Studies of the biogenic amine transporters. II. A brief study on the use of [3H]DA-uptake-inhibition to transporter-binding-inhibition ratios for the in vitro evaluation of putative cocaine antagonists.
The cocaine receptor on the dopamine transporter is a logical target binding site for the design and synthesis of novel agents for evaluation as possible cocaine antagonists. Although there is no widely accepted and validated assay for detecting a cocaine antagonist, one commonly accepted strategy is to compare the IC50 value of a test agent for inhibition of [3H]dopamine uptake and its IC50 value for inhibition of the binding of a transporter ligand such as [125I]RTI-55. The goal of such a comparison is to guide the synthesis of agents which have high "uptake-to-binding ratios", i.e. agents which are much more potent in the binding assay than they are in the uptake assay. In the present study we tested the hypothesis that ratios different from unity can result from the fact that the two assays are conducted under markedly different conditions. The results showed that conducting the uptake and binding assays under identical conditions reduced the GBR12935 uptake-to-binding ratio of 6.20 (under standard assay conditions) to 0.36. These data indicate that uptake-to-binding ratios must be interpreted with caution, and emphasizes the need for simpler and less expensive methods than cocaine self-administration paradigms to screen compounds as modulators of cocaine reinforcement.
Rothman
R B
RB
Clinical Psychopharmacology Section, Addiction Research Center, NIDA, NIH, Baltimore, MD 21224.
Becketts
K M
KM
Radesca
L R
LR
de Costa
B R
BR
Rice
K C
KC
Carroll
F I
FI
Dersch
C M
CM
D000818:Animals; D001679:Biogenic Amines / Q000502:physiology*; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D003042:Cocaine / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D004298:Dopamine / Q000493:pharmacokinetics*; D050483:Dopamine Plasma Membrane Transport Proteins; D007457:Iodine Radioisotopes; D008297:Male; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D014179:Neurotransmitter Uptake Inhibitors / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology*; D010879:Piperazines / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014316:Tritium
D001679:Biogenic Amines; D002352:Carrier Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; D007457:Iodine Radioisotopes; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D014179:Neurotransmitter Uptake Inhibitors; D010879:Piperazines; D014316:Tritium; C069723:2beta-carbomethoxy-3beta-(4-iodophenyl)tropane; C021279:(1R-(exo,exo))-3-(4-fluorophenyl)-8-methyl-8- azabicyclo(3.2.1)octane-2-carboxylic acid, methyl ester; C044630:1-(2 (diphenylmethoxy)ethyl)-4-(3-phenylpropyl)piperazine; D003042:Cocaine; D004298:Dopamine