Silibinin inhibits renal cell carcinoma via mechanisms that are independent of insulin-like growth factor-binding protein 3.
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.


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.


CONCLUSIONS
Silibinin suppresses SN12K1 cell growth and, at high doses, increases cell death. These effects are independent of IGFBP-3.
Cheung
Catherine W
CW
Department of Medicine, The University of Queensland, Brisbane, Australia.
Vesey
David A
DA
Nicol
David L
DL
Johnson
David W
DW
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D000975:Antioxidants / Q000494:pharmacology*; D015153:Blotting, Western; D002292:Carcinoma, Renal Cell / Q000188:drug therapy*; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D007680:Kidney Neoplasms / Q000188:drug therapy*; D000077385:Silybin; D012838:Silymarin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
D000972:Antineoplastic Agents, Phytogenic; D000975:Antioxidants; D018972:Insulin-Like Growth Factor Binding Protein 3; D012838:Silymarin; D000077385:Silybin