There is an increasing drive within the pharmaceutical and personal care communities to reduce, if not eliminate, the use of animals in the testing of new medicines and beauty treatments. This has been long-argued by animal welfare organisations and is driven not only by the high numbers (and cost) of animals used for toxicity and efficacy testing – companies use tens of thousands of animals for such tests each year – but also due to the low success rates of animal studies. Typically, nine out of ten drugs that enter human clinical trials fail because they are unsafe or ineffective, despite having demonstrated promising results in animals. In December 2022, a significant step was taken in this direction; there was a landmark change in legislature that states animal studies are no longer required for the approval of new medicines by the FDA. This was seen as a triumphant landmark decision. However, the question of what will replace the typical lab rats, rabbits and primates remains.
In this vain, researchers are looking towards computer algorithms to replace animal testing. Recent progress has been staggering, but some gaps remain in this technology. Researchers are also developing “organoids” as non-animal, in vitro tools to test new medicines. Organoids are 3-dimensional (3D)clusters of cells that form structures that mimic the architecture and function of a particular organ. They are typically grown from stem cells that subsequently differentiate into cell clusters of interest, for example brain, kidney, liver, cardiac and cancer, which are key organoids for drug efficacy testing and toxicity analysis. Embryonic stem cells or induced pluripotent stem cells are most commonly used stems cells for the growth of organoids and they are often embedded within 3D hydrogel scaffolds to help support their growth and promote differentiation. The most commonly used hydrogel within 3D cell culture and organoid growth is the solubilised basement membrane matrix secreted by Engelbreth-Hol-Swarm mouse sarcoma cells; commercially known as Matrigel. This hydrogel scaffold is of course animal derived, but it also comes with a handful of other drawbacks including its lack of batch to batch reproducibility and it contains a plethora of growth factors that can induce cell response that can lead to poor reproducibility and reliability in drug efficacy and toxicity experiments.
To maintain the animal-free direction of travel, synthetic hydrogels are being developed and adopted for both organoid manufacture and growth. One of the main advantages of synthetic hydrogels is that they can be easily engineered to mimic the physical and chemical properties of the extracellular matrix (ECM) of a particular organ. The ECM is a complex network of proteins and carbohydrates that surrounds and supports cells in the body, and it plays an important role in regulating cell behaviour. By mimicking the properties of the ECM, synthetic hydrogels can provide an environment that is similar to the natural tissue, which can promote cell clustering as well as the growth and differentiation of organoids. Moreover, they can be manufactured with no variability, allowing users to achieve reproducible and reliable results.
Synthetic hydrogels are made from a wide variety of materials, such as polyethylene glycol (PEG), recombinant hyaluronic acid and self-assembling peptides. Peptides are small, biologically active molecules that can be designed to self-assemble into 3D fibrillar structures that mimic the structure and function of the ECM, and they can be used to control the physical and chemical properties of the hydrogel. This allows for a high degree of control over the microenvironment, which is highly attractive for controlled organoid growth. In addition, peptide hydrogels can also be used to deliver growth factors and other molecules that are important for both the growth and differentiation of organoids, and can be designed to release such molecules over time to mimic the natural signalling of the tissue. Furthermore, peptide hydrogels have the ability to be functionalised with specific ligands and receptors to mimic the specific micro environment of the organ of interest. This can increase the specificity and accuracy of organoid growth and mimicry of the organ of interest, which in turn increases the efficiency and accuracy of the drug discovery process. Despite these advantages, some challenges remain including cost of production and the need to develop user protocols for each different biological assay. Research is continuing apace in these areas, and it is highly likely that 3D organoids will become an indispensable tool for biological research, drug discovery and drug screening within a few years, hence enabling a tangible reduction of animal testing.
