Progestin regulation of cellular proliferation.
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Animals↗
Biomedical subjects
R L Sutherland
Publications and source records attributed to R L Sutherland.
Progestin regulation of estrogen receptor messenger RNA in human breast cancer cells.
Progestin antagonism of estrogen action is thought to be due, at least in part, to progestin down-regulation of the estrogen receptor (ER). The molecular mechanisms subserving this effect, and the functional consequences in terms of target cell sensitivity to estrogens, are poorly understood. The present study was undertaken to address these issues with particular emphasis on progestin regulation of ER gene expression at the mRNA level. The T-47D human breast cancer cell line was treated with the synthetic progestin, ORG 2058, and the resultant changes in ER mRNA and ER levels determined by Northern analysis and radioligand binding, respectively. Treatment of T-47D cells with ORG 2058 resulted in rapid down-regulation of ER mRNA levels to a nadir of 35-40% of control by 6 h. This fall in ER mRNA levels was accompanied by a slower but more sustained fall in ER binding to a nadir of 20% of control at 24 h. Between 12 and 24 h ER mRNA levels recovered partially while ER ligand binding continued to fall. At 48 h both ER mRNA and ER concentrations remained depressed, although the latter to a greater extent. ER mRNA half-life was determined by [3H]uridine incorporation to be approximately 60 min and was unaffected by progestin treatment during the early rapid phase of ER mRNA down-regulation. These data demonstrate that progestins cause rapid down-regulation of the ER mRNA and suggest that during the early rapid phase of this effect, reduced transcription of the ER gene rather than altered ER mRNA half-life mediate this effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Breast Neoplasms↗
Inverse relationship between estrogen receptor and epidermal growth factor receptor mRNA levels in human breast cancer cell lines.
Epidermal growth factor receptors (EGF-R) are present in a number of human breast cancer cell lines and tumor biopsies. Furthermore, it has been suggested that EGF-R levels are higher in estrogen receptor negative (ER-) than in ER+ human breast tumors and that EGF-R status may be a prognostic indicator in breast cancer. The present study was undertaken to establish whether there is a quantitative relationship between EGF-R and ER mRNA concentrations in a series of 10 well-characterized human breast cancer cell lines. All cell lines expressed detectable quantities of EGF-R mRNA by Northern analysis but the relative abundance of EGF-R mRNA varied more than 50-fold. Two transcripts corresponding to the 10.5- and 5.8-kb mRNAs described in other cell types were present but in different relative proportions in different cell lines. When these lines were divided into an ER+ and an ER- group based on their ability to bind estradiol, ER- cell lines were shown to express significantly higher concentrations of EGF-R mRNA than did ER+ cell lines (p less than 0.005). Furthermore, linear-regression analysis revealed a significant inverse relationship between ER and EGF-R mRNA concentrations both within the group of 10 human breast cancer cell lines as a whole (r = 0.66) and within the 6 functionally ER + lines (r = 0.77). This demonstration of a significant (p less than 0.005) inverse relationship between the concentrations of ER and EGF-R mRNAs in ER + cell lines raises the possibility of reciprocal regulation of the expression of these genes in human breast cancer.
Blotting, Northern↗
Regulation of epidermal growth factor receptor by progestins and glucocorticoids in human breast cancer cell lines.
