Genotoxicity refers to the capability of a substance to damage the genetic information of cells (changes of the structure, sequence, and/or number of genes), which can have direct or indirect effects, such as induction of mutations, activation or inactivation of genes. DNA repair or apoptosis pathways are normally activated to repair or control the damage; however, if the damage is fixed, mutagenesis and even cancer can happen. Many times the changes are permanent and heritable, thus they can affect both somatic cells and germ cells, which will be passed on to future generations. From the definition, it is clear that all mutagens have genotoxicity but genotoxic compounds are not necessarily mutagenic. Genotoxicity affects the health of the patients and even their babies, thus is an important aspect to consider during IND-enabling. What's more, genotoxicity assays are also common in vitro tests to predict carcinogenicity. Creative Biolabs has developed various approaches for the estimation of the genotoxicity of drug candidates and helping customers gather information for IND-enabling.
The aim of genotoxicity tests is determining if a drug candidate will damage genetic materials in cells and cause cancer. In such tests, after exposure to the compound, DNA damage (e.g. point mutations, strand break, cross-linking, structural and/or numerical chromosomal aberrations, and loss of excision repair) in cells are measured. There are a variety of genotoxicity tests that can be performed in bacterial, yeast, and mammalian cells. Ames test and Escherichia coli reverse mutation assay are two in vitro mutagenicity tests methods based on bacteria cells, while mammalian chromosome aberration test and mammalian cell gene mutation test are based on mammalian cells. Ames test and Comet assay are two of the most popular methods used to evaluate the chemicals' potential to cause DNA damage and cancer.
Ames Test (Bacterial Reverse Mutation Assay)
Ames test employs auxotrophic mutant bacteria strains that require histidine from the environment for growth. In Ames Test, if the tested substance is capable of creating mutations (genotoxic) that result in a prototrophic state of the strains, cells should have normal growth of on a histidine-free medium.
Comet Assay (Single Cell Gel Electrophoresis Assay)
Comet assay is one of the most common genotoxicity tests. Cells are lysed by detergents and salts and the DNA released goes through agarose gel electrophoresis under a near neutral pH condition. The more double-strand breaks that a cell contains, the faster the DNA will migrate toward the anode. This technique is quite sensitive to detect DNA damage, easy and cheap to perform, and fast to get the test results.
Other in vitro and in vivo toxicology tests such as mouse lymphoma TK+/- assay, SOS/umu assay, and in vitro and in vivo micronucleus test are also used in the determination of genotoxicity of compounds.
Creative Biolabs also provides other drug discovery services. For more detailed information, please feel free to contact us or directly sent us an inquiry.
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