Discovery and Preclinical Characterization of BIIB129, a Covalent, Selective, and Brain-Penetrant BTK Inhibitor for the Treatment of Multiple Sclerosis.

Multiple sclerosis (MS) is a chronic disease with an underlying pathology characterized by inflammation-driven neuronal loss, axonal injury, and demyelination. Bruton's tyrosine kinase (BTK), a nonreceptor tyrosine kinase and member of the TEC family of kinases, is involved in the regulation, migration, and functional activation of B cells and myeloid cells in the periphery and the central nervous system (CNS), cell types which are deemed central to the pathology contributing to disease progression in MS patients. Herein, we describe the discovery of BIIB129 (25), a structurally distinct and brain-penetrant targeted covalent inhibitor (TCI) of BTK with an unprecedented binding mode responsible for its high kinome selectivity. BIIB129 (25) demonstrated efficacy in disease-relevant preclinical in vivo models of B cell proliferation in the CNS, exhibits a favorable safety profile suitable for clinical development as an immunomodulating therapy for MS, and has a low projected total human daily dose.

A Tiny Pocket Packs a Punch: Leveraging Pyridones for the Discovery of CNS-Penetrant Aza-indazole IRAK4 Inhibitors.

We herein report the discovery, synthesis, and evolution of a series of indazoles and azaindazoles as CNS-penetrant IRAK4 inhibitors. Described is the use of structure-based and property-based drug design strategically leveraged to guide the property profile of a key series into a favorable property space while maintaining potency and selectivity. Our rationale that led toward functionalities with potency improvements, CNS-penetration, solubility, and favorable drug-like properties is portrayed. In vivo evaluation of an advanced analogue showed significant, dose-dependent modulation of inflammatory cytokines in a mouse model. In pursuit of incorporating a highly engineered bridged ether that was crucial to metabolic stability in this series, significant synthetic challenges were overcome to enable the preparation of the analogues.

Discovery of BIO-8169─A Highly Potent, Selective, and Brain-Penetrant IRAK4 Inhibitor for the Treatment of Neuroinflammation.

Interleukin receptor associated kinase 4 (IRAK4) plays an important role in innate immune signaling through Toll-like and interleukin-1 receptors and represents an attractive target for the treatment of inflammatory diseases and cancer. We previously reported the development of a potent, selective, and brain-penetrant imidazopyrimidine series of IRAK4 inhibitors. However, lead molecule BIO-7488 (1) suffered from low solubility which led to variable PK, compound accumulation, and poor in vivo tolerability. Herein, we describe the discovery of a series of pyridone analogs with improved solubility which are highly potent, selective and demonstrate desirable PK profiles including good oral bioavailability and excellent brain penetration. BIO-8169 (2) reduced the in vivo production of pro-inflammatory cytokines, was well tolerated in safety studies in rodents and dog at margins well above the predicted efficacious exposure and showed promising results in a mouse model for multiple sclerosis.

The Discovery of 7-Isopropoxy-2-(1-methyl-2-oxabicyclo[2.1.1]hexan-4-yl)-N-(6-methylpyrazolo[1,5-a]pyrimidin-3-yl)imidazo[1,2-a]pyrimidine-6-carboxamide (BIO-7488), a Potent, Selective, and CNS-Penetrant IRAK4 Inhibitor for the Treatment of Ischemic Stroke.

Interleukin receptor-associated kinase 4 (IRAK4) is a key node of signaling within the innate immune system that regulates the production of inflammatory cytokines and chemokines. The presence of damage-associated molecular patterns (DAMPs) after tissue damage such as stroke or traumatic brain injury (TBI) initiates signaling through the IRAK4 pathway that can lead to a feed-forward inflammatory loop that can ultimately hinder patient recovery. Herein, we describe the first potent, selective, and CNS-penetrant IRAK4 inhibitors for the treatment of neuroinflammation. Lead compounds from the series were evaluated in CNS PK/PD models of inflammation, as well as a mouse model of ischemic stroke. The SAR optimization detailed within culminates in the discovery of BIO-7488, a highly selective and potent IRAK4 inhibitor that is CNS penetrant and has excellent ADME properties.

