Evaluation of covalent binding of flutamide and its risk assessment using ¹⁹F-NMR

Abstract

1. The formation of reactive metabolites (RMs) is a problem in drug development that sometimes results in severe hepatotoxicity. As detecting RMs themselves is difficult, a covalent binding assay using expensive radiolabelled tracers is usually performed for candidate selection.

2. This study aimed to provide a practical approach toward the risk assessment of hepatotoxicity induced by covalent binding before candidate selection.

3. We focused on flutamide because it contains a trifluoromethyl group that shows a strong singlet peak by ¹⁹F nuclear magnetic resonance (NMR) spectrometry. The covalent binding of flutamide was evaluated using quantitative NMR and its risk for hepatotoxicity was assessed by estimating the RM burden, an index that reflects the body burden associated with RM exposure by determining the extent of covalent binding, clinical dose and in vivo clearance. The extent of covalent binding and RM burden was 296 pmol/mg/h and 37.9 mg/day, respectively. Flutamide was categorised as high risk with an RM burden >10 mg/day consistent with its clinical hepatotoxicity.

4. These results indicate that a combination of covalent binding assay using ¹⁹F-NMR and RM burden is useful for the risk assessment of RMs without using radiolabelled compounds.

Keywords:

• Reactive metabolites
• F nuclear magnetic resonance
• quantitative nuclear magnetic resonance
• reactive metabolite burden
• hepatotoxicity
• covalent binding

Acknowledgements

The authors thank ASCA Corporation for English language editing.

Disclosure statement

The authors report no conflict of interest.