Humanised metabolism models for in vitro screening
Species differences in drug metabolism and responsiveness between mice and humans mean that it is difficult to extrapolate results obtained in animal trials to humans. Therefore humanised mice for the key drug metabolising enzymes, transporters and the transcription factors that regulate them can provide new insights into the drug development process.
Our transgenic screening and safety models programme has developed an impressive range of humanised and knockout (KO) models that are all available from a single source on the same genetic background. All humanisations are done using a targeted integration strategy to ensure physiological expression levels and tissue distribution.
This world-leading programme represents a significant advance on current safety and toxicology models through improved prediction of the human drug response. Humanised models offer the ability to flag up potential drug-drug interaction and metabolite issues earlier in the drug development pathway.
The models are grouped into four key panels covering each element of the drug metabolism pathway – nuclear receptors, cytochrome (CYP) P450 enzymes, transporters and a reporter panel. The development of in vitro systems could be used as a fast and efficient screen to determine which in vivo model is best suited to answer the particular safety or toxicology issue.
Models currently available for in vitro development
The nuclear receptors, PXR and CAR, play a key role in the regulation of genes involved in metabolism.
- Hence, understanding their interactions is both important and complex, particularly due to the cross-talk between receptors.
- The Receptor Panel offers two key advances in the study of PXR and CAR that will further the dissection of their involvement in the study of drug metabolism.
- Firstly, the fact that each nuclear receptor has been humanised means these models more closely resemble the situation in man than wild type mice.
- Secondly, the range of models available, including single and double humanised plus KO models for both receptors, means it is now easier to isolate which receptor is involved in which step of metabolism.
The CYP Panel contains KO and humanised models for the major Phase 1 CYP genes that are involved in drug metabolism.
- Within the CYP3A family (which metabolise >50 percent of marketed drugs) there is a KO of the entire murine Cyp3a locus and models humanised for CYP3A4 and CYP3A7. Within the CYP2C family (which metabolise more than 20 percent of marketed drugs) there is a Cyp2c KO and a model humanised for CYP2C9.
- Finally within the CYP2D family there is a Cyp2d KO and a model humanised for CYP2D6.
- Many of these models are available on a human PXR or CAR background.
- These models can be used alongside existing CYP in vitro assays to determine human-specific induction or inhibition and identify human specific metabolites.
Among the ABC trans-membrane proteins the MDR1 & MRP2 genes are a major confounding factor for drug development and are believed to play a key role in drug resistance.
- MDR1 encodes for P-glycoprotein (P-gp) and is known to export a large number of drugs including cytotoxic agents and immunosuppressants. MRP2 is important in mediating the transport of anionic drugs and metabolites.
- The Transporter Panel includes both KO and humanised forms of both mouse Mdr1 genes – Mdr1a & b and also a double KO and humanisation of Mdr1a/b. It also contains a humanised MRP2 mouse.
The Reporter Panel enables visualisation of the induction of key metabolism genes via luciferase and lacZ activation.
- These models provide direct in vivo information of the ability of drugs to induce or repress specific CYP’s, transporter genes and the transcription factors that regulate them.
- Key genes tagged with a reporter include: CYP2D6, CYP2B6, MDR1, Cyp3a11 and CYP3A4. Moreover, many of these reporter genes are on a PXR/CAR background.
- Additional benefits of the reporter panel include the assessment of organ-specific enzyme induction, for example liver versus intestine and the easy read out of the in vivo interaction of a compound with PXR and CAR.
These models have been developed by Scottish Enterprise together with our Research Providers – CXR Biosciences and TaconicArtemis. More information about the Nuclear Receptor Panel can be found in the following publication: “A novel panel of mouse models to evaluate the role of human pregnane X receptor and constitutive androstane receptor in drug response”. Scheer, N., Ross, J., Rode, A., Zevnik, B., Niehaves, S., Faust, N. and Wolf, C.R. (2008) J. Clin. Invest. 118:3228-3239. Prof Ron Evans of the Salk Institute is an advisor to the TSM Programme.
The next step
If you are interested in exploring any of these exciting opportunities further, from either a research or commercialisation perspective, please contact us