Human breast cancer cells secrete a number of autocrine peptides which modulate their proliferation rates. The known effects of steroid hormones on breast cancer cell proliferation may be mediated in part by altering the production of these growth factors and/or their interactions with cellular receptor sites. Receptors for epidermal growth factor (EGF), which also bind the autocrine growth factor, alpha-transforming growth factor, are present on a number of breast cancer cell lines and it has previously been shown that T-47D and MCF-7 cells respond to progestins with an increase in the concentration of EGF receptors (EGF-R). In the present study we examined the effects of both progestins and glucocorticoids on EGF binding in 10 human breast cell lines. Five of these lines were progesterone receptor positive and all lines expressed the glucocorticoid receptor (GR). All cell lines were initially incubated for 24 hr with increasing concentrations of the synthetic progestin, medroxyprogesterone acetate (MPA), and the level of specifically bound EGF was determined. An increase in specific binding of EGF was confirmed in two PR-positive lines but, in addition, increases in EGF binding were observed in 4 PR-negative cell lines. In these last lines the synthetic glucocorticoid, dexamethasone, was a more potent inducer of EGF binding than MPA, a known glucocorticoid agonist, while the high-affinity PR ligand, ORG 2058, was without effect. Furthermore, MPA competed with dexamethasone for binding to GR in these cell lines, supporting the view that the induction of EGF binding by MPA in these cells was mediated via the GR. This conclusion was further supported by studies in which addition of the glucocorticoid and progestin antagonist, RU 486, inhibited the effect of ORG 2058 in two cell lines and completely abrogated the effect of dexamethasone in two other lines. Detailed binding studies revealed that the increase in EGF binding was accompanied by an increase in the concentration of EGF-R. This effect was observed when EGF binding was assayed at either 0 degree or 37 degrees C. Further studies demonstrated that the increases in EGF binding following ORG 2058 and dexamethasone treatment were accompanied by increases in EGF-R mRNA levels. Our data illustrate that the binding of EGF by some human breast cancer cells can be regulated by both progestins and glucocorticoids acting via their respective receptors and inducing increases in EGF-R mRNA levels.
Breast Neoplasms↗
Modulation of estrogen receptor and epidermal growth factor receptor mRNAs by phorbol ester in MCF 7 breast cancer cells.
Previous studies have demonstrated an inverse relationship between estrogen receptor (ER) and epidermal growth factor receptor (EGF-R) gene expression in human breast cancer cells. This relationship was further investigated in MCF 7 cells treated with 12-O-tetradecanoylphorbol-13-acetate (TPA). Exposure to 10 nM TPA resulted in a time-dependent increase in EGF-R mRNA, first apparent at 3 h and maximal between 9 and 24 h. There was a concomitant fall in ER mRNA with a maximum decline to 15-20% of control between 12 and 24 h. Although EGF-R mRNA levels declined between 24 and 72 h, both EGF-R mRNA and EGF-R binding remained above control levels and this was accompanied by a sustained depression of ER mRNA. These data support the view that ER and EGR-R gene expression is inversely regulated in human breast cancer and describe for the first time an inhibitory effect of a phorbol ester on steroid hormone receptor gene expression.
Breast Neoplasms↗
Points of action of estrogen antagonists and a calmodulin antagonist within the MCF-7 human breast cancer cell cycle.
Tamoxifen and other structurally related nonsteroidal antiestrogens possess properties in addition to their estrogen antagonist activity including inhibition of both calmodulin and protein kinase C. The present studies were designed to test whether the estrogen-reversible (estrogen receptor mediated) and estrogen-irreversible effects of nonsteroidal antiestrogens on cell cycle progression in vitro were mediated at the same or different points within the cell cycle and if the estrogen-irreversible effects coincided temporally with that of a calmodulin antagonist, R24571. Initial experiments investigated the effects of ICI 164384, a pure estrogen antagonist, on proliferation kinetics in asynchronous cultures of MCF-7 human breast cancer cells. At concentrations greater than 1 nM ICI 164384 significantly reduced growth rate while at greater than or equal to 50 nM, ICI 164384 completely arrested growth after the first 24 h of exposure. Concentrations up to 5 microM failed either to cause more profound effects on growth or induce cytotoxicity. Growth inhibition was associated with a decrease in the proportion of S phase cells and an accumulation of cells in G1 phase, and was completely reversed by the simultaneous addition of equimolar estradiol. In order to identify the points of action within the cell cycle of ICI 164384, and the estrogen-reversible and estrogen-irreversible components of the nonsteroidal estrogen antagonist, hydroxyclomiphene, and the calmodulin antagonist, R24571, experiments were undertaken with MCF-7 cells synchronized by mitotic selection. The mean point of action was assessed by delaying addition of the drugs for increasing time periods following mitotic selection and using DNA flow cytometry to determine the proportion of the population affected by drug administration at a specific time within G1 phase. These studies showed that sensitivity to ICI 164384 was restricted to the early part of G1 phase and that the mean time of action was 4.9 h after the beginning of G1 for this pure estrogen antagonist. The mean times of action of the estrogen-reversible (4.1 h into G1 phase) and estrogen-irreversible (4.1 h) mechanisms of action of hydroxyclomiphene, and R24571 (4.0 h), all appeared to be within a similar time frame in early to mid G1 phase. It is concluded that ICI 164384 inhibits breast cancer cell proliferation by inducing a transition delay in G1 phase and that the point of action of this pure estrogen antagonist in early G1 phase is indistinguishable temporally from that of nonsteroidal antiestrogens and calmodulin antagonists.
