Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Estradiol is converted to catechol estrogens via 2- and 4-hydroxylation by cytochrome P450 enzymes. 4-Hydroxyestradiol elicits biological activities distinct from estradiol, most notably an oxidant stress response induced by free radicals generated by metabolic redox cycling reactions. In this study, we have examined 2- and 4-hydroxylation of estradiol by microsomes of human uterine myometrium and of associated myomata. In all eight cases studied, estradiol 4-hydroxylation by myoma has been substantially elevated relative to surrounding myometrial tissue (minimum, 2-fold; mean, 5-fold). Estradiol 2-hydroxylation in myomata occurs at much lower rates than 4-hydroxylation (ratio of 4-hydroxyestradiol/2-hydroxyestradiol, 7.9 +/- 1.4) and does not significantly differ from rates in surrounding myometrial tissue. Rates of myometrial 2-hydroxylation of estradiol were also not significantly different from values in patients without myomata. We have used various inhibitors to establish that 4-hydroxylation is catalyzed by a completely different cytochrome P450 than 2-hydroxylation. In myoma, alpha-naphthoflavone and a set of ethynyl polycyclic hydrocarbon inhibitors (5 microM) each inhibited 4-hydroxylation more efficiently (up to 90%) than 2-hydroxylation (up to 40%), indicating > 10-fold differences in Ki (<0.5 microM vs. > 5 microM). These activities were clearly distinguished from the selective 2-hydroxylation of estradiol in placenta by aromatase reported previously (low Km, inhibition by Fadrozole hydrochloride or ICI D1033). 4-Hydroxylation was also selectively inhibited relative to 2-hydroxylation by antibodies raised against cytochrome P450 IB1 (rat) (53 vs. 17%). These data indicate that specific 4-hydroxylation of estradiol in human uterine tissues is catalyzed by a form(s) of cytochrome P450 related to P450 IB1, which contribute(s) little to 2-hydroxylation. This enzyme(s) is therefore a marker for uterine myomata and may play a role in the etiology of the tumor.
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PMID:4-Hydroxylation of estradiol by human uterine myometrium and myoma microsomes: implications for the mechanism of uterine tumorigenesis. 756 5

There is convincing evidence that a reduced expression of the E-cadherin cell-cell adhesion molecule associates with low tumor grade and poor prognosis in prostate cancer patients. However, little is known on how E-cadherin levels are regulated in human prostate cancer cells. We have inspected the effect of both androgens and estrogen on the expression of E-cadherin in the hormone-responsive LNCaP prostate tumor cell line, which is endowed with both androgen and estrogen receptors. Using both Dot Blot analysis and immunocytochemistry we have observed that either steroid significantly increased E-cadherin levels in these cells; this effect was not reversed by the simultaneous addition of the relevant antagonist, hydroxyflutamide or ICI-182,780.
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PMID:Sex steroids up-regulate E-cadherin expression in hormone-responsive LNCaP human prostate cancer cells. 762 77

The actions of 17 beta-estradiol (E2) and protein kinase C (PKC) appear to converge in the regulation of expression of certain growth modulatory genes, such as the growth factor amphiregulin (AR). AR is known to modulate cell growth by binding to the epidermal growth factor receptor. In the current report we established the mechanisms of the PKC-activating phorbol ester tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) and the steroid hormone E2 on the induction of AR expression in human breast carcinoma cell lines. TPA (100 nM) and E2 (1 nM) induce AR messenger RNA (mRNA) expression by 6- to 8-fold and 3- to 6-fold, respectively, in a time- and dose-dependent manner. In addition, immunoreactive AR protein is induced by both TPA and E2 by 6- to 8-fold and 2- to 4-fold, respectively. The PKC-modulating drugs, bryostatin and H-7, and antiestrogens (ICI 164,384 and 4-hydroxytamoxifen) interfere with AR induction by TPA and estrogen, respectively. The effects of TPA and E2 on the induction of AR mRNA were both closely associated with enhanced transcription of the AR gene. However, TPA had an additional effect at the posttranscriptional level by stabilizing the AR mRNA. The protein synthesis inhibitor, cycloheximide, prevented AR induction by TPA, suggesting that a component of the TPA induction of AR is indirect and dependent upon protein synthesis. Conversely, the E2 induction of AR transcription was found to be a direct response, independent of protein synthesis. The results presented herein thus demonstrate that TPA and E2 are able to stimulate AR gene transcription by two separate mechanisms.
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PMID:Estrogen and phorbol esters regulate amphiregulin expression by two separate mechanisms in human breast cancer cell lines. 764 7

