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Biomedical subjects

L C Murphy

Publications and source records attributed to L C Murphy.

At least 109 records · Page 6Linked to original sources
PubMed1986

Progestin regulation of epidermal growth factor receptor in human mammary carcinoma cells.

Epidermal growth factor (EGF) receptors are present in human breast cancer and probably mediate the effects of EGF and the autocrine effects of alpha-transforming growth factors, produced by breast cancer cells. Steroid hormones influence the growth of some human cancers, and both direct and indirect effects on cell proliferation have been proposed. One potential indirect effect of steroids would be to augment sensitivity to other endocrine and autocrine factors by up-regulation of their receptors. We therefore investigated the effects of various steroids on EGF receptor expression in T-47D, MCF-7, and BT 20 human mammary carcinoma cells in culture. Preincubation of T-47D cells for 24 h with a series of androgens, estrogens, glucocorticoids, and progestins resulted in a significant enhancement of specific 125I-EGF binding in the presence of progestins only. Increased binding of EGF was associated with neither a change in cell number nor changes in the specific binding of concanavalin A, insulin, or calcitonin but was accompanied by an increase in lactogenic receptor expression. When assayed at 20 degrees C, increased EGF binding was due to an increase in receptor number (33,380 +/- 7,410 sites/cell in control cultures; 67,460 +/- 20,330 sites/cell in cultures treated with 1 nM medroxyprogesterone acetate for 24 h; P less than 0.05) without a change in receptor affinity. Two- to 3-fold increases in receptor number were also apparent when binding was measured at 4 degrees C, indicating that the effect was due to an increase in expression of receptor at the cell surface rather than progestin effects on internalization and degradation. These data illustrate that the expression of EGF receptor in some breast cancer cells is regulated in part by mechanisms mediated via the progesterone receptor, since the effect was confined to progestins, potency among a series of progestins was correlated with their affinities for progesterone receptor, and sensitivity among the three cell lines studied was related to the presence and concentration of cellular progesterone receptor.

Androgens↗
PubMed1985

Differential effects of tamoxifen and analogs with nonbasic side chains on cell proliferation in vitro.

Structural analogs of the nonsteroidal antiestrogen tamoxifen, in which the basic dimethylaminoethoxy side chain was either absent or replaced with a variety of nonbasic side chains, were examined for their ability to inhibit the proliferation of a hormonally responsive cell line, MCF 7 human breast cancer. The degree of inhibition was compared with relative binding affinities for the estrogen receptor (RE) and a microsomal antiestrogen binding site (AEBS). All modifications resulted in loss of detectable affinity for AEBS. Replacement of the basic side chain of tamoxifen with a series of nonbasic side chains reduced affinity for RE by 78-93% except in the case of 1-(4-(1,2-diphenylbut-1-enyl)phenyl)-2,3-butanediol (ICI 145-680) where affinity was unchanged. When the basic side chain of tamoxifen was replaced by a hydroxyl group, to form the estrogenic analog ICI 141389 (Metabolite E), affinity for RE was reduced by 39%. ICI 141389 was a very weak inhibitor of MCF 7 cell growth, showing no significant growth inhibition at concentrations less than 10 microM. Despite the fact that ICI 145680 and tamoxifen had identical affinities for RE, ICI 145680 was a significantly weaker growth inhibitor than tamoxifen over the concentration range studied, i.e. 0.1-20 microM. Differences in potency were greatest at concentrations greater than 7.5 microM where the effects were not reversed by estradiol and where cytotoxicity played a major role in the decrease in cell numbers induced by tamoxifen. Like tamoxifen, ICI 145680 demonstrated both estrogen-reversible (at concentrations between 0.5-7.5 microM) and estrogen-irreversible (10-20 microM) inhibition of MCF 7 cell proliferation which was associated with a concentration-dependent accumulation of cells in the G0/G1 phase of the cell cycle. In contrast to tamoxifen, however, ICI 145680 appeared not to possess cytotoxic activity. Whereas ICI 145680 was without effect on proliferation of the RE negative human breast cancer cell line, MDA-MB-330, at doses less than 20 microM, tamoxifen inhibited growth at concentrations greater than 5 microM, but with changes in cell cycle kinetic parameters that were markedly different from those seen in RE positive cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Breast Neoplasms↗
PubMed1985

Differential sensitivity of human breast cancer cell lines to the growth-inhibitory effects of tamoxifen.

