Access Type

Open Access Dissertation

Date of Award

January 2018

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Pharmaceutical Sciences

First Advisor

Aloke Dutta

Abstract

Parkinson’s disease (PD) is a progressive neurodegenerative disease that develops from gradual depletion of dopamine (DA) and dopaminergic neurons in the substantia nigra pars compacta (SNc) with the accumulation of intraneuronal proteinaceous matter named as Lewy bodies. The four cardinal symptoms associated with PD are tremor, rigidity, bradykinesia, and postural instability. Although the exact mechanism and etiology of PD are not fully understood, several factors have been implicated in the pathogenesis and progression of PD including protein aggregation, oxidative stress, mitochondrial dysfunction, environmental, and genetic factors.

The current therapy of Parkinson’s disease is categorized into four classes: levodopa, DA agonists, monoamine oxidase inhibitors (MAO-Is), catechol-o-methyl transferase inhibitors (COMT-Is) and Dopamine agonist (DA). Even though these medications are available to treat PD, they only reduce the symptoms and do not slow or stop the disease progression; in addition to developing the severe side effects such as dyskinesia and motor fluctuation with long-term therapy. To overcome the concerns associated with current PD medications, a new strategy has been adopted by developing multifunctional molecules to target multiple factors implicated in the pathogenesis of the disease that could be beneficial to treat the patients.

The hypothesis of this dissertation is to develop novel multifunctional dopamine D2/D3 agonist molecules with neuroprotective, antioxidants properties to modulate the pathogenic pathway while addressing the symptomatic deficits. Specifically, our hybrid structure strategy which combines D2/D3 agonist head groups to the other moieties that are suitable to modulate the pathogenic pathway of PD, led to development of molecules to validate our proof of concept.

In this project, the structure activity relationship (SAR) study was carried out based on our hybrid structure strategy template that was previously established. Three main objectives were set forward in this project: the first is to design and develop multifunctional molecules by covalently attaching D2/D3 agonist head groups such as pramipexole and 5-OH-DPAT to various carbazole moieties through a piperazine linker. The lead molecules (-)-11b, (-)-15a and (-)-15c exhibited high affinity for both D2 and D3 receptors whereas in GTPγS functional assay, the compounds showed potent agonist activity at both D2 and D3 receptors (EC50 (GTPγS); D2 = 48.7 nM, D3 = 0.96 nM for 11b, D2 = 0.87 nM, D3 = 0.23 nM for 15a and D2 = 2.29 nM, D3 = 0.22 nM for 15c). In PD animal model study, the test compounds exhibited potent in vivo activity by reversing hypolocomotion in reserpinized rats with a long duration of action compared to the reference drug. In a cellular antioxidant assay, compounds (-)-11b, (-)-15a and (-)-15c exhibited potent activity in reducing oxidative stress induced by neurotoxin 6-hydroxydopamine (6-OHDA). Also, in a cell-based PD neuroprotection model, these lead compounds significantly increased cell survival from toxicity of 6-OHDA, thereby, producing neuroprotection effect. These observations suggest that the lead carbazole-based dopamine agonists are promising multifunctional molecules for a viable symptomatic and disease modifying therapy of PD and should be further investigated. The second objective is to combine D2/D3 agonist head groups with monoamine oxidase inhibiton property. Based on the results from in vitro receptor assays and enzymatic inhibition assay of the generated compounds led to the identification of compounds (−)-33 (D-671) and (±)-42 (D-678) as the lead compounds that demand further modification. The third main objective is to develop novel multifunctional triple reuptake inhibitor based on the modification of the pyran template that was previously established by us to treat the motor, non-motor symptoms like depression associated with PD. The designed compounds were evaluated for their binding affinities for the DAT, SERT, NET in the brain tissue. Based on the results of the affinity data of the initial compounds for the DAT, SERT, NET, cis-isomer compound 60a (D-620) exhibited high affinity for both DAT and NET that could be considered as a dual inhibitor for the monoamine reuptake transporters. According to this finding 60a (D-621) was identified as the lead compound that requires further modification.

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