Generation of novel affibody molecules targeting the EBV LMP2A N-terminal domain with inhibiting effects on the proliferation of nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) induced by latent infection with Epstein-Barr virus (EBV) remains the most common head and neck cancer in Southeast Asia, especially in the southern part of China. It is well known that persistent expression of two EBV latent membrane proteins (LMP1/LMP2A) plays a key role in nasopharyngeal carcinogenesis. Therefore, the therapeutic approach of targeting the LMP1/LMP2A protein and subsequently blocking the LMP1/LMP2A-mediated signalling pathway has been considered for treating patients with NPC. Recently, affibody molecules, a new class of small (similar to 6.5 kDa) affinity proteins, have been confirmed to be powerful generalisable tools for developing imaging or therapeutic agents by targeting specific molecules. In this study, three EBV LMP2A N-terminal domain-binding affibody molecules (Z(LMP2A-N)85, Z(LMP2A-N)110 and Z(LMP2A-N)252) were identified by screening a phage-displayed peptide library, and their high affinity and specificity for the EBV LMP2A N-terminal domain were confirmed by surface plasmon resonance (SPR), indirect immunofluorescence, co-immunoprecipitation and near-infrared small animal fluorescence imaging in vitro and in vivo. Moreover, affibody molecules targeting the EBV LMP2A N-terminal domain significantly reduced the viability of the EBV-positive cell lines C666-1, CNE-2Z and B95-8. Further investigations showed that affibody Z(LMP2A-N)110 could inhibit the phosphorylation of AKT, GSK-3 beta and beta-catenin signalling proteins, leading to suppression of beta-catenin nuclear translocation and subsequent inhibition of c-Myc oncogene expression, which may be responsible for the reduced viability of NPC-derived cell lines. In conclusion, our findings provide a strong evidence that three novel EBV LMP2A N-terminal domain-binding affibody molecules have great potential for utilisation and development as agents for both molecular imaging and targeted therapy of EBV-related NPC.