Parkinson's Disease (PD) is a progressive neurodegenerative disorder characterized by degeneration of the nigrostriatal dopaminergic pathway. The cardinal clinical features of PD include resting tremor, rigidity, difficulty initiating movement, and postural instability. Currently, no ideal therapies are available for slowing the progression of the degeneration process and at the same time relieving symptomatic abnormalities associated with this disease. Although the pathogenesis of PD is poorly understood both oxidative stress and mitochondrial dysfunction resulting from loss of glutathione with increased concentration of free iron have been strongly implicated in dopamine cell death. It is increasingly evident that for a complex disease such as PD, a drug targeting only one target site will only partially address the therapeutic need of the disease. The overall goal in this proposal is to develop multifunctional therapeutic agents which will be useful not only in symptomatic treatment but also could be used as disease-modifying agents by promoting survival of DA neurons. Dopamine D3 preferring agonists besides providing symptomatic relief in PD with less motor complications, have also been shown to act as neuroprotective agents. A D3 preferring compound D-264 derived from our novel hybrid template was shown to be neuroprotective in two different animal models studies. Our studies demonstrated that interaction of D-264 with the D3 receptor along with its other properties e.g. antioxidant, might be responsible for its neuroprotection property. In another preliminary development, unique multifunctional dopamine D2/D3 agonist compounds with a capacity to chelate iron have been developed. Such molecules are not only expected to relieve motor dysfunction in PD but also will have the potential to reduce oxidative stress in the PD brain by chelating with iron which has been implicated in the pathogenesis of the disease. Initial studies indicate facile blood-brain-barrier crossing ability of these compounds, and in cell culture and in vivo MPTP mouse model experiments one of the lead molecules indicated neuroprotection property. We now propose to expand drug development studies based on hybrid D-264 related analogues to improve pharmacokinetic properties to increase bioavailability and to carry out expanded structure activity relationship studies on multivalent iron binding D2/D3 agonists. Selected molecules from these two series of compounds will be evaluated in PD animal models to determine specificity and efficacy. Promising leads from these studies will next be evaluated in neuroprotection studies which include both acute neurotoxicant MPTP and chronic dox-inducible dopaminergic glutathione depletion transgenic mouse models.
Parkinson's Disease (PD) is a progressive neurodegenerative disorder characterized by degeneration of the nigrostriatal dopaminergic pathway. It is estimated that PD affects approximately 1-2 % of people older than 65 years of age. The primary therapeutic agent for PD is L-DOPA which improves the symptoms of the disease by producing dopamine in dopamine depleted neurons. However, long term use of L-dopa gives rise to motor fluctuations with dyskinesias and a decrease in duration of response to a given L-dopa dose. Prolonged use of L-dopa also gives rise to on and off episodes and may lead to toxicity to DA neurons and hence, accelerating the DA neurodegeneration process. It is increasingly evident that for a complex disease such as PD, a drug targeting only one target site will only partially address the therapeutic need of the disease. The overall goal in this proposal is to develop multifunctional therapeutic agents which will be useful not only in symptomatic treatment but also could be used as disease-modifying agents by promoting DA neuron survival.
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