Discovery of structural diverse reversible BTK inhibitors utilized to develop a novel in vivo CD69 and CD86 PK/PD mouse model.

For the past two decades, BTK a tyrosine kinase and member of the Tec family has been a drug target of significant interest due to its potential to selectively treat various B cell-mediated diseases such as CLL, MCL, RA, and MS. Owning to the challenges encountered in identifying drug candidates exhibiting the potency block B cell activation via BTK inhibition, the pharmaceutical industry has relied on the use of covalent/irreversible inhibitors to address this unmet medical need. Herein, we describe a medicinal chemistry campaign to identify structurally diverse reversible BTK inhibitors originating from HITS identified using a fragment base screen. The leads were optimized to improve the potency and in vivo ADME properties resulting in a structurally distinct chemical series used to develop and validate a novel in vivo CD69 and CD86 PD assay in rodents.

Discovery of Phospholipase D Inhibitors with Improved Drug-like Properties and Central Nervous System Penetrance.

Phospholipase D (PLD) is a phospholipase enzyme responsible for hydrolyzing phosphatidylcholine into the lipid signaling molecule, phosphatidic acid, and choline. From a therapeutic perspective, PLD has been implicated in human cancer progression as well as a target for neurodegenerative diseases, including Alzheimer's. Moreover, knockdown of PLD rescues the ALS phenotype in multiple Drosophila models of ALS (amyotrophic lateral sclerosis) and displays modest motor benefits in an SOD1 ALS mouse model. To further validate whether inhibiting PLD is beneficial for the treatment of ALS, a brain penetrant small molecule inhibitor with suitable PK properties to test in an ALS animal model is needed. Using a combination of ligand-based drug discovery and structure-based design, a dual PLD1/PLD2 inhibitor was discovered that is single digit nanomolar in the Calu-1 cell assay and has suitable PK properties for in vivo studies. To capture the in vivo measurement of PLD inhibition, a transphosphatidylation pharmacodynamic LC-MS assay was developed, in which a dual PLD1/PLD2 inhibitor was found to reduce PLD activity by 15-20-fold.

Optimization of a novel piperazinone series as potent selective peripheral covalent BTK inhibitors.

BTK is a tyrosine kinase playing an important role in B cell and myeloid cell functions through B cell receptor (BCR) signaling and Fc receptor (FcR) signaling. Selective inhibition of BTK has the potential to provide therapeutical benefits to patients suffering from autoimmune diseases. Here we report the design, optimization, and characterization of novel potent and highly selective covalent BTK inhibitors. Starting from a piperazinone hit derived from a selective reversible inhibitor, we solved the whole blood cellular potency issue by introducing an electrophilic warhead to reach Cys481. This design led to a covalent irreversible BTK inhibitor series with excellent kinase selectivity as well as good whole blood CD69 cellular potency. Optimization of metabolic stability led to representative compounds like 42, which demonstrated strong cellular target occupancy and inhibition of B-cell proliferation measured by proximal and distal functional activity.

Discovery and Preclinical Characterization of BIIB091, a Reversible, Selective BTK Inhibitor for the Treatment of Multiple Sclerosis.

Multiple Sclerosis is a chronic autoimmune neurodegenerative disorder of the central nervous system (CNS) that is characterized by inflammation, demyelination, and axonal injury leading to permeant disability. In the early stage of MS, inflammation is the primary driver of the disease progression. There remains an unmet need to develop high efficacy therapies with superior safety profiles to prevent the inflammation processes leading to disability. Herein, we describe the discovery of BIIB091, a structurally distinct orthosteric ATP competitive, reversible inhibitor that binds the BTK protein in a DFG-in confirmation designed to sequester Tyr-551, an important phosphorylation site on BTK, into an inactive conformation with excellent affinity. Preclinical studies demonstrated BIB091 to be a high potency molecule with good drug-like properties and a safety/tolerability profile suitable for clinical development as a highly selective, reversible BTKi for treating autoimmune diseases such as MS.

Discovery of BIIB068: A Selective, Potent, Reversible Bruton's Tyrosine Kinase Inhibitor as an Orally Efficacious Agent for Autoimmune Diseases.

