- Significant progress was made on this project, and several papers were published. In one notable article, we describe the discovery of partial transporter substrates which have limited ability to release monoamine transmitters. Such compounds could have utility for treating addiction and ADHD, without causing typical stimulant-associated adverse effects (i.e., abuse liability). Studies of the biogenic amine transporters. 14. Identification of low-efficacy """"""""partial"""""""" substrates for the biogenic amine transporters. (2012) J. Pharmacol. Exp. Ther. 341:251-261. Several compounds have been identified that display low-efficacy, """"""""partial substrate"""""""" activity. Here, we tested the hypothesis that the mechanism of this effect is a slower rate of induced neurotransmitter efflux than that produced by full substrates. Biogenic amine transporter release assays were carried out in rat brain synaptosomes and followed published procedures. (3)H1-methyl-4-phenylpyridinium (MPP(+)) was used to assess release from dopamine (DA) and norepinephrine nerve terminals, whereas (3)H5-hydroxytryptamine (5-HT) was used to assess release from 5-HT nerve terminals. A detailed time-course evaluation of DA transporter (DAT)-mediated efflux was conducted by measuring the efflux of (3)HMPP(+) after the addition of various test compounds. In vivo microdialysis experiments compared the effects of the full substrates ()-1-(2-naphthyl)propan-2-amine (PAL-287) and (S)-N-methyl-1-(2-naphthyl)propan-2-amine (PAL-1046), to that of a partial DAT/5-HT transporter substrate (S)-N-ethyl-1-(2-naphthyl)propan-2-amine (PAL-1045) on extracellular DA and 5-HT in the nucleus accumbens of the rat. The in vitro release assays demonstrated that partial substrate activity occurs at all three transporters. In the DAT efflux experiments, D-amphetamine (full substrate) promoted a fast efflux (K1 = 0.24 min(-1)) and a slow efflux (K2 = 0.008 min(-1)). For the partial DAT substrates, K1 = ∼0.04 min(-1), and K2 approximated zero. The in vivo microdialysis experiments showed that the partial substrate (PAL-1045) was much less effective in elevating extracellular DA and 5-HT than the comparator full substrates. We conclude that low-efficacy partial DAT substrates promote efflux at a slower rate than full substrates, and """"""""partiality"""""""" reflects the ultra-slow K2 constant, which functionally limits the ability of these compounds to increase extracellular DA. We speculate that partial biogenic amine transporter substrates bind to the transporter but are less effective in inducing conformational changes required for reverse transport activity.

Project Start
Project End
Budget Start
Budget End
Support Year
5
Fiscal Year
2012
Total Cost
$405,008
Indirect Cost
Name
National Institute on Drug Abuse
Department
Type
DUNS #
City
State
Country
Zip Code
Solis Jr, Ernesto; Partilla, John S; Sakloth, Farhana et al. (2017) N-Alkylated Analogs of 4-Methylamphetamine (4-MA) Differentially Affect Monoamine Transporters and Abuse Liability. Neuropsychopharmacology 42:1950-1961
McLaughlin, Gavin; Morris, Noreen; Kavanagh, Pierce V et al. (2017) Analytical characterization and pharmacological evaluation of the new psychoactive substance 4-fluoromethylphenidate (4F-MPH) and differentiation between the (±)-threo and (±)-erythro diastereomers. Drug Test Anal 9:347-357
Shekar, Aparna; Aguilar, Jenny I; Galli, Greta et al. (2017) Atypical dopamine efflux caused by 3,4-methylenedioxypyrovalerone (MDPV) via the human dopamine transporter. J Chem Neuroanat 83-84:69-74
Shalabi, Abdelrahman R; Walther, Donna; Baumann, Michael H et al. (2017) Deconstructed Analogues of Bupropion Reveal Structural Requirements for Transporter Inhibition versus Substrate-Induced Neurotransmitter Release. ACS Chem Neurosci 8:1397-1403
Baumann, Michael H (2016) The Changing Face of Recreational Drug Use. Cerebrum 2016:
Drgonova, Jana; Walther, Donna; Hartstein, G Luke et al. (2016) Cadherin 13: human cis-regulation and selectively-altered addiction phenotypes and cerebral cortical dopamine in knockout mice. Mol Med 22:
Hutsell, Blake A; Baumann, Michael H; Partilla, John S et al. (2016) Abuse-related neurochemical and behavioral effects of cathinone and 4-methylcathinone stereoisomers in rats. Eur Neuropsychopharmacol 26:288-297
Sandtner, Walter; Stockner, Thomas; Hasenhuetl, Peter S et al. (2016) Binding Mode Selection Determines the Action of Ecstasy Homologs at Monoamine Transporters. Mol Pharmacol 89:165-75
Banks, Matthew L; Bauer, Clayton T; Blough, Bruce E et al. (2014) Abuse-related effects of dual dopamine/serotonin releasers with varying potency to release norepinephrine in male rats and rhesus monkeys. Exp Clin Psychopharmacol 22:274-284
Baumann, Michael H; Bulling, Simon; Benaderet, Tova S et al. (2014) Evidence for a role of transporter-mediated currents in the depletion of brain serotonin induced by serotonin transporter substrates. Neuropsychopharmacology 39:1355-65

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