Abstract 707: MK1775-mediated gemcitabine sensitization correlates with prolonged DNA damage signaling in S-phase cells.

Abstract

Abstract Pancreatic cancer remains among the most lethal cancers with an overall 5-year survival of <5%. Wee1 inhibition has emerged as a potential approach to sensitize pancreatic cancer to gemcitabine (Gem), the current standard therapy for both local control and metastatic disease. In this study, we first characterized the ability of MK1775, a small molecule Wee1 inhibitor now entering Phase II clinical trials, to sensitize pancreatic cancer cells to Gem. Using a clonogenic survival assay, we tested the effects of MK1775 in a panel of pancreatic cancer cells and found MK1775-mediated Gem sensitization ranged from 80-fold in MiaPaCa2 cells to 12-fold in Panc1 cells. This sensitization was associated with aberrant mitotic entry in MiaPaCa2 and Panc1 cells, but not in the other cells lines tested. In addition, MK1775 potentiated and prolonged Gem-induced DNA damage signaling (γ-H2AX) as determined by 2-parameter flow cytometry. For example, 48 h post-Gem, 35±12% of BxPC3 cells remain γ-H2AX-positive compared to 76±3.7% of cells treated with Gem + MK1775. Using immunofluorescent staining, we further determined that Wee1 inhibition with MK1775 qualitatively changed Gem-induced γ-H2AX nuclear foci to high intensity pan-nuclear γ-H2AX pan-staining. Finally, we tested the ability of the CDK inhibitor roscovitine (Ros) to attenuate MK1775-mediated chemosensitization. Ros not only prevented aberrant mitotic entry in MiaPaCa2 and Panc1 cells, but in each cell line sensitized to Gem by MK1775, Ros inhibited both high-intensity γ-H2AX staining after treatment with Gem + MK1775 and chemosensitization. These results suggest the effects of MK1775 on DNA repair in S-phase cells may be more important for Gem chemosensitization than the effects of MK1775 on the G2-M checkpoint. Citation Format: Leslie A. Parsels, Joshua D. Parsels, Meredith A. Morgan, Theodore S. Lawrence, Jonathan Maybaum. MK1775-mediated gemcitabine sensitization correlates with prolonged DNA damage signaling in S-phase 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 707. doi:10.1158/1538-7445.AM2013-707