Inhibition of Pgp-mediated transport of probe substrates across MDR1-MDCKII cells
The inhibition of probe substrates by test compounds was determined as described under Materials and Methods. A minimum of eight concentrations (n = 3) per test compound were used to determine the IC50 value (calcein-AM, digoxin, vinblastine, and colchicine) using the full four-parameter equation or K value (prazosin) using the Hill equation.
Inhibitor | EACa | Category | Calcein-AM IC50 Valueb | Digoxin B→A IC50 Value | Vinblastine B→A IC50 Value | Colchicine B→A IC50 Value | Prazosin A→B K Valuec | Prazosin B→A IC50 Value |
|---|---|---|---|---|---|---|---|---|
| GF120918 | NNY | I Inhibitor | 0.101 ± 0.014 | 0.055 ± 0.003 | 0.043 ± 0.004 | 0.027 ± 0.002 | 0.050 ± 0.027 | 0.025 ± 0.003 |
| Ranitidine | NNN | I Unambiguous nonsubstrates | No | No | No | No | No | |
| Propranalol | NNN | No | No | No | No | >100e | ||
| Methotrexate | NNN | No | No | No | No | No | ||
| Triamterene | NNN | No | No | No | No | No | ||
| Amprenavir | YYY | I Unambiguous substrates | >100 | No | >100 | 91.3 ± 11.6 | >100 | |
| Prazosind | YYY | >100e | Nod | Nod | 70.7 ± 3.8 | Nod | ||
| Quinidine | YYY | 55.5 ± 2.34 | 14.9 ± 9.0 | 22.9 ± 3.4 | 51.7 ± 9.8 | 14.0 ± 1.23 | ||
| Vinblastine | YYY | >100 | 17.8 ± 2.2 | 89.7 ± 15.6 | 30.1 ± 4.1 | 21.9 ± 11.7 | ||
| Verapamil | NYY | IIA Nontransported substrates | 60.9 ± 8.91 | 10.7 ± 4.1 | 33.5 ± 2.1 | 17.3 ± 1.9 | 1.18 ± 0.20 | 1.55 ± 0.56 |
| Diphenhydramine | NYY | No | No | No | No | Nod | ||
| Ketoconazole | NYY | 10.1 ± 1.6 | 3.07 ± 0.76 | 6.34 ± 1.98 | 5.49 ± 0.98 | 2.38 ± 0.18 | 0.65 ± 0.12 | |
| Daunorubicin | YNN | No | No | >100 | >100 | No | ||
| Colchicine | YNN | IIB1 Transported substrates | No | No | No | No | No | |
| Dexamethasone | YNN | No | No | No | No | No | ||
| Fexofenadine | Y-N | No | No | No | No | No | ||
| Digoxin | Y-N | No | No | No | No | No | ||
| Erythromycin | YYN | IIB2 Transported substrates | No | No | No | No | No | |
| Indinavir | YYN | No | No | No | No | >50 | ||
| Trimethoprim | YYN | No | No | No | No | No | ||
| Cyclosporin A | YNY | IIB3 Transported substrates | 2.22 ± 0.02 | 1.6 ± 0.3 | 6.18 ± 1.90 | 1.36 ± 0.09 | 0.98 ± 0.33 | 0.74 ± 0.12 |
↵ a EAC: E, monolayer efflux; A, drug-stimulated ATPase; C, calcein-AM. Results are reported as yes (Y) or no (N). For efflux, yes = substrate and no = nonsubstrate; for ATPase assay, yes = stimulator and no = no activity; and for calcein-AM assay, yes = response >10% maximum fluorescence and no = response <10% maximum fluorescence. See Polli et al. (2001) for further details.
↵ b IC50 is the concentration of inhibitor required for 50% inhibition of probe transport.
↵ c K value is the concentration of inhibitor required for 50% increase in the prazosin A→B rate.
↵ d Prazosin >50 μM increased LY passive permeability (>20 nm/s), suggesting a breach in the tight junctions between monolayers; therefore, data only up to 50 μM were used in the analysis of IC50 curves.
↵ e Compounds with an IC50 value reported to be greater than a number representing that notable inhibition (>20%) was observed at the highest test concentration. However, an accurate IC50 value could not be determine from the dataset.