In Vivo Pharmacokinetics and Pharmacodynamics of APX001 against Candida spp. in a Neutropenic Disseminated Candidiasis Mouse Model

Abstract

APX001 is the prodrug of APX001A, which is a first-in-class small molecule with a unique mechanism of action that inhibits the fungal enzyme Gwt1 in the glycosylphosphatidylinositol (GPI) biosynthesis pathway. The goal of the present study was to determine which pharmacokinetic/pharmacodynamic (PK/PD) index and magnitude best correlated with efficacy in the murine disseminated candidiasis model for ( = 5), ( = 5), and ( = 4). MIC values ranged from 0.002 to 0.03 mg/liter for , from 0.008 to 0.06 mg/liter for, and from 0.004 to 0.03 mg/liter for Plasma APX001A pharmacokinetic measurements were performed in mice after oral administration of 4, 16, 64, and 256 mg/kg of body weight APX001. Single-dose pharmacokinetic studies exhibited maximum plasma concentration () values of 0.46 to 15.6 mg/liter, area under the concentration-time curve (AUC) from time zero to infinity (AUC) values of 0.87 to 70.0 mg · h/liter, and half-lives of 1.40 to 2.75 h. A neutropenic murine disseminated candidiasis model was utilized for all treatment studies, and drug dosing was by the oral route. Dose fractionation was performed against K1, with total doses ranging from 4 to 1,024 mg/kg/day of APX001 fractionated into regimens of dosing every 3, 6, 8, and 12 h for a 24-h treatment duration. Nonlinear regression analysis was used to determine which PK/PD index best correlated with efficacy on the basis of the reduction in the number of CFU/kidney at 24 h. The 24-h free-drug AUC/MIC ratio (AUC/MIC) was the PK/PD index that best correlated with efficacy (coefficient of determination [] = 0.88). Treatment studies with the remaining strains utilized regimens of 1 to 256 mg/kg of APX001 administered every 6 h for a 24-h duration with and a 96-h study duration with and The dose required to achieve 50% of the maximum effect (ED) and stasis AUC/MIC targets were as follows: for, 3.67 ± 3.19 and 20.60 ± 6.50, respectively; for , 0.38 ± 0.21 and 1.31 ± 0.27, respectively; and for, 7.14 ± 4.54 and 14.67 ± 8.30, respectively. The present studies demonstrated and APX001A and APX001 potency, respectively, against ,, and These results have potential relevance for clinical dose selection and evaluation of susceptibility breakpoints. The identification of a lower AUC/MIC ratio target for suggests that species-specific susceptibility breakpoints should be explored.

APX001 Pharmacokinetic/Pharmacodynamic Target Determination against Aspergillus fumigatus in an In Vivo Model of Invasive Pulmonary Aspergillosis

“…A number of compelling study findings were observed. First, the results are consistent with previous findings in an invasive candidiasis murine model demonstrating that AUC/MEC is the most predictive PK/PD index of the microbiological effect (27). Second, the APX001 dose-response relationships were very similar across a diverse set of A. fumigatus strains, as supported by the high R 2 value (0.80) and relatively close fit to the individual stasis and 1-log-kill targets ( Table 2).…”

“…The median total drug AUC/MEC ratio required to achieve a stasis effect for A. fumigatus was 2,802, and that required to achieve a 1-log kill effect was 5,258. The stasis targets are within the range of AUC/MIC stasis target values that we observed in a murine disseminated candidiasis model with Candida glabrata and Candida auris but notably lower than the values observed with Candida albicans (27). This finding is also reminiscent of that from a PK/PD study with mold-active triazoles, where lower AUC/MEC targets and more fungicidal activity were observed for posaconazole and isavuconazole against A. fumigatus than against C. albicans (35,36,38,39).…”

“…We included a selection of Cyp51 mutants in our study and observed similar results (APX001A MEC, 0.03 to 0.06 mg/liter). It is noteworthy that we also included a laboratory-engineered FKS mutant with echinocandin resistance and demonstrated the similar in vitro potency of APX001A against this strain and wild-type strains, as has been seen in prior analyses of resistant isolates (17,27). Thus, in keeping with the known novel mechanism of action compared to that of existing agents, there was no evidence of cross-resistance in our study.…”

“…Pharmacokinetics. Data from our prior PK study of APX001 were used for the current study analysis (27). The area under the concentration-time curve (AUC) and peak concentrations (C max ) over the dose range were linear (coefficient of determination [R 2 ] ϭ 0.96), including when accounting for drug accumulation due to the frequent administration.…”

Impact of Candida auris infection in a neutropenic murine model

“…However, a limitation of using cyclophosphamide is that it depletes cells of both the innate and the adaptive immune system (25). At high doses of cyclophosphamide ≥200mg/kg, these deplete Tregs, CD8 + DCs, B-cells and CD4 + and CD8 + T-cells that may be important in immunological studies in response to C. auris (23, 24, 26–29).…”