Structure and conformational variability of the HER2-trastuzumab-pertuzumab complex.

Single particle analysis from cryogenic transmission electron microscopy (cryo-EM) is particularly attractive for complexes for which structure prediction remains intractable, such as antibody-antigen complexes. Here we obtain the detailed structure of a particularly difficult complex between human epidermal growth factor receptor 2 (HER2) and the antigen-binding fragments from two distinct therapeutic antibodies binding to distant parts of the flexible HER2, pertuzumab and trastuzumab (HTP). We highlight the strengths and limitations of current data processing software in dealing with various kinds of heterogeneities, particularly continuous conformational heterogeneity, and in describing the motions that can be extracted from our dataset. Our HTP structure provides a more detailed view than the one previously available for this ternary complex. This allowed us to pinpoint a previously overlooked loop in domain IV that may be involved both in binding of trastuzumab and in HER2 dimerization. This finding may contribute to explain the synergistic anticancer effect of the two antibodies. We further propose that the flexibility of the HTP complex, beyond the difficulties it causes for cryo-EM analysis, actually reflects regulation of HER2 signaling and its inhibition by therapeutic antibodies. Notably we obtain our best data with ultra-thin continuous carbon grids, showing that with current cameras their use to alleviate particle misdistribution is compatible with a protein complex of only 162 kDa. Perhaps most importantly, we provide here a dataset for such a smallish protein complex for further development of software accounting for continuous conformational heterogeneity in cryo-EM images.

Structural insights into the bi-specific cross-over dual variable antibody architecture by cryo-EM.

Multi-specific antibodies (msAbs) are being developed as next generation antibody-based therapeutics. Knowledge of the three-dimensional structures, in the full antibody context, of their fragment antigen-binding (Fab) moieties with or without bound antigens is key to elucidating their therapeutic efficiency and stability. However, the flexibility of msAbs, a feature essential for their multi specificity, has hindered efforts in this direction. Cross-Over Dual Variable immunoglobulin (CODVIg) is a promising bispecific antibody format, designed to simultaneously target the interleukins IL4 and IL13. In this work we present the biophysical and structural characterisation of a CODVFab:IL13 complex in the full antibody context, using cryo-electron microscopy at an overall resolution of 4.2 Å. Unlike the 1:2 stoichiometry previously observed for CODVIg:IL4, CODVIg:IL13 shows a 1:1 stoichiometry. As well as providing details of the IL13-CODV binding interface, including the residues involved in the epitope-paratope region, the structure of CODVFab:IL13 also validates the use of labelling antibody as a new strategy for the single particle cryo-EM study of msAbs in complex with one, or more, antigens. This strategy reduced the inherent flexibility of the IL13 binding domain of CODV without inducing either structural changes at the epitope level or steric hindrance between the IL4 and IL13 binding regions of CODVIg. The work presented here thus also contributes to the development of methodology for the structural study of msAbs, a promising platform for cancer immunotherapy.

Deciphering cross-species reactivity of LAMP-1 antibodies using deep mutational epitope mapping and AlphaFold.

Delineating the precise regions on an antigen that are targeted by antibodies has become a key step for the development of antibody therapeutics. X-ray crystallography and cryogenic electron microscopy are considered the gold standard for providing precise information about these binding sites at atomic resolution. However, they are labor-intensive and a successful outcome is not guaranteed. We used deep mutational scanning (DMS) of the human LAMP-1 antigen displayed on yeast surface and leveraged next-generation sequencing to observe the effect of individual mutants on the binding of two LAMP-1 antibodies and to determine their functional epitopes on LAMP-1. Fine-tuned epitope mapping by DMS approaches is augmented by knowledge of experimental antigen structure. As human LAMP-1 structure has not yet been solved, we used the AlphaFold predicted structure of the full-length protein to combine with DMS data and ultimately finely map antibody epitopes. The accuracy of this method was confirmed by comparing the results to the co-crystal structure of one of the two antibodies with a LAMP-1 luminal domain. Finally, we used AlphaFold models of non-human LAMP-1 to understand the lack of mAb cross-reactivity. While both epitopes in the murine form exhibit multiple mutations in comparison to human LAMP-1, only one and two mutations in the Macaca form suffice to hinder the recognition by mAb B and A, respectively. Altogether, this study promotes a new application of AlphaFold to speed up precision mapping of antibody-antigen interactions and consequently accelerate antibody engineering for optimization.

