Covalent adduct Grob fragmentation underlies LSD1 demethylase-specific inhibitor mechanism of action and resistance

Amanda L. Waterbury, Jonatan Caroli, Olivia Zhang, Paloma R. Tuttle, Chao Liu, Jiaming Li, Ji Sung Park, Samuel M. Hoenig, Marco Barone, Airi Furui, Andrea Mattevi & Brian B. Liau

Nat Commun 16, 3156 (2025). 

https://doi.org/10.1038/s41467-025-57477-3

Chromatin modifiers often work in concert with transcription factors (TFs) and other complex members, where they can serve both enzymatic and scaffolding functions. Due to this, active site inhibitors targeting chromatin modifiers may perturb both enzymatic and nonenzymatic functions. For instance, the antiproliferative effects of active-site inhibitors targeting lysine-specific histone demethylase 1A (LSD1) are driven by disruption of a protein-protein interaction with growth factor independence 1B (GFI1B) rather than inhibition of demethylase activity. Recently, next-generation precision LSD1 covalent inhibitors have been developed, which selectively block LSD1 enzyme activity by forming a compact N-formyl flavin adenine dinucleotide (FAD) adduct that spares the GFI1B interaction. However, the mechanism accounting for N-formyl-FAD formation remains unclear. Here we clarify the mechanism of these demethylase-specific inhibitors of LSD1, demonstrating that the covalent inhibitor-FAD adduct undergoes a Grob fragmentation. Using inhibitor analogs and structural biology, we identify structure-activity relationships that promote this transformation. Furthermore, we unveil an unusual drug resistance mechanism whereby distal active-site mutations can promote inhibitor-adduct Grob fragmentation even for previous generation compounds. Our study uncovers the unique Grob fragmentation underlying the mechanism of action of precision LSD1 enzyme inhibitors, offering insight into their reactivity with broader implications for drug resistance.

Size-Dependent Target Engagement of Covalent Probes

László Petri, Ronen Gabizon, György G. Ferenczy, Nikolett Péczka, Attila Egyed, Péter Ábrányi-Balogh, Tamás Takács, and György M. Keserű

Journal of Medicinal Chemistry 2025 68 (6), 6616-6632

DOI: 10.1021/acs.jmedchem.5c00017

Labeling proteins with covalent ligands is finding increasing use in proteomics applications, including identifying nucleophilic residues amenable for labeling and in the development of targeted covalent inhibitors (TCIs). Labeling efficiency is measured by the covalent occupancy of the target or by biochemical activity. Here, we investigate how these observed quantities relate to the intrinsic parameters of complex formation, namely, noncovalent affinity and covalent reactivity, and to experimental conditions, including incubation time and ligand concentration. It is shown that target engagement is beneficially driven by noncovalent recognition for lead-like compounds, which are appropriate starting points for targeted covalent inhibitors owing to their easily detectable occupancy and fixed binding mode, facilitating optimization. In contrast, labeling by fragment-sized compounds is inevitably reactivity-driven as their small size limits noncovalent affinity. They are well-suited for exploring ligandable nucleophilic residues, while small fragments are less appropriate starting points for TCI development.

O-Cyanobenzaldehydes Irreversibly Modify Both Buried and Exposed Lysine Residues in Live Cells

Huan Ling, Lin Li, Liping Duan, Weixue Huang, Jiangnan Zheng, Shijie Zhang, Xinling Li, Xiaorong Qiu, Yang Zhou, Nan Ma, Xiaomei Ren, Jinwei Zhang, Zhen Wang, Yujun Zhao, Ruijun Tian, Zhi-Min Zhang, and Ke Ding

Journal of the American Chemical Society 2025

DOI: 10.1021/jacs.4c18006

Lysine residue represents an attractive site for covalent drug development due to its high abundance (5.6%) and critical functions. However, very few lysines have been characterized to be accessible to covalent ligands and perturb the protein functions, owing to their protonation state and adjacent steric hindrance. Herein, we report a new lysine bioconjugation chemistry, O-cyanobenzaldehyde (CNBA), that enables selective modification of the lysine ε-amine to form iso-indolinones under physiological conditions. Activity-based proteome profiling enabled the mapping of 3451 lysine residues and 85 endogenous kinases in live cells, highlighting its potential for modifying hyper-reactive lysines within the proteome or buried catalytic lysines within the kinome. Further protein crystallography and mass spectrometry confirmed that K271_ABL1 and K162_AURKA are covalently targetable sites in kinases. Leveraging a structure-based drug design, we incorporated CNBA into the core structure of Nutlin-3 to irreversibly inhibit the MDM2-p53 interaction by targeting an exposed lysine K94 on the surface of murine double minute 2. Importantly, we have demonstrated the potential application of CNBA as a lysine-recognized bioconjugation agent for developing new antibody-drug conjugates. The results collectively validate CNBA as a new selective and efficient modifying agent with broad applications for both buried and exposed lysine residues in live cells.

State-of-the-art covalent virtual screening with AlphaFold3

Yoav Shamir, Nir London

bioRxiv 2025.03.19.642201;

doi: https://doi.org/10.1101/2025.03.19.642201

Recent years have seen an explosion in the prominence of covalent inhibitors as research and therapeutic tools. However, a lag in application of computational methods for covalent docking slows progress in this field. AI models such as AlphaFold3 have shown accuracy in ligand pose prediction but were never assessed for virtual screening. We show that AlphaFold3 reaches near-perfect classification (average AUC=98.3%) of covalent active binders over property-matched decoys, dramatically outperforming classical covalent docking tools. We identify a predicted metric that allows to reliably assign a probability of binding and demonstrate it also improves non-covalent virtual screening.

Methods for Kinetic Evaluation of Reversible Covalent Inhibitors from Time-Dependent IC50 Data

L. Mader and J. W. Keillor, 

RSC Med. Chem., 2025

DOI: 10.1039/D5MD00050E

Potent reversible covalent inhibitors are often slow in establishing their covalent modification equilibrium, resulting in time-dependent inhibition. While these inhibitors are commonly assessed using IC50 values, there are no methods available to analyze their time-dependent IC50 data to provide their inhibition (Kiand Ki*) and covalent modification rate (k5and k6) constants, leading to difficulty in accurately ranking drug candidates. Herein, we present an implicit equation that can estimate these constants from incubation time-dependent IC50 values and a numerical modelling method, EPIC-CoRe, that can fit these kinetic parameters from pre-incubation time-dependent IC50 data. The application of these new methods is demonstrated by the evaluation of a known inhibitor, saxagliptin, providing results consistent with those obtained by other known methods. This work introduces two new practical methods of evaluation for time-dependent reversible covalent inhibitors, allowing for rigorous characterization to enable the fine-tuning of their binding and reactivity.

