ABSTRACT
Icofungipen (PLD-118) is the representative of a novel class of antifungals, beta amino acids, active against
Candida
species. It has been taken through phase II clinical trials. The compound actively accumulates in yeast, competitively inhibiting isoleucyl-tRNA synthetase and consequently disrupting protein biosynthesis. As a result, in vitro activity can be studied only in chemically defined growth media without free amino acids that would compete with the uptake of the compound. The MIC of icofungipen was reproducibly measured in a microdilution assay using yeast nitrogen base medium at pH 6 to 7 after 24 h of incubation at 30 to 37°C using an inoculum of 50 to 100 CFU/well. The MICs for 69
Candida albicans
strains ranged from 4 to 32 μg/ml. This modest in vitro activity contrasts with the strong in vivo efficacy in
C. albicans
infection. This was demonstrated in a lethal model of
C. albicans
infection in mice and rats in which icofungipen showed dose-dependent protection at oral doses of 10 to 20 mg/kg of body weight per day in mice and 2 to 10 mg/kg/day in rats. The in vivo efficacy was also demonstrated against
C. albicans
isolates with low susceptibility to fluconazole, indicating activity against azole-resistant strains. The efficacy of icofungipen in mice and rats was not influenced by concomitant administration of equimolar amounts of
l
-isoleucine, which was shown to antagonize its antifungal activity in vitro. Icofungipen shows nearly complete oral bioavailability in a variety of species, and its in vivo efficacy indicates its potential for the oral treatment of yeast infections.
