An <i>ent</i>-Kaurane Diterpenoid from <i>Croton tonkinensis</i> 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.Key words hepatocellular carcinoma; AMP-activated protein kinase; ent-kaurane diterpenoid Hepatocellular carcinoma (HCC) is the most common type of liver cancer with high mortality and causes 662000 deaths worldwide each year. To date, HCC has a life-threatening and unsatisfactory prognosis. Once the diagnosis is confirmed, most patients are already at the advanced stage and have lost the opportunity for surgical intervention. Further characterization of underlying molecular mechanisms in HCC would bring new insights into HCC research and clinical treatment.

A Metabolic Inhibitory Cocktail for Grave Cancers: Metformin, Pioglitazone and Lithium Combination in Treatment of Pancreatic Cancer and Glioblastoma Multiforme

“…The anticancer efficacy of the ent-kaurane diterpenoid ent-18-acetoxy-7b-hydroxy kaur-15-oxo-16-ene (CrT1) derived from the medicinal plant Croton tonkinensis was studied (Sul et al 2013). It was questioned whether CrT1 acts via AMPK.…”

“…CrT1 triggered sub-G1 arrest and caspasemediated apoptosis. CrT1 induced caspase-3, caspase-7, caspase-8, caspase-9 and PARP cleavage, which was hindered by z-VAD-fmk blocking caspase-3 cleavage (Sul et al 2013). CrT1 enhanced p53 and Bax, but decreased Bcl-2 levels and elevated leakage of Cytochrome-C from mitochondria into the cytoplasm.…”

“…CrT1 enhanced p53 and Bax, but decreased Bcl-2 levels and elevated leakage of Cytochrome-C from mitochondria into the cytoplasm. It was shown that CrT1-induced AMPK blocked the mTOR/(p70)S6K pathway (Sul et al 2013). The actions of nilotinib on hepatocellular carcinoma (HCC) were investigated (Yu et al 2013).…”

New avenues for the synthesis of ent-kaurene diterpenoids

“…In 2013, Song and coworkers reported ent-kaurene derivatives as novel AMPK activators. 39 The activation of AMPK in human hepatocellular carcinoma SK-HEP1 cells was found to be responsible for the anti-cancer activity leading to apoptosis induced by these entkaurene diterpenoids. …”

Jaridonin, a Novel Ent-Kaurene Diterpenoid from Isodon rubescens, Inducing Apoptosis via Production of Reactive Oxygen Species in Esophageal Cancer Cells

“…However, the underlying mechanism by which ent-kaurane diterpernoids inhibit cancer cell growth remains controversial. Multiple pathways, including telomerase [13], DNA binding and cleavage [14, 15], p53 [16, 17], phosphatidylinositol 3-kinases (PI3K)/ protein kinase B (AKT) [18, 19], epidermal growth factor receptor (EGFR) signaling [20], AMP-activated protein kinase [21] and nuclear factor-kappa B (NF-κB) [22, 23], have been implicated in anti-cancer activities of this class of diterpenoids.…”