A novel RIPK1 inhibitor reduces GVHD in mice via a nonimmunosuppressive mechanism that restores intestinal homeostasis.

Intestinal epithelial cells (IECs) are implicated in the propagation of T-cell-mediated inflammatory diseases, including graft-versus-host disease (GVHD), but the underlying mechanism remains poorly defined. Here, we report that IECs require receptor-interacting protein kinase-3 (RIPK3) to drive both gastrointestinal (GI) tract and systemic GVHD after allogeneic hematopoietic stem cell transplantation. Selectively inhibiting RIPK3 in IECs markedly reduces GVHD in murine intestine and liver. IEC RIPK3 cooperates with RIPK1 to trigger mixed lineage kinase domain-like protein-independent production of T-cell-recruiting chemokines and major histocompatibility complex (MHC) class II molecules, which amplify and sustain alloreactive T-cell responses. Alloreactive T-cell-produced interferon gamma enhances this RIPK1/RIPK3 action in IECs through a JAK/STAT1-dependent mechanism, creating a feed-forward inflammatory cascade. RIPK1/RIPK3 forms a complex with JAK1 to promote STAT1 activation in IECs. The RIPK1/RIPK3-mediated inflammatory cascade of alloreactive T-cell responses results in intestinal tissue damage, converting the local inflammation into a systemic syndrome. Human patients with severe GVHD showed highly activated RIPK1 in the colon epithelium. Finally, we discover a selective and potent RIPK1 inhibitor (Zharp1-211) that significantly reduces JAK/STAT1-mediated expression of chemokines and MHC class II molecules in IECs, restores intestinal homeostasis, and arrests GVHD without compromising the graft-versus-leukemia (GVL) effect. Thus, targeting RIPK1/RIPK3 in IECs represents an effective nonimmunosuppressive strategy for GVHD treatment and potentially for other diseases involving GI tract inflammation.

Design, synthesis, evaluation and optimization of potent IRAK4 inhibitors alleviating production of inflammatory cytokines in LPS-induced SIRS model.

Interleukin-1 receptor associated kinase-4 (IRAK4) has emerged as a therapeutic target for inflammatory and autoimmune diseases. Through reversing the amide of CA-4948 and computer aided structure-activity relationship (SAR) studies, a series of IRAK4 inhibitors with oxazolo[4,5-b]pyridine scaffold were identified. Compound 32 showed improved potency (IC50 = 43 nM) compared to CA-4948 (IC50 = 115 nM), but suffered from hERG inhibition (IC50 = 5.7 µM). Further optimization led to compound 42 with reduced inhibition of hERG (IC50 > 30 µM) and 13-fold higher activity (IC50 = 8.9 nM) than CA-4948. Importantly, compound 42 had favorable in vitro ADME and in vivo pharmacokinetic properties. Furthermore, compound 42 significantly reduced LPS-induced production of serum TNF-α and IL-6 cytokines in the mouse model. The overall profiles of compound 42 support it as a lead for the development of IRAK4 inhibitors for the treatment of inflammatory and autoimmune disorders.

Discovery, optimization and evaluation of isothiazolo[5,4-b]pyridine derivatives as RIPK1 inhibitors with potent in vivo anti-SIRS activity.

