Carcinogenesis Advance Access published online on October 4, 2007
Carcinogenesis, doi:10.1093/carcin/bgm218
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Silibinin suppresses in vivo growth of human prostate carcinoma PC-3 tumor xenograft
1 Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado at Denver and Health Sciences Center, Denver, Colorado 80262
2 Cancer Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India
3 Lady Davis Institute for Medical Research, Jewish General Hospital and Department of Oncology, McGill University, Montreal, Quebec, Canada
4 University of Colorado Cancer Center, University of Colorado at Denver and Health Sciences Center, Denver, Colorado 80262, USA
* To whom correspondence should be addressed. Phone: (303)-315-1381; Fax: (303)-315-6281; E-mail: Rajesh.Agarwal{at}uchsc.edu
Chemoprevention is an upcoming approach to control cancer including prostate cancer (PCa). Here, we studied the efficacy and associated mechanisms of a chemopreventive agent silibinin against ectopically growing and established advanced human prostate carcinoma PC-3 tumor xenografts in athymic nude mice. Dietary silibinin (0.5%, w/w) did not show any adverse health effect in mice. In first protocol, silibinin started one week prior to xenograft implantation and continued for 60 additional days whereas in the second protocol silibinin treatment was started after 25 days of established tumors for 4, 8 and 16 days. Silibinin inhibited tumor growth rate in both protocols showing upto 35% (P=0.010) and 18-56% (P=0.002 to <0.001) decrease in tumor volume/mouse, and 27% (P<0.01) and 44% (P=0.014) decrease in tumor weight/mouse, respectively. In first protocol, silibinin decreased (P<0.001) tumor cell proliferation and microvessel density but increased (P<0.001) apoptosis. An increase in insulin-like growth factor binding protein-3 (IGFBP-3) expression with a concomitant decrease in vascular endothelial growth factor (VEGF) expression was noted. Silibinin strongly increased phospho-ERK1/2 (extracellular signal-regulated kinase), Cip1/p21 and Kip1/p27 (cyclin-dependent kinase inhibitors) levels but moderately decreased Bcl-2 and survivin levels. In established tumors, similar biomarkers and molecular changes were observed due to silibinin corresponding to its antitumor efficacy. These findings identified in vivo antitumor efficacy of silibinin against PC-3 human PCa in both intervention protocols accompanied with its antiproliferative, proapoptotic and antiangiogenic activities. At molecular level, silibinin increased IGFBP-3, Cip1/p21, Kip1/p27 levels and ERK1/2 activation, and decreased Bcl-2, survivin and VEGF levels in tumors.
Key Words: Prostate cancer • silibinin • ERK1/2 • IGFBP-3 • Cip1/p21
Received July 18, 2007; revised September 17, 2007; accepted September 24, 2007.
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