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Oral Silibinin Inhibits In vivo Human Bladder Tumor Xenograft Growth Involving Down-Regulation of Survivin

Authors' Affiliations: ¹ Department of Pharmaceutical Sciences, School of Pharmacy, and ² University of Colorado Cancer Center, University of Colorado at Denver and Health Sciences Center, Denver, Colorado and ³ Cancer Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India

Requests for reprints: Rajesh Agarwal, Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado at Denver and Health Sciences Center, 4200 East 9th Avenue, Box C238, Denver, CO 80262. Phone: 303-315-1381; Fax: 303-315-6281; E-mail: Rajesh.Agarwal{at}uchsc.edu.

Purpose: Chemoprevention is an upcoming approach to control bladder cancer, which is one of the commonly diagnosed malignancies showing recurrence rate of 70% or even higher. Recently, we observed the in vitro efficacy of silibinin, a flavanolignan, in human bladder transitional cell papilloma RT4 cells. Here, we investigated the antitumor efficacy and associated mechanisms of silibinin in RT4 tumor xenograft.

Experimental Design: RT4 tumor xenograft was implanted s.c. in athymic nude mice, and then animals were oral gavaged with silibinin at 100 and 200 mg/kg doses, 5 days/week for 12 weeks. Tumor growth, body weight, and diet consumption were recorded, and tumors were analyzed for proliferation, apoptosis, and angiogenesis biomarkers and molecular alterations by immunohistochemistry, immunoblot analysis, and ELISA. p53 small interfering RNA was used in cell culture to examine the role of p53 in survivin expression.

Results: Silibinin feeding inhibited tumor xenograft growth without any gross signs of toxicity. Silibinin decreased tumor volume by 51% to 58% (P 0.01) and tumor weight by 44% to 49% (P < 0.05). Silibinin moderately (P < 0.001) decreased cell proliferation and microvessel density and strongly (P < 0.001) increased apoptosis in tumors. Silibinin robustly decreased survivin protein expression and its nuclear localization, as well as tumor-secreted level in mouse plasma, but increased p53 and cleaved caspase-3 levels in tumors. Silibinin-caused decrease in survivin was independent of p53.

Conclusion: These findings identified in vivo antitumor efficacy of silibinin against human bladder tumor cells involving down-regulation of survivin and an increase in p53 expression together with enhanced apoptosis.

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