The Receptor Panel
Nuclear receptors play a major role in regulating the bodies’ response to chemical exposure.
The pregnane x receptor (PXR) and constitutive androstane receptor (CAR) have the ability to bind a wide range of exogenous and endogenous ligands and, as a consequence, to control the level of expression of genes highly relevant to compound metabolism, such as the cytochrome P450s and drug transporters. Sequence variation in PXR and CAR between animals and man results in differences in the ability of exogenous ligands to interact and activate these transcription factors. Experimental data obtained in animal models, or in vitro test systems, may therefore not reflect the interactions which occur in man.
In order to circumvent this problem and to obtain a series of models in which the metabolic consequences of activation of PXR and CAR by exogenous agents can be more accurately evaluated, we have created mouse models in which we have exchanged the corresponding murine genes for their human counterparts. This Receptor Panel of models contains not only humanised mouse models, but also knock outs, that can be used in a coordinated fashion to address these problems. A publication describing these models can be found here.
Receptor Panel: Key Utilities:
1. A more predictive screen for non-genotoxic carcinogenicity in man. Many marketed drugs are non-genotoxic carcinogens in rats and/or mice (e.g. benzodiazepines, barbiturates, phenytoin). Their proliferative effects are believed to be driven through murine nuclear receptors such as PXR and CAR, but do not appear to be supported by human PXR or CAR – an outcome replicated in the hPXR/hCAR mice. Non-genotoxic carcinogenicity is also an area of concern for agrochemical companies, and there is evidence that agrochemical regulators will support novel methods of demonstrating lack of relevance to man. Further information can be found here.
2. Improved Cytochrome P450 (CYP) induction screening. CYP induction is an important cause of drug-drug interactions, and the FDA recommends that candidate drugs are assessed for their induction potential. Current screens for CYP induction have marked limitations. Human hepatocytes show high inter-individual variability, therefore low reproducibility. In addition, some CYP induction (especially through CAR) requires intact metabolic systems, and therefore induction events may be missed in vitro. In vitro PXR transactivation assays are available, but accurate CAR transactivation assays are not. Although CYP induction can be studied in animals, profound species-specific differences in PXR and CAR response limit their relevance to man. Therefore it is not unusual for human induction events to go undetected until a compound enters the clinic or alternatively, rodent specific induction may be observed that is not relevant to man. The humanised receptor mice therefore represent a more accurate and reproducible tool for predicting human CYP induction.
3. In vivo effects of CYP induction. Until now, it has been difficult to study the in vivo implications of CYP induction before entering the clinic, due to the profound species differences outlined above. The humanised receptor mice represent the ideal model for predicting effects of CYP induction on the PK, metabolism and toxicity of novel investigative compounds and likely co-administered drugs.
Download the transADMET mice brochure here.
CASE STUDY 1
Groups | |
Group size | |
Study duration | |
Dosing | |
Endpoints | Liver/body weight ratios - BrdU incorporation analysed as a measure of cell proliferation in the liver
- Haematoxylin and eosin liver and thyroid histopathology
- Expression and activity of Cyp2b10 and Cyp3a11 by Western blotting and enzyme activity assays in liver microsomes
- Plasma liver markers
|
CASE STUDY 2
Groups | |
Optional groups | |
Group size | |
Study duration | |
Dosing | |
Endpoints | - PK samples taken at 2 and 8 hours post-dose on days 1 and 7, terminal PK samples
- RNA extracted from liver for determination of mRNA levels
- Microsomes prepared from liver for enzyme activity analysis
- Optional organ samples taken for toxicological analysis
|
CASE STUDY 2b
| Liver Microsomal Activity (pmol test item/30 min/mg) | [Test Item Plasma] (ng/mL) |
Test compound treated male groups | Pxr-Car Knockout Mouse | Wild Type | Pxr-Car Knockout Mouse | Wild Type |
2 hours | NA | NA | 18,374 ± 1,273 | 18,594 ± 1,962 |
Terminal (7 days) | 192 ± 42 | 1,543 ± 58 | 29,179 ± 12,777 | 0 ± 0 |
CASE STUDY 3
Groups | |
Optional groups | |
Group size | |
Study duration | |
Dosing | |
Endpoints | |
| | Liver Microsomal Activity
(pmol test item/30 min/mg) | [Test item Plasma]
(ng/mL) |
| Test Compound treated male groups | Pxr-Car Knockout Mouse | Wild Type | Pxr-Car Knockout Mouse | Wild Type |
| 2 hours | NA | NA | 18,374 ± 1,273 | 18,594 ± 1,962 |
Terminal
(7 days) | 192 ± 42 | 1,543 ± 58 | 29,179 ± 12,777 | 0 ± 0 |
| | Taconic Model Number Human CYP3A4/3A7
(human promoters) ApoE promoter human CYP3A4 Villin promoter human CYP3A4 Knockout of 8 Cyp3a genes Knockout of 7 Cyp3a genes Genetic Background
Humanized CYP3A4/3A7 Mouse
8842 |
X | | | |
X |
C57BL/6 |
Cyp3a (7-gene) Knockout Mouse
8841 | | | | |
X |
C57BL/6 |
Humanized Liver CYP3A4 Mouse
9048 | |
X | |
X | |
FVB |
Humanized Gut CYP3A4 Mouse
9047 | | |
X |
X | |
FVB |
Humanized Liver & Gut CYP3A4 Mouse
9049 | |
X |
X |
X | |
FVB |
Cyp3a (8-gene) Knockout Mouse*
9011 | | | |
X | |
FVB |
The HRN™ mouse.
A unique mouse model with no hepatic CYP450 activity, that can be used to determine ADME, PK and efficacy in the absence of confounding first-pass metabolism.
In vivo screening PK studies.
Small, cost effective PK studies, where multisampling techniques in mouse or rat mean compound and animal use is minimised.
Drug development solutions.
CXR combines proprietary technologies with improved application of traditional preclinical techniques and assays, including in vitro and in vivo ADME and Toxicology studies; cell culture; and an extensive analytical capability.
