Innovative in Vitro Method To Predict Rate and Extent of Drug Delivery to the Brain across the Blood-Brain Barrier

The relevant parameters for predicting rate and extent of access across the blood-brain barrier (BBB) are f(u,plasma) (unbound fraction in plasma), V-u,V-brain (distribution volume in brain) and K-p,K-uu,K-brain (ratio of free concentrations in plasma and brain). Their estimation still requires animal studies and in vitro low throughput experiments which make difficult the screening of new CNS candidates. The aim of the present work was to develop a new whole in vitro high throughput method to predict drug rate and extent of access across the BBB. The system permits estimation of f(u,plasma), V-u,V-brain and K-p,K-uu,K-brain in a single experimental system, using in vitro cell monolayers in different conditions. From the ratios of the apparent permeability values (P-app) with the adequate mathematical analysis the relevant parameters can be estimated. P-app of ten model compounds has been obtained in MDCKII and MDCK-Mdr1cell monolayers in the absence and presence of albumin and brain homogenate. The ratio of P-app in the absence and presence of albumin allows estimation of in vitro f(u,plasma).P-app in the presence of brain homogenate is used to estimate f(u,brain) and V-u,V-brain.K-p,K-uu,K-brain is estimated from the apical to basal versus basal to apical clearances. The BBB parameters obtained with new method were predictive of the in vivo behavior of candidates. In vitro f(u,piasma), K-p,K-u,K-brain and V-u,V-brain (calculated with P-app from MDCKII cell line) presented a good correlation with in vivo f(u,phosma), K-p,K-uu,K-CCF and V-u,V-brain published values (r = 0.92; r = 0.85; and r = 0.99 respectively). Despite its simplicity the predictive performance is fairly good considering the reduced number of tested compounds with different physicochemical and transport properties. Further experimental modifications could be checked to optimize the method, but the present data support its feasibility. As other in vitro cell culture models, the system is suitable for miniaturization and robotization to allow high throughput screening of CNS candidates