Characterization of the Major DNA Adduct Formed by α-Hydroxy-<i>N</i>-desmethyltamoxifen in Vitro and in Vivo

G, Gamboa da Costa; Lp, Hamilton; Beland, Frederick A.; Marques, M. Matilde

doi:10.1021/tx990187b

Cited by 26 publications

(36 citation statements)

References 41 publications

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“…Both adducts had UV spectra (Figure 1, inset) closely resembling those reported for the N 2 -deoxyguanosyl adducts through the R-carbon of tamoxifen (65,71,72), N-desmethyltamoxifen (66,73), N,N-didesmethyltamoxifen (67), and 4-hydroxytamoxifen (74), which suggested a similar substitution pattern.…”

Section: Resultssupporting

confidence: 65%

DNA Adduct Formation in the Livers of Female Sprague−Dawley Rats Treated with Toremifene or α-Hydroxytoremifene

Costa

Pereira

Churchwell

et al. 2007

Chem. Res. Toxicol.

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Toremifene, an analogue of tamoxifen in which the ethyl side chain has been replaced with a 2-chloroethyl substituent, is used as a chemotherapeutic agent in postmenopausal women with advanced breast cancer. Toremifene is metabolized in a manner similar to that of tamoxifen, with alpha-hydroxytoremifene being a predominant metabolite in incubations in vitro. DNA adducts have been detected previously in liver DNA upon the administration of toremifene to rats; however, the identity of these adducts is unknown. In the present study, we have characterized the DNA adducts produced by alpha-hydroxytoremifene and have compared the extent of hepatic DNA adduct formation in rats administered toremifene, alpha-hydroxytoremifene, or tamoxifen. alpha-Hydroxytoremifene was synthesized, further activated by sulfation, and then reacted with salmon testis DNA. After enzymatic hydrolysis to deoxynucleosides, HPLC analysis indicated the formation of two major DNA adducts, which were characterized as (E)- and (Z)-alpha-(deoxyguanosin-N2-yl)toremifene on the basis of 1H NMR and mass spectral analyses. To assess the formation of toremifene DNA adducts in vivo, female Sprague-Dawley rats were treated intraperitoneally with toremifene, alpha-hydroxytoremifene, or tamoxifen. 32P-Postlabeling analyses of hepatic DNA from the tamoxifen-treated rats indicated three DNA adducts at a total level of 2,200 +/- 270 adducts/108 nucleotides. DNA adducts were not detected (<5 adducts/108 nucleotides) in the livers of rats treated with toremifene. Two DNA adducts, of which the major one coeluted with the 3',5'-bis-phosphate of (E)-alpha-(deoxyguanosin-N2-yl)toremifene, were present at a level of 57 +/- 12 adducts/108 nucleotides in hepatic DNA from rats administered alpha-hydroxytoremifene. The low level of hepatic DNA adduct formation observed with both toremifene and alpha-hydroxytoremifene, as compared to that with tamoxifen, may be due to the limited esterification of alpha-hydroxytoremifene and/or the poor reactivity of alpha-sulfoxytoremifene.

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Section: Resultssupporting

confidence: 65%

DNA Adduct Formation in the Livers of Female Sprague−Dawley Rats Treated with Toremifene or α-Hydroxytoremifene

Costa

Pereira

Churchwell

et al. 2007

Chem. Res. Toxicol.

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“…The synthesis of 12-hydroxy-NVP ( 5 ) involved the thermodynamically controlled generation of the NVP anion at C12, followed by a simple direct oxidation with MoOPH . Attempts to convert this NVP metabolite into the metabolically plausible reactive electrophile 12-sulfoxy-NVP ( 7 ; Scheme ), by reacting 12-hydroxy-NVP with the SO 3 ·pyridine complex , were unsuccessful, presumably due to secondary reactions with the pyridine rings of the starting material. As an alternative, we tested the acetylation of 12-hydroxy-NVP; however, when 12-acetoxy-NVP was reacted with nucleophiles, acetyl transfer was consistently favored over nucleophilic attack on the NVP moiety.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Characterization of DNA Adducts from the HIV Reverse Transcriptase Inhibitor Nevirapine

Antunes

Duarte

Santos

et al. 2008

Chem. Res. Toxicol.