Discovery of YJZ5118: A Potent and Highly Selective Irreversible CDK12/13 Inhibitor with Synergistic Effects in Combination with Akt Inhibition

Jianzhang Yang, Yu Chang, Kaijie Zhou, Weixue Huang, Jean Ching-Yi Tien, Pujuan Zhang, Wenyan Liu, Licheng Zhou, Yang Zhou, Xiaomei Ren, Rahul Mannan, Somnath Mahapatra, Yuping Zhang, Rudana Hamadeh, Grafton Ervine, Zhen Wang, George Xiaoju Wang, Arul M. Chinnaiyan, and Ke Ding

J. Med. Chem. 2025
https://doi.org/10.1021/acs.jmedchem.5c00127

Cyclin-dependent kinases 12 and 13 (CDK12/13) have emerged as promising therapeutic targets for castration-resistant prostate cancer (CRPC) and other human cancers. Despite the development of several CDK12/13 inhibitors, challenges remain in achieving an optimal balance of potency, selectivity and pharmacokinetic properties. Here, we report the discovery of YJZ5118, a novel, potent and highly selective covalent inhibitor of CDK12/13 with reasonable pharmacokinetic profiles. YJZ5118 effectively inhibited CDK12 and CDK13 with IC50 values of 39.5 and 26.4 nM, respectively, while demonstrating high selectivity over other CDKs. Mass spectrometry analysis, cocrystal structure determination, and pulldown-proteomic experiments confirmed the compound’s covalent binding mode with CDK12/13. Functionally, YJZ5118 efficiently suppressed the transcription of DNA damage response genes, induced DNA damage, and triggered apoptosis. Moreover, the compound significantly inhibited the proliferation of multiple tumor cell lines, particularly prostate cancer cells. Notably, YJZ5118 exhibited synergistic effects with Akt inhibitors both in vitro and in vivo.

Structure-based development of a covalent inhibitor targeting Streptococcus pyogenes over Staphylococcus aureus sortase A

Hailing Zhou, Ziqi Yuan, Xiang-Na Guan, Chuan Yue, Wei Wu, Lefu Lan, Jianhua Gan, Tao Zhang, Cai-Guang Yang

Chemistry. 2025

https://doi.org/10.1002/chem.202500464

Sortase A (SrtA), a cysteine transpeptidase critical for surface protein anchoring in Gram-positive pathogens, represents an attractive antivirulence target. While covalent SrtA inhibitors show therapeutic potential, existing compounds lack species selectivity. Through structure-guided design, we developed T10, a covalent inhibitor selectively targeting Streptococcus pyogenes SrtA (SpSrtA) over Staphylococcus aureus SrtA (SaSrtA). Molecular docking revealed that shortening a "C=C" bond in lead compound ML346 eliminated SaSrtA inhibition due to steric hindrance from W194, while maintaining SpSrtA binding. X-ray crystallography confirmed T10's covalent modification of Cys208 in SpSrtA. T10 demonstrated two fold enhanced inhibitory potency and species-specific disruption of M-protein anchoring and biofilm formation in Streptococcus pyogenes, without affecting Staphylococcus aureus viability. In a Galleria mellonella infection model, T10 conferred potent protection against lethal infection. This work demonstrates the development of narrow-spectrum antivirulence agents through a structure-based rational strategy.

Comprehensive Characterization of Bruton’s Tyrosine Kinase Inhibitor Specificity, Potency, and Biological Effects: Insights into Covalent and Noncovalent Mechanistic Signatures

Antonia C. Darragh, Andrew M. Hanna, Justin H. Lipner, Alastair J. King, Nicole B. Servant, and Mirza Jahic

ACS Pharmacol. Transl. Sci. 2025
https://doi.org/10.1021/acsptsci.4c00540

Uncovering a drug’s mechanism of action and possible adverse effects are critical components in drug discovery and development. Moreover, it provides evidence for why some drugs prove more effective than others and how to design better drugs altogether. Here, we demonstrate the utility of a high-throughput in vitro screening platform along with a comprehensive panel to aid in the characterization of 15 Bruton’s tyrosine kinase (BTK) inhibitors that are either approved by the FDA or presently under clinical evaluation. To compare the potency of these drugs, we measured the binding affinity of each to wild-type BTK as well as a clinically relevant resistance mutant of BTK (BTK C481S). In doing so, we discovered a considerable difference in the selectivity and potency of these BTK inhibitors to the wild-type and mutant proteins. Some of this potentially contributes to the adverse effects experienced by patients undergoing therapy using these drugs. Overall, noncovalent BTK inhibitors showed stronger potency for both the wild-type and mutant BTK when compared with that of covalent inhibitors, with the majority demonstrating a higher specificity and less off-target modulation. Additionally, we compared biological outcomes for four of these inhibitors in human cell-based models. As expected, we found different phenotypic profiles for each inhibitor. However, the two noncovalent inhibitors had fewer off-target biological effects when compared with the two covalent inhibitors. This and similar in-depth preclinical characterization of drug candidates can provide critical insights into the efficacy and mechanism of action of a compound that may affect its safety in a clinical setting.

Rational Design of Stapled Covalent Peptide Modifiers of Oncoprotein E6 from Human Papillomavirus

ACS Chem. Biol. 2025

https://doi.org/10.1021/acschembio.4c00878

Human Papillomavirus (HPV) is linked to multiple cancers, most significantly cervical cancer, for which HPV infection is associated with nearly all cases. Essential to the oncogenesis of HPV is the function of the viral protein E6 and its role in degrading the cell cycle regulator p53. Degradation of p53, and the resultant loss of cell cycle control, is mediated by E6 recruitment of the E3 ubiquitin ligase E6AP and subsequent ubiquitination of p53. Here, we report the design of a stapled peptide that mimics the LxxLL α-helical domain of E6AP to bind and covalently label a cysteine residue specific to HPV-16 E6. Several acrylamide- and haloacetamide-based warheads were evaluated for reactivity and specificity, and a panel of hydrocarbon-stapled peptides was evaluated for enhanced binding affinity and increased proteolytic stability. Structure-based modeling was used to rationalize the observed trends in the reactivity of the warheads and the impact of the hydrocarbon staple position on the binding affinity of the stapled peptides. The development of a proteolytically stable and reactive peptide represents a new class of peptide-based inhibitors of protein–protein interactions with a potential therapeutic value toward HPV-derived cancers.

Design of Benzyl-triazolopyrimidine-Based NADPH Oxidase Inhibitors Leads to the Discovery of a Potent Dual Covalent NOX2/MAOB Inhibitor

Beatrice Noce, Sara Marchese, Marta Massari, Chiara Lambona, Joana Reis, Francesco Fiorentino, Alessia Raucci, Rossella Fioravanti, Mariana Castelôa, Alessandro Mormino, Stefano Garofalo, Cristina Limatola, Lorenzo Basile, Andrea Gottinger, Claudia Binda, Andrea Mattevi, Antonello Mai, and Sergio Valente

Journal of Medicinal Chemistry 2025

DOI: 10.1021/acs.jmedchem.4c02644

NADPH oxidases (NOXs) are enzymes dedicated to reactive oxygen species (ROS) production and are implicated in cancer, neuroinflammation, and neurodegenerative diseases. VAS2870 is a covalent inhibitor of mainly NOX2 and NOX5. It alkylates a conserved active-site cysteine, blocking productive substrate binding. To enhance potency and selectivity toward NOXs, we conducted some chemical modifications, leading to the discovery of compound 9a that preferentially inhibits NOX2 with an IC50 of 0.155 μM, and only upon its preactivation. We found that 9a, bearing a pargyline moiety, is also able to selectively inhibit MAOB over MAOA (465-fold) with an IC50 of 0.182 μM, being the first-in-class dual NOX2/MAOB covalent inhibitor. Tested in the BV2 microglia neuroinflammation model, 9a decreased ROS production and downregulated proinflammatory cytokines as iNOS, IL-1β, and IL-6 expression more efficiently than the single target inhibitors (rasagiline for MAOB and VAS2870 for NOXs) but also, more importantly, than their combination.

