Mutagenicity and Genotoxicity | OECD 490

The In Vitro Mammalian Cell Gene Mutation Test using the Thymidine Kinase Gene, conducted according to OECD 490, is a widely accepted in vitro mutagenicity test used in genotoxicity testing and genetic toxicology programs.

Commonly referred to as the Mouse Lymphoma Assay (MLA), this assay evaluates the mutagenic potential of chemicals, pharmaceuticals, biocides, and other test materials. The test is internationally accepted by regulatory authorities and is included in genotoxicity testing strategies recommended by frameworks such as OECD, REACH, ICH, and EFSA.

Why Perform an OECD 490 Mouse Lymphoma Assay?

Unlike some other mammalian cell mutation assays, the MLA can identify both:

•    Gene mutations affecting the thymidine kinase (TK) locus

•    Larger genetic alterations, including chromosomal events and deletions affecting the TK gene region

This broad detection spectrum makes OECD TG 490 a valuable component of regulatory genotoxicity testing strategies.

Principle of the In Vitro Mouse Lymphoma Assay

Cultured mammalian cells are exposed to the test item in the presence and absence of a metabolic activation system (S9 mix). Following treatment and an appropriate expression period, cells are evaluated for mutations at the thymidine kinase locus.

Study Scope According to OECD TG 490

Pretesting includes

·         Solubility screening

·         Evaluation of acute cytotoxicity

·         Selection fo dose levels

The initial experiment is performed using the microtiter plate method:

·         With metabolic activation (S9)

·         Without metabolic activation

Based on the outcome of the first experiment, an additional experiment may be required, including:

·         Extended treatment duration in the absence of metabolic activation and/or

·         Modified metabolic activation conditions, such as increased S9 concentration

Where required, analytical verification and formulation analysis can be incorporated into the study design.

Test System

L5178Y TK+/- clone (3.7.2C) (mouse lymphocytes)

Endpoints and Evaluation

The primary endpoint is the mutant frequency (MF) at the thymidine kinase locus.

A test item is considered positive when it induces a biologically relevant and statistically significant increase in mutant frequency compared with concurrent vehicle controls.

In addition, the distribution of small and large colonies is evaluated. This information may provide insight into the nature of the underlying genetic damage, as small colonies are often associated with larger genetic alterations, whereas large colonies typically result from more localized gene mutations.

OECD 490 for Nanomaterials

Nanomaterials present specific challenges for in vitro genotoxicity testing and may require additional characterization and study design considerations. Important aspects are:

• Proof of cellular uptake of the nanoparticles
• Ensuring effective exposure

In many cases the uptake of the particles can be demonstrated using transmission electron microscopy (TEM). For an effective exposure to the cells a stable dispersion of the nanomaterial is important. Our experts are very experienced in this field and support you in developing appropriate testing strategies in accordance with current regulatory requirements.

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Planning an OECD TG 490 Mouse Lymphoma Assay?

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