Echinocandins inhibit the synthesis of β-1,3-D-glucan in Candida and are the first-line
therapy in numerous clinical settings. Their use is limited by poor oral bioavailability, and they are available only as intravenous
therapies. Derivatives of
enfumafungin are novel orally bioavailable
glucan synthase inhibitors. We performed an in vivo pharmacodynamic (PD) evaluation with a novel
enfumafungin derivative,
SCY-078 (formerly MK-3118), in a well-established neutropenic murine model of
invasive candidiasis against C. albicans, C. glabrata, and C. parapsilosis. The
SCY-078 MICs varied 8-fold. Oral doses of 3.125 to 200 mg/kg
SCY-078 salt in sterile water produced peak levels of 0.04 to 2.66 μg/ml, elimination half-lives of 5.8 to 8.5 h, areas under the concentration-time curve from 0 to 24 h (AUC0-24 h) of 0.61 to 41.10 μg·h/ml, and AUC from 0 to infinity (AUC0-∞) values of 0.68 to 40.31 μg·h/ml. The pharmacokinetics (PK) were approximately linear over the dose range studied. Maximum response (Emax) and PK/PD target identification studies were performed with 4 C. albicans, 4 C. glabrata, and 3 C. parapsilosis isolates. The PD index AUC/MIC was explored by using total (tAUC) and free (fAUC)
drug concentrations. The maximum responses were 4.0, 4.0, and 4.3 log10 CFU/kidney reductions for C. albicans, C. glabrata, and C. parapsilosis, respectively. The AUC/MIC was a robust predictor of efficacy (R2, 0.53 to 0.91). The 24-h PD targets were a static dose of 63.5 mg/kg, a tAUC/MIC of 500, and an fAUC/MIC of 1.0 for C. albicans; a static dose of 58.4 mg/kg, a tAUC/MIC of 315, and an fAUC/MIC of 0.63 for C. glabrata; and a static dose of 84.4 mg/kg, a tAUC/MIC of 198, and an fAUC/MIC of 0.40 for C. parapsilosis. The mean fAUC/MIC values associated with a 1-log kill endpoint against these species were 1.42, 1.26, and 0.91 for C. albicans, C. glabrata, and C. parapsilosis, respectively. The static and 1-log kill endpoints were measured relative to the burden at the start of
therapy. The static and 1-log kill doses, as well as the total and free
drug AUC/MIC PD targets, were not statistically different between species but were numerically lower than those observed for
echinocandins.
SCY-078 is a promising novel oral
glucan synthase inhibitor against Candida species, and further investigation is warranted.