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- Andersson, Helén, 1982-, et al.
(författare)
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Tamoxifen-Induced Adduct Formation and Cell Stress in Human Endometrial Glands
- 2010
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Ingår i: Drug Metabolism And Disposition. - : American Society for Pharmacology & Experimental Therapeutics (ASPET). - 0090-9556 .- 1521-009X. ; 38:1, s. 200-207
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Tidskriftsartikel (refereegranskat)abstract
- The beneficial effects of tamoxifen in the prevention and treatment of breast cancer are compromised by an increased risk of endometrial polyps, hyperplasia, and cancer. Tamoxifen is metabolized to an array of metabolites with estrogenic effects but also to reactive intermediates that may form protein and DNA adducts. The aim of this study was to investigate cellular [(3)H]tamoxifen adduct formation by light microscopic autoradiography and cell stress by immunohistochemical analysis of glucose-regulating protein 78 (GRP78), nuclear factor kappaB (NF-kappaB), and caspase 3 in human endometrial explants after short-term incubation with tamoxifen. The cellular expression of tamoxifen-metabolizing enzymes in human endometrial biopsy samples was also determined by immunohistochemistry. The results showed selective [(3)H]tamoxifen adduct formation in glandular and surface epithelia after incubation with a nontoxic concentration of [(3)H]tamoxifen (6 nM). There was also a selective expression of the endoplasmic reticulum stress chaperone GRP78 and activated caspase 3 at these sites after incubation with cytotoxic concentrations of tamoxifen (10-100 microM). The cell stress was preferentially observed in samples from women in the proliferative menstrual phase. No treatment-related expression of NF-kappaB was observed. Constitutive expression of the tamoxifen-metabolizing enzymes CYP1B1, CYP2A6, CYP2B6, CYP2C8/9/19, CYP2D6, and SULT2A1 in glandular and surface epithelia was shown, but there was a large interindividual variation. The colocalization of [(3)H]tamoxifen adducts, expression of GRP78, caspase 3, and tamoxifen-metabolizing enzymes in human glandular and surface epithelia suggest a local bioactivation of tamoxifen at these sites and that epithelial cells are early target sites for tamoxifen-induced cell stress.
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- Bylund, Johan, 1970-, et al.
(författare)
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Amide hydrolysis of a novel chemical series of microsomal prostaglandin e synthase-1 inhibitors induces kidney toxicity in the rat
- 2013
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Ingår i: Drug Metabolism And Disposition. - : American Society for Pharmacology & Experimental Therapeutics (ASPET). - 0090-9556 .- 1521-009X. ; 41:3, s. 634-641
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Tidskriftsartikel (refereegranskat)abstract
- A novel microsomal prostaglandin E synthase 1 (mPGES-1) inhibitor induced kidney injury at exposures representing less than 4 times the anticipated efficacious exposure in man during a 7-day toxicity study in rats. The findings consisted mainly of tubular lesions and the presence of crystalline material and increases in plasma urea and creatinine. In vitro and in vivo metabolic profiling generated a working hypothesis that a bis-sulfonamide metabolite (determined M1) formed by amide hydrolysis caused this toxicity. To test this hypothesis, rats were subjected to a 7-day study and were administered the suspected metabolite and two low-potency mPGES-1 inhibitor analogs, where amide hydrolysis was undetectable in rat hepatocyte experiments. The results suggested that compounds with a reduced propensity to undergo amide hydrolysis, thus having less ability to form M1, reduced the risk of inducing kidney toxicity. Rats treated with M1 alone showed no histopathologic change in the kidney, which was likely related to underexposure to M1. To circumvent rat kidney toxicity, we identified a potent mPGES-1 inhibitor with a low propensity for amide hydrolysis and superior rat pharmacokinetic properties. A subsequent 14-day rat toxicity study showed that this compound was associated with kidney toxicity at 42, but not 21, times the anticipated efficacious exposure in humans. In conclusion, by including metabolic profiling and exploratory rat toxicity studies, a new and active mPGES-1 inhibitor with improved margins to chemically induced kidney toxicity in rats has been identified.
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- Bylund, Johan, et al.
(författare)
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Novel bioactivation mechanism of reactive metabolite formation from phenyl methyl-isoxazoles
- 2012
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Ingår i: Drug Metabolism And Disposition. - : American Society for Pharmacology & Experimental Therapeutics (ASPET). - 0090-9556 .- 1521-009X. ; 40:11, s. 2185-2191
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Tidskriftsartikel (refereegranskat)abstract
- Recently, we described a series of phenyl methyl-isoxazole derivatives as novel, potent, and selective inhibitors of the voltage-gated sodium channel type 1.7 (Bioorg Med Chem Lett 21:3871-3876, 2011). The lead compound, 2-chloro-6-fluorobenzyl [3-(2,6-dichlorophenyl)-5-methylisoxazol-4-yl]carbamate, showed unprecedented GSH and cysteine reactivity associated with NADPH-dependent metabolism in trapping studies using human liver microsomes. Additional trapping experiments with close analogs and mass spectra and NMR analyses suggested that the conjugates were attached directly to the 5′-methyl on the isoxazole moiety. We propose a mechanism of bioactivation via an initial oxidation of the 5′-methyl generating a stabilized enimine intermediate and a subsequent GSH attack on the 5′-methylene. Efforts to ameliorate reactive metabolite generation were undertaken to minimize the potential risk of toxicity. Formation of reactive metabolites could be significantly reduced or prevented by removing the 5′-methyl, by N-methylation of the carbamate; by replacing the nitrogen with a carbon or removing the nitrogen to obtain a carboxylate; or by inserting an isomeric 5′-methyl isoxazole. The effectiveness of these various chemical modifications in reducing GSH adduct formation is in line with the proposed mechanism. In conclusion, we have identified a novel mechanism of bioactivation of phenyl 5-methyl-isoxazol-4-yl-amines. The reactivity was attenuated by several modifications aimed to prevent the emergence of an enimine intermediate. Whether 5′-methyl isoxazoles should be considered a structural alert for potential formation of reactive metabolites is dependent on their context, i.e., 4′-nitrogen.
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