title: Evidence for overlapping substrate specificity between large neutral amino acid (LNAA) and dipeptide (hPEPT1) transporters for PD 158473, an NMDA antagonist.
abstract: OBJECTIVE
  The objective of this research was to investigate the substrate specificity of large neutral amino acid carrier (LNAA) and di/tripeptide (hPEPT1) transporters with respect to PD 158473, an NMDA antagonist.
  
  
  METHODS
  Cellular uptake studies were carried out using two types of Chinese Hamster Ovary (CHO). CHO-K1 cells represent the wild type with inherent large neutral amino acid (LNAA) activity. CHO-PEPT1 cells were generated by stable transfection of hPEPT1 gene into CHO cells. Therefore, these cells possess both LNAA activity and di/tripeptide transporter activities as a result of the transfection. Cellular uptake of PD 158473 was quantified using a HPLC method previously developed in our laboratory.
  
  
  RESULTS
  The utility of the CHO-PEPT1 cell model was demonstrated by determining the uptake kinetics of Gly-Sar, a prototypical dipeptide transporter substrate. Uptake kinetics of PD 158473 displayed two carrier-mediated transport components in CHO-PEPT1 cells, while in CHO-K1 cells the relationship was consistent with classic one component Michaelis-Menten kinetics. These results confirmed the affinity of PD 158473 for both LNAA and di/tripeptide transporters. Further, results from inhibition experiments using these two cell types indicate that the high affinity-low capacity system was the LNAA carrier and the low affinity-high capacity carrier was the di/tripeptide transporter.
  
  
  CONCLUSIONS
  This study demonstrates overlapping substrate specificity between LNAA carrier and di/tripeptide transporter (hPEPT1) for PD 158473, an amino acid analog. Establishing Structure Transport Relationship (STR) for this overlap will aid in a design strategy for increasing oral absorption or targeting specific drugs to selected tissues.
authors.affiliation: Department of Pharmacokinetics, Dynamics and Metabolism, Parke-Davis Pharmaceutical Research, Division of Warner-Lambert Company, Ann Arbor, Michigan 48105, USA. narayanan.surendran@wl.com
authors.forename: N
authors.initials: N
authors.lastname: Surendran
authors.forename: K M
authors.initials: KM
authors.lastname: Covitz
authors.forename: H
authors.initials: H
authors.lastname: Han
authors.forename: W
authors.initials: W
authors.lastname: Sadee
authors.forename: D M
authors.initials: DM
authors.lastname: Oh
authors.forename: G L
authors.initials: GL
authors.lastname: Amidon
authors.forename: R M
authors.initials: RM
authors.lastname: Williamson
authors.forename: C F
authors.initials: CF
authors.lastname: Bigge
authors.forename: B H
authors.initials: BH
authors.lastname: Stewart
mesh_terms: D026905:Amino Acid Transport Systems; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D002352:Carrier Proteins / Q000378:metabolism*; D006224:Cricetinae; D004151:Dipeptides / Q000378:metabolism; D009281:Naphthalenes / Q000378:metabolism*; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*
chemical_list: D026905:Amino Acid Transport Systems; D000596:Amino Acids; D002352:Carrier Proteins; D004151:Dipeptides; D009281:Naphthalenes; C119559:PD 158473; D016194:Receptors, N-Methyl-D-Aspartate; C004194:glycylsarcosine; D010649:Phenylalanine