Spotlight pubs.acs.org/crt
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NH3 IS METABOLICALLY RECYCLED FOR GLUTAMINE DERIVATIVE SYNTHESIS IN BREAST CANCER CELLS AND FACILITATES TUMOR GROWTH Tumor cells have increased nutrient consumption, resulting in metabolic waste accumulation in the poorly vascularized tumor microenvironment. Accordingly, cancer cells generate increased amounts of ammonia (NH3), generally considered to be a toxic waste product. However, researchers led by Marcia C. Haigis demonstrated that NH3 is metabolically recycled and used as a fundamental nitrogen source to sustain increased demand for amino acid synthesis ((2017) Science, DOI: 10.1126/ science.aam9305). Estrogen receptor (ER) positive breast cancer cells show increased expression of glutamate dehydrogenase (GDH), an enzyme that assimilates NH3. The authors performed metabolic tracing analysis in these cells and found that NH3 released during glutaminolysis was assimilated by GDH-catalyzed reductive amination for synthesis of glutamate and downstream metabolites. Radiolabeled time course tracing indicated that NH3 was rapidly and efficiently converted into glutamate and that proline and aspartate were produced using the nitrogen in secondary reactions. The researchers found that even supraphysiological NH3 concentrations could be assimilated into metabolic pathways in breast cancer cells without inducing toxicity or stress. Moreover, when NH3 accumulated in culture media, GDH-expressing breast cancer cells displayed accelerated growth and increased proliferation. This effect was abrogated in GDH-depleted breast cancer cells, which secreted more NH3 into the media under the same conditions, suggesting an impairment in NH3 recycling. The scientists observed similar results in vivo when they measured NH3 concentrations in the interstitial fluid of mice with ER-(+) xenograft tumors. NH3 levels in the tumor microenvironment ranged from 0.8−3 mM and appeared to increase tumor proliferation and growth, while plasma NH3 concentrations were in the 300 μM range, consistent with those in control mice. A GDH-depleted xenograft model displayed significantly decreased tumor growth and reduced levels of glutamate, aspartate, and proline, three metabolites associated with tumorigenesis. This work indicates that GDH-mediated NH3 recycling supports breast cancer cell proliferation. Abigail Druck Shudofsky
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iron-limited conditions, fluorescence microscopy and flow cytometry indicated that VF−FL treatment selectively labeled only the vibrio bacteria. Incubating vibrio bacteria with VF−FL in iron-rich media had no effect, suggesting that the significant fluorescence increase seen earlier was mediated by the irondependent acquisition pathway. Competition experiments with exogenous VF confirmed that bacterial transport of VF−FL was through VF-dependent mechanisms. Taken together, these data indicate that the ability of VF−FL to detect and specifically label vibrio bacteria is mediated by the siderophore moiety under ironlimited conditions. The conjugate probe can be used to detect and identify vibrio pathogens within microbiota. Abigail Druck Shudofsky
SYNTHESIS OF A SIDEROPHORE-BASED VIBRIO-SPECIFIC PROBE
Reprinted from P.-H.C. Chen et al. (2017) ACS Chem. Biol., 12, 2720−2724. Copyright © 2017 American Chemical Society.
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GLOBAL NEONICOTINOID CONTAMINATION OF HONEY SAMPLES Neonicotinoid insecticides are absorbed by plants and contaminate nectar and pollen. As such, they impact pollinators, such as bees, as well as other organisms. Pesticide residue in honey can indicate local environmental contamination. As neonicotinoids are widely used around the world, a group led by Edward Mitchel assessed neonicotinoid concentrations in honey from assorted global regions to determine the extent of contamination ((2017) Science, 358, 109−111). The authors evaluated 198 honey samples from a broad representation of biomes, acquired from six continents and from islands in the Caribbean and Pacific. They measured levels of five commonly used neonicotinoids: acetamiprid, clothianidin, imidacloprid, thiacloprid, and thiamethoxam. The scientists
Siderophores are high-affinity iron chelators secreted by many microbes under iron-limiting conditions. Once iron-bound, the small molecules are recognized by cell-specific receptors and transported into bacteria. A group led by Tsung-Shing Andrew Wang developed a siderophore−fluorophore conjugate probe that selectively targets and efficiently labels vibrio bacteria ((2017) ACS Chem. Biol., 12, 2720−2724). The Gram-negative, halophilic pathogens produce the siderophore vibrioferrin (VF). As VF is exclusive to vibrio bacteria, the scientists synthesized a VF−fluorophore conjugate, VF−FL. When VF−FL was incubated with bacterial strains for 4 h in ironlimited minimal media, a dose- and time-dependent fluorescent response was observed in Vibrio parahemolyticus, V. cholerae, and V. vulnif icus. Members of four other bacterial genera were unresponsive to VF−FL treatment. When the vibrio strains were coincubated with Staphylococcus aureus or Escherichia coli under © 2017 American Chemical Society
Published: December 18, 2017 2095
DOI: 10.1021/acs.chemrestox.7b00316 Chem. Res. Toxicol. 2017, 30, 2095−2096
Chemical Research in Toxicology
Spotlight
