Modern perspectives on covalent and reversible covalent inhibitors: From selectivity to clinical translation

Covalent inhibitors have re-emerged as powerful agents in drug discovery, offering the advantages of high potency, sustained target engagement, and the potential to overcome resistance mechanisms. Traditionally viewed with caution due to concerns over off-target reactivity and toxicity, covalent drugs are now recognized as transformative therapeutic options, particularly in oncology, virology, and immunology. The discovery of selective electrophilic warheads and advances in computational chemistry have enabled precise targeting of nucleophilic amino acid residues such as cysteine, lysine, and serine. In parallel, the development of reversible covalent inhibitors has introduced a new dimension to drug design by combining durable binding with controllable pharmacodynamics, exemplified by recent breakthroughs in KRAS G12C inhibitors. This review summarizes the mechanistic principles, chemical strategies, and clinical progress of both irreversible and reversible covalent inhibitors. Special emphasis is placed on warhead innovations, resistance management, and the integration of structural and chemo proteomic tools in guiding selectivity. With several FDA-approved covalent drugs and an expanding pipeline of clinical candidates, covalent and reversible covalent inhibitors are poised to redefine the landscape of targeted therapeutics.