CYP3A4 and pregnane X receptor humanized mice

Area of Science:

• Pharmacology and Toxicology
• Genetics and Genomics
• Biochemistry

Background:

• Significant species differences exist in cytochrome P450 (P450) enzyme expression and activity.
• Accurate prediction of human drug and carcinogen metabolism requires relevant animal models.

Purpose of the Study:

• To generate and characterize humanized mouse models for key human P450 enzymes and xenobiotic receptors.
• To investigate the physiological roles and drug metabolism functions of human CYP3A4 (hCYP3A4) in vivo.
• To study the mechanisms underlying gender differences in CYP3A4 expression and response.

Main Methods:

• Utilized bacterial artificial chromosomes (BAC) and P1 phage artificial chromosomes (PAC) genomic clones to create transgenic mice.
• Generated and characterized mouse lines expressing human CYP1A1, CYP1A2, CYP2E1, CYP2D6, CYP3A4, and CYP3A7.
• Developed a pregnane X receptor-humanized mouse (hPXR) model to study human PXR activation.

Main Results:

• The hCYP3A4 mouse model demonstrated CYP3A4's role in altering estrogen levels, leading to lactation deficiency and low pup survival.
• Established the critical importance of intestinal CYP3A4 in the pharmacokinetics of orally administered drugs.
• Elucidated mechanisms for gender-based differences in CYP3A4 expression (adult female > adult male).
• The hPXR mouse model showed specific responses to human PXR activators like rifampicin, unlike rodent activators.

Conclusions:

• Humanized mouse models are valuable tools for predicting human drug metabolism and understanding P450 physiological functions.
• Intestinal CYP3A4 plays a significant role in the oral bioavailability of drugs.
• These models help explain human gender differences in drug metabolism and response.
• Humanized xenobiotic receptor models are essential for studying species-specific responses to drug metabolism modulators.