Binding of aldose reductase inhibitors: Correlation of crystallographic and mass spectrometric studies

Aldose reductase is a NADP(H)-dependent enzyme, believed to be strongly imp licated in the development of degenerative complications of Diabetes Mellit us. The search for specific inhibitors of this enzyme has thus become a maj or pharmaceutic challenge. In this study, we applied both X-ray crystallogr aphy and mass spectrometry to characterize the interactions between aldose reductase and four representative inhibitors: AminoSNM, Imirestat, LCB3071, and IDD384. If crystallography remains obviously the only way to get an ex tensive description of the contacts between an inhibitor and the enzymatic site, the duration of the crystallographic analysis makes this technique in compatible with high throughput screenings of inhibitors. On the other hand , dissociation experiments monitored by mass spectrometry permitted us to e valuate rapidly the relative gas-phase stabilities of the aldose reductase- inhibitor noncovalent complexes. Ln our experiments, dissociation in the ga s-phase was provoked by increasing the accelerating voltage of the ions (Vc ) in the source-analyzer interface region: the Ve value needed to dissociat e 50% of the noncovalent complex initially present (Vc(50)) was taken as a gas-phase stability parameter of the enzyme-inhibitor complex. Interestingl y, the Vc(50) were found to correlate with the energy of the electrostatic and H-bond interactions involved in the contact aldose reductase/inhibitor (Ee1-H), computed from the crystallographic model. This finding may be spec ially interesting in a context of drug development. Actually, during a drug design optimization phase, the binding of the drug to the target enzyme is often optimized by modifying its interatomic electrostatic and H-bond cont acts, because they usually depend on a single atom change on the drug, and are easier to introduce than the hydrophobic interactions. Therefore, the V c(50) may help to monitor the chemical modifications introduced in new inhi bitors. X-ray crystallography is clearly needed to get the details of the c ontacts and to rationalize the design. Nevertheless, once the cycle of chem ical modification is engaged, mass spectrometry can be used to select a pri ori the drug candidates which are worthy of further crystallographic invest igation. We thus propose to use the two techniques in a complementary way, to improve the screening of large collections of inhibitors. (C) 1999 Ameri can Society for Mass Spectrometry.