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The Importance of Toxicology Research in Preclinical Studies


Before a study reaches Phase I clinical trials, scientists spend years conducting preclinical research. One vital part of this includes performing toxicology research on a particular medication or pharmaceutical product. The U.S. Food and Drug Administration (FDA) put great emphasis on the importance of preclinical safety evaluations.

According to the FDA’s guidance for industry on preclinical safety evaluation, pharmacokinetic research needs to include experimental medicines or biopharmaceutical products that represent drugs meant for toxicity testing. This administration route should be similar to the one which will be used in clinical trials.

During toxicity testing, systemic exposure should be monitored, along with patterns of absorption. Before beginning a clinical trial, it will be necessary to provide information on absorption, clearance, and disposition of each compound in animal models in order to anticipate safety of exposure in human subjects.

Additionally, the methods for evaluating absorption, clearance, and disposition should be equivalent in animal and human models. It is important to determine the metabolism of tested drugs and how they will react within the human body. There are two types of strategies to use in toxicology research. These are:

1. Single Dose Toxicity Study
With single dose studies, useful information may be gathered on local toxicity or the connection between dosage and systemic reaction. Along with single dose testing, information on the dose-response relationships can also be obtained from animal model efficacy studies. When designing this type of study, it is imperative to incorporate safety pharmacology parameters.

2. Repeated Dose Toxicity Study
The dosing regimen in preclinical studies needs to follow the regimen that will be used in clinical trials. Some researchers choose daily repeated dosing while others use intermittent dosing, the choice will depend upon the particular medications that are being developed and tested. Repeated dose studies will need to monitor toxicokinetic effects.

Animal toxicity studies usually take between one to three months for biotechnology-derived pharmaceutical products. For any medications that are intended for short-term use – less than seven days typically – a toxicity study lasting two weeks is generally adequate for federal regulations and marketing authorization.

On the other hand, for medication meant to treat chronic disease, toxicity studies lasting approximately six months are typically required. Various pharmaceutical products may trigger or suppress an immune response, in which case, immunotoxicity studies may be added in preclinical trials.
https://www.pharmamodels.net/blog/importance-toxicology-research-preclinical-studies/


Non-clinical studies in the process of new drug development - Part II: Good laboratory practice, metabolism, pharmacokinetics, safety and dose translation to clinical studies


Regulatory toxicology studies
Regulatory toxicology studies are mandatory in the drug development process and aim to evaluate the toxicity level of a substance using protocols that follow the guidelines recommended to conduct non-clinical studies of pharmaceutical products. In addition, it is important to emphasize that they have to be conducted in compliance with the GLP principles. After the preliminary toxicity studies, the GLP studies should be conducted in two animal species (with the exception of mutagenicity tests). The planning of these studies could be based on the data obtained by the exploratory studies of both efficacy and toxicity. These findings could help to define doses, the duration of study, and any side effects that could require special attention. Some GLP toxicology studies are required before beginning clinical trials, but others could be conducted during different phases of the clinical trials; this will be discussed further in this section.

Although there are no unique and standard plans for drug development, it is recommended to perform genotoxicity studies (in vitro and in vivo) as well as a study of dose selection and repeated-dose toxicity (28 days), before the first exposure of humans to the substance. Usually, with these studies series, together with pharmacokinetic, efficacy, safety pharmacology and substance chemical characterization studies, it is possible to submit a dossier to the regulatory agencies to request permission to start the tests in humans. It is important to emphasize that for toxicology studies following GLP principles, the test article should be in its final formulation, in other words, in the same formulation that will be used to treat individuals during the clinical studies, together with its complete chemical certificate of analysis. In addition, the route of administration should be, preferably, the same as that intended for human treatment. These requirements are clearly described in the guidelines of non-clinical studies of the main regulatory agencies, such as the FDA, European Medicines Agency (EMA) and Agência Nacional de Vigilância Sanitária (ANVISA, Brazil).

