Site-specific tamoxifen-DNA adduct formation: Lack of correlation with mutational ability in Escherichia coli

Damon Anthony Lowes, K Brown, R T Heydon, E A Martin, T W Gant

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Abstract

We have mapped sites of tamoxifen adduct formation, in the loci gene using the polymerase STOP assay, following reaction in vitro with alpha-acetoxytamoxifen and horseradish peroxidase (HRP)/ H2O2 activated 4-hydroxytamoxifen For both compounds, most adduct formation occurred on guanines. However, one adenine, within a run of guanines, generated a strong polymerase STOP site with activated 4-hydroxytamoxifen, and a weaker STOP site with alpha-acetoxytamoxifen at the same location. In Escherichia coil the lac I gene reacted with 4-hydroxytamoxifen was more likely to be mutated (2 orders of magnitude) than when reacted with alpha-acetoxytamoxifen, despite the greater DNA adduct formation by a-acetoxytamoxifen. This correlates with the greater predicted ability of activated 4-hydroxytamoxifen adducts to disrupt DNA structure than alpha-acetoxytamoxifen adducts. For lac I reacted with activated 4-hydroxytamoxifen, a hot spot of base mutation was located in the region of the only adenosine adduct. No mutational hot spots were observed with alpha-acetoxytamoxifen, Our data clearly shows a lack of correlation between gross adduct number, as assayed by P-32-postlabeling and mutagenic potential. These data indicate the importance of minor adduct formation in mutagenic potential and further that conclusions regarding the mutagenicity of a chemical may not be reliably derived from the gross determination of adduct formation.

Original languageEnglish
Pages (from-to)10989-10996
Number of pages8
JournalBiochemistry
Volume38
Issue number34
DOIs
Publication statusPublished - 24 Aug 1999

Keywords

  • ALPHA-HYDROXYTAMOXIFEN
  • IN-VITRO
  • METABOLIC-ACTIVATION
  • TRANSGENIC RATS
  • BREAST-CANCER
  • LIVER
  • IDENTIFICATION
  • REPLICATION
  • HEPATOCYTES
  • 4-HYDROXYTAMOXIFEN
  • alpha-hydroxytamofixen
  • in-vitro
  • metabolic-activation
  • transgenic rats
  • breast-cancer
  • liver
  • identification
  • replication
  • hepatocytes
  • 4-hydroxytamoxifen

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