Effect of cyclic RGD peptide on cell adhesion and tumor metastasis.

Several kinds of cyclic peptides containing an L-arginine-glycine-L-aspartic acid RGD sequence were synthesized by the liquid phase method, and we investigated their effects on the attachment of mouse B16 melanoma cells onto fibronectin-coated well. Cyclo (GRGDSPA) inhibited the cell attachment at a 20-fold lower concentration than the linear form. The cell adhesion was inhibited by the synthetic peptides with the following relative order of activity: cyclo (GRGDSPA) much greater than cyclo (GRGD) greater than cyclo (RGDS), cyclo (GRGDSP) greater than cyclo (GRGDS) greater than cyclo (RGDSP), cyclo (RGDSPA). Cyclo (GRGDSPA) was more effective at inhibiting cell attachment to vitronectin than it was at competing with fibronectin attachment, as reported in the case of GRGDSP. Moreover, cyclo (GRGDSPA) significantly reduced the formation of colonies in mice injected with B16-FE7 melanoma cells.