Readout: Papp (A→B), Papp (B→A), Efflux ratio, % Recovery
Controls: with and without Pgp inhibitor; Atenolol, Propanolol, Taxel-1
The Caco-2 cells are cultured to confluency, trypsinized and seeded onto a filter transwell insert at a density of ~32,000 cells/well in DMEM cell culture medium. Cells are grown in a humidified atmosphere of 5% CO2 at 37 °C. Following an overnight attachment period (24 h after seeding), the cell medium is replaced with fresh medium in both the apical and basolateral com-partments every other day. The cell monolayers are used for transport studies 21 days post seeding after measuring the TEER values (>600 Ohms/cm2). The apical sides and basolateral sides are washed consecutively with HBSS 2.5% (v/v), HEPES (pH 7.4) or HBSS 2.5% (v/v), HEPES 10% (v/v), and Fetal Bovine Serum (pH 7.4) at 37 °C in an incubator under an atmosphere of 5% CO2.
Donor working solution is prepared by dilution of DMSO stock of test article or positive control with transport media to 10 µM.
For A → B directional transport, the donor working solution (with test article or positive control, with or without Pgp inhibitor) is added to the apical (A) compartment and the transport media as receiver working solution is added to the basolateral (B) compartment. For B → A directional transport, the donor working solution (with positive control or test article, with or without Pgp inhibitor) is added to the basolateral (B) compartment and transport media as receiver working solution is added to the apical (A) compartment.
The cells are incubated in a humidified atmosphere of 5% CO2 at 37 °C for 90 minutes.
At the end of the incubation, samples are taken from both donor and receiver compartments and transferred into 96-well assay plates containing internal standard solution (IS) in each well. After centrifugation, the supernatant solutions are transferred to clean 96 well plates and analyzed by LC-MS/MS. The MS detection is performed using a Sciex API 4000 instrument. Each compound is analyzed by reversed phase HPLC.
The parameters Papp (apparent permeability) and efflux ratio are calculated as follows:
Papp = (dQ/dt) × (1/C0) × (1/A)
Efflux ratio = Papp [B → A] / Papp [A → B]
where dQ/dt is the permeability rate, C0 is the initial concentration in the donor compartment, and A is the surface area of the cell monolayer (0.33cm2). The Papp value is a rate measured in cm/s.
Calculated Papp is ranked as low (<1×106 cm/s), moderate (1-10×10-6 cm/s), and high (>10×106 cm/s).
Comparing the efflux ratios generated in the presence and absence of a Pgp inhibitor identifies whether the test article is a Pgp substrate. A compound is considered to be a Pgp substrate when the efflux ratio in the absence of inhibitor is >1.99 and is significantly reduced (≤ 1) in the presence of an inhibitor.
Recovery is calculated as follows:
%Recovery = (Total compound mass in donor and receiver compartments at the end of the incubation / Initial compound mass in the donor compartment) x 100.
DMEM Dulbecco’s Modified Eagle Medium
HBSS Hank’s Buffered Salt Solution
HEPES 4-(2-Hydroxyethyl)-1-piperazineethanesulfonic acid
HPLC High-performance liquid chromatography
Pgp P-glycoprotein 1, also known as multidrug resistance protein 1 (MDR1)
LC Liquid chromatography
MS Mass spectrometry
TEER Transepithelial Resistance (in Ohm/cm2)
Caco-2 Permeability Assay