Receptor-interacting protein kinase-1 (RIPK1) is involved in the necroptosis pathway, which regulates inflammatory signaling and cell death in a variety of diseases, including inflammatory and neurodegenerative disorders. We identified a novel hit compound 36 by a cell-based screening assay (anti-necroptosis EC50 = 58 nM). Starting from compound 36, we designed a series of scaffolds to improve anti-necroptosis activity, physicochemical properties and metabolic stability. The isothiazolo[5,4-b]pyridine backbone proved to be a promising scaffold which provided a number of potent necroptosis inhibitors. Compound 56, for example, effectively blocked necroptosis in both human and mouse cells (EC50 = 1-5 nM). A binding assay showed that compound 56 potently binds to RIPK1 (Kd = 13 nM), but not RIPK3 (Kd > 10,000 nM). Kinase functional assay (ADP-Glo) confirmed that compound 56 inhibits RIPK1 phosphorylation with an IC50 at 5.8 nM. Importantly, compound 56 displayed excellent cross-species liver microsomal metabolic stability (t1/2 > 90 min). Furthermore, compound 56 exhibited favorable in vitro safety profiles in hERG and CYP assays. Finally, pre-treatment with 56 significantly reduced hypothermia and lethal shock in the systemic inflammatory response syndrome mice model. Taken together, compound 56 represented a promising prototype for the development of therapeutic agent to treat inflammation-related diseases.

Design, synthesis, and evaluation of novel CXCR4 antagonists based on an aminoquinoline template.

The chemokine receptor CXCR4 has been explored as a drug target due to its involvement in pathological conditions such as HIV infection and cancer metastasis. Here we report the structure-activity relationship study of novel CXCR4 antagonists based on an aminoquinoline template. This template is devoid of the chiral center in the classical tetrahydroquinoline (THQ) ring moiety and therefore can be easily synthesized. A number of potent CXCR4 antagonists were identified, exemplified by compound 3, which demonstrated excellent binding affinity with CXCR4 receptor (IC50 = 57 nM) and inhibited CXCL12 induced cytosolic calcium increase (IC50 = 0.24 nM). Furthermore, compound 3 potently inhibited CXLC12/CXCR4 mediated cell migration in a transwell invasion assay. The simplified synthetic approach combined with good physicochemical properties (e.g. MW 362, clogP 2.1, PSA 48, pKa 7.0 for compound 3) demonstrate the potential of this aminoquinoline template as a novel scaffold to develop CXCR4 antagonists.

A novel hedgehog inhibitor for the treatment of hematological malignancies.

The hedgehog-smoothened (HH/SMO) pathway has been proposed as a potential therapeutic target for hematological malignancies. Our previous studies designed a series of HH inhibitors with novel scaffolds distinctive from vismodegib, the first Food and Drug Administration-approved HH inhibitor for the treatment of basal-cell carcinoma and medulloblastoma. In the present study, we evaluated these HH inhibitors against blood cancers and found that HH78 displayed potent activity in suppressing the HH signaling pathway. HH78 competitively bound to SMO and suppressed the transcriptional activity of GLI by the luciferase reporter gene assay and the measurement of HH/SMO-downregulated genes, including cyclin D2, cyclin E, PTCH1, PTCH2, and GLI. HH78 at low micromolar concentrations induced significant cancer cell apoptosis showed by increased caspase-3 activation, annexin V-staining and downregulated prosurvival proteins, including c-Myc, Bcl-2, Mcl-1, and Bcl-xL. In contrast, vismodegib did not show any effects on these apoptotic events. HH78 also suppressed the activation of the AKT/mTOR pathway, which cross-talks with the HH/SMO pathway. Finally, HH78 inhibited the growth of human leukemia K562 in nude mice xenografts with no overt toxicity. Collectively, the present study identified a novel HH inhibitor with great potential for the treatment of hematological malignancies.

Discovery of a potent hedgehog pathway inhibitor capable of activating caspase8-dependent apoptosis.

