Suberoylanilide Hydroxamic Acid Mediates Enhanced Apoptosis In Nasopharyngeal Carcinoma Through Induction Of Epstein-Barr Virus Lytic Cycle And Activation Of Caspase-3

Abstract

Epstein-Barr virus (EBV) persists in tightly latent form in nasopharyngeal carcinoma (NPC) evading immune surveillance. Induction of EBV lytic cycle will lead to expression of a much larger number of viral proteins which may serve as potential therapeutic targets for the cancer. We previously showed that suberoylanilide hydroxamic acid (SAHA), a FDAapproved histone deacetylase inhibitor, could strongly induce viral lytic cycle in EBV-positive gastric carcinoma cells. In this study, we tested SAHA for its ability to induce EBV lytic cycle in NPC cell lines including HONE1-EBV, HK1-EBV, HA and NA. Following treatment with 5- 10 μM SAHA, increased replication of EBV DNA (8-70 folds), expression of immediate early (Zta and Rta), early (BMRF1) and late (gp350/220) viral lytic proteins (up to 60% of cells expressing BMRF1) and production of infectious viral particles were observed in all four NPC cell lines. Furthermore, enhanced killing of EBV-positive NPC cells, compared with that of EBV-negative counterparts, was demonstrated by MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide] assay. Higher percentage of EBV-positive than EBV-negative NPC cells expressing annexin V suggested that enhanced killing of EBV-positive NPC cells was related to apoptosis. Increased expression of cleaved poly(ADP-ribose) polymerase (PARP) and cleaved caspase-3 in EBV-positive compared with that in EBV-negative NPC cells indicated that enhanced apoptosis was mediated by activation of caspase-3. In conclusion, SAHA is a potent inducing agent of EBV lytic cycle and can mediate enhanced apoptosis of NPC cells.