205 Targeting Homologous Repair to Overcome Genotoxic Therapy Resistance in Pancreatic Cancer

Abstract

OBJECTIVES/GOALS: Pancreatic ductal adenocarcinoma (PDAC) is a relatively radioresistant disease, and inhibition of DNA homologous recombination (HR) repair in combination with radiation therapy (RT) is a potentially attractive strategy to overcome radioresistance. We have found that the expression of the HR protein RAD18 is upregulated in PDAC cells. METHODS/STUDY POPULATION: Standard clonogenic assays, γH2aX foci staining, HR-GFP reporter assay, and western blot analysis of DNA damage response proteins were performed in MIA-PaCa2 (MP2) and PANC-1 cells following knockdown of RAD18 in cells via short hairpin RNA (shRNA). Drug targeting of RAD18 was achieved through the use of a USP-7 inhibitor, P5091. Cells with or without stable knockdown of RAD18 were implanted orthotopically in the pancreas of athymic nude mice and treated with sham radiation or radiation to a dose of 20 Gy in 5 daily fractions once tumors reached 100-150 mm3. RESULTS/ANTICIPATED RESULTS: Stable knockdown of RAD18 in MP2 and PANC-1 resulted in decreased radiation clonogenic survival in vitro (dose enhancement factor (DEF)=1.52 and 1.51, respectively), decreased DNA repair after radiation as measured by the increased number of γH2aX nuclear foci assay at 6, 12, and 24 hours (all p<0.05), decreased HR activation following DNA damage via an HR-GFP reporter assay (p=0.039), and increased tumor growth delay following radiation in vivo (p<0.001). P5091 treatment of both MP2 and PANC-1 resulted in efficient knockdown of RAD18, which was confirmed through western blotting, qRT-PCR, and luciferase reporter assays. P5091 increased radiosensitization, yH2aX nuclear foci remained elevated at 12 and 24 hours (p<0.05), and HR repair was also reduced (p=0.014). DISCUSSION/SIGNIFICANCE: Herein, we show the HR repair protein RAD18, and that modulation of RAD18 expression correlates with in vitro and in vivo radiosensitization through altered HR-mediated DNA repair. USP7 inhibition successfully reduced RAD18 expression and resulted in enhanced radiosensitization.