KRAS G12C fragment screening renders new binding pockets.

KRAS genes belong to the most frequently mutated family of oncogenes in cancer. The G12C mutation, found in a third of lung, half of colorectal and pancreatic cancer cases, is believed to be responsible for a substantial number of cancer deaths. For 30 years, KRAS has been the subject of extensive drug-targeting efforts aimed at targeting KRAS protein itself, but also its post-translational modifications, membrane localization, protein-protein interactions and downstream signalling pathways. So far, most KRAS targeting strategies have failed, and there are no KRAS-specific drugs available. However, clinical candidates targeting the KRAS G12C protein have recently been developed. MRTX849 and recently approved Sotorasib are covalent binders targeting the mutated cysteine 12, occupying Switch II pocket.Herein, we describe two fragment screening drug discovery campaigns that led to the identification of binding pockets on the KRAS G12C surface that have not previously been described. One screen focused on non-covalent binders to KRAS G12C, the other on covalent binders.

An end-to-end automated platform process for high-throughput engineering of next-generation multi-specific antibody therapeutics.

Next-generation multi-specific antibody therapeutics (MSATs) are engineered to combine several functional activities into one molecule to provide higher efficacy compared to conventional, mono-specific antibody therapeutics. However, highly engineered MSATs frequently display poor yields and less favorable drug-like properties (DLPs), which can adversely affect their development. Systematic screening of a large panel of MSAT variants in very high throughput (HT) is thus critical to identify potent molecule candidates with good yield and DLPs early in the discovery process. Here we report on the establishment of a novel, format-agnostic platform process for the fast generation and multiparametric screening of tens of thousands of MSAT variants. To this end, we have introduced full automation across the entire value chain for MSAT engineering. Specifically, we have automated the in-silico design of very large MSAT panels such that it reflects precisely the wet-lab processes for MSAT DNA library generation. This includes mass saturation mutagenesis or bulk modular cloning technologies while, concomitantly, enabling library deconvolution approaches using HT Sanger DNA sequencing. These DNA workflows are tightly linked to fully automated downstream processes for compartmentalized mammalian cell transfection expression, and screening of multiple parameters. All sub-processes are seamlessly integrated with tailored workflow supporting bioinformatics. As described here, we used this platform to perform multifactor optimization of a next-generation bispecific, cross-over dual variable domain-Ig (CODV-Ig). Screening of more than 25,000 individual protein variants in mono- and bispecific format led to the identification of CODV-Ig variants with over 1,000-fold increased potency and significantly optimized production titers, demonstrating the power and versatility of the platform.

Discovery of 6-(2,4-Dichlorophenyl)-5-[4-[(3S)-1-(3-fluoropropyl)pyrrolidin-3-yl]oxyphenyl]-8,9-dihydro-7H-benzo[7]annulene-2-carboxylic acid (SAR439859), a Potent and Selective Estrogen Receptor Degrader (SERD) for the Treatment of Estrogen-Receptor-Positive Breast Cancer.

More than 75% of breast cancers are estrogen receptor alpha (ERα) positive (ER+), and resistance to current hormone therapies occurs in one-third of ER+ patients. Tumor resistance is still ERα-dependent, but mutations usually confer constitutive activation to the hormone receptor, rendering ERα modulator drugs such as tamoxifen and aromatase inhibitors ineffective. Fulvestrant is a potent selective estrogen receptor degrader (SERD), which degrades the ERα receptor in drug-resistant tumors and has been approved for the treatment of hormone-receptor-positive metastatic breast cancer following antiestrogen therapy. However, fulvestrant shows poor pharmacokinetic properties in human, low solubility, weak permeation, and high metabolism, limiting its administration to inconvenient intramuscular injections. This Drug Annotation describes the identification and optimization of a new series of potent orally available SERDs, which led to the discovery of 6-(2,4-dichlorophenyl)-5-[4-[(3S)-1-(3-fluoropropyl)pyrrolidin-3-yl]oxyphenyl]-8,9-dihydro-7H-benzo[7]annulene-2-carboxylic acid (43d), showing promising antitumor activity in breast cancer mice xenograft models and whose properties warranted clinical evaluation.

