Selective Oxidation of Anilines to Azobenzenes and Azoxybenzenes by a Molecular Mo Oxide Catalyst.

Aromatic azo compounds, which play an important role in pharmaceutical and industrial applications, still face great challenges in synthesis. Herein, we report a molybdenum oxide compound, [N(C4 H9 )4 ]2 [Mo6 O19 ] (1), catalyzed selective oxidation of anilines with hydrogen peroxide as green oxidant. The oxidation of anilines can be realized in a fully selectively fashion to afford various symmetric/asymmetric azobenzene and azoxybenzene compounds, respectively, by changing additive and solvent, avoiding the use of stoichiometric metal oxidants. Preliminary mechanistic investigations suggest the intermediacy of highly active reactive and elusive Mo imido complexes.

FeCl3-Promoted Annulation of 2-Haloindoles: Switchable Synthesis of Spirooxindole-chromeno[2,3-b]indoles and Spirooxindole-chromeno[3,2-b]indoles.

Electrophilic indoles bearing a leaving group at C2 undergo C3-regioselective dearomative hydroaryloxylation and subsequent 1,2-tertiary alkyl migration/aromatization. This is the first ring-opening migration of the spiroindolenine intermediate formed by the C3 nucleophilic addition reaction. Various spiro-oxindole-chromeno[3,2-b]/[2,3-b]indoles were successfully synthesized in excellent yields (up to 98%). This reaction features selective ring-opening migration (C-C/C-O) of the tertiary alkyl group from the indole C3 position to the C2 position stereoselectively, providing a unique synthetic method for constructing novel polycyclic indole skeletons.

Maintenance of Primary Hepatocyte Functions In Vitro by Inhibiting Mechanical Tension-Induced YAP Activation.

Hepatocytes are the primary functional cells of the liver, performing its metabolic, detoxification, and endocrine functions. Functional hepatocytes are extremely valuable in drug discovery and evaluation, as well as in cell therapy for liver diseases. However, it has been a long-standing challenge to maintain the functions of hepatocytes in vitro. Even freshly isolated hepatocytes lose essential functions after short-term culture for reasons that are still not well understood. In the present study, we find that mechanical tension-induced yes-associated protein activation triggers hepatocyte dedifferentiation. Alleviation of mechanical tension by confining cell spreading is sufficient to inhibit hepatocyte dedifferentiation. Based on this finding, we identify a small molecular cocktail through reiterative chemical screening that can maintain hepatocyte functions over the long term and in vivo repopulation capacity by targeting actin polymerization and actomyosin contraction. Our work reveals the mechanisms underlying hepatocyte dedifferentiation and establishes feasible approaches to maintain hepatocyte functions.

Novel Triapine Derivative Induces Copper-Dependent Cell Death in Hematopoietic Cancers.

Triapine, an iron chelator that inhibits ribonucleotide reductase, has been evaluated in clinical trials for cancer treatment. Triapine in combination with other chemotherapeutic agents shows promising efficacy in certain hematologic malignancies; however, it is less effective against many advanced solid tumors, probably due to the unsatisfactory potency and pharmacokinetic properties. In this report, we developed a triapine derivative IC25 (10) with potent antitumor activity. 10 Preferentially inhibited the proliferation of hematopoietic cancers by inducing mitochondria reactive oxygen species production and mitochondrial dysfunction. Unlike triapine, 10 executed cytotoxic action in a copper-dependent manner. 10-Induced up-expression of thioredoxin-interacting protein resulted in decreased thioredoxin activity to permit c-Jun N-terminal kinase and p38 activation and ultimately led to the execution of the cell death program. Remarkedly, 10 showed good bioavailability and inhibited tumor growth in mouse xenograft models. Taken together, our study identifies compound 10 as a copper-dependent antitumor agent, which may be applied to the treatment of hematopoietic cancers.

An Ursolic Acid Derived Small Molecule Triggers Cancer Cell Death through Hyperstimulation of Macropinocytosis.

Macropinocytosis is a transient endocytosis that internalizes extracellular fluid and particles into vacuoles. Recent studies suggest that hyperstimulation of macropinocytosis can induce a novel nonapoptotic cell death, methuosis. In this report, we describe the identification of an ursolic acid derived small molecule (compound 17), which induces cancer cell death through hyperstimulation of macropinocytosis. 17 causes the accumulation of vacuoles derived from macropinosomes based on transmission electron microscopy, time-lapse microscopy, and labeling with extracellular fluid phase tracers. The vacuoles induced by 17 separate from other cytoplasmic compartments but acquire some characteristics of late endosomes and lysosomes. Inhibiting hyperstimulation of macropinocytosis with the specific inhibitor amiloride blocks cell death, implicating that 17 leads to cell death via macropinocytosis, which is coincident with methuosis. Our results uncovered a novel cell death pathway involved in the activity of 17, which may provide a basis for further development of natural-product-derived scaffolds for drugs that trigger cancer cell death by methuosis.

