Dosage-dependent antifungal efficacy of V-echinocandin (LY303366) against experimental fluconazole-resistant oropharyngeal and esophageal candidiasis

Abstract

V-echinocandin (VER-002; LY303366) is a semisynthetic derivative of echinocandin B and a potent inhibitor of fungal (1, 3)-beta-D-glucan synthase. We studied the antifungal efficacy, the concentrations in saliva and tissue, and the safety of VER-002 at escalating dosages against experimental oropharyngeal and esophageal candidiasis caused by fluconazole-resistant Candida albicans in immunocompromised rabbits. Study groups consisted of untreated controls, animals treated with VER-002 at 1, 2.5, and 5 mg/kg of body weight/day intravenously (i.v.), animals treated with fluconazole at 2 mg/kg/day i.v., or animals treated with amphotericin B at 0.3 mg/kg/day. VER-002-treated animals showed a significant dosage-dependent clearance of C. albicans from the tongue, oropharynx, esophagus, stomach, and duodenum in comparison to that for untreated controls. VER-002 also was superior to amphotericin B and fluconazole in clearing the organism from all sites studied. These in vivo findings are consistent with the results of in vitro time-kill assays, which demonstrated that VER-002 has concentration-dependent fungicidal activity. Esophageal tissue VER-002 concentrations were dosage proportional and exceeded the MIC at all dosages. Echinocandin concentrations in saliva were greater than or equal to the MICs at all dosages. There was no elevation of serum hepatic transaminase, alkaline phosphatase, bilirubin, potassium, or creatinine levels in VER-002-treated rabbits. In summary, the echinocandin VER-002 was well tolerated, penetrated the esophagus and salivary glands, and demonstrated dosage-dependent antifungal activity against fluconazole-resistant esophageal candidiasis in immunocompromised rabbits.

FIG. 1

Time-kill assay of VER-002 and amphotericin B against C. albicans in antibiotic medium 3. Concentrations of VER-002 (VER) and amphotericin B (AmB) at 0.01, 0.1, and 0.25 μg/ml were studied in relation to a growth control. Data plotted are the mean ± SEM from three separate experiments for each growth curve, including the control and amphotericin B at 0.25 μg/ml. As the SEM was small for several time points, the error bars may not always be apparent in the time-kill curves.

FIG. 2

Response of experimental OPEC caused by fluconazole-resistant C. albicans in immunocompromised rabbits to antifungal therapy measured by mean log (CFU per gram) concentration of organism in the tongue, oropharynx, esophagus, stomach, and duodenum in untreated controls (control) (n = 18), rabbits treated with VER1 (n = 9), VER2.5 (n = 9), and VER5 (n = 9), rabbits treated with amphotericin B at 0.3 mg/kg/day (AmB) (n = 9), and rabbits treated with fluconazole at 1 mg/kg/day (FLU) (n = 9). Values are given as mean ± SEM. ∗, P < 0.05; †, P < 0.01; and ¶, P < 0.001, in comparison to untreated controls by the Kruskal-Wallis nonparametric analysis of variance test with Dunn's correction for multiple comparisons.

FIG. 3

Concentration-effect relationship for VER-002 in the treatment of experimental OPEC. The relationship follows an inhibitory effect sigmoidal E_max model with no effect at a concentration of 0 and complete inhibition at a concentration extrapolated to infinity. Depicted are the fitted curve and the scatter of the observed values: (A) Residual fungal burden in esophageal tissue versus near-peak concentrations of VER-002 in plasma; (B) residual fungal burden in esophageal tissue versus concentrations of VER-002 in esophageal tissue 24 h after dosing. The coefficients of determination between observed and predicted data (r) were 0.8781 and 0.9302, respectively. Note the steep negative slope over a small concentration range, indicating the presence of a narrow threshold concentration for antifungal efficacy.

FIG. 4

Antifungal effect on microscopic morphology of the cell structure of fluconazole-resistant C. albicans in glossal tissue of rabbits treated with VER2.5, amphotericin B at 0.3 mg/kg/day, and fluconazole at 2 mg/kg/day. (A) Untreated controls; (B) VER2.5; (C) amphotericin B; (D) fluconazole. Gomori methenamine silver stain magnification, ×428 was used. (original magnification, ×630). (A and B) Transition from predominantly hyphae and pseudohyphae in untreated controls to predominance of yeast-like structures in rabbits treated with VER2.5. Rabbits treated with amphotericin B and fluconazole had no significant changes (C and D) in cell wall morphology.