Suppression of c-myc expression and c-Myc function in response to sustained DNA damage in MCF-7 breast tumor cells.

The topoisomerase II inhibitors teniposide (VM-26), doxorubicin, and amsacrine (m-AMSA), as well as ionizing radiation, induce a transient suppression of c-myc mRNA, which correlates with growth inhibition of MCF-7 breast tumor cells. To further assess the involvement of c-mvc in the DNA damage-induced signal transduction pathways of the breast tumor cell, we determined the influence of sustained DNA damage on c-myc expression, c-Myc protein levels and c-Myc function. Continuous exposure of MCF-7 breast tumor cells to VM-26 induced DNA strand breaks that were sustained for at least 9 hr. DNA strand breakage was accompanied by a decline in c-myc transcripts and c-Myc protein levels by >90% after VM-26 exposure for 24 hr. The activity of a transcriptional target of the c-Myc protein, ornithine decarboxylase, was reduced by approximately 75% within 9 hr of DNA damage, in parallel to the declines in c-myc mRNA and protein levels. Extended exposure to VM-26 resulted in an initial loss of approximately 35% of the cell population followed by the death of additional cells such that by 72 hr only 50% of the cells were viable. Although apoptosis was evident 72 hr after initiating drug exposure [based on cell cycle analysis, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays, and an assessment of cell morphology], the primary phase of cell killing, which occurred during the first 24 hr was non-apoptotic. These studies indicate that non-apoptotic pathways can also mediate cell death in the breast tumor cell and support the role of c-myc expression, c-Myc protein, and c-Myc function as elements of the DNA damage response pathway in the breast tumor cell.

Rb dephosphorylation and suppression of E2F activity in human breast tumor cells exposed to a pharmacological concentration of estradiol.

This report characterizes the influence of a pharmacological concentration of estradiol on growth arrest and cell death in MCF-7 breast tumor cells, with a focus on elements of the Rb-E2F cell-cycle regulatory pathway. Continuous exposure of MCF-7 breast tumor cells to 100 microM estradiol produces a marked reduction in the G1 and S phase populations and a corresponding increase in the G2/M population within 24 h; after 48 h, accumulation of cells in G1 becomes evident while after 72 h the cells appear to be equally distributed between the G1 and G2/M phases. The accumulation of cells in G1 is temporally associated with dephosphorylation of the Rb protein and suppression of E2F activity. Estradiol also produces an initial burst of cell death with loss of approximately 40% of the tumor cell population within 24 h; however, there is no tangible evidence for the occurrence of apoptosis based on terminal transferase end-labeling of DNA, DNA fragmentation analysis by alkaline unwinding, cell-cycle analysis or cell morphology. In addition to the lack of caspase-3 in MCF-7 cells, the absence of apoptosis could be related, at least in part, to the fact that estradiol promotes a rapid reduction in levels of the E2F-1 and Myc proteins. Overall, these studies are consistent with the concept that alterations in the levels and/or activity of the E2F family of proteins as well as proteins interacting with the E2F family may influence the nature of the antiproliferative and cytotoxic responses of the breast tumor cell.

Estradiol enhances liposome-mediated uptake, preferential nuclear accumulation and functional expression of exogenous genes in MDA-MB231 breast tumor cells.

