Orthogonal IMiD-Degron Pairs Induce Selective Protein Degradation in Cells.

Immunomodulatory imide drugs (IMiDs) including thalidomide, lenalidomide, and pomalidomide, can be used to induce degradation of a protein of interest that is fused to a short zinc finger (ZF) degron motif. These IMiDs, however, also induce degradation of endogenous neosubstrates, including IKZF1 and IKZF3. To improve degradation selectivity, we took a bump-and-hole approach to design and screen bumped IMiD analogs against 8380 ZF mutants. This yielded a bumped IMiD analog that induces efficient degradation of a mutant ZF degron, while not affecting other cellular proteins, including IKZF1 and IKZF3. In proof-of-concept studies, this system was applied to induce efficient degradation of TRIM28, a disease-relevant protein with no known small molecule binders. We anticipate that this system will make a valuable addition to the current arsenal of degron systems for use in target validation.

Identification and Optimization of a Ligand-Efficient Benzoazepinone Bromodomain and Extra Terminal (BET) Family Acetyl-Lysine Mimetic into the Oral Candidate Quality Molecule I-BET432.

The bromodomain and extra terminal (BET) family of proteins are an integral part of human epigenome regulation, the dysregulation of which is implicated in multiple oncology and inflammatory diseases. Disrupting the BET family bromodomain acetyl-lysine (KAc) histone protein-protein interaction with small-molecule KAc mimetics has proven to be a disease-relevant mechanism of action, and multiple molecules are currently undergoing oncology clinical trials. This work describes an efficiency analysis of published GSK pan-BET bromodomain inhibitors, which drove a strategic choice to focus on the identification of a ligand-efficient KAc mimetic with the hypothesis that lipophilic efficiency could be drastically improved during optimization. This focus drove the discovery of the highly ligand-efficient and structurally distinct benzoazepinone KAc mimetic. Following crystallography to identify suitable growth vectors, the benzoazepinone core was optimized through an explore-exploit structure-activity relationship (SAR) approach while carefully monitoring lipophilic efficiency to deliver I-BET432 (41) as an oral candidate quality molecule.

Design, Synthesis, and Characterization of I-BET567, a Pan-Bromodomain and Extra Terminal (BET) Bromodomain Oral Candidate.

Through regulation of the epigenome, the bromodomain and extra terminal (BET) family of proteins represent important therapeutic targets for the treatment of human disease. Through mimicking the endogenous N-acetyl-lysine group and disrupting the protein-protein interaction between histone tails and the bromodomain, several small molecule pan-BET inhibitors have progressed to oncology clinical trials. This work describes the medicinal chemistry strategy and execution to deliver an orally bioavailable tetrahydroquinoline (THQ) pan-BET candidate. Critical to the success of this endeavor was a potency agnostic analysis of a data set of 1999 THQ BET inhibitors within the GSK collection which enabled identification of appropriate lipophilicity space to deliver compounds with a higher probability of desired oral candidate quality properties. SAR knowledge was leveraged via Free-Wilson analysis within this design space to identify a small group of targets which ultimately delivered I-BET567 (27), a pan-BET candidate inhibitor that demonstrated efficacy in mouse models of oncology and inflammation.

Development of an intracellular quantitative assay to measure compound binding kinetics.

Contemporary drug discovery typically quantifies the effect of a molecule on a biological target using the equilibrium-derived measurements of IC50, EC50, or KD. Kinetic descriptors of drug binding are frequently linked with the effectiveness of a molecule in modulating a disease phenotype; however, these parameters are yet to be fully adopted in early drug discovery. Nanoluciferase bioluminescence resonance energy transfer (NanoBRET) can be used to measure interactions between fluorophore-conjugated probes and luciferase fused target proteins. Here, we describe an intracellular NanoBRET competition assay that can be used to quantify cellular kinetic rates of compound binding to nanoluciferase-fused bromodomain and extra-terminal (BET) proteins. Comparative rates are generated using a cell-free NanoBRET assay and by utilizing orthogonal recombinant protein-based methodologies. A screen of known pan-BET inhibitors is used to demonstrate the value of this approach in the investigation of kinetic selectivity between closely related proteins.

Discovery of a Novel Bromodomain and Extra Terminal Domain (BET) Protein Inhibitor, I-BET282E, Suitable for Clinical Progression.

The functions of the bromodomain and extra terminal (BET) family of proteins have been implicated in a wide range of diseases, particularly in the oncology and immuno-inflammatory areas, and several inhibitors are under investigation in the clinic. To mitigate the risk of attrition of these compounds due to structurally related toxicity findings, additional molecules from distinct chemical series were required. Here we describe the structure- and property-based optimization of the in vivo tool molecule I-BET151 toward I-BET282E, a molecule with properties suitable for progression into clinical studies.

