A cell-based screen identifies ATR inhibitors with synthetic lethal properties for cancer-associated mutations

Oncogene activation has been shown to generate replication-born DNA damage, also known as replicative stress. The primary responder to replicative stress is not Ataxia-Telangiectasia Mutated (ATM) but rather the kinase ATM and Rad3-related (ATR). One limitation for the study of ATR is the lack of potent inhibitors. We here describe a cell-based screening strategy that has allowed us to identify compounds with ATR inhibitory activity in the nanomolar range. Pharmacological inhibition of ATR generates replicative stress, leading to chromosomal breakage in the presence of conditions that stall replication forks. Moreover, ATR inhibition is particularly toxic for p53-deficient cells, this toxicity being exacerbated by replicative stress-generating conditions such as the overexpression of cyclin E. Notably, one of the compounds we identified is NVP-BEZ235, a dual phosphatidylinositol-3-OH kinase (PI3K) and mTOR inhibitor that is being tested for cancer chemotherapy but that we now show is also very potent against ATM, ATR and the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs).

Isolation of a C5-deprotonated imidazolium, a crystalline "abnormal" N-heterocyclic carbene

The discovery two decades ago of metal-free stable carbenes, especially imidazol-2-ylidenes [N-heterocyclic carbenes (NHCs)], has led to numerous breakthroughs in organic and organometallic catalysis. More recently, a small range of complexes has been prepared in which alternative NHC isomers, namely imidazol-5-ylidenes (also termed abnormal NHCs or aNHCs, because the carbene center is no longer located between the two nitrogens), coordinate to a transition metal. Here we report the synthesis of a metal-free aNHC that is stable at room temperature, both in the solid state and in solution. Calculations show that the aNHC is more basic than its normal NHC isomer. Because the substituent at the carbon next to the carbene center is a nonbulky phenyl group, a variety of substitution patterns should be tolerated without precluding the isolation of the corresponding aNHC.

Aging of proteins: isolation and identification of a fluorescent chromophore from the reaction of polypeptides with glucose

Proteins exposed to glucose over long periods are known to undergo physicochemical changes including crosslinking and formation of brown fluorescent pigments of poorly characterized structure. Acid hydrolysis of both browned poly(L-lysine) and browned bovine serum albumin is found to release a major fluorescent chromophore, which after alkalinization is extractable into organic solvents and which can be purified by silica gel chromatography. The fluorescence properties of this compound very closely resemble those of the bulk browned polypeptides. By NMR, mass spectroscopy, and chemical derivatization, this compound is assigned the structure 2-(2-furoyl)-4(5)-(2-furanyl)-1H-imidazole (FFI). Confirmation was obtained by independent chemical synthesis from furylglyoxal and ammonia. The incorporation of two peptide-derived amine nitrogens and two glucose residues in FFI strongly suggests that peptide-bound FFI precursors are implicated in the crosslinking of proteins by glucose in vivo. This reaction has potential implications in the understanding of glucose-mediated protein modifications and their role in the complications of diabetes and aging.

The isolation and identification of a new mutagen from fried ground beef: 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)

A new mutagenic compound has been isolated from ground beef which was fried at 300 degrees C for 5.5 min on each side. The new mutagen was purified using an aqueous acid extraction, XAD-2 adsorption-solvent elution, a series of preparative and analytical h.p.l.c. purification steps, and monitored with the Ames/Salmonella assay. This study reveals a new mutagen member of the amino-imidazoazaarene class of aromatic amines, having a mol. w of 224, and a formula of C13H12N4 as determined by high-resolution mass spectrometry. N.m.r. spectrometry supports the structure, 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP), for the new mutagen. The 1-methyl and 3-methyl synthesized isomers of PhIP were compared to the purified mutagen. The two isomers had identical mass spectra to the purified compound, but only the 1-methyl isomer showed similar u.v. and n.m.r. spectra. The two synthetic isomers were separable by h.p.l.c. and the beef derived component co-eluted with the 1-methyl-PhIP isomer. PhIP has a specific activity in the Ames/Salmonella assay of 1950 revertants/microgram. Although it is not as mutagenic as other compounds isolated from fried beef (e.g. MeIQx, 58 000 revertants/microgram) it is the most abundant mutagenic compound by mass in fried beef. PhIP is present at approximately 15 p.p.b. of the original weight of uncooked beef (accounting for 75% of the mass of genotoxic material) and contributes 18% of the total mutagenicity of the fried beef.

