Telomerase is required for the unlimited lifespan of cancer cells. Pancreatic cancers are almost always positive for telomerase activity and inhibiting telomerase in these cells could limit their lifespan. In this project, we have characterized the biology of telomeres in a panel of 11 pancreatic cancer cell lines and have examined the effects of GRN163L (Imetelstat), a potent telomerase inhibitor, on these cells. GRN163L inhibited telomerase in all 11 pancreatic cancer cell lines, with IC50 ranging from 50 nM to 200 nM. Continuous exposure of AsPC-1, CAPAN1 and CD18 cells to 1 μM GRN163L resulted in telomere shortening, induction of crisis, and loss of the cultures. Crisis In these cells was accompanied by activation of a DNA damage response (γ-H2AX) and evidence of both senescence (SA-β-galactosidase) and apoptosis (Floating cells, sub-G1 DNA content, PARP1 cleavage). In L3.6 cells, continuous GRN163L exposure led to the emergence of a GRN163L-resistant sub-population of cells. Over the last year, these cells have been expanded at successively higher concentrations of GRN163L and are still dividing in the presence of 10 μM GRN163L. To shorten telomeres and limit the lifespan of these cells, an alternate approach was to use inhibitors of poly(ADP-ribose)polymerases (PARP) to block the parsylation of TRF1 and TRF2, thereby enhancing the telomerase-inhibitory activity of the Shelterin complex. Our results show that combining GRN163L with the general PARP inhibitor 3-aminobenzamide (3AB) was sufficient to shorten telomeres and limit the lifespan of the GRN163L-L3.6 resistant cells. These experiments were then repeated in the parental L3.6 cells to determine if 3AB could be used to block the development of GRN163L-resistance. Whereas 3AB alone was not sufficient to induce crisis, 3AB did synergize with GRN163L to accelerate the timing of crisis and block the emergence of GRN163L resistant cells. These results raise the possibility that inhibitors of poly(ADP-ribose)polymerases could be exploited in the clinic to accelerate the effects of anti-telomerase therapies.

Citation Format: Katrina M. Burchett, Michel M. Ouellette. Inhibitors of telomerase and of poly(ADP-Ribose)polymerases synergize to limit the lifespan of pancreatic cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 704. doi:10.1158/1538-7445.AM2013-704