A rapid screening system to determine drug affinities for the intestinal dipeptide transporter 2: affinities of ACE inhibitors.
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.
Moore
V A
VA
Pharmaceutical Scienices Research Institute, Aston Pharmacy School, Aston University, Birmingham, UK.
Irwin
W J
WJ
Timmins
P
P
Lambert
P A
PA
Chong
S
S
Dando
S A
SA
Morrison
R A
RA
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
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