Identification of potential bivalent inhibitors from natural compounds for acetylcholinesterase through in silico screening using multiple pharmacophores

The symptomatic cure observed in the treatment of Alzheimer's disease (AD) by FDA approved drugs could possibly be due to their specificity against the active site of acetylcholinesterase (AChE) and not by targeting its pathogenicity. The AD pathogenicity involved in AChE protein is mainly due to amyloid beta peptide aggregation, which is triggered specifically by peripheral anionic site (PAS) of AChE. In the present study, a workflow has been developed for the identification and prioritization of potential compounds that could interact not only with the catalytic site but also with the PAS of AChE. To elucidate the essential structural elements of such inhibitors, pharmacophore models were constructed using PHASE, based on a set of fifteen best known AChE inhibitors. All these models on validation were further restricted to the best seven. These were transferred to PHASE database screening platform for screening 89,425 molecules deposited at the “ZINC natural product database”. Novel lead molecules retrieved were subsequently subjected to molecular docking and ADME profiling. A set of 12 compounds were identified with high pharmacophore fit values and good predicted biological activity scores. These compounds not only showed higher affinity for catalytic residues, but also for Trp86 and Trp286, which are important, at PAS of AChE. The knowledge gained from this study, could lead to the discovery of potential AChE inhibitors that are highly specific for AD treatment as they are bivalent lead molecules endowed with dual binding ability for both catalytic site and PAS of AChE.