Membrane transport of camptothecin: facilitation by human P-glycoprotein (ABCB1) and multidrug resistance protein 2 (ABCC2)

BACKGROUND: The purpose of the present study was to continue the investigation of the membrane transport mechanisms of 20-(S)-camptothecin (CPT) in order to understand the possible role of membrane transporters on its oral bioavailability and disposition. METHODS: The intestinal transport kinetics of CPT were characterized using Caco-2 cells, MDCKII wild-type cells and MDCKII cells transfected with human P-glycoprotein (PGP) (ABCB1) or human multidrug resistance protein 2 (MRP2) (ABCC2). The effects of drug concentration, inhibitors and temperature on CPT directional permeability were determined. RESULTS: The absorptive (apical to basolateral) and secretory (basolateral to apical) permeabilities of CPT were found to be saturable. Reduced secretory CPT permeabilities with decreasing temperatures suggests the involvement of an active, transporter-mediated secretory pathway. In the presence of etoposide, the CPT secretory permeability decreased 25.6%. However, inhibition was greater in the presence of PGP and of the breast cancer resistant protein inhibitor, GF120918 (52.5%). The involvement of additional secretory transporters was suggested since the basolateral to apical permeability of CPT was not further reduced in the presence of increasing concentrations of GF120918. To investigate the involvement of specific apically-located secretory membrane transporters, CPT transport studies were conducted using MDCKII/PGP cells and MDCKII/MRP2 cells. CPT carrier-mediated permeability was approximately twofold greater in MDCKII/PGP cells and MDCKII/MRP2 cells than in MDCKII/wild-type cells, while the apparent K(m )values were comparable in all three cell lines. The efflux ratio of CPT in MDCKII/PGP in the presence of 0.2 μM GF120918 was not completely reversed (3.36 to 1.49). However, the decrease in the efflux ratio of CPT in MDCKII/MRP2 cells (2.31 to 1.03) suggests that CPT efflux was completely inhibited by MK571, a potent inhibitor of the Multidrug Resistance Protein transporter family. CONCLUSIONS: The current results provide evidence that PGP and MRP2 mediate the secretory transport of CPT in vitro. However, the involvement of other transporters cannot be ruled out based on these studies. Since these transporters are expressed in the intestine, liver and kidney variations in their expression levels and/or regulation may be responsible for the erratic oral absorption and biliary excretion of CPT observed in human subjects

Effects of Duloxetine in Rats Trained to Discriminate Between 2- and 22- hr Food Deprivation

Color poster with text and graphs.Duloxetine inhibits serotonin and norepinephrine transporters, and is clinically used to treat depression, pain, and generalized anxiety disorder. Duloxetine has been shown to reduce food intake in several species. The purpose of this study was to examine the effects of duloxetine in non-restricted rats trained to discriminate between 22- and 2-hour food deprivation to gain better understanding of neurochemicals mediating the discriminative stimulus effects of 22-hour food deprivation.University of Wisconsin--Eau Claire Office of Research and Sponsored Programs

Effects of Duloxetine in Rats Trained to Discriminate Between 2 and 22 hr Food Deprivation

Color poster with text, graphs, and tables.Duloxetine inhibits serotonin and norepinephrine transporters, and is clinically used to treat depression, pain, and generalized anxiety disorder. Duloxetine has been shown to reduce food intake in several species. The purpose of this study was to examine the effects of duloxetine in non-restricted rats trained to discriminate between 22- and 2-hour food deprivation to gain better understanding of neurochemicals mediating the discriminative stimulus e ects of 22-hour food deprivation.University of Wisconsin--Eau Claire Office of Research and Sponsored Programs