Methanobactin, a copper-acquisition compound from methane-oxidizing bacteria

Siderophores are extracellular iron-binding compounds that mediate iron transport into many cells. We present evidence of analogous molecules for copper transport from methane-oxidizing bacteria, represented here by a small fluorescent chromopeptide (C45N12O14H62Cu, 1216 daltons) produced by Methylosinus trichosporium OB3b. The crystal structure of this compound, methanobactin, was resolved to 1.15 angstroms. It is composed of a tetrapeptide, a tripeptide, and several unusual moieties, including two 4-thionyl-5-hydroxy-imidazole chromophores that coordinate the copper, a pyrrolidine that confers a bend in the overall chain, and an amino-terminal isopropylester group. The copper coordination environment includes a dual nitrogen- and sulfur-donating system derived from the thionyl imidazolate moieties. Structural elucidation of this molecule has broad implications in terms of organo-copper chemistry, biological methane oxidation, and global carbon cycling.

Action of biologically-relevant oxidizing species upon uric acid. Identification of uric acid oxidation products

Uric acid is an end-product of purine metabolism in Man, and has been suggested to act as an antioxidant in vivo. Products of attack upon uric acid by various oxidants were measured by high performance liquid chromatography. Hypochlorous acid rapidly oxidized uric acid, forming allantoin, oxonic/oxaluric and parabanic acids, as well as several unidentified products. HOCl could oxidize all these products further. Hydrogen peroxide did not oxidize uric acid at detectable rates, although it rapidly oxidized oxonic acid and slowly oxidized allantoin and parabanic acids. Hydroxyl radicals generated by hypoxanthine/xanthine oxidase or Fe2(+)-EDTA/H2O2 systems also oxidized uric acid to allantoin, oxonic/oxaluric acid and traces of parabanic acid. Addition of ascorbic acid to the Fe2(+)-EDTA/H2O2 system did not increase formation of oxidation products from uric acid, possibly because ascorbic acid can 'repair' the radicals resulting from initial attack of hydroxyl radicals upon uric acid. Mixtures of methaemoglobin or metmyoglobin and H2O2 also oxidized uric acid: allantoin was the major product, but some parabanic and oxonic/oxaluric acids were also produced. Caeruloplasmin did not oxidize uric acid under physiological conditions, although simple copper (Cu2+) ions could, but this was prevented by albumin or histidine. The possibility of using oxidation products of uric acid, such as allantoin, as an index of oxidant generation in vivo in humans is discussed.

Targeting DDX3 with a small molecule inhibitor for lung cancer therapy

Lung cancer is the most common malignancy worldwide and is a focus for developing targeted therapies due to its refractory nature to current treatment. We identified a RNA helicase, DDX3, which is overexpressed in many cancer types including lung cancer and is associated with lower survival in lung cancer patients. We designed a first-in-class small molecule inhibitor, RK-33, which binds to DDX3 and abrogates its activity. Inhibition of DDX3 by RK-33 caused G1 cell cycle arrest, induced apoptosis, and promoted radiation sensitization in DDX3-overexpressing cells. Importantly, RK-33 in combination with radiation induced tumor regression in multiple mouse models of lung cancer. Mechanistically, loss of DDX3 function either by shRNA or by RK-33 impaired Wnt signaling through disruption of the DDX3-β-catenin axis and inhibited non-homologous end joining-the major DNA repair pathway in mammalian somatic cells. Overall, inhibition of DDX3 by RK-33 promotes tumor regression, thus providing a compelling argument to develop DDX3 inhibitors for lung cancer therapy.

