PIR and breast cancer: In order to determine the therapeutic potential of piR-823 in breast cancer treatment in vivo, a xenograft model was established using immunodeficient female nude mice by transplantation with the human breast cancer cell MCF-7, followed by a cancer cell-targeted delivery of magnetic HA-nanoparticles pre-loaded with anti-piR-823 oligonucleotides through tail vein injection (Figure 4A).