I04-Macromolecular Crystallography
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Stéphane
Bourg
,
Matthieu
Place
,
Chloé
Copin
,
Apirat
Chaikuad
,
Thomas
Robert
,
Hanna
Holzmann
,
Susanne
Müller
,
Stéphane
Bach
,
Sandrine
Ruchaud
,
Stefan
Knapp
,
Frédéric
Buron
,
Sylvain
Routier
,
Pascal
Bonnet
Open Access
Abstract: CLK1 is one of the four human isoforms of the cdc2-like (CLK) kinases that has been suggested as a therapeutic target in diverse diseases based on its important role regulating mRNA splicing. For example, CLKs and closely related kinases such as DYRK1A have been targeted in Alzheimer’s disease and other diseases in which splice site selection contributes to the disease development. Here we have developed an efficient in silico fragment-based ligand design approach to identify novel CLK1 inhibitors with excellent ligand efficiency based on an imidazo[2,1-b][1,3,4]thiadiazole fragment. More than one million docking poses were generated from 26,225 unique virtual compounds, and after applying several filtering steps, 11 compounds were selected, synthesized and their CLK1 inhibition and cellular potency were evaluated. Gratifyingly, inhibitor potencies were in excellent agreement with predicted values and crystallographic data of an inhibitor bound to CLK1 confirmed the unusual binding mode of the compounds.
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Oct 2026
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I03-Macromolecular Crystallography
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Francesco Aleksy
Greco
,
Kamal Rayees
Abdul Azeez
,
Marko
Mitrović
,
Saran Aswathaman
Sivashanmugam
,
Martin Peter
Schwalm
,
Franziska
Preuss
,
Deep
Chatterjee
,
Viktoria
Morasch
,
Sebastian
Mathea
,
Thomas
Hanke
,
Susanne
Müller
,
Stefan
Knapp
Open Access
Abstract: Integrin-linked kinase (ILK) is a pseudokinase that directly interacts with β-integrins and plays a pivotal role in regulating focal adhesion function. ILK has been implicated in the development of various diseases, particularly cancer. However, currently, no validated ligands for ILK have been reported. Here, we describe the identification of 3-cyano-quinolines that potently bind to ILK (KD = ∼250 nM), and crystallographic studies revealed a type I binding mode. A medicinal chemistry campaign exploring structure–activity relationships (SAR) using a robust parallel synthesis approach provided comprehensive SAR and identified regions amenable to modification. In addition, we demonstrated that the optimized 3-cyano-quinoline 1 (DHP) modulates actin cytoskeletal dynamics. This work highlights the first validated ILK ligands and establishes a foundation for future translational efforts, such as the development of selective PROTACs targeting ILK for degradation by the ubiquitin system.
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May 2026
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I04-Macromolecular Crystallography
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Philipp
Münick
,
Dimitrios-Ilias
Balourdas
,
Julianne S.
Funk
,
Büşra
Yüksel
,
Danai
Mavridi
,
Justin
Heftel
,
Birgit
Dreier
,
Jonas V.
Schaefer
,
Birgit
Schäfer
,
Stefan
Knapp
,
Tümay
Telatar
,
Baki
Akgül
,
Andreas
Plückthun
,
Thorsten
Stiewe
,
Andreas C.
Joerger
,
Volker
Dötsch
Abstract: The tumor suppressor p53 is the most frequently mutated protein in tumors and a target for drug development. More than 2000 cancer-associated p53 missense mutations have been reported, most of them located in the DNA-binding domain (DBD). Due to the low intrinsic thermostability of the latter, they often lead to unfolding at physiological temperature. Stabilizing the DBD with small molecules has been shown to be effective in reactivating the cavity-creating cancer mutant Y220C. Unfortunately, the majority of p53 mutants seem to lack druggable binding pockets for small molecules. Here we show that a designed ankyrin repeat protein (DARPin) that binds to the p53 DBD stabilizes temperature-sensitive (TS) p53 cancer mutants, thereby compensating for mutation-induced loss of stability. We determined high-resolution crystal structures of multiple DARPin–mutant p53 complexes, providing mechanistic insights into this mode of stabilization. Reporter gene assays across a comprehensive panel of cancer-associated mutants revealed reactivation of the majority of TS mutants, whereas DNA-contact mutants and those with local misfolding of the DNA-binding surface remained inactive, as expected. We demonstrate that this reactivation induces the transcription of canonical p53 target genes and elicits antiproliferative effects in cancer cell lines. A combination of this DARPin with an mRNA/lipid nanoparticle-based transfection approach may have the potential to reactivate most TS p53 mutants and resensitize cancer cells to chemotherapy.
