Pancreatic cancer is a devastating disease with very poor prognosis and few treatment options. The Notch pathway has been implicated in the development of pancreatic cancer, and in particular both Notch2 and Notch3 are known to be important in this disease. In this report, we examined the in vivo efficacy of an antibody that was initially identified by binding to Notch2 and was subsequently shown to block signaling of both human and mouse Notch2 and Notch3. Utilizing a panel of minimally-passaged, patient-derived, pancreatic adenocarcinoma xenograft tumors, we performed in vivo growth inhibition and tumorigenicity studies with the Notch2/3 antibody alone or combined with the standard-of-care chemotherapeutic gemcitabine. We demonstrated that the Notch2/3 antibody was active as a single agent, and when combined with gemcitabine, the combination therapy resulted in improved efficacy over that of gemcitabine alone. Utilizing an in vivo limiting dilution tumorigenicity assay, we found that the cancer stem cell (CSC) frequency was increased by gemcitabine as a single agent, but significantly decreased by the combination of anti-Notch2/3 and gemcitabine. Analysis of cell surface markers associated with pancreatic cancer stem cells indicated that gemcitabine treatment results in an increase in the percentage of CSCs, while the Notch2/3 antibody significantly reduced the CSC population. Utilizing this pancreatic cancer xenograft model, we analyzed the ability of the Notch 2/3 antibody to delay tumor recurrence following gemcitabine induced tumor regression. While gemcitabine-treated tumors re-grew rapidly following treatment termination, the ability of tumors to recur was significantly delayed by the Notch2/3 antibody suggesting that the delay in tumor recurrence is in part due to the Notch2/3 antibody-mediated decrease in CSC frequency. Gene set enrichment analysis in tumors that responded to anti-Notch2/3 revealed that various stem cell gene sets were up-regulated in tumors treated by gemcitabine alone, but down-regulated by the combination of anti-Notch2/3 and gemcitabine. Findings from this study suggest that antagonists of Notch signaling may act as chemotherapeutic-sensitizing agents by interfering with CSC self renewal pathways and thereby enhancing the cytotoxic effects of chemotherapy on CSCs.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1014. doi:1538-7445.AM2012-1014