The effectiveness of anti-estrogens in treating estrogen-dependent diseases is limited by the acquired resistance of some diseases to anti-estrogens. This effect could occur by the export of anti-estrogens by cell membrane transport proteins. To study this phenomenon we have expressed human estrogen receptor (hER) and an estrogen-sensitive reporter in wild-type yeast and two transport-defective strains. In the wild-type strain, the most effective anti-estrogen was nafoxidine. 4-Hydroxy tamoxifen and clomiphene were inactive whereas tamoxifen had significant inhibitory activity in the wild-type strain. Using a strain missing the ABC-cassette transporter Snq2, clomiphene had anti-estrogenic activity. 4-Hydroxy tamoxifen had anti-estrogenic activity only in yeast lacking the transporter Pdr5. Whole cell binding assays indicated that 4-hydroxy tamoxifen is exported by Pdr5. Environmental chemicals such as polychlorinated biphenyls function as partial estrogens and anti-estrogens in yeast. In the absence of Pdr5 or Snq2, the estrogenic activity of 4-hydroxy, 2',4',6'-trichloro biphenyl (3-PCB) was substantially reduced in comparison to its activity in the wild-type strain. Interestingly, the antiestrogenic activity of 3-PCB was equivalent in the wild-type and transporter-defective strains. Our results suggest a novel role for ABC-cassette transporters in regulating the activity of clinical and environmental anti-estrogens.

• PMID: 9207217
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Journal Article | Research Support, Non-U.S. Gov't

Authors

Tran DQ, Jin L, Chen J, McLachlan JA, Arnold SF

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