Abstract
Abstract Nasopharyngeal carcinoma (NPC) is strongly associated with Epstein-Barr virus (EBV). We examined the in vitro and in vivo effects of suberoylanilide hydroxamic acid (SAHA), a FDA-approved histone deacetylase inhibitor, on EBV lytic cycle induction in NPC and investigated the cellular consequences. Micromolar concentrations of SAHA potently induced EBV lytic cycle with replication of EBV DNA, expression of immediate early (Zta and Rta), early (BMRF1) and late (gp350) lytic proteins and production of infectious viral particles in culture supernatants in three of four EBV-positive NPC cell lines. One NPC cell line had abortive EBV lytic cycle (no EBV DNA replication or late lytic protein expression) induction. Same concentrations of SAHA effected enhanced killing of EBV-positive NPC cells in comparison with EBV-negative counterparts, as measured by MTT assay. Increased percentages of annexin V-positive and TUNEL-positive cells and proteolytic cleavage of poly (ADP-ribose) polymerase (PARP), caspase-3, -7 and -9 in EBV-positive versus EBV-negative NPC were also observed. Immunofluorescence staining and flow cytometry showed that the majority of NPC cells (>85%) expressing Zta, BMRF1 or gp350 lytic protein co-expressed cleaved caspase-3. Tracking of expression of EBV lytic protein and cleaved caspase-3 showed that proportion of NPC cells co-expressing EBV lytic protein and cleaved caspase-3 increased over time. Furthermore, knockdown of Zta expression by short-hairpin RNA significantly decreased proteolytic cleavage of caspase-3 in SAHA-treated EBV-positive NPC cells whilst overexpression of Zta induced apoptosis of EBV-positive NPC cells, confirming that lytic cycle induction programmed NPC cells to apoptosis. Interestingly, inhibition of EBV DNA replication and late lytic protein expression by phosphonoformic acid did not impact on SAHA's induced cell death in NPC, suggesting that early rather than late phase of EBV lytic cycle contributed to the apoptotic effect. In vivo effects of SAHA on EBV lytic cycle induction and tumor growth suppression were observed in NPC xenografts established in nude mice. Taken together, our data indicated that activation of lytic cycle from latent cycle of EBV by SAHA effects apoptosis and tumor growth suppression of NPC thereby providing experimental evidence for virus-targeted therapy against EBV-positive cancer. This project is funded by NPC Area of Excellence (AoE/M 06/08 Center for Nasopharyngeal Carcinoma Research) and Epstein-Barr virus research (# 20004525) grants of AKSC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4715. doi:1538-7445.AM2012-4715
Published Version
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