Aberrant activation of Hedgehog (Hh) signaling is associated with the development of numerous human cancers. Vismodegib is the first Hh inhibitor approved for anti-cancer therapy by targeting Smoothened (SMO), a critical regulator of the Hh pathway. However, acquisition of drug resistance to vismodegib occurs overtime. Apoptosis is a prevalent form of programmed cell death that is executed by caspases. Induction of tumor cell apoptosis represents an attractive therapeutic strategy to eliminate tumor cells. To explore new Hh antagonists with apoptosis-inducing activity, we screened a set of ∼300 potential SMO antagonists with novel scaffold structures. Hh003 was found to induce caspase-dependent apoptosis while vismodegib did not activate apoptotic response in human colon and pancreatic cancer cells. Compared to vismodegib, Hh003 exerted similar inhibitory effects on the Hh pathway. Hh003 could induce caspase8 activation and the silence of caspase8 significantly inhibited Hh003-induced apoptosis. Remarkably, Hh003 showed stronger inhibitory effects on the formation of tumor colonies in vitro and colorectal tumor growth in vivo than vismodegib. These findings suggest that Hh003 exerts enhanced anti-tumor effects by activating caspase8-dependent apoptosis compared to vismodegib. The combined property of Hh inhibition and apoptosis induction of Hh003 presents great potential for the development of novel anti-cancer therapy.

Design, synthesis, and evaluation of novel porcupine inhibitors featuring a fused 3-ring system based on the 'reversed' amide scaffold.

The Wnt signaling pathway is an essential signal transduction pathway which leads to the regulation of cellular processes such as proliferation, differentiation and migration. Aberrant Wnt signaling is known to have an association with multiple cancers. Porcupine is an enzyme that catalyses the addition of palmitoleate to a serine residue in Wnt proteins, a process which is required for the secretion of Wnt proteins. Here we report the synthesis and structure-activity-relationship of the novel porcupine inhibitors based on a 'reversed' amide scaffold. The leading compound 53 was as potent as the clinical compound LGK974 in a cell based STF reporter gene assay. Compound 53 potently inhibited the secretion of Wnt3A, therefore was confirmed to be a porcupine inhibitor. Furthermore, compound 53 showed excellent chemical and plasma stabilities. However, the clearance of compound 53 in liver microsomal tests was moderate to high, and the solubility of compound 53 was suboptimal. Collective efforts toward further optimization of this novel tricyclic template to develop better porcupine inhibitors will be subsequently undertaken and reported in due course.

Discovery of a 6-(pyridin-3-yl)benzo[d]thiazole template for optimization of hedgehog and PI3K/AKT/mTOR dual inhibitors.

Vismodegib is the first FDA approved cancer therapy based on inhibition of aberrant hedgehog signaling. Like most cancer therapies, vismodegib suffered from resistance, even during clinical development. Numerous reports demonstrated that simultaneous blockage of hedgehog and PI3K/AKT/mTOR pathways resulted in significantly superior outcomes compared with single agent alone in a number of animal disease models. The dual hedgehog and PI3K/AKT/mTOR inhibition represented a promising approach not only to overcoming the resistance but also to delaying its onset. Here we report a series of compounds based on a 6-(pyridin-3-yl)benzo[d]thiazole template which have demonstrated significant inhibition of both hedgehog and PI3K/AKT/mTOR signaling pathways. This new scaffold can serve as a lead for further optimization.

Exploration of the linkage elements of porcupine antagonists led to potent Wnt signaling pathway inhibitors.

The Wnt signaling pathway is a pivotal developmental pathway. It operates through control of cellular functions such as proliferation, differentiation, migration and polarity. Aberrant Wnt signaling has been implicated in the formation and metastasis of tumors. Porcupine is a component of the Wnt signaling pathway. It is a member of the membrane-bound O-acyltransferase family of proteins. Porcupine catalyzes the palmitoylation of Wnt proteins, a process which is essential to their secretion and activity. Here we report a novel series of compounds obtained by a scaffold hybridization strategy from two known porcupine inhibitor classes. The leading compound 62 demonstrated subnanomolar (IC50 0.11 nM) inhibition of Wnt signaling in a paracrine cellular reporter gene assay. Compound 62 also potently inhibited Wnt secretion into culture medium, an indication of direct inhibition of the porcupine protein. Furthermore, compound 62 showed excellent chemical, plasma and liver microsomal stabilities. Collectively, these results strongly support further optimization of this novel scaffold to develop better Wnt pathway inhibitors.

