Carcinogenesis, Vol 18, 539-543, Copyright © 1997 by Oxford University Press
MR Osborne, IR Hardcastle and DH Phillips
The drug tamoxifen shows evidence of genotoxicity and induces liver tumours
in rats. Covalent DNA adducts have been detected in the liver of rats
treated with tamoxifen and these arise, at least in part, from its
metabolite alpha-hydroxytamoxifen. This probably undergoes conjugation in
the liver tissue to give an ester, which alkylates DNA. We have prepared
alpha-acetoxytamoxifen as a model for this reactive intermediate and
studied its reaction with DNA in vitro. The products of this reaction were
chromatographically identical to DNA adducts found in the liver of rats
treated with tamoxifen. We have isolated three of these products as the
nucleosides TG1, TG2 and TA1 and identified them by ultraviolet, mass and
proton magnetic resonance spectroscopy. TG1 and TG2 were
tamoxifen-deoxyguanosine adducts in which the alpha-position of tamoxifen
was linked to the amino group of guanine; TG1,
(E)-4-[4-[2-(dimethylamino)ethoxy]phenyl]-3,4-diphenyl-2- (9beta-de
oxyribofuranosyl-6-oxopurin-2-ylamino)-3-butene; TG2, (Z) isomer of TG1. In
TG2, the tamoxifen group had undergone trans-cis isomerization. The minor
product TA1 was a tamoxifen-deoxyadenosine adduct, where linkage was
through the amino group of adenine: (E)-4-[4- [2-(dimethylamino)
ethoxy]phenyl]-3,4-diphenyl-2-(9beta- deoxyribofuranosylpurin
-6-ylamino)-3-butene. These three adducts accounted for >90% of the
reaction products (approximately 67% TG1, 18% TG2 and 7% TA1); trace
products included other stereoisomers of these and dinucleotide adducts
which resisted enzymatic digestion.
ARTICLES
Minor products of reaction of DNA with alpha-acetoxytamoxifen
Section of Molecular Carcinogenesis, Haddow Laboratories, Sutton, Surrey, UK.
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