Optimization of Naphthyridones into Selective TATA-Binding Protein Associated Factor 1 (TAF1) Bromodomain Inhibitors.

Bromodomain containing proteins and the acetyl-lysine binding bromodomains contained therein are increasingly attractive targets for the development of novel epigenetic therapeutics. To help validate this target class and unravel the complex associated biology, there has been a concerted effort to develop selective small molecule bromodomain inhibitors. Herein we describe the structure-based efforts and multiple challenges encountered in optimizing a naphthyridone template into selective TAF1(2) bromodomain inhibitors which, while unsuitable as chemical probes themselves, show promise for the future development of small molecules to interrogate TAF1(2) biology. Key to this work was the introduction and modulation of the basicity of a pendant amine which had a substantial impact on not only bromodomain selectivity but also cellular target engagement.

Optimization of a Series of RIPK2 PROTACs.

Receptor-interacting serine/threonine protein kinase 2 (RIPK2) is an important kinase of the innate immune system. Herein, we describe the optimization of a series of RIPK2 PROTACs which recruit members of the inhibitor of apoptosis (IAP) family of E3 ligases. Our PROTAC optimization strategy focused on reducing the lipophilicity of the early lead which resulted in the identification of analogues with improved solubility and increased human and rat microsomal stability. We identified a range of IAP binders that were successfully incorporated into potent RIPK2 PROTACs with attractive pharmacokinetic profiles. Compound 20 possessed the best overall profile with good solubility, potent degradation of RIPK2, and associated inhibition of TNFα release. A proof-of-concept study utilizing a slow release matrix demonstrated the feasibility of a long-acting parenteral formulation with >1 month duration. This represents an attractive alternative dosing paradigm to oral delivery, especially for chronic diseases where compliance can be challenging.

Fragment-based Scaffold Hopping: Identification of Potent, Selective, and Highly Soluble Bromo and Extra Terminal Domain (BET) Second Bromodomain (BD2) Inhibitors.

The profound efficacy of pan-BET inhibitors is well documented, but these epigenetic agents have shown pharmacology-driven toxicity in oncology clinical trials. The opportunity to identify inhibitors with an improved safety profile by selective targeting of a subset of the eight bromodomains of the BET family has triggered extensive medicinal chemistry efforts. In this article, we disclose the identification of potent and selective drug-like pan-BD2 inhibitors such as pyrazole 23 (GSK809) and furan 24 (GSK743) that were derived from the pyrrole fragment 6. We transpose the key learnings from a previous pyridone series (GSK620 2 as a representative example) to this novel class of inhibitors, which are characterized by significantly improved solubility relative to our previous research.

Optimization of a Series of 2,3-Dihydrobenzofurans as Highly Potent, Second Bromodomain (BD2)-Selective, Bromo and Extra-Terminal Domain (BET) Inhibitors.

Herein, a series of 2,3-dihydrobenzofurans have been developed as highly potent bromo and extra-terminal domain (BET) inhibitors with 1000-fold selectivity for the second bromodomain (BD2) over the first bromodomain (BD1). Investment in the development of two orthogonal synthetic routes delivered inhibitors that were potent and selective but had raised in vitro clearance and suboptimal solubility. Insertion of a quaternary center into the 2,3-dihydrobenzofuran core blocked a key site of metabolism and improved the solubility. This led to the development of inhibitor 71 (GSK852): a potent, 1000-fold-selective, highly soluble compound with good in vivo rat and dog pharmacokinetics.

Template-Hopping Approach Leads to Potent, Selective, and Highly Soluble Bromo and Extraterminal Domain (BET) Second Bromodomain (BD2) Inhibitors.

A number of reports have recently been published describing the discovery and optimization of bromo and extraterminal inhibitors which are selective for the second bromodomain (BD2); these include our own work toward GSK046 (3) and GSK620 (5). This paper describes our approach to mitigating the genotoxicity risk of GSK046 by replacement of the acetamide functionality with a heterocyclic ring. This was followed by a template-hopping and hybridization approach, guided by structure-based drug design, to incorporate learnings from other BD2-selective series, optimize the vector for the amide region, and explore the ZA cleft, leading to the identification of potent, selective, and bioavailable compounds 28 (GSK452), 39 (GSK737), and 36 (GSK217).

Structure-Based Design of a Bromodomain and Extraterminal Domain (BET) Inhibitor Selective for the N-Terminal Bromodomains That Retains an Anti-inflammatory and Antiproliferative Phenotype.