Replacement of amide with bioisosteres led to a new series of potent adenosine A2A receptor antagonists.

We have previously reported a series of 2,4,6-trisubstituted pyrimidines as potent A2A receptor antagonists. The leading compounds often feature a potentially labile acetamide functional group which tends to hydrolyze under acidic conditions. Here we report the replacement of the acetamide functional group with bioisosteres. This effort led us to a new series of adenosine A2A receptor antagonists with improved potency and chemical stability.

Scaffold hopping approach to a new series of smoothened antagonists.

The hedgehog (Hh) signaling pathway is a key regulator during embryonic development, while in adults, it has limited functions such as stem cell maintenance and tissue repair. The aberrant activity of the Hh signaling in adults has been linked to numerous human cancers. Inhibition of Hh signaling therefore represents a promising approach toward novel anticancer therapies. The Smoothened (Smo) receptor mediates Hh signaling. Here we report a new series of Smo antagonists which were obtained by a scaffold hopping strategy. Compounds from this new scaffold demonstrated decent inhibition of Hh pathway signaling. The new scaffold can serve as a starting point for further optimization.

Synthesis and evaluation of dihydrofuro[2,3-b]pyridine derivatives as potent IRAK4 inhibitors.

Interleukin-1 receptor-associated kinase 4 (IRAK4) is a key regulator to control downstream NF-κB and MAPK signals in the innate immune response and has been proposed as a therapeutic target for the treatment of inflammatory and autoimmune diseases. Herein, a series of IRAK4 inhibitors based on a dihydrofuro[2,3-b]pyridine scaffold was developed. Structural modifications of the screening hit 16 (IC50 = 243 nM) led to IRAK4 inhibitors with improved potency but high clearance (Cl) and poor oral bioavailability, as exemplified by compound 21 (IC50 = 6.2 nM, Cl = 43 ml/min/kg, F = 1.6%, LLE = 5.4). Structure modification aimed at improving LLE and reducing clearance identified compound 38. Compound 38 showed significantly improved clearance while maintained excellent biochemical potency against IRAK4 (IC50 = 7.3 nM, Cl = 12 ml/min/kg, F = 21%, LLE = 6.0). Importantly, compound 38 had favorable in vitro safety and ADME profiles. Furthermore, compound 38 reduced the in vitro production of pro-inflammatory cytokines in both mouse iBMDMs and human PBMCs and was orally efficacious in the inhibition of serum TNF-α secretion in LPS-induced mouse model. These findings suggested that compound 38 has development potential as an IRAK4 inhibitor for the treatment of inflammatory and autoimmune disorders.

Synthesis and characterization of potent RIPK3 inhibitors based on a tricyclic scaffold.

Background: Necroptosis is an important form of regulated cell death involved in inflammatory diseases, degenerative diseases and cancer. RIPK3 is an interesting target for intervention of necroptosis-associated diseases. Methodology: Herein the authors report the synthesis of a series RIPK3 inhibitors under the guidance of structure-based drug design which leads to the identification of compound 37. Results: Compound 37 potently rescued human and mouse cells from necroptotic stimuli TNF-α, Smac mimetic, z-VAD and LPS + z-VAD, displayed high affinity to RIPK3 (Kd = 14 nM) but no observable affinity to RIPK1 and inhibited RIPK3 kinase function. Importantly, compound 37 significantly alleviated TNF-induced systemic inflammatory response syndrome in the mouse model. Conclusion: These results support compound 37 as a prototype RIPK3 inhibitor for lead optimization.

Design, synthesis, and evaluation of potent RIPK1 inhibitors with in vivo anti-inflammatory activity.

