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Biomedical subjects

M E Lippman

Publications and source records attributed to M E Lippman.

At least 235 records · Page 13Linked to original sources
PubMed1985

Relationship between the expression of estrogen-regulated genes and estrogen-stimulated proliferation of MCF-7 mammary tumor cells.

The growth of MCF-7 cells was arrested by 24 h of isoleucine deprivation. Following replenishment of the medium, the incorporation of uridine and thymidine into trichloroacetic acid-precipitable material began to increase slowly and gradually rose to the level of cycling cells. The addition of 5 X 10(-9) M estradiol to growth-arrested cells dramatically shortened the time of onset of macromolecular synthesis and increased the overall amount of precursor incorporation 2- to 4-fold over the level obtained by arrested control cells. The increase in uridine incorporation preceded the increase in thymidine incorporation by 6 h. Inhibition of protein synthesis with cycloheximide blocked the recovery of macromolecular synthesis in both control and estrogen-treated cells. Actinomycin D was ineffective in blocking the estrogen-stimulated recovery of macromolecular synthesis at concentrations known to inhibit pre-rRNA synthesis (10(-8) M). At higher concentrations, uridine and thymidine incorporation were inhibited in a dose-dependent manner. Inhibition of RNA polymerase II activity with alpha-amanitin similarly blocked both the recovery of the cells from isoleucine starvation and the potentiation of this by estradiol. Dihydrofolate reductase and thymidine kinase activities are both stimulated by estradiol in MCF-7 cells. In cycling cells, estrogen stimulates a 2-fold increase in their messenger RNAs (mRNAs) within 24 h. The level of dihydrofolate reductase mRNA is unaffected by isoleucine starvation, and estrogen caused no change in dihydrofolate reductase mRNA levels over a 24-h period following reversal of growth arrest. Similar results were observed for the 600-nucleotide pS2 mRNA that has been identified as an estrogen-induced RNA in MCF-7 cells. In contrast, thymidine kinase mRNA was found to be increased by estrogen at 24 h, but not at 12 h, following reversal of growth arrest. This increase correlates with increases in thymidine, but not uridine incorporation. These data indicate that the estrogen-stimulated increase in thymidine incorporation following release from growth arrest is dependent on new RNA synthesis. However, the hormone did not increase the levels of three estrogen-regulated mRNAs coordinately with the increases observed in uridine incorporation.

Amanitins↗
PubMed1984

A novel nuclear form of estradiol receptor in MCF-7 human breast cancer cells.

Nuclear estrogen receptor from MCF-7 cells undergoes a time-dependent, hormone-inducible transformation to a form that is less extractable from nuclei and less exchangeable with ligand. This receptor-modifying, intranuclear event is independent of receptor loss (processing) and appears associated with hormone responsiveness (progesterone-receptor induction) in these cells. The magnitude of receptor loss, however, is variable and apparently not a prerequisite for hormone action to induce progesterone receptor.

Breast Neoplasms↗
PubMed1984

Effects of antiestrogens on the estrogen-regulated pS2 RNA and the 52- and 160-kilodalton proteins in MCF7 cells and two tamoxifen-resistant sublines.

The effects of estradiol and antiestrogens on two estrogen-regulated proteins (52 and 160 kDa) and an estrogen-inducible mRNA (pS2) have been measured in the MCF7 human breast cancer cell line and two tamoxifen-resistant sublines. In MCF7 cells, tamoxifen (or nafoxidine) alone does not significantly affect pS2 mRNA levels nor transcription of the pS2 gene but completely antagonizes the ability of estradiol to increase pS2 RNA levels. The estrogen-mediated increase in pS2 mRNA levels resembles that of two estrogen-regulated proteins (52 and 160 kDa) that are released from MCF7 cells into the culture medium. This is distinct from the estrogen-mediated increase in progesterone receptor which is also obtained by tamoxifen treatment. In the two tamoxifen-resistant sublines (R27 and RTx6), tamoxifen does not increase pS2 mRNA levels or 160-kDa protein production but increases the production of the 52-kDa protein. These results show that in these tamoxifen-resistant cells, tamoxifen has become fully estrogenic for one, but not all estrogen-regulated responses.

Breast Neoplasms↗
PubMed1984

An assessment of current achievements in the systemic management of breast cancer.

Over the past twenty years, breast cancer has come to be much more commonly regarded and treated as a systemic disease. Conventional chemotherapy and endocrine therapy used according to schedules that are tolerable to patients are generally effective and often induce worthwhile responses; nevertheless, the responses in general have a median duration of less than a year, and these therapies are rarely if ever curative. Continued efforts to use available agents with mere modifications of schedule and intensity seem unlikely to substantially improve upon the modest success already achieved. Rather, we desperately need radically new schedules, new agents (especially non-myelosuppressive agents), and new approaches (e.g. monoclonal antibody targeting of drugs, toxins, or radionuclides, perhaps combined with tumor sensitizing agents such as heat). It is our hope that consideration of some of these issues will encourage others to be bolder in devising the next generation of clinical trials.

