Parkinson's disease (PD) is a debilitating neurodegenerative disorder characterized by progressive and substantial loss of dopaminergic neurons in the substantia nigra compacta (SNc), resulting in severe neurological signs including tremors, bradykinesia, and rigidity. The existing approaches to PD treatment are mainly focused on alleviating the motor symptoms by compensating for neurochemical deficits, but they fail to halt the progression of the neurodegenerative process. The lack of effective neuroprotective drugs for PD is primarily attributed to a limited understanding of the complex mechanisms involved in the degenerative processes of the nigral dopaminergic system. However, recent elucidation of apoptotic pathways and oxidative stress signaling has offered some important clues that boost hope for development of novel neuroprotective strategies for PD. In this regard, we uncovered a key apoptotic cell death pathway during oxidative insult in PD models involving the proteolytic activation of a novel PKC isoform, PKC4, by caspase-3 to promote apoptosis in dopaminergic neurons. Suppression of proteolytic activation of PKC4 using dominant negative mutants, a caspase-cleavage site resistant mutant, or siRNAs completely rescued dopaminergic neurons from Parkinsonian toxins MPP+ and 6-OHDA- induced apoptotic cell death. Interestingly, we also found that PKC4 is highly expressed in nigral dopaminergic neurons as compared to other cells. Collectively, these findings indicate that PKC4 is a key downstream proapoptotic kinase in dopaminergic cells and may be a promising therapeutic target for PD. Importantly, treatment with the PKC4 inhibitor rottlerin offered excellent protection against behavioral deficits, neurochemical depletion, and nigral dopaminergic neuronal damage in the classic MPTP-induced animal model of PD, confirming that PKC4 is a viable target for development of neuroprotective agents for PD. As a next logical step, this SBIR phase-I application proposes to develop a series of new PKC4 small molecule inhibitors and optimize them to identify lead compounds with a high therapeutic index. The specific objectives of the proposal are: i) To design and synthesize a series of novel PKC4 inhibitor analogs, ii) To profile the selectivity and inhibitory potency of PKC4 inhibitors using a high throughput kinase profiling system, iii) To determine the potential neuroprotective effects of the PKC4 inhibitors in cell culture models of PD. The combination of a validated therapeutic target, integrative study design, and excellent expertise will help us accomplish these important goals. We anticipate identifying a set of lead compounds for testing in PD animal models for future Phase-II application. The overall approach is expected to lead to development of a mechanism- based neuroprotective agent for treatment of PD.
Public Health Relevance: Parkinson's disease is a major progressive neurodegenerative disorder characterized by the cardinal motor symptoms of rigidity, bradykinesia, tremors, and postural instability. The existing therapeutic approach for Parkinson's disease only treats the symptoms and fails to prevent the progression of the neurodegenerative process. Recently, we identified that PKC4 is a novel therapeutic target for development of neuroprotective agents because the kinase plays a key role in apoptotic cell death of nigral dopaminergic neurons. The proposed studies will develop a series of small molecule PKC4 inhibitors and evaluate their neuroprotective properties in Parkinson's disease models. Overall, the knowledge gained from this proposal will lead to development of an effective neuroprotective drug for treatment of Parkinson's disease.
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