Organic
peroxides used in the chemical and pharmaceutical industries have a reputation for being potent skin
tumor promoters and inducers of epidermal
hyperplasia. Their ability to trigger
free radical generation is critical for their carcinogenic properties. Short-term in vivo exposure of mouse skin to
cumene hydroperoxide (Cum-OOH) causes severe oxidative stress and formation of spin-trapped radical adducts. The present study was designed to determine the effectiveness of Cum-OOH compared to 12-O-tetradecanoylphorbol-13-acetate (TPA) in the induction of
tumor promotion in the mouse skin, to identify the involvement of
cyclooxygenase-2 (COX-2) in oxidative metabolism of Cum-OOH in keratinocytes, and to evaluate morphological changes and outcomes of oxidative stress in skin of SENCAR mice throughout a two-stage
carcinogenesis protocol. Dimethyl-
benz[a]anthracene (DMBA)-initiated mice were treated with Cum-OOH (32.8 micro mol) or TPA (8.5 nmol) twice weekly for 20 weeks to promote
papilloma formation. Skin
carcinoma formed only in DMBA/Cum-OOH-exposed mice. Higher levels of oxidative stress and
inflammation (as indicated by the accumulation of peroxidative products,
antioxidant depletion, and
edema formation) were evident in the DMBA/Cum-OOH group compared to DMBA/TPA treated mice. Exposure of keratinocytes (HaCaT) to Cum-OOH for 18 h resulted in expression of COX-2 and increased levels of
PGE(2). Inhibitors of COX-2 efficiently suppressed oxidative stress and
enzyme expression in the cells treated with Cum-OOH. These results suggest that COX-2-dependent oxidative metabolism is at least partially involved in Cum-OOH-induced inflammatory responses and thus
tumor promotion.