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.