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A model to describe how a point mutation of the estrogen receptor alters the structure-function relationship of
S Y Jiang1, C J Parker, V C Jordan
1Department of Human Oncology, University of Wisconsin Comprehensive Cancer Center, Madison 53792.
Abstract:
The antiestrogen tamoxifen [(Z)-1(p-beta-dimethylamino-ethoxyphenyl)-1,2- diphenylbut-1-ene] is an effective anticancer agent for the treatment of hormone responsive breast cancer. Previous studies have demonstrated that a point mutation in the estrogen receptor (ER) resulted in an alteration of the pharmacology of 4-hydroxytamoxifen, the active metabolite of tamoxifen (Jiang et al, Mol Endocrinol 6:2167-2174, 1992). We have extended our studies to evaluate the effect of a point mutation, a Val substitution for Gly at amino acid 400 in the ligand binding domain of ER, on the pharmacology of other antiestrogens in ER stable transfectants derived from the ER-negative breast cancer cell line MDA-MB-231 CL10A. The compounds were tested with or without estradiol-17 beta (E2) for their effects on cell growth in cells expressing the wild type ER (S30) or the mutant ER (ML alpha 2H) or in control antisense ER transfectant AS23 which does not express ER protein. MCF-7 cells, which express the wild type ER, were also used as a control. The growth of AS23 cells was not affected by any of the compounds at a concentration of 1 microM. E2 stimulated the growth of MCF-7 cells but inhibited the growth of ER transfectants S30 and ML alpha 2H. The ML alpha 2H cells were about 10 to 100-fold less sensitive to E2 and antiestrogens than S30 and MCF-7 cells. Keoxifene, an antiestrogen with a high affinity for the ER, maintained antiestrogenic activities in both ER transfectants and MCF-7 cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
A specific mutation in the estrogen receptor (ER) reduces sensitivity to estradiol and antiestrogens like tamoxifen in breast cancer cells. This finding impacts understanding of hormone therapy resistance.
Area of Science:
- Endocrinology
- Molecular Biology
- Cancer Research
Background:
- Tamoxifen is an effective antiestrogen for hormone-responsive breast cancer.
- Estrogen receptor (ER) mutations can alter antiestrogen drug efficacy.
- Previous studies linked ER mutations to altered 4-hydroxytamoxifen pharmacology.
Purpose of the Study:
- To investigate the impact of a specific ER ligand binding domain mutation (Gly400Val) on antiestrogen pharmacology.
- To evaluate antiestrogen efficacy in ER-negative breast cancer cells engineered to express wild-type or mutant ER.
- To compare the effects of estradiol-17 beta (E2) and antiestrogens on cell growth in different ER-expressing cell lines.
Main Methods:
- Utilized ER-negative MDA-MB-231 CL10A cells stably transfected with wild-type ER (S30) or mutant ER (ML alpha 2H).
- Included control antisense ER transfectant (AS23) and MCF-7 cells (wild-type ER).
- Assessed cell growth effects of E2 and antiestrogens (tamoxifen, keoxifene) with or without E2.
Main Results:
- Mutant ER (ML alpha 2H) cells showed 10-100 fold reduced sensitivity to E2 and antiestrogens compared to wild-type ER cells (S30, MCF-7).
- E2 stimulated MCF-7 cell growth but inhibited S30 and ML alpha 2H cell growth.
- Keoxifene retained antiestrogenic activity in both wild-type and mutant ER transfectants.
Conclusions:
- The Gly400Val mutation in the ER ligand binding domain significantly reduces cellular response to E2 and antiestrogens.
- This ER mutation may contribute to antiestrogen resistance in breast cancer.
- Keoxifene demonstrates retained efficacy despite the ER mutation, suggesting potential therapeutic value.