In eight estrogen receptor (ER)-positive breast cancer cell lines (including three sublines of MCF-7) and five ER-negative breast lines, the action of the nonsteroidal antiestrogen, tamoxifen, was studied, and the concentrations of ER and antiestrogen binding site were measured. The concentration of antiestrogen binding site was significantly [P less than 0.005] greater in ER-positive cells [236,600 +/- 29,900 (SE) sites/cell] than in ER-negative cell lines [66,600 +/- 16,800 sites/cell]. In ER-positive cell lines, a cell cycle phase-specific growth-inhibitory effect, 20% inhibitory dose less than 0.1 to 1.0 microM, was seen which was shown for some representative cell lines to be estrogen reversible. Within this group of cell lines, the degree of tamoxifen-induced inhibition of growth correlated with control population doubling time, but not ER or antiestrogen binding site concentration. The changes in cell cycle kinetic parameters characteristic of all ER-positive lines were a decrease in percentage of S-phase cells and a corresponding increase in percentage of G0-G1 cells. In all cell lines, 5 to 12.5 microM tamoxifen caused cytotoxicity, and this was shown to be estrogen-irreversible in 3 representative cell lines; moreover, estradiol synergistically enhanced the cytotoxic effects of tamoxifen under some experimental conditions. The cell cycle effects of tamoxifen in three ER-negative cell lines (Hs0578T, MDA-MB-231, MDA-MB-330) were decreased proportions of G0-G1 cells with an increase in percentages of S and G2+M cells. These results implied that the mechanism of tamoxifen cytotoxicity may differ in ER-positive and ER-negative breast cancer cells. However, although the ER-negative BT-20 line was much less sensitive to tamoxifen than were the ER-positive cells, growth inhibition and cytotoxicity in this line were associated with a slight decrease in percentage of S-phase cells. These results confirm that ER-positive breast cancer cells are more sensitive (4- to greater than 75-fold) than ER-negative breast cells to the growth-inhibitory effects of tamoxifen and demonstrate that, in all ER-positive cells, growth inhibition and cytotoxicity are accompanied by characteristic changes in cell cycle kinetic parameters. In contrast, different mechanisms may be involved in the effects of tamoxifen on different ER-negative cell lines.

Breast Neoplasms↗
PubMed1984

Microsomal binding sites for nonsteroidal anti-estrogens in MCF 7 human mammary carcinoma cells. Demonstration of high affinity and narrow specificity for basic ether derivatives of triphenylethylene.

In the presence of estradiol, at a concentration sufficient to saturate the estrogen receptor, the antiestrogenic and anti-tumor agent tamoxifen was bound to a high affinity (KD = 0.97 +/- 0.15 nM at 4 degrees C) saturable binding site (141,300 +/- 20,100 sites/cell) in MCF 7 human mammary carcinoma cells. The distribution of this site between cytosol, mitochondrial, microsomal (heavy and light), and nuclear fractions paralleled that of NADPH-cytochrome c reductase, an enzyme marker for endoplasmic reticulum. The interaction between tamoxifen and the high affinity site was influenced by changes in pH, ionic strength, and temperature. The kinetic rate constants k+1 and k-1 showed strong temperature dependence, but KD was unaffected by changes in temperature. Competition studies employing analogs of the anit-estrogens tamoxifen, clomiphene, and CI 628 revealed narrow specificity for triphenylethylene derivatives with basic ether side chains.

Breast Neoplasms↗
PubMed1984

Correlation of lactogenic receptor concentration in human breast cancer with estrogen receptor concentration.

