Development of a Novel Strategy for Targeted Delivery of siRNA to B lymphocytes

Abstract

This study describes “proof of concept” experiments for development of a novel therapy to target B cells in pathological settings such as cancer and inflammation. Targeted biological therapies including monoclonal antibodies (mAbs) have revolutionised medicine, thus biological therapies are increasingly used in the treatment of patients with a range of diseases including cancer. However, despite significant progress in the treatment modalities, haematological malignancies remain a leading cause of cancer related mortality. Though RNA interference (RNAi) is a promising strategy for cancer gene therapy, targeted delivery of siRNAs into cells is a key challenge to their therapeutic application. One approach to target intracellular delivery could be to harness cell surface receptors that are internalised upon ligation by mAb. Thus, single-chain fragment of variable regions (scFv) mediated siRNA delivery into diseased B cells via cell surface receptors is a promising strategy. The approach involves generating an engineered scFv-protamine fusion protein to deliver siRNA specifically to B cells via CD22. For this purpose, gene constructs that combine the VH and VL of mAb (Cy34.1.2) targeting mouse CD22 and HA22, a scFv that targets human CD22, were fused to a truncated protamine peptide. Gene constructs have been produced for the expression of fusion proteins using a range of expression systems. HA22 fusion protein was expressed as secretable protein in serum-free cultures of mammalian cells. The protein was shown to retain specificity of binding to CD22 on B cells with subsequent internalisation and was also able to deliver fluorescently-labelled siRNA into B cells. The feasibility of harnessing protamine peptide for siRNA delivery was verified in tumour cells expressing αvβ6 integrin using the A20FMDV2-protamine peptide. Furthermore, siRNAs to MCL1 and PLK1 genes delivered with HA22 fusion protein to malignant B cells induced apoptosis. This study demonstrates the potential for systemic, cell-type specific, antibody-mediated siRNA delivery.