Iron(III)-Catalyzed Arylation of Spiro-Epoxyoxindoles with Phenols/Naphthols towards the Synthesis of Spirocyclic Oxindoles.

An efficient and highly regioselective iron(III)-catalyzed Friedel-Crafts-type arylation of spiro-epoxyoxindoles with phenols was developed for rapid access to 3-(3-indolyl)-oxindole-3-methanols, which could be further elaborated into benzofuranyl-spirooxindoles under Mitsunobu conditions. When spiro-epoxyoxindoles were reacted with naphthols in the presence of a catalytic amount of FeCl3 ⋅6 H2 O in dichloromethane, they underwent a tandem Friedel-Crafts-type arylation and O-cyclization to yield novel naphthofuranyl-spirooxindoles in excellent yields. This method is applied to enable the efficient and highly regioselective synthesis of a small-molecule inhibitor of the sodium channel Nav 1.7 (±)-XEN402, which is currently in a phase IIb clinical trial for the treatment of pain.

TGF-ß Signaling in Stem Cell Regulation.

The transforming growth factor-ß (TGF-ß) family of cytokines, including TGF-ß, bone morphogenic proteins (BMPs), and activin/nodal, is a group of crucial morphogens in embryonic development, and plays key roles in modulating stem/progenitor cell fate. TGF-ß signaling is essential in maintaining the pluripotency of human pluripotent stem cells (hPSCs), including both human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), and its modulation can direct lineage-specific differentiation. Recent studies also demonstrate TGF-ß signaling negatively regulates reprogramming and inhibition of TGF-ß signaling can enhance reprogramming through facilitating mesenchymal-to-epithelial transition (MET). This chapter introduces methods of modulating somatic cell reprogramming to iPSCs and neural induction from hPSCs through modulating TGF-ß signaling by chemical approaches.

Atg5-independent autophagy regulates mitochondrial clearance and is essential for iPSC reprogramming.

Successful generation of induced pluripotent stem cells entails a major metabolic switch from mitochondrial oxidative phosphorylation to glycolysis during the reprogramming process. The mechanism of this metabolic reprogramming, however, remains elusive. Here, our results suggest that an Atg5-independent autophagic process mediates mitochondrial clearance, a characteristic event involved in the metabolic switch. We found that blocking such autophagy, but not canonical autophagy, inhibits mitochondrial clearance, in turn, preventing iPSC induction. Furthermore, AMPK seems to be upstream of this autophagic pathway and can be targeted by small molecules to modulate mitochondrial clearance during metabolic reprogramming. Our work not only reveals that the Atg5-independent autophagy is crucial for establishing pluripotency, but it also suggests that iPSC generation and tumorigenesis share a similar metabolic switch.

Generation of Self-Renewing Hepatoblasts From Human Embryonic Stem Cells by Chemical Approaches.

UNLABELLED: Somatic stem cells play crucial roles in organogenesis and tissue homeostasis and regeneration and may ultimately prove useful for cell therapy for a variety of degenerative diseases and injuries; however, isolation and expansion of most types of somatic stem cells from tissues are technically challenging. Human pluripotent stem cells are a renewable source for any adult cell types, including somatic stem cells. Generation of somatic stem cells from human pluripotent stem cells is a promising strategy to get these therapeutically valuable cells. Previously, we developed a chemically defined condition for mouse hepatoblast self-renewal through a reiterative screening strategy. In the present study, we efficiently generated hepatoblasts from human embryonic stem cells by a stepwise induction strategy. Importantly, these human embryonic stem cell-derived hepatoblasts can be captured and stably maintained using conditions previously established for mouse hepatoblast self-renewal, which includes basal media supplemented with insulin, transferrin, sodium selenite, epidermal growth factor, glycogen synthase kinase 3 inhibitor, transforming growth factor ß receptor inhibitor, lysophosphatidic acid, and sphingosine 1-phosphate. The cells can stably retain hepatoblast phenotypes during prolonged culture and can differentiate into mature hepatocytes through in vitro provision of hepatocyte lineage developmental cues. After being embedded into three-dimensional Matrigel, these cells efficiently formed bile duct-like structures resembling native bile duct tissues. These human embryonic stem cell-derived hepatoblasts would be useful as a renewable source for cell therapy of liver diseases. SIGNIFICANCE: Somatic stem cells have been proposed as promising candidates for cell-based therapy; however, isolation of somatic stem cells from adult tissues is usually invasive and technically challenging. In the present study, hepatoblasts from human embryonic stem cells were efficiently generated. These human hepatoblasts were then stably captured and maintained by a growth factor and small molecule cocktail, which included epidermal growth factor, glycogen synthase kinase 3 inhibitor, transforming growth factor ß receptor inhibitor, lysophosphatidic acid, and sphingosine 1-phosphate. These human embryonic stem cell-derived hepatoblasts would be useful as a renewable source for cell therapy of liver diseases.

