Development of specifically functionalized antagonists for the exploration of multivalent receptor-ligand interactions

Complex macromolecular interactions govern most biological processes and misregulation of these interactions can lead to disease. In many instances, these complex systems are governed by multivalent interactions, which can play an important role in regulating the specificity and avidity of biological processes. Consequently, there is intense interest in elucidating the molecular basis for these interactions and in developing tools to manipulate them.; The ring-opening metathesis polymerization (ROMP) has emerged as a powerful method for constructing defined polymeric displays. Researchers have utilized these displays to present a wide range of biologically relevant epitopes and as tools for probing complex macromolecular interactions. To further extend the utility of multivalent ligands generated by ROMP, we have explored methods for the introduction of a specific end label at one of the polymer termini. Based upon our initial studies, we developed four new capping agents that efficiently introduce protected acid, protected amine and ketone functional groups at a polymer terminus. We were able to exploit these functional groups for the introduction of fluorescent reporter groups as well as the defined attachment of the polymers to surfaces. Application of these novel multivalent ligands to our studies of selectin-ligand interactions provided new insights into the role of multivalency in these systems as well as a new method for screening potential selectin antagonists.; We also exploited multivalent receptor-ligand interactions for the development of a selective targeting strategy for cancerous cells. Recognition of the alpha-galactosyl (alpha-Gal) epitope [Galalpha(1--3)Galbeta(1--4)GlcNAc] on foreign tissue leads to antibody-mediated destruction of those tissues and multivalency plays an important role in this recognition event. We hypothesized that this feature could be used to selectively target cancer-relevant cells that express a high level of a cancer-associated receptor over normal tissue that express a low level of that same receptor. To that end, we synthesized bifunctional conjugates that contain the alpha-Gal epitope and a selective antagonist for the alphavbeta3 integrin, which is overexpressed on tumor-associated blood vessels. These conjugates were effective cytotoxic agents against a cell line that expresses a high level of alphavbeta3 but not cytotoxic for cells with a medium or low levels of alphavbeta3.