‘Direct-to-biology’ drives optimisation of a cell-active covalent 1 inhibitor of WRN helicase

1S. M. Rowe, A. Price, D. J. Murphy, J. Lin, E. N. Nartey, A. Chaikuad, K. Wong, J. E. Cottom, N. O. Concha, R. A. Reid, E. R. Dickinson, M. Jundt, K. Kammerer, M. Steidel, T. Mathieson, T. Werner, E. K. Grant, C. K. Stanborough, M. Rouah, J. Wojno-Picon, P. Pogány, J. Pettinger, D. J. Norman, H. Wilders, F. Rianjongdee, G. Valdes-Garcia, N. Nevins, R. Shenje, R. K. Thalji, C. Chung, H. C. Eberl, G. Neubauer, D. House, Y. Rao, M. P. Martino and J. T. Bush, 

ChemRxiv, 2025

https://doi.org/10.26434/chemrxiv-2025-tvdzn

We report a ‘direct-to-biology’ (D2B) approach for optimising covalent acrylamide binders of protein targets and apply this to the identification of a selective and cell-active inhibitor of Werner (WRN) helicase. Inhibition of WRN helicase activity exhibits a synthetic lethal relationship with cancers displaying high microsatellite instability (MSI-H) and is being pursued as a therapeutic strategy in the clinic. Using intact-protein liquid chromatography-mass spectrometry (LC-MS) screening, we identified acrylamide fragment binders of the WRN helicase domain and then used covalent D2B chemistry to optimise these initial hits. Our efforts ultimately afforded a potent covalent inhibitor of WRN-mediated DNA unwinding, which displays selective, concentration-dependent cellular engagement of WRN, and demonstrates synthetic lethality in an MSI-H setting. Furthermore, our inhibitor targets a distinct conformation of WRN helicase compared to the current clinical covalent inhibitor, presenting a complementary approach for covalent inhibition of WRN helicase. This work demonstrates how D2B chemistry platforms can be used to explore structure-activity relationships in a modular fashion, while reducing investment of human and material resources.

Morita–Baylis–Hillman Adduct Chemistry as a Tool for the Design of Lysine-Targeted Covalent Ligands

Marco Paolino, Giusy Tassone, Paolo Governa, Mario Saletti, Matteo Lami, Riccardo Carletti, Filippo Sacchetta, Cecilia Pozzi, Maurizio Orlandini, Fabrizio Manetti, Massimo Olivucci, and Andrea Cappelli

ACS Medicinal Chemistry Letters 2025

DOI: 10.1021/acsmedchemlett.4c00479 

The use of Targeted Covalent Inhibitors (TCIs) is an expanding strategy for the development of innovative drugs. It is driven by two fundamental steps: (1) recognition of the target site by the molecule and (2) establishment of the covalent interaction by its reactive group. The development of new TCIs depends on the development of new warheads. Here, we propose the use of Morita–Baylis–Hillman adducts (MBHAs) to covalently bind Lys strategically placed inside a lipophilic pocket. A human cellular retinoic acid binding protein II mutant (M2) was selected as a test bench for a library of 19 MBHAs. The noncovalent interaction step was investigated by molecular docking studies, while experimentally the entire library was incubated with M2 and crystallized to confirm covalent binding with the target lysine. The results, rationalized through covalent docking analysis, support our hypothesis of MBHAs as reactive scaffolds for the design of lysine-TCIs.

Orally Bioavailable and Site-Selective Covalent STING Inhibitor Derived from a Macrocyclic Marine Diterpenoid

Guang-Hao Niu, Wan-Chi Hsiao, Po-Hsun Lee, Li-Guo Zheng, Yu-Shao Yang, Wei-Cheng Huang, Chih-Chien Hsieh, Tai-Yu Chiu, Jing-Ya Wang, Ching-Ping Chen, Chen-Lung Huang, May-Su You, Yi-Ping Kuo, Chien-Ming Wang, Zhi-Hong Wen, Guann-Yi Yu, Chiung-Tong Chen, Ya-Hui Chi, Chun-Wei Tung, Shu-Ching Hsu, Teng-Kuang Yeh, Ping-Jyun Sung, Mingzi M. Zhang, and Lun Kelvin Tsou

Journal of Medicinal Chemistry 2025

DOI: 10.1021/acs.jmedchem.4c02665

Pharmacological inhibition of the cGAS-STING-controlled innate immune pathway is an emerging therapeutic strategy for a myriad of inflammatory diseases. Here, we report GHN105 as an orally bioavailable covalent STING inhibitor. Late-stage diversification of the briarane-type diterpenoid excavatolide B allowed the installation of solubility-enhancing functional groups while enhancing its activity as a covalent STING inhibitor against multiple human STING variants, including the S154 variant responsible for a genetic autoimmune disease. Selectively engaging the membrane-proximal Cys91 residue of STING, GHN105 dose-dependently inhibited cGAS-STING signaling and type I interferon responses in cells and in vivo. Moreover, orally administered GHN105 exhibited on-target engagement in vivo and markedly reversed key pathological features in a delayed treatment of the acute colitis mouse model. Our study provided proof of concept that the synthetic briarane analog GHN105 serves as a safe, site-selective, and orally active covalent STING inhibitor and devises a regimen that allows long-term systemic administration.

Discovery of Elironrasib (RMC-6291), a Potent and Orally Bioavailable, RAS(ON) G12C-Selective, Covalent Tricomplex Inhibitor for the Treatment of Patients with RAS G12C-Addicted Cancers

James Cregg, Kristof Pota, Aidan C. A. Tomlinson, Jason Yano, Abby Marquez, Yang Liu, Christopher J. Schulze, Kyle J. Seamon, Matthew Holderfield, Xing Wei, Yongxian Zhuang, Yu Chi Yang, Jingjing Jiang, Yue Huang, Ruiping Zhao, Yun Ling, Zhican Wang, Michael Flagella, Zhengping Wang, Mallika Singh, John E. Knox, Robert Nichols, David Wildes, Jacqueline A. M. Smith, Elena S. Koltun, and Adrian L. Gill

Journal of Medicinal Chemistry 2025

DOI: 10.1021/acs.jmedchem.4c02313

The discovery of elironrasib (RMC-6291) represents a significant breakthrough in targeting the previously deemed undruggable GTP-bound, active KRASG12C. To target the active state of RAS (RAS(ON)) directly, we have employed an innovative tri-complex inhibitor (TCI) modality involving formation of a complex with an inhibitor, the intracellular chaperone protein CypA, and the target protein KRASG12C in its GTP-bound form. The resulting tri-complex inhibits oncogenic signaling, inducing tumor regressions across various preclinical models of KRASG12C mutant human cancers. Here we report structure-guided medicinal chemistry efforts that led to the discovery of elironrasib, a potent, orally bioavailable, RAS(ON) G12C-selective, covalent, tri-complex inhibitor. The investigational agent elironrasib is currently undergoing phase 1 clinical trials (NCT05462717, NCT06128551, NCT06162221), with preliminary data indicating clinical activity in patients who had progressed on first-generation inactive state-selective KRASG12C inhibitors.