Radical-induced metal-free alkynylation of aldehydes by direct C-H activation.

A direct C(sp(2) )H alkynylation of aldehyde C(O)H bonds with hypervalent iodine alkynylation reagents provides ynones under metal-free conditions. In this method, 1-[(triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS-EBX) constitutes an efficient alkynylation reagent for the introduction of the triple bond. The substrate scope is extended to a variety of (hetero)aromatic, aliphatic, and α,ß-unsaturated aldehydes.

A combination of the telomerase inhibitor, BIBR1532, and paclitaxel synergistically inhibit cell proliferation in breast cancer cell lines.

Breast cancer is one of the most significant causes of female cancer death worldwide. Paclitaxel, an extensively used breast cancer chemotherapeutic has limited success due to drug resistance. 2-[(E)-3-naphtalen-2-yl-but-2-enoylamino]-benzoic acid (BIBR1532), a small molecule pharmacological inhibitor of telomerase activity, can inhibit human cancer cell proliferation as well. Thus, to enhance breast cancer treatment efficacy, we studied the combination of BIBR1532 and paclitaxel in breast cancer cell lines. Cell viability assays revealed that BIBR1532 or paclitaxel alone inhibited proliferation in a dose-dependent manner, and combining the drugs synergistically induced growth inhibition in all breast cell lines tested independent of their p53, ER, and HER2 status. The drug combination also synergistically inhibited colony formation of MCF-7 cells in a dose-dependent manner. Annexin V-PI staining and Western blot assays on PARP cleavage and caspase-8 and caspase-3 revealed that BIBR1532 in combination with paclitaxel was more potent than either agent alone in promoting MCF-7 cell apoptosis. Cell cycle analysis indicated that BIBR1532 induced a G1 phase arrest and paclitaxel arrested cells at the G2/M phase. The drug combination dramatically blocked S cells from entering the G2/M phase. Our results suggest the potential of telomerase inhibition as an effective breast cancer treatment and that used in conjunction with paclitaxel; it may potentiate tumor cytotoxicity.

Self-renewal of hepatoblasts under chemically defined conditions by iterative growth factor and chemical screening.

UNLABELLED: Tissue-specific stem/progenitor cells are essential to mediate organogenesis and tissue homeostasis. In addition, these cells have attracted significant interest for their therapeutic potential. However, it remains challenging to expand most types of these cells in vitro. In this study we devised a screening strategy aimed at identifying growth factors and small molecules that can sustain self-renewal of mouse hepatoblasts. This approach began with a defined basal condition, on top of which collections of growth factors and bioactive small molecules were screened for maintaining self-renewal of primary hepatoblasts. The initially identified proteins and small molecules were then combined in the basal media for subsequent screening to identify additional molecules that can synergistically promote hepatoblast self-renewal. This strategy was performed iteratively to eventually define a small molecule and growth factor cocktail, including epidermal growth factor, glycogen synthase kinase 3 inhibitor, transforming growth factor ß receptor inhibitor, lysophosphatidic acid, and sphingosine 1-phosphate, which was sufficient to sustain long-term self-renewal of the murine hepatoblasts under chemically defined conditions. These expanded hepatoblasts retain the ability to respond to liver developmental cues and produce functional hepatocytes and form bile duct-like structures. CONCLUSION: Our work established a chemically defined condition that allows long-term expansion of hepatoblasts, improved our understanding of hepatoblast self-renewal, and highlights the power of phenotypic screening to enable self-renewal of somatic stem/progenitor cells.

Lysophosphatidic acid accelerates lung fibrosis by inducing differentiation of mesenchymal stem cells into myofibroblasts.

Lung fibrosis is characterized by vascular leakage and myofibroblast recruitment, and both phenomena are mediated by lysophosphatidic acid (LPA) via its type-1 receptor (LPA1). Following lung damage, the accumulated myofibroblasts activate and secrete excessive extracellular matrix (ECM), and form fibrotic foci. Studies have shown that bone marrow-derived cells are an important source of myofibroblasts in the fibrotic organ. However, the type of cells in the bone marrow contributing predominantly to the myofibroblasts and the involvement of LPA-LPA1 signalling in this is yet unclear. Using a bleomycin-induced mouse lung-fibrosis model with an enhanced green fluorescent protein (EGFP) transgenic mouse bone marrow replacement, we first demonstrated that bone marrow derived-mesenchymal stem cells (BMSCs) migrated markedly to the bleomycin-injured lung. The migrated BMSC contributed significantly to α-smooth muscle actin (α-SMA)-positive myofibroblasts. By transplantation of GFP-labelled human BMSC (hBMSC) or EGFP transgenic mouse BMSC (mBMSC), we further showed that BMSC might be involved in lung fibrosis in severe combined immune deficiency (SCID)/Beige mice induced by bleomycin. In addition, using quantitative-RT-PCR, western blot, Sircol collagen assay and migration assay, we determined the underlying mechanism was LPA-induced BMSC differentiation into myofibroblast and the secretion of ECM via LPA1. By employing a novel LPA1 antagonist, Antalpa1, we then showed that Antalpa1 could attenuate lung fibrosis by inhibiting both BMSC differentiation into myofibroblast and the secretion of ECM. Collectively, the above findings not only further validate LPA1 as a drug target in the treatment of pulmonary fibrosis but also elucidate a novel pathway in which BMSCs contribute to the pathologic process.

