Prevention of UV-Induced Carcinogenesis by Cyanidin-3-glucoside

Chemoprevention has emerged as a potentially viable approach to reduce skin cancer in high risk individuals. Many naturally occurring substances present in the human diet have been identified as potential chemopreventive agents (1-4). Investigations using animal models and epidemiological studies indicate that consumption of phytochemicals (compounds derived from plants, such as fruits and vegetables) might reduce the incidence of cancers and other chronic diseases (5-9). Constituents and micronutrients in vegetables and fruits include phytochemicals, vitamins, and minerals, all of which have been found to exhibit both complementary and overlapping mechanisms of chemopreventive activities in multistage carcinogenesis (1 0). A recent study demonstrated that topical applications of plant-derived chemicals, slJch as (-)-epigallocatechin gallate (EGCG) from green tea and silibinin from milk thistle plant inhibited carcinogenesis and selectively increased apoptosis in UV-treated mouse skin (11,12). Skin cancer is the most common human cancer (13-19). UVB (280-320 nm) is the major carcinogenic component of sunlight for human skin cancer (13-18) and reactive oxygen species (ROS) are considered to be involved in the mechanism of UVB-induced carcinogenesis (20-22). Previous studies indicate that various berry antocyanins possess a broad spectrum of therapeutic properties (23,24). Our laboratories have shown that blackberry extracts inhibit AP-1 and cell transformation by perturbing the mitogenic signaling pathway (25). We isolated cyanidin-3-glucoside (C3G) from blackberries according to the method described previously (26). This compound is a member of the anthocyanin family, the largest group of pigments present in many berries, dark grapes, cabbages and other pigmented foods (24). In our preliminary study, we have shown that pretreatment of cells with C3G inhibited UVB-and TPA-induced activation of NF-KB, MAPK, and AP-1 and expression of bothcyclooxygenase-2 (COX-2) and tumor necrosis factor a (TNFa). C3G exhibited a potent antioxidant activity, stronger than ascorbate, scavenged UVB-induced generation of reactive oxygen species (ROS). C3G also diminished TPA-induced neoplastic transformation in JB6 cells. C3G treatment decreased the incident of nonmalignant and malignant skin tumors per mouse induced by 12-0-tetradecanolyphorbol-13-acetate (TPA) in 7, 12-dimethylbenz(a)anthracene (DMBA)-initiated mouse skin. A large number of studies suggest that TNF is a candidate linking molecule between inflammation and cancer (27-30). COX-2 expression may be induced by a wide range of stimuli, including LPS and TNF, as well as growth factors such as EGF (31,32). The products of the COX-2 enzyme are prostaglandins, which include PGE2, are key inflammation mediators (33,34-36). Therefore, TNF-a might not be just a major inflammatory mediator, it might also be a major mediator that links chronic inflammation to cancer development. The overall hypothesis of this application is that C3G functions as an antioxidant and inhibits oxidative stress, activation of transcription factors, and inflammat9.!)' signaling proteins, leading to protection against UVB-induced carcinogenesis. Four Specific Aims are proposed.~