Minicircle-oriP-IFNγ: A Novel Targeted Gene Therapeutic System for EBV Positive Human Nasopharyngeal Carcinoma

Background: Nonviral vectors are attractively used for gene therapy owing to their distinctive advantages. Our previous study has demonstrated that transfer of human IFN gamma gene into nasopharyngeal carcinoma (NPC) by using a novel nonviral vector, minicircle (mc), under the control of cytomegalovirus (CMV) promoter was effective to inhibit tumor growth. However, therapies based on CMV promoter cannot express the targeted genes in cancer tissues. Previous studies indicated that the development of human NPC was closely associated with Epstein-Barr virus (EBV) and demonstrated the transcriptional enhancer function of oriP when bound by EBV protein. Therefore, the present study is to explore the targeted gene expression and the anti-tumor effect of a novel tumor-specific gene therapeutic system (mc-oriP-IFN gamma) in which the transgene expression was under the transcriptional regulation of oriP promoter. Methodology/Principal Findings: Dual-luciferase reporter assay and ELISA were used to assess the expression of luciferase and IFN gamma. WST assay was used to assess the cell proliferation. RT-PCR was used to detect the mRNA level of EBNA1. RNAi was used to knockdown the expression of EBNA1. NPC xenograft models in nude mice were used to investigate the targeted antitumor efficacy of mc-oriP-IFN gamma. Immunohistochemistry was used to detect the expression and the activity of the IFN gamma in tumor sections. Our results demonstrated that mc-oriP vectors mediated comparable gene expression and anti-proliferative effect in the EBV-positive NPC cell line C666-1 compared to mc-CMV vectors. Furthermore, mc-oriP vectors exhibited much lower killing effects on EBV-negative cell lines compared to mc-CMV vectors. The targeted expression of mc-oriP vectors was inhibited by EBNA1-siRNA in C666-1. This selective expression was corroborated in EBV-positive and -negative tumor models. Conclusions/Significance: This study demonstrates the feasibility of mc-oriP-IFN gamma as a safe and highly effective targeted gene therapeutic system for the treatment of EBV positive NPC.