Aengus Mac Sweeney

This paper presents the experimental protein–ligand datasets used as benchmarks in the CASP 16 blind prediction experiment—the first CASP round to incorporate targets from pharmaceutical discovery projects. We have assembled and characterized protein‐ligand complexes for four proteins that are known or candidate drug targets: human chymase, human cathepsin G, human autotaxin, and the SARS‐CoV‐2 main protease. The collection encompasses over 200 co‐crystal structures at resolutions better than 2.7 Å, paired with binding affinity measurements for approximately 160 compounds covering a broad affinity range (nanomolar to high micromolar). These data enabled the CASP16 pose‐prediction and affinity‐prediction challenges. Many systems feature potentially challenging characteristics, including chymase's electropositive surface and acidic ligands, which require proper handling of titratable ligand groups; autotaxin complexes with and without zinc coordination; and a SARS‐CoV‐2 protease crystal form exhibiting an unusually open active site conformation. We describe the experimental approaches—from protein production and crystallization to binding assay development—that yielded these reference data. Contributed by scientists at F. Hoffmann‐La Roche and Idorsia Pharmaceuticals, these datasets represent actual drug discovery projects and therefore provide a realistic testbed for assessing how computational methods perform on pharmaceutically relevant targets. An accompanying paper in the present special journal issue provides a comprehensive assessment of the pose and affinity predictions for these pharmaceutical protein‐ligand systems.

Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2) are key enzymes in the kynurenine pathway of the catabolism of the essential amino acid tryptophan. Both enzymes actively contribute to the immunosuppressive microenvironment in many types of cancer. Selective or dual inhibition of these enzymes could, therefore, be beneficial in combination with other immunotherapies such as immune-checkpoint therapy. In a fragment-based approach, we optimized fragment 3 into a series of potent imidazo[5,1-b]thiazole, imidazo[1,5-a]pyridine and pyrazine IDO1 inhibitors. The introduction of the triazole side chain resulted in a reduced enzyme-to-cell potency shift for IDO1 inhibition, albeit at the expense of TDO2 potency, and allowed the discovery of potent and cellular active IDO1 inhibitors. Moreover, despite the propensity of the imidazole motif to inhibit cytochrome P450 enzymes (CYP), we were able to discover potent IDO1 inhibitors devoid of CYP inhibition. Imidazo[1,5-a]pyrazine (R)-100 has an overall suitable profile, which warrants further investigation.

In this study, we performed the hit-to-lead optimization of a SARS-CoV-2 Mpro diazepane hit (identified by computational methods in a previous work) by combining computational simulations with high-throughput medicinal chemistry (HTMC). Leveraging the 3D structural information of Mpro, we refined the original hit by targeting the S1 and S2 binding pockets of the protein. Additionally, we identified a novel exit vector pointing toward the S1' pocket, which significantly enhanced the binding affinity. This strategy enabled us to transform, rapidly with a limited number of compounds synthesized, a 14 μM hit into a potent 16 nM lead compound, for which key pharmacological properties were subsequently evaluated. This result demonstrated that combining computational technologies such as machine learning, molecular docking, and molecular dynamics simulation with HTMC can efficiently accelerate hit identification and subsequent lead generation.

Galectin‐3 (Gal‐3), a β‐galactoside‐binding lectin, is implicated in diverse cellular functions ranging from immune response modulation to tissue homeostasis. Notably, increased Gal‐3 expression has been linked to the progression of numerous diseases, including cancer, fibrosis, and cardiovascular disorders, underscoring its potential as a therapeutic target. Small molecule inhibitors have been discovered and are valuable tools to study such diseases. We report here the discovery of novel, galactose‐based, small molecule inhibitors such as compound 12 which are orally bioavailable and show efficacy in a mouse model of acute liver injury and fibrosis (CCl₄ model). The use of structure‐based drug design (docking of a virtual library of amides based on acid 2) was key in the process towards potent, nanomolar inhibitors.

