Up-regulation of antioxidant enzymes and coenzyme Q10 in a human oral cancer cell line with acquired bleomycin resistance

Bleomycin (BLM) is an anti-cancer drug that can induce formation of reactive oxygen species (ROS). To investigate the association between up-regulation of antioxidant enzymes and coenzyme Q10 (CoQ10) in acquired BLM resistance, one BLM-resistant clone, SBLM24 clone, was selected from a human oral cancer cell line, SCC61 clone. The BLM resistance of SBLM24 clone relative to a sub-clone of SCC61b cells was confirmed by analysis of clonogenic ability and cell cycle arrest. CoQ10 levels and levels of Mn superoxide dismutase, glutathione peroxidase 1, catalase and thioredoxin reductase 1 were augmented in SBLM24 clone although there was also a mild increase in the expression of BLM hydrolase. Suppression of CoQ10 levels by 4-aminobenzoate sensitized BLM-induced cytotoxicity. The results of suppression on enhanced ROS production by BLM and the cross-resistance to hydrogen peroxide in SBLM24 clone further demonstrated the development of adaptation to oxidative stress during the formation of acquired BLM resistance.