Silibinin prevents lung tumorigenesis in wild-type but not in iNOS-/- mice: potential of real-time micro-CT in lung cancer chemoprevention studies

Clin Cancer Res. 2011 Feb 15;17(4):753-61. doi: 10.1158/1078-0432.CCR-10-2290. Epub 2010 Dec 10.


Purpose: Sustained nitric oxide (NO) generation positively correlates with lung cancer development and progression. Herein, we genetically confirmed this role of iNOS and evaluated the chemopreventive efficacy of silibinin in carcinogen-treated B6/129 wild-type (WT) and iNOS(-/-) mice.

Experimental design: Male B6/129-Nos2(tm1Lau) (iNOS(-/-)) and B6/129PF2 WT mice were injected i.p. with 1 mg/g body weight urethane once weekly for 7 consecutive weeks, followed by silibinin gavage (742 mg/kg body weight) for 5 d/wk for 18 weeks.

Results: Quantification of micro-CT data in real-time showed that silibinin significantly decreases urethane-induced tumor number and size in WT mice, consistent with measurements made ex vivo at study termination. Genetic ablation of iNOS decreased urethane-induced tumor multiplicity by 87% (P < 0.001) compared to WT mice. Silibinin decreased tumor multiplicity by 71% (P < 0.01) in WT mice, but did not show any such considerable effect in iNOS(-/-) mice. Tumors from WT mice expressed more iNOS (P < 0.01) but almost similar eNOS and nNOS than those in silibinin-treated mice. In these tumors, silibinin moderately (P < 0.01) inhibited cell proliferation but strongly (P < 0.01) reduced the number of newly formed nestin-positive microvessels. Silibinin decreased VEGFR2 level, and STAT3 and NF-κB activation in tumors.

Conclusions: The lack of effect of silibinin in iNOS(-/-) mice suggests that silibinin exerts most of its chemopreventive and angiopreventive effects through its inhibition of iNOS expression in lung tumors. Our results support iNOS as a potential target for controlling lung cancer, and demonstrate the value of real-time noninvasive micro-CT imaging modality for evaluating the efficacy of lung cancer chemopreventive agents.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Anticarcinogenic Agents / administration & dosage*
  • Cell Proliferation / drug effects
  • Down-Regulation / drug effects
  • Gene Deletion
  • Intermediate Filament Proteins / metabolism
  • Lung / pathology
  • Lung Neoplasms / chemically induced
  • Lung Neoplasms / diagnostic imaging
  • Lung Neoplasms / pathology
  • Lung Neoplasms / prevention & control*
  • Male
  • Mice
  • Mice, Knockout
  • NF-kappa B / metabolism
  • Neovascularization, Pathologic / prevention & control
  • Nerve Tissue Proteins / metabolism
  • Nestin
  • Nitric Oxide Synthase Type II / genetics*
  • Nitric Oxide Synthase Type II / metabolism
  • STAT3 Transcription Factor / metabolism
  • Silybin
  • Silymarin / administration & dosage*
  • Tumor Burden / drug effects
  • Urethane
  • Vascular Endothelial Growth Factor Receptor-2 / metabolism
  • X-Ray Microtomography


  • Anticarcinogenic Agents
  • Intermediate Filament Proteins
  • NF-kappa B
  • Nerve Tissue Proteins
  • Nes protein, mouse
  • Nestin
  • STAT3 Transcription Factor
  • Silymarin
  • Stat3 protein, mouse
  • Urethane
  • Silybin
  • Nitric Oxide Synthase Type II
  • Vascular Endothelial Growth Factor Receptor-2