Toxicology in new drug development

Broadly, the process of Preclinical drug development can be divided into three main components:

- Drug discovery, during which candidate molecules are chosen based on their pharmacological properties.

- Pharmaceutical research includes the preparation process, structure confirmation, formulation, formulation, preparation process research of APIs, quality research and formulation of quality standards, stability research, and research on the selection of packaging materials or containers that are in direct contact with medicines. Pharmaceutical research is an important part of drug research and development, and it is the basis for drug safety and efficacy research.

- Preclinical development, during which a wide range of non-human studies ( toxicity testing, pharmacokinetic analysis, pharmacodynamic analysis, and formulation) are performed.

There have been surveys showing that in the preclinical stage of drug candidates, toxicity problems are the main reason for development failures, accounting for about 40% of all development failures. It can be seen that in the early stages of development, detecting potential toxicity problems as early as possible and determining their safety as much as possible can greatly improve development efficiency and reduce the risk of failure. And more comprehensive and in-depth toxicology research can not only play a role in early warning for the early development of drugs, but also map the potential “withdrawal” risks after the market. Therefore, the success of new drug research and development is absolutely inseparable from the escort of toxicology!

History and background

After the major phytotoxicity, there is a rapid progress in toxicology

In the early part of the 20th century, when new drugs developed unprecedentedly, due to the rush of certain preclinical and clinical trials and the lack of systematic toxicology studies, the safety problems of many new drugs were constantly manifested in clinical applications, leading to many emergence worldwide Serious major drug accidents. For example, “sulfa elixirs” in the United States in the 1930s, “organotin poisoning” in France in the 1950s, “thalidomide” in Germany in the 1960s, and “chloroiodoquinoline” in Japan in the 1970s… these major drugs Harmful incidents have caused widespread international attention to the safety evaluation of therapeutic drugs.

In response to these major clinical pharmacological events, some countries and regions have focused on drug toxicity studies on preclinical research, in order to avoid clinical group pharmacological events caused by insufficient scientific research. In 1972, New Zealand formally proposed the concept of GLP for the first time in its Testing Laboratory Registration Act, which provided new ideas for the quality control and management of non-clinical research in the early stage of drug development.

In 1978, the U.S. FDA launched the “Non-clinical Drug Research Quality Management Practices” (GLP), which regulated the standards of toxicology tests, made toxicity test results more convincing, comparable, and evaluable, and included them in federal regulations. This marked the true birth of GLP regulations. At the end of 1993, my country also issued the “Non-clinical Drug Research Quality Management Code (Trial)”, and formally promulgated and implemented the “Non-clinical Drug Research Quality Management Code” in 2003, gradually requiring non-clinical drugs for drug registration Safety evaluation research must be carried out in an organization that meets GLP requirements.

In 2004, the Institute of Medicine under the FDA issued a report titled “Innovation/Stagnation: Challenge and Opportunity on the Critical Path to New Medical Products”. Based on this report, the FDA formulated the “Critical Path Plan ( Critical Path Initiative, CPI)”. The report pointed out: Although significant progress was made in the field of biomedicine at that time, new technologies and new methods were widely used in the development of new drugs, and each new drug research and development investment reached about 1 billion US dollars, but the efficiency of new drug research and development still showed a downward trend year by year. Among the INDs that entered phase I clinical trials, only 8% passed the final approval; at the same time, 4% of the approved new drugs were forced to withdraw from the market due to various reasons (mainly toxicity). About 30% are marked with black box warnings.

In 2007, the European Union also formulated a similar “Innovation Medicines Initiative (IMI)”, planning to establish a “European Drug Safety Research Center” to try to solve the failure of new drug development due to safety reasons from the EU level. In the same year, The “Environmental Compound Toxicity Test and Evaluation Committee” under the US EPA officially published the 21st century toxicity test “Vision and Strategy” report, calling for the implementation of “compound identification, toxicity pathways, targeted testing, and dose response and extrapolation modeling” Modular, new paradigm changes in toxicity testing.

Unclear toxicological issues, a lot of drugs withdrawn from the market

Since the 1990s, through pharmacokinetics and drug metabolism, after optimizing and improving the absorption and bioavailability of drugs, drug toxicity factors have become one of the main reasons for the failure of new drug development or withdrawal. It is also not shown in Table 1 below. It is hard to see that most of the delisted drugs are accompanied by serious side effects and have to be delisted painfully.

