A chemical and genetic approach to the mode of action of fumagillin

Previous mode of action studies identified methionine aminopeptidase 2 (MetAP-2) as the target of the antiangiogenic natural product fumagillin and its drug candidate analog, TNP-470. We report here that TNP-470-mediated MetAP-2 inhibition blocks noncanonical Wnt signaling, which plays a critical role in development, cell differentiation, and tumorigenesis. Consistent with this finding, antisense MetAP-2 morpholino oligonucleotide injection in zebrafish embryos phenocopies gastrulation defects seen in noncanonical Wnt5 loss-of-function zebrafish mutants. MetAP-2 inhibition or depletion blocks signaling downstream of the Wnt receptor Frizzled, but upstream of Calmodulin-dependent Kinase II, RhoA, and c-Jun N-terminal Kinase. Moreover, we demonstrate that TNP-470 does not block the canonical Wnt/beta-catenin pathway. Thus, TNP-470 selectively regulates noncanonical over canonical Wnt signaling and provides a unique means to explore and dissect the biological systems mediated by these pathways.     

Selective inhibition of amino-terminal methionine processing by TNP-470 and ovalicin in endothelial cells

BACKGROUND: The angiogenesis inhibitors TNP-470 and ovalicin potently suppress endothelial cell growth. Both drugs also specifically inhibit methionine aminopeptidase 2 (MetAP2) in vitro. Inhibition of MetAP2 and changes in initiator methionine removal in drug-treated endothelial cells have not been demonstrated, however. RESUTLS: Concentrations of TNP-470 sufficient to inactivate MetAP2 in intact endothelial cells were comparable to those that inhibited cell proliferation, suggesting that MetAP2 inhibition by TNP-470 underlies the ability of the drug to inhibit cell growth. Both drug-sensitive and drug-insensitive cell lines express MetAP1 and MetAP2, indicating that drug sensitivity in mammalian cells is not simply due to the absence of compensating MetAP activity. With a single exception, detectable protein N-myristoylation is unaffected in sensitive endothelial cells treated with TNP-470, so MetAP1 activity can generally compensate when MetAP2 is inactive. Analysis of total protein extracts from cells pulse-labeled with [(35)S]-methionine following TNP-470 treatment revealed changes in the migration of several newly synthesized proteins. Two of these proteins were identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and cyclophilin A. Purification and amino-terminal sequencing of GAPDH from TNP-470-treated cells revealed partial retention of its initiator methionine, indicating that methionine removal from some, but not all, proteins is affected by MetAP2 inactivation. CONCLUSIONS: Amino-terminal processing defects occur in cells treated with TNP-470, indicating that inhibition of MetAP2 by the drug occurs in intact cells. This work renders plausible a mechanism for growth inhibition by TNP-470 as a consequence of initiator methionine retention, leading to the inactivation of as yet unidentified proteins essential for endothelial cell growth.     

Synthesis of novel 1,3,4-trisubstituted pyrazole derivatives and their evaluation as antitumor and antiangiogenic agents

Several 1,3,4-trisubstituted pyrazole derivatives were synthesized and screened for their cytotoxic effect in a primary 3 tumor cell line test at 10(-4) M drug concentration. Compounds 19 and 20 reduced the growth of one or more of these cell lines to less than 32% and escalated up to evaluation in the full panel of 60 human tumor cell lines at a minimum of 5 concentrations at 10 fold dilutions. Compound N'-(1-[1-[4-nitrophenyl]-3-phenyl-1H-pyrazol-4-yl]methylene)-2-chlorobenzohydrazide 19 proved to be the most active of these derivatives with full panel median growth inhibition (GI50), total growth concentration (TGI) and median lethal concentration (LC50) mean graph mid-point (MG-MID) of 3.79, 12.5 and 51.5 microM, respectively. In addition, compounds 19, 39, 40, 41, 43, 45, 47 were tested for their antiangiogenic properties by testing their ability to inhibit human umbilical vein endothelial cells (HUVECs) proliferation, cord formation and migration in response to chemoattractant. 3-Acetyl-2-(1-(4-nitrophenyl)-3-phenylpyrazol-4-yl)-5-(4-pyridyl)-1,3,4-oxadiazoline 39 showed significant antiangiogenic profile at non-cytotoxic doses, with HUVEC proliferation inhibition IC50 of 7.60 microM, chemotaxis IC50 of 0.86 microM and was superior to the reference celecoxib 2 in both tests. Furthermore, in contrary to the references TNP-470 and celecoxib, all the tested compounds interfered with the migratory function of HUVECs in response to vascular endothelium growth factor (VEGF) rather than the endothelial cells proliferation.     

