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Fast, reliable and sensitive screens of large libraries of compounds for target binding are crucial in drug discovery. Nuclear magnetic resonance (NMR) spectroscopy is gaining importance in finding drug leads because it is more sensitive to weak binding interactions than traditional high-throughput screening methods. The screening method favored by the pharmaceutical industry, structure-activity relationships by NMR (SAR by NMR), screens for binding of small-molecule ligands to a protein by observing changes in the NMR spectrum of the isotopically labeled protein. This method, however, is limited to use with small proteins (less than 40 kDa) and is often time-consuming. Reverse methodologies, based on observing changes in the spectra of the ligands rather than the protein, are gaining popularity. But these methods have a limited range of targets and usually require large quantities of protein.

In a recent study, Gregg Siegal and colleagues of the Leiden Institute of Chemistry at Leiden University introduced an NMR method of screening compound libraries for binding to an immobilized target. Target-immobilized NMR screening (TINS) allows a diverse array of targets to be screened; the target does not need to be soluble or even be a protein. The method also greatly reduces the quantity of target required, as a single sample of the target is sufficient for a flow-through screen. Most notably for drug discovery, TINS takes up substantially less experimental time. “Other NMR methods can take 1 to 3 months to screen a 10,000-compound library. Using TINS it can be done in less than a week,” says Siegal.

Siegal and colleagues immobilize targets on a new gel-based solid support. By using the gel supports, researchers avoid the problems associated with conventional glass supports, which result in poorly defined spectra of dissolved compounds owing to the large difference in magnetic susceptibility of solids versus liquids. By effectively subtracting the spectrum of potential ligands in the presence of the target from the control spectrum of the ligand compounds in the absence of the target, ligands that bind to the target can be identified.

Is TINS the next SAR by NMR? “SAR by NMR has changed the view of the pharmaceutical industry away from a narrow focus of high-throughput screening and therefore has had tremendous impact,” says Siegal. “However, many pharmaceutical companies are now using methods that focus on the NMR spectrum of the compounds to be tested. Therefore, ultimately there may be more users of the TINS methodology than the original SAR by NMR method.”