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    A white mouse is sitting on a cultural medium. Laboratory test tubes in the background.

    Replace, Reduce, Refine. Animal testing in drug development.

    In order to introduce a new medicine to the market, the applicant must demonstrate that the proposed product is safe and effective. This is done by presenting the set of quality, non-clinical and clinical data obtained during the developmental studies, which are then evaluated by regulatory authorities. The volume of the data required, impacting the type and extent of studies, depends on the medicine, which is going to be registered. For small-molecule drugs containing active substances, which are already present in other registered medicinal products, the amount of required data is rather limited and usually encompasses quality and clinical (bioequivalence) study results. In general, studies on animals are not required. On the other side of the scale, are so called “original” medicinal products, for which there is a need to present a vast panel of safety and efficacy data, including toxicity studies performed with the use of animals (for more information on different application types, please read our article about registration of medicinal products – how to choose the right type of application). The scope of non-clinical animal studies required for other types of medicinal products varies and depends on their type, composition, planned application site, and usually lies somewhere in between the two extremities mentioned above. It seems, therefore, that according to the current regulatory requirements some animal testing cannot be avoided when one wants to make sure that the medicine, which will be used in humans, is fully safe. So what can be done to avoid unnecessary harm?

    The 3 Rs principle

    Scientists, professionals in biotechnology and pharmaceutical industry and regulators have been thinking for many years how to limit the sacrifice of animals to the absolute minimum. The result of this cooperation is the introduction of the so called 3 Rs principle.

    The concept was first proposed by the zoologist and physiologist W. M. S. Russell and the microbiologist R. L. Burch in 1959, in order to promote more ethical use of animals in drug product testing and scientific research. The 3Rs are:

    • Replacement: selecting methods which avoid or replace the use of animals in research. Replacement strategies may include the use of tissue cultures or slices, perfused organs, cellular or subcellular fractions.
    • Reduction: using methods that enable researchers to obtain comparable levels of information from fewer animals, or to obtain more information from the same number of animals. The researchers are encouraged to carefully plan the studies to e.g., combine tests, which can be done in parallel, to select appropriate study models to reduce variability (and thus the number of animals per experimental group), to perform thorough literature searches in order to avoid unnecessary replication of studies already performed.
    • Refinement: using methods that alleviate or minimize potential pain, suffering or distress, and enhance animal welfare of the animals used. It applies not only to the experimental procedures, but also to breeding, transportation, housing and husbandry.

    Although the 3Rs concept is not directly linked to the principles of Good Laboratory Practice (GLP), it is worth evoking also the latter in this context. The GLP’s four pillars are: reliability, repeatability, verifiability, and recognition by the scientific society all over the world. Consequently, by applying the GLP rules to the conducted non-clinical studies, the laboratories ensure that the data obtained are reliable and recognized by scientific community and regulatory bodies. There is, therefore, no need to repeat such experiments, thus reducing the need to sacrifice more animals.

    The 3Rs in the regulatory framework

    A mouse is sitting on a human hand wearing a blue laboratory glove. Animal testing in drug development.

    The obligation to protect animals used for scientific purposes is a legal obligation in the European Union (EU), introduced by Directive 2010/63/EU of the European Parliament and of the Council of 22 September 2010. The notion of 3Rs has also been introduced in the regulatory guidelines of the European Medicines Agency (EMA) – first in 1997, when a position paper was adopted on replacing animal studies by in vitro models. This was followed by the works of the Committee for Medicinal Products for Human Use (CHMP) on the “Guideline on the principles of regulatory acceptance of 3Rs (replacement, reduction, refinement) testing approaches”, which was adopted in 2016. The guideline underlines the importance of 3Rs implementation in the drug development, advices on when and where animal studies can be replaced by other methods, and how to best demonstrate the validity of these alternative approaches. The EMA cooperates in this field with large EU initiatives such as the European Centre for the Validation of Alternative Methods (ECVAM) and the European Partnership for Alternative Approaches to Animal Testing (EPAA).