New bisindole alkaloids of the topsentin and hamacanthin classes from the Mediterranean marine sponge Rhaphisia lacazei

Chemical investigation of the Et(2)O extract of the marine sponge Rhaphisia lacazei resulted in the isolation of 13 pure bisindole alkaloids (1-13). Compounds (1-6) belong to the class of topsentins and have already been described. Compounds 7-13 are new products, closely related to the class of hamacanthins. The major compounds 1-3 were tested in vitro for antitumor activity; compounds 2 and 3 showed antiproliferative activity against human bronchopulmonary cancer cells (NSCLC-N6) with an IC(50) of 12 and 6.3 microg/mL, respectively.

Imidazole alkaloids from Lepidium meyenii

Two new imidazole alkaloids (lepidiline A and lepidiline B) have been isolated from a root extract of Lepidium meyenii with the common name Maca and identified as 1,3-dibenzyl-4,5-dimethylimidazolium chloride (1) and 1,3-dibenzyl-2,4,5-trimethylimidazolium chloride (2), respectively. The structures of these two new compounds were determined by spectroscopic methods, as well as single-crystal X-ray diffraction performed on compound 1.

Detection of a carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), in cigarette smoke condensate

A carcinogenic heterocyclic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), was measured in condensate of cigarette mainstream smoke by HPLC. PhIP was detected in all brands of filter-tipped cigarettes analyzed. The mean level of PhIP in the cigarette mainstream smoke was 16.4 ng/cig.

Capillary electrophoresis with chiral selectors: optimization of separation and determination of thermodynamic parameters for binding of tioconazole enantiomers to cyclodextrins

A systematic approach is outlined for optimization of enantiomeric separations in free solution capillary electrophoresis using chiral mobile-phase additives. Maximum electrophoretic mobility difference between the enantiomers occurs when the concentration of free selector is equal to the reciprocal of the average binding constant. General equations and data analysis methods are presented to relate mobilities to equilibrium constants in simple and competitive binding equilibria and used to determine thermodynamic parameters for host-guest complexation of tioconazole enantiomers with a range of cyclodextrin selectors. Selectivities are found to be in the reverse order of binding constants in the series dimethyl-beta-cyclodextrin (K1 = 6.9 x 10(3) M-1, alpha = 1.10) to hydroxypropyl-beta-cyclodextrin (K1 = 0.72 x 10(3) M-1, alpha = 1.29). For beta-cyclodextrin (K1 = 1.32 x 10(3)M-1, alpha = 1.20), delta H zero provides the dominant contribution to binding but delta delta H zero and T delta delta S zero terms give comparable contributions to the selectivity. Addition of alcohol does not affect the selectivity, but allows displacement of the optimum separation conditions to higher cyclodextrin concentration through either competitive binding (with cyclohexanol) or preferential solvation of reactants (with methanol).

An endogenous substance with clonidine-like properties: selective binding to imidazole sites in the ventrolateral medulla

We sought to characterize the interactions of an endogenous clonidine-displacing substance (CDS) with the specific receptor sites to which clonidine and its analogs bind: (a) the non-adrenergic imidazole binding site, which is present in the ventrolateral medulla (VLM) but not the frontal cortex, (b) high-affinity and (c) low-affinity states of the alpha 2-adrenergic receptor, and (d) the alpha 1-adrenergic receptor. CDS, like clonidine, potently and completely inhibited specific p-[3H]aminoclonidine binding to membranes from the VLM or from the frontal cortex. Both CDS and clonidine bound with highest affinity to imidazole binding sites in the VLM, both were 3-fold selective for high-affinity over low-affinity alpha 2-adrenergic receptors, and both exhibited lowest affinity for alpha 1-adrenergic receptors. Unlike clonidine, CDS exhibited 30-fold selectivity for imidazole over alpha 2-adrenergic receptors but showed only a weak preference for alpha 2- over alpha 1-adrenergic receptors, indicating that CDS and clonidine are not identical. We conclude that CDS is an endogenous clonidine-like substance which may be the natural ligand for imidazole binding sites in the VLM. The receptor-binding properties of CDS are consistent with the view that it is a unique and as yet unrecognized compound.

