Opinion: The Debate Over Animal Toxicology Studies

In the United States, the use of animals to test human pharmaceuticals dates to 1937, when a liquid formulation of a sulfa antibiotic dissolved in diethylene glycol resulted in the deaths of 107 adults and children. The incident led to the 1938 Federal Food, Drug, and Cosmetic Act, mandating animal toxicity testing. In 1946, language was incorporated into what became the Nuremberg Code and later the Helsinki Declaration requiring human experiments to be “designed and based on the results of animal experimentation [author’s italics] and a knowledge of the natural history of the disease.”

The previous statement was written by Andrew Ivy, a strong proponent of animal research. Still, it was not clear such a requirement would improve the safety or efficacy of human drug development. Today, the FDA generally requires preclinical testing of any new drug or biological therapeutic in animals “for pharmacologic activity and acute toxicity” before human clinical trials begin. However, recently, the FDA indicated it was open to considering alternative models of testing, or new approach methodologies (NAMs):

A weight-of-evidence approach is practiced for biotechnology-derived products when a carcinogenicity assessment is warranted. Genotoxicity [damage to DNA or chromosomes] testing is generally inappropriate for biological products and is not part of the assessment. When sufficient information is available, the need to conduct additional nonclinical studies, regardless of whether the biologic is active and testable in a rodent bioassay, is not warranted. If the assessment does not suggest carcinogenic potential, a rodent bioassay is considered unlikely to add value, and no additional nonclinical testing of biologic products is recommended. Prior knowledge of target-based risks figures prominently in developing a strategy to assess the carcinogenic risk of each new biologic because the nonspecific activity of such molecules is generally considered to be low.

The FDA’s Center for Drug Evaluation and Research also encourages exploring the use of NAMs to improve regulatory efficiency and potentially expedite drug development. All of these discussions apply to new drugs or biological ones. No animal studies are required for generic chemical drugs because their chemical structures are identical to the reference products’ structures. Biosimilars have presented a dilemma; their molecular structure may be highly similar but not identical to the reference products’ makeup, which actually varies from batch to batch. The Biologics Price Competition and Innovation Act (BPCIA) states that the data required for FDA approval shall include animal studies (including an assess­ment of toxicity). This requirement of the BPCIA has caused significant confusion and resulted in delays in the approval of biosimilars.

In most cases a correlation between animal toxicology and safe use of biological products in humans cannot be made because of the differences in the receptors between humans and animals. This is well established.

Biosimilar developers, with a mindset of new drug development, took the toxicology studies to a different level, submitting studies that were refused by the FDA. The worst examples were (number rejected/number submitted): Inflectra (infliximab; 2/4), Cyltezo (adalimumab; 2/6), Mvasi (bevacizumab; 2/7), Retacrit (epoetin alfa; 13/15), and Ziextenzo (pegfilgrastim; 8/13). For example, for Mvasi (bevacizumab), mice and rat studies were reported to demonstrate that the high mannose variants in the biosimilar candidate were not meaningful—an irrelevant exercise because rodents do not have receptors to bind monoclonal antibodies.

The same is true about testing trastuzumab in mice (Trazimera and Herzuma), where trastuzumab does not identify the neu receptor. For the etanercept biosimilars Eticovo and Erelzi, studies were conducted in mice and rats that were irrelevant for the same reason. Fifteen animal toxicology studies were reported for an epoetin biosimilar (Retacrit) to justify higher antidrug antibodies than the reference product produced—an irrational approach. It was later determined that the differences were due to formulation and route of administration.

Testing biosimilars in species that do not present receptors is irrelevant, as the European Medicines Agency and the FDA have repeatedly pointed out. Genotoxicity testing is disallowed because it is irrelevant. However, the difference between how a chemical species interacts with the body vs biological molecules remains included in the approval guidelines. A reference biological product that has undergone extensive multispecies testing has established safety in humans; when it comes to biosimilars, analytical similarity alone is enough to demonstrate that there is no risk of unexpected response.

The most misleading advice comes from the WHO; it states that toxicology studies in monkeys should be avoided, animal toxicology studies should be conducted at several different doses, and immunogenicity testing in animals should be evaluated—all of which are irrational suggestions; unfortunately, many countries follow the WHO guidance, such as India, leading to inappropriate approval of biosimilars. The following points are important to keep in mind:

• Unlike chemical drugs, biological drugs do not elicit a pharmacologic response across species and there is no extrapolation to human safety.
• The new FDA advice discourages animal testing of new biologicals.
• Animal immunogenicity testing is irrelevant; the human immune response has a different infrastructure than for any type of animal species.
• No animal testing can be used to justify any differences in analytical similarity; for example, an unidentified and unreported impurity in a biosimilar candidate vs a reference product cannot be proven irrelevant by any animal testing.
• Multiple species testing, as reported, is of little value for the same arguments.
• Differences in antidrug antibodies in humans can never be resolved with any testing protocol in animals.

In summary, a detailed review of over 100 biosimilars approved in the United States and European Union by the author reveals that none of the animal toxicology studies was pivotal in the approval of the product; essentially, there was sufficient evidence without them for a regulatory decision. Now that the agencies have 2 decades of experience in approving biosimilars, it is about time that clear guidelines against animal toxicology testing are adopted. The advantages of this guidance will include:

• Developers will be forced to produce a more analytically similar product because they cannot rely on animal testing to justify any significant differences in the structure.
• It could prevent the approval of biosimilars that may not be adequately confirmed to be biosimilar based on irrelevant animal toxicology testing.
• There would be a significant reduction in the testing time and cost—both relevant to making biosimilars affordable.
• Animal suffering would be reduced.

The only justified use of animal studies is in animal pharmacology testing in larger species such as monkeys. The pharmacokinetic profile provides an additional element of analytical similarity—how the body views the molecule, which is the same justification for clinical pharmacology testing in humans.