My country’s GLP is developing rapidly

In September 2003, my country officially implemented the drug GLP regulations, and the accompanying drug toxicology disciplines have made considerable progress in both the regulatory toxicology research level, or the basic research and applied basic research. According to statistics, as of the end of 2012, more than 50 GLP institutions across the country have passed the inspection of the CFDA certification center, and 5 units have passed the GLP inspection of OECD member countries, and passed the non-clinical safety evaluation research certified by the American Society of Pathologists (CAP) There is only one institution; as of the end of 2016, 19 testing institutions across the country have successively obtained and announced GLP certification from OECD member states, including 8 in the Netherlands, 9 in Belgium, and 2 in Germany. With the establishment of international drug safety evaluation research outsourcing organizations (CRO), preclinical drug safety evaluation standards tend to be globalized and integrated, and the international mutual recognition of evaluation results has become a major trend. my country is in the GLP regulations and international talents. , Toxicology technology, equipment, laboratory animals and other aspects will quickly integrate with international standards.

Pharmaceutical Toxicology Professional Committee: Threading needles and taking the lead in learning

The Pharmaceutical Toxicology Professional Committee is a secondary society under the Chinese Pharmacological Society. It was established in 1984 and its full name is the Pharmaceutical Toxicology Professional Committee of the Chinese Pharmacological Society. Its affiliates are the Institute of Toxicology and Drugs of the Academy of Military Medical Sciences and the National Shanghai New Drug Safety Evaluation Research center. After the establishment of the Chinese Pharmacological Society-Pharmaceutical Toxicology Professional Committee, it began to promote the implementation of the drug evaluation method in China; in 1989, the concept of “GLP” was first proposed in China and the formulation and implementation of my country’s GLP; in 1990, it began to participate in the formulation of 1985 Revision of drug safety evaluation guidelines and participation in the formulation of national drug toxicity testing technical guidelines. It is particularly worth mentioning that he was responsible for the drafting and implementation of the earliest GLP in my country. In recent years, my country’s pharmaceutical toxicology research has achieved fruitful research results, especially in the construction of pharmaceutical toxicology disciplines and personnel training, the formulation and implementation of GLP specifications, and the preclinical safety evaluation of innovative drugs, government decision-making consultation, new drug review and risk assessment 1. It has played an irreplaceable role in spreading scientific knowledge of drug toxicology and ensuring people’s drug safety services.

Technology

Basic content of drug toxicology

Drug toxicology, as a discipline that studies the harmful effects of drugs on the body, on the one hand, explores the damaging effects of drugs on the body, and clarifies the relationship between the molecular structure of drugs and their toxic effects; on the other hand, it studies the absorption of drugs in the body, The process and law of distribution, metabolism, and excretion expound the influence of the body’s defense system on drug toxicity. Normally, drug toxicology studies are required in the preclinical and clinical stages of new drug development. The research category belongs to drug description toxicology, mainly observing and studying the effects and effects of drugs on the human body and the environment, including preclinical toxicology studies and Clinical toxicology research.

The research content of drug preclinical description toxicology includes various preclinical safety evaluation tests, including acute toxicity, repeated administration toxicity, safety pharmacology, special toxicity (genetic toxicity, reproductive toxicity, carcinogenicity), toxicokinetics, Other toxicity (irritation, allergy, hemolysis), as well as immunotoxicity and dependence. The purpose of the research is to find out the symptoms of the drug’s toxic reaction, the duration and end of the time, the dose level of the non-toxic reaction, the distance between the dose of the toxic reaction and the effective dose (that is, the treatment window or safety range), and the toxic reaction Nature and reversibility, etc.

The research content of drug clinical description toxicology includes safety evaluation in phase I to III clinical trials, and adverse reaction monitoring after the drug is marketed. Medical statistics and epidemiological investigation are mainly used as research methods. The purpose of its research is to observe the toxic and side effects of people using drugs, and to track the possible adverse effects of patients of different genders, ages, and levels after long-term medication and the potential impact on the next generation.

What are the mechanisms of drug toxicity?

