Organ-on-a-chip: paving the way towards animal-free research?
29th June 2022 - Last modified 19th October 2023
20 years of Alto. 20 years of science. #8
By Peter Cussell PhD, Science Writer
As part of Alto Marketing’s 20 year celebrations, we’re looking back at some of the most important advances in science over this time in our blog series “20 years of Alto. 20 years of science.” Here we take a look at the long-standing link between the biomedical science and pharmaceutical industries and animal testing – could emerging technology pose a real alternative to in vivo research?
Animal testing is one of the most established methods in all of medical science, and has an inalienable relationship with the study of human health and disease. This is no surprise; animal models have been used to test every clinically approved pharmaceutical in use today, and has contributed to almost all major medical breakthroughs of the last century. But there is a big problem. Animal tests are very unreliable predictors of effects in humans.
As advances in microfluidic technology and increasing societal pressure drive a shift towards alternative animal-free methods. We ask the question, are these really good enough to replace in vivo (animal) models?
The animal testing conundrum
Pharmaceutical regulatory bodies such as the European Medicine Agency mandate the use of experimental animals for many stages of preclinical testing, including absorption, distribution, metabolism, efficacy and safety. Despite the wide implementation of in vivo testing though, 8 out of 9 (89%) of drug candidates that enter human trials fail [1]. This is usually due to poor safety or efficacy; things that should have been picked up at the preclinical stage, which is in place to identify such faults. This poor success rate is a significant problem for an industry that wastes time, money and effort, not to mention the lives of many animal subjects, in the development of clinical failures, while many human diseases remain bereft of effective treatment options.
The main limitation of animal testing is that it’s very hard to extract high-quality data from a living being: Since most physiological functions rely upon a combination of precise interactions at the level of tissues, cells, proteins and genes, it is difficult to reveal the underlying mechanism behind a response to a toxin or drug by studying a whole animal subject. Because of this, most animal testing in broad use today is fairly arbitrary, relying on dosing subjects before they are sacrificed and analysed post-mortem in many cases.
On top of the various practical limitations and poor data yield that can be extracted from animals, there is also a growing and global societal pressure to move away from animal testing practises. This is beginning to translate into legislation too: the US Environmental Protection Agency published a directive in September 2019 in which is stated that funding for animal testing will be reduced by 30% in 2025 and will be abolished completely by 2035 [2].
Clearly then, there is a growing need for improved in vitro systems to reduce and replace experimental animals. But what’s the alternative? Scientists have strived for many years to create accurate in vitro models as a replacement for animal-based pharmaceutical testing, but capturing the complexity of human physiology using cellular models has proved to be a substantial challenge. Traditional (2D) cell culture models have often been used alongside animal research but because they lack metabolic features of living systems, measurements like toxicity can be easily over/underestimated. While useful for some of the preliminary research and development stages, a much higher level of complexity is required to present a serious alternative to animal models.
Thankfully, advances in cell culture and microfluidics over the past two decades have given rise to a powerful new tool that could solve the conundrum…
The next generation of in vitro modelling
Listed as one of the top 10 emerging technologies by the World Economic Forum [3], Organ-on-a-chip (OOAC) technology seeks to mimic the precise physiological environment of human systems, organs and tissues through a combination of microfluidic channels and 3D cultured cells organised into a tightly-controlled matrix. This ground-breaking technology offers scientists an insight into the precise underlying mechanisms behind drug responses while also enabling enhanced, more accurate disease modelling.
So, what exactly is OOAC? In short, an OOAC comprises of a credit-card sized microchip with in-built chambers for cell culturing, and microfluidic channels that supply the cells with nutrients. Using these chips, an accurate, living, 3D cellular system can be constructed that closely represents the precise physiological environment of the body, providing a window to activities happening at a cellular and molecular scale. These clever microchips contain sensors that feed back a wealth of information on things like toxicity and metabolism in real time.
The true power of OOAC technology lies in its adaptability to specified physiological environments – OOAC has been adapted for a host of different tissues including skin, blood vessels, lung, heart, kidney, liver, intestine, and even the gut microbiome![4] Each of these includes a network of tissue-specific cells, to which environmental parameters such as concentration gradients and pH can be finely manipulated by the researcher. Since the cultured cells are constantly fed with nutrients, they can survive for much longer than traditional cell cultures, allowing experiments to be run over a much larger time frame.
