#615 In-vitro genotoxicity testing – mammalian cell assay

Objective of the study

The aim of genotoxicity testing is to:

predict genotoxic potential
identify genotoxic carcinogens at an early stage
elucidate the mechanism of action of some carcinogens.

Mammalian cell assays include a combined test for structural and numerical chromosome aberrations in mammalian cells and a test for gene mutation in mammalian cells.

The purpose of the in vitro chromosome aberration test is to identify agents that cause structural chromosome aberrations in cultured mammalian somatic cells. The in vitro mammalian cell gene mutation test can be used to detect gene mutations induced by chemical substances.

These tests are used to screen for possible mammalian mutagens and carcinogens. Many compounds that are positive in this test are mammalian carcinogens; however, there is not a perfect correlation between this test and carcinogenicity. Correlation is dependent on chemical class and there may be carcinogens that are not detected by these tests because they appear to act through mechanisms other than direct DNA damage or genotoxic mechanisms.

Circumstances under which the study is recommended to be required

The mammalian cell assays are always required.

Test organism

The following assays are generally recommended:

In vitro chromosome aberration test: Chinese hamster ovary or Chinese hamster lung fibroblast (V79) cells, hypoxanthine-guanine phosphoribosyl transferase (hgprt) gene locus, accompanied by an appropriate in vitro test for clastogenicity;
In vitro mammalian cell gene mutation test: Mouse lymphoma L5178Y cells, thymidine kinase (tk) gene locus, with assay conditions maximized for small colony expression or detection;
In vitro mammalian cell gene mutation test: Chinese hamster ovary cells strain AS52, xanthine-guanine phosphoribosyl transferase (xprt) gene locus.

If other mammalian cell assays are conducted, the applicant should provide a justification.

Test substance

Technical grade active ingredient

Typical endpoints of the study

Specific endpoints of the various assays can be found in the testing guidelines cited below

Test guidelines

The following test guidelines may be used for the mammalian cell assays:

OECD Guidelines for the Testing of Chemicals. Test No. 473: In vitro mammalian chromosomal aberration test

OECD Guidelines for the Testing of Chemicals. Test No. 476: In vitro mammalian cell gene mutation test

US EPA Health Effects Test Guidelines. OPPTS 870.5300. In vitro mammalian cell gene mutation test.

US EPA Health Effects Test Guidelines. OPPTS 870.5375. In vitro mammalian chromosome aberration test.

EC Testing Method B.10. Mutagenicity. In vitro mammalian chromosome aberration test. Council Regulation (EC) No 440/2008.
EC Testing Method B.17. Mutagenicity. In vitro mammalian cell gene mutation test. Council Regulation (EC) No 440/2008.