Effect of silibinin on the growth and progression of primary lung tumors in mice.
BACKGROUND
Silibinin, a flavanone from milk thistle, inhibits the growth of tumors in several rodent models. We examined the effects of dietary silibinin on the growth, progression, and angiogenesis of urethane-induced lung tumors in mice.


METHODS
A/J mice (15 per group) were injected with urethane (1 mg/g body weight) or saline alone and fed normal diets for 2 weeks, after which they were fed diets containing different doses of silibinin (0%-1% [wt/wt] silibinin) for 18 or 27 weeks. Immunohistochemistry and Western blot analysis were used to examine angiogenesis and enzymatic markers of inflammation, proliferation, and apoptosis. All statistical tests were two-sided.


RESULTS
Urethane-injected mice exposed to silibinin had statistically significantly lower lung tumor multiplicities than urethane-injected mice fed the control diet lacking silibinin (i.e., control mice). Mice that received urethane and 1% (wt/wt) dietary silibinin for 18 weeks had 93% fewer large (i.e., 1.5-2.5-mm-diameter) lung tumors than control mice (mean number of tumors/mouse: 27 in the urethane group versus 2 in the urethane + 1% silibinin group, difference = 25 tumors/mouse, 95% confidence interval [CI] = 13 to 37 tumors/mouse, P = .005). Lung tumors of silibinin-fed mice had 41%-74% fewer cells positive for the cell proliferation markers proliferating cell nuclear antigen and cyclin D1 than lung tumors of control mice. Tumor microvessel density was reduced by up to 89% with silibinin treatment (e.g., 56 microvessels/400x field in tumors from control mice versus 6 microvessels/400x field in tumors from urethane + 1% silibinin-treated mice [difference = 50 microvessels/400x field, 95% CI = 46 to 54 microvessels/400x field; P<.001]). Silibinin decreased lung tumor expression of vascular endothelial growth factor (VEGF) and of inducible nitric oxide synthase and cyclooxygenase-2, two enzymes that promote lung tumor growth and progression by inducing VEGF expression.


CONCLUSIONS
Silibinin inhibits lung tumor angiogenesis in an animal model and merits investigation as a chemopreventive agent for suppressing lung cancer progression.
Singh
Rana P
RP
4200 E. 9th Ave., Box C238, Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado Cancer Center, Denver, CO 80262, USA.
Deep
Gagan
G
Chittezhath
Manesh
M
Kaur
Manjinder
M
Dwyer-Nield
Lori D
LD
Malkinson
Alvin M
AM
Agarwal
Rajesh
R
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D014408:Biomarkers, Tumor / Q000378:metabolism*; D015153:Blotting, Western; D002273:Carcinogens; D049109:Cell Proliferation / Q000187:drug effects; D019938:Cyclin D1 / Q000187:drug effects; D051546:Cyclooxygenase 2 / Q000187:drug effects; D004195:Disease Models, Animal; D016222:Fibroblast Growth Factor 2 / Q000187:drug effects; D007150:Immunohistochemistry; D007249:Inflammation / Q000188:drug therapy; D008175:Lung Neoplasms / Q000098:blood supply / Q000139:chemically induced / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008833:Microcirculation / Q000187:drug effects; D009389:Neovascularization, Pathologic / Q000188:drug therapy; D052247:Nitric Oxide Synthase Type II / Q000187:drug effects; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000187:drug effects; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D000077385:Silybin; D012838:Silymarin / Q000494:pharmacology; D014520:Urethane; D042461:Vascular Endothelial Growth Factor A / Q000187:drug effects
D000970:Antineoplastic Agents; D014408:Biomarkers, Tumor; D002273:Carcinogens; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D018809:Proliferating Cell Nuclear Antigen; D012838:Silymarin; D042461:Vascular Endothelial Growth Factor A; D016222:Fibroblast Growth Factor 2; D019938:Cyclin D1; D014520:Urethane; D000077385:Silybin; D052247:Nitric Oxide Synthase Type II; D051546:Cyclooxygenase 2