Only by understanding the mechanism of toxicity can the problem be solved from the root cause. From the perspective of drug discovery and development, studying the mechanism of drug toxicity can increase and improve the relevance of drug safety evaluation. Generally speaking, toxicologists often analyze the following basic questions to study the molecular mechanism of poisons, such as how do poisons enter the body or cells? How is it distributed and metabolized in the body? How to interact with target molecules? How to exert its toxic effects at the molecular level? How does the organism respond to poisonous attacks? What will be the downstream biological consequences of a poisonous attack? Wait, etc…. Through years of accumulation and summary, the current drug toxicity mechanism can be roughly divided into the following three categories:

☆Main pharmacology

It refers to the expanded pharmacological effect caused by the direct action of the drug on the target, and has nothing to do with the physical and chemical properties of the compound itself, such as pH value, amphipathic, etc. For example, the developmental toxicity caused by ACEI, due to the complex structure of these compounds, can cause developmental toxicity before birth in humans and experimental animals, suggesting that the effect may be related to the inhibition of ACE. In fact, the developmental abnormalities of ACE knockout mice are similar to the developmental toxicity of ACE inhibitors. Since the adverse reactions caused by the expanded pharmacological effects mostly only occur at levels exceeding the effective dose, it can be avoided by paying close attention to the dose in clinical use.

☆Secondary Pharmacology

Effects mediated by targets other than the main pharmacodynamic target can also lead to toxicity. For example, fenfluramine is a type 2C serotonin receptor agonist, which is clinically used for weight loss treatment, but the drug also has an agonistic effect on type 2B serotonin receptors and causes heart valve disease and pulmonary hypertension. In addition, the main pharmacodynamic effect of non-steroidal anti-inflammatory drugs is to inhibit COX-2, and the toxic effect of inducing gastrointestinal ulcers is related to the inhibitory effect on COX-1. New non-steroidal anti-inflammatory drugs such as plugs Lecoxib and others are COX-2 selective inhibitors without gastrointestinal side effects mediated by secondary pharmacological effects.

☆Chemical-mediated toxicity

The occurrence of this type of toxicity is closely related to the physical and chemical properties of a specific compound, but has nothing to do with the target of the drug, such as oxidative stress, phospholipid disease or hemolysis. Amphiphilic compounds can be inserted into cell membranes and interfere with phospholipid metabolism, which can easily lead to phospholipid disease. For example, various amphipathic amine drugs have different pharmacological activities and different structures, but they can all induce phospholipid disease. Chemical-mediated toxicity is often related to special chemical groups and metabolic activation processes. For example, terminal acetylene groups can easily lead to the inhibition of drug-metabolizing enzymes, and polycyclic aromatic hydrocarbons can easily intercalate into DNA double strands and cause gene mutations.

Toxicity mechanism research technology

Regarding the mechanism of drug toxicity, many mature research technologies have been applied, including two aspects, namely, toxicological genomics technology, gene knockout and RNA interference technology.

☆Toxicological Genomics Technology

That is, the organic combination of functional genomics and conventional toxicology methods. Currently, the most widely used functional genomics technologies include genomics, transcriptomics, proteomics, and metabolomics. Genomics studies the genome of organisms by analyzing the nucleotide sequence, genome structure and composition, while the latter three omics techniques measure the expression levels of organisms’ gene transcripts, proteins, and endogenous metabolites.

☆ Gene knockout and RNA interference technology

Gene knockout refers to a sequence whose sequence is known but its function is unknown. It changes the genetic gene of an organism, causing the function of a specific gene to be lost, so that part of the function is blocked, and it can further affect the organism, and then speculate The biological function of the gene is knock out. RNA interference is a phenomenon in which exogenous and endogenous double-stranded RNA induces RNA-specific degradation of homologous target genes in organisms, leading to post-transcriptional gene silencing, that is, knock down.

In the development process of a new drug, the first thing to overcome is the efficacy, and then the safety evaluation in terms of toxicity will be carried out. In the development process of many candidate drugs, due to the lack of pharmacological-toxicological data basis for a certain series of drugs in a certain field , Or the person in charge’s ability to predict some structural fragments is not enough. When a large amount of manpower, material and financial resources are invested, and the project gradually progresses to large animals, sometimes there will be a “painful” toxicity problem. For the team, it was extremely embarrassing. Because if you bite the bullet and continue to develop, then the risks in the future can be imagined; if the project is stranded because of this, the early efforts will make you cry. Therefore, some candidate drugs that are about to enter the development phase must have a certain degree of foresight about the toxicity problems that may occur in the future, otherwise, the road from candidate drugs to new drugs on the market will be full of thrills and excitement!