Abstract by Kristine Langthaler

Introduction and aim: Central nervous system (CNS) disorders are a global burden, with their increasing prevalence outpacing the development of new medical treatments. Ensuring drug delivery to the brain is a huge challenge. This challenge necessitates investigations that heavily rely on the clinical translational capabilities derived from in vivo experiments. In this context, the minipig has gained attention as a potential preclinical model. Therefore, the main aim of the project was to evaluate new methods for determining pharmacokinetic (PK) parameters, including systemic PK  (CL and V_ss) and brain PK (K_{p,brain ,} K_p,uu,brain, V_u,brain) using the Göttingen minipig. Additionally, I aimed to investigate brain penetration and blood-brain barrier (BBB) penetration classification (restricted K_p,uu,brain <0.3; partially restricted K_p,uu,brain >0.3 to <0.7; unrestricted >0.7 to <1.3; active uptake: K_p,uu,brain >1.3) by developing an in vitro setup to predict brain PK and evaluate this model against in vivo determined values. The overall goal was to evaluate the minipig as a model for supporting human PK-based predictions in CNS drug research. 

Results: In this project we demonstrated for a reference set of drugs using minipig hepatocyte intrinsic clearance, that applying a regression corrected in vitro to in vivo extrapolation (IVIVE) approach could predict clearance (96 % within 2-fold observed). Furthermore, we explored the extent of in vivo brain penetration in minipig by determining K_p,uu,brain from in vivo K_p,brain and in vitro drug free fractions via equilibrium dialysis. Knowing minipig may hold an elevated transporter level of P-glycoprotein and breast-cancer resistant protein. These levels have only been determined on porcine but given the minipigs resemblance that could pose a concern for use of minipigs in CNS drug research. However, at a functional level, no such evidence was found for human P-glycoprotein substrates, but a greater variation for these compounds were demonstrated when comparing K_p,uu,brain across species. Furthermore, the intra-brain distribution (V_u,brain) was determined using brain slices to support K_p,uu,brain estimates. Changing the BBB penetration classification of 5 basic compounds (with a total of 17 compounds). In the brain slice experiment a trend was observed, of lower lysosomal trapping of basic drug compounds and a less effective transporter uptake (by LAT1) in the minipig slices. The in vitro experiment to determine extent of brain penetration captured a similar BBB classification for 8 out of 12 tested drug compounds, showing its potential to guide compound selection for progression in vivo in drug research.

Overall, these studies support the notion that the minipig could be considered a suitable alternative species in CNS drug research due to its enzyme similarity to humans, the successful establishment of IVIVE, the demonstration of comparable K_p,uu,brain values across other non-rodents, and ability to estimate V_u,brain.

Keywords: Brain penetration, blood-brain barrier, P-glycoprotein, breast-cancer resistant protein, transporters, species differences, in vitro to in vivo extrapolations, clearance.