Our recent studies have shown that the cellular gene at the mouse mammary tumor virus (MMTV) integration site in the int-5 locus in BALB/c D2 precancerous hyperplastic alveolar nodules is identical to the gene encoding aromatase (CYP19), a member of the cytochrome P450 gene superfamily. MMTV integrated within the 3' untranslated region of the aromatase gene is responsible for the overexpression of this gene (int-5/aromatase) in mammary tumors. This paper describes the biological significance of overexpression of int-5/aromatase in D2 tumor cells. Using a cell line derived from the D2 tumor, we have demonstrated the effect of the aromatase substrate, androstenedione, on the proliferation of tumor cells. Proliferative effects of androstenedione were blocked by an aromatase inhibitor, providing evidence for the role of int-5/aromatase in this process. Furthermore, the androstenedione-mediated proliferation was inhibited by the addition of anti-estrogen ICI 164,384, suggesting that the estrogen formed from the conversion of androstenedione by int-5/aromatase acts like a mitogen to stimulate the growth of D2 tumor cells. This model with its known mechanism of aromatase activation should prove useful for studying the role of intra-tumoral estrogen in mammary cancer, for evaluating the effects of aromatase inhibitors, and for comparing breast cancer treatments.
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PMID:The overexpression of int-5/Aromatase, a novel MMTV integration locus gene, is responsible for D2 mammary tumor cell proliferation. 787 87

The MVLN cell line was established in our laboratory from MCF-7 cells by stable transfection with the luciferase gene under the control of an estrogen-responsive element from the Xenopus vitellogenin A2 gene. This cell line allowed us to visualize the induction by hydroxytamoxifen of a heterogeneity in the cell population with regard to the expression of the luciferase gene. Treated cells lost their estradiol-inducible luciferase activity, progressively and irreversibly; the luciferase expression of 80% of the cells was irreversibly inactivated by a 12-day hydroxytamoxifen treatment. We showed that this inactivation process was specific for an estrogenic response and was mediated by the estrogen receptor. Tamoxifen itself gave rise to such an inactivation, whereas other compounds belonging to the triphenylethylenic family but differently substituted on the ethylenic carbon and the ICI 164,384 compound were not as efficient. This irreversible inactivation was accompanied by a sharp decrease in the luciferase mRNA level; however, the estrogen receptor function and the cellular transcriptional machinery were not affected by the treatment. Although this antiestrogen treatment neither affected the estrogen-dependent cell growth nor irreversibly inhibited the expression of the natural pS2 gene, these results highly suggest that long-term antiestrogen therapy may lead to some heterogeneity in tumor cells throughout the course of patient treatment.
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PMID:Hydroxytamoxifen induces a rapid and irreversible inactivation of an estrogenic response in an MCF-7-derived cell line. 795 15

The acquired ability of tamoxifen to stimulate tumor growth has been suggested as one mechanism for the development of treatment failure in breast cancer. We have reported that tamoxifen-stimulated MCF-7 breast tumors in nude mice display reduced tamoxifen levels as compared with tamoxifen-inhibited tumors and an altered metabolite profile with isomerization of trans-4-hydroxytamoxifen to a weak antiestrogen and the production of metabolite E, an estrogenic metabolite. To investigate further the importance of tamoxifen metabolism in this model, we quantified levels of tamoxifen and major metabolites in tamoxifen-stimulated as compared with tamoxifen-inhibited MCF-7 tumors growing in nude mice and employed tamoxifen analogs resistant to metabolism. Tamoxifen-stimulated tumors have a relative abundance of cis-4-hydroxytamoxifen and metabolite E. However, in vivo treatment of mice carrying tamoxifen-stimulated tumors with fixed-ring nonisomerizable tamoxifen analogs or with nafoxidine, a nonsteroidal antiestrogen with a different structure, nonetheless resulted in tumor growth stimulation. Tumors were also stimulated by a deoxytamoxifen analog resistant to conversion to metabolite E. Growth of tamoxifen-stimulated tumors was inhibited by a pure steroidal antiestrogen, ICI 182,780, suggesting the need for clinical trials of this drug in patients with tamoxifen resistance. Growth of tamoxifen-stimulated tumors was further stimulated by estrogen replenishment, and this estrogen stimulation could be blocked by tamoxifen indicating that tamoxifen has both agonist and antagonist properties in these tumors. This study suggests that tamoxifen-stimulated tumor growth in this model is not due to isomerization or metabolism of tamoxifen to less antiestrogenic or more estrogenic metabolites. The mechanisms by which tamoxifen acquires more potent in vivo agonist properties, resulting in tumor growth stimulation over time, remain to be defined.
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PMID:The importance of tamoxifen metabolism in tamoxifen-stimulated breast tumor growth. 819 71

