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.

Elucidation of the GSK3α Structure Informs the Design of Novel, Paralog-Selective Inhibitors.

Glycogen synthase kinase 3 (GSK3) remains a therapeutic target of interest for diverse clinical indications. However, one hurdle in the development of small molecule GSK3 inhibitors has been safety concerns related to pan-inhibition of both GSK3 paralogs, leading to activation of the Wnt/ß-catenin pathway and potential for aberrant cell proliferation. Development of GSK3α or GSK3ß paralog-selective inhibitors that could offer an improved safety profile has been reported but further advancement has been hampered by the lack of structural information for GSK3α. Here we report for the first time the crystal structure for GSK3α, both in apo form and bound to a paralog-selective inhibitor. Taking advantage of this new structural information, we describe the design and in vitro testing of novel compounds with up to ∼37-fold selectivity for GSK3α over GSK3ß with favorable drug-like properties. Furthermore, using chemoproteomics, we confirm that acute inhibition of GSK3α can lower tau phosphorylation at disease-relevant sites in vivo, with a high degree of selectivity over GSK3ß and other kinases. Altogether, our studies advance prior efforts to develop GSK3 inhibitors by describing GSK3α structure and novel GSK3α inhibitors with improved selectivity, potency, and activity in disease-relevant systems.

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.

Discovery of Potent Selective Nonzinc Binding Autotaxin Inhibitor BIO-32546.

Autotaxin (ATX) is a lysophospholipase D that is the main enzyme responsible for generating LPA in body fluids. Although ATX was isolated from a conditioned medium of melanoma cells, later it was discovered to play a critical role in vascular and neuronal development. ATX has also been implicated in primary brain tumor, fibrosis, and rheumatoid arthritis, as well as neurological diseases such as multiple sclerosis, Alzheimer's disease, and neuropathic pain. As ATX and LPA levels are increased upon neuronal injury, a selective ATX inhibitor could provide a new approach to treat neuropathic pain. Herein we describe the discovery of a novel series of nonzinc binding reversible ATX inhibitors, particularly a potent, selective, orally bioavailable, brain-penetrable tool compound BIO-32546, as well as its synthesis, X-ray cocrystal structure, pharmacokinetics, and in vivo efficacy.

Discovery of Potent and Brain-Penetrant Tau Tubulin Kinase 1 (TTBK1) Inhibitors that Lower Tau Phosphorylation In Vivo.

Structural analysis of the known NIK inhibitor 3 bound to the kinase domain of TTBK1 led to the design and synthesis of a novel class of azaindazole TTBK1 inhibitors exemplified by 8 (cell IC50: 571 nM). Systematic optimization of this series of analogs led to the discovery of 31, a potent (cell IC50: 315 nM) and selective TTBK inhibitor with suitable CNS penetration (rat Kp,uu: 0.32) for in vivo proof of pharmacology studies. The ability of 31 to inhibit tau phosphorylation at the disease-relevant Ser 422 epitope was demonstrated in both a mouse hypothermia and a rat developmental model and provided evidence that modulation of this target may be relevant in the treatment of Alzheimer's disease and other tauopathies.

Mechanisms of Regulation and Diverse Activities of Tau-Tubulin Kinase (TTBK) Isoforms.

Tau-tubulin kinase 1 (TTBK1) is a CNS-specific, kinase that has been implicated in the pathological phosphorylation of tau in Alzheimer's Disease (AD) and Frontotemporal Dementia (FTD). TTBK1 is a challenging therapeutic target because it shares a highly conserved catalytic domain with its homolog, TTBK2, a ubiquitously expressed kinase genetically linked to the disease spinocerebellar ataxia type 11. The present study attempts to elucidate the functional distinctions between the TTBK isoforms and increase our understanding of them as distinct targets for the treatment of neurodegenerative disease. We demonstrate that in cortical neurons, TTBK1, not TTBK2, is the isoform responsible for tau phosphorylation at epitopes enriched in tauopathies such as Serine 422. In addition, although our elucidation of the crystal structure of the TTBK2 kinase domain indicates almost identical structural similarity with TTBK1, biochemical and cellular assays demonstrate that the enzymatic activity of these two proteins is regulated by a combination of unique extra-catalytic sequences and autophosphorylation events. Finally, we have identified an unbiased list of neuronal interactors and phosphorylation substrates for TTBK1 and TTBK2 that highlight the unique cellular pathways and functional networks that each isoform is involved in. This data address an important gap in knowledge regarding the implications of targeting TTBK kinases and may prove valuable in the development of potential therapies for disease.

