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 (7). 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 (S)-methyl group on the VHL ligand markedly enhanced degradation. The optimized degrader, U42, 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 U42 as a lead compound and provide strong rationale for advancing NAMPT-directed PROTACs as a therapeutic strategy in breast cancer.