidal activity of FK 027 against various gram-negative bacteria, including Proteus species, Citrobacter freundii, Enterobacter aerogenes, and S. marcescens, was greater than that of cefaclor, cephalexin, and amoxicillin. The therapeutic activities of FK 027 in mice infected with gram-negative bacilli were far superior to the activities of cefaclor, cephalexin, and amoxicillin, but they were inferior to the activities of these reference drugs against infection with Staphylococcus aureus.

Immunoactive peptides, FK-156 and FK-565. I. Enhancement of host resistance to microbial infection in mice.

The protective effect of an immunoactive peptide, D-lactoyl-L-alanyl-gamma-D-glutamyl-(L)-meso-diaminopimelyl-(L)-glycine (FK-156) and a related compound, heptanoyl-gamma-D-glutamyl-(L)-meso-diaminopimelyl-(D)-alanine (FK-565) was determined in mice with various kinds of microbial infections. FK-156 and FK-565 were given to mice either subcutaneously or orally before challenge. The drugs enhanced significantly the defense of mice against acute systemic infections induced by various extracellular and facultative intracellular organisms, and subcutaneous abscess by Staphylococcus aureus. The protective effect of these drugs against Escherichia coli infection differed considerably depending on the route of administration; FK-156 was only effective by the parenteral route; however, FK-565 was effective by both parenteral and oral routes. After subcutaneous dosing with FK-156, the enhancement of host defense of mice against E. coli infection was more rapid than against Listeria infection. The enhancing effects of FK-156 and FK-565 on host defense of mice against pseudomonal infection was more potent than other immunoactive drugs.

In Vivo Antibacterial Activity of S-3578, a New Broad-Spectrum Cephalosporin: Methicillin-Resistant Staphylococcus aureus and Pseudomonas aeruginosa Experimental Infection Models

ABSTRACT The in vivo antibacterial activity of S-3578, a new parental cephalosporin, was compared with those of cefepime, ceftriaxone, ceftazidime, imipenem-cilastatin, and vancomycin. The efficacy of S-3578 against systemic infections caused by methicillin-resistant Staphylococcus aureus (MRSA) SR3637 (50% effective dose [ED50], 7.21 mg/kg of body weight) was almost the same as that of vancomycin. In contrast, cefepime and imipenem-cilastatin were less active against this pathogen (ED50s, >100 and >100 mg/kg, respectively). S-3578 was the most effective compound against penicillin-resistant Streptococcus pneumoniae SR20946 (ED50, 1.98 mg/kg). S-3578 (10 mg/kg) induced a significant reduction in the numbers of viable MRSA SR17764 and Pseudomonas aeruginosa SR10396 organisms in polymicrobial pulmonary infections. The therapeutic efficacy of S-3578 was more potent than that of the combination of vancomycin and ceftazidime. High levels of S-3578 were detected in plasma in vivo, and its efficacy against experimentally induced infections in mice caused by MRSA and P. aeruginosa reflected its potent in vitro activity. We conclude that S-3578 is a promising new cephalosporin for the treatment of infections caused by gram-positive and -negative bacteria, including MRSA and P. aeruginosa.

In Vitro Activity of S-3578, a New Broad-Spectrum Cephalosporin Active against Methicillin-Resistant Staphylococci

ABSTRACT The in vitro antibacterial activity of S-3578, a new parenteral cephalosporin, against clinical isolates was evaluated. The MICs of the drug at which 90% of the isolates were inhibited were 4 μg/ml for methicillin-resistant Staphylococcus aureus (MRSA) and 2 μg/ml for methicillin-resistant Staphylococcus epidermidis, which were fourfold higher than and equal to those of vancomycin, respectively. The anti-MRSA activity of S-3578 was considered to be due to its high affinity for penicillin-binding protein 2a (50% inhibitory concentration, 4.5 μg/ml). In time-kill studies with 10 strains each of MRSA and methicillin-susceptible S. aureus, S-3578 caused more than a 4-log10 decrease of viable cells on the average at twice the MIC after 24 h of exposure, indicating that it had potent bactericidal activity. Furthermore, in population analysis of MRSA strains with heterogeneous or homogeneous resistance to imipenem, no colonies emerged from about 109 cells on agar plates containing twice the MIC of S-3578, suggesting the low frequency of emergence of S-3578-resistant strains from MRSA. S-3578 was also highly active against penicillin-resistant Streptococcus pneumoniae (PRSP), with a MIC90 of 1 μg/ml, which was comparable to that of ceftriaxone. S-3578 also had antibacterial activity against a variety of gram-negative bacteria including Pseudomonas aeruginosa, though its activity was not superior to that of cefepime. In conclusion, S-3578 exhibited a broad antibacterial spectrum and, particularly, had excellent activity against gram-positive bacteria including methicillin-resistant staphylococci and PRSP. Thus, S-3578 was considered to be worthy of further evaluation.

Temperature-Sensitive R Plasmid Obtained from Naturally Isolated Drug-Resistant Vibrio cholerae (Biotype El Tor)

A temperature-sensitive fi− R plasmid, pJY1, which confers resistance to chloramphenicol, streptomycin, and sulfonamide, was found in a drug-resistant strain of Vibrio cholerae (biotype El Tor) isolated in the Philippines in 1973. The R plasmid is temperature sensitive for transferability but not for stability in the hosts. pJY1 is stably maintained either in V. cholerae or in Escherichia coli at a range of culture temperatures from 27 to 42°C. Compatibility tests with reference R plasmids revealed that pJY1 belongs to the J group. Growth of V. cholerae carrying pJY1 is poor on TCBS (thiosulfate-citrate-bile-sucrose) selective plates when the microbe is subcultured in nutrient broth at temperatures higher than 37°C. Images

In vitro and in vivo activities of CS-758 (R-120758), a new triazole antifungal agent

ABSTRACT The activity of CS-758 (R-120758), a new triazole antifungal agent, was evaluated and compared with those of fluconazole, itraconazole, and amphotericin B in vitro and with those of fluconazole and itraconazole in vivo. CS-758 exhibited potent in vitro activity against clinically important fungi. The activity of CS-758 against Candida spp. was superior to that of fluconazole and comparable or superior to those of itraconazole and amphotericin B. CS-758 retained potent activity against Candida albicans strains with low levels of susceptibility to fluconazole (fluconazole MIC, 4 to 32 μg/ml). Against Aspergillus spp. and Cryptococcus neoformans, the activity of CS-758 was at least fourfold superior to those of the other drugs tested. CS-758 also exhibited potent in vivo activity against murine systemic infections caused by C. albicans, C. neoformans, Aspergillus fumigatus, and Aspergillus flavus. The 50% effective doses against these infections were 0.41 to 5.0 mg/kg of body weight. These results suggest that CS-758 may be useful in the treatment of candidiasis, cryptococcosis, and aspergillosis.