In this step, the genotoxicity tests previously described (in vitro Ames No. 471 (4) and in vitro micronucleus No. 487 (36)) should be performed in accordance with the GLP requirements, even when it has already undertaken exploratory studies. Thus, the in vivo micronucleus test No. 474 (37) is also recommended, as it provides relevant genotoxicity data of a substance involved in active processes, such as metabolization, pharmacokinetics and DNA repair, which are not totally detected by an in vitro system. This test evaluates micronucleus formation in erythrocyte samples from the bone marrow or from rodents’ peripheral blood samples, allowing the identification of possible cytogenetic damage, resulting in micronucleus formation and chromosomal alterations. In many cases, the genotoxicity assays, performed according to the GLP principles, are conducted before the repeated dose toxicity tests for decision-making reasons. However, it depends on the strategy programmed for each substance and on the obtained preliminary data. Also, execution of the GLP genotoxicity test concomitant with initial repeated dose toxicity studies is common.

The toxicity data described in the guidelines suggested by the FDA comprise an important basis for the IND application; however, it depends on the intended application of each substance and can vary case-by-case. After the authorization to start clinical studies, other non-clinical toxicity studies should be conducted; for example, sub-chronic and chronic studies. The toxicity evaluation is normally classified in accordance with a chronological scale, such as the acute studies that are performed to verify the substance effect using single or repeated dose administration for 24 h. Indeed, sub-acute studies are those that comprise the toxic effects for 30 days, whereas sub-chronic studies are defined by the toxic effect of a substance between 30 and 90 days. Studies that are superior to 90 days are normally classified as chronic. However, this classification can be specific for some species; for example, chronic studies can be performed for six months in rodents and 9 months in non-rodents (41).

The sub-chronic study (90 days) can be conducted in parallel with phase I clinical studies. This study is very similar to the toxicity study of 28 days, and the guidelines for both require a daily treatment with at least three doses of the substance and the vehicle, together with clinical, biochemical, hematological, anatomical and histological analysis that are detailed in each guideline. Despite standard measurements, some additional analyses could be included for the observation of a particular effect of the substance, mainly when several toxic effects are described. These tests should be conducted in accordance with the GLP principles; together with the clinical data obtained from phase I, these can help to decide whether the study should continue or not to phase II.

As previously described in this section, the toxicology tests are very important and require high responsibility from the non-clinical and clinical teams. The available amount of substances could require specific protocols and requirements from the regulatory point of view. For example, the development of vaccines frequently does not require reproductive toxicity, mutagenicity or carcinogenicity tests. On the other hand, each substance has particular characteristics and is developed for the treatment of a specific and complex disease; for this reason, the development program should be analyzed case-by-case. Although the regulatory agencies suggest a basic battery of tests to be performed, it is fundamental that the developmental team anticipates possible additional side effects to elaborate a complete clinic plan with important information and avoiding unnecessary studies. Thus, the previous and direct contact between the pharmaceutical industry and the regulatory agencies is highly recommended, aiming to establish the most appropriate tests for each drug candidate.

Conclusion and perspectives

In this review, we highlighted the most recent and relevant aspects necessary to conduct non-clinical studies to attend the guidelines to develop new drugs recommended by major regulatory agencies. Although great efforts in recent years have been occurring to reduce, and perhaps in the future, ban the use of animals in the process of new drug development, several alternative methods are being adopted and recommended by the main international regulatory agencies. However, the use of animals in the new drug development process is still required.

Based on this review, it is possible to conclude that there is no single recommended sequence for the achievement of non-clinical studies during the process of new drug development (Figure 1). Many of the studies may be performed in parallel, and the sequence may vary widely depending on the disease. The use of GLP standards is absolutely necessary, especially for the evaluation of safety studies, and is a decisive factor for the acceptance of non-clinical studies in other countries where GLP has been recommended since 1970. Although Brazil adopts practically the same procedures (guidelines) recommended by the FDA and EMA, few laboratories or national institutions can conduct non-clinical studies in accordance with GLP requirements necessary for new drug registration purposes. The lack of reproducibility and reliability of non-clinical studies has been a limiting factor in the process of new drugs development for some national pharmaceutical companies.

Therefore, the need for high quality standard animals, associated with well-designed protocols, qualified human resources, use of positive and negative controls, blind experiment execution, proper use of statistical analyses, among other aspects, are mandatory factors to obtain reliable and reproducible non-clinical results. Non-clinical studies should be strictly performed in accordance with good institutional scientific practices and also employing GLP requirements (indispensable for the request and approval of a IND) in order to ensure the quality, reproducibility and reliability of non-clinical data, which will support the early clinical studies contributing to the successful development of a new drug.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5188860/