- Structure-activity relationships imply different mechanisms of action for ochratoxin A-mediated cytotoxicity and genotoxicity
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Ochratoxin A (OTA) is a fungal toxin that is classified as a possible human carcinogen based on sufficient evidence for carcinogenicity in animal studies. The toxin is known to promote oxidative DNA damage through production of reactive oxygen species (ROS). The toxin also generates covalent DNA adducts, and it has been difficult to separate the biological effects caused by DNA adduction from that of ROS generation. In the current study, we have derived structure-activity relationships (SAR) for the role of the C5 substituent of OTA (C5-X = Cl) by first comparing the ability of OTA, OTBr (C5-X = Br), OTB (C5-X = H), and OTHQ (C5-X = OH) to photochemically react with GSH and 2′-deoxyguanosine (dG). OTA, OTBr, and OTHQ react covalently with GSH and dG following photoirradiation, while the nonchlorinated OTB does not react photochemically with GSH and dG. These findings correlate with their ability to generate covalent DNA adducts (direct genotoxicity) in human bronchial epithelial cells (WI26) and human kidney (HK2) cells, as evidenced by the 32P-postlabeling technique. OTB lacks direct genotoxicity, while OTA, OTBr, and OTHQ act as direct genotoxins. In contrast, their cytotoxicity in opossum kidney epithelial cells (OK) and WI26 cells did not show a correlation with photoreactivity. In OK and WI26 cells, OTA, OTBr, and OTB are cytotoxic, while the hydroquinone OTHQ failed to exhibit cytotoxicity. Overall, our data show that the C5-Cl atom of OTA is critical for direct genotoxicity but plays a lesser role in OTA-mediated cytotoxicity. These SARs suggest different mechanisms of action (MOA) for OTA genotoxicity and cytotoxicity and are consistent with recent findings showing OTA mutagenicity to stem from direct genotoxicity, while cytotoxicity is derived from oxidative DNA damage.
- Hadjeba-Medjdoub, Kheira,Tozlovanu, Mariana,Pfohl-Leszkowicz, Annie,Frenette, Christine,Paugh, Robert J.,Manderville, Richard A.
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experimental part
p. 181 - 190
(2012/06/01)
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- COMPOUNDS AND COMPOSITIONS USEFUL IN THE TREATMENT OF NEOPLASIA
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There is described compounds for use in therapy, said compounds being defined by Formula (1): There is also described an anti-proliferative composition comprising one or more compounds according to Formula (1), and a method of treatment of neoplasia comprising the administration of such a compound or composition.
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Page/Page column 98-99
(2008/06/13)
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- Ochratoxin A forms a carbon-bonded C8-deoxyguanosine nucleoside adduct: Implications for C8 reactivity by a phenolic radical
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The ability of the carcinogenic fungal toxin Ochratoxin A (OTA, 1) to react with deoxyguanosine (dG) has been assessed using electrospray mass spectrometry and NMR. Photoexcitation of OTA (100 μM) in the presence of 50 mol equiv of dG led to the isolation and identification of the C8-deoxyguanosine nucleoside adduct 4. Importantly, the same adduct was formed upon oxidative activation of OTA using horseradish peroxidase (HRP)/H2O2 or the transition metals Fe(II) and Cu(II), as evidenced by mass spectrometry. Because the mutagenicity and subsequent carcinogenicity of OTA are believed to stem from oxidative DNA damage (strand scission and oxidative base products) and formation of guanine-specific DNA adducts, the adduct 4 confirms the ability of OTA to react covalently with dG and has important implications for the mechanism of action of OTA and other chlorophenolic toxins that undergo oxidation to yield phenoxyl radicals. The C8 position of dG is susceptible to radical attack, as was amply proven through formation of the hydroxyl radical-derived DNA lesion, 8-oxodeoxyguanosine. The adduct 4 is the first structurally characterized nucleoside adduct of a chlorophenolic toxin, and its formation has important implications for the mutagenicity of phenolic xenobiotics. Copyright
- Dai, Jian,Wright, Marcus W.,Manderville, Richard A.
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p. 3716 - 3717
(2007/10/03)
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- Photochemically catalyzed reaction of ochratoxin a with D- and L-cysteine
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The photolysis (> 300 nm) of ochratoxin A (OTA, N-{[(3R)-5-chloro-8-hydroxy-3-methyl-1-oxo-7-isochromanyl]carbonyl}-3- phenyl-L-alanine, 1) in the presence of excess (2 and 12 molar equiv) cysteine (CySH) has been investigated and found to yield sulfur adducts 5 and 6 that are characterized by liquid chromatography-mass spectrometry and 1H-NMR spectroscopy. The adduct 5 was ascribed to the Michael addition conjugate resulting from covalent attachment of CySH to the ochratoxin quinone (4) generated by photooxidation of OTA. This species was also formed by photolysis of a synthetic sample of the hydroquinone of OTA (ochratoxin hydroquinone, 3) in the presence of 12 equiv L-CySH. The conjugate 5 derived from photolysis of 3 with L-CySH was used for 1H-NMR analysis. The sulfur adduct 6 was the major species detected from covalent attachment of CySH to photoactivated OTA, and it resulted from direct displacement of the OTA Cl atom by CySH. The implications of the cysteinyl adducts to the in vivo toxicity of OTA are discussed, with particular emphasis given to conjugate 5, as products from the photooxidative pathway may be of relevance to the nephrotoxic properties of OTA.
- Brow, Mark E.,Dai, Jian,Park, Gyungse,Wright, Marcus W.,Gillman, Ivan G.,Manderville, Richard A.
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p. 649 - 656
(2007/10/03)
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- Ochratoxin A acts as a photoactivatable DNA cleaving agent
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The ability of ochratoxin A to photoinduce DNA cleavage is described; in the presence of DNA the photoreaction yields the non-chlorinated derivative, ochratoxin B, while a hydroquinone derivative is produced under anaerobic conditions.
- Gillman, Ivan G.,Yezek, Jennifer M.,Manderville, Richard A.
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p. 647 - 648
(2007/10/03)
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- Crystal Structures and Conformational Analysis of Ochratoxin A and B: Probing the Chemical Structure causing Toxicity
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Studies performed on two metabolites from Aspergillus ochraceus, ochratoxin A (1) and B (2), have yielded information related to the steric, conformational, and electric considerations that could contribute to the different toxicities of these metabolites
- Bredenkamp, Martin W.,Dillen, Jan L. M.,Rooyen, Petrus H. van,Steyn, Pieter S.
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p. 1835 - 1840
(2007/10/02)
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