Chemoprevention of oral cancer by lyophilized strawberries

Abstract

Background/aim: Oral cancer represents approximately 2.5% of all cancers in the United States, with five- and 10-year survival rates of 62% and 51%. In the present study, lyophilized strawberries (LS) were evaluated for their potential to inhibit tumorigenesis in the hamster cheek pouch (HCP) model of oral cancer and for their ability to modify expression of several genes relevant to oral cancer development.

Materials and methods: HCPs were painted three times a week for six weeks with 0.2% 7,12-dimethylbenz(a)anthracene (DMBA). Hamsters were given 5% or 10% LS in their diet prior to, during, and after, or only after carcinogen treatment. Animals were sacrificed 12 weeks from the beginning of DMBA treatment and the number of total lesions and tumors was determined.

Results: A significant difference (p<0.01-0.04) in the number of tumors was found between the LS-treated groups and the carcinogen controls. Histological examination of HCPs revealed a significant reduction in mild and severe dysplasia following 12 weeks of treatment with LS. Molecular analysis revealed that genes related to tumor development were modulated by LS.

Conclusion: These experiments support previous studies in HCP that demonstrated a chemopreventive activity by black raspberries and show, to our knowledge for the first time, that strawberries can inhibit tumor formation in an animal model of oral cancer.

Keywords: Chemoprevention; hamster cheek pouch; oral cancer; strawberries.

Figure 1

Changes in gene expression in dysplastic hamster cheek pouchs (HCP) after six weeks of post-initiation treatment with 5% lyophilized strawberries (LS). Analyses were performed on cheek pouches from hamsters treated with 7,12-dimethylbenz(a)anthracene (DMBA) alone, DMBA plus 5% LS post-initiation, and cheek pouches from untreated controls. Quantitative reverse transcription polymerase chain reactions (RT-qPCR) were run in triplicate using 10 TaqMan Gene Expression assays (nine target genes and one endogenous reference gene) for each cheek pouch with Actb as the reference gene. There was a significant increase (**, p-value <0.001) in expression of p13^Arf, p16, and Trp53 (tumor-suppressor genes) and Bcl2 (anti-apoptosis gene) in cheek pouches of hamsters treated with DMBA when contrasted to untreated control HCP. After treatment of cheek pouches for six weeks with 5% LS pellets, there was a significant reduction in expression of p16 and p13^Arf and a significant increase in expression of Trp53 and Bcl2 (*, p-value <0.05) when compared to DMBA treatment only. Cyclin B2 (Ccnb2) mRNA expression was non-significantly increased by DMBA treatment and was reduced slightly in expression after LS treatment.

Figure 2. Hamster cheek pouch histopathology

Hematoxylin and eosin stained sections of hamster cheek pouch 12 weeks after commencement of DMBA treatment. A, normal epithelium; B, mild dysplasia with adjacent area of hyperplasia; C, severe dysplasia; D, carcinoma in-situ (×200).