title: An ent-kaurane diterpenoid from Croton tonkinensis induces apoptosis by regulating AMP-activated protein kinase in SK-HEP1 human hepatocellular carcinoma cells.
abstract: Hepatocellular carcinoma (HCC) is the most common type of liver cancer with high mortality worldwide. Traditional chemotherapy for HCC is not widely accepted by clinical practitioners because of its toxic side effects. Thus, there is a need to identify chemotherapeutic drugs against HCC. AMP-activated protein kinase (AMPK) is a biologic sensor for cellular energy status that acts a tumor suppressor and a potential cancer therapeutic target. The traditional Vietnamese medicinal plant Croton tonkinensis shows cytotoxicity in various cancer cells; however, its anticancer mechanism remains unclear. In this study, we determined whether the ent-kaurane diterpenoid ent-18-acetoxy-7β-hydroxy kaur-15-oxo-16-ene (CrT1) isolated from this plant plays a role as a chemotherapeutic drug targeting AMPK. CrT1 blocked proliferation in dose- and time-dependent manners in human hepatocellular carcinoma SK-HEP1 cells. CrT1 induced sub-G(1) arrest and caspase-dependent apoptosis. CrT1 activated caspase-3, -7, -8, -9, and poly(ADP-ribose) polymerase, and its effect was inhibited by z-VAD-fmk suppressing caspase-3 cleavage. CrT1 induced increases in p53 and Bax levels but decreased Bcl(2) levels. In addition, CrT1 resulted in increased translocation of cytochrome c into the cytoplasm. We showed that CrT1-activated AMPK activation was followed by modulating the mammalian target of rapamycin/p70S6K pathway and was inactivated by treating cells with compound C. Treatment with CrT1 and aminoimidazole carboxamide ribonucleotide (AICAR) synergistically activated AMPK. CrT1-induced AMPK activation regulated cell viability and apoptosis. These results suggest that CrT1 is a novel AMPK activator and that AMPK activation in SK-HEP1 cells is responsible for CrT1-induced anticancer activity including apoptosis.
authors.affiliation: Surgical Oncology Research Lab., Chungnam National University Hospital, Daejeon 301–721, Republic of Korea.
authors.forename: Young Hoon
authors.initials: YH
authors.lastname: Sul
authors.forename: Myung Sun
authors.initials: MS
authors.lastname: Lee
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Cha
authors.forename: Phuong Thien
authors.initials: PT
authors.lastname: Thuong
authors.forename: Nguyen Minh
authors.initials: NM
authors.lastname: Khoi
authors.forename: In Sang
authors.initials: IS
authors.lastname: Song
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D029802:Croton; D045786:Diterpenes, Kaurane / Q000494:pharmacology*; D006801:Humans; D018515:Plant Leaves
chemical_list: D000970:Antineoplastic Agents; D045786:Diterpenes, Kaurane; D055372:AMP-Activated Protein Kinases