Abstract 1315: Combination of Wee1 inhibition with targeted and standard chemotherapy in preclinical models of pancreatic ductal adenocarcinoma

Abstract Introduction: Pancreatic ductal adenocarcinoma (PDA) is the fourth leading cause of cancer death and has a 5-year survival rate of less than 7%. The poor prognosis associated with PDA is related in part to a lack of screening tests to promote early detection and ineffective systemic targeted therapies. Adavosertib (AZD1775, MK1775) is a selective Wee1 inhibitor with promising preclinical activity in PDA and synergy with cytotoxic chemotherapy in other cancer types. Wee1 is a tyrosine kinase that activates in the G2M cell cycle checkpoint in response to DNA damage. Inhibition of Wee1 with adavosertib prevents the phosphorylation of CDC2, thus allowing unrepaired DNA to enter mitosis and ultimately succumb to mitotic catastrophe. The purpose of this study was to investigate adavosertib in combination with standard chemotherapy and other targeted agents in preclinical models of PDA. Methods: Athymic nude mice were implanted with PDA PDX models on the right and left flanks. When the average tumor volume reached 100-300 mm3, mice were randomized into one of the following treatments: vehicle, adavosertib, irinotecan, navitoclax, capecitabine, adavosertib + irinotecan, or adavosertib + navitoclax, adavosertib + capecitabine. Tumor volume was calculated using the following equation: volume = (length × width) × 0.52. Four pancreatic cancer cell lines were plated in 96-well plates and Cell Titer-Glo proliferation assays were performed to determine the most effective combination doses of irinotecan, 5FU, or navitoclax with adavosertib in vitro. Combination effects were analyzed using CalcuSyn software. The most effective doses within each cell line were selected and used for Caspase 3/7 apoptosis assays and cell cycle analyses by flow cytometry. Western blots were performed to evaluate changes in downstream effectors. Results: In vivo, the combination of adavosertib with either irinotecan or navitoclax resulted in decreased tumor growth compared to the respective single agents. The combination of adavosertib with irinotecan, 5FU, or navitoclax in vitro resulted in greater antiproliferative effects in all cell lines, and the several combinations were synergistic in all cell lines as determined by CI values less than 1. Navitoclax increased apoptosis in several cell lines both as a single agent and was enhanced in combination with adavosertib. Irinotecan proved to be more cell cycle dependent and significantly altered the cell cycle in all cell lines. Irinotecan increased phospho-CDC2 and decreased PHH3, while adavosertib increased gamma-H2AX as a single agent and in combination. Conclusions: The combination of adavosertib with either irinotecan, 5FU, or navitoclax in vivo decreased tumor growth and had enhanced antiproliferative effects in vitro. These data support future studies with adavosertib in combination with standard therapies or navitoclax to treat PDA. Citation Format: Sarah J. Hartman, Stacey M. Bagby, Betelehem W. Yacob, Dennis M. Simmons, Tonia E. Tse, Christopher H. Lieu, S. Lindsey Davis, Alexis D. Leal, Jennifer R. Diamond, Wells A. Messersmith, Todd M. Pitts. Combination of Wee1 inhibition with targeted and standard chemotherapy in preclinical models of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1315.