The bromodomain and extraterminal domain (BET) family of epigenetic regulators comprises four proteins (BRD2, BRD3, BRD4, BRDT), each containing tandem bromodomains. To date, small molecule inhibitors of these proteins typically bind all eight bromodomains of the family with similar affinity, resulting in a diverse range of biological effects. To enable further understanding of the broad phenotype characteristic of pan-BET inhibition, the development of inhibitors selective for individual, or sets of, bromodomains within the family is required. In this regard, we report the discovery of a potent probe molecule possessing up to 150-fold selectivity for the N-terminal bromodomains (BD1s) over the C-terminal bromodomains (BD2s) of the BETs. Guided by structural information, a specific amino acid difference between BD1 and BD2 domains was targeted for selective interaction with chemical functionality appended to the previously developed I-BET151 scaffold. Data presented herein demonstrate that selective inhibition of BD1 domains is sufficient to drive anti-inflammatory and antiproliferative effects.

GSK973 Is an Inhibitor of the Second Bromodomains (BD2s) of the Bromodomain and Extra-Terminal (BET) Family.

Pan-BET inhibitors have shown profound efficacy in a number of in vivo preclinical models and have entered the clinic in oncology trials where adverse events have been reported. These inhibitors interact equipotently with the eight bromodomains of the BET family of proteins. To better understand the contribution of each domain to their efficacy and to improve from their safety profile, selective inhibitors are required. This Letter discloses the profile of GSK973, a highly selective inhibitor of the second bromodomains of the BET proteins that has undergone extensive preclinical in vitro and in vivo characterization.

GSK789: A Selective Inhibitor of the First Bromodomains (BD1) of the Bromo and Extra Terminal Domain (BET) Proteins.

Pan-bromodomain and extra terminal (BET) inhibitors interact equipotently with all eight bromodomains of the BET family of proteins. They have shown profound efficacy in vitro and in vivo in oncology and immunomodulatory models, and a number of them are currently in clinical trials where significant safety signals have been reported. It is therefore important to understand the functional contribution of each bromodomain to assess the opportunity to tease apart efficacy and toxicity. This article discloses the in vitro and cellular activity profiles of GSK789, a potent, cell-permeable, and highly selective inhibitor of the first bromodomains of the BET family.

Design and Synthesis of a Highly Selective and In Vivo-Capable Inhibitor of the Second Bromodomain of the Bromodomain and Extra Terminal Domain Family of Proteins.

Pan-bromodomain and extra terminal domain (BET) inhibitors interact equipotently with the eight bromodomains of the BET family of proteins and have shown profound efficacy in a number of in vitro phenotypic assays and in vivo pre-clinical models in inflammation or oncology. A number of these inhibitors have progressed to the clinic where pharmacology-driven adverse events have been reported. To better understand the contribution of each domain to their efficacy and improve their safety profile, selective inhibitors are required. This article discloses the profile of GSK046, also known as iBET-BD2, a highly selective inhibitor of the second bromodomains of the BET proteins that has undergone extensive pre-clinical in vitro and in vivo characterization.

Neonatal management and outcomes during the COVID-19 pandemic: an observation cohort study.

BACKGROUND: The risk of vertical and perinatal transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, which causes COVID-19), the most appropriate management, and the neonate's risk of developing COVID-19 during the perinatal period are unknown. Therefore, we aimed to elucidate best practices regarding infection control in mother-newborn dyads, and identify potential risk factors associated with transmission. METHODS: In this observational cohort study, we identified all neonates born between March 22 and May 17, 2020, at three New York Presbyterian Hospitals in New York City (NY, USA) to mothers positive for SARS-CoV-2 at delivery. Mothers could practice skin-to-skin care and breastfeed in the delivery room, but had to wear a surgical mask when near their neonate and practice proper hand hygiene before skin-to-skin contact, breastfeeding, and routine care. Unless medically required, neonates were kept in a closed Giraffe isolette in the same room as their mothers, and were held by mothers for feeding after appropriate hand hygiene, breast cleansing, and placement of a surgical mask. Neonates were tested for SARS-CoV-2 by use of real-time PCR on nasopharyngeal swabs taken at 24 h, 5-7 days, and 14 days of life, and were clinically evaluated by telemedicine at 1 month of age. We recorded demographics, neonatal, and maternal clinical presentation, as well as infection control practices in the hospital and at home. FINDINGS: Of 1481 deliveries, 116 (8%) mothers tested positive for SARS-CoV-2; 120 neonates were identified. All neonates were tested at 24 h of life and none were positive for SARS-CoV-2. 82 (68%) neonates completed follow-up at day 5-7 of life. Of the 82 neonates, 68 (83%) roomed in with the mothers. All mothers were allowed to breastfeed; at 5-7 days of life, 64 (78%) were still breastfeeding. 79 (96%) of 82 neonates had a repeat PCR at 5-7 days of life, which was negative in all; 72 (88%) neonates were also tested at 14 days of life and none were positive. None of the neonates had symptoms of COVID-19. INTERPRETATION: Our data suggest that perinatal transmission of COVID-19 is unlikely to occur if correct hygiene precautions are undertaken, and that allowing neonates to room in with their mothers and direct breastfeeding are safe procedures when paired with effective parental education of infant protective strategies. FUNDING: None.

