Promising anti-Alzheimer's dimer bis(7)-tacrine reduces beta-amyloid generation by directly inhibiting BACE-1 activity.

The regulation of alpha-, beta-, (BACE-1), and gamma-secretase activities to alter beta-amyloid (Abeta) generation is considered to be one of the most promising disease-modifying therapeutics for Alzheimer's disease. In this study, the effect and mechanisms of bis(7)-tacrine (a promising anti-Alzheimer's dimer) on Abeta generation were investigated. Bis(7)-tacrine (0.1-3muM) substantially reduced the amounts of both secreted and intracellular Abeta in Neuro2a APPswe cells without altering the expression of APP. sAPPalpha and CTFalpha increased, while sAPPbeta and CTFbeta decreased significantly in Neuro2a APPswe cells following the treatment with bis(7)-tacrine, indicating that bis(7)-tacrine might activate alpha-secretase and/or inhibit BACE-1 activity. Furthermore, bis(7)-tacrine concentration-dependently inhibited BACE-1 activity in cultured cells, and also in recombinant human BACE-1 in a non-competitive manner with an IC(50) of 7.5muM, but did not directly affect activities of BACE-2, Cathepsin D, alpha- or gamma-secretase. Taken together, our results not only suggest that bis(7)-tacrine may reduce the biosynthesis of Abeta mainly by directly inhibiting BACE-1 activity, but also provide new insights into the rational design of novel anti-Alzheimer's dimers that might have disease-modifying properties.