Assay of TNP-470 and its two major metabolites in human plasma by high-performance liquid chromatography-mass spectrometry

In this study, a sensitive, specific assay for the determination of TNP-470 and its two major metabolites M-IV (also know as AGM-1883) and M-II in human plasma is reported. The assay involves liquid-liquid extraction of acidified plasma followed by reversed-phase high-performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry. A liquid-liquid extraction using an organic solvent mixture (methyl-tert-butyl-ether-hexane, 1:1, v/v) is used in place of solid-phase extraction because it provides consistent recoveries for all analytes, including the internal standard. Retention times for the analytes and internal standard are less than 7 min. Within- and between-day precision is < or = 6.5% and < or = 13.3% relative standard deviation, respectively, for the three analytes. The lower limits of quantitation are 0.25, 0.5, and 1.0 ng/mL for TNP-470, M-IV, and M-II, respectively.     

RK-805, an endothelial-cell-growth inhibitor produced by Neosartorya sp., and a docking model with methionine aminopeptidase-2

We found that a fungus Neosartorya sp. produced an angiogenesis inhibitor, RK-805. By spectroscopic analyses and semi-synthetic methods from fumagillin, the structure of RK-805 was identified as 6-oxo-6-deoxyfumagillol, which has not been reported as a natural product. RK-805 preferentially inhibited the growth of human umbilical vein endothelial cells (HUVECs) rather than that of human normal fibroblast in cell proliferation assays and blocked endothelial cell migration induced by vascular endothelial growth factor (VEGF). Moreover, RK-805 selectively inhibited methionine aminopeptidase-2 (MetAP2), but not methionine aminopeptidase-1 (MetAP1). The docked structure of RK-805 complexed with human MetAP2 indicated that not only a covalent bond between a nucleophilic imidazole nitrogen atom of His231 and the carbon of the reactive spirocyclic epoxide of RK-805, but also a hydrogen bond between NH (Asn329) and the carbonyl group of RK-805 at C-6 promote close contact in the binding pocket of the enzyme. Taken together, these results suggest that structure activity relationships of RK-805 derivatives at both C-4 and C-6, in comparison with ovalicin and TNP-470, would be useful for development of new angiogenesis inhibitors.     

A case of cross-reactivity

Studies using chemical inhibitors have suggested that p38 MAP kinase is a key regulator of Wnt/β-catenin signaling. In this issue, Verkaar et?al. (2011) show that cross-reactivity of p38 inhibitors with casein kinase Iδ/? is responsible for Wnt/β-catenin pathway inhibition.     

Negative feedback regulation of Wnt signaling by G�¦�-mediated reduction of Dishevelled

Wnt signaling is known to be important for diverse embryonic and post-natal cellular events and be regulated by the proteins Dishevelled and Axin. Although Dishevelled is activated by Wnt and involved in signal transduction, it is not clear how Dishevelled-mediated signaling is turned off. We report that guanine nucleotide binding protein beta 2 (Gnb2; Gβ₂) bound to Axin and Gβ₂ inhibited Wnt mediated reporter activity. The inhibition involved reduction of the level of Dishevelled, and the Gβ₂γ₂ mediated reduction of Dishevelled was countered by increased expression of Axin. Consistent with these effects in HEK293T cells, injection of Gβ₂γ₂ into Xenopus embryos inhibited the formation of secondary axes induced either by XWnt8 or Dishevelled, but not by β-catenin. The DEP domain of Dishevelled is necessary for both interaction with Gβ_2γ2 and subsequent degradation of Dishevelled via the lysosomal pathway. Signaling induced by Gβ_2γ2 is required because a mutant of Gβ₂, Gβ₂ (W332A) with lower signaling activity, had reduced ability to downregulate the level of Dishevelled. Activation of Wnt signaling by either of two methods, increased Frizzled signaling or transient transfection of Wnt, also led to increased degradation of Dishevelled and the induced Dishevelled loss is dependent on Gβ₁ and Gβ₂. Other studies with agents that interfere with PLC action and calcium signaling suggested that loss of Dishevelled is mediated through the following pathway: Wnt/Frizzled→Gβγ→PLC→Ca⁺²/PKC signaling. Together the evidence suggests a novel negative feedback mechanism in which Gβ₂γ₂ inhibits Wnt signaling by degradation of Dishevelled.     

