Tacrine-benzofunan hybrids as multi-target directed ligands for Alzheimer´s disease treatment

Objectives: Develop single molecules able to target multiple distinct AD hallmarks. Multi-target directed ligands (MTDLs) should bring the benefit of a synergistic enhancement of therapeutic effects compared to a single-target acting drug. Methods: To achieve MTDL we combined the scaffold of the known acetylcholinesterase (AChE) inhibitor tacrine with a benzofuran unit through a methylene chain. Tacrine-benzofuran hybrids were synthesized from substituted salicylaldehydes and 2-aminobenzoicacid as the available starting materials. The influence of hybrids on the hydrolytic activity of human recombinant AChE and butyrylcholinesterase from human serum were in vitro evaluated by Ellman’s assay while inhibitory potency against human recombinant beta-secretase was studied by a FRET assay using M-2420 as substrate. Inhibition of AChE-induced beta-amyloid(1-40) aggregation and spontaneous beta-amyloid(1-42) aggregation was investigated by a Thioflavin T-based fluorescence assay. Results: Promising new tacrine-benzofuran hybrids, which could be further developed for an effective treatment of AD, were designed, synthesized and in vitro characterized. In particular, the most interesting derivatives within this series showed inhibitory potency against human AChE in the low nanomolar range, a mixed-type mechanism of inhibition, which has been associated with the ability of partially inhibit AChE-induced Aβ fibril formation, were able to significantly inhibit amyloid self-aggregation (at x0.2 concentration) and resulted in potent beta-secretase inhibitors with inhibitory potency in the low micromolar range. Conclusions: The new tacrine-benzofuran hybrids showed an MTDL profile and were able to reduce the hydrolytic activity of human AChE, to potentially prevent amyloid production through the inhibition of human beta-secretase activity and interfere with amyloid aggregation.