Silibinin triggers apoptotic signaling pathways and autophagic survival response in human colon adenocarcinoma cells and their derived metastatic cells

Apoptosis. 2011 Oct;16(10):1042-53. doi: 10.1007/s10495-011-0631-z.

Abstract

Silibinin, a flavonolignan isolated from the milk thistle plant (Silybum marianum), possesses anti-neoplastic properties. In vitro and in vivo studies have recently shown that silibinin inhibits the growth of colorectal cancer (CRC). The present study investigates the mechanisms of silibinin-induced cell death using an in vitro model of human colon cancer progression, consisting of primary tumor cells (SW480) and their derived metastatic cells (SW620) isolated from a metastasis of the same patient. Silibinin induced apoptotic cell death evidenced by DNA fragmentation and activation of caspase-3 in both cell lines. Silibinin enhanced the expression (protein and mRNA) of TNF-related apoptosis-inducing ligand (TRAIL) death receptors (DR4/DR5) at the cell surface in SW480 cells, and induced their expression in TRAIL-resistant SW620 cells normally not expressing DR4/DR5. Caspase-8 and -10 were activated demonstrating the involvement of the extrinsic apoptotic pathway in silibinin-treated SW480 and SW620 cells. The protein Bid was cleaved in SW480 cells indicating a cross-talk between extrinsic and intrinsic apoptotic pathway. We demonstrated that silibinin activated also the intrinsic apoptotic pathway in both cell lines, including the perturbation of the mitochondrial membrane potential, the release of cytochrome c into the cytosol and the activation of caspase-9. Simultaneously to apoptosis, silibinin triggered an autophagic response. The inhibition of autophagy with a specific inhibitor enhanced cell death, suggesting a cytoprotective function for autophagy in silibinin-treated cells. Taken together, our data show that silibinin initiated in SW480 and SW620 cells an autophagic-mediated survival response overwhelmed by the activation of both the extrinsic and intrinsic apoptotic pathways.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenocarcinoma / pathology
  • Adenocarcinoma / secondary
  • Amino Acid Chloromethyl Ketones / pharmacology
  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects*
  • Autophagy / drug effects*
  • BH3 Interacting Domain Death Agonist Protein / metabolism
  • Caspase 10 / metabolism
  • Caspase 3 / metabolism
  • Caspase 8 / metabolism
  • Caspase Inhibitors
  • Cell Line, Tumor
  • Colonic Neoplasms / pathology*
  • Humans
  • Macrolides / pharmacology
  • Oligopeptides / pharmacology
  • Receptors, TNF-Related Apoptosis-Inducing Ligand / biosynthesis
  • Signal Transduction / drug effects
  • Silybin
  • Silymarin / pharmacology*
  • TNF-Related Apoptosis-Inducing Ligand / metabolism
  • Up-Regulation

Substances

  • Amino Acid Chloromethyl Ketones
  • Antineoplastic Agents
  • BH3 Interacting Domain Death Agonist Protein
  • Caspase Inhibitors
  • Macrolides
  • Oligopeptides
  • Receptors, TNF-Related Apoptosis-Inducing Ligand
  • Silymarin
  • TNF-Related Apoptosis-Inducing Ligand
  • benzyloxycarbonyl-isoleucyl-glutamyl-threonyl-aspartic acid fluoromethyl ketone
  • benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone
  • Silybin
  • bafilomycin A1
  • Caspase 10
  • Caspase 3
  • Caspase 8