Exposure of p53 mutated estrogen-receptor-negative MDA-MB231 human breast tumor cells to a pharmacological concentration of estradiol enhances liposome-mediated uptake and expression of SV-40 luciferase. Unexpectedly, the effect of estradiol on SV-40 expression is evident even when estradiol exposure occurs after the initial uptake phase; this suggests that estradiol may influence gene expression by mechanisms other than increasing gene uptake alone, such as altering the intracellular distribution of the gene. We determined that while uptake of SV-40 luciferase is increased only three-fold by estradiol, there is a 30-fold increase in the nuclear/cytoplasmic ratio of the gene. In order to demonstrate that the influence of estradiol on gene uptake and expression is translated into a functional response, the effects of estradiol on the function of an exogenous gene, in this case the apoptotic function of p53, were assessed in the p53 mutated MDA-MB231 breast tumor cell. While liposome-mediated delivery of CMV-p53 alone was ineffective in promoting cell death, incubation with estradiol and the liposomal p53 complex resulted in a two-fold increase in cell killing over that observed in cells transfected with the corresponding mock vector (empty vector for p53). Evidence that cell killing was occurring through apoptosis included apoptotic body formation, cell shrinkage and an increase in fluorescence after terminal transferase end-labeling. The capacity of estradiol to promote apoptosis in MDA-MB231 cells by a p53-liposome complex is likely to be related to the preferential redistribution of the gene from the cytoplasm to the nucleus which could occur during both the uptake and post-uptake phases. Consequently, although direct effects on gene expression, and the stability of message and protein cannot be ruled out, the predominant effect of estradiol in this experimental system appears to be to influence DNA translocation from the cytoplasm to the cell nucleus.

Sustained enhancement of liposome-mediated gene delivery and gene expression in human breast tumour cells by ionizing radiation.

PURPOSE: To investigate whether irradiation improves the delivery and expression of liposome-DNA complexes in human breast tumour cells. MATERIALS AND METHODS. MDA-MB231 and MCF-7 human breast tumour cells were transfected with a liposomal SV40-luciferase complex and irradiated immediately after, at 24h after or 24h prior to transfection and in the presence or absence of serum. The amount of luciferase plasmid in the cell was evaluated after extraction by the Hirt procedure, while luciferase expression was measured using a luminescence assay. RESULTS: Ionizing radiation enhanced the liposome-mediated delivery and expression of the SV40-luciferase transgene in MDA-MB231 breast tumour cells both in the absence and presence of serum as well as in MCF-7 breast tumour cells. Improved transgene delivery and expression was observed at a clinically relevant dose of 2 Gy, and was dose-dependent over a dose range of 2-10 Gy. The effects of irradiation on transgene expression were observed with irradiation immediately prior to exposure of the cells to the liposome-transgene complex, with irradiation up to 24 h before or up to 24 h after initiation of exposure. CONCLUSIONS: Irradiation at 24 h prior to exposure of breast tumour cells to the liposome-transgene complex appears to be the optimal approach for enhancing transgene delivery and expression. These findings suggest that ionizing radiation could promote the utility of gene therapy in the treatment of breast cancer.

Enhancement of liposomal gene delivery in human breast cancer cells by dimethyl sulfoxide.

Non-toxic concentrations ( 1%) of dimethyl sulfoxide (DMSO) enhance the liposomal delivery of DNA to both MCF-7 and MDA-MB-231 human breast tumor cells. Uptake of SV-40-luciferase was enhanced in MCF-7 cells by 14-fold while uptake of CMV-beta-galactosidase was increased 10-fold. In MDA-MB-231 cells, uptake of SV-40-luciferase was increased by approximately 70%. A mixture of ethanol and polyethylene glycol (45:55) at a concentration of 1% produced less pronounced improvements in transgene delivery to MCF-7 cells (a 70% increase in SV-40-luciferase uptake and a 4-fold increase in CMV-beta-galactosidase uptake) but no improvement in SV-40-luciferase gene delivery to MDA-MB-231 cells. These studies suggest that select pharmaceutical adjuvants which dissolve clinically useful drugs may have promise as non-toxic vehicles for improving transgene delivery. However, the relative effectiveness of these adjuvants is likely to vary depending on both the nature of the gene being delivered as well as the tumor cell which is the target for uptake of the exogenous gene.

Estradiol enhances gene delivery to human breast tumor cells.