RIPK1 plays a key role in the necroptosis pathway that regulates inflammatory signaling and cell death in various diseases, including inflammatory and neurodegenerative diseases. Herein, we report a series of potent RIPK1 inhibitors, represented by compound 70. Compound 70 efficiently blocks necroptosis induced by TNFα in both human and mouse cells (EC50 = 17-30 nM). Biophysical assay demonstrates that compound 70 potently binds to RIPK1 (Kd = 9.2 nM), but not RIPK3 (Kd > 10,000 nM). Importantly, compound 70 exhibits greatly improved metabolic stability in human and rat liver microsomes compared to compound 6 (PK68), a RIPK1 inhibitor reported in our previous work. In addition, compound 70 displays high permeability in Caco-2 cells and excellent in vitro safety profiles in hERG and CYP assays. Moreover, pre-treatment of 70 significantly ameliorates hypothermia and lethal shock in SIRS mice model. Lastly, compound 70 possesses favorable pharmacokinetic parameters with moderate clearance and good oral bioavailability in SD rat. Taken together, our work supports 70 as a potent RIPK1 inhibitor and highlights its potential as a prototypical lead for further development in necroptosis-associated inflammatory disorders.

Ring closure strategy leads to potent RIPK3 inhibitors.

Necroptosis is a form of regulated necrotic cell death that is independent of caspases. Receptor-interacting protein kinase 3 (RIPK3) has been identified as a key regulator for necroptosis, and has been proposed as a potential therapeutic target for the treatment of diseases associated with necroptosis. In this report, we describe the design, synthesis, and evaluation of a series of novel RIPK3 inhibitors. The lead compound 38 exhibited potent activity (EC50 = 0.42 µM) in blocking TNFα, Smac mimetic and z-VAD (TSZ) induced cell death in HT-29 cells. Mechanistic studies showed that compound 38 bound to RIPK3 with high affinity (Kd = 7.1 nM), and inhibited RIPK3 kinase activity in a ADP-Glo functional assay. In addition, compound 38 displayed good selectivity over another necroptosis regulator RIPK1 (Kd = 6000 nM). Furthermore, compound 38 demonstrated excellent in vitro safety profiles with minimal inhibition of CYP isozymes and hERG potassium channel. Lastly, compound 38 efficiently blocked hypothermia and death in mice in the TNFα-induced systemic inflammatory response syndrome model.

Oxidative desulfurization of model oil over Ta-Beta zeolite synthesized via structural reconstruction.

As to metallosilicate zeolites, ions with larger size such as Ta5+ in the gels greatly retarded their crystallization during the hydrothermal synthesis, affording long-winded synthesis periods, up-limited framework-substituted metal contents, or even frustrated outcome. An efficient hydrothermal synthesis strategy for metallosilicate, in this case of Ta framework-substituted *BEA zeolite, via structural reconstruction was proposed to stride the gap. The Ta content in our developed Ta-Beta-Re-50 zeolite achieved up to 5.48 % (Si/Ta = 52), breaking through the limitation of Ta contents for conventional method (Si/Ta > 100). Additionally, this Ta-Beta-Re zeolite possessed nanosized crystals (20-40 nm) and short crystallization time (8 h), significantly improving space-time yields of practical zeolite production. Through spectroscopic study, it was confirmed that the existence of zeolite structural units intensively facilitated the formation of nucleation and crystal growth. This innovative Ta-Beta zeolite demonstrated high catalytic performances for oxidation desulfurization, far outperforming traditional fluoride-mediated Ta-Beta-F, which was ascribed to its excellent diffusion properties and incredible high isolated Ta contents. Additionally, the catalytic performance of Ta-Beta-Re could be regenerated after simple calcination and the deactivation may be caused by pore blocking of organics. This work provides a new method for rationally design and construction of metallosilicate materials with high activity for catalytic oxidation applications, which can bridge the conceptual and technical gap between periodic trends and zeolite material synthesis.

Hydrothermal synthesis of boron-free Zr-MWW and Sn-MWW zeolites as robust Lewis acid catalysts.

