Extracts from Citrus unshiu promote immune-mediated inhibition of tumor growth in a murine renal cell carcinoma model

Aim of this study: Citrus unshiu (Satsuma mandarin, SM) is a citrus fruit the peel of which has been used as a traditional Chinese medicine to treat common cold, relieve exhaustion, and cancer. In this study, we examined how effectively the content and peel extracts of SM can suppress cancer growth. The mechanism underlying cancer-suppressing properties of SM was investigated in tumor-bearing mice with renal carcinoma cell, Renca. Materials and methods: Effectiveness of SM in tumor suppression was evaluated by measuring size of tumor mass in tumor-bearing mice treated with various doses of SM content and peel extracts. Proliferation of tumor cells and splenocytes was determined by MTT assay and [H-3]TdR uptake, respectively. Relevant immunological mechanisms were chased by assaying cytokines including TGF-beta, IL-6, IFN-gamma, and TNF-alpha by ELISA. Results: The content and peel extracts of SM inhibited the growth of tumor cells in tumor-bearing mice. Especially, average tumor volume of two groups treated with 3 and 30 mg peel extracts per mouse weight (kg) were significantly decreased to 52.32% (p<0.05) and 68.72% (p<0.01), respectively. To identify tumor regression mechanism, anti-tumor cytokines measured in Con A-activated splenocytes from tumor-bearing mice. IFN-gamma was increased in both of the peel extract-treated groups, while TNF-alpha, which had been decreased by tumor growth, was rescued to the normal level in SM content and peel extracts-treated groups. However, SM content and peel extracts did not inhibit proliferation and tumor-proliferative cytokines including TGF-beta and IL-6 production of tumor cells. Conclusion: These results indicate that SM content and peel extracts have anti-tumor properties in the tumor-bearing murine model. The mechanism underlying the anti-tumor effects of SM extracts is strongly suggested to be via boosting cytokines such as IFN-gamma and TNF-alpha, enhancing immune-mediated anti-tumor properties. (C) 2010 Elsevier Ireland Ltd. All rights reserved.