New leukotriene B4 receptor antagonist: leucettamine A and related imidazole alkaloids from the marine sponge Leucetta microraphis

Three new imidazole alkaloids, leucettamines A [1] and B [2] and leucettamidine [3], have been isolated from the Palauan sponge Leucetta microraphis. Their structures were established on the basis of extensive spectral analyses. Leucettamine A showed potent leukotriene B4 receptor binding activity (K(i) = 1.3 microM), while leucettamine B was essentially inactive (K(i) = 100 microM) and leucettamidine showed significant activity (K(i) = 5.3 microM). With leucettamine A identified as a pure LTB4 receptor antagonist, a new structure lead is presented to inflammation therapy.

Makaluvamines H-M and damirone C from the pohnpeian sponge Zyzzya fuliginosa

Seven new pyrroloiminoquinone alkaloids, makaluvamines H-M [19-24] and damirone C[25], together with the known compounds, makaluvamines C[13], D[14], and G[17], were isolated from the sponge Zyzzya fuliginosa collected at Nahpali Island, Pohnpei, Micronesia. The structures of the new compounds were elucidated by interpretation of spectral data. The chemotaxonomic relationships involving the makaluvamines and related pyrroloiminoquinone alkaloids are discussed.

Reversed phase liquid chromatography of alkyl-imidazolium ionic liquids

Eleven 1-alkyl-3-methyl imidazolium ionic liquid (IL) salts were analyzed in reversed phase mode with a Kromasil C18 column. The mobile phases were water-rich acetonitrile solutions (water content > or =70%, v/v) without any added salts. It is shown that it is possible to separate different ILs sharing the same cation and differing by the anion when salt-free mobile phases are used. When a buffer, acetate or phosphate salt, or any salt, such as sodium chloride or sodium tetrafluorobarate, is added to the mobile phase, the ILs differing only by their anions cannot be separated. ILs with different alkyl chains in the imidazolium cation are separated by mobile phases with or without added salts following a hydrophobic interaction behavior: log k is proportional to nC, the carbon number of the alkyl chain. Important differences in ion/stationary phase interactions are observed depending on the ionic content of the mobile phase. With salt-free mobile phases, the IL/C18 stationary phase interactions correspond to concave isotherms associated with fronting peaks for all ILs. With mobile phase containing 0.01 M of salt, tailing IL peaks correspond to convex adsorption isotherms. Also, the IL retention factor depends on the concentration and nature of the added salt. Hexafluorophosphate chaotropic anions can adsorb on the Kromasil C18 surface dramatically increasing the imidazolium cation retention factors.

Bisindole alkaloids of the topsentin and hamacanthin classes from a marine sponge Spongosorites sp

Seven new (1 and 3-8) and seven known (2 and 9-14) bisindole alkaloids of the topsentin and hamacanthin classes were isolated from the MeOH extract of a marine sponge Spongosorites sp. by bioactivity-guided fractionation. The structure of compound 7 is a revision from our previous report. The planar structures were established on the basis of NMR and MS spectroscopic analyses. Configurations of these compounds were defined by NMR spectroscopy and optical rotation. It is noteworthy that both R and S isomers were isolated for the hamacanthins (1-4, 9, 10, 15, and 16), while a single stereoisomer was isolated for dihydrohamacanthins (5, 11-14, 17, and 18). Compounds 1-4, 6, and 8-14 showed marginal cytotoxicity against five human solid tumor cell lines, and compound 2 showed weak antibacterial activity against clinically isolated methicillin-resistant strains.

Triazole and dihydroimidazole alkaloids from the marine sediment-derived fungus Penicillium paneum SD-44

A novel triazole carboxylic acid, penipanoid A (1), two new quinazolinone alkaloids, penipanoids B (2) and C (3), and a very recently reported quinazolinone derivative (4) were isolated from the marine sediment-derived fungus Penicillium paneum SD-44. Their structures were elucidated by spectroscopic analysis, and the structure for 1 was confirmed by X-ray crystallographic analysis. Compound 1 represents the first example of a triazole derivative from marine sediment-derived fungi, and compound 2 is a rare quinazolinone derivative having a dihydroimidazole ring system. The cytotoxicity of compounds 1 and 4 and the antimicrobial activity of 1-4 were evaluated.