Tryptophan-2,3-dioxygenase (TDO2) and indoleamine-2,3-dioxygenase (IDO1) are structurally distinct heme enzymes that catalyze the conversion of L-tryptophan to N-formyl-kynurenine, and play important roles in metabolism, inflammation, and tumor immune surveillance. The enzymes can adopt an inactive, heme-free (apo) state or an active, heme-containing (holo) state, with the balance between them varying dynamically according to biological conditions. Inhibitors of holo-TDO2 are known but, despite several advantages of the heme-free state as a drug target, no inhibitors of apo-TDO2 have been reported. We describe the discovery of the first apo-TDO2 binding inhibitors, to our knowledge, and their inhibition of cellular TDO2 activity at low nanomolar concentrations. The crystal structure of a potent, small molecule inhibitor bound to apo-TDO2 reveals its detailed binding interactions within the large, hydrophobic heme binding pocket of the active site.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a global pandemic of coronavirus disease (COVID-19) since its emergence in December 2019. As of January 2024, there has been over 774 million reported cases and 7 million deaths worldwide. While vaccination efforts have been successful in reducing the severity of the disease and decreasing the transmission rate, the development of effective therapeutics against SARS-CoV-2 remains a critical need. The main protease (Mpro) of SARS-CoV-2 is an essential enzyme required for viral replication and has been identified as a promising target for drug development. In this study, we report the identification of novel Mpro inhibitors, using a combination of deep reinforcement learning for de novo drug design with 3D pharmacophore/shape-based alignment and privileged fragment match count scoring components followed by hit expansions and molecular docking approaches. Our experimentally validated results show that 3 novel series exhibit potent inhibitory activity against SARS-CoV-2 Mpro, with IC₅₀ values ranging from 1.3 μM to 2.3 μM and a high degree of selectivity. These findings represent promising starting points for the development of new antiviral therapies against COVID-19.

Tryptophan-2,3-dioxygenase (TDO2) and indoleamine-2,3-dioxygenase (IDO1) catalyze the conversion of L-tryptophan to N-formyl-kynurenine and play important roles in metabolism, inflammation, and tumor immune surveillance. Their enzymatic activities depend on their heme contents, which vary dynamically according to biological conditions. Inhibitors binding to heme-containing holo-TDO2 are known, but to date no inhibitor that binds to the heme-free state (apo-TDO2) has been reported. We describe the discovery of the first apo-TDO2 targeting inhibitors, to our knowledge, together with their co-crystal structures and inhibition of cellular TDO2 activity at low nanomolar concentrations.

To identify starting points for therapeutics targeting SARS-CoV-2, the Paul Scherrer Institute and Idorsia decided to collaboratively perform an X-ray crystallographic fragment screen against its main protease. Fragment-based screening was carried out using crystals with a pronounced open conformation of the substrate binding pocket. Of 631 fragments soaked, a total of 29 hits bound either in the active site (24 hits), a remote binding pocket (2 hits) or at crystal packing interfaces (3 hits). Notably, two fragments with a pose sterically incompatible with a more occluded crystal form were identified. Two isatin-based electrophilic fragments bound covalently to the catalytic cysteine residue. Our structures also revealed a surprisingly strong influence of the crystal form on the binding pose of three published fragments used as positive controls, with implications for fragment screening by crystallography. Synopsis: An X-ray crystallographic screen on SARS-CoV-2 3CL protease resulted in 29 fragment hits, including two isatin-based reversible covalent binders, and revealed a strong influence of the crystal form used for fragment soaking on the bound conformation of three additional reference fragments.

The alternative pathway (AP) of the complement system is a key contributor to the pathogenesis of several human diseases including age-related macular degeneration, paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), and various glomerular diseases. The serine protease factor B (FB) is a key node in the AP and is integral to the formation of C3 and C5 convertase. Despite the prominent role of FB in the AP, selective orally bioavailable inhibitors, beyond our own efforts, have not been reported previously. Herein we describe in more detail our efforts to identify FB inhibitors by high-throughput screening (HTS) and leveraging insights from several X-ray cocrystal structures during optimization efforts. This work culminated in the discovery of LNP023 (41), which is currently being evaluated clinically in several diverse AP mediated indications.

UDP-3-O-((R)-3-hydroxymyristoyl)-N-glucosamine deacetylase (LpxC) is as an attractive target for the discovery and development of novel antibacterial drugs to address the critical medical need created by multi-drug resistant Gram-negative bacteria. Using a scaffold hopping approach on a known family of methylsulfone hydroxamate LpxC inhibitors, several hit series eliciting potent antibacterial activities against Enterobacteriaceae and Pseudomonas aeruginosa were identified. Subsequent hit-to-lead optimization, using co-crystal structures of inhibitors bound to Pseudomonas aeruginosa LpxC as guides, resulted in the discovery of multiple chemical series based on i) isoindolin-1-ones, ii) 4,5-dihydro-6H-thieno[2,3-c]pyrrol-6-ones and iii) 1,2-dihydro-3H-pyrrolo[1,2-c]imidazole-3-ones. Synthetic methods, antibacterial activities and relative binding affinities, as well as physico-chemical properties that allowed compound prioritization are presented. Finally, in vivo properties of lead molecules which belong to the most promising pyrrolo-imidazolone series such as 18d, are discussed.