against Staphylococcus aureus (both methicillin-sensitive and -resistant strains) and Clostridium dif f icile, with respective minimal inhibitory concentrations of 1.0 and 2.6 μM. Further experiments suggest that phocoenamicin modifies transmembrane ionic gradients and depolarizes bacterial membranes, disrupting membrane potential without affecting membrane integrity. Abigail Druck Shudofsky
found that 75% of all honey samples contained at least one neonicotinoid, 45% of samples contained two or more, and 10% contained four or five. The frequency of occurrence of individual neonicotinoids varied by region, reflecting differences in pesticide usage, and multiple contaminations were most frequent in Asia, Europe, and North America. Maximum, average, and median total neonicotinoid concentrations were highest in samples from those continents, with a maximum of 56 ng/g. The global average total neonicotinoid concentration in contaminated samples was 1.8 ng/g. While still well below the admissible limits for human consumption according to U.S. and EU regulations, this average concentration is in the bioactive range and has been shown to cause sublethal detrimental effects on nontarget insects such as bees, resulting in growth, behavioral, learning, and performance deficits along with decreased immune efficiency, reproductive and respiratory function, and cognitive and neurological disorders. These deficits have been observed at concentrations as low as 0.10 ng/g. This work demonstrates that pollinators are globally exposed to neonicotinoids, often in multiples and at harmful concentrations. Abigail Druck Shudofsky
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THIOSEMICARBAZONE METALLOPROTEINASE INHIBITORS OF SNAKE VENOM-INDUCED HEMORRHAGE
Reprinted from F. B. Ferreira et al. (2017) ACS Med. Chem. Lett., 8, 1136−1141. Copyright © 2017 American Chemical Society.
NOVEL SPIROTETRONATE ANTIBIOTIC ISOLATED FROM METABOLITES OF MARINE MAMMAL MICROBIOTA
The toxic effects of snake venom include damage caused by necrosis and hemorrhage. While snake antivenoms can neutralize systemic injury, they are less effective at reversing local damage. With the objective of decreasing local tissue damage in snakebite victims, a group led by Carlos Mauricio R. Sant’Anna in collaboration with Arthur E. Kümmerle and Veridiana M. R. Á vila used structure-based molecular modeling to rationally design and synthesize inhibitors of snake venom metalloproteinases (SVMPs), zinc-dependent proteolytic enzymes that induce hemorrhage ((2017) ACS Med. Chem. Lett., 8, 1136−1141). The authors targeted the SVMP isolated from Bothrops pauloensis venom (BpMP-I) and then used a crystallographic structure of a related SVMP in complex with a pipetidomimetic inhibitor to construct a 3D homology model for the enzyme. As the ZnII ion is essential for the catalytic mechanism of metalloproteinases, the scientists constructed ligands containing thiosemicarbazone groups, which can act as Zn-chelators, and performed molecular docking studies. After studying the docking geometries of the most active thiosemicarbazone compound, the authors connected a carboxylate group to its iminic carbon to improve anti-BpMP-I potency. Molecular docking predicted that the modification would improve activity, as the carboxylate group would be involved in a hydrogen bond with the NH group of a peptidic residue. The team then synthesized the modeled compound (5b) and evaluated it in an in vitro BpMP-I inhibition assay. In accordance with the predictions, the structural modification greatly enhanced the inhibitory activity of the compound; 5b was over 1700-times more active than its parent. The 5b treatment completely eliminated local hemorrhage caused by B. pauloensis whole venom in animals. Molecular docking scores indicate 5b would also effectively bind to the catalytic sites of SVMPs present in other snake species, suggesting this compound as a general agent for the treatment of SVMP-induced hemorrhagic effects. Abigail Druck Shudofsky
Reprinted from J. L. Ochoa et al. (2017) ACS Infect. Dis., DOI: 10.1021/acsinfecdis.7b00105. Copyright © 2017 American Chemical Society.
Studies have shown that bacterial pathogens important in human disease are also present in marine mammals. As such, a team led by Roger G. Linington analyzed the intestinal microbiota of four such species for the production of bioactive metabolites with activity against human pathogens ((2017) ACS Infect. Dis., DOI: 10.1021/acsinfecdis.7b00105). Analysis of 48 commensal microorganisms cultured from a harbor porpoise yielded the discovery of a novel small molecule polyketide antibiotic. A metabolite fraction from Micromonospora auratinigra demonstrated high-potency activity against Gram-positive bacteria. The scientists isolated and identified a single bioactive component with a mass of 1070.4 Da and a molecular formula of C56H75ClO18. Using multiple spectroscopic techniques and chemical derivatization methods, the researchers elucidated the structure of the newly identified metabolite. Phocoenamicin, named after the harbor porpoise genus Phocoena, has a novel spirotetronate macrocyclic core with a carbon skeleton containing 23 chiral centers. It possesses structural features including two 6-deoxy sugars and a diol side chain that are unique among spirotetronate polyketides. Phocoenamicin is potent 2096
DOI: 10.1021/acs.chemrestox.7b00316 Chem. Res. Toxicol. 2017, 30, 2095−2096
