Multivalent cyclic RGD ligands: influence of linker lengths on receptor binding

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• 作者：Holger Kubas ; Martin Schä ; fer ; Ulrike Bauder-Wü ; st ; Matthias Eder ; Dö ; rte Oltmanns ; Uwe Haberkorn ; Walter Mier ; Michael Eisenhut
• 关键词：Multivalency ; Peptides ; Linker length ; α ; _vβ ; ₃ integrin ; Angiogenesis
• 刊名：Nuclear Medicine and Biology
• 出版年：2010
• 出版时间：November 2010
• 年：2010
• 卷：37
• 期：8
• 页码：885-891
• 全文大小：461 K

文摘

Peptides involving the RGD motive (arginine–glycine–aspartic acid) recognize members of the integrin receptor family. Since the receptors are located mainly on the surface of endothelial cells, structural modifications including multimers of c(RGDfE) were recently found to improve the binding avidity for α_vβ₃ integrin significantly. The multivalent RGD peptides exhibited rather loose linkages partly including oligo(ethylene glycol) spacers (EG_n) with different chain lengths. Therefore, the dependence of multivalent RGD systems with and without EG_n linkers were investigated on their binding properties to cultured α_vβ₃ integrin-expressing U87MG cells.

Methods

We synthesized a series of di-, tri- and tetravalent rigid scaffolds (terephthalic acid, trimesic acid and adamantane-1,3,5,7-tetracarboxylic acid) conjugated to c(RGDyK) ligands, which were linked contiguously or separated by the oligo(ethylene glycol) spacers. The inhibition constants of these c(RGDyK) derivatives were determined by competition assays with ¹²⁵I-labeled echistatin.

Results

While c(RGDyK) function is a relative weak competitor against [¹²⁵I]echistatin (K_i, 329±18 nM) for α_vβ₃ integrin-expressing U87MG cells, RGD dimers improved the competition potency considerably (K_i, 64±23 nM). This effect was even more pronounced with the RGD trimers (K_i, 40±7 nM) and tetramers (K_i, 26±9 nM). The introduction of EG_n spacers and the increase of linker lengths proved to be detrimental since more competitors were needed to compete with [¹²⁵I]echistatin. The EG₆ group, for example, reduced the inhibition constants by 29 % (dimer), 57 % (trimer) and 97 % (tetramer).

Conclusion

The binding experiments performed with the three forms of multivalent RGD ligands indicate the weakening of competitive potency against [¹²⁵I]echistatin with the introduction of EG_n spacers. This effect may be related to the decrease of the effective RGD molarity, which becomes most prominent within the tetravalent series.