Assessing the impact of gut vs. liver CYP3A4 metabolism on bioavailability.
The problem
First-pass metabolism is commonly the limiting factor in the oral bioavailability of a drug. The impact of first-pass hepatic metabolism has been accepted for many years. It is increasingly recognised that first-pass intestinal metabolism also plays a major role in limiting oral bioavailability.
It is therefore desirable to compare and rank the impact of intestinal vs. hepatic first-pass metabolism in preclinical studies. However, existing techniques such as animal gut perfusion studies are expensive and require a high level of technical expertise.
The solution
In humans, CYP3A4 catalyzes the metabolism of over 50% of drugs in clinical use[1]. CYP3A4 accounts for approximately 30% and 80% of the total CYP abundance in the liver and intestine, respectively, and is therefore the major contributor to both hepatic and intestinal first-pass metabolism.
The transADMETTM mouse panel includes models with liver-specific and intestine-specific CYP3A4 expression, driven by tissue-specific ApoE and villin promoters. Critically, these mice are on a Cyp3a knockout background, so there is no interference from murine Cyp3a genes.
The Humanized Liver CYP3A4 Mouse and Humanized Gut CYP3A4 Mouse provide a powerful new tool for preclinical characterisation of first-pass hepatic vs. intestinal metabolism and offer an alternative to surgical techniques such as gut perfusion studies.
Example study design
Example results
The Humanized Liver CYP3A4 and Humanized Gut CYP3A4 Mice demonstrate the pronounced effect of intestinal CYP3A4 mediated metabolism on oral bioavailability of docetaxel:
Figure 1: Pharmacokinetic parameters estimated for docetaxel (10 mg/kg) in wild type, Humanized Liver CYP3A4 Mouse, Humanized Gut CYP3A4 Mouse and Cyp3a (8-gene) Knockout Mouse.
The contribution of intestinal CYP3A4 to the clearance of docetaxel after i.v. administration was almost negligible, the plasma AUC in Humanized Gut CYP3A4 Mice being only 28% lower than that in KO mice. In contrast, after oral administration, docetaxel plasma exposure in Humanized Gut CYP3A4 Mice was reduced to levels comparable to those in wild-type mice.
Humanized Liver and Gut CYP3A4 Mice can be used to demonstrate the influence of gut vs. liver metabolism on oral bioavailability of test compounds.
Availability
CXR and Taconic have partnered to make the transADMETTM CYP3A Models commercially available.
Contract services: CXR are co-exclusive suppliers of contract research services using transADMET TM mice. We also offer consultancy and advice to our customers.
For more information on contract research services at CXR using the transADMETTM mice, contact us here or at transadmet@cxrbiosciences.com.
Off the shelf mice: Mice may be purchased directly from Taconic by both academic and for-profit customers. To purchase transADMETTM mice, please visit the relevant model webpages:
For questions regarding distribution of these models, please contact Dr. Megan MacBride.
[1] Guengerich FP. (1999) Cytochrome P-450 3A4: regulation and role in drug metabolism. Annu Rev Pharmacol Toxicol 39:1-17.
The HRN™ mouse.
A unique mouse model with no hepatic CYP450 activity, that can be used to determine the effects of first-pass hepatic CYP 450 metabolism on the pharmacokinetics, efficacy and toxicity of compounds.
In vivo screening PK studies.
Small, cost effective PK studies, where multisampling techniques in mouse mean compound and animal use is minimised.
