Title:Practical Application of Rodent Transporter Knockout Models to Assess
Brain Penetration in Drug Discovery
Volume: 15
Issue: 1
Author(s): Elin Eneberg*, Christopher R. Jones, Thomas Jensen, Kristine Langthaler and Christoffer Bundgaard
Affiliation:
- Department of Translational DMPK, H. Lundbeck A/S, Valby, 2500 Copenhagen, Denmark
Keywords:
CNS, blood-brain-barrier, ABC transporters, P-gp, BCRP, Kp, uu, drug discovery.
Abstract:
Background and Objective: Compound X is a drug candidate for the treatment of neurodegenerative
diseases. Its brain distribution was evaluated as part of the lead identification and
optimization activities undertaken in early drug discovery.
Methods: The brain distribution of compound X was studied in genetic transporter knockout rodent
models, in vivo models with a chemical inhibitor, and in vitro transporter cell systems.
Results: Compound X was found to be a substrate for human Breast Cancer-Resistance Protein
(BCRP) in vitro (efflux ratio 8.1) and rodent Bcrp in vivo (Kp, uuKO/Kp, uuWT = 0.15/0.057 =
2.7, p< 0.05) but not a substrate for human P-glycoprotein (P-gp) in vitro (efflux ratio 1.0) nor
rodent P-gp in vivo (Kp, uuKO/Kp, uuWT = 0.056/ 0.051 = 1.1, p> 0.05). When both transporters
were knocked out in vivo, Kp, uu increased to 0.51±0.02. A similar pattern observed across compounds
with related chemistry corroborating the structure-activity relationship.
Conclusion: While in vitro assays showed compound X to be a substrate for human BCRP and not
P-gp, in vivo studies indicated a synergistic effect between rodent efflux transporters. However,
this only accounted for ~50% of restricted BBB-transport, suggesting involvement of other efflux
transporters. Considering Kp, uu as a key criterion for assessing the technical quality of CNS candidates
before progression into clinical development, it is important to identify relevant screening
assays for a better understanding of low Kp, uu and brain distribution in pre-clinical models for
translation to humans.
