EBNA1 inhibitors have potent and selective antitumor activity in xenograft models of Epstein–Barr virus-associated gastric cancer

Background and aims Epstein–Barr virus (EBV)-associated gastric carcinoma (EBVaGC) is the most common EBV-associated cancer and accounts for ~ 10% of all gastric cancers (GC). Epstein–Barr virus nuclear antigen 1 (EBNA1), which is critical for the replication and maintenance of the EBV latent genome, is consistently expressed in all EBVaGC tumors. We previously developed small molecule inhibitors of EBNA1. In this study, we investigated the efficacy and selectivity of an EBNA1 inhibitor in cell-based and animal xenograft models of EBV-positive and EBV-negative gastric carcinoma. Methods We tested the potency of an EBNA1 inhibitor, VK-1727, in vitro and in xenograft studies, using EBV-positive (SNU719 and YCCEL1) and EBV-negative (AGS and MKN74) GC cell lines. After treatment, we analyzed cell viability, proliferation, and RNA expression of EBV genes by RT-qPCR. Results Treatment with VK-1727 selectively inhibits cell cycle progression and proliferation in vitro. In animal studies, treatment with an EBNA1 inhibitor resulted in a significant dose-dependent decrease in tumor growth in EBVaGC xenograft models, but not in EBV-negative GC xenograft studies. Gene expression analysis revealed that short term treatment in cell culture tended towards viral gene activation, while long-term treatment in animal xenografts showed a significant decrease in viral gene expression. Conclusions EBNA1 inhibitors are potent and selective inhibitors of cell growth in tissue culture and animal models of EBV-positive GC. Long-term treatment with EBNA1 inhibitors may lead to loss of EBV in mouse xenografts. These results suggest that pharmacological targeting of EBNA1 may be an effective strategy to treat patients with EBVaGC.