Halobenzoquinone-induced potential carcinogenicity associated with p53-mediated cell cycle pathway.

2,6-Dibromo-1,4-benzoquinone (2,6-DBBQ) and 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), two emerging halobenzoquinones (HBQs), have the highest detection frequencies and levels in drinking water among all HBQs. They are more toxic than the regulated disinfection byproducts. Quantitative structure toxicity relationship analysis predicted that HBQs are a class of potential bladder carcinogens. However, direct experimental evidence for the carcinogenicity of 2,6-DBBQ and 2,6-DCBQ is lacking and the associated toxicity mechanisms remain unclear. In this study, we confirmed the potential carcinogenicity of 2,6-DBBQ and 2,6-DCBQ using an in vitro malignant transformation assay, evaluated their cytotoxicity and genotoxicity, and investigated their toxicity mechanisms. The results showed that 2,6-DBBQ and 2,6-DCBQ significantly decreased the viability of human uroepithelial SV-HUC-1 cells and induced DNA damage in SV-HUC-1 cells, and chromosomal damage in HepG2 cells, and malignant transformation of SV-HUC-1 cells. Moreover, transcriptome sequencing revealed that 2,6-DBBQ and 2,6-DCBQ activated the p53-mediated cell cycle pathway in bladder cancer. In the p53-mediated cell cycle pathway, 2,6-DBBQ and 2,6-DCBQ induced cell cycle arrest at the S phase by downregulating p53 and upregulating p21. Additionally, 2,6-DBBQ and 2,6-DCBQ may have produced excessive reactive oxygen species, damaging DNA and chromosomes. These results not only first confirm the potential carcinogenicity of 2,6-DBBQ and 2,6-DCBQ but also provide an important reference for exploring the cytotoxicity and genotoxicity mechanisms of these HBQs.