Breast Neoplasms↗
Modulation of the growth-inhibitory effects of progestins and the antiestrogen hydroxyclomiphene on human breast cancer cells by epidermal growth factor and insulin.
The molecular basis of the growth-inhibitory effects of progestins or antiestrogens in human breast cancer has not been fully elucidated. Both direct actions and indirect actions, where the growth inhibition results from modulation of the production of, and/or the response to, growth factors, have been proposed. In this study the ability of some growth factors to modulate progestin-induced inhibition of cell proliferation was investigated in vitro, using T-47D human breast cancer cells. When T-47D cells grown in insulin-containing medium were treated for 4 to 5 days with the synthetic progestin, ORG 2058, at a concentration of 10 nM, cell numbers were reduced to 10 to 20% of control. Simultaneous treatment with epidermal growth factor (EGF) and ORG 2058 led to a partial reversal of the growth-inhibitory effect of the progestin. The magnitude of the effect of EGF was concentration dependent, being half-maximal at 0.48 ng/ml (0.08 nM) and maximal at concentrations greater than 5 ng/ml (greater than 0.8 nM), where cell numbers were increased by 50% compared to those in the presence of ORG 2058 alone. ORG 2058 was no more potent in the absence of insulin, and, after several passages in insulin-free medium, addition of insulin failed to modulate the effect of ORG 2058. However, when maximal concentrations of insulin (5 micrograms/ml) and EGF (10 ng/ml) were administered together with ORG 2058, insulin and EGF appeared to act synergistically to reduce the ORG 2058-induced inhibition of proliferation. In similar experiments in which cells were treated with hydroxyclomiphene, a potent antiestrogen, insulin was shown to partially reverse the growth-inhibitory effects of hydroxyclomiphene. Significant increases in cell number above hydroxyclomiphene-treated controls were apparent at insulin concentrations greater than 50 ng/ml, and at 5 micrograms/ml the increase was approximately 2-fold. In contrast to the situation with progestins, simultaneous treatment with EGF and insulin had only an additive effect in reversing the growth-inhibitory effect of the antiestrogen. The results are compatible with the hypothesis that part of the growth-inhibitory effects of progestin and antiestrogen on human breast cancer cell proliferation is mediated by inhibition of autocrine growth factor production. However, they do not exclude more direct mechanisms involving modulation of progesterone and/or estrogen receptors by EGF and/or insulin.(ABSTRACT TRUNCATED AT 400 WORDS)
Breast Neoplasms↗
Effects of 1,25-dihydroxyvitamin D3 on cell-cycle kinetics of T 47D human breast cancer cells.
