COMPARISON OF IN VITRO PHOTOTOXICITY TEST METHODS: 3T3 NRU PT VS. ENHANCED PHOTOTOXICITY SCREENING ASSAY IN RECONSTITUTED SKIN (EPARS).

This study by scientists at MB Research Labs demonstrated that MatTek’s EpiDerm in vitro human tissue equivalent provided more in vivo-like test results for phototoxicity testing than the 3T3 Neutral Red Uptake Phototoxicity Test. Currently, only the 3T3 Neutral Red Uptake Phototoxicity Test (3T3-NRU PT) has been approved as a non-animal phototoxicity test by governmental regulatory agencies. However, the 3T3-NRU PT test has serious drawbacks as a model for human skin. Specifically, the test uses a monolayer cell culture consisting of mouse tumor cells, the test is overly sensitive resulting in many false positives, and test substances must be soluble in tissue culture media. MB Research Labs has developed a more relevant in vitro system based on MatTek’s EpiDerm three-dimensional, differentiated human keratinocyte tissue cultures, which can accommodate a wide range of vehicles and allow direct topical application of test substances, termed “Enhanced Phototoxicity Assay in Reconstructed Skin” (EPARS). In this study, MB Research Labs presented a side-by-side comparison between the 3T3-NRU PT test and the EPARS test systems using the same Solar Simulated Light (SSL) source of UV and visible light and the 8 reference standard chemicals used for validation of the 3T3-NRU PT. The EPARS test correctly predicts with 100% accuracy the phototoxic potential of all reference test substances. The concentrations of test agents needed to obtain the EC50s in the EPARS MTT viability test, when compared to the Neutral Red assay in 3T3 fibroblasts, is one to two orders of magnitude higher, reflecting the thickness and complexity of EpiDerm’s in vivo-like three-dimensional tissue structure. Therefore, the EPARS test better approximates the exposure levels of chemicals needed to induce phototoxic effect in animal tests and actual human skin. In addition, the most important practical advantage gained over the 3T3 NRU PT is that test substances can be applied topically, overcoming both the pH and solubility problems encountered when dosing via the culture media.

3T3 Neutral Red Uptake Phototoxicity Test, 3T3-NRU PT, EPARS MTT viability test, Enhanced Phototoxicity Assay in Reconstructed Skin (EPARS), EpiDerm, Exposure levels of chemicals, False positives, Monolayer cell culture, Mouse tumor cells, Non-animal phototoxicity test, Side-by-side comparison, Solar Simulated Light (SSL), Three-dimensional, differentiated human keratinocyte cultures, Topical application