Antineoplastic Agents↗
PubMed1984

Modulation of glucocorticoid receptors by mitogenic stimuli, glucocorticoids and retinoids in normal human cultured T cells.

Human T lymphocytes can be maintained in cell culture by the addition of conditioned medium (CM) containing a T cell growth factor (TCGF). This system provides an opportunity to study the presence and modulation of glucocorticoid receptors (GR) by various factors in these cells. GR were present in T cells grown from each of 22 normal individuals; the binding capacity (mean = 3851 +/- 2880 sites/cell) and affinity (Kd = 7.4 X 10(-9)) were similar in rested cultured T cells (CTC) to those reported in peripheral blood T lymphocytes. Treatment of rested CTC with stimuli such as phytohemagglutinin (PHA), CM, or 12-O-tetradecanoylphorbol-13-acetate (TPA) results in a mean increase in GR binding capacity of 3.1-, 3.2- or 2.4-fold respectively without modification of binding affinity. Using an exchange assay to measure occupied and unoccupied GR, we examined the effects of cortisol on its own receptor. Treatment of rested CTC with 10(-7) M cortisol for 24 h decreased GR by more than 50%. Cortisol treatment also blocked the induction of GR by PHA and CM. Since retinoids have been shown to modulate the immune response and to alter the effects of PHA and phorbol esters on lymphocytes, we examined their effects on GR. Retinol decreased GR activity in CTC but only at concentrations which inhibit cell growth. It is concluded that GR activity in human T cells can be modulated by several important factors involved in lymphocyte function.

Cells, Cultured↗
PubMed1984

The impact of primary irradiation treatment of localized breast cancer on the ability to administer systemic adjuvant chemotherapy.

The impact of primary irradiation of localized breast cancer on the ability to administer Adriamycin-cytoxan adjuvant chemotherapy to patients with stage II breast cancer was examined. Patients were prospectively randomized to receive either irradiation or mastectomy as local therapy and did not differ with respect to other prognostic variables that might influence tolerance to chemotherapy. All of the patients received chemotherapy dose escalations (or reductions) until maximal tolerated drug doses were established. Patients receiving irradiation had minimally greater myelosuppression which was nearly totally explainable by lymphopenia. Irradiated patients required dose reduction nearly twice as often as mastectomy patients although commonly their dose could be reescalated. Patients managed with radiotherapy received slightly less drug than patients treated with mastectomy when treated to an identical degree of bone marrow suppression. The primary management of breast cancer by irradiation does not induce substantial changes in the ability of patients to tolerate adjuvant chemotherapy.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1984

A randomized attempt to increase the efficacy of cytotoxic chemotherapy in metastatic breast cancer by hormonal synchronization.

Human breast cancer cells in tissue culture can be growth inhibited by tamoxifen, an inhibition that can be reversed by estrogen. The question of whether tamoxifen inhibition of breast cancer followed by estradiol reversal would increase the efficacy of chemotherapy was asked. One hundred ten patients were prospectively randomized to chemotherapy consisting of cytoxan (750 mg/m2) and Adriamycin (30 mg/m2) on day 1 plus 5-fluorouracil (5-FU) (500 mg/m2) and methotrexate (MTX, 40 mg/m2) on day 8 versus the same chemotherapy plus tamoxifen (20 mg/m2) on days 2-6 and premarin (0.625 mg every 12 hours for three days) on day 7. Chemotherapy was given in 21-day cycles. The first 55 patients were randomized to a regimen in which 5-FU preceded MTX by 24 hours; thereafter, all patients received MTX followed in one hour by 5-FU. No difference in any response parameter was seen between these two 5-FU/MTX schedules. A limited number of patients with inflammatory breast cancer had a significantly higher response rate (93% versus 61%; p = 0.03) than patients with recurrent metastatic disease. Time to progression (13 versus 17 months) and survival (17 versus 23 months) of responders significantly favored the treatment arm including tamoxifen and premarin. Whereas an additive effect of hormones plus chemotherapy cannot be entirely excluded as the explanation for the improved results with the addition of tamoxifen for four days plus one day of premarin, results suggest that further efforts to increase the efficacy of chemotherapy by perturbing tumor growth rates may be worthwhile.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1984

Hormonal control of plasminogen activator secretion in ZR-75-1 human breast cancer cells in culture.