The crystal structure of the catalytic domain of tau tubulin kinase 2 in complex with a small-molecule inhibitor.

Tau proteins play an important role in the proper assembly and function of neurons. Hyperphosphorylation of tau by kinases such as tau tubulin kinase (TTBK) has been hypothesized to cause the aggregation of tau and the formation of neurofibrillary tangles (NFTs) that lead to the destabilization of microtubules, thereby contributing to neurodegenerative diseases such as Alzheimer's disease (AD). There are two TTBK isoforms with highly homologous catalytic sites but with distinct tissue distributions, tau phosphorylation patterns and loss-of-function effects. Inhibition of TTBK1 reduces the levels of NFT formation involved in neurodegenerative diseases such as AD, whereas inhibition of TTBK2 may lead to the movement disorder spinocerebellar ataxia type 11 (SCA11). Hence, it is critical to obtain isoform-selective inhibitors. Structure-based drug design (SBDD) has been used to design highly potent and exquisitely selective inhibitors. While structures of TTBK1 have been reported in the literature, TTBK2 has evaded structural characterization. Here, the first crystal structure of the TTBK2 kinase domain is described. Furthermore, the crystal structure of human TTBK2 in complex with a small-molecule inhibitor has successfully been determined to elucidate the structural differences in protein conformations between the two TTBK isoforms that could aid in SBDD for the design of inhibitors that selectively target TTBK1 over TTBK2.

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.

Analysis of a vinculin homolog in a sponge (phylum Porifera) reveals that vertebrate-like cell adhesions emerged early in animal evolution.

The evolution of cell-adhesion mechanisms in animals facilitated the assembly of organized multicellular tissues. Studies in traditional animal models have revealed two predominant adhesion structures, the adherens junction (AJ) and focal adhesions (FAs), which are involved in the attachment of neighboring cells to each other and to the secreted extracellular matrix (ECM), respectively. The AJ (containing cadherins and catenins) and FAs (comprising integrins, talin, and paxillin) differ in protein composition, but both junctions contain the actin-binding protein vinculin. The near ubiquity of these structures in animals suggests that AJ and FAs evolved early, possibly coincident with multicellularity. However, a challenge to this perspective is that previous studies of sponges-a divergent animal lineage-indicate that their tissues are organized primarily by an alternative, sponge-specific cell-adhesion mechanism called "aggregation factor." In this study, we examined the structure, biochemical properties, and tissue localization of a vinculin ortholog in the sponge Oscarella pearsei (Op). Our results indicate that Op vinculin localizes to both cell-cell and cell-ECM contacts and has biochemical and structural properties similar to those of vertebrate vinculin. We propose that Op vinculin played a role in cell adhesion and tissue organization in the last common ancestor of sponges and other animals. These findings provide compelling evidence that sponge tissues are indeed organized like epithelia in other animals and support the notion that AJ- and FA-like structures extend to the earliest periods of animal evolution.

Structural determinant for inducing RORgamma specific inverse agonism triggered by a synthetic benzoxazinone ligand.

BACKGROUND: The nuclear hormone receptor RORγ regulates transcriptional genes involved in the production of the pro-inflammatory interleukin IL-17 which has been linked to autoimmune diseases such as rheumatoid arthritis, multiple sclerosis and inflammatory bowel disease. This transcriptional activity of RORγ is modulated through a protein-protein interaction involving the activation function 2 (AF2) helix on the ligand binding domain of RORγ and a conserved LXXLL helix motif on coactivator proteins. Our goal was to develop a RORγ specific inverse agonist that would help down regulate pro-inflammatory gene transcription by disrupting the protein protein interaction with coactivator proteins as a therapeutic agent. RESULTS: We identified a novel series of synthetic benzoxazinone ligands having an agonist (BIO592) and inverse agonist (BIO399) mode of action in a FRET based assay. We show that the AF2 helix of RORγ is proteolytically sensitive when inverse agonist BIO399 binds. Using x-ray crystallography we show how small modifications on the benzoxazinone agonist BIO592 trigger inverse agonism of RORγ. Using an in vivo reporter assay, we show that the inverse agonist BIO399 displayed specificity for RORγ over ROR sub-family members α and ß. CONCLUSION: The synthetic benzoxazinone ligands identified in our FRET assay have an agonist (BIO592) or inverse agonist (BIO399) effect by stabilizing or destabilizing the agonist conformation of RORγ. The proteolytic sensitivity of the AF2 helix of RORγ demonstrates that it destabilizes upon BIO399 inverse agonist binding perturbing the coactivator protein binding site. Our structural investigation of the BIO592 agonist and BIO399 inverse agonist structures identified residue Met358 on RORγ as the trigger for RORγ specific inverse agonism.

