Growth inhibition and regression of lung tumors by silibinin: modulation of angiogenesis by macrophage-associated cytokines and nuclear factor-kappaB and signal transducers and activators of transcription 3.
The latency period for lung tumor progression offers a window of opportunity for therapeutic intervention. Herein, we studied the effect of oral silibinin (742 mg/kg body weight, 5 d/wk for 10 weeks) on the growth and progression of established lung adenocarcinomas in A/J mice. Silibinin strongly decreased both tumor number and tumor size, an antitumor effect that correlates with reduced antiangiogenic activity. Silibinin reduced microvessel size (50%, P < 0.01) with no change in the number of tumor microvessels and reduced (by 30%, P < 0.05) the formation of nestin-positive microvessels in tumors. Analysis of several proteins involved in new blood vessel formation showed that silibinin decreased the tumor expression of interleukin-13 (47%) and tumor necrosis factor-alpha (47%), and increased tissue inhibitor of metalloproteinase-1 (2-fold) and tissue inhibitor of metalloproteinase-2 (7-fold) expression, without significant changes in vascular endothelial growth factor levels. Hypoxia- inducible factor-1 alpha expression and nuclear localization were also decreased by silibinin treatment. Cytokines secreted by tumor cells and tumor-associated macrophages regulate angiogenesis by activating nuclear factor-kappaB (NF-kappaB) and signal transducers and activators of transcription (STAT). Silibinin decreased the phosphorylation of p65NF-kappaB (ser276, 38%; P < 0.01) and STAT-3 (ser727, 16%; P < 0.01) in tumor cells and decreased the lung macrophage population. Angiopoietin-2 (Ang-2) and Ang-receptor tyrosine kinase (Tie-2) expression were increased by silibinin. Therapeutic efficacy of silibinin in lung tumor growth inhibition and regression by antiangiogenic mechanisms seem to be mediated by decreased tumor-associated macrophages and cytokines, inhibition of hypoxia-inducible factor-1 alpha, NF-kappaB, and STAT-3 activation, and up-regulation of the angiogenic inhibitors, Ang-2 and Tie-2.
Tyagi
Alpna
A
Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado Denver, Denver, CO 80262, USA.
Singh
Rana P
RP
Ramasamy
Kumaraguruparan
K
Raina
Komal
K
Redente
Elizabeth F
EF
Dwyer-Nield
Lori D
LD
Radcliffe
Richard A
RA
Malkinson
Alvin M
AM
Agarwal
Rajesh
R
D000230:Adenocarcinoma / Q000188:drug therapy* / Q000276:immunology / Q000378:metabolism; D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D016207:Cytokines / Q000187:drug effects / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D015151:Immunoblotting; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000276:immunology / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects / Q000276:immunology; D008297:Male; D051379:Mice; D055806:Microvessels / Q000187:drug effects; D016328:NF-kappa B / Q000187:drug effects / Q000276:immunology; D009389:Neovascularization, Pathologic / Q000188:drug therapy* / Q000276:immunology; D050796:STAT3 Transcription Factor / Q000187:drug effects / Q000276:immunology; D015398:Signal Transduction / Q000187:drug effects; D000077385:Silybin; D012838:Silymarin / Q000494:pharmacology
D020533:Angiogenesis Inhibitors; D016207:Cytokines; D016328:NF-kappa B; D050796:STAT3 Transcription Factor; D012838:Silymarin; C494087:Stat3 protein, mouse; D000077385:Silybin