Fast NMR Methods for Measuring in the Direct and/or Competition Mode the Dissociation Constants of Chemical Fragments Interacting with a Receptor.

Ligand-based NMR screening represents a powerful method in fragment-based drug discovery for the identification of chemical matter interacting with the receptor of interest. The large dynamic range of these methods allows the detection of weakly binding ligands. However, the methodology has not been extensively used for quantifying the strength of these interactions. This knowledge is important for ranking fragments according to their binding strength and for prioritizing structure-based and medicinal chemistry activities. Rapid NMR methods for measuring the dissociation constant in direct and competition modes are presented here. The theory underpinning these methods are presented, along with their application to the measurement of the binding affinities of several ligands of the heat shock protein 90.

Differential Water Thermodynamics Determine PI3K-Beta/Delta Selectivity for Solvent-Exposed Ligand Modifications.

Phosphoinositide 3-kinases (PI3Ks) are involved in important cellular functions and represent desirable targets for drug discovery efforts, especially related to oncology; however, the four PI3K subtypes (α, ß, γ, and δ) have highly similar binding sites, making the design of selective inhibitors challenging. A series of inhibitors with selectivity toward the ß subtype over δ resulted in compound 3(S), which has entered a phase I/Ib clinical trial for patients with advanced PTEN-deficient cancer. Interestingly, X-ray crystallography revealed that the modifications making inhibitor 3(S) and related compounds selective toward the ß-isoform do not interact directly with either PI3Kß or PI3Kδ, thereby confounding rationalization of the SAR. Here, we apply explicit solvent molecular dynamics and solvent thermodynamic analysis using WaterMap in an effort to understand the unusual affinity and selectivity trends. We find that differences in solvent energetics and water networks, which are modulated upon binding of different ligands, explain the experimental affinity and selectivity trends. This study highlights the critical role of water molecules in molecular recognition and the importance of considering water networks in drug discovery efforts to rationalize and improve selectivity.

Automated harvesting and processing of protein crystals through laser photoablation.

Currently, macromolecular crystallography projects often require the use of highly automated facilities for crystallization and X-ray data collection. However, crystal harvesting and processing largely depend on manual operations. Here, a series of new methods are presented based on the use of a low X-ray-background film as a crystallization support and a photoablation laser that enable the automation of major operations required for the preparation of crystals for X-ray diffraction experiments. In this approach, the controlled removal of the mother liquor before crystal mounting simplifies the cryocooling process, in many cases eliminating the use of cryoprotectant agents, while crystal-soaking experiments are performed through diffusion, precluding the need for repeated sample-recovery and transfer operations. Moreover, the high-precision laser enables new mounting strategies that are not accessible through other methods. This approach bridges an important gap in automation and can contribute to expanding the capabilities of modern macromolecular crystallography facilities.

Discovery of (2S)-8-[(3R)-3-methylmorpholin-4-yl]-1-(3-methyl-2-oxobutyl)-2-(trifluoromethyl)-3,4-dihydro-2H-pyrimido[1,2-a]pyrimidin-6-one: a novel potent and selective inhibitor of Vps34 for the treatment of solid tumors.

Vps34 (the human class III phosphoinositide 3-kinase) is a lipid kinase involved in vesicle trafficking and autophagy and therefore constitutes an interesting target for cancer treatment. Because of the lack of specific Vps34 kinase inhibitors, we aimed to identify such compounds to further validate the role of this lipid kinase in cancer maintenance and progression. Herein, we report the discovery of a series of tetrahydropyrimidopyrimidinone derivatives. Starting with hit compound 1a, medicinal chemistry optimization led to compound 31. This molecule displays potent activity, an exquisite selectivity for Vps34 with excellent properties. The X-ray crystal structure of compound 31 in human Vps34 illustrates how the unique molecular features of the morpholine synthon bestows selectivity against class I PI3Ks. This molecule exhibits suitable in vivo mouse PK parameters and induces a sustained inhibition of Vps34 upon acute administration. Compound 31 constitutes an optimized Vps34 inhibitor that could be used to investigate human cancer biology.

