Chemoprevention of oral cancer in hamster cheek pouch by topical application of lyophilized black raspberries

B7

Introduction and Purpose: Oral cancers represent 2.3% of US cancers and account for a sixth of the worldwide cancer burden. Oral cancer is directly linked to tobacco exposure and has a poor prognosis. 5- and 10-year survival rates are 59% and 48%, respectively, and have not changed dramatically over the past three decades. 20%-40% of patients will develop a locoregional recurrence or a second primary tumor. Since current treatments are relatively ineffective for long-term survival, it appears germane to develop and evaluate novel strategies for prevention of secondary tumors and inhibition of primary tumor development.. An animal model that mimics the major characteristics of human oral cancer is the hamster cheek pouch (HCP); a model has been used to evaluate chemoprevention by natural and synthetic food products. In the current study, we examined the ability of topically applied LBR to inhibit the progression of established premalignant lesions into malignant oral cancer. This method of administration mimics a delivery system that is amenable to humans for prevention of primary tumors or recurrence.
 >Methods: Lyophilized black raspberries (LBR) were suspended to a 10% concentration in a 1:1 mixture of saliva substitute and 2% methylcellulose. Premalignant lesions were established by application of 0.2% 7,12-dimethylbenz(a)anthracene (DMBA) in DMSO to both HCPs for 6 weeks at which time premalignant lesions were present. One cheek pouch of each hamster was treated topically with 0.1 ml of LBR suspension, 3x per week, for six weeks; the contralateral pouch of the same animal was treated with 0.1 ml of the vehicle. Animals were sacrificed and examined at 12 weeks to determine the effect of berries on tumor incidence and multiplicity. To evaluate the effect of LBR on early premalignant oral lesions, treated and control cheek pouches containing carcinogen-induced lesions were harvested at 0, 2, 4, 7, 10, and 14 days after berry administration. mRNA was isolated from HCP and relative expression of cancer-relevant genes was determined using real-time PCR.
 >Results: Treatment of hamsters with the carcinogen or berries did not affect weight gain or food consumption. LBR administration inhibited tumor formation by 37% and 42% in separate animal experiments using the same lot of berries. After 7 days of LBR treatment of HCP, Bax, Ccnb2, Cdk2na(p13-ARF), Cdk2na(p16), and p53 showed increasing expression, whereas Cdk2 and Bcl2, showed decreasing expression; the expression of c-myc and Vegf remained constant.
 >Conclusions: These experiments provide evidence of prevention of oral cancer by a natural food product under conditions that mimic those present in former tobacco users and an assessment of the ability to modulate gene expression and inhibit oral cancer development when given in a delivery mode that is suitable for administration to the human oral mucosa.
 >Acknowledgements. Grant support: Prevent Cancer Foundation and OSU Comprehensive Cancer Center, MCC Program.
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