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May 2026
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I04-Macromolecular Crystallography
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Fabiana Izidro A. L.
Layng
,
Huiyu
Ren
,
Nicole A.
Bakas
,
Dhanya R.
Panickar
,
Lester J.
Lambert
,
Maria
Celeridad
,
Jiaqian
Wu
,
Laurent
De Backer
,
Preeti
Chandrachud
,
Allison S.
Limpert
,
Mitchell
Vamos
,
Apirat
Chaikuad
,
Betsaida B.
Verdugo
,
Patrick M.
Hagan
,
Sonja N.
Brun
,
Lutz
Tautz
,
Stefan
Knapp
,
Reuben J.
Shaw
,
Guy S.
Salvesen
,
Douglas J.
Sheffler
,
Nicholas D. P.
Cosford
Abstract: Autophagy inhibition represents a promising therapeutic approach for the management of various cancers including nonsmall cell lung cancer (NSCLC). We previously reported SBP-7455, a dual inhibitor of unc-51-like kinase 1 (ULK1) and its homologue ULK2 and described its effects on triple-negative breast cancer (TNBC) cells. Herein we report the design, synthesis, and characterization of SBP-5147 and SBP-7501, two new dual ULK1/2 inhibitors that are cytotoxic against NSCLC cells, inhibit autophagic flux in A549 cells, and present greater oral exposure than SBP-7455 at a lower dose. In addition, SBP-5147 effectively modulates autophagy and increases the expression of major histocompatibility complex (MHC) class I in NSCLC cells, which may support the rationale for ULK1/2 inhibition as a strategy to overcome resistance to immunotherapy. Together these data support the use of ULK inhibitors as part of a cancer treatment strategy, either as a single agent or in combination with current therapies.
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Feb 2026
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I03-Macromolecular Crystallography
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Christopher
Lenz
,
Lewis
Elson
,
Johannes
Dopfer
,
Frederic
Farges
,
Andreas
Kramer
,
Frank
Löhr
,
Susanne
Müller
,
Stéphanie M.
Guéret
,
Herbert
Waldmann
,
Volker
Dötsch
,
Krishna
Saxena
,
Stefan
Knapp
Open Access
Abstract: Developing new E3 ligase ligands for the design of heterobivalent molecules, such as PROteolysis TArgeting Chimeras (PROTACs), requires careful evaluation of target engagement (TE). Characterizing protein–protein interactions (PPIs) is therefore essential in drug discovery, as it enables the assessment of ligand binding to sites that are often difficult to target. Degrons, peptide motifs recognized by E3 ligases, may serve as valuable starting points for designing E3 ligands. However, many degrons are highly polar and lack intrinsic membrane permeability, requiring alternative strategies for efficient cellular delivery. In this study, we used the SPRY domain-containing SOCS box protein 2 (SPSB2) E3 ligase as a model system to develop TE strategies in vitro and in cellulo using polar degron-based peptides. By conjugating various polycationic cell-penetrating peptides (CPPs) to the degron sequence, we present a study demonstrating cellular delivery. We obtained a high-resolution crystal structure and used various biophysical techniques to assess the influence of each modification, while confocal microscopy and BRET-based assays confirmed successful cellular delivery as well as potent TE.
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Dec 2025
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I03-Macromolecular Crystallography
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Emily C.
Hank
,
Nicholas D.
D'Arcy-Evans
,
Emma R.
