Successful Incorporation of Exosome-Capturing Antibody-siRNA Complexes into Multiple Myeloma Cells and Suppression of Targeted mRNA Transcripts

Nucleic acid medicines have been developed as new therapeutic agents against various diseases; however, targeted delivery of these reagents into cancer cells, particularly hematologic cancer cells, via systemic administration is limited by the lack of efficient and cell-specific delivery systems. We previously demonstrated that monoclonal antibody (mAb)-oligonucleotide complexes targeting exosomal microRNAs with linear oligo-D-arginine (Arg) linkers were transferred into solid cancer cells and inhibited exosomal miRNA functions. In this study, we developed exosome-capturing anti-CD63 mAb-conjugated small interfering RNAs (siRNAs) with branched Arg linkers and investigated their effects on multiple myeloma (MM) cells. Anti-CD63 mAb-conjugated siRNAs were successfully incorporated into MM cells. The incorporation of exosomes was inhibited by endocytosis inhibitors. We also conducted a functional analysis of anti-CD63 mAb-conjugated siRNAs. Ab-conjugated luciferase+ (luc+) siRNAs significantly decreased the luminescence intensity in OPM-2-luc+ cells. Moreover, treatment with anti-CD63 mAb-conjugated with MYC and CTNNB1 siRNAs decreased the mRNA transcript levels of MYC and CTNNB1 to 52.5% and 55.3%, respectively, in OPM-2 cells. In conclusion, exosome-capturing Ab-conjugated siRNAs with branched Arg linkers can be effectively delivered into MM cells via uptake of exosomes by parental cells. This technology has the potential to lead to a breakthrough in drug delivery systems for hematologic cancers.