UMLS:C0476089 - FACTA Search

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Query: UMLS:C0476089 (endometrial cancer)
11,379 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tamoxifen (TXF), a triphenylethylene antiestrogen, is the major therapeutic agent for breast cancer. In rare cases, TXF treatment appears to increase incidence of endometrial cancer. Also in rats, TXF was found to induce hepatocellular carcinoma. Previous studies suggested that metabolism of TXF may contribute to its antiestrogenic and anticancer activity. The current study demonstrates a novel route of TXF metabolism. TXF is metabolized by rat and human liver microsomes into a reactive intermediate (txf*) which binds irreversibly to microsomal proteins. The binding requires NADPH and O2 and is inhibited by CO, inhibitors of P-450, and antibodies to rat NADPH-P450 reductase, indicating catalysis by P450. Phenobarbital treatment of rats markedly increases binding, suggesting the involvement of induced P450s. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins from incubation of [14C] TXF with phenobarbital-treated microsomes exhibits a major radiolabeled zone which corresponds to a molecular weight of approximately 54,000, suggesting binding to a P-450. Cysteine and glutathione inhibited the binding of TXF without significantly affecting P-450-mediated metabolism of TXF, possibly by reacting with txf* or by competing for the same binding sites. Exposure of phenobarbital-treated microsomes and control-microsomes to 50 degrees C for 90 s, which inactivates the flavin-containing monooxygenase (FMO), diminished binding and pH 8.6 enhanced binding. Also, alternate FMO substrates inhibited binding. These findings indicate that P-450 and possibly FMO catalyze the reactions leading to the formation of txf*. However, incubations with single-labeled and dual-radiolabeled tamoxifen or with [14C]TXF-N-oxide demonstrated that monodesmethyl-TXF and TXF-N-oxide, the principal P-450 and FMO-mediated metabolites, respectively, are not on the major route of txf* formation, indicating that txf* could not be an aldehyde derived from tamoxifen nitrone. Thus, though the structure of txf* was not characterized, certain possibilities were excluded. Speculations on the structure of txf* and on its possible pharmacological and toxicological activity are presented.
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PMID:Cytochrome P-450-mediated activation and irreversible binding of the antiestrogen tamoxifen to proteins in rat and human liver: possible involvement of flavin-containing monooxygenases in tamoxifen activation. 193 68

The biosynthesis of estrogens is catalyzed by aromatase P450 (P450arom), the product of the CYP19 gene. The tissue-specific expression of the CYP19 gene is regulated by means of tissue-specific promoters through the use of alternative splicing mechanisms. Thus, transcripts containing various 5'-untranslated termini are present in human placenta and other fetal tissues, ovary, brain, and adipose stromal cells. Sequence corresponding to untranslated exon 1.4 is present in 5'-termini of transcripts expressed in adipose tissue and fetal liver, as well as adipose stromal cells in primary culture in the presence of dexamethasone and fetal calf serum (FCS). Identification of hormone-responsive, tissue-specific promoter regions, as well as growth factor-response elements upstream of exon 1.4, may provide insight into the regulation of estrogen biosynthesis in adipose tissue, which is implicated in the development of breast and endometrial cancer. The goals of the present study were to define the 1.4 promoter region with respect to the start of transcription and to characterize the region(s) responsible for conferring glucocorticoid responsiveness on aromatase expression. The transcription initiation site was identified by means of primer extension and S1 nuclease protection analyses. No TATA-like sequence was evident upstream of this site. Various deletion mutations of the upstream flanking region of exon 1.4 and including part of exon 1.4 were made using polymerase chain reaction or restriction enzyme digestion. The genomic fragments were fused upstream of the chloramphenicol acetyltransferase (CAT) reporter gene. These constructs were transfected into adipose stromal cells and fetal hepatocytes in primary culture in medium containing FCS with or without dexamethasone. The -560/+10 base pair (bp) construct expressed CAT activity after a putative silencer element was deleted, and expression was induced by dexamethasone about 3-fold. Transfection of the -330/+170 bp construct, which contains an upstream glucocorticoid response element (GRE) as well as an Sp1-like sequence in untranslated exon 1.4, resulted in an 8-fold stimulation of expression of CAT activity by dexamethasone. The upstream GRE as well as the Sp1-like sequence in untranslated exon 1.4 were mutated separately, and together, to further confirm whether the GRE or Sp1 binding site play a role in the regulation of promoter 1.4-driven transcription. Mutation of either the GRE or Sp1 binding site, or both, in the -330/+170 bp construct, resulted in loss of dexamethasone-induced CAT reporter gene expression.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Characterization of the sequences of the human CYP19 (aromatase) gene that mediate regulation by glucocorticoids in adipose stromal cells and fetal hepatocytes. 777 80

