Drug discovery and development is a very expensive and long process. From target identification until marketing, approximately $1.3 billion and 12 years pass by (Wouters et al. 2020). Before entering the clinical phase, a drug candidate has to pass a broad battery of in silico-, in vitro-, and in vivo-based tests to determine its efficacy, metabolism, pharmacokinetic toxicity, and safety pharmacology (DiMasi 2001). Nevertheless, nine out of ten candidates fail in the clinical phases due to unexpected low efficacy or intolerable adverse effects (Harrison 2016). The most frequent cause for drug failures in clinical trials and for post-approval withdrawals in the United States and Europe is drug-induced liver injury (DILI) (Walker et al. 2020; Ostapowicz et al. 2002; Larry and Pageauz 2005)
The human liver is responsible for managing the endogenous and exogenous metabolism in the body, including glucose homeostasis, xenobiotic metabolism, and detoxification (Xu et al. 2005). Due to its location, blood flow, and functional role, it is the first organ, after the gastrointestinal system, to be confronted with enterally applied xenobiotics. Thus, it is also the initial target for medication-induced damage (David and Hamilton 2010). However, no biomarker or model exists for the reliable prediction of DILI in preclinical studies.
The current methods of predicting DILI are animal studies and in vitro hepatotoxicity testing, which often do not translate to humans (Godoy et al. 2013; Lauschke et al. 2016; Lauschke et al. 2019; Bell et al. 2017). Animals are of limited use to predict the response in humans because they differ from humans in several respects, such as the expression of metabolizing enzymes (Lossi et al. 2016). The gold standard of in vitro hepatotoxicity testing is 2D monoculture of primary human hepatocytes (PHH) (Lauschke et al. 2019; Lauschke et al. 2016; Godoy et al. 2013). In this model, PHHs grow flat on optimized plastic surfaces under static conditions, without contact with other liver cell types. This leads to a rapid loss of hepatocyte physiological functions, such as phase I and II enzyme and clearance activities, within 48–72 hr of culture (Godoy et al. 2013).
Given the shortfalls of animal testing and 2D monoculture, there is an urgent need for new, more predictive non-animal hepatotoxicity testing methods. Novel methods for the early assessment of drug toxicities could save money, resources, and working time. In addition, a reliable in vitro hepatotoxicity testing model would reduce the number of animal experiments within the framework of the 3R (Replacement, Reduction, and Refinement) animal welfare principles and, above all, save human lives.
Advanced 3D in vitro systems, such as liver organoids, are described as a very promising tool to better predict the efficacy and toxicity of preclinical drug candidates in humans, as they retain hepatocyte function long-term. Human induced pluripotent stem cells (iPSCs) could provide a suitable cell source with unlimited supply for the establishment of these advanced in vitro cell models (Robinton and Daley 2013). IPSCs have the capability to differentiate into nearly every cell type, organize into organ-specific architecture, self-renew, and self-organize, making them an attractive option for studying the reaction of human organs to xenobiotics in preclinical phases (Inoue et al. 2014).
In this work, liver organoids were differentiated from ChiPSC18 cells cultivated with the Cellartis DEF-CS 500 Culture System—a robust media for efficient expansion of human iPSCs in a feeder-free and defined environment. The differentiation was based on the publication of Wang et al. (2019) and others (Wang et al. 2018; Wu et al. 2019; Gieseck et al. 2014; Meier et al. 2017; Gerbal-Chaloin et al. 2014; Olgasi et al. 2020).