Test No. 482: Genetic Toxicology: DNA Damage and Repair, Unscheduled DNA Synthesis in Mammalian Cells in vitro

The Test Guideline for Unscheduled DNA Synthesis (UDS) in mammalian cells in vitro describes procedures utilizing primary cultures, human lymphocytes or established cell lines, to detect DNA repair synthesis after excision and removal of a stretch of DNA containing the region of damage induced by chemical or physical agents. The test is based commonly on the incorporation of tritium-labelled thymidine (3H-TdR) into the DNA of mammalian cells which are not in the S-phase of the cell cycle. The uptake of 3H-TdR may be determined by autoradiography or by liquid scintillation counting (LSC) of DNA from the treated cells. Mammalian cells in culture, unless primary rat hepatocytes are used, are treated with the test substance (solid, liquid, vapour or gas) with and without exogenous mammalian metabolic activation. At least two cell cultures for autoradiography and six cell cultures for LSC are necessary for each experimental point. Multiple concentrations of the test substance over a range adequate to define the response should be used. A test substance producing neither a statistically significant dose-related increase in radiolabel incorporation (expressed either in grains per nucleus or as dpm/ìg DNA), nor a statistically significant and reproducible positive response at any one of the test points is considered not active in this system.  Read more...