Acetaminophen-induced proliferation of breast cancer cells involves estrogen receptors.

Previous studies have shown that acetaminophen, a common analgesic/antipyretic, induces proliferation of cultured breast cancer cells containing both estrogen and progesterone receptors (ER+/PR+). The main objective of this study was to evaluate the involvement of ERs in this effect. First, the effects of therapeutic acetaminophen concentrations were compared in breast cancer cells with high ERs and in T47Dco cells with lower ERs, to determine if acetaminophen-induced proliferation depends on ER levels. Second, the effects of two antiestrogens (ICI 182,780 and 4'-hydroxytamoxifen) on acetaminophen-induced proliferation were determined in three human breast cancer cell lines: two ER+/PR+ (MCF7, T47D) and one ER-/PR- (MDA-MB-231). Third, ER binding assays were performed in MCF7 cells to determine if acetaminophen competed with estradiol for binding to ERs. Proliferation endpoints monitored included percent cells in the DNA synthesis phase of the cell cycle, 3H-thymidine incorporation into DNA, and cell number. Acetaminophen did not induce DNA synthesis in T47Dco cells, but did in cells with higher ER levels, suggesting high ER levels are necessary for acetaminophen to induce proliferation. Antiestrogens inhibited acetaminophen-induced proliferation in ER+/PR+ cells while no effects were observed in ER-/PR- cells, further supporting ER involvement. However, acetaminophen did not compete with estradiol for binding to ERs in ER+/PR+ cells. Collectively, these data suggest that acetaminophen induces breast cancer cell proliferation via ERs without binding to ERs like estradiol. The second purpose of this study was to determine if acetaminophen is estrogenic/antiestrogenic in vivo (uterotrophic assays). Acetaminophen has no antiestrogenic/estrogenic activity in mice or rats uteri.

Positional isomers of acetaminophen differentially induce proliferation of cultured breast cancer cells.

This study demonstrates that acetaminophen (p-acetamidophenol) stimulates proliferation of estrogen-responsive cultured breast cancer cells and assesses if the proliferative activity of p-acetamidophenol is influenced by the -OH moiety position on the benzene ring. The effects of p-, m-, and o-acetamidophenol on cell number and on percentage cells in S phase of the cell cycle were determined for two estrogen receptor positive, human breast cancer cell lines, T47D and MCF7. Therapeutic concentrations of p-acetamidophenol (0.1 mM) significantly increased breast cancer cell proliferation. The relative order of potency of isomers in stimulating proliferation in both cell types was p- > m- > o-acetamidophenol, indicating the -OH position on the benzene ring influences the proliferation output in cultured breast cancer cells.

Acetaminophen alters estrogenic responses in vitro: stimulation of DNA synthesis in estrogen-responsive human breast cancer cells.

A limited number of studies have investigated the estrogenic potential of acetaminophen but none has reported its effects on breast cells. Many compounds that alter estrogen-mediated processes in various tissues contain p-phenolic moieties. Acetaminophen is a commonly used analgesic/antipyretic that also contains a p-phenol. This study tested the hypothesis that therapeutic concentrations of acetaminophen alter estrogen-responsive human breast cancer cell DNA synthesis. To this end, a modified E-screen assay was developed to determine the response to acetaminophen of two dichotomous types of human breast cancer cell lines: estrogen-responsive (MCF7, T47D, ZR-75-1) and estrogen-nonresponsive (MDA-MB-231, HS578T). Cells were placed in estradiol-free medium and then exposed to 3 nM estradiol or 0.03-1 mM acetaminophen. The proliferative response was assessed by determining [3H]thymidine incorporation into DNA and by determining the percentage of cells in the DNA synthesis (S) phase of the cell cycle. Concentrations of acetaminophen commonly attained in human plasma with therapeutic doses of this drug (approximately 0.1 mM) were found as effective as estradiol in stimulating DNA synthesis in estrogen-responsive breast cancer cells. Higher acetaminophen concentrations (1 mM) stimulated estrogen-responsive cells to a lesser extent. The combination of estradiol and acetaminophen did not stimulate DNA synthesis in estrogen-responsive cells more than either agent alone. Neither acetaminophen nor estradiol stimulated DNA synthesis in estrogen-nonresponsive human breast cancer cells. These novel findings demonstrate that therapeutic acetaminophen concentrations specifically stimulate estrogen-responsive breast cancer cell DNA synthesis, suggesting that this drug may exert estrogenic effects.