Selective inhibition of mutant isocitrate dehydrogenase 1 (IDH1) via disruption of a metal binding network by an allosteric small molecule.

Cancer-associated point mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) confer a neomorphic enzymatic activity: the reduction of α-ketoglutarate to d-2-hydroxyglutaric acid, which is proposed to act as an oncogenic metabolite by inducing hypermethylation of histones and DNA. Although selective inhibitors of mutant IDH1 and IDH2 have been identified and are currently under investigation as potential cancer therapeutics, the mechanistic basis for their selectivity is not yet well understood. A high throughput screen for selective inhibitors of IDH1 bearing the oncogenic mutation R132H identified compound 1, a bis-imidazole phenol that inhibits d-2-hydroxyglutaric acid production in cells. We investigated the mode of inhibition of compound 1 and a previously published IDH1 mutant inhibitor with a different chemical scaffold. Steady-state kinetics and biophysical studies show that both of these compounds selectively inhibit mutant IDH1 by binding to an allosteric site and that inhibition is competitive with respect to Mg(2+). A crystal structure of compound 1 complexed with R132H IDH1 indicates that the inhibitor binds at the dimer interface and makes direct contact with a residue involved in binding of the catalytically essential divalent cation. These results show that targeting a divalent cation binding residue can enable selective inhibition of mutant IDH1 and suggest that differences in magnesium binding between wild-type and mutant enzymes may contribute to the inhibitors' selectivity for the mutant enzyme.

A highly potent and selective Vps34 inhibitor alters vesicle trafficking and autophagy.

Vps34 is a phosphoinositide 3-kinase (PI3K) class III isoform that has attracted major attention over the recent years because of its role in autophagy. Herein we describe the biological characterization of SAR405, which is a low-molecular-mass kinase inhibitor of Vps34 (KD 1.5 nM). This compound has an exquisite protein and lipid kinase selectivity profile that is explained by its unique binding mode and molecular interactions within the ATP binding cleft of human Vps34. To the best of our knowledge, this is the first potent and specific Vps34 inhibitor described so far. Our results demonstrate that inhibition of Vps34 kinase activity by SAR405 affects both late endosome-lysosome compartments and prevents autophagy. Moreover, we show that the concomitant inhibition of Vps34 and mTOR, with SAR405 and the US Food and Drug Administration-approved mTOR inhibitor everolimus, results in synergistic antiproliferative activity in renal tumor cell lines, indicating a potential clinical application in cancer.

Structures of a pan-specific antagonist antibody complexed to different isoforms of TGFß reveal structural plasticity of antibody-antigen interactions.

Various important biological pathways are modulated by TGFß isoforms; as such they are potential targets for therapeutic intervention. Fresolimumab, also known as GC1008, is a pan-TGFß neutralizing antibody that has been tested clinically for several indications including an ongoing trial for focal segmental glomerulosclerosis. The structure of the antigen-binding fragment of fresolimumab (GC1008 Fab) in complex with TGFß3 has been reported previously, but the structural capacity of fresolimumab to accommodate tight interactions with TGFß1 and TGFß2 was insufficiently understood. We report the crystal structure of the single-chain variable fragment of fresolimumab (GC1008 scFv) in complex with target TGFß1 to a resolution of 3.00 Å and the crystal structure of GC1008 Fab in complex with TGFß2 to 2.83 Å. The structures provide further insight into the details of TGFß recognition by fresolimumab, give a clear indication of the determinants of fresolimumab pan-specificity and provide potential starting points for the development of isoform-specific antibodies using a fresolimumab scaffold.

