Selected phage particles could be amplified by infecting bacteria, resulting in an amplification stage also to the generation of more phage particles, which may be submitted to another circular of panning. Keywords: DNA-encoded chemical substance libraries, combinatorial chemistry, medication discovery Ligand breakthrough: a central issue in chemistry, biology RP 54275 and biomedical sciences The breakthrough of particular ligands that bind to proteins targets appealing represents a task of fundamental importance both for preliminary research and for commercial applications. Many medication discovery programs focus on the visit a molecule that interacts with a validated protein target (1C3). Similarly, the deciphering of complex biochemical processes in basic research often relies on the availability of specific reagents, which bind (or even block) macromolecular structures of interest, thus allowing their visualization, quantification or functional investigation (4C6). The advent of monoclonal antibodies by hybridoma technology has revolutionized many areas of scientific research. This innovation (for which Cesar Milstein and Georges K?hler were awarded the Nobel Prize in Medicine and Physiology in 1984) has made it possible to detect individual macromolecular structures with an unprecedented level of precision, using affinity reagents of exquisite specificity (7). The formidable advances of the last few decades in the molecular characterization of biochemical and cellular processes would have been unthinkable without the use of monoclonal antibody reagents. It would be highly desirable if, in addition to monoclonal antibodies, small organic ligands to protein targets of interest could be readily available. The value of small organic ligands capable of high-affinity binding to a cognate protein is illustrated by the versatility of the biotin / (strept)avidin system (8). Derivatives of biotin are recognized by avidin or streptavidin with dissociation constants in the sub-picomolar range. These tight-binding complexes have found numerous applications not only for the development of specific reagents in biochemistry and immunology, but also in areas as diverse as chemical synthesis (9), nuclear medicine (10), and material sciences (11), to name just a few. For many years, the discovery of small organic ligands to protein targets has been performed by screening very large sets of organic molecules (termed chemical libraries), TNRC21 one by one (1C3, 12). Large pharmaceutical companies typically construct and assay chemical libraries comprising one million organic molecules or more, using high-throughput screening procedures. It has been estimated that the assembly of such libraries may cost between 0.4 and 2 billion U.S. dollars (i.e., approximately 1,000 $ per compound, times 1 million compounds) (13). While the value of high-throughput library screening has been demonstrated in various pharmaceutical applications, it is not uncommon that binding molecules of sufficient affinity and specificity (called hits) cannot be discovered using conventional screening campaigns (14). In light of these considerations, considerable efforts have been devoted and continue to be devoted to the discovery and development of methods which facilitate the identification of specific binding molecules to macromolecular targets and proteins in particular. DNA-encoded chemical library technology enables the construction and screening of compound sets of unprecedented size and, as a consequence, the discovery of small organic ligands. When library size grows, the concentration of individual library members decreases, to an extent that those molecules may RP 54275 no longer be detectable even with the most sophisticated analytical methods. However, DNA tags allow the amplification, identification and relative quantification of molecules in very large libraries. From encoded libraries of polypeptides to DNA-encoded chemical libraries The advent of encoded combinatorial libraries of polypeptides has not only played an important role for the engineering of proteins with novel properties, with applications in many research fields, but has also been conceptually instrumental for the genesis of DNA-encoded chemical libraries. For this reason, it is convenient to briefly discuss a few milestones in this research area. In 1985, George P. Smith proposed the use of filamentous phage as tools for the display of polypeptides on the surface of these bacterial viruses (15). In a popular implementation, peptides or proteins would be genetically fused at the N-terminal end of the minor coat protein pIII of filamentous phage. The resulting viral particle features a potential functional property (e.g., a binding phenotype, embodied by the polypeptide on the phage surface), while simultaneously bearing the corresponding genetic information (i.e., genotype) as part of RP 54275 the modified phage genome [Figure 1]. The central idea is that genotype and.