A Surrogate BBB Model MDCK-MDR1 Cells

Early assessment of the ability of a drug candidate to penetrate the CNS is critical during the drug discovery selection process, especially for therapeutic indications that require delivery to a CNS site of action. Equally important is the ability to design drugs for non-CNS indications that have minimal brain penetration to avoid undesirable CNS side effects. In vitro BBB models using primary and immortalized brain capillary endothelial cells are described in the previous sections. The Ma-dine Darby canine kidney (MDCK) cell-line is increasingly used as a substitute for the more labor-intensive in vitro BBB models in passive permeability and membrane transport studies. 

Drags are tested at 10 p,M concentration and in two directions (apical to basolateral (a-b) and basolateral to apical (b-a)). Monolayer efflux studies are conducted at 37 °C in a humidified incubator with shaking (90 rpm) for 60 min. Transendothelial electrical resistance is measured with an Endohm Meter (World Precision Instruments, New Haven, CT). Reference drags for paracellular transport (14C-mannitol), tran-scellular transport (3H-propranolol), and Pgp efflux (amprenavir) should be included in each experiment. Concentrations of 14C-mannitol and 3H-propranolol are measured by liquid scintiallation counting. Amprenavir is analyzed by cassette LC/MS/MS analysis along with the test drags. 

The apparent permeability (Papp) is calculated with the equation  

Mahar Doan et al. (2002) used the assay to classify 93 CNS and non-CNS drags. The CNS set of drugs had a 7-fold lower incidence of passive permeability values 150 nm/s compared with the non-CNS set. The majority of drugs (72 %) were not Pgp substrates. The CNS drug set had a 3-fold lower incidence of Pgp-mediate efflux than the non-CNS drug set. For CNS delivery, they concluded that drugs should ideally have an in vitro passive permeability 150 nm/s and not be a good (b-a/a-b ratio 2.5) Pgp substrate. 

The MDR1-MDCK transport assay was evaluated by Polli et al. (2001). The scientist compared the Pgp transport assay with the calcein-AM and ATPase 

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