The complex pathophysiology of Alzheimer's disease (AD), explained by several interrelated hypotheses, indicates that targeting multiple targets simultaneously could be a reasonable and attractive approach for its treatment. We followed this approach in the context of our master's thesis, where we designed, synthesised and biochemically evaluated five indazole dual inhibitors of butyrylcholine esterase (BChE) and p38α mitogen-activated protein kinase (p38α MAPK). The role and concentration of BChE in the brain are increased in AD, whereas p38α MAPK plays an important role in mediating the inflammatory response. Thus, simultaneous inhibition of BChE and p38α MAPK in the treatment of AD could increase cholinergic stimulation and reduce neuroinflammation.
The design was based on the compound ARRY-371797, which is a selective inhibitor of p38α MAPK, but also shows some structural similarities with BChE inhibitors. For all compounds, the indazole ring from ARRY-371797 and the 2,4-difluorophenoxy group were retained. We also retained the dimethylamine moiety, as it forms important cation-π interactions with Trp82 in the choline-binding pocket of BChE. We investigated how the inhibitory activity on both enzymes is affected by: 1) the binding of methylcyclohexane to sites N1 and N2 of the indazole ring, 2) the chain extension of the N-(2-(dimethylamino)ethyl)amide fragment by 1 C atom, and 3) the reduction of amide to amine. The inhibitory activity of the compounds was evaluated by Ellman method and ADP-Glo test.
In the case of compound 9A, we found that if methylcyclohexane is bound to the N1 site of the indazole ring, the inhibitory activity on the BChE enzyme towards ARRY-371797 is increased. It is even more enhanced when this substituent is bound to the N2 site, since in the case of compound 9B we were able to obtain BChE inhibition at nanomolar concentration (IC50 = 0.1669 µM), suggesting an energetically more favourable shift of the acyl loop in the active site of BChE. On the other hand, the substitution at the N2 instead of the N1 site leads to a deterioration of the inhibitory activity on p38α MAPK, due to the slightly changed conformation of the compound in the binding site. Despite the impairment of the inhibitory activity on p38α MAPK, it was still largely preserved in the case of compound 9B (IC50 = 6.776 µM). Based on these results, compound 9B represents the best example of a dual inhibitor. With regard to the extension of the N-(2-(dimethylamino)ethyl)amide fragment by 1 C atom, we found that it has no significant effect on the inhibitory activity on both BChE and p38α MAPK. The reduction of amide to amine resulted in the loss of inhibitory activity on BChE in compound 11A, confirming the important role of carbonyl oxygen. In compounds 9A, 9B, 10A and 10B, we also achieved selective activity on BChE towards AChE. This chemical space exploration has therefore provided valuable information that will help in the further development of dual inhibitors.
|
