Selectin antagonists

Although most work to date has focused on the enzyme inhibition aspect, it is possible that the monoclonal VAP-1 antibody discussed above may well be closer to the clinic. The task of designing small molecules to interfere with cell-cell recognition is certainly feasible, but this will not be a trivial effort, more akin to the search for selective selectin antagonists which has proven to be very challenging. As confidence grows in the pharmaceutical industry that SSAO/VAP-1 is a validated target, it is inevitable that considerable resources will be directed to all avenues to block the functional action of this protein. 

W. Stahl, U. Sprengard, G. Kretzschmar, and H. Kunz, Synthesis of deoxy sialyl Lewis analogues, potential selectin antagonists, Angew. Chem. Int. Ed. Engl. 33 2096 (1994). 

Henrichsen D, Ernst B, Magnani JL, Wang WT, Meyer B, Peters T, Bioaffinity NMR spectroscopy Identification of an E-selectin antagonist in a substance mixture by transfer NOE, Angew. Chem. Int. Ed. Eng., 38 98-102, 1999. 

Meyer et al. recently reported transfer NOE (nuclear overhauser effect) (trNOE) (88), which detects the strong negative trNOE effect of receptor-bound molecules compared to the weak, positive trNOE of unbound compounds without the need of receptor labeling the method was used to identify an E-selectin antagonist from an artificially assembled 10-member library of saccharides (89). 

For example, a relative IC50 value (rICso) of 0.1 corresponds to an IC50 value of approximately 100 pM (for more details with respect to in vitro and in vivo evaluation of selectin antagonists, see Section 16.4.4). 

To further improve the activity of selectin antagonists, various groups have attempted to access additional (preferentially hydrophobic) interactions with the receptor. DeFrees et al. [139] showed... 

FIGURE 16.21 Selectin antagonists designed to be preorganized in the bioactive conformation. 

FIGURE 16.22 Selectin antagonists identified using 3D-pharmacophores to search 3D-database. 

FIGURE 16.24 Selectin antagonists containing additional hydrophobic substituents. 

Modifications of the different carbohydrate components of sLe have been extensively investigated and a comprehensive summary has recently been published [106a, 142]. Therefore, we will focus only on selected examples that illustrate the efforts of numerous research groups in academia and the pharmaceutical industry to develop drug-like selectin antagonists with acceptable pharmacodynamic and pharmacokinetic properties. 

A number of different competitive cell-free and cell-based binding assays under static and hydrodynamic flow conditions have been used to obtain affinity data for selectin ligands. In addition to the fact that different positive controls have been used, this makes a direct comparison of reported binding affinities difficult. Therefore, in this chapter, we quote relative affinities wherever possible (Section 16.4.3). Another problem that has a negative effect on assay reliabihty has been encountered in cases where acidic ion exchange resins are used in the final step of the antagonist synthesis [170]. Small amounts of polyanions released from the resin were found to be potent selectin inhibitors, especially for P-selectin. These polyanions are difficult to remove and are not detectable by routine analysis. As a result, published assay data for P-selectin antagonists should be considered with caution. 

Finally, routine animal models for inflammatory diseases can be used for testing the in vivo efficacy of selectin antagonists the murine peritonitis model and the ear edema model are the most common. In the murine peritonitis model [200], the migration of leukocytes in response to an acute inflammatory stimulus is assessed by intraperitoneal injection of thioglycolate. In the arachidonic acid- or croton oil-induced ear edema model [131,201], inflammation is measured as neutrophil infiltration, represented by myeloperoxidase activity in ear biopsy samples. 

Kolb, H C, Design and synthesis of a macrocyclic E-selectin antagonist, Bioorg. Med. Chem. Lett., 1, 2629-2634, 1997. 

Kretzschmar, G, Toepfer, A, Hiils, C, Krause, M, Pitfalls in the synthesis and biological evaluation of sialyl Lewis mimetics as potential selectin antagonists. Tetrahedron, 53, 2485-2494, 1997. 

Several groups have employed polyamino acid backbones as templates for the display of multiple carbohydrate residues [164,165]. For example, potent E-selectin antagonists have been generated from poly lysine [166,167] These materials are highly effective inhibitors of leukocyte rolling. Multivalent polylysine displays have also been used to inhibit Shiga-like toxin binding [168]. 

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