The influence of estradiol on the delivery of plasmid DNA to estrogen receptor positive MCF-7 human breast cancer cells was studied by the use of a reporter assay and by histochemical staining. Continuous exposure to estradiol enhanced the lipofectamine-mediated delivery of both pSV40-luciferase and pCMV beta-galactosidase in a concentration-dependent manner. Estradiol increased both the amount of pCMV beta-galactosidase per cell and the total fraction of cells competent to receive the transgene. The efficiency of transgene delivery to MCF-7 cells was further improved by repeating the transfection procedure in the presence of estradiol. Although overall gene uptake was reduced in control cells when studies were performed at room temperature (as opposed to 37 degrees C), potentiation of gene uptake by estradiol was maintained. At a concentration of 100 microM, estradiol also enhanced delivery of the transgene to estrogen receptor negative MDA-MB-231 breast tumor cells, indicating that the potentiating effects of estradiol are not mediated through the estrogen receptor. These studies are the first to raise the possibility that gene delivery to breast tumor cells can be improved by estradiol in single- or repeated-treatment regimens.

Induction of DNA damage, inhibition of DNA synthesis, and suppression of c-myc expression by the topoisomerase I inhibitor, camptothecin, in MCF-7 human breast tumor cells.

Previous work from this laboratory has demonstrated an association between the suppression of c-myc expression and the antiproliferative activity of both topoisomerase II inhibitors and ionizing radiation in MCF-7 breast tumor cells. These findings suggested that suppression of c-myc expression could be related to the induction of DNA damage in this cell line. The present studies were designed to determine whether the inhibition of topoisomerase I (and the consequent induction of DNA strand breaks) would also result in the suppression of c-myc expression. At camptothecin concentrations of 1 microM and below, there was no detectable damage (single- or double-strand breaks) in bulk DNA or suppression of c-myc expression. At camptothecin concentrations of 5, 10, and 25 microM, where suppression of c-myc expression was observed, strand breaks in bulk DNA were also detected. These findings are consistent with the idea that suppression of c-myc expression could be a component of the DNA damage response pathway in MCF-7 breast tumor cells. In contrast to the absence of detectable damage to bulk DNA or suppression of c-myc expression at the lower concentrations of camptothecin, DNA synthesis was inhibited over the entire range of drug concentrations and demonstrated a strong correspondence with growth inhibition. These observations support the concept that growth inhibition of MCF-7 cells by camptothecin is closely related to the early suppression of DNA synthesis.

Influence of ionizing radiation on proliferation, c-myc expression and the induction of apoptotic cell death in two breast tumour cell lines differing in p53 status.

PURPOSE: To determine the capacity of ionizing radiation to inhibit proliferation, to suppress c-myc expression and to induce apoptotic cell death in the p53 wild-type MCF-7 cell line and the p53 mutated MDA-MB231 cell line. MATERIALS AND METHODS: Growth inhibition and cell killing were determined by cell number and trypan blue exclusion. Apoptosis was assessed through cell morphology and fluorescent end-labelling. c-myc expression was monitored by Northern blotting. RESULTS: Inhibition of cell proliferation by ionizing radiation was similar in both cell lines. MDA-MB231 cells accumulated in G2 while MCF-7 cells accumulated in both the G1 and G2 phases of the cell cycle after irradiation. There was no evidence of apoptosis in either cell line. In MCF-7 cells, growth inhibition correlated closely with an early dose-dependent suppression of c-myc expression; in MDA-MB231 cells, there was no correspondence between growth inhibition and a transient, dose-independent reduction in c-myc message. CONCLUSIONS: These findings suggest that in the absence of classical apoptotic cell death, radiosensitivity is not predictably related to the p53 status of the cell. While both p53 and c-myc may be linked to the DNA damage response pathway, neither p53 nor c-myc are essential for growth arrest in response to ionizing radiation.

Ionizing radiation and teniposide increase p21(waf1/cip1) and promote Rb dephosphorylation but fail to suppress E2F activity in MCF-7 breast tumor cells.

Ionizing radiation and the topoisomerase II inhibitor, teniposide (VM-26) both increase levels of the cyclin dependent kinase inhibitor, p21(waf1/cip1) and promote dephosphorylation of the retinoblastoma tumor suppressor protein, Rb, in MCF-7 breast tumor cells, perturbations associated with suppression of the activity of the transcription factor, E2F. However, studies using an E2F binding site-luciferase reporter plasmid transfected into MCF-7 cells failed to demonstrate a reduction in E2F activity in response to VM-26 or to ionizing radiation. In contrast, E2F activity (both basal and E1A stimulated) could be suppressed by transfection with a plasmid expressing Rb, indicating that the capacity of E2F to bind to Rb and to be inactivated by Rb is functionally intact in MCF-7 cells. These findings in MCF-7 breast tumor cells suggest that E2F activity may not be directly susceptible to modulation by endogenous p21(waf1/cip1) and Rb.

