OPTIMIZATION OF COUMARIN-BASED MULTITARGET LIGANDS: DISCOVERY OF POTENT WATER-SOLUBLE AND BRAINPERMEANT NEUROPROTECTIVE AChE-MAO B INHIBITORS

The treatment of Alzheimer’s disease (AD) and other age-related neurodegenerative disorders (NDs) still remains an unmet clinical need exacerbated by the increase of life-expectancy and elderly population.1 Their complex multifactorial nature accounts for the lack of therapies capable of delaying or reverse the pathologic conditions although exerting a symptomatic relief. Current research is focused on new targets and innovative therapeutic strategies, among which the so-called multitarget approach2 holds the promise of a synergistic effect arising from the combination of multiple biological activities. As for AD, the inhibition of enzymatic activities of both acetylcholinesterase (AChE) and monoamine oxidases B (MAO-B) has been considered a viable option to counteract two well-established altered pathways underlying the disease, i.e., cholinergic deficit and oxidative stress conditions, respectively. Starting from a potent single-target MAO-B inhibitor, we recently reported a structure-based hybridization approach (Figure 1) that allowed the discovery of dual AChE-MAO B inhibitors exhibiting nanomolar inhibitory potencies.4 Then, molecular modifications were focused on the basic tail region addressing the improvement of water solubility through the modulation of basicity and geometry. This design strategy led us identifying a multipotent hit compound displaying excellent in vitro inhibitory activities (hMAO B IC50 = 30 nM, eeAChE IC50 = 1.03 μM, selectivity ratio hMAO B/A = 94) along with low cytotoxicity and promising neuroprotective effect against pro-apoptotic oxidative insults in SH-SY5Y cell lines. In addition, pharmacokinetic relevant properties, namely aqueous solubility and lipophilicity, were experimentally determined by applying the turbidimetric method and RP-HPLC technique. Low eudismic ratios on both enzymatic targets revealed a negligible effect of chirality on binding affinities. Interestingly, the optimized multitarget hit behaved as a brain permeant agent without suffering from P-gp mediated extrusion activity.