Scaletti
,
Carlos
Benítez-Buelga
,
Olov
Wallner
,
Florian
Ortis
,
Kaixin
Zhou
,
Liuzhen
Meng
,
Alicia
Del Prado
,
Patricia
Calvo
,
Ingrid
Almlöf
,
Elisée
Wiita
,
Karen
Nierlin
,
Sara
Kosenina
,
Andreas
Krämer
,
Alice
Eddershaw
,
Mario
Kehler
,
Maeve
Long
,
Ann-Sofie
Jemth
,
Holly
Dawson
,
Josephine
Stewart
,
Adam
Dickey
,
Mikhael E.
Astorga
,
Marek
Varga
,
Evert J.
Homan
,
Martin
Scobie
,
Stefan
Knapp
,
Leandro
Sastre
,
Pal
Stenmark
,
Miguel
De Vega
,
Thomas
Helleday
,
Maurice
Michel
Diamond Proposal Number(s):
[15806, 21625]
Open Access
Abstract: Bifunctional DNA glycosylases employ an active site lysine or the N-terminus to form a Schiff base with an abasic (AP) site base excision repair intermediate. For 8-oxoguanine DNA glycosylase 1 (OGG1), cleaving this reversible structure is the rate-determining step in the initiation of 8-oxoguanine (8-oxoG) repair in DNA. Evolution has led OGG1 to use a product-assisted catalysis approach, where the excised 8-oxoG acts as a Brønsted base for cleavage of a Schiff base intermediate. However, the physicochemical properties of 8-oxoG significantly limit the inherent enzymatic turnover leading to a weak, cellularly absent, AP lyase activity. We hypothesized that chemical synthesis of purine analogues enables access to complex structures that are suitable as product-like catalysts. Herein, the nucleobase landscape is profiled for its potential to increase OGG1 Schiff base cleavage. 8-Substituted 6-thioguanines emerge as potent and selective scaffolds enabling OGG1 to cleave AP sites opposite any canonical nucleobase by β-elimination. This effectively broadens the enzymatic substrate scope of OGG1, shaping a complete, artificial AP-lyase function. In addition, a second class of compounds, 6-substituted pyrazolo-[3,4-d]-pyrimidines, stimulate OGG1 function at high pH, while thioguanines govern enzymatic control at acidic pH. This enables up to 20-fold increased enzyme turnover and a de novo OGG1 β-elimination in conditions commonly not tolerated. The tool compounds employed here are non-toxic in cells and stimulate the repair of AP sites through a natural, APE1 dependent pathway, as opposed to previously reported β,δ-lyase stimulator TH10785.
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Oct 2025
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I03-Macromolecular Crystallography
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Laura
Hillebrand
,
Guiqun
Wang
,
Alexander
Rasch
,
Benedikt
Masberg
,
Apirat
Chaikuad
,
Thales
Kronenberger
,
Ellen
Günther
,
Michael
Forster
,
Antti
Poso
,
Michael
Lämmerhofer
,
Stefan A.
Laufer
,
Stefan
Knapp
,
Matthias
Gehringer
Diamond Proposal Number(s):
[36057]
Open Access
Abstract: While cysteine targeting in kinases is well established and widely used, covalent interactions with other amino acids remain much less explored. We aimed to develop covalent inhibitors targeting tyrosine residues in the protein kinases JAK3 and MK2 using structure-based design principles to generate small sets of ligands containing tyrosine-reactive sulfonyl fluoride and the less-explored fluorosulfate warheads. While the JAK3 inhibitors failed to achieve covalent binding, the fluorosulfate-bearing MK2 inhibitor 42, which had been designed as an allosteric binder, unexpectedly formed a bond with the “catalytic” lysine, additionally uncovering a unique interaction at the hinge region. This highlights the untapped potential of fluorosulfates and provides a rare example of the use of this electrophile for lysine targeting in kinases. Our results highlight the limitations of traditional design methods and support the integration of fragment/lead-like covalent library screening to discover unanticipated interactions.
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Aug 2025
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I04-1-Macromolecular Crystallography (fixed wavelength)
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Yeojin
Kim
,
Aleksandar
Lučić
,
Christopher
Lenz
,
Frederic
Farges
,
Martin P.
Schwalm
,
Krishna
Saxena
,
Thomas
Hanke
,
Peter G.