Identification of Covalent Cyclic Peptide Inhibitors Targeting Protein–Protein Interactions Using Phage Display

 Sijie Wang, Franco F. Faucher, Matilde Bertolini, Heeyoung Kim, Bingchen Yu, Li Cao, Katharina Roeltgen, Scott Lovell, Varun Shanker, Scott D. Boyd, Lei Wang, Ralf Bartenschlager, and Matthew Bogyo

Journal of the American Chemical Society 2025

DOI: 10.1021/jacs.4c15843

Peptide macrocycles are promising therapeutics for a variety of disease indications due to their overall metabolic stability and potential to make highly selective binding interactions with targets. Recent advances in covalent macrocycle peptide discovery, driven by phage and mRNA display methods, have enabled the rapid identification of highly potent and selective molecules from large libraires of diverse macrocycles. However, there are currently limited examples of macrocycles that can be used to disrupt protein–protein interactions and even fewer examples that function by formation of a covalent bond to a target protein. In this work, we describe a directed counter-selection method that enables identification of covalent macrocyclic ligands targeting a protein–protein interaction using a phage display screening platform. This method utilizes binary and ternary screenings of a chemically modified phage display library, employing the stable and weakly reactive aryl fluorosulfate electrophile. We demonstrate the utility of this approach using the SARS-CoV-2 spike-ACE2 protein–protein interaction and identify multiple covalent macrocyclic inhibitors that disrupt this interaction. The resulting compounds displayed antiviral activity against live virus that was irreversible after washout due to the covalent binding mechanism. These results highlight the potential of this screening platform for developing covalent macrocyclic drugs that disrupt protein–protein interactions with long lasting effects.

Site-specific activation of the proton pumpinhibitor rabeprazole by tetrathiolate zinccentres

Teresa Marker, Raphael R. Steimbach, Cecilia Perez-Borrajero, Marcin Luzarowski, Eric Hartmann, Sibylle Schleich, Daniel Pastor-Flores, Elisa Espinet, Andreas Trumpp, Aurelio A. Teleman, Frauke Gräter, Bernd Simon, Aubry K. Miller & Tobias P. Dick 

Nat. Chem. (2025). https://doi.org/10.1038/s41557-025-01745-8

Proton pump inhibitors have become top-selling drugs worldwide. Serendipitously discovered as prodrugs that are activated by protonation in acidic environments, proton pump inhibitors inhibit stomach acid secretion by covalently modifying the gastric proton pump. Despite their widespread use, alternative activation mechanisms and potential target proteins in non-acidic environments remain poorly understood. Employing a chemoproteomic approach, we found that the proton pump inhibitor rabeprazole selectively forms covalent conjugates with zinc-binding proteins. Focusing on DENR, a protein with a C4 zinc cluster (that is, zinc coordinated by four cysteines), we show that rabeprazole is activated by the zinc ion and subsequently conjugated to zinc-coordinating cysteines. Our results suggest that drug binding, activation and conjugation take place rapidly within the zinc coordination sphere. Finally, we provide evidence that other proton pump inhibitors can be activated in the same way. We conclude that zinc acts as a Lewis acid, obviating the need for low pH, to promote the activation and conjugation of proton pump inhibitors in non-acidic environments.

Proteomic Ligandability Maps of Phosphorus(V) Stereoprobes Identify Covalent TLCD1 Inhibitors

Hayden A. Sharma, Michael Bielecki, Meredith A. Holm, Ty M. Thompson, Yue Yin, Jacob B. Cravatt, Timothy B. Ware, Alex Reed, Molham Nassir, Tamara El-Hayek Ewing, Bruno Melillo, J Fernando Bazan, Phil S. Baran, Benjamin F. Cravatt

bioRxiv 2025.01.31.635883; 

doi: https://doi.org/10.1101/2025.01.31.635883

Activity-based protein profiling (ABPP) of stereoisomerically defined sets of electrophilic compounds (‘stereoprobes’) offers a versatile way to discover covalent ligands for proteins in native biological systems. Here we report the synthesis and chemical proteomic characterization of stereoprobes bearing a P(V)-oxathiaphospholane (OTP) reactive group. ABPP experiments identified numerous proteins in human cancer cells that showed stereoselective reactivity with OTP stereoprobes, and we confirmed several of these liganding events with recombinant proteins. OTP stereoprobes engaging the poorly characterized transmembrane protein TLCD1 impaired the incorporation of monounsaturated fatty acids into phosphatidylethanolamine lipids in cells, a lipidomic phenotype that mirrored genetic disruption of this protein. Using AlphaFold2, we found that TLCD1 structurally resembles the ceramide synthase and fatty acid elongase families of coenzyme A-dependent lipid processing enzymes. This structural similarity included conservation of catalytic histidine residues, the mutation of which blocked the OTP stereoprobe reactivity and lipid remodeling activity of recombinant TLCD1. Taken together, these data indicate that TLCD1 acts as a lipid acyltransferase in cells, and that OTP stereoprobes function as inhibitors of this enzymatic activity. Our findings thus illuminate how the chemical proteomic analysis of electrophilic compounds can facilitate the functional annotation and chemical inhibition of a key lipid metabolic enzyme in human cells.

Covalent Destabilizing Degrader of AR and AR-V7 in Androgen-Independent Prostate Cancer Cells

Charlotte M Zammit, Cory Nadel, Ying Lin, Sajjan Koirala, Patrick Ryan Potts, Daniel K Nomura

bioRxiv 2025.02.12.637117; 

doi: https://doi.org/10.1101/2025.02.12.637117

Androgen-independent prostate cancers, correlated with heightened aggressiveness and poor prognosis, are caused by mutations or deletions in the androgen receptor (AR) or expression of truncated variants of AR that are constitutively activated. Currently, drugs and drug candidates against AR target the steroid-binding domain to antagonize or degrade AR. However, these compounds cannot therapeutically access largely intrinsically disordered truncated splice variants of AR, such as AR-V7, that only possess the DNA binding domain and are missing the ligand binding domain. Targeting intrinsically disordered regions within transcription factors has remained challenging and is considered undruggable. Herein, we leveraged a cysteine-reactive covalent ligand library in a cellular screen to identify degraders of AR and AR-V7 in androgen-independent prostate cancer cells. We identified a covalent compound EN1441 that selectively degrades AR and AR-V7 in a proteasome-dependent manner through direct covalent targeting of an intrinsically disordered cysteine C125 in AR and AR-V7. EN1441 causes significant and selective destabilization of AR and AR-V7, leading to aggregation of AR/AR-V7 and subsequent proteasome-mediated degradation. Consistent with targeting both AR and AR-V7, we find that EN1441 completely inhibits total AR transcriptional activity in androgen-independent prostate cancer cells expressing both AR and AR-V7 compared to AR antagonists or degraders that only target the ligand binding domain of full-length AR, such as enzalutamide and ARV-110. Our results put forth a pathfinder molecule EN1441 that targets an intrinsically disordered cysteine within AR to destabilize, degrade, and inhibit both AR and AR-V7 in androgen-independent prostate cancer cells and highlights the utility of covalent ligand discovery approaches in directly targeting, destabilizing, inhibiting, and degrading classically undruggable transcription factor targets.

Covalent-Allosteric Inhibitors: Do We Get the Best of Both Worlds?

