Pharmacotherapy of Parkinson’s disease: Progress or regress?

Abstract

Parkinson's disease (PD) is a chronic, progressive disease of the central nervous system (CNS), characterized by a slow loss of dopaminergic neurons in the substantia nigra, leading to significant decrease in dopamine (DA) levels in the striatum. Currently used drugs, such as levodopa (L-DOPA), amantadine, dopamine agonists (D) or anticholinergic drugs, are not effective enough, and do not eliminate the causes of disease. Many research centers are conducting research on new forms of currently used drugs (e.g. Duodopa, XP21279, IPX066), new drugs of already known groups (e.g. safinamide), medicines that suppress side effects of L-DOPA (e.g. AFQ056, fipamezole), and, finally, compounds with a novel mechanism of action (e.g. PMY50028, A2A receptor antagonists). A lot of scientific reports indicate an important role of A2A receptors in the regulation of the central movement system, so a new group of compounds - selective antagonists of A2A receptors (e.g. istradefylline, preladenant, SYN115) - has been developed and their potential use in PD has been examined. Clinical studies of A2A receptor antagonists have shown that this group of compounds can shorten off periods and at the same time they do not worsen dyskinesias in patients with PD. Moreover, there is ongoing research on new forms of treatment, such as gene therapy. Attempts to apply the viral vector AAV-2, which will be able to infect neurons with a variety of genes, including the gene of glutamate decarboxylase (GAD), neurturin (NTN), or aromatic L-amino acid decarboxylase, are currently being carried out. The results of phase I and II clinical studies showed some efficacy of this form of treatment, but the method requires further studies. An analysis of potential future therapies of Parkinson's disease suggests that some progress in this field has been made.