A critical prerequisite for any drug discovery program is the availability of robust ways to study the disease in question and evaluate how experimental treatments impact disease phenotypes. Disease models ranging from patient-derived cell lines to whole animal models that recapitulate disease phenotypes are indispensable for target identification and validation, proof-of-concept (i.e., for efficacy) experiments and pre-clinical toxicology studies.
The biology of any disease is complex and developing a ‘good’ disease model requires a comprehensive understanding of the underlying disease mechanisms and pathogenesis, both of which are gained by gathering Real-World Evidence and modeling the disease. Given this catch 22 situation, i.e., how can you make a good model of a disease when it is nearly impossible to fully understand a disease? it’s not surprising that one of the major roadblocks in the development of novel therapies is the lack of robust and reliable animal models.
While no hard statistics are available on the proportion of clinical trials that fail as a result of inadequate disease modeling, it is worth noting that 90% of clinical drug development fails, and an analysis of trials carried out from 2010 to 2017 concluded that lack of clinical efficacy was the culprit in 40%–50% of cases (1 and references within). It should be noted that failures due to clinical safety are usually detected very early during development or during Phase I or II clinical trials, resulting in a complete halt to the study, and there are many examples of toxicity-related clinical failures. This means that drugs that appeared to be efficacious and safe in preclinical (including model) studies didn’t exhibit the same efficacy and safety profiles in actual human patients.
To address the shortcomings of in vitro cell-based assays, such as those that rely on primary or immortalized rodent or animal cells, two popular solutions have emerged. These are the organ-on-a-chip devices and 3D organoids. This article will introduce both of these solutions and discusses the applications, benefits and drawbacks, and experimental complications of each. We hope that this overview will assist scientists in experimental planning and design.
So, what are organ-on-a-chip devices and 3D organoids?
Organ-on-a-chip
Organ-on-a-chip devices are microfluidic systems engineered to recreate organ-specific functions in vitro. About the size of a USB stick, these platforms use tiny channels and chambers to create controlled environments to mimic the in vivo physiological conditions of the organ of interest. Commercially-available devices usually contain 2-4 different cell types that aim to recapitulate the essential cellular, structural, and environmental features necessary for normal organ function.
There are various approaches to developing an organ-on-a-chip. One common method involves creating multiple microfluidic channels that can be independently controlled, allowing researchers to culture different cell types while maintaining optimal conditions for each, though multi-organ systems are very challenging. These devices can incorporate mechanisms to apply mechanical forces, chemical gradients, and electrical signals, with the goal of recreating the environment that cells experience in living organs. Manufacturers typically use immortalized cell lines and primary cells to check and validate their devices during development, ensuring consistent performance across different experimental conditions.
One major advantage of using organ-on-a-chip devices is their commercial availability and standardization. They are purchased in a ready-to-go format, which may be attractive for laboratories without budget constraints that don’t want to spend time developing methods for organoid culture. The microfluidics allow flow rate adjustments and enable researchers to control conditions across multiple channels simultaneously. This level of control makes it possible to recreate different physiological processes that are relevant in drug discovery and disease modeling (2).
3D organoids
3D organoids are sophisticated cell-derived models that self-assemble into 3D structures designed to recapitulate the structural and functional aspects of human organs and tissues. These models typically contain 4-6 or even more different cell types in one 3D spheroid shaped organoid, creating heterogeneities that are considered to more closely mimic in vivo environments than 2D monolayer models.
Organoids may be generated through several distinct approaches. One popular method uses induced pluripotent stem cells (iPSCs) that differentiate into multicellular structures. This approach offers flexibility in donor selection and enables relatively long-term experiments due to the long-lived nature of iPSCs. In contrast, tumor organoids are derived directly from patient tissue samples, preserving the genetic and phenotypic characteristics of the original tumor. A newer approach involves “assembloids” or “organoids-by-assembly,” where multiple iPSC-derived cell types are pre-differentiated separately and then assembled together, providing greater control over cellular composition (and assisting with complex cell culture media demands and requirements).
Morphologically, organoids can adopt various three-dimensional shapes, including spherical balls (aka “spheroids”), donuts, tubular structures (as seen in pancreatic organoids), or branching patterns (this is characteristic of intestinal organoids and breast tumor organoids). These diverse morphologies reflect the remarkable ability of organoids to self-organize according to intrinsic developmental programs.
Figure: (left) 3D spheroid organoids (size range: 50µm – 150µm in diameter). (center) a 3D spheroid shaped like a “donut” and stained with 5(6)-Carboxyfluorescein (green). (right) an example of a microfluidic chip designed with multiple channels.
Now that we have provided a brief overview of what 3D organoids and organ-on-a-chip devices are, let’s weigh them up! How do the two compare in experimental flexibility, physiological relevance in relation to drug discovery, and economic considerations and scalability?
Experimental flexibility
Cellular composition control: Organoids enable customizable cellular composition through the “organoids-by-assembly” approach, which allows researchers to precisely control which cell types are included and their ratios, including ratiometric adjustments of the culture media (e.g., 3:1 neuronal vs. glial cells). In contrast, organ-on-a-chip devices provide standardized cellular compositions that ensure reproducibility across experiments but with the drawback of limited experimental flexibility.
Donor selection: Organoids offer flexibility in working with multiple genetic backgrounds and patient-derived samples, which allows for comprehensive population studies. Organ-on-a-chip devices provide selectively validated, consistent (unchanging) donor profiles that reduce experimental variability while limiting genetic diversity across populations.