Discovery and optimization of pyrimidone indoline amide PI3Kß inhibitors for the treatment of phosphatase and tensin homologue (PTEN)-deficient cancers.

Compelling molecular biology publications have reported the implication of phosphoinositide kinase PI3Kß in PTEN-deficient cell line growth and proliferation. These findings supported a scientific rationale for the development of PI3Kß-specific inhibitors for the treatment of PTEN-deficient cancers. This paper describes the discovery of 2-[2-(2,3-dihydro-indol-1-yl)-2-oxo-ethyl]-6-morpholin-4-yl-3H-pyrimidin-4-one (7) and the optimization of this new series of active and selective pyrimidone indoline amide PI3Kß inhibitors. 2-[2-(2-Methyl-2,3-dihydro-indol-1-yl)-2-oxo-ethyl]-6-morpholin-4-yl-3H-pyrimidin-4-one (28), identified following a carefully designed methyl scan, displayed improved physicochemical and in vitro pharmacokinetic properties. Structural biology efforts enabled the acquisition of the first X-ray cocrystal structure of p110ß with the selective inhibitor compound 28 bound to the ATP site. The nonplanar binding mode described herein is consistent with observed structure-activity relationship for the series. Compound 28 demonstrated significant in vivo activity in a UACC-62 xenograft model in mice, warranting further preclinical investigation. Following successful development, compound 28 entered phase I/Ib clinical trial in patients with advanced cancer.

Structure-based library design and the discovery of a potent and selective mast cell ß-tryptase inhibitor as an oral therapeutic agent.

A solid phase combinatorial library was designed based on X-ray structures and in-silico models to explore an inducible S4+ pocket, which is formed by a simple side-chain rotation of Tyr95. This inducible S4+ pocket is unique to ß-tryptase and does not exist for other trypsin-like serine proteases of interest. Therefore, inhibitors utilizing this pocket have inherent advantages for being selective against other proteases in the same family. A member of this library was found to be a potent and selective ß-tryptase inhibitor with a suitable pharmacokinetic profile for further clinical evaluation.

Sulfonylthiadiazoles with an unusual binding mode as partial dual peroxisome proliferator-activated receptor (PPAR) γ/δ agonists with high potency and in†vivo efficacy.

Compounds that simultaneously activate the peroxisome proliferator-activated receptor (PPAR) subtypes PPARγ and PPARδ have the potential to effectively target dyslipidemia and type II diabetes in a single pharmaceutically active molecule. The frequently observed side effects of selective PPARγ agonists, such as edema and weight gain, are expected to be overcome by using partial instead of full agonists for this nuclear receptor family. Herein we report the discovery, synthesis, and optimization of a novel series of sulfonylthiadiazoles that are active as partial agonists. The initial compound 6 was discovered by high-throughput screening as a moderate partial PPARδ agonist; its optimization was based on the X-ray crystal structure in complex with PPARδ. In contrast to other PPARδ agonists, this ligand does not interact directly with residues from the activation helix AF-2, which might be linked to its partial agonistic effect. Interestingly, the thiadiazole moiety fills a novel subpocket, which becomes accessible after moderate conformational rearrangement. The optimization was focused on introducing conformational constraints and replacing intramolecular hydrogen bonding interactions. Highly potent molecules with activity as dual partial PPARγ/δ agonists in the low nanomolar range were then identified. One of the most active members, compound 20 a, displayed EC50 values of 1.6 and 336 nM for PPARδ and γ, respectively. The X-ray crystal structure of its complex with PPARδ confirms our design hypothesis. Compound 20 a clearly displayed in vivo activity in two chronic mice studies. Lipids were modified in a beneficial way in normolipidemic mice, and the development of overt diabetes could be prevented in pre-diabetic db/db mice. However, body weight gain was similar to that observed with the PPARγ agonist rosiglitazone. Hence, active compounds from this series can be considered as valuable tools to elucidate the complex roles of dual PPARγ/δ agonists for potential treatment of metabolic syndrome.

Molecular shape and medicinal chemistry: a perspective.

