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Antimicrobial Agents and Chemotherapy, February 2003, p. 601-606, Vol. 47, No. 2
0066-4804/03/$08.00+0 DOI: 10.1128/AAC.47.2.601-606.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Biological Research Laboratories,1 Laboratory Animal Science and Toxicology Research Laboratories,2 Pharmacokinetics and Drug Delivery Research Laboratories, Sankyo Co., Ltd., Shinagawa-ku, Tokyo 140-8710,3 Teikyo University Institute of Medical Mycology, Hachioji, Tokyo 192-0395,4 Toho University School of Medicine, Ohta-ku, Tokyo 143-8540, Japan5
Received 8 July 2002/ Returned for modification 21 August 2002/ Accepted 21 October 2002
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CS-758, formerly R-120758, is a novel triazole, which has potent activity against Candida albicans and also against strains that have low levels of susceptibility to FLC in vitro (5). Previously, we established a new model of experimental murine OPC (6). In this study, we investigated the therapeutic efficacy of CS-758 against experimental murine OPC induced by C. albicans strains that have various susceptibilities to FLC.
(This research was presented at the 41st Interscience Conference on Antimicrobial Agents and Chemotherapy [Y. Kamai, M. Kubota, Y. Kamai, N. Maeda, T. Hosokawa, T. Fukuoka, K. Uchida, H. Yamaguchi, and S. Kuwahara, Abstr. 41st Intersci. Conf. Antimicrob. Agents Chemother., abstr. 2151, p. 253, 2001; Y. Kamai, M. Kubota, T. Fukuoka, K. Uchida, H. Yamaguchi, and S. Kuwahara, Abstr. 41st Intersci. Conf. Antimicrob. Agents Chemother., abstr. 2152, p. 253, 2001].)
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Organisms. We used six strains of C. albicans. C. albicans SANK51486 was stored in our laboratory. C. albicans 2010A, 2033A, 2035B, 2054A, and 2085A, which were isolated from the oral cavities of different patients, were provided by Scott G. Filler of Harbor-University of California, Los Angeles, Research and Education Institute. For the in vitro study, the test organisms were cultured on Sabouraud dextrose agar (SDA; Eiken Chemical Co., Ltd., Tokyo, Japan). For the in vivo study, the test organisms grown on SDA were inoculated into YPG medium consisting of 0.5% yeast extract (Difco Laboratories, Detroit, Mich.), 1% peptone (Difco Laboratories), and 2% glucose (Wako Pure Chemical Industries, Ltd.), and incubated at 35°C overnight with shaking.
In vitro susceptibility testing. The MICs for the test organisms were determined by the broth microdilution method described in NCCLS document M27-A (10).
Animals. Specific-pathogen-free male ddY mice (age, 4 weeks) were purchased from Japan SLC, Inc., Shizuoka, Japan. The mice were used for the experiments after an acclimation period of 6 days. The mice were immunosuppressed by subcutaneous injection of 4 mg of cortisone acetate (Tokyo Kasei Kogyo Co., Ltd., Tokyo, Japan) per mouse 2 days before, on the day of, and 3 days after inoculation. During the period of immunosuppression the mice were given tetracycline hydrochloride (0.5 mg/ml in drinking water; Achromycin V; Wyeth Lederle Japan, Ltd., Tokyo, Japan) for the prevention of bacterial infection. Mice were given food and water ad libitum throughout the experiments. All animal experiments were carried out according to the guidelines provided by the Institutional Animal Care and Use Committee of Sankyo Co., Ltd.
Experimental murine OPC. Experimental murine OPC was induced by a previously reported procedure (6). Test organisms cultured in YPG medium were harvested, washed with sterile physiological saline, and suspended in sterile physiological saline. The suspension was adjusted to 1.0 x 108 cells/ml. Before inoculation, the mice were anesthetized by intraperitoneal injection of 27.5 µg of dimorpholamine (Theraptique; Eisai Co., Ltd., Tokyo, Japan), 219 µg of xylazine (Bayer Yakuhin, Ltd., Osaka, Japan), and 1.28 mg of pentobarbital sodium (Nembutal; Dainippon Pharmaceutical Co., Ltd., Osaka, Japan) per mouse. Cotton-wool balls (diameter, 3 mm) were saturated with 100 µl of the test organism suspension of 1.0 x 108 cells/ml and then placed sublingually in the oral cavity for about 2 h.
