Pro/antioxidant Status in Murine Skin Following Topical Exposure to Cumene Hydroperoxide Throughout the Ontogeny of Skin Cancer

A. A. Shvedova^1,2*, E. R. Kisin¹, A. Murray², C. Kommineni¹, V. Vallyathan¹, and V. Castranova^1,2

¹Pathology and Physiology Research Branch, National Institute for Occupational Safety and Health, 1095 Willowdale Road, m/s 2015, Morgantown, West Virginia, USA; fax: (304) 285-5938; E-mail: ats1@cdc.gov

²Physiology and Pharmacology Department, West Virginia University, Morgantown, WV, USA

^* To whom correspondence should be addressed.

Received April 30, 2003

---

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 µmol) 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 PGE₂. 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.

---

KEY WORDS: cumene hydroperoxide, 12-O-tetradecanoylphorbol-13-acetate, oxidative stress, tumor promotion, skin

---