A natural ent­kaurane diterpenoid induces antiproliferation in ovarian cancer cells via ERK1/2 regulation and inhibition of cellular migration and invasion.

Ovarian cancer is one of the most common causes of female mortalities from gynecological tumors. An ent­kaurane diterpenoid compound CRT1 (ent­18­acetoxy­7ß­hydroxy kaur­15­oxo­16­ene), mainly isolated from the Vietnamese herb Croton tonkinesis has been used in folk medicine in Vietnam for cancer treatment. However, the effect of this compound on human ovarian cancer cells has not yet been reported. The objective of the present study was to determine the effect of CRT1 on the cell viability, apoptosis and metastasis of SKOV3 human ovarian cancer cells using a Cell Counting Kit­8 assay, flow cytometric analysis of Annexin V­fluorescein isothiocyanate/propidium iodide staining, western blot analysis, soft agar colony forming assay, wound healing assay and Matrigel invasion assay. The results revealed that CRT1 possessed significant anti­proliferative effects on SKOV3 cells. CRT1 treatment at 25 and 50 µM induced apoptosis, enhanced the percentage of Annexin V­positive cells, increased the expression of pro­apoptotic protein B­cell lymphoma 2 (Bcl­2)­associated X protein, cytochrome c release from the mitochondria to the cytosol, cleaved caspase­3, caspase­7, caspase­9, and poly (adenosine diphosphate­ribose) polymerase. However, it decreased the expression of Bcl­2 in a dose­dependent manner. The percentage of necrotic cells increased following CRT1 treatment at <10 µM. CRT1 at 50 µM significantly induced the phosphorylation of extracellular signal­regulated kinase (ERK). Growth inhibition and the apoptotic effects of CRT1 could be reversed by PD98059, an ERK inhibitor. Additionally, CRT1 inhibited cell migration and invasion via ERK1/2 activation in SKOV3 cells. These results indicated that CRT1, an ent­kaurane diterpenoid, may be a potential inhibitor of ovarian cancer by the activating ERK1/2/p90 ribosomal S6 kinase signaling pathway.

Fatty acid synthase inhibition by amentoflavone suppresses HER2/neu (erbB2) oncogene in SKBR3 human breast cancer cells.

Fatty acid synthase (FASN) is a potential therapeutic target for treatment of cancer and obesity, and is highly elevated in 30% of HER2-overexpressing breast cancers. Considerable interest has developed in searching for novel FASN inhibitors as therapeutic agents in treatment of HER2-overexpressing breast cancers. Amentoflavone was found to be effective in suppressing FASN expression in HER2-positive SKBR3 cells. Pharmacological inhibition of FASN by amentoflavone specifically down-regulated HER2 protein and mRNA, and caused an up-regulation of PEA3, a transcriptional repressor of HER2. In addition, pharmacological blockade of FASN by amentoflavone preferentially decreased cell viability and induced cell death in SKBR3 cells. Palmitate reduced the cytotoxic effect of amentoflavone, as the percentage of viable cells was increased after the addition of exogenous palmitate. Amentoflavone-induced FASN inhibition inhibited the translocation of SREBP-1 in SKBR3 cells. Amentoflavone inhibited phosphorylation of AKT, mTOR, and JNK. The use of pharmacological inhibitors revealed that the modulation of AKT, mTOR, and JNK phosphorylation required synergistic amentoflavone-induced FASN inhibition and HER2 activation in SKBR3 cells. These results suggest that amentoflavone modulated FASN expression by regulation of HER2-pathways, and induced cell death to enhance chemopreventive or chemotherapeutic activity in HER2-positive breast cancers.

Magnolol-induced apoptosis in HCT-116 colon cancer cells is associated with the AMP-activated protein kinase signaling pathway.

Colon cancer is the third most common malignancy around the world. Surgery, chemotherapy, and radiotherapy are generally used to treat colon cancer, but no effective therapy for advanced colon carcinoma is available. Therefore, there is a need to identify other therapeutic agents against this disease. Magnolol, a hydroxylated biphenyl compound present in Magnolia officinalis, exerts anticancer potential and low toxicity. Emerging evidence has suggested that activation of AMP-activated protein kinase (AMPK), a potential cancer therapeutic target is involved in apoptosis in colon cancer cells. However, the effects of magnolol on human colon cancer through activation of AMPK remain unexplored. In this study, we explored whether magnolol exerts an antiproliferative effect, and induces apoptosis in HCT-116 human colon cancer cells. Magnolol displayed several apoptotic features, including propidium iodide labeling, DNA fragmentation, and caspase-3 and poly(ADP-ribose) polymerase cleavages. We showed that magnolol induced the phosphorylation of AMPK in dose- and time-dependent manners. The selective AMPK inhibitor compound C abrogated the effect of magnolol on AMPK activation, suppression of proliferation, and caspase-3 cleavage. Magnolol downregulated expression of the antiapoptotic protein Bcl2, upregulated expression of pro-apoptotic protein p53 and Bax, and caused the release of mitochondrial cytochrome c. Magnolol-induced p53 and Bcl2 expression was abolished in the presence of compound C. Magnolol inhibited migration and invasion of HCT-116 cells through AMPK activation. These findings demonstrate that AMPK mediates the anticancer effects of magnolol through apoptosis in HCT-116 cells.

