Abstract: A peptide derivative selected from a list of peptide derivatives with a sequence derived from human serum albumin fragment EPI-X4 is provided, which binds to CXCR4 with about 1000-fold stronger efficiency than EPI-X4. The peptide derivatives comprise length variants as well as modifications by length variants, D-amino acids, coupling of fatty acids, cholesterol or polymers, acetyl substitutions of amino groups, amination of carboxyl groups. Further provided are pharmaceutical compositions of the peptide derivative.