Validation of in vitro cell-based human blood-brain barrier model using clinical positron emission tomography radioligands to predict in vivo human brain penetration.

We have evaluated a novel in vitro cell-based human blood-brain barrier (BBB) model that could predict in vivo human brain penetration for compounds with different BBB permeabilities using the clinical positron emission tomography (PET) data. Comparison studies were also performed to demonstrate that the in vitro cell-based human BBB model resulted in better predictivity over the traditional permeability model in discovery organizations, Caco-2 cells. We evaluated the in vivo BBB permeability of [(18)F] and [(11)C]-compounds in humans by PET imaging. The in vivo plasma-brain exchange parameters used for comparison were determined in humans by PET using a kinetic analysis of the radiotracer binding. For each radiotracer, the parameters were determined by fitting the brain kinetics of the radiotracer using a two-tissue compartment model of the ligand-receptor interaction. Bidirectional transport studies with the same compounds as in in vivo studies were carried out using the in vitro cell-based human BBB model as well as Caco-2 cells. The in vitro cell-based human BBB model has important features of the BBB in vivo and is suitable for discriminating between CNS and non-CNS marketed drugs. A very good correlation (r(2) = 0.90; P < 0.001) was demonstrated between in vitro BBB permeability and in vivo permeability coefficient. In contrast, a poor correlation (r(2) = 0.17) was obtained between Caco-2 data and in vivo human brain penetration. This study highlights the potential of this in vitro cell-based human BBB model in drug discovery and shows that it can be an extremely effective screening tool for CNS programs.