Author(s): Cheung CW, Vesey DA, Nicol DL, Johnson DW
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Abstract OBJECTIVE: To investigate whether silibinin, a flavonoid antioxidant with anticancer properties that inhibits cellular growth via the up-regulation of insulin-like growth factor binding protein 3 (IGFBP-3), inhibits renal cell carcinoma (RCC) growth via the IGFBP-3 pathway. MATERIALS AND METHODS: Cell morphology, DNA synthesis by thymidine incorporation, viability assessed by 3,4,5 dimethylthiazol-2,5 diphenyl tetrazolium bromide (MTT) assays, trypan blue exclusion, and lactate dehydrogenase (LDH) release, apoptosis and IGFBP-3 protein (Western blotting) were evaluated in silibinin-treated SN12K1 cells (a cell line derived from metastatic RCC) in the presence or absence of IGFBP-3 immunoneutralization. RESULTS: Silibinin suppressed SN12K1 DNA synthesis at 24 and 48 h incubation by a mean (SD) of at least 68 (10)\% of the control values at > or =2 micromol/L (P < 0.05). At high concentrations (>80 micromol/L) cell viability was compromised, as shown by decreased MTT uptake of 62 (10)\% of control values (P < 0.001), reduced cell counts of > or =77 (9)\% of control values (P < 0.05), elevated LDH release of 212 (49)\% of control (P < 0.001), and the presence of necrotic and apoptotic cells on immunofluorescence staining. Removing endogenous IGFBP-3 by neutralizing with anti-IGFBP-3 antibody increased DNA synthesis by 240 (35)\% of control for 24 h, (P < 0.001). However, on Western blot analysis of IGFBP-3 levels in conditioned media incubated in the presence of silibinin there was down-regulation of protein expression. CONCLUSION: Silibinin suppresses SN12K1 cell growth and, at high doses, increases cell death. These effects are independent of IGFBP-3.
This article was published in BJU Int
and referenced in Journal of Cancer Science & Therapy