Isotopes are atoms of the same chemical element, which have different masses due to the different number of neutrons in the nucleus, and can be divided into light and heavy isotopes. According to the physical properties, isotopes can be divided into two forms: radioactivity and stability. Radioactive isotopes (e.g., 3H, 14C) undergo their own decay process and emit radiation energy. They are unstable and have a physical half-life. Stable isotopes are non-radioactive and have stable physical properties. They exist in nature in a certain proportion (abundance) and are harmless to human body. Chemical synthesis can be used to mark them into drug molecules and track them through instruments such as temperament and liquid.

1. Two main directions of "isotope labeling" in drug development

Pharmacokinetic study

In terms of the sensitivity of quantitative analysis, radioisotope labeled compounds are higher than stable isotope labeled compounds, and the measurement of radioactivity is not affected by non-radioactive impurities and chemical states, so the quantitative analysis is more simple and the analysis result is more accurate. Radioactive isotope labeling compounds in addition to solve conventional analysis method cannot solve the problem, more importantly, can be used as a tracer, thus to study the distribution, metabolism and efficacy of drugs in the body, action mechanism, etc., for the pharmacokinetic study of drugs to provide important basis, at the same time to provide innovative drug research and development methods.

Toxicity studies

The study of potential toxicity is a necessary link in the discovery and clinical process of drugs. Previous toxicity studies mostly used in vitro and animal experiments on a large number of compounds, which required a lot of money and time and could not explain the mechanism of toxicity. Compounds labeled with stable isotopes can be used to track drug metabolism, identify the causes of toxicity, and predict the potential toxicity of new compounds.

2. Stable isotope labeling

Compared with radioisotope labeling reagent, stable isotope labeling reagent has the most important advantages such as no radioactivity, no need for complex radiochemical equipment and radiation protection measures, and no environmental pollution. At present, studies on stable isotope separation technologies such as 15N, 18O, 20Ne, 22Ne and 13C have been completed in China, and the preparation and detection technology of stable isotope labeling reagent has been gradually researched and developed domestically, so as to break the foreign monopoly.

3. Stable isotope tracer

The stable isotopes commonly used in the pharmaceutical field are 2H, 13C, 15N and 18O. Strictly speaking, stable isotopes refer to the isotopes that do not occur or are very difficult to occur radioactive decay in an element. For example, 12C and 13C are both stable isotopes of carbon, and in metabolic research, "stable isotopes" are often used to represent the stable isotopes with low natural abundance. Carbon mainly exists in the form of 12C in nature, 13C only accounts for 1.11%, while nitrogen is mainly 14N, and 15N only accounts for 0.37%.