According to the invention the amino acid sequences identified as SEQ ID NOs: 1-7 all comprise a binding motif which is essential for interaction of said sequences with amino acid residues of the Ig1-to-lg2 reciprocal binding site of FGFR located in the Ig2 module, said binding motif has the following formula Q/E-(x) 3 -x p , wherein x p is a hydrophobic amino acid residue and (x) 3 is an amino ac