Increasing human life expectancy prompts the development of novel remedies for cognitive decline: 44 million people worldwide are affected by dementia, and this number is predicted to triple by 2050. Acetylcholinesterase and N-methyl-d-aspartate receptors represent the targets of currently available drugs for Alzheimer's disease, which are characterized by limited efficacy. Thus, the search for therapeutic agents with alternative or combined mechanisms of action is wide open. Since variations in 3',5'-cyclic adenosine monophosphate, 3',5'-cyclic guanosine monophosphate, and/or nitric oxide levels interfere with downstream pathways involved in memory processes, evidence supporting the potential of phosphodiesterase (PDE) inhibitors in contrasting neurodegeneration should be critically considered. For the preparation of this Review, more than 140 scientific papers were retrieved by searching PubMed and Scopus databases. A systematic approach was adopted when overviewing the different PDE isoforms, taking into account details on brain localization, downstream molecular mechanisms, and inhibitors currently under study, according to available in vitro and in vivo data. In the context of drug repurposing, a section focusing on PDE5 was introduced. Original computational studies were performed to rationalize the emerging evidence that suggests the role of PDE5 inhibitors as multi-target agents against neurodegeneration. Moreover, since such compounds must cross the blood-brain barrier and reach inhibitory concentrations in the central nervous system to exert their therapeutic activity, physicochemical parameters were analyzed and discussed. Taken together, literature and computational data suggest that some PDE5 inhibitors, such as tadalafil, represent promising candidates.

Therapeutic Potential of Phosphodiesterase Inhibitors against Neurodegeneration: The Perspective of the Medicinal Chemist.

Phosphodiesterase-5 (PDE5) inhibitors can be used as clinical agents for the treatment of erectile dysfunction and pulmonary hypertension. A series of aryl-chromeno-pyrrol derivatives were previously identified as PDE5 inhibitors in our lab. Herein, these molecules were subjected to 3D-QSAR analysis with CoMFA and CoMSIA methods to gain deeper insight into the structural requirements for their bioactivities. Receptor- and ligand-based alignment were used and compared to find the alignment-related factors that affect the accuracy of QSAR models. The receptor-based CoMFA and CoMSIA models, which were generated by superimposing the docking conformations directly in the protein binding site, gave more significant results for 38 training set compounds and 5 test set molecules. Comparison of the two alignments revealed that spatial arrangement of the ligands is the principal factor in determining the reliability of the 3D-QSAR models. Detailed analysis of the receptor-based CoMSIA-SE contour maps provided much helpful information to improve the bioactivities of aryl-chromeno-pyrrol analogs as PDE5 inhibitors.

Zhong Li

Papers

3D-QSAR modeling of Phosphodiesterase-5 inhibitors: evaluation and comparison of the receptor- and ligand-based alignments