    Another activity taken by the European regulator is the periodic review of its other guidelines, with the purpose to implement the 3Rs principle. As an example, it is worth mentioning that when the first guidelines for the biosimilas were issued, they described the need to demonstrate comparability of the biosimilar medicinal product to its reference biological product using animal models of the target diseases, and also to run the toxicology testing. However, as the scientific knowledge and the experience of the EMA with the biosimilars increased, above mentioned requirements have been one by one withdrawn from the guidelines. They were considered not compliant with the 3Rs principle, as more precise information could have been derived from other studies, and animal testing was proven not necessary. Also in case of e.g., cytotoxic products to be used in cancer patients, the scope of toxicological animal studies described in the guidelines is limited, as the compounds are otherwise known to be toxic. Similar approach was recently taken by the US Food and Drug Administration (FDA). In the FDA Modernization Act 2.0, which was passed by the Senate in September 2022, the requirement for animal studies was removed for biological medicinal products, which are biosimilar or interchangeable with another biological product.

    Full ban on animal studies for cosmetics. Is it doable for pharma?

    In 2013 the European Union fully banned animal testing in the cosmetic industry, as per the Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009 on cosmetic products. It is now forbidden to market or sell in the EU the cosmetics, where the finished product or any of their ingredients have been tested on animals. The work on this legislation started in 1993, and it was a long and complicated process. The ban has already been introduced in an amendment to the previous legislation (Council Directive 76/768/EEC of 27 July 1976 on the approximation of the laws of the Member States relating to cosmetic products), but was not fully applicable. The will to stop animal testing was there, but what made it impossible for many years to act on, was the lack of appropriate methodology, which would replace the in vivo studies. All in all, the regulators had to make sure that the products introduced to the market were safe for humans.

    The developers of new medicines have to assure the same. Can it be done without animal testing? For many medicines, sure, it can be done, and it has already been done (as mentioned above). But what if we stopped animal testing completely? Can’t we assess the toxicity of new drugs from computer modeling? To identify possible adverse effects in humans from the in vitro studies? To some extent we can, and we do. But we must also keep in mind the magnitude of the risk we would be taking with such complete renouncement. History has already taught us that this risk is immense!
    Historically speaking, the regulation of drug product manufacturing and introduction to the market is fairly recent and dates back to the XX century. Before that, basically anyone could produce and sell a “medicine”. This lack of regulations led to some tragic outcomes. In 1937, a preparation called “Elixir Sulfanilamide” was developed, which contained diethylene glycol (DEG) as one of its excipients. Nowadays we know that DEG is a toxic substance, but at the time it was not known. As a result, more than 100 people were poisoned and died. Another tragic example is a well-known story of thalidomide – a popular drug, which was used by pregnant women all over the world, as it reduced morning sickness. Nobody knew at the time that it was also teratogenic. As a consequence, more than 10 thousand children were born with more or less severe malformations of the limbs, and many of them died shortly after birth [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3123518/]. The number of pregnancies lost due to thalidomide is not possible to be fully assessed. This tragedy could have been avoided had the studies on potential toxicity of thalidomide on reproduction and foetal development been performed.

    The expected future of animal testing

    We probably all agree that the use of animal testing should be limited wherever possible. This is why it is important to continue initiatives such as ECVAM and EPAA and work on reliable, properly validated in vitro models. One interesting option is the 3D cell cultures. These models, also called organoids, are derived from 3 kinds of human or animal stem cells – embryonic pluripotent stem cells, adult somatic stem cells, and induced pluripotent stem cells. As a result, their ability to behave like natural body organs is way beyond standard cell cultures, or even tissue cultures. Grown in vitro, organoids mimic the structure and function of human or animal organs e.g., brain, liver, lung, kidney, and intestine, and are already used in research on e.g., virus infections (COVID-19, MERS-CoV, Zika), cystic fibrosis, Alzheimer’s or Parkinson’s disease, and cancer (called tumoroids, as they are derived from cells biopsied from patients’ tumours). Their potential is also used in toxicology.

    So the future seems optimistic. With the engagement of scientific community and biotech and pharma industries, it may one day be possible to fully stop animal testing. For the time being, it is important to always keep in mind and implement the 3Rs rule, and perhaps add one more “R” to it – respect – for the sacrifice the animals make, so we, humans, can live a healthier life.

    This article was written out of respect and gratitude to the animals, which sacrificed their lives in several projects in which the author was involved.