The replication of several human and animal cancer cell lines is regulated in vitro and in vivo by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], the hormonally active form of vitamin D3. We have examined the effects of concentrations of 1,25-(OH)2D3, which inhibit cellular replication, on the cell-cycle kinetics of a 1,25-(OH)2D3-responsive human breast cancer cell line, T 47D. After 6 or 7 days of treatment, a time period representing approximately five cell population doublings of control cultures, concentrations of 1,25-(OH)2D3 in the range 10(-9) M to 10(-6) M caused a time- and concentration-dependent decrease in cell numbers. Treatment of cells growing in charcoal-treated fetal calf serum with 10(-8) M 1,25-(OH)2D3 for 6 days reduced cell numbers to 49% +/- 9% (n = 9) of control, and this was associated with a marked increase in the proportion of cells in the G2 + M phase of the cell cycle from 9.7% +/- 0.5% (n = 11) to 19.6% +/- 2.3% (n = 9), significant by paired analysis (P less than 0.002). At higher concentrations of 1,25-(OH)2D3 (10(-7)-10(-6) M), there was a concentration-dependent decline in S phase and increases in both G0/G1 and G2 + M phase cells. Detailed analysis of the temporal changes in cell-cycle phase distribution following treatment with 2.5 X 10(-8) and 10(-7) M 1,25-(OH)2D3 showed an initial accumulation of cells in G0/G1 and depletion of S phase cells during the first 24 hr of treatment. This decline in S phase cells was not accompanied by a decline in % G2 + M indicating a transition delay in G2 or mitosis. At the lower dose these changes returned to control values at 48 hr and at later times were associated with a slight but consistent decline in G0/G1 phase and an increase in G2 + M. In contrast cells treated with 10(-7) M 1,25-(OH)2D3 had significantly elevated % G0/G1 cells at days 2 and 3, consistent with a transition delay through G1 phase. This was confirmed in stathmokinetic experiments which demonstrated an approximate sevenfold decrease in the rate of exit of cells from G0/G1 following 4 days of exposure to 10(-7) M 1,25-(OH)2D3. This accumulation of cells in G0/G1 was accompanied by a fall in % S phase cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Breast Neoplasms↗
Progestin inhibition of progesterone receptor gene expression in human breast cancer cells.
The present study was designed to investigate whether inhibition of progesterone receptor (PR) gene transcription and/or regulation of PR mRNA half-life were involved in the progestin-mediated decrease of PR in T-47D human breast cancer cells. Cells were treated with the progestin ORG 2058 and PR mRNA measured by Northern blot analysis of total RNA. A major PR mRNA around 13.5 kilobases and minor species around the 28S ribosomal RNA subunit were decreased upon ORG 2058 treatment. The decrease was not detectable until 2-3 h after treatment and was the same at all ORG 2058 concentrations (1-100 nM) tested. The decrease in PR mRNA was unaffected by actinomycin D in the first 3 h but was inhibited thereafter. There was a partial recovery of PR mRNA levels 24 h after ORG 2058 exposure. Immunoblot analysis showed that immunoreactive PR decreased in parallel with PR mRNA. The rate of protein loss in the first 12 h after progestin treatment was related to the ORG 2058 concentration used. Nuclear run-on experiments showed that ORG 2058 caused a decrease of up to 70% in the transcription rate of the PR gene. The half-life of PR mRNA was shown to be 2-2.5 h by [3H]uridine incorporation, which was much shorter than estimates obtained using actinomycin D, and was unaffected by ORG 2058. In summary, these data have shown that the mechanism by which progestins decrease the concentration of PR includes inhibition of transcription of the PR gene.
Blotting, Northern↗
1,25-Dihydroxyvitamin D3 and the regulation of human cancer cell replication.
Several human and animal cancer cell lines have been shown to possess specific high affinity receptors for 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). The replication of several of these cell types has also been shown to be regulated by this hormone, both in vitro and in vivo. To further understand the mechanisms of these actions, we have examined cancer cells in vitro and in vivo. The in vitro studies extend our previous reports on the treatment of human breast cancer cells (T 47D) with 10(-9) to 10(-6) M 1,25-(OH)2D3, which resulted in a dose- and time-dependent decrease in cell numbers over 6 days. Treatment with 10(-8) M 1,25-(OH)2D3, which reduced cell numbers to approximately one half of those found in control cultures at 6 days, was associated with a doubling of the proportion of cells in the G2 + M phase of the cell cycle and was accompanied by a significant decline in the proportion of G0/G1 cells. At higher concentrations there was a significant decline in S phase cells with accumulation of cells in both G0/G1 and G2 + M phases. The antiestrogen, tamoxifen, at a concentration which caused similar effects on cell number, resulted in proportional decreases in both S and G2 + M phase cells and accumulation of G0/G1 cells. The effects of 1,25-(OH)2D3 on T 47D cell proliferation were associated with time- and concentration-dependent reductions in epidermal growth factor receptor levels to a minimum level of about half that seen in control cultures. The in vivo experiments extend our previous studies, which demonstrated marked inhibition of the growth of human cancer xenografts in immunosuppressed mice by 1,25-(OH)2D3. Xenograft growth was inhibited with 1,25-(OH)2D3 (0.1 microgram ip three times per week) but growth was rapidly restored when the 1,25-(OH)2D3 was withdrawn. Thus, there are clear-cut time- and dose-dependent, yet reversible, effects of 1,25-(OH)2D3 on the replication of human cancer cells in vitro and in vivo, which are possibly mediated through changes in growth factor receptor levels. Further study of these effects may advance understanding of the hormonal control of cellular replication in human cancers.