Estrogen-induced uterine insulin-like growth factor I (IGF-I) expression has been demonstrated to mediate at least in part the uterotrophic action of estradiol. We studied the effects of tamoxifen, a partial antagonist to the estrogen receptor widely used in the treatment of breast cancer, and ICI 182780, a pure antagonist to the estrogen receptor, on uterine weight and uterine IGF-I gene expression in the rat. Tamoxifen increased uterine weight to 125% of control values and doubled uterine IGF-I expression. In contrast, ICI 182780 reduced uterine weight to 60% of control and uterine IGF-I gene expression to 13% of control. These results demonstrate for the first time that uterine IGF-I expression is a molecular marker that correlates with the effects of partial agonists and antagonists to the estrogen receptor on the uterus. Furthermore, the induction of uterine IGF-I expression by tamoxifen provides a molecular mechanism to account for the uterotrophic effects which are commonly seen with tamoxifen therapy and which have been associated with endometrial neoplasia.
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PMID:Insulin-like growth factor I gene expression in the uterus is stimulated by tamoxifen and inhibited by the pure antiestrogen ICI 182780. 824 6

A substantial proportion of patients with breast cancer are treated with the antioestrogen tamoxifen. As with other endocrine therapies, clinical experience has shown that some tumours in which growth is initially attenuated by tamoxifen treatment become resistant to continued drug treatment and resume growth. The mechanisms underlying the development of tamoxifen resistance have yet to be described but represent an important focus of research with the aim of defining what other therapies might be effective following tamoxifen treatment. Secondly, an understanding of tamoxifen resistance might suggest means to develop more effective agents for primary treatment of the disease. The development of pure antioestrogens, for example ICI 164,384 and ICI 182,780, which differ pharmacologically from tamoxifen in being entirely free of oestrogen partial-agonist activity, together with cell and animal models of tamoxifen resistant human breast cancer, has revealed one mechanism which might be of considerable clinical significance. Pure antioestrogens were shown to inhibit the proliferation of a greater proportion of tumor cells than tamoxifen in vitro, a differential effect that was attributed to the oestrogenic activity of tamoxifen. Subsequently, cell culture studies have shown that breast cancer cell lines selected for resistance to tamoxifen can still remain sensitive to the growth inhibitory action of pure antioestrogens. Similarly, the growth of human breast tumours in nude mice, which is initially attenuated by tamoxifen but then resumes, can be inhibited by pure antioestrogens. Both types of experiment are consistent with the view that tamoxifen resistance in these model systems is due to the oestrogenic action of tamoxifen. Thus, it can be predicted that in some patients whose tumours recur during tamoxifen therapy, a further response to pure antioestrogen treatment might occur. Studies to examine this hypothesis are currently being undertaken with ICI 182,780. One mechanism which might account for the experimental observations is an intrinsic heterogeneity amongst breast tumour cells in their response to tamoxifen, i.e. that there are at least two different populations of cells; one population which responds to tamoxifen as an antioestrogen and one which "reads" tamoxifen as an oestrogen. The growth advantage thus conferred on the latter population would lead to its predominance. If this is what actually happens in a proportion of human tumours, it can be argued that primary treatment of the tumour with a pure antioestrogen, rather than tamoxifen, would be preferred since a more complete and longer-lasting response would be predicted. Recent comparative studies with human breast tumours grown in nude mice support these predictions.
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PMID:Are breast tumours resistant to tamoxifen also resistant to pure antioestrogens? 827 23

