Dopamine transporter-dependent and -independent striatal binding of the benztropine analog JHW 007, a cocaine antagonist with low abuse liability

Authors: KOPAJTIC, THERESA - National Institutes Of Health (NIH); LIU, YI - Duquesne University; SURRATT, CHRISTOPHER - Duquesne University; Donovan, David; NEWMAN, AMY - National Institutes Of Health (NIH); KATZ, JONATHAN - National Institutes Of Health (NIH)

Submitted to: Journal of Pharmacology and Experimental Therapeutics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2010
Publication Date: 12/20/2010
Citation: Kopajtic, T.A., Liu, Y., Surratt, C.K., Donovan, D.M., Newman, A.H., Katz, J.L. 2010. Dopamine transporter-dependent and -independent striatal binding of the benztropine analog JHW 007, a cocaine antagonist with low abuse liability. Journal of Pharmacology and Experimental Therapeutics. 335(3):703-714.

Interpretive Summary: Problem: Cocaine abuse is a growing concern world-wide. It is difficult to identify treatments for cocaine abuse, e.g. inhibitors of cocaine binding, that are not stimulatory (and potentially conferring a high abuse liability). Understanding the binding characteristics of cocaine inhibitors might help elucidate the binding mechanism of not just the inhibitor but also cocaine, and might reveal potential secondary sites that could confer the antagonistic effect on cocaine binding. Accomplishments: A compound JHW 007 has been developed that is a candidate treatment for cocaine abuse, it has a high affinity for the the cocaine binding site in the brain (dopamine transporter; DAT). Unlike typical DAT ligands, has relatively low abuse liability and blocks effects of cocaine, including its self-administration. This work describes the binding characteristics of JHW007 in tissues from wild type and DAT knockout rodent brains are described. Contribution of Accomplishment to Solving the Problem: The compound JHW007 shows promise as a candidate treatment for cocaine abuse. There are multiple [3H]JHW 007 binding sites obtained in brain tissue from mice lacking the DAT, suggesting these as yet unidentified sites might be potential contributors to the cocaine-antagonist effects of JHW 007. These findings indicate potential novel binding sites that may contribute to the antagonism of cocaine.

Technical Abstract: The benztropine analog JHW 007 displays high affinity for the dopamine transporter (DAT), but unlike typical DAT ligands, has relatively low abuse liability and blocks effects of cocaine,including its self-administration. To determine sites responsible for the cocaine-antagonist effects of JHW 007, its in vitro binding was compared to that of WIN 35,428 in rats, mice, and human DAT (hDAT)-transfected cells. A one-site model, with Kd values of 4.21 (rat) and 8.99 nM (mouse) best fit the [3H]WIN 35,428 data. [3H]JHW 007 binding best fit a two-site model (rat: 7.40/4400 nM; mouse: 8.18/2750 nM), although a one-site fit was observed with hDAT membranes (43.7 nM). Drugs selective for the norepinephrine and serotonin transporters had relatively low affinity in competition with [3H]JHW 007 binding. Pharmacological analysis excluded previously identified JHW 007 sites as contributing to its multiple-site binding. The association of [3H]WIN 35,428 best fit a one-phase model, whereas the association of [3H]JHW 007 best fit a two-phase model in all tissues. Because cocaine-antagonist effects of JHW 007 have been previously observed soon after injection, its rapid association observed here may contribute to those effects. Multiple [3H]JHW 007 binding sites were obtained in tissue from mice lacking the DAT, suggesting these as yet unidentified sites as potential contributors to the cocaine-antagonist effects of JHW 007. Unlike WIN 35,428, the binding of JHW 007 was Na+- independent. This feature of JHW 007 has been linked to the conformational status of the DAT, which in turn may contribute to the antagonism of cocaine.