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3T3 Phototoxicity (OECD 432)

The 3T3 Neutral Red Uptake (NRU) Phototoxicity assay is a 96-well cytotoxicity-based assay that utilizes BALB/c 3T3 mouse fibroblasts to measure the concentration-dependent reduction in neutral red uptake by the cells after exposure to a test material in the presence and absence of UVA light. Duplicate 96-well plates containing a monolayer of 3T3 cells are exposed to serial dilutions of a test material. One of the plates is exposed to 5 J/cm2 of UVA while the other plate is kept in the dark. Neutral red uptake (NRU) by cells exposed to the test chemical in the presence of UVA exposure is compared to the NRU by cells exposed to the test chemical in the absence of UVA exposure to evaluate phototoxicity.

 

Test Material Compatibility

The assay is well suited for water-soluble materials, and test materials may also be dissolved in intermediate solvents so that they are compatible with the test system. An initial solubility test is performed to find the most suitable solvent when the solubility of a test chemical is unknown.

Test materials that are found to be insoluble or otherwise incompatible with this test system (3T3 NRU Phototox) may be tested using our 3-D Reconstructed Human Epidermis Phototoxicity assay.

 

Specialized Protocols

The assay and test platform may be adjusted to accommodate specific testing needs. (Read about our work with solid state materials) Specialized protocols may be prepared as requested through consultation with the Study Director.

Quick Facts

Assay Model: 3T3 cells seeded in duplicate 96-well plates

Endpoints: calculated using Phototox 2.0 software (supplied by ZEBET)

  1. IC50 (the concentration of test material that causes a 50% decrease in viability, relative to the solvent control)
  2. PIF (Photo-Irritation-Factor) compares the IC50 of treated cells in the presence of UVA exposure to the IC50 of treated cells in the absence of UVA exposure.
  3. MPE (Mean Photo Effect) compares the response curve of treated cells in the presence of UVA exposure to the response curve of treated cells in the absence of UVA exposure.

Specialized protocols may be prepared as requested through consultation with an IIVS Study Director.

3T3 NRU Photoxicity Assay: Phototoxicity assay - overview of the procedure. Duplicate plates of test chemical 3T3 cells are exposed in the presence or absence of UVA.
Example of chlorpromazine (positive control) dose responses in presenceand absence of UVA.
Addition of Neutral Red for 3T3 Phototoxicity Assay
Applications

The 3T3 NRU phototoxicity assay is generally used to test the phototoxic potential of chemicals and ingredients, rather than final products and formulations.

Test Material Compatibility

The assay is best suited for water-soluble materials; however, test materials may be dissolved in intermediate solvents so that they are compatible with the test system. At IIVS, an initial solubility test is performed to find the most suitable solvent when the solubility of a test chemical is unknown.

Test materials that are found to be insoluble or otherwise incompatible with this test system (3T3 NRU Phototox) may be tested using our 3-D Reconstructed Human Epidermis Phototoxicity assay.

Specialized Protocols

Test article concentrations may be adjusted as necessary to accommodate specific physical characteristics or client needs. Specialized protocols may be prepared as requested through consultation with the Study Director.

Alternate assays measuring the potential for phototoxic action may be employed using 3-dimensional reconstructed human epidermal tissue models. Please contact IIVS for more information.

Validation Status

OECD TG432

Phototoxicity Comparisons: Comparison of the responses between phototoxic and non-phototoxic test materials.

Phototoxicity Comparisons: Comparison of the responses between phototoxic and non-phototoxic test materials.

Watch a training video on the 3T3 Phototoxicity assay

For more information on how this assay could be used by your organization, please contact IIVS.

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