A fluorometric assay for high-throughput screening targeting nicotinamide phosphoribosyltransferase

Nicotinamide adenine dinucleotide (NAD) plays a crucial role in many cellular processes. As the rate-limiting enzyme of the predominant NAD biosynthesis pathway in mammals, nicotinamide phosphoribosyltransferase (Nampt) regulates the cellular NAD level. Tumor cells are more sensitive to the NAD levels, making them more susceptible to Nampt inhibition than their nontumorigenic counterparts. Experimental evidence has indicated that Nampt might have proangiogenic activity and supports the growth of some tumors, so Nampt inhibitors may be promising as antitumor agents. However, only four Nampt inhibitors have been reported, and no high-throughput screening (HTS) strategy for Nampt has been proposed to date, largely limiting the drug discovery targeting Nampt. Therefore, the development of a robust HTS strategy for Nampt is both imperative and significant. Here we developed a fluorometric method for a Nampt activity assay by measuring the fluorescence of nicotinamide mononucleotide (NMN) derivative resulting from the enzymatic product NMN through simple chemical reactions. Then we set up an HTS system after thorough optimizations of this method and validated that it is feasible and effective through a pilot screening on a small library. This HTS system should expedite the discovery of Nampt inhibitors as antitumor drug candidates.