Chemoproteomics in covalent cancer drug discovery

Covalent small-molecule drugs have re-emerged as an important class of targeted therapeutics because they can sustain target engagement and exploit nucleophilic residues inaccessible to reversible ligands. However, covalent pharmacology has historically been constrained by concerns about nonspecific reactivity and limited ability to measure target engagement and selectivity in native biological systems. Competitive activity-based protein profiling and related chemoproteomic methods address this limitation by quantifying target occupancy, identifying unintended protein engagement and localizing modified residues across the proteome. These measurements provide a mechanistic framework for evaluating whether electrophilic ligands are selective enough to advance. Here, we review how chemoproteomics has strengthened the development of covalent cancer therapeutics by linking covalent engagement to selectivity, function and translational prioritization.