We have conducted a clinical trial of a novel pure antiestrogen, 7 alpha-[9-(4,4,5,5,5-pentafluoropentylsulfinyl)nonyl]estra-1,3,5,(1 0)-triene-3,17 beta-diol (ICI 182780), to assess its tolerance, pharmacokinetics, and short term biological effects in women with primary breast cancer. Fifty-six patients were randomized to either a control group (n = 19), in which they received no preoperative treatment, or a treatment group (n = 37), in which they received daily i.m. injections of ICI 182780 at doses of 6 mg (n = 21) or 18 mg (n = 16) for 7 days prior to primary breast surgery. Serum drug concentrations, gonadotropin levels, and sex hormone-binding globulin levels were measured during the study period by radioimmunoassay. Expression of estrogen receptors (ER), progesterone receptors, the estrogen-induced protein pS2, and the cell proliferation-related antigen Ki67 was determined immunocytochemically in pre- and poststudy tumor samples. Treatment with ICI 182780 caused no serious drug-related adverse events and had no effect on serum gonadotropin or sex hormone-binding globulin levels. Minor adverse events occurred in 5 patients receiving the 6-mg dose and 3 patients receiving the 18-mg dose. The serum concentration of ICI 182780 was dose dependent but showed variation between individuals. There was evidence of an approximately 3-fold drug accumulation over the short treatment period but steady state levels were not reached by the end of the 7 days. In patients with ER-positive tumors, treatment with ICI 182780 was associated with significant reductions in the tumor expression of ER (median ER index, 0.72 before versus 0.02 after treatment; P < 0.001), progesterone receptor (median progesterone receptor index, 0.50 before versus 0.01 after treatment; P < 0.05), and Ki67 (median Ki67 labeling index, 3.2 before versus 1.1 after treatment; P < 0.05). Treatment with ICI 182780 also resulted in a significant reduction in pS2 expression (P < 0.05) but this appeared unrelated to tumor ER status. In conclusion, ICI 182780 was well tolerated after short term administration and produced demonstrable antiestrogenic effects in human breast tumors in vivo, without showing evidence of agonist activity. These properties identify ICI 182780 as a candidate agent with which to evaluate whether a pure estrogen antagonist offers any additional benefit in the treatment of human breast cancer over conventional nonsteroidal antiestrogens, typified by tamoxifen, which exhibit variable degrees of agonist activity.
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PMID:Investigation of a new pure antiestrogen (ICI 182780) in women with primary breast cancer. 827 77

Estrogen is essential for the growth of the normal mammary gland and most estrogen receptor (ER)-positive mammary carcinomas. To better understand the differences between the estrogen response pathways in normal and tumor cells, we have stably transfected ER-negative immortal, nontumorigenic human mammary epithelial cells and ER-negative breast cancer cells with an ER-encoding expression vector. Unexpectedly, estrogen treatment (1.0 nM) inhibited the proliferation of ER-transfected nontumorigenic and tumor-derived cells. The control transfectants and parental cells exhibited no response to estrogen concentrations as high as 1.0 microM. This inhibitory effect was attributed to a decreased growth rate and a perturbation of the cell cycle distribution by estrogen treatment of the ER transfectants. The inhibitory response was blocked by cotreatment with the antiestrogen ICI 164,384 as predicted for a pure antagonist of estrogen action. However, treatment with the antiestrogen hydroxytamoxifen caused growth inhibition, implying that hydroxytamoxifen acts as an agonist of estrogen action in ER-transfected cells. Since estrogen is a mitogenic and not a growth-inhibitory stimulus for ER-positive breast cancers and cell lines, we tested the effect of constitutive, high level expression of the ER in ER-positive tumor cells. Stable transfection of ER-positive MCF-7 and T47D cells with the ER expression vector yielded cells with varying amounts of ER. At ER levels comparable to those found in the ER-negative transfected cells, the MCF-7 and T47D ER transfectants were not inhibited by estrogen. These data suggest that ER-positive breast cancer cells can tolerate higher constitutive levels of ER expression than ER-negative cells. The mechanism by which this is accomplished may be an essential step in the process which yields ER-positive tumors.
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PMID:Estrogen inhibits the growth of estrogen receptor-negative, but not estrogen receptor-positive, human mammary epithelial cells expressing a recombinant estrogen receptor. 840 91


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