Screening Technologies for Lead Structure Discovery

Various methods have been developed to screen large compound libraries for biological effects to filter out active molecules and assess their therapeutic value for a given indication. Three phases can be distinguished: A broad automated introductory screening for hits, a more detailed screening of chemical analogues around a hit to establish a first structure-activity relationship, and lead optimization to find candidates for clinical testing. The development of in vitro test systems using pure, genetically engineered proteins and the full arsenal of in vitro biochemical methods to characterize the function of individual gene products was a prerequisite for high-throughput screening. The studied libraries often consist of molecules from former drug development projects. As such, they are rather inefficient in terms of molecular size and modest screening hit activity in the micromolar range. Small compounds with high ligand efficiency and sufficient space for structural optimization are particularly promising. Enzyme function and inhibition can be monitored by the generation of chromogenic reaction products or radioactively labeled compounds. Also, enzyme-linked immunosorbent assays are used. Cell-based assays are used to study changes in cellular or organismal function beyond the mere binding of a test compound to a given protein target. Primary testing on vertebrate animals has been phased out for ethical reasons. However, it is increasingly being replaced by whole-animal screening using nematodes. Alternatively, virtual computer screening has been developed to screen large compound libraries by docking candidate ligands into the known spatial structure of a target protein. Biophysical methods are applied such as surface plasmon resonance, fluorescence, microscale thermophoresis, microcalorimetry, NMR spectroscopy, fragment soaking in protein crystals. Small molecule fragments covalently attached to the exposed thiol group of cysteine residues allow the study of binding to flat, solvent-exposed surface depressions to generate hits as a starting point for the design of antagonists disrupting protein-protein interfaces. https://sn.pub/k19jip