Tamoxifen induces deregulation of [Ca2+] in human breast cancer cells.

Tamoxifen is a clinically useful estrogen antagonist at or below 10(-6) M concentration. However, above this concentration tamoxifen exerts non-ER mediated cytotoxicity. Such cytotoxic effects are lethal or sublethal. The lethal effects lead to cell death while the sublethal effects may lead to cellular transformation and response modification participating in the process of tumor resistance or even tumor stimulation. Deregulation of intracellular ionized calcium ([Ca2+]i) could lead to genomic instability and deregulation of oncogene expression which might participate in the process of carcinogenesis and/or tumor promotion. Tamoxifen may cause tumor stimulation due to deregulation of [Ca2+]i or its consequences such as activity of protein kinase C, calmodulin and related protein kinases. Precise understanding of such mechanism is important for avoiding tamoxifen induced tumor resistance or tumor stimulation. The deregulation of [Ca2+]i was studied on fluo-3/AM loaded MCF-7 human breast cancer cells following acute and chronic treatment of tamoxifen and calcium ionophore ionomycin. The elevation of [Ca2+]i preceded the death of MCF-7 cells following treatment with ionomycin as previously reported on other cells. Tamoxifen above 10(-6) M also caused an increase in [Ca2+]i preceding the death of MCF-7 cells. However, below this concentration, tamoxifen caused a decrease in [Ca2+]i without any signs of cytotoxicity. The present data clearly demonstrate a tamoxifen-induced increase in [Ca2+]i and cell death only at the concentration-range in which non-E R mediated cytotoxicity is reported.

Human breast cancer cell growth inhibition and deregulation of [Ca2+]i by estradiol.

Estradiol inhibits the growth of human breast cancer MCF-7 cells at supramicromolar concentrations. The mechanism of such phenomenon remains to be unravelled. Confocal laser scanning microscopic studies suggest elevation of [Ca2+]i preceding bleb formation and cellular injury following acute and chronic treatment of ionomycin and estradiol at supramicromolar concentration. Phase contrast morphological study demonstrates metaphase-arrested cells and giant multinuclear cells possibly due to lack of cytokinesis caused by estradiol. There is a striking similarity between the morphological changes caused by estradiol and enforced overexpression of cyclin-dependent kinase inhibitor p21waft/cip1. Such similarity together with the reported key role of intracellular ionized calcium [ca2+]i in regulating cyclin and deregulation of [Ca2+]i by estradiol raises the possibility of deregulation of gene expression leading to inhibition of cyclin-dependent proliferative signals participating in inhibition of growth in MCF-7 cells.

Antitumor activity of a novel antiestrogen (Analog II) on human breast cancer cells.

Analog II (1,1-dichloro-cis-2,3-diarylcyclopropane), previously shown to be a pure antiestrogen in mice, was examined for potential antitumor activity on human breast cancer cells in culture. In this study, Analog II produced a dose-related antiproliferative effect on the growth of estrogen receptor (ER)-positive MCF-7 human breast cancer cells over a concentration range of 10(-11) to 10(-5) M. Analog II increased the fraction of MCF-7 cells in the G2/M phase of the cell cycle. Further, this compound inhibited the growth of ER-negative MDA-MB-231 human breast cancer cells over a concentration range of 10(-9) to 10(-6) M. Using scanning electron microscopy to evaluate drug-induced changes in cellular morphology, it was observed that Analog II decreased the length and density of microvilli on both MCF-7 and MDA-MB-231 cells. The effects of Analog II on MCF-7 and MDA-MB-231 cell proliferation and morphology were not reversed in the presence of estradiol. In addition, the induction of estrogen-dependent genes in MCF-7 cells was not reversed by Analog II. It was observed that non-specific cytotoxicity may be responsible for part of the Analog II-induced inhibition on MCF-7 and MDA-MB-231 cell proliferation. However, the antitumor activity of this compound was found to be specific to human breast cancer cells since it did not alter the proliferation or viability of non-breast A-549 human lung cancer cells. In conclusion, these results indicate that Analog II is a potent antitumor agent, has a unique antitumor mechanism in breast cancer cells and may be effective in the treatment of breast cancer.

