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Endoxifen (4-hydroxy-N-desmethyl-tamoxifen) has anti-estrogenic effects in breast cancer cells with potency similar to 4-hydroxy-tamoxifen

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Abstract

Purpose

Tamoxifen is an effective drug for the treatment and prevention of breast cancer. It is extensively metabolized by the human cytochrome P450 enzyme system into several metabolites. Of these, 4-hydroxy-tamoxifen (4-OH-Tam) is an active metabolite, which has greater anti-estrogenic potency than the parent drug, tamoxifen. We reported recently that 4-hydroxy-N-desmethyl-tamoxifen (endoxifen) could also be active. The progesterone receptor (PR) messenger ribonucleic acid (mRNA) expression is commonly studied as a marker of estrogenic effect in breast cancer cells and PR levels in breast cancer patients are correlated with tamoxifen response. We, therefore, determined the effect of endoxifen and 4-OH-Tam on 17β-estradiol (E2)-induced PR mRNA expression in an estrogen receptor-positive human breast cancer cell line.

Methods

MCF-7 cells were treated with drugs for 24 h. The total ribonucleic acid (RNA) was harvested and transcribed into complementary deoxyribonucleic acids (cDNAs). The PR mRNA level was measured by using real-time reverse transcription polymerase chain reaction (RT-PCR). The PR expression data were normalized using a glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene expression. We measured the metabolite concentrations in the cultured media by high performance liquid chromatography (HPLC) to determine whether there was conversion of one metabolite to the other.

Results

Consistent with previous reports, the dose–response of the E2 effect on the PR expression indicated an ED50 value of approximately 60 pM and the maximum induction of PR mRNA was nearly ten-fold. When 10−10 M E2 was used, induction of the PR expression was observed in 2 h and reached its maximum at 24 h. In this assay, neither endoxifen nor 4-OH-Tam alone produced any change in the PR mRNA expression. However, both endoxifen and 4-OH-Tam decreased the E2-induced PR expression with similar potency. There was very little interconversion between the two metabolites during the culture.

Conclusions

Since endoxifen is present at greater concentrations than 4-OH-Tam in human plasma of breast cancer patients receiving chronic tamoxifen, these results provide further evidence that endoxifen is as important as, or more important than, 4-OH-Tam to the anti-estrogenic action of tamoxifen.

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Acknowledgments

This work was supported in part by a Pharmacogenetic Network Grant from the NIGMS, Bethesda, Maryland, USA (U-01-GM61373), by a Clinical Pharmacology Training Grant to the Division of Clinical Pharmacology at Indiana University School of Medicine, Indiana, USA (T-32-GM04825), and by a PhRMA Foundation Grant (Indiana Center for Excellence in Clinical Pharmacology, Indiana, USA).

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  1. Young Chai Lim

    Present address: Department of Pharmacology and Research Institute of Medical Sciences, Chonnam National University Medical School, Kwangju, Korea

Authors and Affiliations

  1. Division of Clinical Pharmacology, Indiana University School of Medicine, 1001 West 10th Street, WD Myers Bldg., W7123, Indianapolis, Indiana, 46202, USA

    Young Chai Lim, Zeruesenay Desta, David A. Flockhart & Todd C. Skaar

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Correspondence to Todd C. Skaar.

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Lim, Y.C., Desta, Z., Flockhart, D.A. et al. Endoxifen (4-hydroxy-N-desmethyl-tamoxifen) has anti-estrogenic effects in breast cancer cells with potency similar to 4-hydroxy-tamoxifen. Cancer Chemother Pharmacol 55, 471–478 (2005). https://doi.org/10.1007/s00280-004-0926-7

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