Abstract:We describe a new method of combinatorial screening in which building blocks, instead of being linked together chemically, are placed on the surface of nanoparticles. Two-or three-dimensional structures form on the surface of these particles through the close approach of different building blocks, with sufficient flexibility to be able to adapt and interact with putative binding sites in biological systems. The particles assemble without the need for formation of chemical bonds, so libraries comprised of many structures can be prepared rapidly, with large quantities of material available for testing. Screening methods can include solid and solution-phase binding assays, or tissue culture models, for example looking for structures which can change the behaviour of cells in a disease-modifying manner.

Although strong binding interactions between protein receptor and ligand do not require the participation of a large number of amino acids in either site, short peptide chains are generally poor at recreating the types of protein-protein interactions which take place during cell recognition and signalling process, probably because their flexible backbones prevent the side chains from forming sufficiently rigid and stable epitopes, which can take part in binding with the desired strength and specificity. In a recently-reported study, it was shown that a proto-epitope containing F, R and S amino acids has the ability to down-regulate TNF secretion by macrophages. This paper extends these findings, putting those amino acids into a short cyclic peptide scaffold, and determining the optimal configuration required to overcome the problems of conformational instability, and give rise to molecules which have potential as therapeutic agents in human disease, such as rheumatoid arthritis.

Using a novel drug discovery technology reported in previous issues of this journal cyclic peptides have been created which are able to down-regulate secretion of inflammatory cytokines, in vitro, by stimulated cells of the macrophage cell line J774. The cytokines in question, TNF-alpha and IL-6, are strongly implicated in etiology of diseases such as rheumatoid arthritis. Studies are reported here using the CAIA animal model for rheumatoid arthritis, which show that the peptides identified are indeed able to impact on inflammation of joints, induced in vivo. The results suggest that these peptides are effective at a dose which could be viable in man, and at which no adverse side effects are evident in the short term.

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