Culture duration: Organoids can be cultured for 4-6 weeks or even longer, enabling chronic exposure studies and observation of time-dependent effects such as disease progression and long-term toxicity assessment. On the other hand, organ-on-a-chip devices are typically viable for shorter durations; this is often less than 4 weeks and may be as short as 7-10 days in some cases. These shorter timeframes may be suitable for acute studies but preclude studies of chronic effects.
Analytical approaches: Because organoids are custom-made to suit the experimental goal and application, they inherently support multiple assay options and flexible analytical methods across various endpoints. In contrast, organ-on-a-chip devices offer pre-defined readouts that provide real-time monitoring capabilities albeit within potentially limited parameters.
Case study example: The experimental flexibility of organoids is exemplified in recent studies to model non-alcoholic steatohepatitis (NASH), a severe and prevalent form of non-alcoholic fatty liver disease with limited treatment options and for which better disease models are urgently required. For example, researchers in the Netherlands created genetically-diverse liver organoid models (incorporating multiple cell types at specific ratios) and conducted extended culture studies to observe disease progression over time. That study used organoids in diverse analytical approaches including lipid staining and CRISPR-based screening platforms (3).
Physiological relevance in relation to drug discovery
Drug development applications: Organoids have utility throughout the drug development process from initial target finding and validation to late-stage preclinical development, while organ-on-a-chip devices are off-the-shelf products that, depending on the disease and drug design, may be suitable for parts of the development process but are limited by their shorter culture duration.
Human disease modeling: Organoids enable “non-clinical trials” using genetically-confirmed, multi-donor models that can assess genetic variation effects on drug responses and disease progression. Organ-on-a-chip systems offer the advantage of precisely controlled environments that replicate certain organ functions and mechanical forces, but operate within defined parameters that might limit experimental flexibility.
Physiological maturation: As mentioned above, extended organoid culture allows cellular and tissue maturation that more closely resembles in vivo characteristics; this is very valuable for chronic disease studies and age-related research. Organ-on-a-chip devices maintain cells in defined physiological states with controlled mechanical and chemical stimuli but may not capture long-term maturation processes.
Experimental consistency: Because organoids can be used throughout the drug development process, they can reduce the need for model transitions and maintain experimental continuity. Organ-on-a-chip systems provide highly standardized conditions that ensure reproducible results between laboratories, but different products might be necessary (if available) for different development stages.
Economic considerations and scalability
Upfront investment: Organoids require significantly lower per-experiment costs and offer scalable implementation, though they may require initial method development and assay design support. Organ-on-a-chip devices likely involve higher upfront costs but come with validated workflows and support from field application engineers.
Throughput: Organoids are commonly cultured in 96-well formats that support moderate high-throughput experiments, such as compound screening, whereas organ-on-a-chip systems typically operate in single/8/12/24-24 well formats that allow for detailed monitoring but limit capacity to scale-up an assay.
Scalability: Organoids can be readily scaled for large compound libraries, multi-donor studies, and comprehensive screening programs. In contrast, organ-on-a-chip solutions may be more suitable for focused studies requiring precise environmental control.
Development stage utility: Organoids offer a bespoke, versatile solution from early discovery through to late-stage preclinical studies. This may reduce costs associated with shifting to new technologies while maintaining experimental consistency. Organ-on-a-chip systems offer specialized capabilities that may complement existing workflows in specific applications, though comprehensive programs and evaluations typically require multiple different systems.
Learn more and get in touch!
While organoids and organ-on-a-chip devices are both major advances over previous models, we believe that organoids offer superior versatility for drug discovery. Their scalability, extended culture times and ability to span early discovery through preclinical development make them the practical choice for modern pharmaceutical research.
For assay set-up and guidance on implementing organoids in your research as well as established organoid culture protocols, please contact Tempo Support here.
Related articles from Tempo Bioscience
iPSC Culture: What Every Researcher Needs to Know
Culturing and Characterising Organoids – What Do We Need to Know?
Human Liver Organoids as a New Model for Non-Alcoholic Fatty Liver Disease
References:
- Sun D, Gao W, Hu H, Zhou S. Why 90% of clinical drug development fails and how to improve it? Acta Pharm Sin B. 2022 Jul;12(7):3049-3062.
- Park SE, Georgescu A, Huh D. Organoids-on-a-chip. Science. 2019 Jul;364(6444):960-965.
- Hendriks D, Brouwers JF, Hamer K, et al. https://www.nature.com/articles/s41587-023-01680-4. Nat Biotechnol. 2023 Feb 23. doi: 10.1038/s41587-023-01680-4. Epub ahead of print. PMID: 36823355.
Karen O’Hanlon Cohrt is an independent Science Writer with a PhD in biotechnology from Maynooth University, Ireland (2011). After her PhD, Karen relocated to Denmark where she held postdoctoral positions in mycology and later in human cell cycle regulation, before moving to the world of drug discovery. Karen has been a full-time science writer since 2017, and has since then held numerous contract roles in science communication and editing spanning diverse topics including diagnostics, molecular biology, and gene therapy. Her broad research background provides the technical know-how to support scientists in diverse areas, and this in combination with her passion for learning helps her to keep abreast of exciting research developments as they unfold. Karen is currently based in Ireland, and you can follow her on Linkedin here.
