Phosphorylated Akt/PKB controls cell growth and apoptosis in intraductal papillary-mucinous tumor and invasive ductal adenocarcinoma of the pancreas

CEACAM6 gene silencing impairs anoikis resistance and in vivo metastatic ability of pancreatic adenocarcinoma cells

Anoikis is the apoptotic response induced in normal cells by inadequate or inappropriate adhesion to substrate. It is postulated that resistance to anoikis facilitates tumorigenesis and metastasis. Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) is an immunoglobulin superfamily member overexpressed in a number of human cancers and implicated in anoikis resistance. We tested the effect of CEACAM6 gene silencing on anoikis in pancreatic adenocarcinoma cell lines. Anoikis was induced in PANC1, Capan2, MiaPaCa2 and Mia(AR) (a MiaPaCa2-derived anoikis-resistant subline) by culture in poly-2-hydroxyethylmethacrylate-coated wells. Anoikis was quantified by YO-PRO-1/propidium iodide staining and flow cytometry. The role of caspase activation was determined using fluorometric profiling and the caspase inhibitor Z-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-fmk). CEACAM6 expression was suppressed by RNA interference. Using a nude mouse orthotopic xenograft model, we assessed the effect of this treatment on in vivo metastatic ability. Anoikis resistance was associated with increased CEACAM6 expression. CEACAM6-specific short interfering ribonucleic acid (siRNA), but not control siRNA, increased susceptibility to caspase-mediated anoikis, an effect abrogated by Z-VAD-fmk, and decreased Akt phosphorylation (Ser-473) under anchorage-independent conditions. CEACAM6 gene silencing reversed the acquired anoikis resistance of Mia(AR) and inhibited its in vivo metastatic ability. CEACAM6 warrants further investigation as a novel therapeutic target for the treatment of pancreatic adenocarcinoma.

Antiproliferative effect of octreotide on gastric cancer cells mediated by inhibition of Akt/PKB and telomerase

AIM: To investigate the antiproliferative effect of octreotide, a long-acting analogue of somatostatin, on gastric cancer cell line SGC7901 and its possible molecular mechanisms.

METHODS: Gastric cancer cell line SGC7901 employed in the study was treated with 0.008, 0.04, 0.2, 1, 5 and 25 μg·mL^-1 of octreotide respectively for 24 h to evaluate the antiproliferative effect of somatostatin analog on the tumor cells by MTT assay method. To elucidate the underlying mechanism, the cells were exposed to 1 μg·mL^-1 of octreotide for 0, 12, 24 and 48 h, when their Akt/PKB and telomerase activities were respectively determined using PCR-ELSIA and nonradioactive protein kinase assay protocols. The same experimental procedures were also performed in the control cells that were treated with corresponding vehicles instead of somatostatin analog.

RESULTS: After exposed to octreotide for 24 h at the concentrations of more than 1 μg·mL^-1, SGC7901 cells exhibited a dose-dependent inhibition of growth with the inhibiting rate to be as high as 34.66% when 25 μg·mL^-1 of octreotide was applied. The Akt/PKB and telomerase activity of SGC7901 cells was significantly inhibited when the cells were exposed to 1 μg·mL^-1 of octreotide for 12, 24 and 48 h compared with that of their control counterparts (P < 0.01), both of which exhibited in a time-dependent manner.

CONCLUSION: The antiproliferative effect of octreotide on SGC7901 cells might be mediated by the inhibition of Akt/PKB and telomerase.