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  • Title: Macrocyclization in the design of Grb2 SH2 domain-binding ligands exhibiting high potency in whole-cell systems.
    Author: Wei CQ, Gao Y, Lee K, Guo R, Li B, Zhang M, Yang D, Burke TR.
    Journal: J Med Chem; 2003 Jan 16; 46(2):244-54. PubMed ID: 12519063.
    Abstract:
    While most SH2 domains bind phosphotyrosyl (pTyr) containing peptides in extended fashion, the growth factor receptor-bound protein 2 (Grb2) SH2 domain preferentially binds ligands in bend conformations. Accordingly, incorporation of bend-inducing functionality into synthetic ligands could potentially enhance their affinity for this SH2 domain. A macrocyclic tripeptide mimetic that contains a simplified pTyr surrogate lacking an alpha-nitrogen has recently been shown to exhibit high Grb2 SH2 domain-binding affinity in extracellular ELISA-based assays. However, the same compound is largely ineffective in whole-cell assays. It is known that acidic functionality originating from the alpha-nitrogen of pTyr residues or from the alpha-position of P0 pTyr mimetics not only increases binding affinity of peptides to Grb2 SH2 domains in extracellular assays but also enhances potency in cell-based systems. Such functionality is absent from the previously reported macrocycle. Therefore, the current study was undertaken to examine the effects of introducing carboxylic functionality at the pTyr mimetic alpha-position of macrocyclic ligands. It was found that such a modification not only enhanced Grb2 SH2 domain binding in extracellular assays but also conferred high efficacy in whole-cell systems. The most potent compound of the current study exhibited an IC(50) value of 0.002 microM in an extracellular ELISA-based assay, and in MDA-MB-453 cells, it both inhibited the association of Grb2 with p185(erbB-2) and exhibited antimitogenic effects with submicromolar IC50 values.
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