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

Abstract

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 V 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.

Chemopreventive effects of silymarin and silibinin on N-butyl-N-(4-hydroxybutyl) nitrosamine–induced urinary bladder carcinogenesis in male ICR mice

“…Survivin is a member of a class of inhibitors of apoptosis and seems to block apoptosis by interfering with the caspase activation pathway. Our studies have shown that silibinin down-regulates the expression of survivin in human bladder transitional-cell papilloma RT4 cells in vitro (10) and in tumor xenograft (30). In the present study, survivin was significantly less expressed in normal bladder urothelium but highly expressed in OH-BBNinduced bladder urothelium with different stages of carcinogenesis, which was strongly decreased by silymarin or silibinin treatment.…”

Molecular Mechanisms of Silibinin-Mediated Cancer Chemoprevention with Major Emphasis on Prostate Cancer

“…Likewise, silibinin-fed SCID mice injected with SN12K1 cells exhibited a reduction in tumor size (54). Consistent with these results, several studies have shown that silibinin inhibits growth as well as induces apoptosis in several urinary bladder cancer cell lines which were associated with an increase in p53 expression, downregulation of survivin, cyclin D1, ERK1/2 phosphorylation and nuclear phospho-p65, cleavage of caspases, PARP, and Cip1/p21, and mitochondrial release of cytochrome c, Omi/HtrA2, and apoptosis-inducing factor (55)(56)(57)(58)(59)(60). This silibinin-mediated inhibition was also observed in rat models of urinary bladder cancer reducing lesions (60).…”

Chemopreventive and Chemotherapeutic Effects of Intravesical Silibinin against Bladder Cancer by Acting on Mitochondria

“…1A). Accumulating evidence indicates that silibinin has anticancer activity in various tumor cells, including cancers of prostate (5)(6)(7)(8)(9), breast (10,11), skin (12), colon (13), lung (14), kidney (15,16), and bladder (17)(18)(19)(20). There is increasing interest in elucidating the mechanisms of action for silibinin as an effective agent for chemoprevention and chemotherapy against various types of cancers.…”

“…RT4 (a well-differentiated papillary noninvasive tumor phenotype) cells (17,19,20). In addition, oral administration of silibinin has been reported to prevent N-butyl-N-(4-hydroxybutyl)nitrosamine (OH-BBN)-induced mouse bladder carcinogenesis (28), suggesting a value of silibinin in bladder cancer prevention and therapy.…”