Cardiotonic steroids attenuate ERK phosphorylation and generate cell cycle arrest to block human hepatoma cell growth

J Steroid Biochem Mol Biol. 2011 Jul;125(3-5):181-91. doi: 10.1016/j.jsbmb.2010.12.016. Epub 2011 Jan 6.


Recent studies revealed the potential of Na(+)/K(+)-ATPase as a target for anticancer therapy and showed additional modes of action of cardiotonic steroids (CSs), a diverse family of naturally derived compounds, as inhibitors of Na(+)/K(+)-ATPase. The results from epidemiological studies showed significantly lower mortality rates in cancer patients receiving CSs, which sparked interest in the anticancer properties of these drugs. The present study was designed to investigate the anticancer effect of CSs (ouabain or cinobufagin) and to elucidate the molecular mechanisms of CS activity in hepatoma cell lines (HepG2 and SMMC-7721). Ouabain and cinobufagin significantly inhibited cell proliferation by attenuating the phosphorylation of extracellular regulated kinase (ERK) and down-regulating the expression of C-myc. These CSs also induced cell apoptosis by increasing the concentration of intracellular free calcium ([Ca(2+)](i)) and induced S phase cell cycle arrest by down-regulating the expression of Cyclin A, cyclin dependent kinase 2 (CDK2) and proliferating cell nuclear antigen (PCNA) as well as up-regulating the expression of cyclin dependent kinase inhibitor 1A (p21(CIP1)). Overexpression of ERK reversed the antiproliferation effect of ouabain or cinobufagin in HepG2 and SMMC-7721 cells. Currently, the first generation of CS-based anticancer drugs (UNBS1450 and Anvirzel) are in Phase I clinical trials. These data clearly support their potential use as cancer therapies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects
  • Blotting, Western
  • Bufanolides / pharmacology*
  • Calcium / metabolism
  • Carcinoma, Hepatocellular / metabolism
  • Carcinoma, Hepatocellular / pathology
  • Cell Cycle / drug effects*
  • Cell Line, Tumor
  • Cell Proliferation / drug effects*
  • Cell Survival / drug effects
  • Cyclin A / genetics
  • Cyclin A / metabolism
  • Cyclin-Dependent Kinase 2 / genetics
  • Cyclin-Dependent Kinase 2 / metabolism
  • Cyclin-Dependent Kinase Inhibitor p21 / genetics
  • Cyclin-Dependent Kinase Inhibitor p21 / metabolism
  • Extracellular Signal-Regulated MAP Kinases / metabolism*
  • Hep G2 Cells
  • Humans
  • Microscopy, Confocal
  • Ouabain / pharmacology*
  • Phosphorylation / drug effects*
  • Proliferating Cell Nuclear Antigen / genetics
  • Proliferating Cell Nuclear Antigen / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction


  • Bufanolides
  • Cyclin A
  • Cyclin-Dependent Kinase Inhibitor p21
  • Proliferating Cell Nuclear Antigen
  • Ouabain
  • CDK2 protein, human
  • Cyclin-Dependent Kinase 2
  • Extracellular Signal-Regulated MAP Kinases
  • Calcium
  • cinobufagin