The alpha(V)beta(3) integrin receptor plays an important role in human tumor metastasis and tumor-induced angiogenesis. The in vivo inhibition of this receptor by antibodies or by cyclic peptides containing the RGD sequence may in the future be used to selectively suppress these diseases. Here we investigate the influence of N-methylation of the active and selective alpha(V)beta(3) antagonist cyclo(RGDfV) (L1) on biological activity. Cyclo(RGDf-N(Me)V-) (P5) was found to be even more active than L1 and is one of the most active and selective compounds in inhibiting vitronectin binding to the alpha(V)beta(3) integrin. Its high-resolution, three-dimensional structure in water was determined by NMR techniques, distance geometry calculations, and molecular dynamics calculations, providing more insight into the structure-activity relationship.

The R V β 3 integrin is implicated in human tumor metastasis and in angiogenesis. The design of lowmolecular-mass R V β 3 antagonists by "spatial screening" led to the highly active peptides c(RGDFV) and c(RGDFV).Here the influence of the amino acids in positions 4 and 5 flanking the RGD-sequence on the inhibition of vitronectin and fibrinogen binding to the isolated R V β 3 and R IIb β 3 receptors was investigated. The influence of the side chain and the backbone conformation on activity and selectivity was studied. The compounds were divided into conformational classes. For each class at least one representative peptide was subjected to detailed structure determination in solution. The peptides of classes 1, 2, and 3 show a βII′/γ-turn arrangement with the D-amino acid in the i + 1 position of the βII′-turn. By contrast, the peptides of class 4 reveal a modified βII′/γ-turn pattern with glycine in the i + 1 position of the βII′-turn and the D-amino acid in the i + 1 position of the γ-turn. Class 1 is divided into two subclasses: besides the βII′/γ-turn arrangement a γ/γ-turn motif is found for two members of this class. Structure-activity relationship (SAR) investigations show that the amino acid in position 4 and the proton of the amide bond between residues 3 and 4 are essential for high biological activities toward R V β 3 . By contrast, the amino acid in position 5 has no influence on the activity. A bent conformation of the RGD-sequence, as observed for the peptides of classes 1 and 2, fits the R V β 3 better than the R IIb β 3 receptor and so increases the selectivity of these peptides.

Rheumatoid arthritis (RA) is an inflammatory disease associated with intense angiogenesis and vascular expression of integrin αvβ3. Intra-articular administration of a cyclic peptide antagonist of integrin αvβ3 to rabbits with antigen-induced arthritis early in disease resulted in inhibition of synovial angiogenesis and reduced synovial cell infiltrate, pannus formation, and cartilage erosions. These effects were not associated with lymphopenia or impairment of leukocyte function. Furthermore, when administered in chronic, preexisting disease, the αvβ3 antagonist effectively diminished arthritis severity and was associated with a quantitative increase in apoptosis of the angiogenic blood vessels. Therefore, angiogenesis appears to be a central factor in the initiation and persistence of arthritic disease, and antagonists of integrin αvβ3 may represent a novel therapeutic strategy for RA.