Abstract 2964: AZD7762-mediated gemcitabine sensitization does not require G2-M checkpoint abrogation in pancreatic cancer cells

Chk1 inhibition is a promising approach to sensitize pancreatic cancer to gemcitabine (Gem), the current standard therapy for both local control and metastatic disease. One hallmark and proposed biomarker of Chk1 inhibition is abrogation of the DNA damage-induced G2-M checkpoint and aberrant mitotic entry. It is unclear, however, whether this effect is necessary for chemosensitization. In this study, we tested the hypothesis that G2-M checkpoint abrogation is required for Gem sensitization in cells treated with the Chk inhibitor AZD7762. We first evaluated the ability of AZD7762 to abrogate the G2-M checkpoint in 6 pancreatic cancer cell lines. While AZD7762 sensitized each cell line to a moderately toxic concentration of Gem, G2-M checkpoint abrogation was only observed in 4 of the lines; AsPC1, MiaPaCa2, M-Panc96 and Panc1. Furthermore, only MiaPaCa2 and Panc1 cells underwent premature mitotic entry when treated with Gem + AZD7762. We next tested the hypothesis that G2-M checkpoint abrogation was responsible for AZD7762-mediated Gem sensitization by using the Cdk inhibitors roscovitine and purvalanol A to preserve the checkpoint in the presence of AZD7762 by directly inhibiting cyclinB-cdk1 and mitotic entry. While both Cdk inhibitors blocked mitosis in cells treated with Gem + AZD7762, the effects on chemosensitization varied. Only in AsPC1 and Panc1 cells did roscovitine prevent both G2-M checkpoint abrogation and Gem sensitization. Furthermore, cyclin B1 siRNA prevented AZD7762-mediated G2-M checkpoint abrogation in MiaPaCa2 and Panc1 cells, but did not prevent chemosensitization, suggesting AZD7762-mediated Gem sensitization does not require G2-M checkpoint abrogation. In addition to abrogating the Gem-induced G2-M checkpoint, AZD7762 promotes S-phase progression. Initial studies suggest AZD7762 may sensitize cells to Gem by abrogating the S-phase checkpoint and permitting S-phase progression in the presence of Gem-induced DNA damage. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2964. doi:10.1158/1538-7445.AM2011-2964