PDPK1 and breast cancer: Tominaga et al. [47] demonstrated that injection of brain metastatic cancer cell-derived exosomes into the tail vein of mice resulted in more brain metastasis compared with mice treated with human mammary tumor cell-derived exosomes.The exosome-derived miR-181c promotes destruction of the BBB through the abnormal localization of actin via downregulation of its target gene, 3-phosphoinositide-dependent protein kinase-1 (PDPK1).