The presence of receptors for lactogenic hormones in human breast cancer tissue has been documented previously, but the relationship between the expression of these receptors and estrogen receptor (ER) status has not been adequately studied. In this report, the specificity of 125I-human growth hormone (HGH) binding in both cultured human breast cancer cell lines and tumor biopsies was studied to establish that HGH was a suitable ligand for investigating lactogenic receptor concentration in these tissues. In addition, the relationship between specific binding of 125I-HGH and ER concentration in human breast cancer was investigated. Specific 125I-HGH binding to 14 breast cancer cell lines in long term culture and to membrane preparations (microsomal and plasma membrane fractions) from 31 breast cancer biopsy specimens was examined. Human prolactin and HGH were approximately equipotent in inhibiting binding of 125I-HGH to both cultured breast cancer cell lines and to membrane preparations from breast cancer biopsy specimens. Competitive inhibition experiments using lactogenic and somatogenic hormones established that the specificity of 125I-HGH binding to breast cancer biopsy material was similar to that of cultured breast cancer cell lines and similar to that reported for subprimate lactogenic receptors. Saturable, high-affinity (Ka = 0.53 to 2.33 nM-1), low-capacity (330 to 6560 sites/cell) growth hormone binding sites were found on each of the ER-positive cell lines, whereas no specific 125I-HGH binding to ER-negative cell monolayers was detected. When all cell lines were considered, a significant linear correlation (r = 0.745, p less than 0.001) between ER and lactogenic receptor concentrations was found. Significant specific 125I-HGH binding, greater than 1% of the total radioactivity added, was detected in 20 of 31 (65%) breast tumor biopsy specimens. The mean affinity and capacity of the lactogenic receptor as measured in 8 separate membrane preparations were Ka = 0.52 +/- 0.09 (S.E.) nM-1 and 255 +/- 85 fmol/mg protein. Membrane preparations from ER-negative tumors (less than 3 fmol ER/mg cytosol protein) bound significantly less 125I-HGH than did membrane preparations from ER-positive tumor biopsies (1.22 +/- 0.44 versus 3.21 +/- 0.56%, p less than 0.05). A significant linear correlation between specifically bound 125I-HGH and ER concentration (r = 0.412, p less than 0.02) was demonstrated in the 31 breast cancer biopsy specimens studied.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding, Competitive↗
PubMed1984

A new human breast carcinoma cell line (PMC42) with stem cell characteristics. III. Hormone receptor status and responsiveness.

PMC42 is a new human breast carcinoma cell line. In this report the content of estrogen, progesterone, and glucocorticoid receptors in PMC42 has been determined. The estrogen receptor content (1,750 cytoplasmic sites and 350 nuclear sites) was lower than that described for MCF7 and T47D. The cells would not proliferate in serum-free medium without the addition of beta-estradiol (optimum concentration 10(-8) M) or progesterone (5 X 10(-8) M). The addition of both hormones induced a more than additive increase in proliferation (P less than .005, n = 18). Similarly, addition of insulin or hydrocortisone induced proliferation; however, in this case, the effect of the hormones together was only additive. The addition of tamoxifen (10(-6) M) led to a significant decrease in cell numbers and inhibited the stimulatory effects of 10(-8) M beta-estradiol.

Breast Neoplasms↗
PubMed1984

Factors affecting the sensitivity of T-47D human breast cancer cells to tamoxifen.

Cell proliferation kinetics during growth of an estrogen receptor-positive human breast carcinoma cell line, T-47D, was defined, and some factors which modify its response to tamoxifen were investigated in vitro. T-47D cells were estrogen responsive when grown in charcoal-stripped fetal calf serum, but the addition of 17 beta-estradiol did not fully restore the growth rate to that observed in the same concentration of fetal calf serum. Tamoxifen had both a low-dose, estrogen-reversible, growth-inhibitory effect and a high-dose, estrogen-irreversible, growth-inhibitory and cytotoxic effect on T-47D cells. Tamoxifen-induced growth inhibition was associated with a decrease in the percentage of S-phase cells and, to a lesser extent, G2-M-phase cells and an increase in G0-G1-phase cells. Plateau-phase cells were considerably less sensitive than were exponentially growing cells, and this was accompanied by a fall in unoccupied estrogen receptor content from 4407 +/- 655 (S.E.) sites/cell in exponentially growing cultures to 1420 +/- 315 sites/cell in plateau-phase cultures. T-47D cells were more sensitive to tamoxifen cytostasis when grown in fetal calf serum rather than charcoal-stripped fetal calf serum. However, with both types of growth medium, the sensitivity to tamoxifen was inversely related to the serum concentration, e.g., the 50%-inhibitory dose concentration increased 75-fold as the fetal calf serum concentration was increased from 0.25 to 10%. Addition of insulin to the culture medium had no effect on the growth rate, estrogen receptor content, or tamoxifen sensitivity of T-47D cells. These results illustrate that the conditions under which cells are cultured markedly affect their sensitivity to tamoxifen and highlight the need to specify these conditions when reporting effects of this drug.

Breast Neoplasms↗
PubMed1983

The interaction of estrogen- and antiestrogen-receptor complexes with polynucleotides.