Antitumor mechanism of action of a cyclopropyl antiestrogen (compound 7b) on human breast cancer cells in culture.

Cyclopropyl compound 7b [(Z)-1,1-dichloro-2-[4-[2-(dimethylamino)ethoxy] phenyl]-2-(4-methoxyphenyl)-3-cyclopropane] has been shown to be a pure antiestrogen in mouse uterine tissue. Antitumor activity was examined by evaluating the influence of 7b on the proliferation, estrogen receptor (ER) affinity and cell-surface morphology of ER-positive and ER-negative human breast cancer cells in culture. The antiproliferative potency of 7b was found to be equal to tamoxifen in ER-positive MCF-7 human breast cancer cells. Further, the antiproliferative activities of 7b and tamoxifen were reversed by coadministration of estradiol. Accordingly, the antiproliferative activity of compound 7b appears to be estrogen-mediated since it did not influence the growth of either ER-negative MDA-MB-231 human breast cells or A-549 human lung cancer cells in culture. An ER-dependent mechanism of action is also supported by the specific binding affinity of 7b for ER in MCF-7 cells. Further, a study of cell surface morphology using scanning electron microscopy (SEM) revealed that 7b reduced the density and distribution of microvilli (MV) on MCF-7 cells, which was reversed by coadministration of estradiol. Compound 7b did not alter the cell surface morphology of ER-negative MDA-MB-231 cells. In conclusion, 7b inhibited the growth of ER-positive MCF-7 cells in an estradiol-reversible manner, and had no effect on either ER-negative MDA-MB-231 cells or A-549 lung cancer cells. The results of this study confirm an antiestrogenic mechanism of action for 7b as previously observed in vivo and suggest that 7b would be effective in the treatment of estrogen-dependent breast cancer or as a prophylactic treatment for women with a high risk of breast cancer development.

Influence of cyclopropyl antiestrogens on the cell cycle kinetics of MCF-7 human breast cancer cells.

Five cyclopropyl compounds, previously shown to exhibit pure antiestrogenic activity in the mouse uterotropic assay and antiproliferative activity of MCF-7 human breast cancer cells in culture, were examined for their influence on the cell cycle kinetics of MCF-7 cells. The DNA-histogram of a single cell suspension was obtained on Coulter Epics V after fixing the cells in 70 % ethyl alcohol and staining in propidium iodide. Tamoxifen increased the percentage of cells in G1-phase with a concomitant decrease in percentage of cells in S-phase, in an estradiol reversible manner. Cyclopropyl compound 7a increased the percentage of cells in G1-phase, in an estradiol-irreversible manner. Further, compounds 5a, 5c, 7a and 7b decreased the percentage of cells in S-phase and increased percentage of cells in the G2M-phase, in an estradiol-irreversible manner. Of the five cyclopropyl compounds tested, only 4d had no influence on the cytokinetic parameters, even though this compound was found to exhibit antiproliferative activity on MCF-7 cells equal to that of tamoxifen. In conclusion, all of the cyclopropyl compounds, except 4d, altered cell cycle parameters of MCF-7 cells in a manner different than that of tamoxifen. Thus, the results of this study indicate that, although these cyclopropyl compounds are antiestrogenic, they produce antiproliferative activity by a distinct mechanism of action in estrogen receptor positive breast cancer cells.

Sulofenur cytotoxicity and changes in cytosolic calcium and mitochondrial membrane potential in human colon adenocarcinoma cell lines.

