Can Tox21 robot take the gamble on animals out of toxicity testing?
Alternatives to Animal Testing, Experimentation and Dissection - An Animal Rights Article from


Animals 24-7
April 2016

Testing device uses cells instead of animals

WASHINGTON D.C.––Can a robot detect substance toxicity toward humans faster and more accurately than a traditional test on rats, mice, fish, or other animals?

tox21 robot
The Tox21 robot. (EPA photo)

rabbit in lab
Lab rabbit. (PETA photo)

The developers of the Tox21 robot, whose name is short for “Toxicology in the 21st Century,” are betting that the robot can outperform traditional tests––and betting, as well, that the robot can take the gamble out of toxicity testing that results from the differences in how humans and animal models digest and absorb chemical substances.

Developed by the toxicology establishment

For additional twist, the Tox21 robot developers are not animal advocates or other outsiders from the regulatory process, trying to overturn the biomedical research and safety testing establishment.

Rather, the Tox21 robot has emerged from the establishment, from an eight-year collaboration among the four U.S. government agencies most involved in toxicology research: the Environmental Protection Agency, the National Toxicology Program, the National Institute of Environmental Health Sciences, and the Food & Drug Administration.

10,000 chemicals

Explains the Tox21 web site, “Using a high-throughput robotic screening system housed at the National Center for Advancing Translational Sciences, researchers are testing a collection of 10,000 environmental chemicals and approved drugs, called the Tox21 10K library, for their potential to disrupt biological pathways that may result in toxicity. The team prioritizes promising compounds identified from primary screening for further in-depth investigation.”

lab fish
Lab fish. (McMurry University photo)

Translation: there are only so many ways that chemicals can enter the human body and interact with it in ways that can cause harm. Tox21 looks at the points of entry for hints of vulnerability to each chemical being tested. Only if there are signs of vulnerability is the chemical flagged for more comprehensive testing, which may involve animal testing, or may not, depending on what sort of symptoms might be indicated.

mitochondrial toxicants
Potential mitochondrial toxicants, as identified by a Tox21 screening process. (NIH photo)

Cell-based assays

Elaborated Anna Azvolinsky in the January 26, 2016 edition of The Scientist, describing data published the same day in the peer-reviewed journal Nature Communications, “To reduce harm to animals and decrease the cost and time it takes to generate animal-safety data, Ruili Huang, an informatics group leader at NCATS, and her colleagues screened 10,000 chemicals through 30 different automated cell-based assays,” meaning a type of test that determines the biologically active characteristics of each chemical.

All of the chemicals were of special interest to the EPA, National Toxicology Program, or the National Institutes of Health.

Endocrine signaling

“Each assay,” Azvolinsky wrote, “assesses the ability of the chemicals to interact with either a nuclear receptor pathway or a cellular stress response pathway, including mitochondrial signaling pathways. The nuclear receptor assays include testing environmental chemicals for their abilities to disrupt endocrine signaling, which can result in harmful effects on development, reproduction, and neurological functions.”

The Nature Communications study, Azvolinsky said, “demonstrates an ability to test environmental chemicals found in drugs, food and food packaging, consumer products, and chemicals produced during manufacturing and industrial processes, using cell-based assays,” instead of live animals.

“Very efficient”

“The system is very efficient,” Huang told Azvolinsky. “We can test all the chemicals at 15 different concentrations each and in three independent experiment runs in one week. With animal testing, this would take years.”

But the Tox21 robot is not quite ready to take over toxicity testing entirely.

“We can partly predict animal and human toxicity data,” Huang said, “but the information is not perfect. We still need to add chemical structure data to achieve a more accurate prediction,” explained Huang.

Still developmental work to do

Added British government toxicologist Fiona Sewell, “The [Tox21] data has so far been more predictive of human rather than animal toxicity,” which remains a concern of regulators.

Even in application to humans, Sewell cautioned, “This [study] is a positive first step, but there is still a long way to go before we reach the ultimate goal of being able to assess the safety of chemicals to humans without using animals.”

During the next several years the Tox21 10k library is to be expanded to cover data on about 80,000 chemicals, and to include a variety of additional assays.

Shift from in vivo to in vitro

The Tox21 program began in 2008, recounted BioCentury staff writer Mark Zipkin, “not only to reduce unnecessary use of animals, but to find better and faster ways of predicting which chemicals and drug development candidates might be toxic, because animal results translate so poorly to humans.

“We propose a shift from primarily in vivo animal studies to in vitro assays, in vivo assays with lower organisms, and computational modeling for toxicity assessments,” jointly explained then-National Humane Genome Research Institute director Francis S. Collins, EPA research and development director George M. Gray, and National Toxicology Program associate director John R. Bucher.

Following P&G path

Procter & Gamble, the largest U.S. consumer chemical maker, had already pursued similar approaches for nearly a quarter century, in fulfilling a 1984 agreement P&G had reached with the late Henry Spira. founder of Animal Rights International. Since then P&G has spent more than $350 million to develop and win regulatory approval for more than 50 alternatives to animal tests.

The Tox21 robot evolved from a high throughput test that National Institutes of Health Chemical Genomics Center director Christopher Austin early in the program described to Elizabeth Weise of USA Today as being “done in a 3-by-5-inch glass tray with 1,536 tiny wells, each a fraction of a millimeter across. A few hundred human cells grown in a test tube go into each well,” Weise wrote. “The testing machine drips a different chemical into each well. After some time has passed, the machine shines a laser through each well to see how many cells remain. A computer analyzes the toxicity of each compound based on how the cells react.”

USGS Photo

Only 2,500 substances tested in 30 years

National Institutes of Health director Elias Zernouni indicated to Weise that this relatively quick and simple test might replace animal-based methods which as of 2008 had rigorously tested only about 2,500 potentially toxic compounds in 30 years.

National Institutes of Environmental Health Sciences head Samuel Wilson told Reuters that automated laboratories could, at the time, already use non-animal methods to test 100,000 compounds at up to 15 different concentrations in only two days. 

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