As the polynucleotide domain of the estrogen receptor (Re) is a possible site for the modulation of Re activity, the interaction of antiestrogen (4-hydroxytamoxifen and tamoxifen)-receptor complexes (4-OH-Tam-Re and Tam-Re) with polynucleotides (oligodeoxynucleotide-cellulose, DNA-cellulose, and polyribonucleotide-agarose) was investigated and compared with that of the 17 beta-estradiol-receptor complex (E2-Re). E2-Re- and anti-Re-E2-complexes were optimally bound to oligo(dT)-cellulose and poly(U)-agarose at 0.15 M KCl and pH 7.6. Temperature activation of the Re was not required for these selective interactions to occur, but they were inhibited by 10 mM sodium molybdate. OH-Tam-Re and E2-Re demonstrated similar selectivity for different deoxynucleotide bases [oligo(dG) greater than oligo(dT) greater than or equal than oligo(dC) greater than oligo(dA) greater than or equal to oligo(dI)] and different ribonucleotide bases [poly(G) = poly(I) greater than poly(U) greater than poly(A) greater than or equal to poly(C)]. Quantitatively, Tam-Re bound significantly less to oligo(dT)-cellulose than did OH-Tam-Re, which did not differ significantly from E2-Re, a result probably related to the dissociation of the lower affinity ligand from the Re/oligo(dT)-cellulose during the assay procedure. Unoccupied Re also bound selectively to these synthetic polynucleotides. It is concluded that: 1) selective binding of Re to synthetic polynucleotides is inhibited by 10 mM sodium molybdate; 2) estradiol is not essential for selective binding to synthetic polynucleotides, since unoccupied Re was only slightly less efficiently bound than E2-Re; and 3) selective binding of Re to synthetic polynucleotides was unaffected by the agonist or antagonist properties of the ligand bound at the steroid-binding site. These data suggest that nonsteroidal antiestrogens are unlikely to exert their antagonist activity by modulating the function of the polynucleotide-binding site of Re.

Animals↗
PubMed1983

Antitumor activity of clomiphene analogs in vitro: relationship to affinity for the estrogen receptor and another high affinity antiestrogen-binding site.

The antitumor activity of three enclomiphene (trans-1- (p-beta-diethylaminoethoxyphenyl)1,2-diphenyl-2-chloroethylene) analogs and the cis isomer zuclomiphene was investigated in MCF 7 human mammary carcinoma cells in culture. Relative antitumor activity was compared with relative binding affinities (RBAs) for the nuclear estrogen receptor (RE; estradiol = 100%) and a microsomal antiestrogen-binding site (AEBS; tamoxifen = 100%) measured in cell-free extracts from MCF 7 cells. Modifications in the structure of the diethylaminoethoxy side chain influenced affinity of both RE and AEBS. Deethylation of the side chain (9599) reduced affinity for both sites by 65-70%, while a diethylaminoproproxy side chain (6866) resulted in a 3-fold increase in affinity for RE (enclomiphene = 2%; 6866 = 6%), but reduced the RBA for AEBS by 66% (enclomiphene = 140%; 6866 = 45%). Conversion of the ether linkage to an amine (10222) increased affinity for RE (10222 = 5%), but markedly reduced affinity for the AEBS (10222 = 15%). All five compounds inhibited the growth of MCF 7 cells in culture, but with markedly different potencies. At low doses (0.25-1.0 microM), where the growth-inhibitory effects were reversed by estradiol (except in the case of zuclomiphene), the relative antitumor activity (6866 greater than 10222 greater than enclomiphene greater than 9599 greater than zuclomiphene) was in the same order as RBA for RE. At higher doses (greater than 2.5 microM), where the growth-inhibitory effects were unaffected or partially reversed by estradiol, the relative potencies of these compounds as antitumor agents changed. Zuclomiphene became the most active, while the potency of enclomiphene increased relative to 6866 and 10222 (zuclomiphene greater than enclomiphene greater than 6866 greater than 10222 greater than 9599). At these doses, estrogen-irreversible antitumor activity was unrelated to affinity for RE, but showed some correlation with affinity for AEBS. It is concluded that the major effect of these compounds on mammary carcinoma growth in vitro is an estrogen-reversible growth-inhibitory effect, the magnitude of which is correlated with affinity for RE. However, studies with zuclomiphene and estrogen-irreversible doses of enclomiphene and 6866 indicate that these antiestrogens also influence cell proliferation in vitro by mechanisms that probably do not involve RE.

Antineoplastic Agents↗
PubMed1983

Effects of biologically active metabolites of tamoxifen on the proliferation kinetics of MCF-7 human breast cancer cells in vitro.