Sulofenur treatment (12.5 microM-1 mM) of colon adenocarcinoma cell lines resulted in dose- and time-dependent cell killing. LYc5 cells were viable longer than GC3/c1 cells. Each concentration resulted in elevation of cytosolic calcium [Ca2+]i) for both cell lines. At lower doses, elevation was delayed for LYc5 cells. GC3/c1 cells after 1 mM treatment in Ca(2+)-free HBSS showed no rise of [Ca2+]i. GC3/c1 cells after carbonyl cyanide-m-chlorophenylhydrazone rapidly lost rhodamine 123 fluorescence from mitochondria; after 1 mM sulofenur, fluorescence faded slowly. Following treatment, cells became rounded, blebs formed and the cells died. Results suggest that elevated [Ca2+]i plays an important role in sulofenur cytotoxicity.

Differential cytotoxicity in mouse epidermal JB6 cells: a potential mechanism for oxidant tumor promotion.

It has been suggested that superior antioxidant defense systems protect promotion-sensitive (p+t) mouse epidermal JB6 clone 41 cells from excessive deleterious effects of oxidants, allowing their clonal expansion in contrast to that of promotion-resistant (p-) clone 30 cells. In support of this concept, we report that oxidants produced by xanthine/xanthine oxidase cause more cytotoxicity, cellular damage, and cell death in p-cells. Cell surface blebbing, an early morphological consequence of oxidative injury, was detected in cultures grown on glass coverslips. While a rise in cytosolic ionized calcium ([Ca2+]i) preceding bleb formation was observed in both p+ and p- cells by digital imaging fluorescence microscopy, elevated levels of [Ca2+]i were sustained longer in p- cells. This increase was dependent on the levels of extracellular ionized calcium ([Ca2+]e) in p+ but not p- cells. We conclude that the superior antioxidant defense or improved Ca2+ buffering of promotable clone 41 cells protects them from more severe deregulation of [Ca2+]i and, as a consequence, from excessive cytotoxicity after exposure to oxidant promoters.

A comparison of the antitumor activity of two triarylcyclopropyl antiestrogens (compounds 4d and 5c) on human breast cancer cells in culture.

Compound 4d ((E)- and (Z)-1,1-Dichloro-2-[4-(benzyloxy)-phenyl]2,3-bis(4-methoxyphenyl) cyclopropane) and compound 5c ((Z)-1,1-Dichloro-2-[4-(benzyloxy)-phenyl]- 2-(4-methoxyphenyl)-3-phenylcyclopropane) are two members of a novel series of triarylcyclopropyl compounds which have been shown to be pure antiestrogens. In the present study, the antiproliferative activity of 4d and 5c was examined on estrogen receptor (ER)-positive MCF-7 and ER-negative MDA-MB-231 human breast cancer cells and A-549 human lung cancer cells. Compound 4d inhibited the growth of MCF-7 cells in a dose-related manner over a concentration range of 10(-13) to 10(-5) M while compound 5c inhibited MCF-7 cell growth in a dose-related manner over a concentration range of 10(-9) to 10(-5) M. Further, neither compound altered the growth of MDA-MB-231 or A-549 cells. Co-administration of estradiol reversed the antiproliferative activity of 4d but not 5c on MCF-7 cells. Both compounds bound specifically to ER in MCF-7 cells; however, the relative binding activity of 4d was five times greater than estradiol and 5000 times greater than 5c. The influence of 4d and 5c on the cell surface morphology of MCF-7 and MDA-MB-231 cells was studied using scanning electron microscopy. Both compounds, at a concentration of 10(-6) M, reduced the density of microvilli on MCF-7 cells, which was reversed by co-administration of estradiol (10 (-8) M). These compounds did not alter the cell surface morphology of ER-negative MDA-MB-231 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between [Ca2+]i and cell death using an in vivo model: a study using the ced-1 mutant strain of C. elegans.

