Peroxidase Activation of 4-Hydroxytamoxifen to Free Radicals Detected by EPR Spectroscopy

• Published in: Free radical biology & medicine Vol. 22; no. 3; pp. 423 - 431
• Main Authors: Davies, Adrian M., Malone, Mark E., Martin, Elizabeth A., Jones, Russell M., Jukes, Rebekah, Lim, Chang-Kee, Smith, Lewis L., White, Ian N.H.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 1997
• Subjects: 4-hydroxytamoxifen; 4-hydroxytoremifene; DNA Adducts; DNA damage; Electron Spin Resonance Spectroscopy; Free radical; Free Radicals; Glutathione; Glutathione - analogs & derivatives; Glutathione - metabolism; Glutathione Disulfide; Horseradish Peroxidase - metabolism; Hydrogen Peroxide - metabolism; Macromolecular Substances; Oxidation-Reduction; Peroxidase; Phosphorus Radioisotopes; Spin Labels; Tamoxifen; Tamoxifen - analogs & derivatives; Tamoxifen - metabolism; 4-hydroxytamoxifen; DNA damage; Peroxidase; 4-hydroxytoremifene; Tamoxifen; Free radical; Glutathione
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/S0891-5849(96)00345-0

4-Hydroxytamoxifen is a major metabolite of the antiestrogenic drug tamoxifen used in the treatment of women with breast cancer. 4-Hydroxytamoxifen is broken down by a horseradish peroxidase/H 2O 2 system very much more rapidly than tamoxifen and causes much greater DNA damage determined by 32P-postlabelling. EPR spin trapping of 4-hydroxytamoxifen reaction products in the presence of the free radical trap 5,5-dimethyl-1-pyrroline N-oxide, together with glutathione as a hydrogen donor, resulted in the generation of a species with the characteristics of the glutathione thiyl radical (a N ∼ 15.3 G, a H ∼ 16.2 G). Support for the creation of thiyl radicals comes from the close to stoichiometric time dependent formation of glutathione disulfide concomitant with the loss of glutathione. Similar results were obtained using 4-hydroxytoremifene but no radical formation or glutathione loss could be detected using 3-hydroxytamoxifen (droloxifene). On-line LC-ESI MS analysis of the incubation products from 4-hydroxytamoxifen has identified three products with a protonated molecular mass of 773, consistent with the formation of dimers of 4-hydroxytamoxifen. The role that radical mechanisms have in the carcinogenic effects of tamoxifen in the endometrium or other target organs of women taking this drug remains to be established. Copyright © 1996 Elsevier Science Inc.