Three of these novel cyclic peptides impaired CXCR4 function in vitro (competition with anti-CXCR4 antibody binding, ligand dependent migration, calcium efflux and P-Erk activation) and in vivo, reducing lung metastases in mice injected with B16-CXCR4 mouse melanoma cells and K7M2 mouse osteosarcoma cells. The gene discussed is CXCR4; the disease is melanoma.