title: A rapid screening system to determine drug affinities for the intestinal dipeptide transporter 2: affinities of ACE inhibitors.
abstract: OBJECTIVE
  To assess the affinities of a series of ACE inhibitors for the di/tri/oligopeptide transport system (DTS) using a rapid in vitro system.
  
  
  METHODS
  Monolayers of Caco-2 cells were cultured in plastic wells for 7-9 days and the uptake of Gly-[3H]L-Pro was used as an affinity probe. Gly-[3H]L-Pro (50 nM), together with excess L-Pro (10 mM), to suppress uptake of any [3H]L-Pro produced by degradation of the probe, was incubated with the test compound (usually 1 mM) at pH 6 for 3-mins. The uptake of radiolabel was determined by liquid scintillation counting.
  
  
  RESULTS
  A 2-dimensional six-domain model of the transporter based on the structure of a phosphinate ACE inhibitor (SQ-29852) was constructed to facilitate interpretation of the competitor affinities. The SQ-29852 molecule was divided into six binding domains (A-F) based on functional groups within these regions and the effects of structural variation in four of these domains (A, C-E) were explored. A series of dipeptide-like compounds varying within specific domains were selected from a large number of commercially available ACE inhibitors and SQ-29852 analogues. Domain A had a preference for an uncharged group, with bulky hydrophobic groups reducing affinity. Domain C exhibited a preference for a positive charge over a neutral function, with the space this functional group occupies contributing to affinity. Domain D favoured lipophilic residues and domain E retained activity when the carboxylic acid was esterified.
  
  
  CONCLUSIONS
  The test system is able to reveal structure-activity relationships of peptidomimetic agents and may well serve as a design tool to optimise affinity for the DTS.
authors.affiliation: Pharmaceutical Scienices Research Institute, Aston Pharmacy School, Aston University, Birmingham, UK.
authors.forename: V A
authors.initials: VA
authors.lastname: Moore
authors.forename: W J
authors.initials: WJ
authors.lastname: Irwin
authors.forename: P
authors.initials: P
authors.lastname: Timmins
authors.forename: P A
authors.initials: PA
authors.lastname: Lambert
authors.forename: S
authors.initials: S
authors.lastname: Chong
authors.forename: S A
authors.initials: SA
authors.lastname: Dando
authors.forename: R A
authors.initials: RA
authors.lastname: Morrison
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000465:Algorithms; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000378:metabolism*; D018938:Caco-2 Cells; D003470:Culture Media; D004151:Dipeptides / Q000378:metabolism; D004353:Drug Evaluation, Preclinical; D006801:Humans; D008954:Models, Biological; D009943:Organophosphorus Compounds / Q000378:metabolism; D011392:Proline / Q000031:analogs & derivatives / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D000806:Angiotensin-Converting Enzyme Inhibitors; D003470:Culture Media; D004151:Dipeptides; D009943:Organophosphorus Compounds; C073119:TAP1 protein, human; C015248:glycylproline; D011392:Proline; C054518:ceronapril