Calcitriol↗
Effect of medroxyprogesterone acetate on proliferation and cell cycle kinetics of human mammary carcinoma cells.
The effect of medroxyprogesterone acetate (MPA) on breast cancer cell proliferation kinetics was investigated in ten human breast cell lines growing as monolayer cultures. Significant inhibition of growth occurred only in the estrogen receptor-positive, progesterone receptor-positive cell lines, T-47D, MCF-7, ZR 75-1, BT 474, and MDA-MB-361. Among these cell lines sensitivity to MPA varied widely; concentrations required for 20% inhibition of growth ranged from 0.04 nM for T-47D to greater than 100 nM for ZR 75-1 cells. Furthermore, although the most sensitive line, T-47D, had the highest level of PR, sensitivity to MPA was not correlated with PR levels among the responsive cell lines. More detailed studies were undertaken with the T-47D cell line. The growth-inhibitory response was confined to the progestins: MPA, ORG 2058, R5020, and progesterone, while androgens, estrogens, and glucocorticoids were without effect over the same concentration range (0.1-100 nM). MPA-induced growth inhibition was associated with a significant decrease in the proportion of S-phase cells with an accumulation of cells in the G0-G1 phase of the cell cycle. Cells began to accumulate in G0-G1 after 12 h of drug treatment and the effect was maximal by 24 h, i.e., maximal effects were observed during the first cell cycle following drug treatment. By contrast, significant accumulation in G0-G1 required exposure of MCF-7 cells to MPA for at least two cell cycle times, i.e., 48 h and the effect was still increasing at 96 h. Stathmokinetic studies revealed that in both cell lines accumulation in the G0-G1 phase was due to an MPA-induced increase in the G1 transit time. These data indicate that MPA and other progestins have direct growth inhibitory effects on estrogen receptor-positive and progesterone receptor-positive human breast cancer cells in vitro and these effects can be accounted for by a decrease in the rate at which cells traverse the G1 phase of the cell cycle.
Breast Neoplasms↗
Genetic instability and the development of steroid hormone insensitivity in cultured T 47D human breast cancer cells.
The estrogen receptor (ER)-positive human breast cancer cell line T 47D exhibited genetic instability under cell culture conditions which maintained almost continuous exponential growth. This resulted in the spontaneous generation of three ER-positive sublines with a range of DNA ploidies and distinctive phenotypes. One of these sublines, T 47D-5, exhibited resistance to the growth-inhibitory effects of the synthetic nonsteroidal antiestrogen tamoxifen and the synthetic progestin ORG 2058, in marked contrast to "wild type" T 47D cells (designated T 47D-7 in this study). T 47D-5 cells were cloned by limiting dilution and 11 clonal cell lines were tested for sensitivity to tamoxifen. Although all clones of T 47D-5 were significantly less sensitive than T 47D-7 cells, a spectrum of sensitivities was observed. Three clones, T 47D-5-13, T 47D-5-21, and T 47D-5-23, were further characterized by measuring the concentrations of receptors for estrogen, progesterone, growth hormone, and epidermal growth factor and responses to estradiol, tamoxifen, and progestin, in terms of both induction of specific proteins and effects on cellular proliferation. Although the T 47D-5 subline and clone T 47D-5-23 were insensitive to both the growth-stimulatory effects of estradiol and the inhibitory effects of tamoxifen, this was not related to the concentration of ER or its ability to induce progesterone receptor. Estrogen receptor levels were similar in resistant and sensitive clones of T 47D-5 [70,000-81,000 sites/cell] and were 2.5-fold greater than in the sensitive T 47D-7 line [32,600 +/- 5,000 (SEM) sites/cell]. Northern blots showed no difference in the size of ER mRNA transcripts between sensitive and resistant clones. Estradiol treatment increased progesterone receptor (PR) levels in all cell lines but the magnitude and sensitivity of this response were unrelated to growth responses indicating a divergence in estrogenic control of cellular proliferation and specific protein synthesis within these clones. T 47D-5, T 47D-5-13, T 47D-5-21, and T 47D-5-23 were all insensitive to the growth-inhibitory effects of ORG 2058. The progestin was also unable to increase lactogenic and epidermal growth factor receptor concentrations in these four lines in contrast to the response in T 47D-7 cells. The insensitivity to progestin in the T 47D-5 subline and its three clonal cell lines could be accounted for, in part, by a 75-80% reduction in PR levels when compared with T 47D-7 cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Breast Neoplasms↗
Regulation of epidermal growth factor receptor levels by 1,25-dihydroxyvitamin D3 in human breast cancer cells.
