3D cell culture technology is rapidly gaining traction in drug discovery workflows, in particular for in vitro testing and simulation of disease progression and therapeutic response. Adding further momentum is the recent introduction of the UK roadmap to phase out animal testing with organon-a-chip and organoid methodologies set to become a critical aspect of many preclinical testing protocols.1 Building on the original 3Rs principle of Replacement, Reduction, and Refinement, efforts are shifting to introduce non-animal-based methods into research.
By bridging the gap between in vitro and in vivo models, 3D cell cultures can provide fundamental information on cellular functions, signalling pathways, and nuclear activities. Through accurately mimicking human tissue-like structures, 3D models provide a better representation of the in vivo environment, than traditional 2D cell cultures, and can therefore provide useful predictive insights into in vivo responses to drug treatment. However, 3D models are not yet widespread in preclinical testing, often hindered by limitations associated with their development and standardisation. Overcoming these challenges will require innovative solutions to reduce variability and increase reproducibility before 3D models can be adopted as standard.
3D Models to More Accurately Model In Vivo Conditions
3D models offer significant advantages over traditional 2D cell models, increasing cell-to-cell contacts and allowing the culture to grow and interact with the surrounding extracellular environment, more accurately reflecting living tissue (Figure 1.).
The very first example of a 3D cell model was in 1970, when Sutherland and colleagues developed a multicellular spheroid culture to create a functional phenotype of cancer cells, and then used the model to evaluate these cells’ response to radiotherapy. Spheroids are simple cellular aggregates that contain both internal and external layers of cells with varying exposure to the external environment, simulating the gradient of nutrients and oxygen seen in in vivo conditions.
The next phase of 3D cell culturing included organoids: more complex structures than spheroids, offering a simplified model system of organs that better reflect organ architecture and functionality.4 Further to this, researchers developed organ-on-a-chip, the most advanced model-type to date that mimics the activities, mechanisms, and physiological processes of organs and organ systems, and has the potential to replace animal models in drug testing studies (Figure 2.).
