RT Journal Article SR Electronic T1 FUNCTIONAL ASSESSMENT OF MULTIPLE P-GLYCOPROTEIN (P-GP) PROBE SUBSTRATES: INFLUENCE OF CELL LINE AND MODULATOR CONCENTRATION ON P-GP ACTIVITY JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 1679 OP 1687 DO 10.1124/dmd.105.005421 VO 33 IS 11 A1 Mitchell E. Taub A1 Lalitha Podila A1 Diane Ely A1 Iliana Almeida YR 2005 UL http://dmd.aspetjournals.org/content/33/11/1679.abstract AB Compounds known to modulate P-glycoprotein (P-gp) activity were evaluated in cell monolayers expressing P-gp for their effects on the secretory transport of P-gp substrates paclitaxel, vinblastine, and digoxin. Paclitaxel has been proposed to selectively interact with a binding site on P-gp that is distinct from the vinblastine and digoxin-binding site. Using Madin-Darby canine kidney (MDCK)-multidrug resistance-1 (MDR1), MDCK-wild-type (WT), and Caco-2 cell monolayers, the basal-to-apical (BL-AP) apparent permeability (Papp) of [3H]paclitaxel, [3H]vinblastine, and [3H]digoxin in the presence of various concentrations of a series of structurally diverse P-gp substrates and modulators of P-gp function were determined. MDCK-WT cell monolayers demonstrated active secretory transport of all P-gp substrate probes, although the sensitivity to inhibition by verapamil was lower than that demonstrated in MDCK-MDR1 cell monolayers. When evaluated as competitive inhibitors, several known P-gp substrates had no effect or only a slight modulatory effect on the BL-AP Papp of all probe substrates in MDCK-MDR1 cells. The secretory transport of P-gp substrates in MDCK-WT cells was more sensitive to inhibition by known P-gp modulators compared with MDCK-MDR1 cells. Low concentrations of ketoconazole (1–3 μM) activated the BL-AP Papp of [3H]vinblastine and [3H]digoxin in MDCK-MDR1 cells but not in MDCK-WT or Caco-2 cells. Determination of secretory transport in P-gp expressing cell monolayers, such as MDCK-MDR1 and Caco-2, may be complicated by substrate cooperativity and allosteric binding, which may result in the activation of P-gp. In addition, expression of other efflux transporters in these cell lines introduces additional complexity in distinguishing which transporter is responsible for substrate recognition and transport. The American Society for Pharmacology and Experimental Therapeutics