Specific, high affinity receptors for 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] have been demonstrated in human breast cancer cells. In addition, 1,25-(OH)2D3 has been shown to inhibit replication in some human breast cancer cell lines, although the mechanism(s) of this anti-tumor activity remain undefined. There is currently considerable interest in the role of autocrine growth factors in the control of breast cancer cell proliferation and the effects of steroid hormones on their production, receptor binding, and action. Since the epidermal growth factor (EGF) receptor mediates the effects of both EGF and the autocrine growth factor, alpha-transforming growth factor, we investigated the effect of 1,25-(OH)2D3 on EGF receptor levels in several human breast cancer cell lines. Preincubation of T-47D cells with 1,25-(OH)2D3 for 24 h resulted in a significant concentration-dependent decline in the specific binding of [125I]EGF. The effect was observed when EGF binding was assayed at either 0 or 37 degrees C, both before and after treatment with acid to remove receptor bound endogenous ligand. This indicated that the effect on [125I]-EGF binding was not due to effects of 1,25-(OH)2D3 on receptor internalization and degradation or receptor occupancy. The half-maximal inhibitory concentration of 1,25-(OH)2D3 was approximately 2 nM. The decrease in EGF binding was due to a decrease in receptor number from 2,900 sites/cell in control cultures to 2,330 and 1,730 sites/cell in cells treated for 24 h with 10(-8) and 10(-6) M 1,25-(OH)2D3, respectively. There was no change in the affinity of the receptor for EGF following treatment with 1,25-(OH)2D3 [Kd = 0.075 +/- 0.006 nM (+/- SEM) for control and Kd = 0.083 +/- 0.004 nM for treated cells]. Decreased EGF receptor levels were also achieved with a number of analogues of 1,25-(OH)2D3 in accordance with their affinities for the 1,25-(OH)2D3 receptor, i.e., potencies for decreasing EGF binding in T-47D cells were in the order: 1,25-(OH)2D3 greater than 1,24,25-trihydroxyvitamin D3 greater than 1,25,26-trihydroxyvitamin D3 greater than 24,25-dihydroxyvitamin D3 greater than or equal to 25-hydroxyvitamin D3. Specific, saturable EGF binding to MCF-7 cells was also reduced by 1,25-(OH)2D3 while binding to BT-20 and HBL-100 cells was unaffected by this treatment.(ABSTRACT TRUNCATED AT 400 WORDS)
Breast Neoplasms↗
Human growth hormone binds to lactogenic receptors in bovine, ovine and rat adrenals.
The distribution of 125I radioactivity in the liver, kidneys, adrenals and serum of male rats was measured 10 minutes after an intravenous bolus of 125I-labelled human growth hormone (hGH) was administered in the presence or absence of a large excess of ovine growth hormone or ovine prolactin. The hGH binding sites in the adrenals had displacement properties characteristic of lactogenic receptors, whereas those in the liver had displacement properties characteristic of somatogenic receptors. Bovine and ovine adrenal microsomal membrane fractions contained high affinity (Ka = 1.4-3.3 nM-1) binding sites for hGH which showed ligand specificity typical of lactogenic receptors. It is concluded that the hGH binding site in the adrenal gland is a classical lactogenic receptor and that this tissue is a convenient and rich (42.6 +/- 6.4 fmol hGH specifically bound/mg protein) source of receptor suitable for further characterization.
