Alkaloids from <i>Stephania venosa</i> as Chemo-Sensitizers in SKOV3 Ovarian Cancer Cells <i>via</i> Akt/NF-κB Signaling

Abstract

Crebanine (CN), tetrahydropalmatine (THP), O-methylbulbocapnine (OMBC) and N-methyl tetrahydropalmatine (NMTHP) are isoquinoline derived natural alkaloids isolated from tubers of Stephania venosa.We investigated chemo-sensitizing effects of these alkaloids in ovarian cancer cells and evaluated underlying molecular mechanisms involved in chemo-sensitivity. Detection of cell apoptosis was evaluated by using flow cytometry. Cell viability was analyzed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Chou-Talalay median effect principle was used to evaluate potential drug interactions. Protein analyses were performed on ovarian carcinoma cells using Western blotting upon treatment with anticancer drug and alkaloids. Aporphine alkaloids, such as CN and OMBC, enhanced cisplatin sensitivity in intrinsic cisplatin resistant SKOV3 cells, but not in cisplatin sensitive A2780 cells. Protoberberine alkaloids, such as THP and NMTHP, had no synergistic effect on cisplatin sensitivity in either cell line. Chemo-sensitizing effects of CN and OMBC in SKOV3 cells were mediated via activating apoptosis-induced cell death through caspase-3, -8 and cleaved poly ADP-ribose polymerase (PARP) and via inhibiting anti-apopotic and survival protein expression, such as Bcl-xL, Baculoviral IAP repeat-containing protein 3 (cIAP-2), survivin and interleukin (IL) -6. Cisplatin stimulated protein kinase B (Akt) and nuclear factor-kappaB (NF-κB) signaling pathways, but not mitogen-activated protein kinase (MAPK), activator protein 1 (AP-1) and signal transducer and activator of transcription 3 (STAT3) in SKOV3 cells. Akt/NF-κB signaling was blocked by CN and OMBC leading to increased sensitization to cisplatin. These findings demonstrate that CN and OMBC sensitizes SKOV3 cells to cisplatin via inhibition of Akt/NF-κB signaling and the down regulation of NF-κB mediated gene products. Our results suggest that alkaloids obtained from S. venosa could be used as chemosensitizers in ovarian cancer to sensitize and minimize the dose related toxicity of platinum-based chemotherapeutic drugs.Key words ovarian cancer; aporphine; cisplatin sensitivity; apoptosis; chemo-sensitizer Although platinum based chemotherapy is an effective treatment option for ovarian cancer patients, platinum drug resistance and the associated side effects are major limitations of the current therapeutic concepts. Cellular resistance to platinum can arise from various mechanisms related to decreased drug influx, increased DNA adduct repair, detoxification of platinum by intracellular thiols such as glutathione, alterations in intracellular signaling pathways and an increased efflux of drugs.1,2) Exposure to cisplatin induces several cellular responses with consequent changes in growth regulation. Recent data suggest that the mitogen activated protein (MAP) kinase pathway, 3) the signal transducer and activator of transcription (STAT) pathway 4) and the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway 5) get activated in response t...

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