Hui Tao, Bo Yang, Atena Farhangian, Ke Xu, Tongtong Li, Zhong-Yin Zhang, and Jianing Li

Journal of Medicinal Chemistry 2025

DOI: 10.1021/acs.jmedchem.4c02760

Covalent-allosteric inhibitors (CAIs) may achieve the best of both worlds: increased potency, long-lasting effects, and reduced drug resistance typical of covalent ligands, along with enhanced specificity and decreased toxicity inherent in allosteric modulators. Therefore, CAIs can be an effective strategy to transform many undruggable targets into druggable ones. However, CAIs are challenging to design. In this perspective, we analyze the discovery of known CAIs targeting three protein families: protein phosphatases, protein kinases, and GTPases. We also discuss how computational methods and tools can play a role in addressing the practical challenges of rational CAI design.

Site-Specific Molecular Glues for the 14-3-3/Tau pS214 ProteinProtein Interaction via Reversible Covalent Imine Tethering

DOI

Ansgar Oberheide,   Maxime van den Oetelaar,   Jakob Scheele,   Jan Borggräfe,   Semmy Engelen,   Michael Sattler,   Christian Ottmann,   Peter Cossar  and  Luc Brunsveld  

  

RSC Med Chem 2025  

https://doi.org/10.1039/D4MD00833B

Protein-protein interactions (PPIs) are key regulators of various cellular processes. Modulating PPIs with small molecules has gained increasing attention in drug discovery, particularly targeting the 14-3-3 protein family, which interacts with several hundred client proteins and plays a central role in cellular networks. However, targeting a specific PPI of the hub protein 14-3-3, with its plethora of potential client proteins, poses a significant selectivity challenge. This not only involves the selectivity of 14-3-3 PPIs with other client proteins, but also the selective stabilization of a specific 14-3-3 binding site within a protein partner featuring several binding sites. The interaction of 14-3-3 with Tau, characterized by different phospho-site driven binding modes, forms a valuable, disease-relevant, 14-3-3 multivalent model PPI to explore this selectivity issue. This work presents the identification and early-stage optimization of small molecule fragment-like stabilizers for a specific binding site of the 14-3-3/Tau PPI. Using different biophysical assays, the stabilizing potency of the imine-bond forming molecules was mapped and X-ray crystallography studies provided structural data on the binding mode of the ternary complexes. Exploiting the unique topologies and functionalities of the different binding sites enabled the engineering of selectivity for this initial molecular glue matter for the pS214 binding site, over a second 14-3-3 binding site in Tau (pS324). These reversible covalent tool compounds will allow for the further exploration of the role of 14-3-3 in Tau aggregation.

Structural Basis for Substrate Binding, Catalysis and Inhibition of Breast Cancer Target Mitochondrial Creatine Kinase by Covalent Inhibitor via Cryo-EM

Merve Demir,*, Laura Koepping, Ya Li, Lynn Fujimoto, Andrey Bobkov, Jianhua Zhao,  Taro Hitosugi, Eduard Sergienko

Structure, 2024
https://doi.org/10.1016/j.str.2025.01.008

Mitochondrial creatine kinases (MtCKs) are key players in maintaining energy homeostasis in cells that work with cytosolic creatine kinases for energy transport from mitochondria to cytoplasm. The inhibition of breast cancer growth by cyclocreatine targeting CKs indicates dependence of cancer cells on the “energy shuttle” for cell growth and survival. Hence, understanding key mechanistic features of creatine kinases and their inhibition plays an important role in the development of cancer therapeutics. Herein, we present mutational and structural investigations on understudied ubiquitous MtCK that showed closure of the loop comprising His61 is specific to and relies on creatine binding and mechanism of phosphoryl transfer depends on electrostatics of active site. We demonstrate that previously identified pan-CK covalent inhibitor CKi inhibit breast cancer cell proliferation; however, our biochemical and structural data indicated that inhibition by CKi is highly dependent on covalent link formation and conformational changes upon creatine binding are not observed.

Total syntheses of cyclohelminthol I–IV reveal a new cysteine-selective covalent reactive group

DOI

Thomas T. Paulsen, Anders E. Kiib, Gustav J. Wørmer, Stephan M. Hacker and Thomas B. Poulsen  

Chemical Science, 2025

https://doi.org/10.1039/D4SC08667H

Biocompatible covalent reactive groups (CRGs) play pivotal roles in several areas of chemical biology and the life sciences, including targeted covalent inhibitor design and preparation of advanced biologic drugs, such as antibody–drug conjugates. In this study, we present the discovery that the small, chlorinated polyketide natural product cyclohelminthiol II (CHM-II) acts as a new type of cysteine/thiol-targeting CRG incorporating both reversible and irreversible reactivity. We devise the first syntheses of four simple cyclohelminthols, (±)-cyclohelminthol I–IV, with selective chlorinations (at C2 and C5) and a Ni-catalyzed reductive cross coupling between an enone, a vinyl bromide and triethylsilyl chloride as the key steps. Unbiased biological profiling (cell painting) was used to discover a putative covalent mechanism for CHM-II in cells with subsequent validation experiments demonstrating mechanistic similarity to dimethyl fumarate (DMF) – a known (covalent) drug used in the treatment of multiple sclerosis. Focused biochemical experiments revealed divergent thiol-reactivity inherent to the CHM-II scaffold and through further chemical derivatization of CHM-II we applied activity-based protein profiling (ABPP)-workflows to show exclusive cysteine-labelling in cell lysate. Overall, this study provides both efficient synthetic access to the CHM-II chemotype – and neighboring chemical space – and proof-of-concept for several potential applications of this new privileged CRG-class within covalent chemical biology.

Highly Optimized CNS Penetrant Inhibitors of EGFR Exon20 Insertion Mutations

William McCoull, Clare Thomson, Erin Braybrooke, Christina Chan, Nicola Colclough, Miguel A. Cortés González, Sabina Cosulich, Nichola L. Davies, Nicolas Floc’h, Ryan Greenwood, David Hargreaves, Peng Huang, Thomas A. Hunt, Tony Johnson, Peter Johnström, Jason G. Kettle, Mikhail Kondrashov, Demetrios H. Kostomiris, Songlei Li, Andrew Lister, Scott Martin, Darren McKerrecher, Neville McLean, J. Willem M. Nissink, Jonathan P. Orme, Paige Orwig, Martin J. Packer, Stuart Pearson, Lina Qin, Catarina Felisberto-Rodrigues, Adriana Savoca, Magnus Schou, Stephen Stokes, Aisha M. Swaih, Sara Talbot, Michael J. Tucker, Richard A. Ward, Emma Wadforth, Chunli Wang, Joanne Wilson, and Yawen Yang

Journal of Medicinal Chemistry 2025

DOI: 10.1021/acs.jmedchem.4c02811

Despite recent advances in the inhibition of EGFR (epidermal growth factor receptor), there remains a clinical need for new EGFR Exon20 insertion (Ex20Ins) inhibitors that spare EGFR WT. Herein, we report the discovery and optimization of two chemical series leading to ether 23 and biaryl 36 as potent, selective, and brain-penetrant inhibitors of Ex20Ins mutants. Building on our earlier discovery of alkyne 5 which allowed access to CNS property space for an Ex20Ins inhibitor, we utilized structure-based design to move to lower lipophilicity and lower CLint compounds while maintaining a WT selectivity margin. During optimization, aldehyde oxidase (AO) metabolism was identified as a human clearance risk, and through SAR exploration, lower AO metabolism was achieved. Potency and WT margin were optimized across a range of Ex20Ins mutants including the potential acquired resistance T790M mutant and efficacy demonstrated in an LXF2478 Ex20Ins ASV model with margin to EGFR WT in vivo.