Chemical approaches to stem cell biology and therapeutics.

Small molecules that modulate stem cell fate and function offer significant opportunities that will allow the full realization of the therapeutic potential of stem cells. Rational design and screening for small molecules have identified useful compounds to probe fundamental mechanisms of stem cell self-renewal, differentiation, and reprogramming and have facilitated the development of cell-based therapies and therapeutic drugs targeting endogenous stem and progenitor cells for repair and regeneration. Here, we will discuss recent scientific and therapeutic progress, as well as new perspectives and future challenges for using chemical approaches in stem cell biology and regenerative medicine.

Chemical approaches to studying stem cell biology.

Stem cells, including both pluripotent stem cells and multipotent somatic stem cells, hold great potential for interrogating the mechanisms of tissue development, homeostasis and pathology, and for treating numerous devastating diseases. Establishment of in vitro platforms to faithfully maintain and precisely manipulate stem cell fates is essential to understand the basic mechanisms of stem cell biology, and to translate stem cells into regenerative medicine. Chemical approaches have recently provided a number of small molecules that can be used to control cell self-renewal, lineage differentiation, reprogramming and regeneration. These chemical modulators have been proven to be versatile tools for probing stem cell biology and manipulating cell fates toward desired outcomes. Ultimately, this strategy is promising to be a new frontier for drug development aimed at endogenous stem cell modulation.

Discovery of new antimalarial chemotypes through chemical methodology and library development.

In an effort to expand the stereochemical and structural complexity of chemical libraries used in drug discovery, the Center for Chemical Methodology and Library Development at Boston University has established an infrastructure to translate methodologies accessing diverse chemotypes into arrayed libraries for biological evaluation. In a collaborative effort, the NIH Chemical Genomics Center determined IC(50)'s for Plasmodium falciparum viability for each of 2,070 members of the CMLD-BU compound collection using quantitative high-throughput screening across five parasite lines of distinct geographic origin. Three compound classes displaying either differential or comprehensive antimalarial activity across the lines were identified, and the nascent structure activity relationships (SAR) from this experiment used to initiate optimization of these chemotypes for further development.

Rapid induction and long-term self-renewal of primitive neural precursors from human embryonic stem cells by small molecule inhibitors.

Human embryonic stem cells (hESCs) hold enormous promise for regenerative medicine. Typically, hESC-based applications would require their in vitro differentiation into a desirable homogenous cell population. A major challenge of the current hESC differentiation paradigm is the inability to effectively capture and, in the long-term, stably expand primitive lineage-specific stem/precursor cells that retain broad differentiation potential and, more importantly, developmental stage-specific differentiation propensity. Here, we report synergistic inhibition of glycogen synthase kinase 3 (GSK3), transforming growth factor ß (TGF-ß), and Notch signaling pathways by small molecules can efficiently convert monolayer cultured hESCs into homogenous primitive neuroepithelium within 1 wk under chemically defined condition. These primitive neuroepithelia can stably self-renew in the presence of leukemia inhibitory factor, GSK3 inhibitor (CHIR99021), and TGF-ß receptor inhibitor (SB431542); retain high neurogenic potential and responsiveness to instructive neural patterning cues toward midbrain and hindbrain neuronal subtypes; and exhibit in vivo integration. Our work uniformly captures and maintains primitive neural stem cells from hESCs.

Chemical strategies for stem cell biology and regenerative medicine.

Stem cell technology holds great promises for the cures of devastating diseases, injuries, aging, and even cancers as it is applied in regenerative medicine. Recent breakthroughs in the development of induced pluripotent stem cell techniques and efficient differentiation strategies have generated tremendous enthusiasm and efforts to explore the therapeutic potential of stem cells. Small molecules, which target specific signaling pathways and/or proteins, have been demonstrated to be particularly valuable for manipulating cell fate, state, and function. Such small molecules not only are useful in generating desired cell types in vitro for various applications but also could be further developed as conventional therapeutics to stimulate patients' endogenous cells to repair and regenerate in vivo. Here, we focus on recent progress in the use of small molecules in stem cell biology and regenerative medicine.