In chemico sequential testing strategy for assessing the photoallegic potential

Area of Science:

• Toxicology
• Dermatology
• Chemical Safety

Background:

• Non-animal testing for photoallergy lacks regulatory validation.
• Current methods like UV-VIS and ROS assays have high sensitivity but low specificity, leading to false positives.
• A need exists for more specific follow-up assessments in photosafety evaluations.

Purpose of the Study:

• To develop an in chemico photoallergy testing method, the photo-direct peptide reactivity assay (photo-DPRA).
• To evaluate the predictive performance of photo-DPRA and a sequential testing strategy (STS) for chemical photoallergy.
• To provide a follow-up assessment for chemicals identified as false positives by initial photoreactivity assays.

Main Methods:

• Selection of 34 photoallergens and 16 non-photoallergens based on photosafety data.
• Application of UV-VIS spectral analysis, ROS/micellar ROS assays, photo-DPRA, and 3T3 neutral red uptake phototoxicity testing (3T3 NRU PT).
• Development and testing of a sequential testing strategy (STS) combining multiple assays.

Main Results:

• The photo-DPRA demonstrated potential as a specific in chemico assay for photoallergy.
• The sequential testing strategy (STS), integrating photo-DPRA with other methods, showed high prediction performance.
• The combined approach effectively addressed key events in photoallergy mechanisms.

Conclusions:

• The developed photo-DPRA and STS offer a promising strategy for predicting chemical photoallergic potential.
• This approach can serve as a valuable follow-up assessment, particularly for chemicals flagged by less specific initial tests.
• The findings support the advancement of non-animal testing methods in regulatory toxicology.