Antineoplastic agents. 362. Isolation and X-ray crystal structure of dibromophakellstatin from the Indian ocean sponge Phakellia mauritiana

Bioassay-guided isolation procedures using human tumor cell lines led to isolation of dibromophakellstatin (4) from the Republic of Seychelles sponge Phakellia mauritiana. The isolation, X-ray crystal structure elucidation, absolute stereochemistry, and antineoplastic activity have been summarized. P. mauritiana was also found to contain dibromophakellin (1), debromohymenialosine (2), thymidine, deoxyuridine, and thymine.

New imidazole alkaloids from the Indonesian sponge Leucetta chagosensis

Chemical investigation of the sponge Leucetta chagosensis collected in Indonesia afforded five new imidazole alkaloids, naamine F (2), naamine G (3), kealiinine A (6), kealiinine B (7), and kealiinine C (8), in addition to the known compound naamine A (1). Naamine G (3) exhibited strong antifungal activity against the phytopathogenic fungus Cladosporium herbarum and also showed mild cytotoxicity against mouse lymphoma (L5178Y) and human cervix carcinoma (HeLa) cell lines. In the brine shrimp assay, kealiinine A (6) was more active than naamine G (3). The structures of the new compounds were unambiguously established by 1D and 2D NMR and MS data.

Uniquely modified imidazole alkaloids from a calcareous Leucetta sponge

A Fijian collection of the calcareous sponge Leucetta sp. was investigated and yielded four new imidazole alkaloids. One compound, (+)-calcaridine A (6), is unique in its overall structure and consists of a geminally substituted 2-aminoimidazolidinone. An additional compound, (-)-spirocalcaridine A (7), is distinctive in its hexahydrocyclopentamidazol-2-ylidenamine spiro-linked to a cyclohexenone. A third compound, (-)-spirocalcaridine B (8), is the OCH(3) analogue of 7. These compounds have unprecedented skeletons and functionality and are the first nonorganometalic chiral aminoimidazoles isolated from calcareous sponges. The two issues discussed here include the challenges associated with the structure elucidations of 6 and 7 and the relationships to previously encountered Leucetta metabolites.

Isolation and structure elucidation of acinetobactin, a novel siderophore from Acinetobacter baumannii

A novel siderophore, called acinetobactin, with both catecholate and hydroxamate functional groups was isolated from low-iron cultures of Acinetobacter baumannii ATCC 19606. The structure was elucidated by chemical degradation, fast-atom bombardment mass spectrometry and 1H and 13C NMR spectroscopy. Acinetobactin was composed of omega-N-hydroxyhistamine, threonine and 2,3-dihydroxybenzoic acid, the last two components forming an oxazoline ring. Acinetobactin was structurally related to anguibactin, a plasmid-encoded siderophore of Vibrio anguillarum. The only difference was that acinetobactin possessed an oxazoline ring instead of a thiazoline ring. Four of 12 other clinical A. baumannii strains examined produced acinetobactin, indicative of strain-to-strain variation in the ability to produce acinetobactin. In addition, a relatively small amount of acinetobactin was also detected in A. haemolyticus ATCC 17906.

Naamidine A is an antagonist of the epidermal growth factor receptor and an in vivo active antitumor agent

The known 2-aminoimidazole alkaloid naamidine A (1) was isolated from a Fijian Leucetta sp. sponge as an inhibitor of the epidermal growth factor (EGF) receptor. The compound exhibited potent ability to inhibit the EGF signaling pathway and is more specific for the EGF-mediated mitogenic response than for the insulin-mediated mitogenic response. Evaluation in an A431 xenograft tumor model in athymic mice indicated that naamidine A exhibited at least 85% growth inhibition at the maximal tolerated dose of 25 mg/kg. Preliminary mechanism of action studies indicate that the alkaloid fails to inhibit the binding of EGF to the receptor and has no effect on the catalytic activity of purified c-src tyrosine kinase.