Discovery of STX-721, a Covalent, Potent, and Highly Mutant-Selective EGFR/HER2 Exon20 Insertion Inhibitor for the Treatment of Non-Small Cell Lung Cancer

Benjamin C. Milgram, Deanna R. Borrelli, Natasja Brooijmans, Jack A. Henderson, Brendan J. Hilbert, Michael R. Huff, Takahiro Ito, Erica L. Jackson, Philip Jonsson, Brendon Ladd, Erin L. O’Hearn, Raymond A. Pagliarini, Simon A. Roberts, Sébastien Ronseaux, Darrin D. Stuart, Weixue Wang, and Angel Guzman-Perez

Journal of Medicinal Chemistry 2025

DOI: 10.1021/acs.jmedchem.4c02377

After L858R and ex19del epidermal growth factor receptor (EGFR) mutations, ex20ins mutations are the third most common class of driver-mutations in non-small cell lung cancer (NSCLC). Unfortunately, first-, second-, and third-generation EGFR tyrosine kinase inhibitors (TKIs) are generally ineffective for ex20ins patients due to insufficient mutant activity and selectivity over wild-type EGFR, leading to dose-limiting toxicities. While significant advances in recent years have been made toward identifying potent EGFR ex20ins mutant inhibitors, mutant vs wild-type EGFR selectivity remains a significant challenge. STX-721 (53) is a potent, irreversible inhibitor of the majority of EGFR/HER2 ex20ins mutants and demonstrates excellent mutant vs wild-type selectivity both in vitro and in vivo. STX-721 is currently in phase 1/2 clinical trials for EGFR/HER2 ex20ins-driven NSCLC.

Species Dependent Metabolism of a Covalent nsP2 Protease Inhibitor with in Vivo Anti-alphaviral Activity

Mohammad Anwar Hossain, Abigail K. Mayo, Anirban Ghoshal, Sharon A. Taft-Benz, Elizabeth J. Anderson, Noah L. Morales, Katia D. Pressey, Ava M. Vargason, Kim L. R. Brouwer, Nathaniel J. Moorman, Mark T. Heise, Timothy M. Willson

bioRxiv 2025.01.13.632788; 

doi: https://doi.org/10.1101/2025.01.13.632788

RA-0002034 (1) is a potent covalent inhibitor targeting the alphavirus nsP2 cysteine protease. The species-dependent pharmacokinetics and metabolism of 1 were investigated to evaluate its therapeutic potential. Pharmacokinetic profiling revealed rapid clearance in mice, predominantly mediated by glutathione S-transferase (GST)-catalyzed conjugation. This metabolic liability contrasted with slower clearance observed in human hepatocytes and preclinical species such as rats, dogs, and monkeys. Cross-species studies confirmed the dominance of GST-driven metabolism in mice, whereas oxidative pathways were more pronounced in dogs. Despite rapid systemic clearance, 1 achieved antiviral efficacy in mice, reducing CHIKV viral loads in multiple tissues. Initial estimations of human hepatic clearance and half-life extrapolated from animal data indicate that b.i.d. dosing of 1 will be possible to maintain concentrations sufficient for antiviral activity in humans. These cross-species pharmacokinetic and metabolism studies support the continued evaluation of 1 as a promising anti-alphaviral therapeutic.

Covalent Plant Natural Product that Potentiates Antitumor Immunity

Misao Takemoto, Sara Delghandi, Masahiro Abo, Keiko Yurimoto, Minami Odagi, Vaibhav Pal Singh, Jun Wang, Reiko Nakagawa, Shin-ichi Sato, Yasushi Takemoto, Asmaa M. A. S. Farrag, Yoshimasa Kawaguchi, Kazuo Nagasawa, Tasuku Honjo, Kenji Chamoto, and Motonari Uesugi

Journal of the American Chemical Society 2025

DOI: 10.1021/jacs.4c17837

Despite the unprecedented therapeutic potential of immune checkpoint antibody therapies, their efficacy is limited partly by the dysfunction of T cells within the cancer microenvironment. Combination therapies with small molecules have also been explored, but their clinical implementation has been met with significant challenges. To search for antitumor immunity activators, the present study developed a cell-based system that emulates cancer-attenuated T cells. The cell-based screening of 232 natural products containing electrophilic reactive functional groups led to the identification of arvenin I, also known as cucurbitacin B 2-O-β-d-glucoside (CuBg), as a plant natural product that activates T cells within the cancer-competitive environment. Chemoproteomic and mechanistic analyses indicated that arvenin I covalently reacts with and hyperactivates MKK3, thereby reviving the mitochondrial fitness of exhausted T cells through the activation of the p38MAPK pathway. In mice, administration of arvenin I enhanced the efficacy of cancer immunotherapy when used alone or in combination with an immune checkpoint inhibitor. These findings highlight the potential of arvenin I as a covalent kinase activator that potentiates antitumor immunity.

CovCysPredictor: Predicting Selective Covalently Modifiable Cysteines Using Protein Structure and Interpretable Machine Learning

Bryn Marie Reimer, Ernest Awoonor-Williams, Andrei A. Golosov, and Viktor Hornak

Journal of Chemical Information and Modeling 2025

DOI: 10.1021/acs.jcim.4c01281

Targeted covalent inhibition is a powerful therapeutic modality in the drug discoverer’s toolbox. Recent advances in covalent drug discovery, in particular, targeting cysteines, have led to significant breakthroughs for traditionally challenging targets such as mutant KRAS, which is implicated in diverse human cancers. However, identifying cysteines for targeted covalent inhibition is a difficult task, as experimental and in silico tools have shown limited accuracy. Using the recently released CovPDB and CovBinderInPDB databases, we have trained and tested interpretable machine learning (ML) models to identify cysteines that are liable to be covalently modified (i.e., “ligandable” cysteines). We explored myriad physicochemical features (pKa, solvent exposure, residue electrostatics, etc.) and protein–ligand pocket descriptors in our ML models. Our final logistic regression model achieved a median F1 score of 0.73 on held-out test sets. When tested on a small sample of holo proteins, our model also showed reasonable performance, accurately predicting the most ligandable cysteine in most cases. Taken together, these results indicate that we can accurately predict potential ligandable cysteines for targeted covalent drug discovery, privileging cysteines that are more likely to be selective rather than purely reactive. We release this tool to the scientific community as CovCysPredictor.

