Induction of lytic cycle of Epstein-Barr virus by a novel organic compound through activation of the c-Jun N-terminal kinase pathway

Abstract

The reactivation of lytic cycle of Epstein-Barr Virus (EBV) is an important component of the emerging lytic induction therapy to specifically target the virus in EBV-associated malignancies. The potency of the lytic induction is central to the effectiveness of the lytic induction therapy. It is hampered by cancer cells that are refractory to lytic induction. This study aims to elucidate novel pathways involved in inducing EBV lytic cycle in epithelial cancer cells using a small organic compound, E11 intermediate (E11.1), and develop new drug combinations to overcome the refractoriness of the cancer cells to lytic induction. E11.1 was found to be the active component in the original E11 compound which has a superior lytic induction capability in both gastric carcinoma (GC) and nasopharyngeal carcinoma (NPC) cells. Timepoint and dose dependent studies were performed to characterize E11.1's lytic reactivation kinetics of EBV in AGS-BDneo cells. Reactive oxygen species (ROS) scavengers and chemical pathway inhibitors were used to investigate the involvement of ROS and major cellular pathways in inducing lytic cycle of EBV by E11.1. Concomitant drug treatment of E11.1 and histone deacetylase (HDAC) inhibitor (suberoylanilide hydroxamic acid or romidepsin) was tested for synergistic action in lytic induction and cell death. E11.1 elicited a rapid kinetics of lytic induction through the activation of c-Jun N-terminal kinase (JNK) pathway in GC and NPC cells and induced the production of ROS and cell death at later timepoints. The combination of E11.1 and HDAC inhibitor reactivated the lytic cycle of EBV synergistically in both GC and NPC lines at 48 hours of treatment. In conclusion, we provided the evidence of activation of JNK pathway in the induction of EBV lytic cycle by E11.1 in EBV-positive epithelial malignancies. E11.1 and HDAC inhibitor induced the lytic cycle of EBV in EBV-positive epithelial cancer cells synergistically resulting in enhanced cell death.