Abstract
Lobeline attenuates the behavioral effects of methamphetamine via inhibition of the vesicular monoamine transporter (VMAT2). To increase selectivity for VMAT2, chemically defunctionalized lobeline analogs, including lobelane, were designed to eliminate nicotinic acetylcholine receptor affinity. The current study evaluated the ability of lobelane analogs to inhibit [3H]dihydrotetrabenazine (DTBZ) binding to VMAT2 and [3H]dopamine (DA) uptake into isolated synaptic vesicles and determined the mechanism of inhibition. Introduction of aromatic substituents in lobelane maintained analog affinity for the [3H]DTBZ binding site on VMAT2 and inhibitory potency in the [3H]DA uptake assay assessing VMAT2 function. The most potent (Ki = 13–16 nM) analogs in the series included para-methoxyphenyl nor-lobelane (GZ-252B), para-methoxyphenyl lobelane (GZ-252C), and 2,4-dichlorphenyl lobelane (GZ-260C). Affinity of the analogs for the [3H]DTBZ binding site did not correlate with inhibitory potency in the [3H]DA uptake assay. It is noteworthy that the N-benzylindole-, biphenyl-, and indole-bearing meso-analogs 2,6-bis[2-(1-benzyl-1H-indole-3-yl)ethyl]-1-methylpiperidine hemifumarate (AV-1-292C), 2,6-bis(2-(biphenyl-4-yl)ethyl)piperidine hydrochloride (GZ-272B), and 2,6-bis[2-(1H-indole-3-yl)ethyl]-1-methylpiperidine monofumarate (AV-1-294), respectively] inhibited VMAT2 function (Ki = 73, 127, and 2130 nM, respectively), yet had little to no affinity for the [3H]DTBZ binding site. These results suggest that the analogs interact at an alternate site to DTBZ on VMAT2. Kinetic analyses of [3H]DA uptake revealed a competitive mechanism for 2,6-bis(2-(4-methoxyphenyl)ethyl)piperidine hydrochloride (GZ-252B), 2,6-bis(2-(4-methoxyphenyl)ethyl)-1-methylpiperidine hydrochloride (GZ-252C), 2,6-bis(2-(2,4-dichlorophenyl)ethyl)piperidine hydrochloride (GZ-260C), and GZ-272B. Similar to methamphetamine, these analogs released [3H]DA from the vesicles, but with higher potency. In contrast to methamphetamine, these analogs had higher potency (>100-fold) at VMAT2 than DAT, predicting low abuse liability. Thus, modification of the lobelane molecule affords potent, selective inhibitors of VMAT2 function and reveals two distinct pharmacological targets on VMAT2.
Footnotes
This research was supported by the National Institutes of Health National Institute on Drug Abuse [Grants DA013519, T32-DA016176].
The University of Kentucky holds patents on lobeline and the analogs described in the current work. A potential royalty stream to L.P.D., G.Z., and P.A.C. may occur consistent with University of Kentucky policy. Both L.P.D. and P.A.C. are founders of and have financial interest in Yaupon Therapeutics and have licensed University of Kentucky patents on some of the compounds evaluated in the current study.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.110.172882.
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ABBREVIATIONS:
- DAT
- dopamine transporter
- DA
- dopamine
- DTBZ
- dihydrotetrabenazine
- nAChR
- nicotinic acetylcholine receptor
- Ro4-1284
- (2R,3S,11bS)-2-ethyl-3-isobutyl-9,10-dimethoxy-2,2,4,6,7,11b-hexahydro-1H-pyrido[2,1-a]isoquinolin-2-ol
- SAR
- structure-activity relationship
- TBZ
- tetrabenazine
- VMAT2
- vesicular monoamine transporter-2
- AV-1-292C
- 2,6-bis[2-(1-benzyl-1H-indole-3-yl)ethyl]-1-methylpiperidine hemifumarate
- AV-1-294
- 2,6-bis[2-(1H-indole-3-yl)ethyl]-1-methylpiperidine monofumarate
- GZ-272B
- 2,6-bis(2-(biphenyl-4-yl)ethyl)piperidine hydrochloride
- GZ-272C
- 2,6-bis(2-(biphenyl-4-yl)ethyl)-1-methylpiperidine hydrochloride
- GZ-252B
- 2,6-bis(2-(4-methoxyphenyl)ethyl)piperidine hydrochloride
- GZ-252C
- 2,6-bis(2-(4-methoxyphenyl)ethyl)-1-methylpiperidine hydrochloride
- GZ-260C
- 2,6-bis(2-(2,4-dichlorophenyl)ethyl)-1-methylpiperidine hydrochloride
- GZ-252B
- para-methoxyphenyl nor-lobelane
- GZ-252C
- para-methoxyphenyl lobelane
- GZ-260C
- 2,4-dichlorphenyl lobelane.
- Received July 15, 2010.
- Accepted September 20, 2010.
- Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics
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