1 What is genotoxic impurities
Genotoxic Impurity (or Genotoxic Impurity, Genotoxic Impurity, GTI) refers to the compound itself, directly or indirectly damage to the cellular DNA, resulting in gene mutation or in vivo mutation, with the possibility of carcinogenicity or tendency. Potential genotoxic impurity (Potential Genotoxic Impurity , PGI) from the structure of similar genotoxic impurities, there is a warning, but without experimental proof of aflatoxins, nitrosamine compounds, methanesulfonate esters and other compounds are common genotoxic impurities, many chemotherapeutic drugs also have a certain degree of genotoxicity, and their adverse reactions are caused by the genotoxicity of chemotherapy drugs on normal cells. drugs to normal cells due to genotoxicity, such as cisplatin, carboplatin, fluorouracil and so on.
2Why focus on the study of genotoxic impurities
Genotoxic substances are characterized by a very low concentration can cause damage to the human body's genetic material, which can lead to genetic mutations and may contribute to the development of tumors. Because of their strong toxicity, they pose a strong threat to the safety of medication, and in recent years, there have been more and more cases of widespread medical errors and forced recalls by the FDA due to trace amounts of genotoxic impurities found in marketed medicines, causing huge economic losses to pharmaceutical companies. For example, a well-known international pharmaceutical giant launched the HIV protease inhibitor Viracept (Viracept, mesylate) in the European market, in July 2007, the EMA suspended all its marketing activities in Europe, because of the discovery of excessive residues of ethyl methanesulfonate in its product, ethyl methanesulfonate is a classic genotoxic impurity, the company paid a huge price for this, the The cause of the residue exceedance was first investigated internally, as ethanol was left behind due to incomplete removal during instrument and equipment cleaning, and reacted with the methanesulfonic acid to form ethyl methanesulfonate. After being asked to address the contamination, the company was also asked to conduct toxicity studies to better assess the risk to patients. Meanwhile as many as 25,000 patients were exposed to this known genotoxicity. It wasn't until all of these issues were resolved that EMA reinstated its marketing authorization in Europe.
In recent years, regulatory agencies such as the ICH, FDA, and EMA have made clearer requirements for genotoxic impurities, and more and more pharmaceutical companies are focusing on the control and detection of genotoxic impurities during the development of new drugs.
3Which compounds are genotoxic impurities
Impurities are structurally diverse, and for the vast majority of impurities, there is often insufficient data from toxicity or carcinogenicity studies to categorize them. In the absence of safety data, these regulations and guidelines use the term "alert structure" to distinguish between common impurities and genotoxic impurities. For impurities containing warning structures, (Q)SAR prediction and ex vivo genotoxicity and carcinogenicity studies should be performed, or the level of the impurity should be kept below the threshold of toxicological concern (TTC).
At present, carcinogens are generally divided into two categories: one is genotoxic carcinogens, carcinogenicity through the direct destruction of genetic material through chemical bonding, most of the chemical carcinogens have genotoxicity; the second category is nongenotoxic carcinogens, usually do not occur with chemical bonding, do not have a direct destruction, but through the genetic material of the indirect mechanism outside of the cause of carcinogenicity (such as the promotion of cell hyperproliferation, etc.). The second category is non-genotoxic carcinogens, which usually do not interact with chemical bonds and do not cause direct damage.)
The warning structures from several publications are summarized in (see PDF of the original article). For more detailed information on the results of genetic impurity alerts, please also refer to the EU's Development of structure alerts for the in vivo micronucleus assay in rodents. Or go to The Carcinogenic Potency Database (CPDB), which contains a list of 1,547 carcinogens, their structural formulae, CAS numbers, sites of action, TTC values, and a host of other information. It should be noted that the presence of a warning structure does not necessarily mean that the impurity is genotoxic, and substances recognized as genotoxic are not necessarily carcinogenic. The physicochemical and other structural characteristics of the impurity (e.g., relative molecular mass, hydrophilicity, molecular symmetry/spatial resistance, reactivity, and rate of biometabolism) may inhibit or modulate its toxicity. The importance of the alert structure is that it indicates possible genotoxicity and carcinogenicity, and provides direction for further safety evaluation of impurities and selection of control strategies.
4Regulatory Requirements and Limits for Genotoxic Impurities
Initially, the ICH issued Guidelines for the Study of Impurities in APIs Q3A (R2), and Guidelines for the Study of Impurities in Pharmaceutical Formulations Q3B (R2), which state that "for potential impurities capable of producing potent pharmacological activity or toxicity, a study is still recommended, even if the level is less than 0.1%," and that "for potential impurities capable of producing potent pharmacological activity or toxicity, a study is still recommended, even if the level is less than 0.1%. In these guidelines, it is mentioned that "for potential impurities capable of producing potent pharmacological activity or toxicity, even if the content is less than 0.1%, structural characterization studies are recommended". In the subsequent revision, it was further clarified that "attention should be paid to potential genotoxic impurities in APIs" and "for very toxic impurities, lower limits may need to be set", but it did not explicitly address the research and control of genotoxic impurities, nor did it put forward specific proposals for the control of genotoxic impurities. However, it does not explicitly address the issue of research and control of genotoxic impurities, nor does it put forward specific research principles, control strategies and limit requirements.
In the EMA (European Medicines Agency) launched the "Guidelines for Limits of Genotoxic Impurities", which introduced the concept of acceptable risk of intake, i.e., toxicant limits, or threshold of toxicological concern (TTC, Threshold of Toxicological Concern). A limit value of TTC (1.5 μg/day) was set, which corresponds to a daily intake of 1.5 μg of a genotoxic impurity and is considered to be an acceptable risk for most medicines (lifetime risk of carcinogenicity is less than 1 in 100,000). Following this threshold, an acceptable level of impurities in an active drug can be calculated based on the expected daily intake. It is important to note that the TTC is a risk management tool that uses a probabilistic approach. If there is a genotoxic impurity and we don't know much about its toxicity level, if its daily intake