Perspective: The Re-emergence of Covalent Modulation in Drug Discovery

Perspective: The Re-emergence of Covalent Modulation in Drug Discovery | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 28 August 2025 V1 Latest version Share on Perspective: The Re-emergence of Covalent Modulation in Drug Discovery Author : Mirza Jahic [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.175637196.69046933/v1 226 views 120 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Covalent inhibitors, once sidelined due to concerns of irreversible toxicity and off-target reactivity, have re-emerged as a powerful strategy in modern drug discovery. Early successes such as aspirin and penicillin were discovered serendipitously, but the development of rationally designed agents like afatinib and ibrutinib, and more recently the clinical validation of KRAS^G12C inhibitors sotorasib and adagrasib, have transformed covalency from a taboo into a deliberate design principle. By forming persistent bonds, covalent inhibitors extend target engagement, enable lower dosing frequency, and unlock access to shallow or “undruggable” binding sites, while mass spectrometry and chemoproteomics provide robust tools for validation. Advances in warhead chemistry, ranging from acrylamides to nitriles, sulfonyl fluorides, and boronic acids along with electrophile-first libraries and proteomic profiling have enabled systematic, rational exploration of this modality. Protein kinases illustrate both promise and limitations: covalent EGFR and BTK inhibitors have delivered transformative therapies, yet noncovalent agents such as pirtobrutinib highlight that covalency is not always superior but context-dependent. Looking forward, diversification of amino acid targets, growth of reversible covalency, expansion into fields beyond oncology, and hybrid modalities such as covalent PROTACs will shape the next decade of discovery. Collectively, these developments underscore that the resurgence of covalent modulation is not simply a revival but a redefinition of therapeutic strategy, with risks that remain real yet outweighed by its potential as a cornerstone of future innovation. Mirza Jahic Contributor [email protected] Perspective: The Re-emergence of Covalent Modulation in Drug Discovery Covalent inhibitors, once viewed with suspicion, have returned to the center of drug discovery with a renewed sense of purpose. For decades, medicinal chemists largely avoided this class of molecules, concerned about irreversible off-target damage, unpredictable toxicities, and the potential for immune sensitization. Indeed, many of the most successful early covalent drugs such as aspirin, penicillin, and omeprazole were discovered serendipitously, with their covalent mechanisms rationalized only after the fact. Yet the landscape has shifted. The deliberate development of targeted covalent inhibitors such as afatinib and ibrutinib demonstrated that electrophiles could be tuned to achieve selective and safe engagement of disease-relevant targets, and the subsequent clinical validation of KRAS^G12C inhibitors like sotorasib and adagrasib marked a turning point. These milestones illustrate how covalent inhibition has transitioned from a scientific taboo into a rationally designed therapeutic strategy. The appeal of covalent modulation lies in its unique pharmacological advantages. By forming a persistent bond, these inhibitors extend target engagement until protein resynthesis, leading to durable efficacy, reduced dosing frequency, and improved patient compliance. They open the door to targets long considered “undruggable,” including shallow binding pockets and protein–protein interaction surfaces that often defy conventional small molecules. The irreversible binding signature also enables straightforward detection of target engagement by mass spectrometry and chemoproteomics, providing a robust means of validating selectivity across the proteome. These attributes make covalent drugs powerful tools, but they are not without liabilities. Off-target modification remains a risk if warheads are overly reactive, and clinical resistance has already emerged through single amino acid substitutions, such as the BTK^C481S mutation. Such observations underscore that covalency is not a universal solution, but rather a context-dependent strategy. The resurgence of this field is fueled by innovations in warhead chemistry and screening technologies. Acrylamides continue to dominate owing to their tractability and thiol selectivity, but the chemical toolbox has grown. Nitriles and cyanoacrylamides provide reversible covalency, offering a balance of durability and safety. Sulfonyl fluorides and fluorosulfates extend the reach of covalency to residues such as lysine, tyrosine, and serine, while boronic acids, aldehydes, and α-ketoamides have established themselves in protease and oncology applications. The central design principle remains the “Goldilocks” challenge: warheads must be reactive enough to capture their intended target but not so promiscuous as to undermine selectivity. At the same time, the adoption of electrophile-first libraries, DNA-encoded covalent collections, and chemoproteomic profiling has made systematic exploration possible. These advances have moved covalent discovery out of the realm of chance and into the era of rational design, where adduct formation can be predicted, measured, and exploited. Protein kinases provide perhaps the clearest example of this paradigm shift. Covalent inhibitors of EGFR, BTK, and JAK3 are now established therapies, using strategically positioned cysteine residues to achieve selectivity within highly conserved protein families. Yet lessons from comparative profiling of BTK inhibitors caution against treating covalency as a default solution. While ibrutinib and other covalent agents have been transformative, newer noncovalent inhibitors such as pirtobrutinib often exhibit greater potency, reduced off-target activity, and activity against resistant mutants. This duality reflects the broader truth: covalency is a tool, not an ideology, and should be applied where its kinetic and structural advantages provide the greatest clinical leverage. Looking forward, the field seems poised for continued expansion and diversification. Advances in chemistry will broaden the scope of covalent targeting beyond cysteine to lysine, tyrosine, and serine. Reversible covalency will grow in importance as a strategy for chronic diseases, where the durability of inhibition must be tempered with long-term safety. The application space will widen well beyond oncology into immunology, infectious disease, neurodegeneration, and rare disorders. Precision medicine approaches are likely to thrive, with covalent inhibitors tailored to patient-specific mutations such as KRAS^G12C or BTK^C481S. Meanwhile, hybrid modalities including covalent PROTACs, degraders, and molecular glues, will push the concept further, combining irreversible engagement with novel mechanisms of action. Taken together, the re-emergence of covalent modulation represents not simply a return to an old idea but a redefinition of drug discovery strategy. It is the convergence of careful warhead design, enabling technologies, and clinical necessity that has transformed covalent inhibitors from scientific curiosities into essential medicines. The risks remain real, but so too does the potential, and the field’s trajectory suggests that covalent modulation will continue to evolve as a powerful and indispensable pillar of therapeutic innovation. Information & Authors Information Version history V1 Version 1 28 August 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Authors Affiliations Mirza Jahic [email protected] Eurofins DiscoverX, LLC View all articles by this author Metrics & Citations Metrics Article Usage 226 views 120 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Mirza Jahic. Perspective: The Re-emergence of Covalent Modulation in Drug Discovery. Authorea . 28 August 2025. DOI: https://doi.org/10.22541/au.175637196.69046933/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. 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