Another exciting feature of OOAC is the ability to create larger models by combining multiple OOAC systems. For example, you can combine multiple elements of a single organ, such as alveolar and bronchial regions in the lung, or marry different organ systems together to create a multiorgan system such as the digestion pathway [5].
Overall, OOAC represents a revolutionary platform that may be able to optimise drug kinetics and dynamics at the preclinical stage with far greater accuracy than animal models.
Future challenges for OOAC
While many in the field regard OOAC as the next generation of in vitro research techniques, there have been some criticisms, and there is still work to do before it can reach wide adoption and large-scale animal replacement.
Immune cells
One of the main criticisms of OOAC is the lack of immune components within the system. If a drug works by stimulating an immunological response, for example, it would be impossible to research without the relevant immune cells being present in the model. However, more recently, researchers have been able to successfully integrate immune cells into some OOAC systems. For example, circulating monocytes have been used in some OOAC systems to evaluate tissue-specific responses to pharmaceuticals, demonstrating the feasibility of integrating an immune component into OOAC [6]. While this is a promising development, it must be stressed that current attempts to add immune cells into OOAC systems are very much in their infancy and will require significant development before use at large scale.
Throughput levels
Another challenge to overcome in the future is throughput. The current barrier to this lies in the amount of data read outs – one microchannel on a single chip can yield overwhelming masses of data. Improved IT power could enable the monitoring of multiple channels in parallel as well as feeding back more functional information, be it cellular, biochemical or genetic, in a single run. The development of improved microsensors will also be important in achieving this and will improve the resolution and quality of data gathered. As augmented data processing capacity and microsensors become available, the multi-OOAC systems will also become more viable [7].
Shifting opinion
While improving technological limitations could expand the power of OOAC systems, the main obstacle to its mass adoption lies within the deeply entrenched nature of animal testing procedures that have been in place for so long. The pharmaceutical industry has embedded processes and infrastructure for industrial scale animal testing, and implementing new technology, such as OOAC, is often seen as a needless disruption. In the face of OOAC offering a more relevant, robust and validated model for much of the preclinical testing phase, and with the emergence of viable commercial OOAC suppliers, it is frustrating to see profit-driven research organisations remaining tentative to adopt such technologies.
To combat this hesitance, there is a need for more education and legislation to encourage decision makers at large pharmaceutical companies towards adopting advanced in vitro technology like OOAC into their testing set-up. There is a valid business case for adopting technologies like OOAC too, with the potential to save businesses significant amounts of money: OOAC will enable more drug candidate failures to be picked up at the preclinical phase and hopefully bring down the vast number of leads that become clinical failures at the point of phase one human trials.
Conclusion
The power of OOAC is clear to see. This amazing technology offers a more relevant cross section of human physiology and pathophysiology, generating a far greater depth of information than any animal model could. But will this really replace animal testing in the near future? Whilst I can envisage next generation in vitro models like OOAC becoming increasingly implemented for much of preclinical testing, I believe that experimental animals will still be in use on some level for years to come. In any case, OOAC technology has the ability to replace much of the preclinical animal testing phases, and could save research organisations significant sums of money if adopted. To implement real change, policy makers and pharmaceutical executives around the globe need to be made more aware of this technology – and the value it could bring.
References
- van Berlo, D. et al. The potential of multi-organ-on-chip models for assessment of drug disposition as alternative to animal testing. Current Opinion in Toxicology. 27, 8-17 (2021).
- U.S. EPA to eliminate all mammal testing by 2035. Science. (2019). https://www.science.org/content/article/us-epa-eliminate-all-mammal-testing-2035
- Top Ten Emerging Technologies. World Economic Forum. (2016). https://www.weforum.org/agenda/2016/06/top-10-emerging-technologies-2016/
- Mittal, R. et al. Organ-on-chip models: Implications in drug discovery and clinical applications. Journal of cellular physiology. 234 8 8352–8380 (2019).
- Boeri, L. et al. Advanced Organ-on-a-Chip Devices to Investigate Liver Multi-Organ Communication: Focus on Gut, Microbiota and Brain. Bioengineering 6 4 91 (2019).
- Ma, C. et al. Organ-on-a-Chip: A New Paradigm for Drug Development. Trends in pharmacological sciences. 42 2 119–133. (2021)
- Horejs, C. Organ chips, organoids and the animal testing conundrum. Nature Reviews Materials. 6 372–373. (2021).