Activity of secreted plasminogen activator (PA) by ZR-75-1 human breast cancer cells in culture is shown to be altered by the addition of physiologically relevant concentrations of the hormones 17 beta-estradiol (E2), insulin, and dexamethasone. After 48 h, E2 stimulated PA activity 6-fold at concentrations as low as 10(-12) M. This stimulation was prevented by the addition of actinomycin D and cycloheximide. The antiestrogen tamoxifen reduced estrogen stimulation of PA, but had slight stimulatory effects on PA secretion by itself. Insulin (5 X 10(-10) M) induced a 2-fold increase in PA activity. Effects of insulin and E2 were additive, suggesting independent sites of control of PA production. Dexamethasone (10(-8) M) decreased PA activity by 20%, but did not inhibit cell growth at the concentration tested. These data suggest that secreted PA activity is differentially regulated by hormones and that effects of PA and growth do not occur in parallel.

Breast Neoplasms↗
PubMed1984

Kinetic alterations in estrogen receptors associated with estrogen receptor processing in human breast cancer cells.

After nuclear translocation of estrogen receptors in MCF-7 human breast cancer cells, a processing takes place resulting in a 30-70% decline in the number of estradiol-binding sites measured in nuclear extracts. We have investigated the mechanism of estrogen receptor processing and obtained evidence that multiple events are involved. We confirm, as others have shown previously, that processing involves a decrease in the amount of estradiol binding in MCF-7 cells. In addition, evidence is provided for the generation of a rapidly dissociating population of estradiol-binding sites as an early event in processing. There is a single, slowly dissociating population of estrogen binding sites when MCF-7 cells are exposed to estradiol in the presence of actinomycin D, an inhibitor of receptor processing. One hour after the addition of sufficient estradiol to induce receptor processing, an additional, more rapidly dissociating population of estrogen binding sites is detected. When cells are exposed to estradiol and ethidium bromide, a drug which shares many actions with actinomycin D, but does not inhibit receptor processing, the rapidly dissociating population of estradiol-binding sites is again observed. Significantly, the loss of estradiol-binding sites from MCF-7 cells associated with processing between 1 and 6 h of estradiol exposure, occurs exclusively from the rapidly dissociating population of sites. Whole cell equilibrium-binding assays were performed with MCF-7 cells after 30 min or 5 h of estradiol exposure to determine whether the detected changes in estradiol dissociation reflected affinity changes in a subpopulation of estrogen-binding sites. Although the number of sites detected per cell varied with the assay method employed, binding to a single saturable class of higher affinity sites is always observed. High affinity estradiol-binding sites were reduced by 45% after a 5-h incubation with estradiol in both assay methods. The loss of estradiol binding during processing may therefore be explained by the conversion of certain high affinity estrogen receptors to a rapidly dissociating form which then fails to rebind hormone, or undergoes subsequent reactions that destroy hormone binding activity. Additionally, after 6 h of exposure to estradiol, the remaining receptor-bound estradiol dissociates from intact cells with a rate increased by 50% over that seen from the slow dissociating receptors present at 1 h.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding Sites↗
PubMed1984

The estrogen receptor in MCF-7 cells: evidence from dense amino acid labeling for rapid turnover and a dimeric model of activated nuclear receptor.

Upon treatment of MCF-7 cells with estradiol at 37 C, practically all of the estrogen receptor is found in the nuclear compartment. This nuclear estrogen receptor form sediments close to 5S on high salt sucrose density gradients, similar to receptor activated in vitro by gentle heating. Upon extraction of the nuclear receptor, this 5S form is not stable at 0-4 C under our buffer conditions and is converted to a 4S form in 10-14 h. Incubation of cells in the presence of dense amino acids for various amounts of time in the absence of estradiol, followed by a 20- to 30-min labeling period with 3 nM [3H]estradiol at 37 C, permits separation of the newly synthesized estrogen receptor on sucrose gradients by means of its different sedimentation properties. With the fresh nuclear extract, we observe a progressive shift to a heavier form on sucrose gradients in proportion to the time of incubation in dense amino acids. The 5S nuclear receptor gradually becomes denser as the time of incubation of cells in dense medium increases and the peak moves from light to heavy without resolving into discrete heavy and light forms at intermediary time points. In contrast, when the nuclear extract, prepared after varying periods of incubation of the cells with dense amino acids and brief treatment with [3H]estradiol, is left standing at 0-4 C for a period of 10-14 h, we observe discrete peaks of heavy and light receptors. The resolution into discrete peaks of heavy and light forms at each time point permits a calculation of the turnover rate for this receptor (t 1/2 = approximately 2.25 h). These findings are consistent with a model in which the 5S nuclear receptor is an oligomer of randomly associated heavy and light monomers, whereas the aged 4S nuclear receptor is a monomer. We conclude from these data that estrogen receptor synthesis is extremely rapid in log growth phase MCF-7 cells; and the activated nuclear receptor appears to be an oligomer of at least two monomers closely related in size and metabolized at a similar rate. The random association between different monomers (heavy and light) results in a broad peak of nuclear receptor and is at least consistent with a dimerization reaction occurring as part of receptor activation.