Marples
,
Jasmin C.
Aschenbrenner
,
Daren
Fearon
,
Frank
Von Delft
,
Andreas
Kramer
,
Stefan
Knapp
Diamond Proposal Number(s):
[29658]
Open Access
Abstract: Tripartite motif-containing protein 21 (TRIM21), and particularly its PRY-SPRY protein interaction domain, plays a critical role in the immune response by recognizing intracellular antibodies targeting them for degradation. In this study, we performed a crystallographic fragment screening (CFS) campaign to identify potential small molecule binders targeting the PRY-SPRY domain of TRIM21. Our screen identified a total of 109 fragments binding to TRIM21 that were distributed across five distinct binding sites. These fragments have been designed to facilitate straightforward follow-up chemistry, making them ideal starting points for further chemical optimization. A subsequent fragment merging approach demonstrated improved activity. To enable functional validation of compounds with full length human TRIM21, we established a NanoBRET assay suitable for measuring target engagement to the main Fc binding site in life cells. The high-resolution structural data and observed binding modes across the different sites highlight the versatility of the PRY-SPRY domain as a target for small-molecule intervention. The presented data provide a solid foundation for structure-guided ligand design, enabling the rational design of more potent and selective compounds, with the goal to develop bivalent molecules such as Proteolysis Targeting Chimeras (PROTACs).
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Jun 2025
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I03-Macromolecular Crystallography
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Open Access
Abstract: Differential scanning fluorimetry screening of the Library of Pharmacologically Active Compounds (LOPAC) identified four hits for the PRYSPRY domain of the human E3 ligase tripartite motif-containing protein 21 (TRIM21). Isothermal titration calorimetry subsequently confirmed suramin as a binder with micromolar affinity. To further investigate the binding mechanism, mouse TRIM21 was used as a structural surrogate due to its improved protein stability and high sequence similarity to the human counterpart. A crystal structure of the complex refined at 1.3 Å resolution revealed a unique binding mode, providing new avenues for targeting TRIM21 and for the development of proteolysis-targeting chimeras (PROTACs).
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Mar 2025
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Claudia
Tredup
,
Suzanne
Ackloo
,
Hartmut
Beck
,
Peter J.
Brown
,
Alex N.
Bullock
,
Alessio
Ciulli
,
Ivan
Dikic
,
Kristina
Edfeldt
,
Aled M.
Edwards
,
Jonathan M.
Elkins
,
Henner F.
Farin
,
Edward A.
Fon
,
Matthias
Gstaiger
,
Judith
Günther
,
Anna-Lena
Gustavsson
,
Sandra
Häberle
,
Laura
Isigkeit
,
Kilian V. M.
Huber
,
Andras
Kotschy
,
Oliver
Krämer
,
Andrew R.
Leach
,
Brian D.
Marsden
,
Hisanori
Matsui
,
Daniel
Merk
,
Florian
Montel
,
Monique P. C.
Mulder
,
Susanne
Müller
,
Dafydd R.
Owen
,
Ewgenij
Proschak
,
Sandra
Röhm
,
Alexandra
Stolz
,
Michael
Sundström
,
Frank
Von Delft
,
Timothy M.
Willson
,
Cheryl H.
Arrowsmith
,
Stefan
Knapp
Open Access
Abstract: Target 2035 is a global initiative that seeks to identify a pharmacological modulator of most human proteins by the year 2035. As part of an ongoing series of annual updates of this initiative, we summarise here the efforts of the EUbOPEN project whose objectives and results are making a strong contribution to the goals of Target 2035. EUbOPEN is a public–private partnership with four pillars of activity: (1) chemogenomic library collections, (2) chemical probe discovery and technology development for hit-to-lead chemistry, (3) profiling of bioactive compounds in patient-derived disease assays, and (4) collection, storage and dissemination of project-wide data and reagents. The substantial outputs of this programme include a chemogenomic compound library covering one third of the druggable proteome, as well as 100 chemical probes, both profiled in patient derived assays, as well as hundreds of data sets deposited in existing public data repositories and a project-specific data resource for exploring EUbOPEN outputs.
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Nov 2024
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