NMR screening in drug discovery Jonathan MM NMR methods in drug discovery have traditionally been used drugs. Many pharmaceutical industry research groups have to obtain structural information for drug targets or embarked on drug discovery programs using NMR screen get-ligand complexes Recently, it has been shown that ing. Although there have been few articles published to NMR may be used as an alternative approach for identification date describing such techniques, it is clear from presenta of ligands that bind to protein drug targets, shifting the tions and discussions at scientific meetings that mphasis of many NMR laboratories towards screening and development of screening tools and protocols has become design of potential drug molecules, rather than structural a priority for these groups. In this review, studies published characterization or otherwise publicly disclosed since 1996 will be dis cussed. Methods developed for NMR screening, as wel application of these methods to specific targets, will be ertex Pharmaceuticals Incorporated, 130 Waverly Street, Cambridge, addressed. Papers covering general methods for detection of binding by NMR, using either relaxation or diffusion Current Opinion in Biotechnology 1999, 10: 54-58 based methods, are beyond the scope of this short review ttp: //biomednet. com/elecref/0958166901000054 The concept of using NMR spectroscopy to detect binding C Elsevier Science Ltd ISSN 0958-1669 of ligands to a protein is well established in the literature Abbreviations [1-4]. Detection of binding by Nmr may be achieved in HTS several ways, using techniques such as chemical shift per MSCS ystal structures turbation, differential line broadening, the transferred NOE lOE, and diffusion-based methods. All of the above tech SAR activity relationships niques have been used by various groups in differin implementations of NMR screening. These methods fall Introduction into two general categories: those that monitor NMR sig- The process of preclinical drug discovery traditionally nals from the protein, or those that monitor the ligands involves two processes: lead generation and lead optimiza- These differing strategies are discussed belo tion. In the former process, molecules are identified that bind a drug target and inhibit in uitro activity, whereas in the Monitoring the protein signals- SAR by NMR latter, potential drug molecules are optimized with respect Structure activity relationships(SAR)by nmR is the fir to in vitro potency and other important parameters reflecting method for NMR screening disclosed in the literature, pre bioavailability, pharmacokinetic or toxicological properties. posed by the group at Abbott Laboratories [5]. SAr by NMR may best be described as a method for totally NMR In structure-based drug design programs, NMR methods are driven ligand design. Sar by NMR relies on a fragment ypically used during lead optimization for characterization based approach, wherein a large library(103-104)of small of the structure and dynamics of the drug target. Such stud- molecules is screened using 2D'H-15N spectra of the tar ies may include solution structure determination of proteins get protein as a readout. From changes in protein amide or protein-ligand complexes, or the rapid determination of chemical shifts, one can readily identify whether binding ligand structures in a protein-ligand complex using either has occurred from one or more components in a mixture of isotope editing/filtering or transferred nuclear Overhauser compounds. As individual peaks in the spectrum are reviewed elsewhere in this issue(see Roberts, pp 42-eare effect(NOE)techniques. These structural methods assigned to specific residues in the primary sequence,the affected peaks in the 2D spectra indicate at what site(s)on the protein the ligand is binding. After deconvolution of Alternatively, it has been shown recently that NMR may the mixture has revealed the identity of the compound(s) also be used for lead generation in drug discovery programs. binding the target, a second screen of close analogs of the In these applications, the process of NMR screening may be first 'hit is performed to optimize the binding affi thought of as occurring in two steps. First, NMR methods the first site. In order to identify small molecules that bind are used to detect weak binding of small molecule scaffolds at a proximal site, the screen is then repeated with the first c a target. Subsequently, the binding information is used to site saturated If small molecule fragments are identified esign much tighter binding inhibitors, or drug leads which occupy several neighboring subsites, one can then Although it has been known for many years that NMR is a incorporating the small molecule fragments with variou sensitive method for detecting binding of a small molecule linking groups. The set of linked compounds is then to a protein [1-3l, only recently have these NMr tech- assayed. If linked effectively, resulting compounds may niques been applied in a systematic way to screen libraries have affinities for the target that are even stronger than the of compounds against a target for the purpose of designing products of the binding constants of the individual