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Characterizing the Reactive Metabolites of Colony-Stimulating Factor 1 Receptor Inhibitor PLX5622 in Liver Microsomes
Shenzhi Zhou1, Thomas Lee2, Xingyu Ji1
1Center for Drug Discovery, Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas 77030, United States.
Chemical Research in Toxicology
|June 27, 2026
Summary
The study investigated the metabolism of PLX5622, a CSF1R inhibitor, in liver microsomes and mice. Researchers identified reactive metabolites and determined that CYP3A is the primary enzyme responsible for PLX5622
Area of Science:
- Pharmacology
- Drug Metabolism
- Biochemistry
Background:
- Colony-stimulating factor 1 receptor (CSF1R) inhibitors like PLX5622 show promise for treating diseases such as rheumatoid arthritis and Alzheimer's disease (AD).
- Understanding drug metabolism, particularly bioactivation into reactive metabolites, is crucial for assessing therapeutic safety and efficacy.
Purpose of the Study:
- To investigate the metabolic fate and potential bioactivation of PLX5622 in mouse and human liver microsomes (MLM/HLM) and in vivo in mice.
- To identify reactive metabolites and the primary enzymes involved in PLX5622 metabolism.
Main Methods:
- LC-MS-based metabolomic approaches were employed to analyze PLX5622 metabolism.
- Reactive intermediates were captured using reduced glutathione (GSH) and methoxyamine (NH2OMe).
- Recombinant human cytochrome P450 (CYP) enzymes and chemical inhibitors were used to identify key metabolic enzymes.
Main Results:
- Twelve PLX5622-GSH adducts and five NH2OMe adducts were identified in HLM and MLM.
- Twenty-two non-trapped metabolites were characterized, resulting from demethylation, hydroxylation, and carbon-carbon cleavage.
- Eight GSH adducts were detected in mouse liver, confirming in vivo bioactivation, with CYP3A identified as the primary enzyme responsible.
Conclusions:
- PLX5622 undergoes metabolic activation, forming reactive metabolites primarily mediated by CYP3A.
- These findings are critical for evaluating the safety profile and potential drug interactions of PLX5622, especially concerning CYP3A.
- Further studies using human primary hepatocytes or liver-on-a-chip systems are recommended to confirm clinical relevance.