Therapeutic efficacy. The test agents were administered orally by gavage once daily for 2 days starting 3 days postinoculation. For the treatment of the infection caused by C. albicans, SANK5148, CS-758, and FLC were administered at 0.4, 2, and 10 mg/kg of body weight/dose and ITC was administered at 10 mg/kg/dose. For the treatment of the infections caused by the other strains, CS-758 and FLC were administered at 2, 10, and 50 mg/kg/dose and ITC was administered at 50 mg/kg/dose. The control group received 0.2 ml of 0.5% CMC-Na. In our preliminary study, the vehicle for ITC (40% 2-hydroxypropyl ß-cyclodextrin) did not influence the viable cell counts compared with those achieved with 0.5% CMC-Na in this model. Each group consisted of six mice. On day 5 postinoculation, the mice were sacrificed and the mandible with the attached tissue was excised. After removal of the bone and teeth, the tissue was homogenized and serial dilutions were cultured on SDA containing 10 µg of chloramphenicol per ml at 35°C for 2 or 3 days. Hereafter, the attached tissue of the mandible without bone or teeth is referred to as "oral tissue." The viable cell counts in the oral tissue were determined by counting the colonies on the SDA plates.
Histopathological study. For the histopathological study, test agents were administered at 10 mg/kg/dose against experimental murine OPC caused by C. albicans SANK51486, as described above. On day 5 postinoculation, the mice were sacrificed and the mandibles with the attached tissue were excised. The tissues were fixed in formalin containing 8% sucrose and embedded in paraffin, after which thin sections of the tongues were prepared and stained with periodic acid-Schiff (PAS).
Statistical analysis. The viable cell counts in the oral tissues were compared between the control group and the treated groups by Dunnett's test. The detection limit was log10 50 CFU/g of tissue in this study. When the culture of the oral tissue was sterile, the value of the detection limit was used for the statistical analysis. P values below 0.05 were considered significant. The SAS system for Windows (release 6.12; SAS Institute Inc.) was used for the analysis.
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8 µg/ml), strains 2010A and 2033A were placed in the FLC-susceptible dose-dependent (FLC-S-DD) category (FLC MICs, 16 to 32 µg/ml), and strain 2035B was placed in the FLC-resistant (FLC-R) category (FLC MICs,
64 µg/ml) (10). CS-758 exhibited the most potent activity against these strains, with MICs ranging from 0.004 to 0.06 µg/ml. |
View this table: [in a new window] |
TABLE 1. In vitro antifungal activity of CS-758 against C. albicans strains used to induce experimental murine OPC
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FIG. 1. Efficacies of CS-758, FLC, and ITC against experimental murine OPC induced by C. albicans SANK51486. Each circle represents the result for an individual mouse. Closed circles, results above the detection limit; open circles, results below the detection limit; bars, mean values (n = 6); ***, P < 0.001 by Dunnett's test.
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FIG. 2. Histopathology of the tongues of mice with experimental OPC induced by C. albicans SANK51486. Typical PAS-stained specimens are shown for the tongues of mice treated with 0.5% CMC-Na (A), 10 mg of CS-758/kg/dose (B), 10 mg of FLC/kg/dose (C), and 10 mg of ITC/kg/dose (D). Bars, 50 µm.
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FIG. 3. Efficacies of CS-758, FLC, and ITC against experimental murine OPC induced by FLC-S C. albicans strains 2085A and 2054A. Each circle represents the result for an individual mouse. Closed circles, results above the detection limit; open circles, results below the detection limit; bars, mean values (n = 6); ***, P < 0.001 by Dunnett's test.
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FIG. 4. Efficacies of CS-758, FLC, and ITC against experimental murine OPC induced by FLC-S-DD C. albicans strains 2010A and 2033A and FLC-R C. albicans strain 2035B. Each circle represents the result for an individual mouse. Closed circles, results above the detection limit; open circles, results below the detection limit; bars, mean values (n = 6); *, P < 0.05 by Dunnett's test; **, P < 0.01 by Dunnett's test; ***, P < 0.001 by Dunnett's test.
