Development of Murine Cyp3a Knockout Chimeric Mice with Humanized Liver

Area of Science:

• Pharmacology
• Genetics
• Biotechnology

Background:

• Conventional chimeric mice with humanized livers (PXB-mice) can be influenced by residual mouse metabolic enzymes, impacting drug metabolism prediction.
• Mouse cytochrome P450 3A (CYP3A) enzymes are a major source of metabolic interference in current models.

Purpose of the Study:

• To develop a novel chimeric mouse model lacking murine CYP3A to improve the prediction of human drug metabolism and pharmacokinetics.
• To overcome limitations of existing humanized liver mouse models by eliminating endogenous mouse CYP3A activity.

Main Methods:

• Development of murine CYP3A knockout (KO) chimeric mice transplanted with human hepatocytes.
• Analysis of human P450s, UGTs, SULTs, and transporter mRNA expression via quantitative real-time-polymerase chain reaction.
• Assessment of midazolam and triazolam metabolic activities in liver and intestinal microsomes.

Main Results:

• Humanized livers in CYP3A KO chimeric mice expressed human P450s, UGTs, SULTs, and transporters similarly to PXB-mice.
• Absence of murine Cyp3a11 mRNA confirmed in the liver and intestine of CYP3A KO chimeric mice.
• Drug metabolism findings for midazolam and triazolam were comparable in liver microsomes but attenuated in intestinal microsomes compared to PXB-mice.

Conclusions:

• Murine CYP3A KO chimeric mice provide a valuable model for studying human drug metabolism, reducing interference from endogenous mouse enzymes.
• Human hepatocyte transplantation in CYP3A KO mice successfully restored human drug-metabolizing enzyme expression, though some murine enzyme upregulation persisted.
• This model offers improved potential for accurate prediction of drug metabolism and pharmacokinetics in humans.