The advantages of using iPSC-differentiated 3D neuronal system for drug screening are likely offset the disadvantages. First, the 3D environment offers some anatomical similarities to mature brain (compared to 2D cultures). The 3D cells better represent the native target of the drug. Whether a 2D configuration is associated with any differences in cell physiology is unknown, and using 3D systems avoids this uncertainty. Second, 3D cultures allow for microscopic evaluation of spatial features related to drug effects in a system that more closely resembles the target tissue. It is certainly possible, if not likely, that cytoskeletal dynamics, such as Tau binding to microtubules, is related to neuronal spatial configuration. Third, our 3D cell system allows us to quantify drug levels that is not available in our traditional 2D assay system. Since the introduction of 3D neuronal culture for Aβ and Tau quantification [14], few studies have utilized this system to evaluate drug efficacy, and there is no report on drug bioavailability in 3D neurons. The physical properties of 3D neuro-spheroids allow LC-MS/MS based quantification of drug exposure and assessment of dose-dependent drug efficacy.