A Concise Synthesis of Fumagillol

A 13-step synthesis of (±)-fumagillol ( 1 ), the direct precursor of the potent angiogenesis inhibitors TNP-470 and fumagillin, from crotonaldehyde, diethylamine, and acrolein (see the scheme) has been achieved. The synthesis features a remarkable hetero-Claisen rearrangement. Small-molecule inhibitors of angiogenesis are promising chemotherapeutic agents for the treatment of cancer and inflammatory diseases.     

Inhibition of Wnt/β-catenin signaling by p38 MAP kinase inhibitors is explained by cross-reactivity with casein kinase Iδ/ɛ

Wnt/β-catenin signaling plays essential roles in embryonic development, adult stem cell maintenance, and disease. Screening of a small molecule compound library with a β-galactosidase fragment complementation assay measuring β-catenin nuclear entry revealed TAK-715 and AMG-548 as inhibitors of Wnt-3a-stimulated β-catenin signaling. TAK-715 and AMG-548 are inhibitors of p38 mitogen-activated protein kinase, which has been suggested to regulate activation of Wnt/β-catenin signaling. However, two highly selective and equally potent p38 inhibitors, VX-745 and Scio-469, did not inhibit Wnt-3a-stimulated β-catenin signaling. Profiling of TAK-715 and AMG-548 against a panel of over 200 kinases revealed cross-reactivity with casein kinase Iδ and ?, which are known activators of Wnt/β-catenin signaling. Our data demonstrate that this cross-reactivity accounts for the inhibition of β-catenin signaling by TAK-715 and AMG-548 and argue against a role of p38 in Wnt/β-catenin signaling.     

Phototaxis in the cyanobacterium Synechocystis sp. PCC 6803: role of different photoreceptors

The second cyanobacterial phytochrome Cph2 from Synechocystis sp. PCC 6803 was suggested as a part of a light-stimulated signal transduction chain inhibiting movement toward blue light. Cph2 has the two bilin binding sites, cysteine-129 and cysteine-1022, that might be involved in sensing of red/far-red and blue light, respectively. Here, we present data on wavelength dependence of the phototaxis inhibition under blue light, indicating that Cph2 itself is the photoreceptor for this blue light response. We found that inhibition of blue-light phototaxis in wild-type cells occurred below the transition point of about 470 nm. Substitution of cysteine-1022 with valine led to photomovement of the cells toward blue light (cph2(-) mutant phenotype). Analysis of mutants lacking cysteine-129 in the N-terminal chromophore binding domain indicated that this domain is also important for Cph2 function or folding of the protein. Furthermore, putative blue-light and phytochrome-like photoreceptors encoded by the Synechocystis sp. PCC 6803 genome were inactivated in wild-type and cph2 knockout mutant background. Our results suggest that none of these potential photoreceptors interfere with Cph2 function, although inactivation of taxD1 as well as slr1694 encoding a BLUF protein led to cells that reversed the direction of movement under blue light illumination in mutant strains of cph2.     

Polygonatum cyrtonema Hua Polysaccharides Protect BV2 Microglia Relief Oxidative Stress and Ferroptosis by Regulating NRF2/HO-1 Pathway

Neuronal-regulated cell death (RCD) due to the accumulation of ROS within the central nervous system (CNS) is one of the crucial causes of central system diseases. Caspase-dependent apoptosis is the only form of RCD. As research progressed, several nonapoptotic cell death pathway RCDs were identified. Ferroptosis is a nonapoptotic RCD characterized by lipid peroxidation and plasma membrane damage. Polygonatum cyrtonema Hua. Polysaccharides (PCP) are an effective antioxidant. Based on this, the protective effect and mechanism of PCP against H₂O₂-induced microglial injury were investigated. Furthermore, the protective mechanism of PCP against ferroptosis in microglia was explored. Our results indicated that PCP could reduce oxidative stress-induced ROS accumulation by activating the NRF2/HO-1 signaling pathway, thus attenuating RCD in microglia. Subsequent studies have revealed that PCP alleviates ferroptosis in microglia due to protein levels of ERASTIN/RSL3 inhibitor SLC7A11/GPX4 by activating the NRF2/HO-1 signaling pathway. Therefore, we hypothesized that PCP exerts antioxidative and anti-ferroptosis effects by activating the expression of the NRF2/HO-1 pathway. This facilitates new ideas for clinically effective prevention and treatment of diseases due to accumulated reactive oxygen species in the CNS. Simultaneously, PCP has the development potential as a new drug candidate for treating CNS diseases.     

