spheroids and eventually released to the media. The alternative interpretation of these data, that 3D configuration of neurons alters their response to drugs, is contradicted by our result showing the same direction of drug effect and is not supported by any known example of altered cell physiology based on 3D vs. 2D cellular configuration. We therefor conclude that the reduced efficacy of BACE1 and γ-secretase inhibitors in 3D configurations is related to reduced drug exposure of cells within the spheroids, an interpretation consistent with our direct measurements of drug concentrations (Fig 9C). While this result may not be unexpected, the difference is substantial even on a microscopic scale over the course of 2 days of treatment.