Adrenal Glands↗
Effects of pharmacological concentrations of estrogens on proliferation and cell cycle kinetics of human breast cancer cell lines in vitro.
High dose estrogen therapy has been used effectively in the treatment of human breast cancer. To understand the mechanisms involved, the effects of high concentrations (5-100 microM) of estrogens were studied in estrogen receptor (ER) positive (T-47D and MCF-7) and ER negative (MDA-MB-330) human breast cancer cell lines in vitro. Inhibition of cellular proliferation was seen with the synthetic estrogen diethylstilbestrol (DES) at concentrations greater than 10 microM in each of the three cell lines. In T-47D cells DES was shown by clonogenic survival assays to be cytotoxic. This effect was evident in both plateau phase and exponentially growing cultures, in contrast to the effects of the antiestrogen tamoxifen, which has minimal effects on plateau phase cells. The effects of DES on the proliferation of exponentially growing cultures were accompanied by changes in cell cycle parameters which included an increase in the percentages of S-phase, G2 + M, and polyploid cells and a corresponding decrease in the percentage of G0-G1 cells. These changes, which contrasted with the known effects of tamoxifen, were not seen in the non- or slowly cycling plateau phase T-47D cells. Such results are consistent with two mechanisms of action of high dose estrogen in vitro: a cell cycle phase-specific effect and cell cycle-independent cytotoxicity. The stereoisomers 17 alpha-estradiol and 17 beta-estradiol had similar potency to DES in inhibiting cell proliferation and inducing these changes in cell cycle parameters in both MCF-7 and MDA-MB-330 cells. The high-dose estrogen effect was ligand specific in that estrone and estriol were less potent than DES, 17 alpha-estradiol and 17 beta-estradiol in inhibiting cell proliferation, and the characteristic cell cycle changes were produced only by concentrations of estriol greater than 75 microM and not at all by estrone at concentrations up to 100 microM. The androgens testosterone and dihydrotestosterone were similar in effect to estrone. The cell cycle changes associated with estrogen-induced growth inhibition in vitro are identical to those observed during regression of ER positive but not ER negative human tumor xenografts in nude mice. However, the role of ER in mediating estrogen-induced regression of ER positive tumors in vivo remains undefined.
Breast Neoplasms↗
Epidermal growth factor partially reverses the inhibitory effects of antiestrogens on T 47D human breast cancer cell growth.
When T 47D human breast cancer cells were treated with 10 nM of the potent antiestrogen, 4-hydroxyclomiphene, growth rate was reduced to about 50% of control. Simultaneous treatment with epidermal growth factor (EGF) and 4-hydroxyclomiphene led to a partial reversal of the growth inhibitory effect of the antiestrogen. The effect of EGF was concentration-dependent being half-maximal at 0.10 ng/ml (0.02 nM) and maximal at concentrations greater than 0.5 ng/ml (greater than 0.08 nM). Furthermore, EGF partially reversed the growth inhibitory effects of several other antiestrogens including tamoxifen, 4-hydroxytamoxifen, and LY 117018. These results are compatible with the hypothesis that part of the growth inhibitory effects of antiestrogens on breast cancer cell proliferation are mediated by inhibition of autocrine secretion of growth stimulatory peptides acting through the EGF receptor.
Breast Neoplasms↗
Mechanisms of growth inhibition by nonsteroidal antioestrogens in human breast cancer cells.