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In this study, we first demonstrated that the test agents were effective against experimental murine OPC induced by azole-susceptible strain C. albicans SANK51486 both mycologically and histopathologically. The results of the histopathological analysis from this experiment reflect the results of the fungal burden study, demonstrating that the fungal burden in the oropharynx could be a suitable indicator of therapeutic efficacy.
We next investigated the therapeutic efficacies of triazoles against experimental murine OPC induced by strains with various susceptibilities to FLC. In those experiments in mice, we observed a strong correlation between the MIC and the therapeutic efficacy of FLC. In particular, against the FLC-S-DD strain for which the FLC MIC was 32 µg/ml, FLC reduced the viable cell counts significantly only at 50 mg/kg/dose, and against the FLC-R strain for which the FLC MIC was 64 µg/ml, FLC had no effect even at 50 mg/kg/dose. These results suggest that in vitro resistance to FLC, as measured by the NCCLS method, is significantly correlated with in vivo resistance to FLC in the OPC model.
For ITC, the interpretive breakpoints in NCCLS document M27-A (10) are as follows: susceptible,
0.12 µg/ml; susceptible dose dependent; 0.25 to 0.5 µg/ml; and resistant,
1 µg/ml. All the strains used in this study were categorized as ITC susceptible or ITC susceptible dose dependent. The therapeutic efficacy of ITC was almost in correlation with its MIC. Although strain 2035B was susceptible to ITC (MIC, 0.12 µg/ml), ITC was not effective in vivo against this strain. The reason for the discrepancy between the MIC and efficacy for ITC remains unknown. Further studies will be needed.
As the efficacy in this model corresponds fairly well to the NCCLS interpretive breakpoints for susceptibility, this model is thought to be useful for prediction of the therapeutic efficacies of new drugs. However, to improve the predictive utility of this model, pharmacokinetic and pharmacodynamic analyses will be needed. Previously, Walsh and colleagues (22) reported on an experimental oropharyngeal and esophageal candidiasis model in rabbits induced by FLC-S and FLC-R C. albicans strains. In their rabbit model, a strong correlation between the in vitro and in vivo activities was described, and it was demonstrated that the FLC concentrations in plasma or esophageal tissue exceeded the MIC for the FLC-S strain at the responsive dose but not that for the FLC-R strain at the unresponsive dose (22). Using the rabbit model, they demonstrated a strong relationship between the fungal burden and the drug concentration in plasma, saliva, and esophageal tissue for V-echinocandin (12). As for our murine OPC model, pharmacokinetic and pharmacodynamic analyses are under way.
In this study, CS-758 was shown to exhibit excellent efficacy against experimental murine OPC including OPC induced by an FLC-R strain. One of the reasons for this excellent efficacy is thought to be the potent in vitro activity of CS-758. In our preliminary study, the plasma drug concentration was sustained above the MICs by at least more than threefold in mice treated with 10 mg of CS-758/kg/dose. In addition, CS-758 was shown to be distributed widely in rat tissue (T. Shibayama, N. Kikuchi, Y. Matsushita, K. Kawai, A. J. John, T. Hirota, and S. Kuwahara, Abstr. 40th Intersci. Conf. Antimicrob. Agents Chemother., abstr. 1090, 2000). The sufficient concentration of CS-758 in plasma and the widespread distribution of the drug in tissue may contribute to the excellent efficacy of CS-758. Compared with FLC, the large discrepancy was observed in the relationship between the MIC of CS-758 and its efficacy. This discrepancy has been observed in a systemic C. albicans infection model (5). From our preliminary data, the concentration of drug in the plasma of mice administered FLC was approximately 10-fold higher than that in the plasma of mice administered the same dose of CS-758. Additionally, the levels of serum protein binding were 12% for FLC (4) and 99% for CS-758 (unpublished data) in mice. These pharmacokinetic profiles may clarify the discrepancy between in vitro activity and efficacy for CS-758. However, CS-758 has potent in vitro activity, with MICs of 0.25 µg/ml or lower for FLC-R C. albicans strains (FLC MICs, 64 µg/ml) other than the strain used in this study (data not shown). Considering these findings, CS-758 is a promising compound for the treatment of OPC including FLC-resistant infections.
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