Received for publication August 15, 2007.
Revised December 3, 2007.
Accepted for publication December 4, 2007.

In Vitro to In Vivo Prediction of P-glycoprotein Based Drug Interactions at the Human and Rodent Blood-Brain Barrier

Abstract

In vitro inhibition of P-glycoprotein (P-gp) expressed in cells is routinely used to predict the potential of in vivo P-gp drug interactions at the human blood-brain barrier (BBB). The accuracy of such predictions has not been confirmed because methods to quantify in vivo P-gp drug interactions at the human BBB have not been available. With the development of a non-invasive Positron Emission Topography (PET) imaging method by our laboratory to determine P-gp based drug interactions at the human BBB, an in vitro-in vivo comparison is now possible. Therefore, we developed a high throughput cell-based assay to determine the potential of putative P-gp inhibitors (including cyclosporine A; CsA) to inhibit (EC₅₀) the efflux of verapamil-bodipy, a model P-gp substrate. LLCPK1-MDR1 cells, expressing recombinant human P-gp, or control cells lacking P-gp (LLCPK1) were used in our assay. Using this assay, quinine, quinidine, CsA and amprenavir were predicted to be the most potent P-gp inhibitors in vivo, at their respective therapeutic maximal unbound plasma concentrations. The in vitro EC₅₀ of CsA (0.6 µM) for P-gp inhibition was virtually the same as our previously determined in vivo unbound EC₅₀ at the rat BBB (0.5 µM). Moreover, at 2.8 µM CsA (total blood concentration), our in vitro data predicted an increase of 129% in [¹¹C]-verapamil distribution into the human brain, a value similar to that observed by us (79%) using PET. These data suggest that our high throughput cell assay has the potential to accurately predict P-gp drug interactions at the human BBB.

Key words: blood-brain barrier, p-glycoprotein