Development of PROTACs Targeting the Moonlighting Enzyme Nicotinamide Phosphoribosyltransferase (NAMPT) for Breast Cancer Therapy

PROTACs (proteolysis-targeting chimeras) enable selective protein degradation through the ubiquitin-proteasome system and offer opportunities to target moonlighting proteins with nonenzymatic functions. We report the design, synthesis, and biological evaluation of NAMPT-directed PROTACs derived from our previously described inhibitor MV78 (<b>7</b>). A modular click chemistry strategy facilitated rapid assembly of a focused library by varying linker architectures and E3 ligase recruiters, with emphasis on the impact of a triazole unit. Structure-activity relationship studies revealed that eliminating the triazole from the linker and introducing an (<i>S</i>)-methyl group on the VHL ligand markedly enhanced degradation. The optimized degrader, <b>U42</b>, exhibited low nanomolar antiproliferative activity, robust intracellular and extracellular NAMPT degradation, excellent metabolic stability, favorable pharmacokinetics, and sustained efficacy in mammosphere models, three-dimensional breast cancer cultures not previously explored with NAMPT degraders. These findings highlight <b>U42</b> as a lead compound and provide strong rationale for advancing NAMPT-directed PROTACs as a therapeutic strategy in breast cancer.