Inhibitory effect of silibinin against azoxymethane-induced colon tumorigenesis in A/J mice.
OBJECTIVE
Colorectal cancer is the second leading cause of cancer-associated deaths, which suggests that more effort is needed to prevent/control this disease. Herein, for the first time, we investigate in vivo the efficacy of silibinin against azoxymethane-induced colon tumorigenesis in A/J mice.


METHODS
Five-week-old male mice were gavaged with vehicle or silibinin (250 and 750 mg/kg) for 25 weeks starting 2 weeks before initiation with azoxymethane (pretreatment regime) or for 16 weeks starting 2 weeks after the last azoxymethane injection (posttreatment regime). The mice were then sacrificed, and colon tissues were examined for tumor multiplicity and size, and molecular markers for proliferation, apoptosis, inflammation, and angiogenesis.


RESULTS
Silibinin feeding showed a dose-dependent decrease in azoxymethane-induced colon tumorigenesis with stronger efficacy in pretreatment versus posttreatment regimen. Mechanistic studies in tissue samples showed that silibinin inhibits cell proliferation as evident by a decrease (P < 0.001) in proliferating cell nuclear antigen and cyclin D1, and increased Cip1/p21 levels. Silibinin also decreased (P < 0.001) the levels of inducible nitric oxide synthase, cyclooxygenase-2, and vascular endothelial growth factor, suggesting its anti-inflammatory and antiangiogenic potential in this model. Further, silibinin increased cleaved caspase-3 and poly(ADP-ribose) polymerase levels, indicating its apoptotic effect. In other studies, colonic mucosa and tumors expressed high levels of β-catenin, insulin-like growth factor-1 receptorβ, phospho Glycogen synthase kinase-3β, and phospho protein kinase B/pAkt proteins in azoxymethane-treated mice, which were strongly lowered (P < 0.001) by silibinin treatment. Moreover, azoxymethane reduced insulin-like growth factor binding protein-3 protein level, which was enhanced by silibinin.


CONCLUSIONS
Silibinin targets β-catenin and IGF-1Rβ pathways for its chemopreventive efficacy against azoxymethane-induced colon carcinogenesis in A/J mice. Overall, these results support the translational potential of silibinin in colorectal cancer chemoprevention.
Ravichandran
Kameswaran
K
Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado Denver, Aurora, Colorado 80045, USA.
Velmurugan
Balaiya
B
Gu
Mallikarjuna
M
Singh
Rana P
RP
Agarwal
Rajesh
R
D042501:Angiogenic Proteins / Q000378:metabolism; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D001397:Azoxymethane; D002273:Carcinogens; D002277:Carcinoma / Q000139:chemically induced* / Q000473:pathology / Q000517:prevention & control*; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000139:chemically induced* / Q000473:pathology / Q000517:prevention & control*; D019610:Cytoprotection / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004353:Drug Evaluation, Preclinical; D018836:Inflammation Mediators / Q000378:metabolism; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D000077385:Silybin; D012838:Silymarin / Q000494:pharmacology* / Q000627:therapeutic use
D042501:Angiogenic Proteins; D000970:Antineoplastic Agents; D000975:Antioxidants; D002273:Carcinogens; D018836:Inflammation Mediators; D012838:Silymarin; D000077385:Silybin; D001397:Azoxymethane
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