Chrysophanic acid blocks proliferation of colon cancer cells by inhibiting EGFR/mTOR pathway.

Inactivation of epidermal growth factor receptor (EGFR) is a prime method used in colon cancer therapy. Here it is shown that chrysophanic acid, a natural anthraquinone, has anticancer activity in EGFR-overexpressing SNU-C5 human colon cancer cells. Chrysophanic acid preferentially blocked proliferation in SNU-C5 cells but not in other cell lines (HT7, HT29, KM12C, SW480, HCT116 and SNU-C4) with low levels of EGFR expression. Chrysophanic acid treatment in SNU-C5 cells inhibited EGF-induced phosphorylation of EGFR and suppressed activation of downstream signaling molecules, such as AKT, extracellular signal-regulated kinase (ERK) and the mammalian target of rapamycin (mTOR)/ribosomal protein S6 kinase (p70S6K). Chrysophanic acid (80 and 120 µm) significantly blocked cell proliferation when combined with the mTOR inhibitor, rapamycin. These findings offer the first evidence of anticancer activity for chrysophanic acid via EGFR/mTOR mediated signaling transduction pathway.

Activation of AMP-activated protein kinase on human gastric cancer cells by apoptosis induced by corosolic acid isolated from Weigela subsessilis.

Corosolic acid is one of the triterpenoids present in the leaves of Weigela subsessilis. The antidiabetic activity of corosolic acid has been reported previously, but to date, the anticancer effects on gastric cancer have been poorly studied. In this study, corosolic acid showed growth inhibition on SNU-601 human gastric cancer cells, with an IC50 value of 16.9 ± 2.9 µM. Corosolic acid also triggered the activation of caspase-3 and poly (ADP-ribose) polymerase, while it was recovered by Z-VAD-FMK. Moreover, the cell growth/apoptosis activities of corosolic acid were regulated by the AMP-activated protein kinase-mammalian target of rapamycin (AMPK-mTOR) signals. These results showed that corosolic acid-mediated AMPK activation leads to inhibition of mTOR, thus providing a possible mechanism of action of corosolic acid in the inhibition of cancer cell growth and the induction of apoptosis.

Down-regulation of human epidermal growth factor receptor 2/neu oncogene by corosolic acid induces cell cycle arrest and apoptosis in NCI-N87 human gastric cancer cells.

Overexpression/amplification of human epidermal growth factor receptor (HER)2/neu (erbB-2) oncogene plays a causal role in carcinogenesis and correlates with a poor clinical prognosis. However, little is known about HER2 in gastric cancer. In this study, we explored the pharmacological activities of natural triterpenoid corosolic acid (CRA) in HER2 signaling and its role in gastric cancer development and progression. In this study, CRA dramatically inhibited HER2 expression in a dose- and time-dependent manner, effectively inhibited cell proliferation, and induced G(0)/G(1) arrest through the induction of p27(kip1) and cyclin D(1) down-regulation. CRA exposure enhanced apoptotic cell death, as confirmed by caspase-3 and poly (ADP-ribose) polymerase cleavage activities. CRA inhibited signaling pathways downstream of HER2, including phospho-proteins such as Akt and Erk. In addition, CRA combined with adriamycin and 5-fluorouracil enhanced this growth inhibition, but not with docetaxel and paclitaxel. These findings demonstrate that CRA suppresses HER2 expression, which in turn promotes cell cycle arrest and apoptotic cell death of gastric cancer cells, providing a rationale for future clinical trials of CRA in the treatment of HER2-positive gastric cancers.

Fatty acid synthase inhibition by amentoflavone induces apoptosis and antiproliferation in human breast cancer cells.

Fatty acid synthase (FASN) is highly expressed in breast carcinomas to support their continuous growth and proliferation, but has low expression level in normal tissues. Considerable interest has been developed in searching for novel FASN inhibitors as a therapeutic target for breast cancer. In present study, amentoflavone was isolated from Selaginella tamariscina, a traditional oriental medicine that has been used to treat cancer for many years, and was found to significantly inhibit the in vitro enzymatic activity of FASN at concentrations above 50 microM. Amentoflavone was also found to decrease fatty acid synthesis by the reduction of [(3)H]acetyl-CoA incorporation into lipids in FASN-overexpressed SK-BR-3 human breast cancer cells. Furthermore, this study showed that amentoflavone, at a concentration greater than 75 microM, increased the cleavage-activity of caspase-3 and poly (ADP-ribose) polymerase (PARP), and administration of pan-caspase inhibitor Z-VAD-FMK completely rescued the SK-BR-3 cells from PARP cleavages. The sequential internucleosomal DNA fragmentation in SK-BR-3 cells was observed at a concentration of 100 microM. A decrease in breast cancer cell growth was observed in SK-BR-3 cells at 12 and 24 h post treatment with 100 microM of amentoflavone, followed by a dramatic suppression after 48 h. The inhibition of cancer-growth by amentoflavone was dose-dependent, showing a slight reduction at 50 microM and significant reduction at concentrations of 75 and 100 microM. FASN-nonexpressed NIH-3T3 normal cell growth was not decreased by amentoflavone-treatment, both in time- and dose-dependent manners. These data provide evidence that amentoflavone isolated from S. tamariscina induced breast cancer apoptosis through blockade of fatty acid synthesis.