An Alkynylpyrimidine-Based Covalent Inhibitor That Targets a Unique Cysteine in NF-κB-Inducing Kinase

NF-κB-inducing kinase (NIK)
is a key enzyme in the noncanonical
NF-κB pathway, of interest in the treatment of a variety of
diseases including cancer. Validation of NIK as a drug target requires
potent and selective inhibitors. The protein contains a cysteine residue
at position 444 in the back pocket of the active site, unique within
the kinome. Analysis of existing inhibitor scaffolds and early structure–activity
relationships (SARs) led to the design of C444-targeting covalent
inhibitors based on alkynyl heterocycle warheads. Mass spectrometry
provided proof of the covalent mechanism, and the SAR was rationalized
by computational modeling. Profiling of more potent analogues in tumor
cell lines with constitutively activated NIK signaling induced a weak
antiproliferative effect, suggesting that kinase inhibition may have
limited impact on cancer cell growth. This study shows that alkynyl
heterocycles are potential cysteine traps, which may be employed where
common Michael acceptors, such as acrylamides, are not tolerated.