Submitted to: Society for Neuroscience Abstracts and Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/10/2007
Publication Date: 11/4/2007
Citation: Kopajtic, T.A., Donovan, D.M., Newman, A.H., Katz, J.L. 2007. Assessment of the in vitro binding of JHW 007, a dopamine transport inhibitor that blocks the effects of cocaine. Society for Neuroscience Abstracts and Proceedings.
Technical Abstract: Benztropine (BZT) and its analogues, like cocaine, bind to the dopamine transporter and block dopamine uptake. However, while BZT analogues bind the DAT with high affinity, they generally do not have cocaine-like behavioral effects. JHW 007 is a BZT analogue that displaces [3H]WIN 35,428 from the DAT with a 7-fold higher affinity than cocaine in rat brain. As a pretreatment, JHW 007 blocks the behavioral effects of cocaine in mice. In contrast to [3H]WIN 35,428, the binding of [3H]JHW 007 in S/W mouse striatum was better fit to a two- than one-site model, with Hi-/Lo-affinity KD values of 11.1/9680. The pharmacology of the JHW 007 high-affinity site in S/W mice appears to be like that for WIN 35,428. Total binding of [3H]WIN 35,428 in striatum of DAT KO mice was not different from nonspecific binding, whereas there was appreciable specific binding of [3H]JHW 007, indicating a site for JHW 007 that is not on the DAT. The binding of [3H]JHW 007 in both DAT WT and KO mice was better fit to a two-site model with Hi-/Lo-affinity KD values of 26.5/7590 and 34.6/4890 nM in WT and KO mice, respectively. Thus there is a high-affinity site for JHW 007 that is not on the DAT. Competition experiments against [3H]JHW 007 binding in striatum with ligands for muscarinic M2, histamine H1, serotonin 5-HT2A, dopamine D3, and Na channel, indicated no significant displacement in striatum of KO mice. However, there was low affinity displacement of [3H]JHW 007 obtained with the dopamine D2 antagonist, L-741626 (Ki=8185 nM), and the sigma1 ligand, rimcazole (Ki=2210 nM). In WT mice both L-741626 (Ki=4740 nM), and the sigma1 ligand, rimcazole (Ki=4740 nM), as well as the histamine H1 antagonist, (+)-chlorpheniramine (Ki=4160 nM) displaced [3H]JHW 007. In whole brain, JHW 007 displaced [3H]pirenzepine from muscarinic M1 sites, respectively with Ki values of 387 and 421 nM in WT and KO mice. Similarly, JHW 007 displaced [3H]mepyramine from histamine H1 sites, respectively with Ki values of 43.5 and 46.5 nM in WT and KO mice. These values are similar to those found previously in S/D rat brain. Taken together, the data suggest two high affinity binding sites for JHW 007 in striatum, of which one is a cocaine binding site whereas the other is not on the dopamine transporter, and is distinct from previously identified targets at which JHW 007 binds.