LRP1 and brain neoplasm: Another peptide that has been used to functionalize lanthanide nanoparticles is Angiopep-2 (Ang2), a peptide designed from the Kunitz domain that binds to low-density lipoprotein receptor-related protein 1 (LRP1) at the blood–brain barrier (BBB) and has been shown to enhance nanosystem accumulation in brain tumors [110].