Comparing Balb/c 3T3, HaCaT and 1BR.3.G for in vitro phototoxicity assessment: a preliminary study

Phototoxicity testing is an important component of the safety assessment of chemicals and cosmetic and pharmaceutical ingredients. The BALB/c 3T3 NRU phototoxicity test is an established in vitro method for identifying phototoxic substances. The development of human-derived models may provide complementary and potentially more human-relevant approaches for phototoxicity assessment. This study aimed to compare the phototoxic responses of HaCaT and 1BR.3.G cells with the established cell model. Cells were exposed to different concentrations of chlorpromazine in the absence or presence of UVA irradiation (4 J/cm², Actinic BL UVA 15W/10 FAM/10X25BOX emitting at 350–370 nm region, 365 nm peak), following the principles of OECD TG 432. Photo-Irritation Factor (PIF) was determined using the NRU and MTT assays under irradiated and non-irradiated conditions. NRU and MTT values obtained were 26.1 ± 6.0 and 25.4 ± 3.1 for HaCaT, and 52.4 ± 28.7 and 28.4 ± 8.2 for 1BR.3.G classifying chlorpromazine as phototoxic. In the case of BALB/c 3T3 a substantial loss of viability in irradiated controls was already observed at low passages (P3–P5), shortly after cell acquisition, suggesting that extensive passaging was unlikely to account for the observed response. Collagen coating and reducing the UVA dose did not provide sufficient viability for reliable phototoxicity testing. Although HaCaT and 1BR.3.G have shown good response with CPZ further studies with a broader range of positive and negative reference chemicals are needed to assess their predictive capacity and applicability. Moreover, comparison with the BALB/c 3T3 model would be desirable.