title: Silibinin prevents lung tumorigenesis in wild-type but not in iNOS-/- mice: potential of real-time micro-CT in lung cancer chemoprevention studies.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
authors.affiliation: Department of Pharmaceutical Sciences, University of Colorado Cancer Center, University of Colorado Denver, Aurora, Colorado, USA.
authors.forename: Kumaraguruparan
authors.initials: K
authors.lastname: Ramasamy
authors.forename: Lori D
authors.initials: LD
authors.lastname: Dwyer-Nield
authors.forename: Natalie J
authors.initials: NJ
authors.lastname: Serkova
authors.forename: Kendra M
authors.initials: KM
authors.lastname: Hasebroock
authors.forename: Alpna
authors.initials: A
authors.lastname: Tyagi
authors.forename: Komal
authors.initials: K
authors.lastname: Raina
authors.forename: Rana P
authors.initials: RP
authors.lastname: Singh
authors.forename: Alvin M
authors.initials: AM
authors.lastname: Malkinson
authors.forename: Rajesh
authors.initials: R
authors.lastname: Agarwal
mesh_terms: D000818:Animals; D016588:Anticarcinogenic Agents / Q000008:administration & dosage*; D049109:Cell Proliferation / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D017353:Gene Deletion; D007381:Intermediate Filament Proteins / Q000378:metabolism; D008168:Lung / Q000473:pathology; D008175:Lung Neoplasms / Q000139:chemically induced / Q000000981:diagnostic imaging / Q000473:pathology / Q000517:prevention & control*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D016328:NF-kappa B / Q000378:metabolism; D009389:Neovascularization, Pathologic / Q000517:prevention & control; D009419:Nerve Tissue Proteins / Q000378:metabolism; D064231:Nestin; D052247:Nitric Oxide Synthase Type II / Q000235:genetics* / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism; D000077385:Silybin; D012838:Silymarin / Q000008:administration & dosage*; D047368:Tumor Burden / Q000187:drug effects; D014520:Urethane; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism; D055114:X-Ray Microtomography
chemical_list: D016588:Anticarcinogenic Agents; D007381:Intermediate Filament Proteins; D016328:NF-kappa B; D009419:Nerve Tissue Proteins; C577485:Nes protein, mouse; D064231:Nestin; D050796:STAT3 Transcription Factor; D012838:Silymarin; C494087:Stat3 protein, mouse; D014520:Urethane; D000077385:Silybin; D052247:Nitric Oxide Synthase Type II; D040301:Vascular Endothelial Growth Factor Receptor-2