Year of Publication

2019

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Pharmacy

Department

Pharmaceutical Sciences

First Advisor

Dr. Linda P. Dwoskin

Abstract

Substance use disorders are serious health concerns in the United States. Furthermore, the National Survey on Drug Use and Health reports a continuous increase in substance use disorders in the United States during the last 10 years. However, there are not many effective pharmacotherapeutics available for substance use disorders. The current dissertation is focused on research aimed at discovering pharmacotherapeutics for substance use disorders. First part of dissertation focused on discovering methamphetamine (METH) use disorder therapeutics targeting specific mechanism of METH action on dopaminergic neurons. The second part of dissertation focused on opioids and cocaine use disorder therapeutics targeting rewarding pathway commonly activated by opioids and cocaine.

With respect to METH, it induces release of dopamine (DA) in neuronal terminals by interacting with the vesicular monoamine transporter-2 (VMAT2) and DA transporter (DAT). VMAT2 inhibitors have been found by our research group to decrease METH-evoked DA release, METH-induced hyperlocomotion, and METH self-administration in rats. However, these VMAT2 inhibitors lacked selectivity and tolerance developed to these pharmacologic effects after repeated administration, thereby limiting their potential as pharmacotherapeutics for METH use disorders. In the current study, analogs from a novel scaffold were found to selectively inhibit VMAT2 and were evaluated using neurochemical and behavioral pharmacological approaches. R- and S-3-(4-methoxyphenyl)-N-(1-phenylpropan-2-yl)propan-1-amine (GZ-11610 and GZ-11608, respectively) exhibited 94- to 3450-fold selectivity for VMAT2 over human-ether-a-go-go (hERG) channel, DAT, serotonin transporter, and nicotinic acetylcholine receptors. GZ-11608 competitively and concentration-dependently inhibited METH-evoked DA release via VMAT2. Also, GZ-11610 (56-300 mg/kg, oral) and GZ-11608 (300 mg/kg, oral; 10-30 mg/kg, s.c.) reduced METH-induced hyperlocomotor activity in METH-sensitized rats. Furthermore, GZ-11608 (1-30 mg/kg, s.c.) inhibited METH self-administration, cue- and METH-induced reinstatement in a dose-dependent manner, and 30 mg/kg (s.c.), 10 mg/kg (s.c.), and 17 mg/kg (s.c.) produced significant effect, respectively. Importantly, the GZ-11608-induced decrease in METH self-administration was not surmounted by increasing the amount of METH available. GZ-11608 did not substitute for METH and did not serve as a reinforcer in rats self-administering METH and drug naïve rats, respectively. Thus, these VMAT2 inhibitors incorporating a new scaffold are novel leads for new pharmacotherapeutics to treat METH use disorders.

Substances with high abuse potential including opioids and cocaine elevate extracellular DA concentration in the nucleus accumbens, and this mechanism has long been considered to underly substance-induced reward. DA in the nucleus accumbens originates from DA neuron cell bodies located in the ventral tegmental area in the midbrain. Interestingly, M5 muscarinic acetylcholine receptors (mAChRs) are proteins that are highly expressed on ventral tegmental area DA neurons. Also, studies investigating M5 mAChRs knockout mice showed reduced responding for cocaine in cocaine self-administration and decreased time spent in cocaine-paired and morphine-paired place preference studies. Pharmacological inhibition of M5 mAChRs function via microinfusing mAChR antagonists exhibiting no selectivity among M1-M5 mAChRs subtypes into the ventral tegmental area where expression of M5 mAChRs are dominant, reduced morphine-induced hyperlocomotion and cocaine seeking behaviors in rats. These studies support therapeutic potential of M5 mAChRs selectivity antagonists in opioids and cocaine use disorders. Thus, in the current study, affinity of a series of pethidine and quinuclidinyl N-phenylcarbamate analogs for M5 mAChRs was evaluated using in vitro and ex vivo neuropharmacological assays. Among the pethidine analogs, compound 6a showed the highest binding affinity at M5 (Ki = 0.38 µM), but also high affinity at M1 and M3 mAChRs (0.67 and 0.37 µM, respectively). Among the quinuclidinyl N-phenylcarbamate analogs, compound 13c exhibited the highest affinity at M5 (Ki = 1.8 nM), but also high affinity at M1, M2, M3 and M4 mAChRs (Ki = 1.6, 13, 2.6, 2.2 nM, respectively). Also, 13c acted as an agonist of mAChRs on oxotremorine-induced DA release from rat striatal slices. In addition, compound 13b was found exhibiting the highest selectivity (17-fold) at M3 over M2 mAChRs, suggesting potential of 13b as a chronic obstructive pulmonary disease therapeutics. Taken together, these novel analogs serve as leads for further discovery of subtype-selective M5 mAChR antagonists that may have potential as therapeutics for substance use disorders, as well as for chronic obstructive pulmonary disease.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2019.302

Funding Information

This work was supported with funding from the National Institute of Health grants U01 DA013519, U01 DA043908, UL1 TR001998, DA030667, and UL1 TR001998.

Available for download on Friday, July 24, 2020

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