980 nm Photobiomodulation Promotes Osteo/Odontogenic Differentiation of the Stem Cells from Human Exfoliated Deciduous Teeth Via the Cross talk Between BMP/Smad and Wnt/β-Catenin Signaling Pathways

Increasing evidence suggests stem cells from human exfoliated deciduous teeth (SHEDs) serve as desirable sources of dentin regeneration. Photobiomodulation (PBM) has shown great potential in enhancing the proliferation and osteogenesis of human bone marrow mesenchymal stem cells (hBMMSCs). However, the specific role of PBM in odontogenic differentiation of SHEDs is little know, and we further investigated potential mechanism of PBM osteo/odontogenisis. A 980 nm diode laser with different energy densities of (0.5, 5, 10 J cm⁻²) in a 100-mW continuous wave was used for irradiation every 24 h. Osteo/odontogenic differentiation of SHEDs was achieved by performing alkaline phosphatase (ALP) and alizarin red staining (ARS) and osteo/odontogenic markers were also evaluated by qRT-PCR and western blotting. Additionally, western blot and immunohistochemical staining were performed to evaluate the levels of BMP/Smad and Wnt/β-catenin signaling-related proteins. We found that PBM at 5 J cm⁻¹ increased mineral deposition and upregulated the expression of related osteo/odontogenic markers along with the elevated expression of β-catenin and phosphorylation level of Smad1/5/9. Furthermore, Wnt signaling inhibition using DKK1 and BMP signaling inhibition using noggin inhibited PBM-induced osteo/odontogenic marker expression when used individually or jointly. In conclusion, PBM induces the osteo/odontogenic differentiation of SHEDs through cross talk between BMP/Smad and Wnt/β-catenin signaling pathways.     

Activation of Hair Cell Growth Factors by Linoleic Acid in Malva verticillata Seed

Hair loss by excessive stress from work and lifestyle changes has become a growing concern, particularly among young individuals. However, most drugs for alopecia impose a plethora of side effects. We have found the powerful impact of Malva verticillata seed extracts on alleviating hair loss. This study further isolated effective chemicals in M. verticillata seed extracts by liquid silica gel column chromatography. Under the screening for the growth rate (%) of human follicles dermal papilla cells (HFDPCs), we identified linoleic acid (LA) and oleic acid in n-hexane of M. verticillate (MH)2 fraction. LA treatment activated Wnt/β-catenin signaling and induced HFDPCs growth by increasing the expression of cell cycle proteins such as cyclin D1 and cyclin-dependent kinase 2. LA treatment also increased several growth factors, such as vascular endothelial growth factor, insulin-like growth factor-1, hepatocyte growth factor, and keratinocyte growth factor, in a dose-dependent manner. Besides, LA significantly inhibited Dickkopf-related protein expression (DKK-1), a primary alopecia signaling by dihydrotestosterone. Our findings suggest that LA treatment may alleviate a testosterone-induced signaling molecule and induces HFDPCs growth by activating Wnt/β-catenin signaling.     

Enantioselective synthesis of a potential key intermediate for the total synthesis of fumagillin

Key intermediate, 7, of a projected total synthesis of the anti-angiogenesis compound Fumagillin 1 and the semi-synthetic analogue TNP-470 2, has been prepared in enantiomerically pure form by employing an early nucleophilic addition ring closure [NARC] sequence to construct the cyclohexene backbone.     