Identification of Novel Organo-Se BTSA-Based Derivatives as Potent, Reversible, and Selective PPARγ Covalent Modulators for Antidiabetic Drug DiscoveryClick to copy article link

Fangyuan Chen, Qingmei Liu, Lei Ma, Cuishi Yan, Haiman Zhang, Zhi Zhou, and Wei Yi

Journal of Medicinal Chemistry 2025 68 (1), 819-831

DOI: 10.1021/acs.jmedchem.4c02803

Recent studies have identified selective peroxisome proliferator-activated receptor γ (PPARγ) modulators, which synergistically engage in the inhibition mechanism of PPARγ-Ser273 phosphorylation, as a promising approach for developing safer and more effective antidiabetic drugs. Herein, we present the design, synthesis, and evaluation of a new class of organo-Se compounds, namely, benzothiaselenazole-1-oxides (BTSAs), acting as potent, reversible, and selective PPARγ covalent modulators. Notably, 2n, especially (R)-2n, displayed a high binding affinity and superior antidiabetic effects with diminished side effects. This is mainly because it can reversibly form a unique covalent bond with the Cys285 residue in PPARγ-LBD. Further mechanistic investigations revealed that it manifested such desired pharmacological profiles primarily by effectively suppressing PPARγ-Ser273 phosphorylation, enhancing glucose metabolism, and selectively upregulating the expression of insulin-sensitive genes. Collectively, our results suggest that (R)-2n holds promise as a lead compound for treating T2DM and also provides an innovative reversible covalent warhead reference for future covalent drug design.

Selective Protein (Post-)modifications through Dynamic Covalent Chemistry: Self-activated SNAr Reactions

Ferran Esteve, Jean-Louis Schmitt, Sergii Kolodych, Oleksandr Koniev, and Jean-Marie Lehn

Journal of the American Chemical Society 2025

DOI: 10.1021/jacs.4c15421

SNAr reactions were remarkably accelerated using a pretargeting and activating unit based on dynamic covalent chemistry (DCvC). A Cys attack at the C–F bond on the aromatic ring of salicylaldehyde derivatives was only observed upon iminium formation with a neighboring Lys residue of model small peptides. Such self-activation was ascribed to the stronger electron-withdrawing capability of the iminium bond with respect to that of the parent aldehyde that stabilized the transition state of the reaction, together with the higher preorganization of the reactive groups in the cationic aldiminium species. This approach was further applied for the functionalization of two antibodies. In both cases, the presence of the aldehyde group in close proximity to the reactive C–F bond resulted in a noteworthy increase in bioconjugation yields, with excellent chemo-selectivity. Whereas the modification of an IgG1 antibody led to stochastic product distributions, microenvironment selectivity was noted when employing IgG4, in line with the lower number of Lys residues in the hinge region of the latter. Additionally, the postfunctionalization of the modified antibodies was attained through the dynamic covalent exchange of the tethered iminium derivative with hydrazides, representing an unprecedented “tag and modify” selective bioconjugation strategy based on DCvC.

Targeted Covalent Modification Strategies for Drugging the Undruggable Targets

Tomonori Tamura, Masaharu Kawano, and Itaru Hamachi

Chemical Reviews 2024

DOI: 10.1021/acs.chemrev.4c00745

The term “undruggable” refers to proteins or other biological targets that have been historically challenging to target with conventional drugs or therapeutic strategies because of their structural, functional, or dynamic properties. Drugging such undruggable targets is essential to develop new therapies for diseases where current treatment options are limited or nonexistent. Thus, investigating methods to achieve such drugging is an important challenge in medicinal chemistry. Among the numerous methodologies for drug discovery, covalent modification of therapeutic targets has emerged as a transformative strategy. The covalent attachment of diverse functional molecules to targets provides a powerful platform for creating highly potent drugs and chemical tools as well the ability to provide valuable information on the structures and dynamics of undruggable targets. In this review, we summarize recent examples of chemical methods for the covalent modification of proteins and other biomolecules for the development of new therapeutics and to overcome drug discovery challenges and highlight how such methods contribute toward the drugging of undruggable targets. In particular, we focus on the use of covalent chemistry methods for the development of covalent drugs, target identification, drug screening, artificial modulation of post-translational modifications, cancer specific chemotherapies, and nucleic acid-based therapeutics.

Covalent-fragment screening identifies selective inhibitors of multiple Staphylococcus aureus serine hydrolases important for growth and biofilm formation

Matthew Bogyo, Tulsi Upadhyay, Emily Woods, Stephen Ahator. Kjersti Julin, Franco Faucher, Marijn Hollander, Nichole Pedowitz, Daniel Abegg, Isabella Hammond, Ifeanyichukwu Eke, Sijie Wang, Shiyu Chen, John Bennett, Jeyun Jo, Christian Lentz, Alex Adibekian, Matthias Fellner

Research Square Preprint 2025

https://doi.org/10.21203/rs.3.rs-5494070/v1

Staphylococcus aureus is a leading cause of bacteria-associated mortality worldwide. This is largely because infection sites are often difficult to localize and the bacteria forms biofilms which are not effectively cleared using classical antibiotics. Therefore, there is a need for new tools to both image and treat S. aureus infections. We previously identified a group of S. aureus serine hydrolases known as fluorophosphonate-binding hydrolases (Fphs), which regulate aspects of virulence and lipid metabolism. However, because their structures are similar and their functions overlap, it remains challenging to distinguish the specific roles of individual members of this family. In this study, we applied a high-throughput screening approach using a library of covalent electrophiles to identify inhibitors for FphB, FphE, and FphH. We identified inhibitors that irreversibly bind to the active-site serine residue of each enzyme with high potency and selectivity without requiring extensive medicinal chemistry optimization. Structural and biochemical analysis identified novel binding modes for several of the inhibitors. Selective inhibitors of FphH impaired both bacterial growth and biofilm formation while Inhibitors of FphB and FphE had no impact on cell growth and only limited impact on biofilm formation. These results suggest that all three hydrolases likely play functional, but non-equivalent roles in biofilm formation and FphH is a potential target for development of therapeutics that have both antibiotic and anti-biofilm activity. Overall, we demonstrate that focused covalent fragment screening can be used to rapidly identify highly potent and selective electrophiles targeting bacterial serine hydrolases. This approach could be applied to other classes of lipid hydrolases in diverse pathogens or higher eukaryotes.

N-Acyl-N-alkyl/aryl Sulfonamide Chemistry Assisted by Proximity for Modification and Covalent Inhibition of Endogenous Proteins in Living Systems

