Identification of reactive intermediate formation and bioactivation pathways in Abemaciclib metabolism by LC-MS/MS:...

Area of Science:

• Pharmacology
• Drug Metabolism
• Medicinal Chemistry

Background:

• Abemaciclib (Verzenio®) is a tyrosine kinase inhibitor (TKI) used in breast cancer treatment.
• Understanding its metabolic profile is crucial for optimizing safety and efficacy.
• No prior studies have detailed the in vitro metabolic profiling or reactive metabolite identification for abemaciclib.

Purpose of the Study:

• To perform in vitro phase I metabolic profiling of abemaciclib (ABC).
• To identify reactive intermediates formed during ABC metabolism.
• To propose a bioactivation pathway and suggest structural modifications for improved drug safety.

Main Methods:

• In vitro phase I metabolic studies using rat liver microsomes (RLMs).
• Utilized potassium cyanide (KCN) as a trapping agent for iminium reactive intermediates.
• Characterization of metabolites and adducts using Liquid Chromatography-Mass Spectrometry/Mass Spectrometry (LC-MS/MS).

Main Results:

• Identified nine in vitro phase I metabolites of abemaciclib.
• Detected three cyano adducts, indicating the formation of reactive intermediates.
• Metabolic pathways included reduction, oxidation, hydroxylation, and cyanide addition.
• A bioactivation pathway for abemaciclib was proposed.

Conclusions:

• The study elucidated the in vitro metabolic fate of abemaciclib, revealing key metabolic pathways and reactive intermediate formation.
• Identification of reactive metabolites provides insights into potential toxic side effects.
• Targeted structural modifications, such as blocking the α-carbon adjacent to piperazine ring nitrogens, may enhance abemaciclib's safety profile while maintaining efficacy.