Anti-Hair Loss Effect of Adenosine Is Exerted by cAMP Mediated Wnt/β-Catenin Pathway Stimulation via Modulation of Gsk3β Activity in Cultured Human Dermal Papilla Cells

In the present study, we investigated the molecular mechanisms of adenosine for its hair growth promoting effect. Adenosine stimulated the Wnt/β-catenin pathway by modulating the activity of Gsk3β in cultured human dermal papilla cells. It also activated adenosine receptor signaling, increasing intracellular cAMP level, and subsequently stimulating the cAMP mediated cellular energy metabolism. The phosphorylation of CREB, mTOR, and GSK3β was increased. Furthermore, the expression of β-catenin target genes such as Axin2, Lef1, and growth factors (bFGF, FGF7, IGF-1) was also enhanced. The inhibitor study data conducted in Wnt reporter cells and in cultured human dermal papilla cells demonstrated that adenosine stimulates Wnt/β-catenin signaling through the activation of the adenosine receptor and Gsk3β plays a critical role in transmitting the signals from the adenosine receptor to β-catenin, possibly via the Gαs/cAMP/PKA/mTOR signaling cascade.     

Restoration of full-length APC protein in SW480 colon cancer cells induces exosome-mediated secretion of DKK-4

Mutations in the adenomatous polyposis coli (APC) tumor suppressor gene are common in both inherited and sporadic forms of colorectal cancer (CRC), and are associated with dysregulated Wnt signaling. Colon carcinoma SW480 cells restored with stable expression of wild-type APC (SW480APC cells) exhibit attenuated Wnt signaling, and reduced tumorigenicity, including increased cell adhesion. We performed a comparative proteomic analysis of exosomes isolated from SW480 and SW480APC cells to examine the effects of restored APC on exosome protein expression. A salient finding of our study was the unique expression of the Wnt antagonist Dickkopf-related protein 4 (DKK4) in SW480APC, but not parental SW480 cell-derived exosomes. Upregulation of DKK4 in SW480APC cells was confirmed by semiquantitative RT-PCR, immunoblotting, and immunogold electron microscopy. Analysis of the DKK4 gene promoter by methylation-specific PCR revealed reduced methylation in SW480APC cells, while RT-PCR demonstrated the downregulation of DNMT-3a, compared to the parental cell line. Our discovery of exosome-mediated secretion of DKK4 opens up the possibility that exosomal DKK4 may be a mechanism used by epithelial colon cells to regulate Wnt signaling which is lost during CRC progression.     

When it is hard to get to with genetics--planar cell polarity under a chemical scalpel

Planar cell polarity (PCP) has been under genetic dissection for decades. More and more fundamental developmental processes have been found relying on PCP signaling. However, mechanisms of how PCP signaling generates asymmetry is still unknown. A recent paper in Chemistry & Biology (Sundberg et?al., 2011) represents the efforts to decipher the intracellular code of polarity signaling.     

Mechanism of alkane transfer-dehydrogenation catalyzed by a pincer-ligated iridium complex

The mechanism of (PCP)Ir-catalyzed transfer-dehydrogenation has been elucidated for the prototypical substrate/acceptor couple, COA/TBE, at 55 degrees C (COA = cyclooctane; TBE = tert-butylethylene). The catalytic cycle may be viewed as the sum of two reactions: (i) hydrogenation of TBE by (PCP)IrH2 and C-H addition of a second mole of TBE to give (PCP)IrH(tert-butylvinyl), and (ii) dehydrogenation of COA by (PCP)IrH(tert-butylvinyl) to give (PCP)IrH2, COE, and TBE. These two stoichiometric reactions have been observed independently and their kinetics determined. The overall catalysis has also been monitored in situ, and (PCP)IrH2 and (PCP)IrH(tert-butylvinyl) have been observed as the resting states; the ratio of these two complexes is found to be proportional to [TBE]2. Based upon the proportionality constant thus obtained and the catalytic rate as a function of [TBE] (which reaches a maximum at ca. 0.3 M), the respective rate constants for the hydrogenation and dehydrogenation segments can be obtained. Good agreement is found between the rates independently obtained from stoichiometric and catalytic runs. Within the overall TBE-hydrogenation reaction, labeling experiments indicate that the rate-determining step is the reductive elimination of TBA (2,2-dimethylbutane) from (PCP)IrH(tert-butylethyl) (which is formed via insertion of TBE into an Ir-H bond of (PCP)IrH2). Based upon considerations of microscopic reversibility, it can be further inferred that the rate-determining step for the alkane dehydrogenations is C-H addition (and not beta-H elimination).