Tomonori Tamura and Itaru Hamachi

Accounts of Chemical Research 2025 58 (1), 87-100

DOI: 10.1021/acs.accounts.4c00628

Selective chemical modification of endogenous proteins in living systems with synthetic small molecular probes is a central challenge in chemical biology. Such modification has a variety of applications important for biological and pharmaceutical research, including protein visualization, protein functionalization, proteome-wide profiling of enzyme activity, and irreversible inhibition of protein activity. Traditional chemistry for selective protein modification in cells largely relies on the high nucleophilicity of cysteine residues to ensure target-selectivity and site-specificity of modification. More recently, lysine residues, which are more abundant on protein surfaces, have attracted attention for the covalent modification of proteins. However, it has been difficult to efficiently modify the ε-amino groups of lysine side-chains, which are mostly (∼99.9%) protonated and thus exhibit low nucleophilicity at physiological pH. Our group revealed that N-acyl-N-alkyl sulfonamide (NASA) moieties can rapidly and efficiently acylate noncatalytic (i.e., less reactive) lysine residues in proteins by leveraging a reaction acceleration effect via proximity. The excellent reaction kinetics and selectivity for lysine of the NASA chemistry enable covalent modification of natural intracellular and cell-surface proteins, which is intractable using conventional chemistries. Moreover, recently developed N-acyl-N-aryl sulfonamide (ArNASA) scaffolds overcome some problems faced by the first-generation NASA compounds. In this Account, we summarize our recent works in the development of NASA/ArNASA chemistry and several applications reported by ourselves and other groups. First, we characterize the basic properties of NASA/ArNASA chemistry, including the labeling kinetics, amino acid preference, and biocompatibility, and compare this approach with other ligand-directed chemistries. This section also describes the principles of nucleophilic organocatalyst-mediated protein acylation, another important protein labeling strategy using the NASA reactive group, and its application to neurotransmitter receptor labeling in brain slices. Second, we highlight various recent examples of protein functionalization using NASA/ArNASA chemistry, such as visualization of membrane proteins including therapeutically important G-protein coupled receptors, gel-based ligand screening assays, photochemical control of protein activity, and targeted protein degradation. Third, we survey covalent inhibition of proteins by NASA/ArNASA-based lysine-targeting. The unprecedented reactivity of NASA/ArNASA toward lysine allows highly potent, irreversible inhibition of several drug targets for the treatment of cancer, including HSP90, HDM2–p53 protein–protein interaction, and a Bruton’s tyrosine kinase mutant that has developed resistance to cysteine-targeted covalent-binding drugs. Finally, current limitations of, and future perspectives on, this research field are discussed. The new chemical labeling techniques offered by NASA/ArNASA chemistry and its derivatives create a valuable molecular toolbox for studying numerous biomolecules in living cells and even in vivo.

Selective Protein (Post-)modifications through Dynamic Covalent Chemistry: Self-activated SNAr Reactions

Ferran Esteve, Jean-Louis Schmitt, Sergii Kolodych, Oleksandr Koniev, and Jean-Marie Lehn

Journal of the American Chemical Society 2025

DOI: 10.1021/jacs.4c15421

SNAr reactions were remarkably accelerated using a pretargeting and activating unit based on dynamic covalent chemistry (DCvC). A Cys attack at the C–F bond on the aromatic ring of salicylaldehyde derivatives was only observed upon iminium formation with a neighboring Lys residue of model small peptides. Such self-activation was ascribed to the stronger electron-withdrawing capability of the iminium bond with respect to that of the parent aldehyde that stabilized the transition state of the reaction, together with the higher preorganization of the reactive groups in the cationic aldiminium species. This approach was further applied for the functionalization of two antibodies. In both cases, the presence of the aldehyde group in close proximity to the reactive C–F bond resulted in a noteworthy increase in bioconjugation yields, with excellent chemo-selectivity. Whereas the modification of an IgG1 antibody led to stochastic product distributions, microenvironment selectivity was noted when employing IgG4, in line with the lower number of Lys residues in the hinge region of the latter. Additionally, the postfunctionalization of the modified antibodies was attained through the dynamic covalent exchange of the tethered iminium derivative with hydrazides, representing an unprecedented “tag and modify” selective bioconjugation strategy based on DCvC.

Vivek Kumar, Jiyun Zhu, Bala C. Chenna, Zoe A. Hoffpauir, Andrew Rademacher, Ashley M. Rogers, Chien-Te Tseng, Aleksandra Drelich, Sharfa Farzandh, Audrey L. Lamb, and Thomas D. Meek

Journal of the American Chemical Society Article 2024

DOI: 10.1021/jacs.4c11620

SARS-CoV-2 3CL protease (Main protease) and human cathepsin L are proteases that play unique roles in the infection of human cells by SARS-CoV-2, the causative agent of COVID-19. Both proteases recognize leucine and other hydrophobic amino acids at the P2 position of a peptidomimetic inhibitor. At the P1 position, cathepsin L accepts many amino acid side chains, with a partial preference for phenylalanine, while 3CL-PR protease has a stringent specificity for glutamine or glutamine analogues. We have designed, synthesized, and evaluated peptidomimetic aldehyde dual-target (dual-acting) inhibitors using two peptide scaffolds based on those of two Pfizer 3CL-PR inhibitors, Nirmatrelvir, and PF-835321. Our inhibitors contain glutamine isosteres at the P1 position, including 2-pyridon-3-yl-alanine, 3-pyridinyl-alanine, and 1,3-oxazo-4-yl-alanine groups. Inhibition constants for these new inhibitors ranged from Ki = 0.6–18 nM (cathepsin L) and Ki = 2.6–124 nM (3CL-PR), for which inhibitors with the 2-pyridon-3-yl-alanal substituent were the most potent for 3CL-PR. The anti-CoV-2 activity of these inhibitors ranged from EC50 = 0.47–15 μM. X-ray structures of the peptidomimetic aldehyde inhibitors of 3CL-PR with similar scaffolds all demonstrated the formation of thiohemiacetals with Cys145, and hydrogen-bonding interactions with the heteroatoms of the pyridon-3-yl-alanyl group, as well as the nitrogen of the N-terminal indole and its appended carbonyl group at the P3 position. The absence of these hydrogen bonds for the inhibitors containing the 3-pyridinyl-alanyl and 1,3-oxazo-4-yl-alanyl groups was reflected in the less potent inhibition of the inhibitors with 3CL-PR. In summary, our studies demonstrate the value of a second generation of cysteine protease inhibitors that comprise a single agent that acts on both human cathepsin L and SARS-CoV-2 3CL protease. Such dual-target inhibitors will provide anti-COVID-19 drugs that remain active despite the development of resistance due to mutation of the viral protease. Such dual-target inhibitors are more likely to remain useful therapeutics despite the emergence of inactivating mutations in the viral protease because the human cathepsin L will not develop resistance. This particular dual-target approach is innovative since one of the targets is viral (3CL-PR) required for viral protein maturation and the other is human (hCatL) which enables viral infection.

Hydralazine inhibits cysteamine dioxygenase to treat preeclampsia and senesce glioblastoma [@MegaMatthewsLab]

Kyosuke Shishikura, Jiasong Li, Yiming Chen, Nate R McKnight, Katelyn A Bustin, Eric W Barr, Snehil R Chilkamari, Mahaa Ayub, Sun Woo Kim, Zongtao Lin, Ren-Ming Hu, Kelly Hicks, Xie Wang, Donald M O'Rourke, J. Martin Bollinger Jr., Zev A Binder, William H Parsons, Kirill A Martemyanov, Aimin Liu, Megan L Matthews

bioRxiv 2024.12.19.629450; 

doi: https://doi.org/10.1101/2024.12.19.629450

The vasodilator hydralazine (HYZ) has been used clinically for ~ 70 years and remains on the World Health Organization's List of Essential Medicines as a therapy for preeclampsia. Despite its longstanding use and the concomitant progress toward a general understanding of vasodilation, the target and mechanism of HYZ have remained unknown. We show that HYZ selectively targets 2-aminoethanethiol dioxygenase (ADO) by chelating its metal cofactor and alkylating one of its ligands. This covalent inactivation slows entry of proteins into the Cys/N-degron pathway that ADO initiates. HYZ's capacity to stabilize regulators of G-protein signaling (RGS4/5) normally marked for degradation by ADO explains its effect on blood vessel tension and comports with prior associations of insufficient RGS levels with human preeclampsia and analogous symptoms in mice. The established importance of ADO in glioblastoma led us to test HYZ in these cell types. Indeed, a single treatment induced senescence, suggesting a potential new HYZ-based therapy for this deadly brain cancer.