Current Topics in Medicinal Chemistry - Volume 15, Issue 10, 2015

Parkinson&aposs disease (PD) is t he second most common form of neurodegenerative disorders that results from the progressive loss of dopaminergic neurons in the midbrain substantia nigra pars compacta (SNpc) triggering profound motor perturbation, as well as cognitive, sensory and mood deficits. Although these symptoms can be improved using currently available dopamine replacement strategies, they are not able to slow the neurodegenerative process that underlies PD progression. Following the discovery of the D3 receptor from molecular cloning, it has gained much attention as a potential therapeutic target for the treatment of PD due to their localization in the limbic regions of the brain as well as pharmacologic similarity to the D2 receptor subtype. Of particular interest, D3 receptor- selective agonists appear to have neuroprotective effects apart from their ability to relieve PD symptoms. Owing to the distinct significance of D3 receptor in mediating diverse neurological effects, it represents a unique target for therapeutic intervention in PD with much less undesirable side effects. Herein, we review progress in the development of D3 receptorselective agonist molecules having a broad spectrum of affinities, selectivities as well as unique pharmacological properties directed at slowing the neurodegeneration process.

Mutations in the gene for leucine-rich repeat kinase 2 (LRRK2) have been linked to several familial and sporadic late-onset cases of Parkinson’s disease. The cumulative data for the effects of mutant forms of this enzyme on neuronal degradation and the pathophysiology of Parkinson’s disease create a compelling case for drug discovery based on inhibition of the mutant forms of LRRK2. This review focuses on structure-activity relationships for inhibitors of LRRK2 and the data supporting a potential role of these agents in treating Parkinson’s disease.

Sialorrhea or excessive drooling is a significant medical issue in Parkinson’s disease (PD) and neurodegenerative disorders, although it is often underreported by patients. Sialorrhea affects a large proportion of PD patients, ranging up to 78% in advanced stages, with many PD patients considering drooling as their worst non-motor symptom. Sialorrhea affects up to a million patients with diverse neurological impairments, including cerebral palsy, amyotrophic lateral sclerosis (ALS), Huntington’s, survivors of stroke and severe traumatic brain injury. Numerous approaches have been attempted to treat sialorrhea in PD patients, including surgical procedures, prosthetic devices, botulinum injections, systemic anticholinergic drugs, and speech and behavioral therapy. A novel drug treatment (NH004) to control the symptoms of sialorrhea is under development. The active ingredient is the anticholinergic drug tropicamide. Anticholinergic drugs work by blocking acetylcholine muscarinic receptors and ultimately decreasing saliva secretion via the reduction of parasympathetic autonomic nervous system activity. The tropicamide is delivered in a thin film designed to adhere to the buccal mucosa and to slowly dissolve within the oral cavity, allowing the drug to reach the underlying salivary gland. A pilot study testing NH004 in PD patients has suggested a potentially useful sialorrhea-reducing effect with NH004 compared to placebo. The advantages of NH004 include local bioavailability with low systemic exposure, rapid onset of action and, importantly, convenience of use for patients. This review summarizes the current knowledge and impact of sialorrhea as a common non-motor symptom in PD, treatment options, the anticholinergic drug tropicamide, the design and development of the thin film drug delivery system, and NH004 for the treatment of sialorrhea.

Parkinson’s disease (PD) is a neurodegenerative disease affecting more than a million people in the USA alone. While there are effective symptomatic treatments for PD, there is an urgent need for new therapies that slow or halt the progressive death of dopaminergic neurons. Significant progress has been made in understanding the pathophysiology of PD, which has substantially facilitated the discovery efforts to identify novel drugs. The tissue-protective erythropoietin (EPO) receptor, EPOR/CD131, has emerged as one promising target for disease-modifying therapies. Recombinant human EPO (rhEPO), several variants of EPO, EPO-mimetic peptides, cell-based therapies using cells incubated with or expressing EPO, gene therapy vectors encoding EPO, and small molecule EPO mimetic compounds all show potential as therapeutic candidates. Agonists of the EPOR/CD131 receptor demonstrate potent anti-apoptotic, antioxidant, and anti-inflammatory effects and protect neurons, including dopaminergic neurons, from diverse insults in vitro and in vivo. When delivered directly to the striatum, rhEPO protects dopaminergic neurons in animal models of PD. Early-stage clinical trials testing systemic rhEPO have provided encouraging results, while additional controlled studies are required to fully assess the potential of the treatment. Poor CNS availability of proteins and challenges related to invasive delivery limit delivery of EPO protein. Several variants of EPO and small molecule agonists of the EPO receptors are making progress in preclinical studies and may offer solutions to these challenges. While EPO was initially discovered as the primary modulator of erythropoiesis, the discovery and characterization of the tissue-protective EPOR/CD131 receptor offer an opportunity to selectively target the neuroprotective receptor as an approach to identify disease-modifying treatments for PD.