title: Membrane transport of camptothecin: facilitation by human P-glycoprotein (ABCB1) and multidrug resistance protein 2 (ABCC2).
abstract: 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 Km values were comparable in all three cell lines. The efflux ratio of CPT in MDCKII/PGP in the presence of 0.2 microM 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.
authors.affiliation: Department of Pharmaceutics, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, New Jersey, USA. lalloo@eden.rutgers.edu <lalloo@eden.rutgers.edu>
authors.forename: Anita K
authors.initials: AK
authors.lastname: Lalloo
authors.forename: Feng R
authors.initials: FR
authors.lastname: Luo
authors.forename: Ailan
authors.initials: A
authors.lastname: Guo
authors.forename: Pankaj V
authors.initials: PV
authors.lastname: Paranjpe
authors.forename: Sung-Hack
authors.initials: SH
authors.lastname: Lee
authors.forename: Viral
authors.initials: V
authors.lastname: Vyas
authors.forename: Eric
authors.initials: E
authors.lastname: Rubin
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Sinko
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D018938:Caco-2 Cells / Q000378:metabolism; D002166:Camptothecin / Q000493:pharmacokinetics*; D018432:Drug Resistance, Multiple; D006801:Humans; D026901:Membrane Transport Proteins / Q000378:metabolism*; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D010539:Permeability; D013696:Temperature
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002166:Camptothecin; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C000715087:ABCC2 protein, human