The ced-1 mutant of the free-living nematode, Caenorhabitis elegans, was used to study cell injury and cell death in relation to changes in intracellular ionized calcium ([Ca2+]i). This animal, which is being genetically characterized, may prove to be extremely useful for certain toxicologic studies because of its small size, optical transparency, rapid generation time, and the morphologic and genetic data currently available. During the development of this animal, 131 of 1,090 ultimate somatic cells undergo programmed cell death. Using mutagenesis techniques, several genes responsible for this death have been identified. In this study, we have taken advantage of the ced-1 mutant in which dead cells accumulate, as they cannot be phagocytized and removed. Although changes in [Ca2+]i have been studied in relation to cell injury and cell death, observations have been essentially restricted to in vitro monolayer cultures because of the methodology involved. To study the relationship between changes in [Ca2+]i and injury in vivo, we selected this animal model for further study and report here the morphological changes following the effects of ionomycin treatment in relation to increases of [Ca2+]i and cell death as measured using the fluorescent probes Fluo-3/AM and propidium iodide, respectively. The technique of confocal laser scanning microscopy is ideally adapted to such measurements in these living animals, and the results can be readily correlated with those made with Nomarski differential interference contrast microscopy as well as with transmission electron microscopy. The results support previous in vitro observations and show that early increases of [Ca2+]i accompany early reactions to injury. Furthermore, the results also show that changes in this small invertebrate metazoan parallel those seen in mammalian systems, including human. Thus, the current study indicates that ced-1 C. elegans can potentially serve as an in vivo model not only for evaluating the possible temporal relationship of [Ca2+]i elevation with cell death but also for evaluating the [Ca2+]i elevation observed in relation to other phenomena and in evaluating toxic agents.

The influence of a novel cyclopropyl antiestrogen (compound 7a) on human breast cancer cells in culture.

Compound 7a ([Z]-1,1,-dichloro-2,3-diphenyl-2-(4-(2- dimethylamino)ethoxy)phenyl) cyclopropane, dihydrogen citrate salt) is a novel cyclopropyl antiestrogen which was shown to be an estrogen antagonist without estrogen agonist activity. The antiproliferative activity of 7a was examined on estrogen receptor (ER) positive MCF-7 and ER-negative MDA-MB-231 human breast cancer cells and A-549 human lung cancer cells. Compound 7a inhibited the growth of MCF-7 cells in a dose-related manner over a concentration range of 10(-9) to 10(-5) M, but did not alter the growth of MDA-MB-231 or A-549 cells. The antiproliferative activity of 7a (10(-7) M) on MCF-7 cells was reversed by co-administration of estradiol (10(-8) M). An ER-dependent mechanism of action is also supported by the specific ER binding of 7a in MCF-7 cells observed in this study. A study of cell surface morphology using scanning electron microscopy (SEM) revealed that compound 7a at 10(-6) M reduced the length and density of microvilli (MV) on MCF-7 cells, which was reversed by co-administration of estradiol (10(-8) M). Compound 7a did not alter the cell surface morphology of ER-negative MDA-MB-231 cells. In conclusion, 7a inhibited the growth of ER-positive MCF-7 cells in an estradiol-reversible manner, and had no effect on ER-negative MDA-MB-231 cells or A-549 lung cancer cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell-growth quantitation methods for the evaluation of antiestrogens in human breast cancer cells in culture.

The antiproliferative activity of the antiestrogen, tamoxifen, on the growth of MCF-7 human breast cancer cells was evaluated using the hemocytometric trypan blue exclusion method, [3H]-thymidine incorporation, and a total protein determination. Tamoxifen was evaluated over a concentration range from 10(-9) to 10(-6) M. The hemocytometric trypan blue exclusion method and [3H]-thymidine incorporation were sensitive enough to demonstrate the inhibitory influence of tamoxifen on the proliferation of MCF-7 cells at a concentration as low as 10(-9) M. A very good correlation of these two methods was observed in the submicromolar concentration range of tamoxifen. The total protein determination method was only sensitive enough to detect the antiproliferative influence of tamoxifen at concentrations above 10(-6) M. In conclusion, the [3H]-thymidine incorporation method was found to be effective and much less time consuming than the hemocytometric trypan blue exclusion method for evaluating the antiproliferative effects of antiestrogens in cultured MCF-7 cells. However, when evaluating antiestrogens, which are cell-cycle specific, the results of the [3H]-thymidine incorporation method should be interpreted with caution.