An innovative strategy based on dual structure-directing agent-facilitated crystallization was proposed to hydrothermally synthesize boron-free Zr-MWW and Sn-MWW metallosilicates that bear great structural diversity for potential pore engineering. The metallosilicates show distinctive features in Lewis acid-catalyzed reactions as efficient heterogeneous solid catalysts.

Design, synthesis, and evaluation of pyrrolidine based CXCR4 antagonists with in vivo anti-tumor metastatic activity.

The chemokine receptor CXCR4 has been proposed as a drug target based on its important functions in HIV infection, inflammation/autoimmune diseases and cancer metastasis. Herein we report the design, synthesis and evaluation of novel CXCR4 antagonists based on a pyrrolidine scaffold. The structural exploration/optimization identified numerous potent CXCR4 antagonists, represented by compound 46, which displayed potent binding affinity to CXCR4 receptor (IC50 = 79 nM competitively displacing fluorescent 12G5 antibody) and inhibited CXCL12 induced cytosolic calcium flux (IC50 = 0.25 nM). Moreover, in a transwell invasion assay, compound 46 significantly mitigated CXCL12/CXCR4 mediated cell migration. Compound 46 exhibited good physicochemical properties (MW 367, logD7.4 1.12, pKa 8.2) and excellent in vitro safety profiles (e.g., hERG patch clamp IC50 > 30 µM and minimal CYP isozyme inhibition). Importantly, 46 displayed much improved metabolic stability in human and rat liver microsomes. Lastly, 46 demonstrated marked efficacy in a cancer metastasis model in mice. These results strongly support 46 as a prototypical lead for the development of promising CXCR4 antagonists as clinical candidates.

Discovery of a Potent RIPK3 Inhibitor for the Amelioration of Necroptosis-Associated Inflammatory Injury.

Necroptosis is a form of regulated necrosis that requires the activation of receptor-interacting kinase 3 (RIPK3 or RIP3) and its phosphorylation of the substrate MLKL (mixed lineage kinase domain-like protein). Necroptosis has emerged as important cell death involved in the pathogenesis of various diseases including inflammatory diseases, degenerative diseases, and cancer. Here, we discovered a small molecule Zharp-99 as a potent inhibitor of necroptosis through blocking the kinase activity of RIPK3. Zharp-99 efficiently blocks necroptosis induced by ligands of the death receptor and Toll-like receptor as well as viral infection in human, rat and mouse cells. Zharp-99 strongly inhibits cellular activation of RIPK3, and MLKL upon necroptosis stimuli. Zharp-99 directly blocks the kinase activity of RIPK3 without affecting RIPK1 kinase activity at the tested concentration. Importantly, Zharp-99 exerts effective protection against TNF-α induced systemic inflammatory response syndrome in the mouse model. Zharp-99 displays favorable in vitro safety profiles and in vivo pharmacokinetic parameters. Thus, our study demonstrates Zharp-99 as a potent inhibitor of RIPK3 kinase and also highlights its potential for further development of new approaches for treating necroptosis-associated inflammatory disorders.

Design, Synthesis, and Characterization of Novel CXCR4 Antagonists Featuring Cyclic Amines.

Chemokine receptor CXCR4 and its natural ligand CXCL12 (also known as stromal cell-derived factor-1, or SDF-1) regulate a broad range of physiological functions. Dysregulation of the CXCL12/CXCR4 axis is involved in numerous pathological conditions such as HIV infection, inflammation and cancer. Herein, we report the design, synthesis, and characterization of novel CXCR4 antagonists based on cyclic amine scaffolds. Compound 24 was identified as a potent CXCR4 receptor antagonist (competitive inhibition of 12G5 binding, IC50 =24 nM; functional inhibition of CXCL12-induced cytosolic calcium increase, IC50 =0.1 nM). In addition, compound 24 potently inhibited cell migration in CXCR4/CXCL12-mediated chemotaxis in a matrigel invasion assay. The absolute configuration of compound 24 was elucidated by X-ray crystallography.