CTSB and neoplasm: This led to their entry into the bloodstream through FcRn-mediated transcytosis, ultimately resulting in extensive accumulation of FDX@mEVs within tumors; once inside the tumor, the prodrugs comprising of an FRRG (Phe-Arg-Arg-Gly) peptide and doxorubicin undergo an enzymatic cleavage by cathepsin B, which releases free DOX specifically in tumors and induces apoptotic cell death without off-target effects.