An Alternative to the Animal-Based DART Screens

Reproductive toxicology studies have historically been conducted in animals. Could an in vitro method using induced pluripotent stem cells alter the landscape? 

In the 1950s, a sedative widely prescribed in Europe and Australia as a treatment for morning sickness was withdrawn in 1961 after it was found to cause severe birth defects and brain damage in more than 10,000 babies. The drug was known as thalidomide, and it remains today one of the biggest examples of what can go wrong when drugs aren’t adequately tested in relevant model systems for reproductive toxic effects.

The disaster prompted many countries to introduce stricter rules for the testing and licensing of drugs and chemicals, including the requirement that developmental and reproductive toxicology (DART) studies be conducted in both rodent and non-rodent animal models.

Today, DART studies are among the most widely ordered toxicology studies in the GLP space; however, the crucial role that animals play may be changing due to the development of new approach methodologies (NAMs) that aim to replace, reduce, or refine the use of research animals. For instance, the Dutch company Toxys, which recently signed a co-marketing agreement with Charles River Laboratories, has developed an alternative assay called ReproTracker®. Using human-induced pluripotent cells to simulate the early fetal development process, an in vitro assay has been developed to rapidly and reliably identify developmental toxicity hazards of new chemicals, cosmetics, and drugs. 

WEBINAR SERIES
Advance Your DART Programs with New Approach Methodologies (NAMs)
Join us for a two-part webinar series that will explore how chemical companies can strategically integrate NAMs and in vitro methods into testing and development workflows. Learn More

Toxys has been developing the ReproTracker platform since 2016, expanding its validation database and refining the technology. Currently, various validation studies of the ReproTracker^® assay suggest that the platform is 85% effective in predicting developmental toxicity compared to animal studies or known human teratogens—substances that negatively affects a fetus during pregnancy. Since the EU banned cosmetics testing, ReproTracker has become a popular choice for cosmetics developers, and it has also proven effective for chemical and drug developers. DART studies for drug candidates could be the next big step for this alternative method.

“It is exciting to see that modern scientific advances, using human-relevant models, can now be applied to predict highly complex processes like developmental toxicity without the use of animals, said Toxys CEO Giel Hendriks. “The collaboration between Toxys and Charles River Laboratories will drive the further validation and applications of ReproTracker.”

Alan Hoberman, PhD, Senior Advisor at Charles River Laboratories and a globally recognized expert in toxicology, said the collaboration puts into place the possibility that a new approach methodology to replace, reduce, or refine the traditional animal DART study for hundreds of new drug candidates could one day be validated and shared with laboratories that routinely perform these preclinical studies. For now, Hoberman said Charles River will be supporting Toxys by conducting bioanalytical studies designed to help establish clear safety margins for using the assay. “For instance, we will be looking at how much of the drug is interacting with the cells in the Toxys assay and what concentration we are seeing effects that are relevant to humans. This is important because the Toxys assay is human-derived cells, and so we want to be able to compare it to the animal model,” said Hoberman.

The Toxys model is not the only attempt to find an alternative to DART studies done in animals. Some labs are experimenting with organoids, which are tissue-engineered cell-based in vitro models that recapitulate many aspects of in vivo tissue. Computationally derived in silico models are also being used to study reproductive toxicology. 

But even though there are questions about whether animal models optimally represent the human situation, cracking open the door to reliable in vitro models won’t be easy. DART studies model the coordinated interactions of multiple organs, systems, and physiological processes over an organism’s life cycle, which are difficult to replicate with existing in vitro methods. In a developing fetus, for example, the placenta acts as a complex organ that cannot currently be fully replicated in vitro. Accurately predicting how a drug is absorbed, distributed, metabolized, and excreted in an in vitro model is also a significant challenge, as is determining when a compound that is not toxic to a single cell type is converted into a toxic form in the liver. 

Alternative methods for assessing developmental and reproductive toxicity are also not necessarily faster than a DART study in an animal because of the time it takes to follow the development of the three types of cells in the early embryo (ectoderm, endoderm, and mesoderm) and further differentiate pluripotential stem cells into specific cell types (e.g., cardiomyocytes, hepatocytes, and neurons).

Still, Hoberman said the alternative models could be a game-changer for drug development, particularly in the Discovery space, as well as the chemical and cosmetics industries. For instance, he said the Toxys assay could provide significant value and assistance in the Discovery realm when drug candidates are being evaluated and de-risked. “Using this assay, you can generate useful information, early on, to screen classes of drugs being considered for long-term development,” says Hoberman. “At a minimum, these in vitro test methods for DART will add to our understanding of a new drug’s likelihood to interfere with the development of the embryo, increasing our confidence in bringing a drug to market that can be used in women of childbearing potential.

Check out these other stories describing alternative approaches that are helping us replace, reduce and refine the use of animal testing.