Autoreactive B cell-derived antibodies form immune complexes that likely play a pathogenic role in autoimmune diseases. In systemic lupus erythematosus (SLE), these antibodies bind Fc receptors on myeloid cells and induce proinflammatory cytokine production by monocytes and NETosis by neutrophils. Bruton's tyrosine kinase (BTK) is a non-receptor tyrosine kinase that signals downstream of Fc receptors and plays a transduction role in antibody expression following B cell activation. Given the roles of BTK in both the production and sensing of autoreactive antibodies, inhibitors of BTK kinase activity may provide therapeutic value to patients suffering from autoantibody-driven immune disorders. Starting from an in-house proprietary screening hit followed by structure-based rational design, we have identified a potent, reversible BTK inhibitor, BIIB068 (1), which demonstrated good kinome selectivity with good overall drug-like properties for oral dosing, was well tolerated across preclinical species at pharmacologically relevant doses with good ADME properties, and achieved >90% inhibition of BTK phosphorylation (pBTK) in humans.

Conserved Outer Tegument Component UL11 from Herpes Simplex Virus 1 Is an Intrinsically Disordered, RNA-Binding Protein.

A distinguishing morphological feature of all herpesviruses is the multiprotein tegument layer located between the nucleocapsid and lipid envelope of the virion. Tegument proteins play multiple roles in viral replication, including viral assembly, but we do not yet understand their individual functions or how the tegument is assembled and organized. UL11, the smallest tegument protein, is important for several distinct processes in replication, including efficient virion morphogenesis and cell-cell spread. However, the mechanistic understanding of its role in these and other processes is limited in part by the scant knowledge of its biochemical and structural properties. Here, we report that UL11 from herpes simplex virus 1 (HSV-1) is an intrinsically disordered, conformationally dynamic protein that undergoes liquid-liquid phase separation (LLPS) in vitro Intrinsic disorder may underlie the ability of UL11 to exert multiple functions and bind multiple partners. Sequence analysis suggests that not only all UL11 homologs but also all HSV-1 tegument proteins contain intrinsically disordered regions of different lengths. The presence of intrinsic disorder, and potentially, the ability to form LLPS, may thus be a common feature of the tegument proteins. We hypothesize that tegument assembly may involve the formation of a biomolecular condensate, driven by the heterogeneous mixture of intrinsically disordered tegument proteins.IMPORTANCE Herpesvirus virions contain a unique tegument layer sandwiched between the capsid and lipid envelope and composed of multiple copies of about two dozen viral proteins. However, little is known about the structure of the tegument or how it is assembled. Here, we show that a conserved tegument protein UL11 from herpes simplex virus 1, a prototypical alphaherpesvirus, is an intrinsically disordered protein that undergoes liquid-liquid phase separation in vitro Through sequence analysis, we find intrinsically disordered regions of different lengths in all HSV-1 tegument proteins. We hypothesize that intrinsic disorder is a common characteristic of tegument proteins and propose a new model of tegument as a biomolecular condensate.

Human PLD structures enable drug design and characterization of isoenzyme selectivity.

Phospholipase D enzymes (PLDs) are ubiquitous phosphodiesterases that produce phosphatidic acid (PA), a key second messenger and biosynthetic building block. Although an orthologous bacterial Streptomyces sp. strain PMF PLD structure was solved two decades ago, the molecular basis underlying the functions of the human PLD enzymes (hPLD) remained unclear based on this structure due to the low homology between these sequences. Here, we describe the first crystal structures of hPLD1 and hPLD2 catalytic domains and identify novel structural elements and functional differences between the prokaryotic and eukaryotic enzymes. Furthermore, structure-based mutation studies and structures of inhibitor-hPLD complexes allowed us to elucidate the binding modes of dual and isoform-selective inhibitors, highlight key determinants of isoenzyme selectivity and provide a basis for further structure-based drug discovery and functional characterization of this therapeutically important superfamily of enzymes.

Novel Structure and Unexpected RNA-Binding Ability of the C-Terminal Domain of Herpes Simplex Virus 1 Tegument Protein UL21.

