Advances in drug development for Parkinson's disease: present status.

The major hallmark of Parkinson's disease (PD) is the progressive loss of dopaminergic neurons in the substantia nigra pars compacta, leading to the characteristic motor symptoms of resting tremors, bradykinesia and rigidity. Research in the field of PD therapy has been partly successful in terms of developing symptomatic treatments, but it also experienced several failures with regard to developing disease-modifying therapies. According to the definition of the Committee to Identify Neuroprotective Agents for Parkinson's, neuroprotection would be any intervention that favorably influences the disease process or underlying pathogenesis to produce enduring benefits for patients. A development of effective neuroprotective therapies resulting in clinically meaningful results is hampered by several factors in all research stages. Novel solutions might be offered by an evaluation of new targets throughout clinical studies, therapies emerging from drug repositioning approaches, multitarget approaches and network pharmacology. Several promising randomized controlled trials are in progress, and the increased collaboration between pharmaceutical companies and basic and clinical researchers has the potential to bring us closer to developing an optimum pharmaceutical approach for the treatment of PD. The aim of the present review is to give an overview of the neuroprotective agents and their targets currently investigated for the treatment of PD in phase I-III clinical trials.