Silibinin triggers apoptotic signaling pathways and autophagic survival response in human colon adenocarcinoma cells and their derived metastatic cells

Abstract

Silibinin, a flavonolignan isolated from the milk thistle plant (Silybum marianum), possesses anti-neoplastic properties. In vitro and in vivo studies have recently shown that silibinin inhibits the growth of colorectal cancer (CRC). The present study investigates the mechanisms of silibinin-induced cell death using an in vitro model of human colon cancer progression, consisting of primary tumor cells (SW480) and their derived metastatic cells (SW620) isolated from a metastasis of the same patient. Silibinin induced apoptotic cell death evidenced by DNA fragmentation and activation of caspase-3 in both cell lines. Silibinin enhanced the expression (protein and mRNA) of TNF-related apoptosis-inducing ligand (TRAIL) death receptors (DR4/DR5) at the cell surface in SW480 cells, and induced their expression in TRAIL-resistant SW620 cells normally not expressing DR4/DR5. Caspase-8 and -10 were activated demonstrating the involvement of the extrinsic apoptotic pathway in silibinin-treated SW480 and SW620 cells. The protein Bid was cleaved in SW480 cells indicating a cross-talk between extrinsic and intrinsic apoptotic pathway. We demonstrated that silibinin activated also the intrinsic apoptotic pathway in both cell lines, including the perturbation of the mitochondrial membrane potential, the release of cytochrome c into the cytosol and the activation of caspase-9. Simultaneously to apoptosis, silibinin triggered an autophagic response. The inhibition of autophagy with a specific inhibitor enhanced cell death, suggesting a cytoprotective function for autophagy in silibinin-treated cells. Taken together, our data show that silibinin initiated in SW480 and SW620 cells an autophagic-mediated survival response overwhelmed by the activation of both the extrinsic and intrinsic apoptotic pathways.

Silibilin-Induces Apoptosis in Breast Cancer Cells by Modulating p53, p21, Bak and Bcl-xl Pathways

“…Several studies showed that silibinin induced apoptosis via increased Bcl-2 family levels, and reduced antiapoptoticmolecules in different carcinoma cells models (Kauntz et al, 2011;Hagelgans et al, 2014). How silibinin induced cell death and associated signal pathway of apoptosis is not clear.…”

Milk Thistle (Silybum Marianum) as a Supportive Phytotherapeutic Agent in Oncology

“…V případě CRC in vitro zkoumání na různých liniích lidského adenokarcinomu prokázalo působení silymarinu na několika úrovních -snížení viability nádorových buněk, zastavení buněč-ného cyklu na různé úrovni dle buněčné linie [14], snížení hladiny cyklinu D1 v buňce indukcí jeho proteazomální degradace [15] a navození apoptózy vnitřní i zevní cestou, a to i u TRAIL (TNF-related apoptosis-induc ing ligand) -rezistentních mutant [16,17]. In vivo studie na potkanech zkoumaly efekt podá-vání per os silymarinu po vystavení kancerogennímu azoxymethanu, který navozuje vznik adenokarcinomu v oblasti kolon.…”

Molecular Mechanisms of Silibinin-Mediated Cancer Chemoprevention with Major Emphasis on Prostate Cancer

“…Silibinin-mediated angiogenesis inhibition was associated with decreased VEGF, cyclooxygenase (COX), hypoxiainducible factor-1α (HIF-1α), inducible nitric oxide synthase (iNOS), nitrotyrosine and nitrite levels, and an increased VEGFR-1 (Flt-1) expression (41,(43)(44)(45). Silibinin inhibited CDK8 and β-catenin signaling which inhibited SW480 tumor growth (46) and initiated an autophagic-mediated survival response in SW480 and SW620 cells (47). Silibinin also suppressed 1,2-dimethylhydrazine (DMH)-induced colon carcinogenesis in rat models via modulating xenobiotic metabolizing enzymes and increasing enzymatic antioxidants to detoxify carcinogens (48,49).…”