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Both estradiol and tamoxifen decrease proliferation and invasiveness of cancer cells transfected with a mutated
1Institut National de la Santé et de la Recherche Médicale, Unité 148 Hormones et Cancer et Université Montpellier, France.
Summary
A mutated estrogen receptor (ER) enabled tamoxifen to inhibit breast cancer cell growth and invasiveness in vitro. However, low ER expression limited tamoxifen's in vivo effectiveness, highlighting the importance of receptor levels for treatment efficacy.
Area of Science:
- Oncology
- Endocrinology
- Molecular Biology
Background:
- Estrogen receptor (ER) status is critical in breast cancer treatment.
- Wild-type ER activation by estradiol inhibits tumor growth, while tamoxifen's efficacy varies.
- A specific ER mutation (at position 400) can convert tamoxifen into an estrogen agonist.
Purpose of the Study:
- To investigate if a mutated ER could induce a tamoxifen-mediated estrogenic response in ER-negative breast cancer cells.
- To evaluate the in vitro and in vivo effects of tamoxifen and estradiol on cancer cells expressing a mutated ER.
Main Methods:
- Transfection of an ER-negative rat cancer cell line with a mutated human ER (Y537S).
- In vitro assessment of cell growth and invasiveness using estradiol, OH-tamoxifen, and ICI 164,384.
- In vivo tumor formation and growth studies in ovariectomized nude mice.
Main Results:
- In vitro, OH-tamoxifen inhibited cell growth and invasiveness similarly to estradiol in cells with the mutated ER.
- ICI 164,384 acted as a pure anti-estrogen, antagonizing estradiol's effects.
- In vivo, tamoxifen inhibited tumor growth in mock-transfected cells via host response, but ER-transfected tumors showed no significant difference in hormone responsiveness compared to controls.
- Low ER expression in vivo limited the observed anti-cancer effects of tamoxifen.
Conclusions:
- Transfection with a mutated ER enabled tamoxifen's estrogenic activity, inhibiting cancer cell growth and invasiveness in vitro.
- The limited in vivo efficacy suggests that sufficient estrogen receptor expression levels are crucial for tamoxifen's therapeutic effects in a host environment.