Molecular functions of the TLE tetramerization domain in Wnt target gene repression.

Wnt signaling activates target genes by promoting association of the co-activator ß-catenin with TCF/LEF transcription factors. In the absence of ß-catenin, target genes are silenced by TCF-mediated recruitment of TLE/Groucho proteins, but the molecular basis for TLE/TCF-dependent repression is unclear. We describe the unusual three-dimensional structure of the N-terminal Q domain of TLE1 that mediates tetramerization and binds to TCFs. We find that differences in repression potential of TCF/LEFs correlates with their affinities for TLE-Q, rather than direct competition between ß-catenin and TLE for TCFs as part of an activation-repression switch. Structure-based mutation of the TLE tetramer interface shows that dimers cannot mediate repression, even though they bind to TCFs with the same affinity as tetramers. Furthermore, the TLE Q tetramer, not the dimer, binds to chromatin, specifically to K20 methylated histone H4 tails, suggesting that the TCF/TLE tetramer complex promotes structural transitions of chromatin to mediate repression.

Reactive oxygen species regulate nucleostemin oligomerization and protein degradation.

Nucleostemin (NS) is a nucleolar-nucleoplasmic shuttle protein that regulates cell proliferation, binds p53 and Mdm2, and is highly expressed in tumor cells. We have identified NS as a target of oxidative regulation in transformed hematopoietic cells. NS oligomerization occurs in HL-60 leukemic cells and Raji B lymphoblasts that express high levels of c-Myc and have high intrinsic levels of reactive oxygen species (ROS); reducing agents dissociate NS into monomers and dimers. Exposure of U2OS osteosarcoma cells with low levels of intrinsic ROS to hydrogen peroxide (H(2)O(2)) induces thiol-reversible disulfide bond-mediated oligomerization of NS. Increased exposure to H(2)O(2) impairs NS degradation, immobilizes the protein within the nucleolus, and results in detergent-insoluble NS. The regulation of NS by ROS was validated in a murine lymphoma tumor model in which c-Myc is overexpressed and in CD34+ cells from patients with chronic myelogenous leukemia in blast crisis. In both instances, increased ROS levels were associated with markedly increased expression of NS protein and thiol-reversible oligomerization. Site-directed mutagenesis of critical cysteine-containing regions of nucleostemin altered both its intracellular localization and its stability. MG132, a potent proteasome inhibitor and activator of ROS, markedly decreased degradation and increased nucleolar retention of NS mutants, whereas N-acetyl-L-cysteine largely prevented the effects of MG132. These results indicate that NS is a highly redox-sensitive protein. Increased intracellular ROS levels, such as those that result from oncogenic transformation in hematopoietic malignancies, regulate the ability of NS to oligomerize, prevent its degradation, and may alter its ability to regulate cell proliferation.

The transcription factor Spn1 regulates gene expression via a highly conserved novel structural motif.

Spn1/Iws1 plays essential roles in the regulation of gene expression by RNA polymerase II (RNAPII), and it is highly conserved in organisms ranging from yeast to humans. Spn1 physically and/or genetically interacts with RNAPII, TBP (TATA-binding protein), TFIIS (transcription factor IIS), and a number of chromatin remodeling factors (Swi/Snf and Spt6). The central domain of Spn1 (residues 141-305 out of 410) is necessary and sufficient for performing the essential functions of SPN1 in yeast cells. Here, we report the high-resolution (1.85 Å) crystal structure of the conserved central domain of Saccharomyces cerevisiae Spn1. The central domain is composed of eight α-helices in a right-handed superhelical arrangement and exhibits structural similarity to domain I of TFIIS. A unique structural feature of Spn1 is a highly conserved loop, which defines one side of a pronounced cavity. The loop and the other residues forming the cavity are highly conserved at the amino acid level among all Spn1 family members, suggesting that this is a signature motif for Spn1 orthologs. The locations and the molecular characterization of temperature-sensitive mutations in Spn1 indicate that the cavity is a key attribute of Spn1 that is critical for its regulatory functions during RNAPII-mediated transcriptional activity.

