Year of Publication

2014

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Pharmacy

Department

Pharmaceutical Sciences

First Advisor

Dr. Linda P. Dwoskin

Abstract

Methamphetamine interacts with vesicular monoamine transporter-2 (VMAT2) to inhibit dopamine (DA) uptake and promotes DA release from presynaptic vesicles, increasing cytosolic DA available for methamphetamine-induced reverse transport by DA transporters. By inhibiting VMAT2, lobelane, a defunctionalized, saturated lobeline analog, decreases methamphetamine-evoked DA release and methamphetamine self-administration in rats. In this dissertation structure-activity relationships around the lobelane structure were investigated on racemic lobelane analogs with varying methylene linker lengths at central piperidine ring. Affinity for dihydrotetrabenazine (DTBZ) sites on VMAT2 and for inhibition of VMAT2 function was determined to be 0.88-63 and 0.024-4.6 µM, respectively, and positively correlated. The most potent and selective analog, (±)-cis-2-benzyl-6-(3-phenylpropyl)piperidine [(±)-GZ-730B], for VMAT2 uptake was identified as the lead. The ability of (±)-GZ-730B to inhibit methamphetamine-evoked [3H]DA release from striatal synaptic vesicles and endogenous DA release from striatal slices was determined. The lead analog-induced inhibition of methamphetamine-evoked vesicular [3H]DA release did not translate to inhibition of methamphetamine-evoked DA release in the more intact striatal slices. Moreover, poor water solubility of these lobelane analogs prohibited further in vivo work. Subsequent work focused on analogs with the C-3 and C-4 carbons in the piperidine ring eliminated to afford racemic acyclic lobelane analogs. Generally, acyclic analogs exhibited greater water solubility and less lipophilicity compared to lobelane. Acyclic analogs exhibited affinities (Ki = 0.096-17 μM) for [3H]DTBZ sites that correlated positively with affinity (Ki = 3.3-300 nM) for inhibition of [3H]DA uptake. Pure enantiomers of potent racemic analogs were synthesized, and found to potently, selectively, and competitively inhibit [3H]DA uptake at VMAT2 and to release vesicular [3H]DA in a biphasic manner. Lead enantiomer (R)-N-(1-phenylpropan-2-yl)-3-phenylpropan-1-amine [(R)-GZ-924] inhibited methamphetamine-evoked [3H]DA release from striatal synaptic vesicles, but not from the more intact striatal slices. Surprisingly, (R)-GZ-924 inhibited nicotine-evoked [3H]DA overflow from striatal slices, revealing nonspecific effects. Importantly, (R)-GZ-924 inhibited methamphetamine self-administration in rats. However, the analog also inhibited food-maintained responding, revealing a lack of specificity. The lead analog will not be pursued further as a pharmacotherapy due to the lack of specificity. Further evaluation of the pharmacophore is needed to discover analogs which specifically inhibit the neurochemical and behavioral effect of methamphetamine.

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