Concise Review: Progress and Challenges in Using Human Stem Cells for Biological and Therapeutics Discovery: Neuropsychiatric Disorders

Abstract

In facing the daunting challenge of using human embryonic and induced pluripotent stem cells to study complex neural circuit disorders such as schizophrenia, mood and anxiety disorders, and autism spectrum disorders, a 2012 National Institute of Mental Health workshop produced a set of recommendations to advance basic research and engage industry in cell-based studies of neuropsychiatric disorders. This review describes progress in meeting these recommendations, including the development of novel tools, strides in recapitulating relevant cell and tissue types, insights into the genetic basis of these disorders that permit integration of risk-associated gene regulatory networks with cell/circuit phenotypes, and promising findings of patient-control differences using cell-based assays. However, numerous challenges are still being addressed, requiring further technological development, approaches to resolve disease heterogeneity, and collaborative structures for investigators of different disciplines. Additionally, since data obtained so far is on small sample sizes, replication in larger sample sets is needed. A number of individual success stories point to a path forward in developing assays to translate discovery science to therapeutics development.

Keywords: Autism spectrum disorders; Bipolar disorder; Drug discovery; Genetics; Induced neuronal cells; Induced pluripotent stem cells; Schizophrenia.

Figure 1. Example of a complex cell-based assay to study complex brain disorders

In vitro-grown human cortical spheroids viewed in cross-section. (A) Organization of a proliferative zone inside a spheroid, where all NPCs are recognized by an anti-SOX2 antibody (red) and those dividing NPCs are shown in green by the expression of the radial glia-specific mitotic marker phospho-vimentin (p-VIM). (B) Spheroids after 137 days of differentiation and staining with anti-CTIP2 and anti-SATB2 antibodies, indicative of layer-specific neurons, and Hoechst dye, marking nuclei. Used with permission from Sergiu Pasca, unpublished data and .

Figure 2. Integrating tissue chips into a multi-organ system for toxicology and efficacy studies

The basic paradigm involves mimicking minimal units of organ function, using biocompatible matrices that allow introduced cells to organize in ways that closely approximate organ structures in vivo (e.g., intestinal crypt, kidney proximal tubule, blood brain barrier, neural circuit). A modular design and connectivity via a microfluidic platform (ideally approximating a circulatory system) allow tissue chips to be integrated into a system that allows compound pharmacokinetics to be measured, as well as toxicity and efficacy (if an adequate disease-relevant assay is incorporated). Used with permission from the National Center for Advancing Translational Sciences.

Figure 3. Integrating multiple reprogrammed cell-based platforms into the drug discovery pipeline

The flexibility of cell reprogramming and differentiation protocols allow for a variety of fit-for-purpose assays for different steps in drug development, including (A) understanding disease mechanisms and identifying druggable targets, (B) high throughput screening (HTS) of compounds and follow-up confirmation, or (C) assessment of pharmacokinetics (PK), toxicity and efficacy at the pre-clinical or ‘virtual clinical trial’ phase. The listed assay types are examples and are not meant to be exhaustive.