The effect of H3K79 dimethylation and H4K20 trimethylation on nucleosome and chromatin structure.

Histone methylation regulates chromatin function dependent on the site and degree of the modification. In addition to creating binding sites for proteins, methylated lysine residues are likely to influence chromatin structure directly. Here we present crystal structures of nucleosomes reconstituted with methylated histones and investigate the folding behavior of resulting arrays. We demonstrate that dimethylation of histone H3 at lysine residue 79 locally alters the nucleosomal surface, whereas trimethylation of H4 at lysine residue 20 affects higher-order structure.

A charged and contoured surface on the nucleosome regulates chromatin compaction.

Local nucleosome-nucleosome interactions in cis drive chromatin folding, whereas interactions in trans lead to fiber-fiber oligomerization. Here we show that peptides derived from the histone H4 tail and Kaposi's sarcoma herpesvirus LANA protein can replace the endogenous H4 tail, resulting in array folding and oligomerization. Neutralization of a LANA binding site on the histone surface enhanced rather than abolished nucleosome-nucleosome interactions. We maintain that the contoured nucleosome surface is centrally involved in regulating chromatin condensation.

Kaposi's sarcoma-associated herpesvirus LANA hitches a ride on the chromosome.

Kaposi's sarcoma-associated herpesvirus (KSHV) latently infects tumor cells and has an etiologic role in Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. Survival in rapidly dividing cells depends on a carefully orchestrated chain of events. The viral genome, or episome, must replicate in concert with cellular genetic material, and then efficiently segregate to progeny nuclei. KSHV achieves this through its latency associated nuclear antigen (LANA), which simultaneously binds to viral DNA and mitotic chromosomes to efficiently partition episomes. LANA's N-terminal region has been shown to be essential for efficient KSHV DNA replication and tethering to mitotic chromosomes. The precise mechanism by which LANA attaches to host chromosomes has been an area of active investigation. We recently reported that this association is mediated by the chromatin components histones H2A and H2B. Binding between LANA and these proteins was demonstrated in vivo and in vitro, and use of an H2A-H2B depleted system demonstrated their central role in LANA's chromosome binding. Further, we provided a structural description of the interaction of LANA's N-terminal chromosome association region with the nucleosome using x-ray crystallography. Our data offer further insight into the mechanism of KSHV latency, and also reveal a new concept for a role of the nucleosome as a docking site for other proteins.

The nucleosomal surface as a docking station for Kaposi's sarcoma herpesvirus LANA.

Kaposi's sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen (LANA) mediates viral genome attachment to mitotic chromosomes. We find that N-terminal LANA docks onto chromosomes by binding nucleosomes through the folded region of histones H2A-H2B. The same LANA residues were required for both H2A-H2B binding and chromosome association. Further, LANA did not bind Xenopus sperm chromatin, which is deficient in H2A-H2B; chromatin binding was rescued after assembly of nucleosomes containing H2A-H2B. We also describe the 2.9-angstrom crystal structure of a nucleosome complexed with the first 23 LANA amino acids. The LANA peptide forms a hairpin that interacts exclusively with an acidic H2A-H2B region that is implicated in the formation of higher order chromatin structure. Our findings present a paradigm for how nucleosomes may serve as binding platforms for viral and cellular proteins and reveal a previously unknown mechanism for KSHV latency.

Nucleosome assembly protein 1 exchanges histone H2A-H2B dimers and assists nucleosome sliding.

Eukaryotic chromatin is highly dynamic and turns over rapidly even in the absence of DNA replication. Here we show that the acidic histone chaperone nucleosome assembly protein 1 (NAP-1) from yeast reversibly removes and replaces histone protein dimer H2A-H2B or histone variant dimers from assembled nucleosomes, resulting in active histone exchange. Transient removal of H2A-H2B dimers facilitates nucleosome sliding along the DNA to a thermodynamically favorable position. Histone exchange as well as nucleosome sliding is independent of ATP and relies on the presence of the C-terminal acidic domain of yeast NAP-1, even though this region is not required for histone binding and chromatin assembly. Our results suggest a novel role for NAP-1 (and perhaps other acidic histone chaperones) in mediating chromatin fluidity by incorporating histone variants and assisting nucleosome sliding. NAP-1 may function either untargeted (if acting alone) or may be targeted to specific regions within the genome through interactions with additional factors.