High levels of apurinic/apyrimidinic endonuclease/redox factor 1 (APE1/Ref-1 or Ref-1) expression have been reported in numerous cancers such that Ref-1 is an emerging target in a variety of cancer types. Ref-1 is a dual function protein with both DNA repair activity as well as redox activity. Ref-1 is responsible for the repair of baseless sites in DNA caused by alkylation and oxidative DNA damage as well as regulating several transcription factors including HIF-1a, NFkB, AP-1, and STAT3. Using siRNA to knockdown Ref-1 in pancreatic ductal adenocarcinoma (PDAC) cells (MIA-PaCa-2), we quantitated Ref-1 expression following transfection with scrambled control and Ref-1 siRNA using Indica Lab's HALO CytoNuclear software. Knockdown of greater than 85% greatly decreases the proliferation of PDAC cells, and supports Ref-1 as a target in pancreatic cancer.

To assess the efficacy of targeting Ref-1 in vivo, a small molecule Ref-1 redox inhibitor, APX3330, was used in combination therapy with a PDAC standard of care agent, Gemcitabine, in a PDAC xenograft mouse model. In this study, NSG mice were treated with: Gemcitabine (35mg/kg), APX3330 (12.5, 25, and 50mg/kg), and combinations of APX3330 and Gemcitabine (12.5, 25, and 50mg/kg), as well as a vehicle control group.

At termination of the study, tumors were harvested, tissue sections prepared, stained for H&E, and immunostained for Ki67 and CD31. Slides were then imaged via Aperio's ScanScope. Immunostains were quantitated to predict the effectiveness of the combination treatment in a PDAC in vivo model. IHC slides from treated tumors were quantified using Aperio's ImageScope software to determine the percent of cell proliferation and angiogenesis in the various treatment groups.

These preclinical studies, demonstrated additive effects of combining APX3330 with Gemcitabine to reduce pancreatic tumor volumes and cell proliferation. Significantly decreased tumor volumes in the combination treatments of APX3330 with Gemcitabine were found compared to each agent alone. All treatments, single or combination yielded tumor volumes significantly different from the vehicle control.

A statistically significant decrease in cell proliferation determined from Ki67 staining was found amongst the 12.5 and 50 mg/kg doses of APX3330, all three combination groups, and in the Gemcitabine group compared to vehicle control. There was a trend toward, yet not statistically significant, increased anti-angiogenic effects in the 12.5 and 25 mg/kg dose groups of APX3330 alone compared to all other treatment groups. This data continues to demonstrate a single agent response of pancreatic tumor cells in a preclinical model using APX3330, but more importantly, a novel combination effect when APX3330 is combined with Gemcitabine in a xenograft model, both via tumor volume and cell proliferation marker, Ki67 supporting the use of APX3330 in combination with Gemcitabine in PDAC patients.

Citation Format: Kyle C. McElyea, Max H. Jacobsen, Max Schmidt, Huiwen Cheng, Mark R. Kelley, George E. Sandusky, Melissa L. Fishel. Efficacy study of APX3330, a Ref-1 redox inhibitor, and Gemcitabine in a mouse pancreatic ductal adenocarcinoma model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5183.