In vitro and in vivo metabolism of ¹⁴C-AZ11, a novel inhibitor of bacterial DNA gyrase/type II topoisomerase

Abstract

1. (2R,4S,4aS)-11-Fluoro-2,4-dimethyl-8-((S)-4-methyl-2-oxooxazolidin-3-yl)-2,4,4a,6-tetrahydro-1H,1'H-spiro [isoxazolo[4,5-g][1,4]oxazino[4,3-a]quinoline-5,5′-pyrimidine]-2′,4′,6′(3′H)-trione (AZ11) is a novel mode-of-inhibition bacterial topoisomerase inhibitor that entered preclinical development for the treatment of Gram-positive bacteria infection.

2. The in vitro biotransformation studies of AZ11 using mouse, rat, dog and human hepatocytes showed low-intrinsic clearance in all species attributed to microsomal metabolism.

3. After a single intravenous administration of [¹⁴C]AZ11 in bile duct cannulated rats, the mean percentage of dose recovered in rat urine, bile and feces was approximately 18, 36 and 42%, respectively. Unchanged AZ11 recovered in rat urine and bile was less than 9% of the dose, indicating that AZ11 underwent extensive metabolism in rats.

4. The most abundant in vivo metabolite detected in urine and bile was M1 formed via ring opening on the piperidine and morpholine rings accounting for 20% of the administered dose. The major fecal metabolite was M5, which accounted for approximately 32% of administered dose. M5 was not formed when AZ11 incubated with rat intestinal microsomes and cytosol but was formed when incubated with fresh rat feces, suggesting that unchanged AZ11 was directly excreted into gut lumen where M5 formed as an intestinal microflora-mediated product. This process could have significant impact on bioavailability or exposure of AZ11 in rat.

• AZ11
• excretion
• mass spectrometry
• metabolism

Acknowledgements

Authors thank Ying Liu and Vladimir Capka for separation and purification of the renal metabolites for NMR analysis; Ryan Bragg and Nick Bushby for providing ¹⁴C-labeled standard; Linda G. Otterson and Michael D. Huband for validating the assay using feces from germ-free rats and their scientific input in microbiology.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.