We found that neurons from five AD patients generated similar levels of Aβ40 and Aβ42 in the absence of any compounds (Fig 9). Although both BACE1 and γ-secretase inhibitors are extremely potent in previously published studies using stable mammalian cell lines, primary 2D mouse neuronal culture, and in vitro enzymatic activity assays [35, 36], our 3D neuro-spheroids seemed to be responding less to these potent inhibitors. Interestingly, the efficacies of the same compounds in two different systems, 2D versus 3D, were quite different. 3D neuro-spheroids showed less reduction of Aβ compared to 2D neurons in the presence of the same concentrations of BACE1 or γ-secretase inhibitors (Fig 9 vs. Figs 7 and 8).
