Chemical Proteomics Identifies Nampt as the Target of CB30865, An Orphan Cytotoxic Compound

Drug discovery based on cellular phenotypes is impeded by the challenge of identifying the molecular target. To alleviate this problem, we developed a chemical proteomic process to identify cellular proteins that bind to small molecules. CB30865 is a potent (subnanomolar) and selective cytotoxic compound of previously unknown mechanism of action. By combining chemical proteomics with biochemical and cellular pharmacology we have determined that CB30865 cytotoxicity is due to subnanomolar inhibition of nicotinamide phosphoribosyltransferase (Nampt), an enzyme present in the NAD biosynthetic pathway. Cancer cells develop dependence on Nampt due to increased energy requirements and the elevated activity of NAD consuming enzymes such as sirtuins and mono and poly(ADP-ribose) polymerases (PARPs). These findings suggest new chemical starting points for Nampt inhibitors and further implicate this enzyme as a target in cancer. ► Using chemical proteomics, Nampt was identified as the target of the orphan compound CB30865 ► CB30865 is a low nanomolar Nampt inhibitor ► CB30865 decreases NAD levels in cells and blocks PAR accumulation in response to DNA damage ► CB30865 cytotoxicity is due to NAD reduction via Nampt inhibition