Structure-activity relationships for substrate recognition by the human dopamine transporter.
Information is available on the structure-activity relationships for dopamine as a substrate for uptake by the dopamine transporter. However, dopamine transport is a complex process involving substrate binding, translocation, release as well as transporter reorientation. The present study examines only the substrate recognition step by assessment of the potency of various dopamine-related compounds in inhibiting the binding of the cocaine analog [3H]2beta-carbomethoxy-3beta-(4-fluorophenyl)tropane ([3H]WIN 35,428) to human dopamine transporters expressed in HEK-293 cells. alpha-Methylation of the side chain, the presence of the amine, and the 2-carbon-length of the side chain were found to be important for binding affinity, whereas beta-hydroxylation of the side chain and methoxylation at the phenyl ring generated weaker compounds. In addition, the presence of both m- and p-OH at the phenyl ring bestowed an increase in potency but the presence of p-OH alone a decrease. N-alkylation (propylation or methylation) had little or an even slightly beneficial effect on affinity, whereas alpha-carbonylation and alpha-methanoylation reduced affinity. Amino naphthalene compounds with a fused benzenoid ring system retained some potency consonant with the extended (i.e. beta-rotameric) trans (=anti) form of the side chain in dopamine when interacting with the transporter. In a second series of experiments, the interaction between dopamine and structural variants was assessed by monitoring the capability of a compound to shift the dopamine inhibition curve to the right as expected for a competitive inhibitor acting at the same site. Appreciable deviation from competitive interaction was observed by removal of the amine from the side chain, by alpha-carbonylation, and by alpha-methanoylation. Two blocker-type compounds, semi-rigid variants of cocaine, also displayed significant deviation. A substrate-based compound, inhibiting cocaine analog binding without interfering with dopamine recognition, could be a cocaine antagonist allowing conformational changes to occur during dopamine uptake.
Appell
Michael
M
Department of Biomedical and Therapeutic Sciences, University of Illinois College of Medicine, Box 1649, Peoria, IL 61656-1649, USA.
Berfield
Janet L
JL
Wang
Lijuan C
LC
Dunn
William J
WJ
Chen
Nianhang
N
Reith
Maarten E A
ME
D001667:Binding, Competitive; D001692:Biological Transport; D002478:Cells, Cultured; D003042:Cocaine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology; D004298:Dopamine / Q000737:chemistry / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins; D006801:Humans; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins; D013329:Structure-Activity Relationship
D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; C021279:(1R-(exo,exo))-3-(4-fluorophenyl)-8-methyl-8- azabicyclo(3.2.1)octane-2-carboxylic acid, methyl ester; D003042:Cocaine; D004298:Dopamine