Design, Synthesis, Biological Evaluation And Molecular Modeling Studies Of Novel Multifunctional Neuroprotective Drugs For The Treatment Of Parkinson\u27s Disease: An Effort Towards The Improvement Of In Vivo Efficacy And Modulation Of Alpha Synuclein Aggregation Property Of The Neuroprotective Parent

Abstract

DESIGN, SYNTHESIS, BIOLOGICAL EVALUATION AND MOLECULAR MODELING STUDIES OF NOVEL MULTIFUNCTIONAL NEUROPROTECTIVE DRUGS FOR THE TREATMENT OF PARKINSON\u27S DISEASE: AN EFFORT TOWARDS THE IMPROVEMENT OF IN VIVO EFFICACY AND MODULATION OF ALPHA SYNUCLEIN AGGREGATION PROPERTY OF THE NEUROPROTECTIVE PARENT MOLECULE (D-264) by GYAN PRAKASH MODI May 2014 Advisor: Dr. Aloke K. Dutta Major: Pharmaceutical Sciences Degree: Doctor of Philosophy Parkinson\u27s disease (PD) is a progressive age-related neurodegenerative disorder of the central nervous system that is characterized by gradual loss of dopaminergic neurons in the substantia nigra region of the brain. The research from the past two decades in PD area has provided more insights into the basic pathogenetic factors of PD such as roles of oxidative stress, aggregation of α-synuclein (ASN) proteins in the form soluble toxic aggregates and fibrils, increased concentration of iron in the PD brain. Levodopa (L-DOPA) became available in 1960 for the treatment of PD and is still being considered as one of the main stream therapy. However, prolog use of L-DOPA gives rise to on and off episode along with motor fluctuations and eventual oxidation of dopamine (DA) derived from L-DOPA further facilitates neurodegeneration. It is increasingly evident that drugs aiming a single target may be inadequate for the treatment of complex diseases such as PD, which is multifactorial in nature. Thus, it is hypothesized that multifunctional drugs having multiple pharmacological activities addressing multiple pathogenic factors of PD will be effective as disease modifying agent for the treatment of this disease. Our aim in the first study was to enhance brain penetration of one of our lead molecule D-264. Our current structure activity relationship study is focused on introduction of methoxy and hydroxyl group at various positions on the accessory binding biphenyl ring of this hybrid molecule. The introduction of hydroxyl group or combination of hydroxyl/methoxy group at a suitable position could further potentiate its antioxidant and neuroprotection property. Among all synthesized compounds in the first series, compound D-433 and D-533 exhibited the highest selectivity for the D3 over D2 receptor in both binding and functional assays. Lead compounds D-433 and D-533 also exhibited potent free radical quenching property, possibly indicating antioxidant activity. The lead compounds were tested in two PD animal models. Both the compounds exhibited higher blood brain barrier crossing ability compared to parent compounds D-264. Furthermore, in MTT assay lead compounds are able to protect MN9D cells from the exposure to neurotoxin MPP+ and 6-OHDA in a dose dependent manner. Compounds D-519 and D-520 were selected as lead molecules from the second series and they exhibited nanomolar to sub nanomolar range affinity at D2/D3 receptors in the receptor binding assay and [35S]GTPγS binding assay. It was concluded from this in vivo study that both D-519 and D-520 was able to efficiently cross blood brain barrier and exhibited high in vivo agonist efficacy. D-519 and D-520 can potentially chelate with Fe(III). Furthermore, D-520 is able to reverse the ASN aggregates induced toxicity at a significant level in PC-12 cells. Finally, three dimensional quantitative structure activity relationship (3DQSAR) studies CoMFA and CoMSIA were performed. Two alignment methods (atom base and flexible) and two charge calculation methods (Gasteinger-Huckel and MOPAC) were used. The presence of carbonyl group attached to piperazine ring and hydrophobic biphenyl ring was found to be one of the most important factors responsible for the D3 selectivity over D2