Treatment of MCF7 human mammary carcinoma cells with the nonsteroidal antioestrogens, tamoxifen and clomiphene, leads to a concentration-dependent decrease in cellular proliferation rate which can be resolved into oestrogen-reversible and oestrogen-irreversible components. This became more clearly apparent when cells were treated with the 4-hydroxylated derivatives of these compounds where, because of enhanced affinity for the oestrogen receptor (ER), the dose-response curves for the two components could be separated. Thus treatment with 4-hydroxyclomiphene resulted in a distinct biphasic effect on cell growth. In the concentration range 10(-10)-10(-8) M, cell proliferation was inhibited in a concentration-dependent manner to a maximum of 60-70%, there was no further effect between 10(-8) and 10(-6) M, but at concentrations greater than 10(-6) M there was another concentration-dependent decrease in cell growth. Studies with a series of vinyl-substituted hydroxytriphenylethylenes revealed that in the nanomolar concentration range, where the effects of the drugs could be completely negated by the simultaneous addition of oestradiol, the potency for growth inhibition was highly correlated with affinity for ER. Such data provide strong evidence that in this concentration range the growth inhibitory effects of nonsteroidal antioestrogens are mediated by the intracellular ER. In the micromolar concentration range the effects of antioestrogens are not completely reversed by oestradiol, potency is not well correlated with affinity for either ER or the antioestrogen binding site (AEBS) but the effect is cell cycle phase-specific. Furthermore, the disparity between the affinity for AEBS (0.8-3.3 nM) and the concentration of drug needed for oestrogen-irreversible growth inhibition (greater than or equal to 2.5 microM) argue against a central role for AEBS in mediating this effect. The observation that triphenylethylene antioestrogens are calmodulin antagonists may provide some insight into potential mechanisms for this oestrogen-irreversible effect. Indeed, in identical experiments two phenothiazine calmodulin antagonists inhibited MCF 7 cell proliferation at concentrations greater than or equal to 2.5 x 10(-6) M. Growth inhibition following administration of fluphenazine, perphenazine and triphenylethylene antioestrogens was accompanied by qualitatively similar changes in the cell cycle kinetic parameters, i.e. accumulation in G1 phase at the expense of S phase cells. These data suggest triphenylethylene antagonism of calmodulin activated cellular processes as a potential mechanism for the oestrogen-irreversible effects of the nonsteroidal antioestrogens.
Breast Neoplasms↗
Studies on the ligand specificity and potential identity of microsomal antiestrogen-binding sites.
Synthetic nonsteroidal antiestrogens are bound intracellularly by two high affinity saturable bindings sites, the estrogen receptor and the microsomal antiestrogen-binding site (AEBS). In order to further define the structural requirements for ligand binding to AEBS from rat liver and the MCF 7 human breast cancer cell line, the relative binding affinities of an extensive series of structurally related ligands were investigated using competitive binding assay techniques. The groups of compounds studied were: analogues of the triphenylethylene antiestrogens, Cl 628 and tamoxifen; analogues of cyclofenil; bibenzyl and stilbene derivatives; analogues of the cytochrome P-450 inhibitor SKF-525A; phenothiazine derivatives; and a series of structurally related compounds with a variety of pharmacological activities. High affinity binding to AEBS required the presence of both a hydrophilic basic aminoether side chain and a hydrophobic aromatic ring structure (di- or tricyclic for maximal affinity). Structural modifications to either influenced binding affinity. Aromatic substitution either raised (CF3) or lowered (OH, OCH3) affinity, apparently by electronic effects transmitted through the benzene nucleus. Side chain structure was the major determinant of binding affinity, but its influence was complex and dependent upon terminal amino group structure, side chain branching and substitution, and tissue source of AEBS. Optimal binding affinity was shown by side chains bearing basic heterocyclic amino terminal groups. Other cellular sites that are known to bind antiestrogens with relatively high affinity include calmodulin, cytochrome P-450, and histamine, dopamine, and muscarinic receptors. Binding studies using a variety of pharmacologically active and radiolabeled ligands selective for these sites, including those for dopamine D1 and D2 receptors ([3H]fluphenazine, [3H]flupenthixol, [3H]spiperone, and [3H]SCH 23390) and histamine H1 receptors ([3H]pyrilamine), demonstrated that several of these compounds interact with AEBS with high affinity. However, the ligand specificity and other binding properties of the AEBS as determined by competitive binding studies and Scatchard analysis show this site to be a molecular entity truly distinct from these other cellular binding sites.
Animals↗