The effects of two major metabolites of tamoxifen, N-demethyltamoxifen (DMT) and 4-hydroxytamoxifen (4OHT), on MCF-7 cell proliferation and cell cycle kinetic parameters were compared with those of the parent compound. All three compounds produced dose-dependent decreases in the rate of cell proliferation which were accompanied by decreases in the percentage of S- and G2-M-phase cells. 4OHT was 100- to 167-fold more potent than both tamoxifen and DMT in producing these effects, and this was correlated with their relative binding affinities (RBAs) for the cytoplasmic estrogen receptor (ER) (17 beta-estradiol = 100, 4OHT = 41, tamoxifen = DMT = 2). At doses less than or equal to 2.5 microM, these effects were completely reversed by 17 beta-estradiol, but the required 17 beta-estradiol:antiestrogen concentration ratios differed, i.e., 1:10 to 1:1 for 4OHT compared with 1:1000 to 1:100 for tamoxifen and DMT. Although the concentrations of 17 beta-estradiol required for reversal were related to affinity of the metabolite for ER, they were 5- to 20-fold lower than predicted from the measured RBAs. When the rate of cell proliferation was measured over a range of concentrations of antiestrogen, in the presence or absence of 17 beta-estradiol, it was highly correlated (r2 = 0.96) with the percentage of S-phase cells. In addition to these 17 beta-estradiol-reversible events, all three compounds caused 17 beta-estradiol-irreversible cytotoxicity at higher concentrations (greater than or equal to 7.5 microM DMT and 4OHT, 10 microM tamoxifen). The order of potency in producing this effect was DMT greater than 4OHT greater than tamoxifen, which correlated with neither the RBAs for ER nor the RBAs for the high-affinity microsomal antiestrogen binding site. These data support the concept that estrogens and antiestrogens compete for a common event which regulates the rate of cell proliferation probably by controlling the proportion of cells entering S phase. Although it appears likely that ER is intimately involved in this regulatory process, 17 beta-estradiol-irreversible mechanisms are also involved in antiestrogen action in vitro.

Biotransformation↗
PubMed1981

A high-affinity binding site for the antioestrogens, tamoxifen and CI 628, in immature rat uterine cytosol which is distinct from the oestrogen receptor.

A high-affinity, saturable antioestrogen binding site, which does not bind oestradiol, has been reported to exist in a number of oestrogen target tissues but not in the immature rat uterus. This study reports the results of a more thorough search for this site in immature rat uterine cytosol. When concentrations of uterine cytoplasmic receptor were selectively depleted by translocation of 90-95% of the cytoplasmic oestrogen receptor to the nucleus, saturation analysis studies revealed that the antioestrogens, tamoxifen and CI 628, were bound to high-affinity, saturable binding sites which were present at about 2.5 times the concentration of the residual oestrogen receptor sites. Oestradiol could only partially inhibit the binding of tritiated antioestrogens to their saturable binding sites in this material indicating that a significant proportion of these sites were distinct from the oestrogen receptor sites. This was confirmed in experiments where oestrogen receptor sites were saturated in vitro with oestradiol and high-affinity, saturable sites for CI 628 and tamoxifen were still present. The CI 628 and tamoxifen had high affinity for these sites with dissociation constants of 1.0-1.6 nmol/l. These specific antioestrogen binding sites were present at about 5% of the concentration of oestrogen receptors in normal immature rat uterine cytosol which probably explains their previous lack of detections in this material.

Animals↗
PubMed1980

High-affinity anti-oestrogen binding site distinct from the oestrogen receptor.

Non-steroidal anti-oestrogens such as tamoxifen, CI 628, nafoxidine and clomiphene, are structurally related synthetic compounds that antagonize the effects of oestrogen on its target tissues, and this activity has led to the use of tamoxifen to treat advanced breast cancer. All these compounds inhibit the binding of tritiated oestradiol to cytosol from oestrogen target tissues, suggesting that anti-oestrogens bind to the oestrogen receptor. This is supported by reports that in the rat uterus and dimethyl-benz (alpha)-anthracene (DMBA)-induced rat mammary carcinoma, oestradiol and anti-oestrogens bind directly to the same number of saturable binding sites. Furthermore, oestrogens and anti-oestrogens are mutually competitive for binding to these sites. It has thus been generally accepted that the anti-oestrogens exert most of their effects through the specific oestrogen receptor. We now report a further high-affinity, anti-oestrogen binding site which may have a role in regulating the effects of non-steroidal anti-oestrogens.

Animals↗