The Optimization of a Novel, Weak Bromo and Extra Terminal Domain (BET) Bromodomain Fragment Ligand to a Potent and Selective Second Bromodomain (BD2) Inhibitor.

The profound efficacy, yet associated toxicity of pan-BET inhibitors is well documented. The possibility of an ameliorated safety profile driven by significantly selective (>100-fold) inhibition of a subset of the eight bromodomains is enticing, but challenging given the close homology. Herein, we describe the X-ray crystal structure-directed optimization of a novel weak fragment ligand with a pan-second bromodomain (BD2) bias, to potent and highly BD2 selective inhibitors. A template hopping approach, enabled by our parallel research into an orthogonal template (15, GSK046), was the basis for the high selectivity observed. This culminated in two tool molecules, 20 (GSK620) and 56 (GSK549), which showed an anti-inflammatory phenotype in human whole blood, confirming their cellular target engagement. Excellent broad selectivity, developability, and in vivo oral pharmacokinetics characterize these tools, which we hope will be of broad utility to the field of epigenetics research.

Application of Atypical Acetyl-lysine Methyl Mimetics in the Development of Selective Inhibitors of the Bromodomain-Containing Protein 7 (BRD7)/Bromodomain-Containing Protein 9 (BRD9) Bromodomains.

Non-BET bromodomain-containing proteins have become attractive targets for the development of novel therapeutics targeting epigenetic pathways. To help facilitate the target validation of this class of proteins, structurally diverse small-molecule ligands and methodologies to produce selective inhibitors in a predictable fashion are in high demand. Herein, we report the development and application of atypical acetyl-lysine (KAc) methyl mimetics to take advantage of the differential stability of conserved water molecules in the bromodomain binding site. Discovery of the n-butyl group as an atypical KAc methyl mimetic allowed generation of 31 (GSK6776) as a soluble, permeable, and selective BRD7/9 inhibitor from a pyridazinone template. The n-butyl group was then used to enhance the bromodomain selectivity of an existing BRD9 inhibitor and to transform pan-bromodomain inhibitors into BRD7/9 selective compounds. Finally, a solvent-exposed vector was defined from the pyridazinone template to enable bifunctional molecule synthesis, and affinity enrichment chemoproteomic experiments were used to confirm several of the endogenous protein partners of BRD7 and BRD9, which form part of the chromatin remodeling PBAF and BAF complexes, respectively.

Optimization of Potent ATAD2 and CECR2 Bromodomain Inhibitors with an Atypical Binding Mode.

Most bromodomain inhibitors mimic the interactions of the natural acetylated lysine (KAc) histone substrate through key interactions with conserved asparagine and tyrosine residues within the binding pocket. Herein we report the optimization of a series of phenyl sulfonamides that exhibit a novel mode of binding to non-bromodomain and extra terminal domain (non-BET) bromodomains through displacement of a normally conserved network of four water molecules. Starting from an initial hit molecule, we report its divergent optimization toward the ATPase family AAA domain containing 2 (ATAD2) and cat eye syndrome chromosome region, candidate 2 (CECR2) domains. This work concludes with the identification of (R)-55 (GSK232), a highly selective, cellularly penetrant CECR2 inhibitor with excellent physicochemical properties.

Discovery of a Bromodomain and Extraterminal Inhibitor with a Low Predicted Human Dose through Synergistic Use of Encoded Library Technology and Fragment Screening.

The bromodomain and extraterminal (BET) family of bromodomain-containing proteins are important regulators of the epigenome through their ability to recognize N-acetyl lysine (KAc) post-translational modifications on histone tails. These interactions have been implicated in various disease states and, consequently, disruption of BET-KAc binding has emerged as an attractive therapeutic strategy with a number of small molecule inhibitors now under investigation in the clinic. However, until the utility of these advanced candidates is fully assessed by these trials, there remains scope for the discovery of inhibitors from new chemotypes with alternative physicochemical, pharmacokinetic, and pharmacodynamic profiles. Herein, we describe the discovery of a candidate-quality dimethylpyridone benzimidazole compound which originated from the hybridization of a dimethylphenol benzimidazole series, identified using encoded library technology, with an N-methyl pyridone series identified through fragment screening. Optimization via structure- and property-based design led to I-BET469, which possesses favorable oral pharmacokinetic properties, displays activity in vivo, and is projected to have a low human efficacious dose.