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

SIMPLE SUMMARY: Although nucleic acid medicines are expected to function as new therapeutic agents, their targeted delivery into cancer cells, particularly hematologic cancer cells, via systemic administration, is limited. Based on our previous finding that tumor cell-derived exosomes are preferentially incorporated into their parental cancer cells, we previously demonstrated that anti-CD63 monoclonal antibody (mAb)-oligonucleotide complexes targeting exosomal microRNAs with linear oligo-D-arginine (Arg) linkers (9mer) were transferred into solid cancer cells and inhibited exosomal miRNA functions. To challenge the delivery of siRNAs into hematologic cancer cells, we developed exosome-capturing anti-CD63 mAb-conjugated small interfering RNAs (siRNA) with branched Arg linkers (9+9mer). Anti-CD63 mAb-conjugated complexes were incorporated into multiple myeloma (MM) cells. Moreover, these exosome-capturing mAb-conjugated siRNAs successfully decreased the mRNA transcript levels of targeted mRNAs in the MM cells. This technology could lead to a breakthrough in drug delivery systems for hematologic cancer therapy. ABSTRACT: 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.