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

Area of Science:

• Drug Development
• Toxicology
• Analytical Chemistry

Background:

• Reactive metabolites (RMs) formation is a significant challenge in drug development, often leading to severe hepatotoxicity.
• Detecting RMs directly is difficult, necessitating expensive radiolabeled tracers for covalent binding assays during candidate selection.

Purpose of the Study:

• To establish a practical method for assessing hepatotoxicity risk from covalent binding before drug candidate selection.
• To utilize 19F-NMR spectrometry for evaluating the covalent binding of drugs containing a trifluoromethyl group.

Main Methods:

• Quantitative 19F-NMR was employed to measure the covalent binding of flutamide.
• The risk of hepatotoxicity was assessed by calculating the Reactive Metabolite (RM) burden, an index incorporating covalent binding extent, clinical dose, and in vivo clearance.

Main Results:

• The covalent binding extent of flutamide was measured at 296 pmol/mg/h.
• The calculated RM burden for flutamide was 37.9 mg/day, categorizing it as high risk (>10 mg/day) and aligning with its known clinical hepatotoxicity.

Conclusions:

• A combined approach using 19F-NMR for covalent binding assays and RM burden estimation provides a valuable tool for assessing RM-induced hepatotoxicity risk.
• This method offers a practical alternative to radiolabeled compounds for early-stage drug development risk assessment.