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.