The invention relates to dendrimer agents presenting polypetides providing the binding domain of a &bgr integrin sub-unit for an ERK MAP kinase, or a variant or modified form of the binding domain, and the use of the dendrimers to inhibit growth of cancer cells. The peptides present more that 8 units of the polypeptide(s) examples of which include the peptide RSKAKNPLYR (SEQ ID No. 6).