Pancreatic cancer is the fourth leading cause of cancer in the western world, with average five year survival rates largely unchanged over the past thirty years. Current therapeutic regimens remain essentially ineffective at prolonging life, demonstrating the need for new treatment modalities. T-oligos, 16-mer DNA oligonucleotides with sequence homology to human telomere termini, have demonstrated cytostatic or cytotoxic effects in multiple types of cancer, including breast cancer, melanoma, glioma, and B-cell lymphoma. The current mechanistic model for T-oligo actions suggests the up-regulation of a DNA-damage-like response involving the activation of DNA damage response proteins, including histone H2A.X, ATM, and Chk2. Coincident with this pathway activation, p53 is stabilized with subsequent up-regulation of p21, thereby initiating cell cycle arrest and senescence or apoptosis. Interestingly, however, p53-deficient cancer cell lines also undergo cytotoxic effects, although the mechanism is poorly understood. Because of its overall effectiveness as a cytotoxic agent in cancer cells, we wished to examine the ability of T-oligos to induce these cytotoxic effects in pancreatic cancer cells. Using a new guanosine-rich 16-mer T-oligo analogue, termed GT-oligo, we observed an apoptotic response in pancreatic cancer cell line at concentrations less than half that required by the best prior T-oligo. After twenty-four hours of exposure, immunoblot analysis revealed the phosphorylation, and therefore activation, of Histone H2A.X, ATM, and Chk2, demonstrating the up-regulation of a DNA-damage-like response. We also observed a G1/S phase cell cycle arrest, indicated by an abrupt decrease in cells incorporating bromodeoxyuridine, as well as an increase in the percentage of cells containing G1/S phase levels of DNA, as gauged by propidium iodide staining. Previous research on the mechanisms of T-oligo cytotoxicity has focused primarily on the earliest DNA-damage signaling responses. Thus, signaling mediators required for the cell cycle arrest induced by T-oligo have not been identified. Our work demonstrates that in pancreatic cancer cells, cdk2 (the activity of which is largely responsible for initiating the G1 to S phase transition in eukaryotic cells) is phosphorylated on tyrosine 14 and threonine 15 residues by hour twenty-four, and thus inactivated. Down-regulation of cdk2 in these cells produces the same G1/S phase arrest as induced by the T-oligo. Studies are currently ongoing to determine the functional requirement of cdk2 in the signaling mechanisms leading to GT-oligo induced cell cycle arrest in pancreatic cancer cells.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4610.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO

American Association for Cancer Research
2009