UNLABELLED: Proteins forming the tegument layers of herpesviral virions mediate many essential processes in the viral replication cycle, yet few have been characterized in detail. UL21 is one such multifunctional tegument protein and is conserved among alphaherpesviruses. While UL21 has been implicated in many processes in viral replication, ranging from nuclear egress to virion morphogenesis to cell-cell spread, its precise roles remain unclear. Here we report the 2.7-Å crystal structure of the C-terminal domain of herpes simplex virus 1 (HSV-1) UL21 (UL21C), which has a unique α-helical fold resembling a dragonfly. Analysis of evolutionary conservation patterns and surface electrostatics pinpointed four regions of potential functional importance on the surface of UL21C to be pursued by mutagenesis. In combination with the previously determined structure of the N-terminal domain of UL21, the structure of UL21C provides a 3-dimensional framework for targeted exploration of the multiple roles of UL21 in the replication and pathogenesis of alphaherpesviruses. Additionally, we describe an unanticipated ability of UL21 to bind RNA, which may hint at a yet unexplored function. IMPORTANCE: Due to the limited genomic coding capacity of viruses, viral proteins are often multifunctional, which makes them attractive antiviral targets. Such multifunctionality, however, complicates their study, which often involves constructing and characterizing null mutant viruses. Systematic exploration of these multifunctional proteins requires detailed road maps in the form of 3-dimensional structures. In this work, we determined the crystal structure of the C-terminal domain of UL21, a multifunctional tegument protein that is conserved among alphaherpesviruses. Structural analysis pinpointed surface areas of potential functional importance that provide a starting point for mutagenesis. In addition, the unexpected RNA-binding ability of UL21 may expand its functional repertoire. The structure of UL21C and the observation of its RNA-binding ability are the latest additions to the navigational chart that can guide the exploration of the multiple functions of UL21.

The unusual fold of herpes simplex virus 1 UL21, a multifunctional tegument protein.

UL21 is a conserved protein in the tegument of alphaherpesviruses and has multiple important albeit poorly understood functions in viral replication and pathogenesis. To provide a roadmap for exploration of the multiple roles of UL21, we determined the crystal structure of its conserved N-terminal domain from herpes simplex virus 1 to 2.0-Å resolution, which revealed a novel sail-like protein fold. Evolutionarily conserved surface patches highlight residues of potential importance for future targeting by mutagenesis.

A monomeric uncleaved respiratory syncytial virus F antigen retains prefusion-specific neutralizing epitopes.

Respiratory syncytial virus (RSV) is the leading infectious cause of severe respiratory disease in infants and a major cause of respiratory illness in the elderly. There remains an unmet vaccine need despite decades of research. Insufficient potency, homogeneity, and stability of previous RSV fusion protein (F) subunit vaccine candidates have hampered vaccine development. RSV F and related parainfluenza virus (PIV) F proteins are cleaved by furin during intracellular maturation, producing disulfide-linked F1 and F2 fragments. During cell entry, the cleaved Fs rearrange from prefusion trimers to postfusion trimers. Using RSV F constructs with mutated furin cleavage sites, we isolated an uncleaved RSV F ectodomain that is predominantly monomeric and requires specific cleavage between F1 and F2 for self-association and rearrangement into stable postfusion trimers. The uncleaved RSV F monomer is folded and homogenous and displays at least two key RSV-neutralizing epitopes shared between the prefusion and postfusion conformations. Unlike the cleaved trimer, the uncleaved monomer binds the prefusion-specific monoclonal antibody D25 and human neutralizing immunoglobulins that do not bind to postfusion F. These observations suggest that the uncleaved RSV F monomer has a prefusion-like conformation and is a potential prefusion subunit vaccine candidate. Importance: RSV is the leading infectious cause of severe respiratory disease in infants and a major cause of respiratory illness in the elderly. Development of an RSV vaccine was stymied when a clinical trial using a formalin-inactivated RSV virus made disease, following RSV infection, more severe. Recent studies have defined the structures that the RSV F envelope glycoprotein adopts before and after virus entry (prefusion and postfusion conformations, respectively). Key neutralization epitopes of prefusion and postfusion RSV F have been identified, and a number of current vaccine development efforts are focused on generating easily produced subunit antigens that retain these epitopes. Here we show that a simple modification in the F ectodomain results in a homogeneous protein that retains critical prefusion neutralizing epitopes. These results improve our understanding of RSV F protein folding and structure and can guide further vaccine design efforts.