Discovery and characterization of novel small-molecule inhibitors targeting nicotinamide phosphoribosyltransferase

Aim Nicotinamide phosphoribosyltransferase （NAMPT） plays an important role in cardiocerebro-vascu- lar physiopathological process. It is also a promising anticancer target. It is highly desirable to discover novel NAMPT inhibitors as anticancer drug candidates and understand their action mode. Methods We carried out a high throughput screening system on a chemical library of 24434 small-molecules. Anti-proliferative activity were further studied on active compounds. Isothermal titration calorimetry and cellular thermal shift assay were used to confirm the target specificity. Molecular modeling and site-directed mutagenesis studies were taken to investigate the binding mode of NAMPT inhibitor. Results Using high throughput screening system targeting NAMPT, we ob- tained a potent NAMPT inhibitor MS0 （China Patent ZL201110447488.9 ） with excellent in vitro activity （IC50 = 9.87 ± 1.15 nmol · L^-1 ） and anti-proliferative activity against multiple human cancer cell lines including stem-like cancer cells. Structure-activity relationship studies yielded several highly effective analogues. These inhibitors spe- cifically bound NAMPT, rather than downstream NMNAT. We provided the first chemical case using cellular ther- mal shift assay to explain the difference between in vitro and cellular activity; MS7 showed best in vitro activity （ IC50 = 0.93 ± 0.29 nmol · L^-1 ） but worst cellular activity due to poor target engagement in living cells. Site-di- rected mutagenesis studies identified important residues for NAMPT catalytic activity and inhibitor binding. Con- clusions The present study provides a class of novel NAMPT inhibitors for future development of anticancer a- gents. Our findings also contribute to deep understanding the action mode of NAMPT inhibitors and NAMPT basic research in cardiocerebro-vascular system.