CXCR4 and cancer: In addition, when EPI-X4-based building blocks are combined with biologically inert polypeptides containing the CXCR4 ligand T22, the resulting biparatopic nanoparticles show a dramatically improved biodistribution in mouse models of CXCR4+ human cancer, faster cell internalization and enhanced target cell death when compared to the version based on a single ligand.