Background: BAL8557 is a water soluble pro-drug, rapidly converted in plasma to the active azole BAL4815. In vitro, BAL4815 showed broadspectrum antifungal activity against all major opportunistic fungi and true pathogenic fungi, including fluconazole-resistant strains. The objective of the present study was to compare the metabolite profiles of all toxicological species with that in man.
Methods: Mixtures (1:1, w:w) of BAL8557 and 4D-BAL8557 (tetradeuterated) or BAL4815 and 4D-BAL4815 were incubated at final concentrations of 1, 10 and 100 μg/mL with mouse, rat, rabbit, dog, cynomolgus monkey and human liver microsomes for 60 minutes and with rat hepatocytes for 24 hours. Incubations were analyzed by capillary- LC-qTof-MS and LC-MS/MS.
Results: In human and cynomolgus monkey microsomes almost no metabolic biotransformation occurred. However, qualitatively the same metabolite pattern of BAL4815 was observed in all species, including human, with the formation of mono-oxidized BAL4815, most probably epoxide or phenol. In rabbit microsomes, an additional di-oxidized metabolite of BAL4815 was obtained, resulting from the hydrolysis of the epoxide. In rat hepatocytes, the glutathion-, cysteine- and Nacetylcysteine- phase 2 conjugates of the mono-oxidized BAL4815 could be identified. No specific metabolite for BAL8557 could be observed. Despite low amounts of metabolite formed, the unique isotopic pattern of the mixture combined with the use of high-resolution qTof-MS and MS/ MS allowed the structural elucidation of the metabolites.
Conclusion: With the formation of the mono-oxidized BAL4815 in animals, similarly to man, all species were qualified as suitable toxicological species.
- TIMM 2nd (2010)