Amino Acids↗
PubMed1984

Antiestrogen binding in antiestrogen growth-resistant estrogen-responsive clonal variants of MCF-7 human breast cancer cells.

Although antiestrogen therapy is effective in the treatment of hormone-responsive breast tumors, approximately 40% of the patients with estrogen receptor-positive tumors fail to respond to antiestrogens. To better understand the mechanisms by which antiestrogens inhibit the growth of hormone-dependent breast cancers, we have investigated the physicochemical properties and binding characteristics of the estrogen receptors with estradiol and antiestrogens and the occurrence of estrogen-noncompetible antiestrogen binding sites in two estrogen-sensitive but tamoxifen-growth-resistant estrogen receptor-positive MCF-7 cell variant clones, R3-98 and R27. In the variant cells, estradiol (10(-8) M) significantly stimulates cell proliferation as in the parent MCF-7 cells, but the antiestrogen tamoxifen (10(-6) M) has no significant effect on growth of the variant cells, whereas antiestrogen strongly inhibits proliferation of the parent MCF-7 cells. All three cell types contain high concentrations of estrogen receptor (150 to 250 fmol/mg protein), and competition binding analysis shows that the relative binding affinity of a series of compounds for estrogen receptor is similar among the three cell types with the affinity of trans-hydroxytamoxifen greater than estradiol greater than alpha-[4-pyrrolidinoethoxy]phenyl-4-hydroxy-alpha'-nitrostilben e greater than tamoxifen. Salt-extracted nuclear receptor complexes prepared from the three cell types showed similar sedimentation behavior on 0.4 M KCl-containing sucrose gradients with [3H]estradiol-labeled receptor complexes sedimenting at 4.2S, whereas receptors complexed with either of the antiestrogens trans-[3H]-hydroxytamoxifen or [3H]alpha-[4-pyrrolidinoethoxy]phenyl-4-hydroxy-alpha'-nitrosti lbene sediment at 5.5S. In all 3 cell types, the nuclear receptor forms react with an estrogen receptor monoclonal antibody, D547Sp gamma, to form complexes which sediment at 8.5S. The nuclear estrogen receptors from the parental MCF-7 and the two variant cells, when covalently labeled with [3H]-tamoxifen aziridine in intact cells and then salt extracted have identical molecular weights of approximately 62,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The covalently labeled nuclear and cytosol receptors in these 3 cell lines also show identical migration in 8 M urea polyacrylamide isoelectric focusing gels consistent with a predominant receptor species of isoelectric point approximately 5.7.(ABSTRACT TRUNCATED AT 400 WORDS)

Breast Neoplasms↗
PubMed1984

Induction of two estrogen-responsive proteins by antiestrogens in R27, a tamoxifen-resistant clone of MCF7 cells.

In an attempt to approach the mechanism by which estrogen and antiestrogen regulate the growth of estrogen receptor-positive breast cancer, we have studied the effects of the antiestrogens tamoxifen (TAM) and 4-hydroxytamoxifen (OH-TAM) on the induction of two estrogen-specific proteins in a variant of MCF7 cells termed R27, cloned for its ability to grow in the presence of TAM. We found that, in the R27 variant, antiestrogens as well as estradiol were able to increase specifically the production of a Mr 52,000 protein which was released into the culture medium. This protein was shown to be identical to the Mr 52,000 glyco-protein induced by estrogen and released by MCF7 cells on the basis of its specific inducibility by physiological concentrations of 17 beta-estradiol and of its resolution in two-dimensional gel analysis. Dose-response analysis showed that, in the R27 variant, TAM and OH-TAM acquired the ability to induce the Mr 52,000 protein at concentrations compatible with their relative affinities for the estrogen receptor, while these antiestrogens were inefficient in the wild MCF7 cells. Whereas the relative increase of the Mr 52,000 protein was similar with TAM, OH-TAM, and 17 beta-estradiol, the general production of Mr 52,000 and of total labeled proteins was less with the antiestrogens than with 17 beta-estradiol. Moreover, OH-TAM displayed a biphasic dose-response curve with inhibitory effects at concentrations above 10 nM, suggesting an additional mechanism. Neither TAM nor OH-TAM had any antiestrogenic effect when added in the presence of 17 beta-estradiol. In the R27 variant, both estradiol and antiestrogens induced the progesterone receptor sites; however, the extent of the stimulation was lower with antiestrogens than with estradiol. This study shows that, in addition to the classical antiestrogen-resistant breast cancer cells, in which the estrogen receptor is absent or inactive, there is another class of antiestrogen-resistant cells in which the drug becomes a full estrogen agonist as evidenced by the induction of the Mr 52,000 estrogen-specific protein, which is not induced in the wild-type cells.

Breast Neoplasms↗