title: Silibinin protects against photocarcinogenesis via modulation of cell cycle regulators, mitogen-activated protein kinases, and Akt signaling.
abstract: Here, we assessed the protective effect of silibinin on UVB-induced skin carcinogenesis in SKH-1 hairless mice. Topical application of silibinin before or immediately after UVB exposure or its dietary feeding resulted in a strong protection against photocarcinogenesis, in terms of tumor multiplicity (60-66%; P < 0.001), tumor volume per mouse (93-97%; P < 0.001) and tumor volume per tumor (80-91%; P < 0.001). Silibinin also moderately inhibited tumor incidence (5-15%; P < 0.01) and delayed tumor latency period (up to 4 weeks; P < 0.01-0.001). To investigate in vivo molecular mechanisms of silibinin efficacy, tumors and uninvolved skin from tumor-bearing mice were examined immunohistochemically for proliferation, p53, apoptosis, and activated caspase-3. Silibinin treatment showed a strong decrease (P < 0.001) in proliferating cell nuclear antigen-positive cells and an increase in p53-positive (P < 0.005-0.001), terminal deoxynucleotidyltransferase-mediated nick end labeling-positive (P < 0.005-0.001), and cleaved caspase-3-positive cells (P < 0.001). Western blot analysis of normal skin and tumor lysates showed that silibinin decreases the levels of cyclin-dependent kinase 2 and cyclin-dependent kinase 4 and associated cyclins A, E, and D1, together with an up-regulation of Cip1/p21, Kip1/p27, and p53. Silibinin also showed a strong phosphorylation of extracellular signal-regulated protein kinase 1/2, stress-activated protein kinase/c-JUN NH2-terminal kinase 1/2, and p38 mitogen-activated protein kinases but inhibited Akt phosphorylation and decreased survivin levels with an increase in cleaved caspase-3. Together, these results show a strong preventive efficacy of silibinin against photocarcinogenesis, which involves the inhibition of DNA synthesis, cell proliferation, and cell cycle progression and an induction of apoptosis. Furthermore, these results also identify in vivo molecular mechanisms of silibinin efficacy against photocarcinogenesis.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, and University of Colorado Cancer Center, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
authors.forename: Gu
authors.initials: G
authors.lastname: Mallikarjuna
authors.forename: Sivanandhan
authors.initials: S
authors.lastname: Dhanalakshmi
authors.forename: Rana P
authors.initials: RP
authors.lastname: Singh
authors.forename: Chapla
authors.initials: C
authors.lastname: Agarwal
authors.forename: Rajesh
authors.initials: R
authors.lastname: Agarwal
mesh_terms: D000284:Administration, Oral; D000287:Administration, Topical; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D001973:Bromodeoxyuridine / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism* / Q000528:radiation effects; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000528:radiation effects; D051379:Mice; D008812:Mice, Hairless; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism* / Q000528:radiation effects; D009381:Neoplasms, Radiation-Induced / Q000201:enzymology / Q000209:etiology / Q000517:prevention & control*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism* / Q000528:radiation effects; D011518:Proto-Oncogene Proteins / Q000378:metabolism* / Q000528:radiation effects; D051057:Proto-Oncogene Proteins c-akt; D000077385:Silybin; D012838:Silymarin / Q000008:administration & dosage*; D012867:Skin / Q000378:metabolism / Q000528:radiation effects; D012878:Skin Neoplasms / Q000201:enzymology / Q000209:etiology / Q000517:prevention & control*; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D014466:Ultraviolet Rays / Q000009:adverse effects*; D015854:Up-Regulation / Q000528:radiation effects
chemical_list: D018797:Cell Cycle Proteins; D011518:Proto-Oncogene Proteins; D012838:Silymarin; D016159:Tumor Suppressor Protein p53; D000077385:Silybin; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D001973:Bromodeoxyuridine