The eight contributions here provide ample evidence that shape as a volume or as a surface is a vibrant and useful concept when applied to drug discovery. It provides a reliable scaffold for "decoration" with chemical intuition (or bias) for virtual screening and lead optimization but also has its unadorned uses, as in library design, ligand fitting, pose prediction, or active site description. Computing power has facilitated this evolution by allowing shape to be handled precisely without the need to reduce down to point descriptors or approximate metrics, and the diversity of resultant applications argues for this being an important step forward. Certainly, it is encouraging that as computation has enabled our intuition, molecular shape has consistently surprised us in its usefulness and adaptability. The first Aurelius question, "What is the essence of a thing?", seems well answered, however, the third, "What do molecules do?", only partly so. Are the topics covered here exhaustive, or is there more to come? To date, there has been little published on the use of the volumetric definition of shape described here as a QSAR variable, for instance, in the prediction or classification of activity, although other shape definitions have been successful applied, for instance, as embodied in the Compass program described above in "Shape from Surfaces". Crystal packing is a phenomenon much desired to be understood. Although powerful models have been applied to the problem, to what degree is this dominated purely by the shape of a molecule? The shape comparison described here is typically of a global nature, and yet some importance must surely be placed on partial shape matching, just as the substructure matching of chemical graphs has proved useful. The approach of using surfaces, as described here, offers some flavor of this, as does the use of metrics that penalize volume mismatch less than the Tanimoto, e.g., Tversky measures. As yet, there is little to go on as to how useful a paradigm this will be because there is less software and fewer concrete results.Finally, the distance between molecular shapes, or between any shapes defined as volumes or surfaces, is a metric property in the mathematical sense of the word. As yet, there has been little, if any, application of this observation. We cannot know what new application to the design and discovery of pharmaceuticals may yet arise from the simple concept of molecular shape, but it is fair to say that the progress so far is impressive.

Design, synthesis, and biological activity of potent and selective inhibitors of mast cell tryptase.

A new series of novel mast cell tryptase inhibitors is reported, which features the use of an indole structure as the hydrophobic substituent on a m-benzylaminepiperidine template. The best members of this series display good in vitro activity and excellent selectivity against other serine proteases.

Design, synthesis and characterization of a novel class of coumarin-based inhibitors of inducible nitric oxide synthase.

Inducible nitric oxide synthase (iNOS) has been implicated in various central and peripheral pathophysiological diseases. Our high throughput screening initially identified a weak inhibitor of iNOS, thiocoumarin 13. From this lead, a number of potent derivatives were prepared that demonstrate favorable potency, selectivity and kinetics. Compound 30 has an IC50 of 60 nM for mouse iNOS and 185-fold and 9-fold selectivity for bovine eNOS and rat nNOS, respectively. In cellular assays for iNOS, this compound has micromolar potency. Furthermore, two compounds (16 and 30) demonstrate a reasonable pharmacokinetic profile in rodents. The synthesis, SAR, and biological activity of this novel class of compounds is described.

Escherichia coli FolC structure reveals an unexpected dihydrofolate binding site providing an attractive target for anti-microbial therapy.

In some bacteria, such as Escherichia coli, the addition of L-glutamate to dihydropteroate (dihydrofolate synthetase activity) and the subsequent additions of L-glutamate to tetrahydrofolate (folylpolyglutamate synthetase (FPGS) activity) are catalyzed by the same enzyme, FolC. The crystal structure of E. coli FolC is described in this paper. It showed strong similarities to that of the FPGS enzyme of Lactobacillus casei within the ATP binding site and the catalytic site, as do all other members of the Mur synthethase superfamily. FolC structure revealed an unexpected dihydropteroate binding site very different from the folate site identified previously in the FPGS structure. The relevance of this site is exemplified by the presence of phosphorylated dihydropteroate, a reaction intermediate in the DHFS reaction. L. casei FPGS is considered a relevant model for human FPGS. As such, the presence of a folate binding site in E. coli FolC, which is different from the one seen in FPGS enzymes, provides avenues for the design of specific inhibitors of this enzyme in antimicrobial therapy.