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Nevirapine (NVP) is a non-nucleoside reverse transcriptase inhibitor used against the human immunodeficiency virus type 1 (HIV-1), mostly to prevent mother-to-child HIV transmission in developing countries. One of the limitations of nevirapine use is severe hepatotoxicity, which raises concerns about its administration, particularly in the perinatal and pediatric settings. Nevirapine metabolism involves oxidation of the 4-methyl substituent to 12-hydroxy-NVP and the formation of phenolic derivatives. Further metabolism of 12-hydroxy-NVP by phase II esterification may produce electrophilic derivatives capable of reacting with DNA to yield covalent adducts, which could potentially be involved in the initiation of mutagenic and carcinogenic events. In the present study, we have investigated the reactivity of the synthetic model electrophile, 12-mesyloxy-NVP, toward 2'-deoxynucleosides and DNA. Parallel synthetic studies were conducted with 12-bromo-NVP and 3',5'- O-bis( tert-butyldimethylsilyl)-2'-deoxynucleosides, using palladium(0) catalysis. Multiple adducts from deoxyguanosine, deoxyadenosine, and deoxycytidine were isolated in the reactions with 12-mesyloxy-NVP and characterized by NMR and MS. The adduct structures consistently involved binding through C12 of NVP and N7 or N9 of deoxyguanosine; N1, N3, or N9 of deoxyadenosine; and N3 of deoxycytidine. Reactions conducted under palladium(0) catalysis yielded adducts through O (6) and N1 of deoxyguanosine, N1 of deoxyadenosine, and N3 of deoxycytidine. At least seven deoxynucleoside-NVP adducts were present in DNA reacted with 12-mesyloxy-NVP and enzymatically hydrolyzed. Four of these adducts were identified as 12-(deoxyadenosin-N1-yl)nevirapine, 12-(deoxycytidin-N3-yl)nevirapine, 12-(deoxyguanosin- O(6)-yl)nevirapine, and 12-(deoxyadenosin- N(6)-yl)nevirapine. One depurinating adduct, 12-(guanin-N7-yl)nevirapine, was identified in the thermal neutral DNA hydrolysate. If formed in vivo, some of these adducts would have considerable mutagenic potential. Our results thus suggest that NVP metabolism to 12-hydroxy-NVP may be a factor in NVP hepatocarcinogenicity.

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“…15,16), which are proven mutagenic lesions in mammalian cells (17,18). Analogous reactions may also occur with other phase I metabolites of tamoxifen (19,20).…”

Section: Introductionmentioning

confidence: 98%

Tamoxifen Forms DNA Adducts in Human Colon after Administration of a Single [14C]-Labeled Therapeutic Dose

et al. 2007

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Tamoxifen is widely prescribed for the treatment of breast cancer and is also licensed in the United States for the prevention of this disease. However, tamoxifen therapy is associated with an increased occurrence of endometrial cancer in women, and there is also evidence that it may elevate the risk of colorectal cancer. The underlying mechanisms responsible for tamoxifen-induced carcinogenesis in women have not yet been elucidated, but much interest has focused on the role of DNA adduct formation. We investigated the propensity of tamoxifen to bind irreversibly to colorectal DNA when given to 10 women as a single [14 C]-labeled therapeutic (20 mg) dose, f18 h before undergoing colon resections. Using the sensitive technique of accelerator mass spectrometry, coupled with high-performance liquid chromatography separation of enzymatically digested DNA, a peak corresponding to authentic dG-N 2 -tamoxifen adduct was detected in samples from three patients, at levels ranging from 1 to 7 adducts/10 9 nucleotides. No [14 C]-radiolabel associated with tamoxifen or its major metabolites was detected. The presence of detectable CYP3A4 protein in all colon samples suggests that this tissue has the potential to activate tamoxifen to A-hydroxytamoxifen, in addition to that occurring in the systemic circulation, and direct interaction of this metabolite with DNA could account for the binding observed. Although the level of tamoxifeninduced damage displayed a degree of interindividual variability, when present, it was f10 to 100 times higher than that reported for other suspect human colon carcinogens such as 2-amino-1-methyl-6-phenyimidazo [4,5-b]pyridine. These findings provide a mechanistic basis through which tamoxifen could increase the incidence of colon cancers in women.

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Characterization of the Major DNA Adduct Formed by α-Hydroxy-N-desmethyltamoxifen in Vitro and in Vivo

Cited by 26 publications

References 41 publications

DNA Adduct Formation in the Livers of Female Sprague−Dawley Rats Treated with Toremifene or α-Hydroxytoremifene

DNA Adduct Formation in the Livers of Female Sprague−Dawley Rats Treated with Toremifene or α-Hydroxytoremifene

Synthesis and Characterization of DNA Adducts from the HIV Reverse Transcriptase Inhibitor Nevirapine

Tamoxifen Forms DNA Adducts in Human Colon after Administration of a Single [14C]-Labeled Therapeutic Dose

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