Preclinical study of LMP1-RNAi-based anti-tumor therapy in EBV-positive nasopharyngeal carcinoma

RNA interference (RNAi) treatment has been proven to be an important therapeutic approach in cancer based on downregulation of target-oncogenes, but its clinical efficacy still needs further investigation. LMP1 is usually presented by Epstein-Barr virus (EBV)-positive tumor cells like EBV-associated nasopharyngeal carcinoma (NPC) and acts as an oncogene in tumorigenesis. However, the mechanism of LMP1 as a proto-oncogene in nasopharyngeal carcinoma is still unclear. Two sequence-specific shRNAs 1 and 2 were designed to target the different nucleotide loci of EBV latent antigen LMP1 gene and a series of in vivo and in vitro experiments were performed to investigate the therapeutic effect of sequence-specific shRNAs targeting LMP1 and its related molecular mechanisms in EBV-positive NPC. LMP1-shRNA2 generated a truncated LMP1 mRNA and protein, whereas LMP1-shRNA1 completely blocked LMP1 mRNA and protein expression. Both LMP1-shRNAs inhibited the proliferation and migration of NPC cells overexpressing LMP1 (NPC-LMP1) as well as the NPC-associated myeloid-derived suppressor cell (MDSC) expansion in vitro. However, LMP1-shRNA2 maintained the immunogenicity of NPC-LMP1 cells, which provoked MHC-class I-dependent T cell recognition. LMP1-shRNAs inhibited tumor growth in nude mice but did not reach statistical significance compared to control groups, while the LDH nanoparticle loaded LMP1-shRNAs and the antigen-specific T cells induced by NPC-LMP1 cells treated with LMP1-shRNA2 significantly reduced tumor growth in vivo. LMP1-RNAi-based anti-tumor therapy could be a new hope for the clinical efficacy of RNAi treatment of tumors like NPC.