The expression of P450 aromatase and other steroidogenic enzymes were evaluated in 42 endometrioid endometrial carcinomas, 23 endometrial hyperplasias, and 7 normal endometrial specimens. These findings were correlated with clinicopathological findings to elucidate the possible biological significance of in situ estrogen production in the development of human endometrial carcinoma. Only weak aromatase immunoreactivity was observed in vascular walls and myometrial cells. In contrast, strong aromatase stromal immunoreactivity was observed in 28 of 42 (66.7%) endometrial carcinomas. However, no stromal immunoreactivity was seen in normal or hyperplastic endometrial specimens. Immunoreactivity in the carcinoma stromal cells was significantly increased at sites of invasion. These aromatase-positive cells were immunohistochemically negative for other steroidogenic enzymes involved in estrogen biosynthesis. In situ hybridization studies revealed aromatase mRNA hybridization signals in stromal cells but not in carcinoma cells. The distribution of aromatase mRNA correlated well with the immunohistochemical localization of aromatase enzyme. Quantitation of aromatase activity demonstrated 8.75 +/- 2.75 pmol/hour/mg of protein for endometrial carcinomas (22 specimens) and 0.98 +/- 1.95 pmol/hour/mg of protein for normal endometrial specimens (4 specimens). Aromatase activity was found in both estrogen receptor-positive and -negative endometrial carcinomas. Aromatase did not vary with respect to the menopausal status of patients with endometrial carcinoma. These results suggest that estrogen is produced in situ in endometrial carcinoma but not in benign endometrial lesions. Such locally synthesized estrogen may act on carcinoma cells in a paracrine fashion to promote tumor growth. Additional investigations are necessary, but increased aromatase expression in the stromal cells of endometrial carcinoma may therefore play an important role in the development of human endometrioid endometrial carcinoma.
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PMID:Aromatase in human endometrial carcinoma and hyperplasia. Immunohistochemical, in situ hybridization, and biochemical studies. 785 58

Tamoxifen is the major therapeutic agent for the treatment of hormone-dependent breast cancer. Tamoxifen treatment appears to be associated with an increased incidence of endometrial carcinoma in humans and hepatocellular carcinoma in rats. These carcinogenic effects of tamoxifen might be induced by the formation of a tamoxifen reactive intermediate that binds covalently to macromolecules. Liver microsomal cytochrome P450s (CYPs) catalyze the metabolism of tamoxifen, forming a reactive intermediate that binds irreversibly to microsomal proteins, primarily to a 54 kDa protein (Mani, C. and Kupfer, D., Cancer Res., 51, 6052-6058, 1991). The current study identifies the P450 enzymes that catalyze the activation of tamoxifen to a reactive intermediate in rats and humans. Among the species examined, rats, chickens and humans demonstrate low tamoxifen binding activity, ranging from 0.1 to 0.4 nmol bound/mg protein/h. In contrast, hamsters and mice exhibit high binding, 1.2 and 1.6 nmol/mg protein/h respectively. Treatment of male rats with phenobarbital or pregnenolone-16 alpha-carbonitrile (PCN) markedly elevated the binding of tamoxifen to liver microsomal proteins. Methylcholanthrene treatment had no effect on binding. These findings suggested the involvement of CYP3A in catalysis of the covalent binding. Alternate substrates of CYP3A, cortisol and erythromycin, inhibited tamoxifen binding in liver microsomes from PCN- and phenobarbital-treated rats. Treatment of rats with troleandomycin (TAO), an inducer of CYP3A, followed by the dissociation of the TAO-CYP3A complex, elevated the covalent binding to liver microsomes approximately 3-fold. Antibodies against rat CYP3A1 strongly inhibited tamoxifen binding to liver microsomes from PCN- and phenobarbital-treated rats, whereas the antibodies anti-CYP2B1/2B2 did not inhibit binding. In humans, tamoxifen binding was inhibited by the anti-rat CYP3A1 IgG and also by alternate substrates of CYP3A. These results indicate that the activation of tamoxifen to a reactive intermediate by rat and human liver microsomes is principally catalyzed by CYP3A enzymes.
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PMID:Involvement of cytochrome P4503A in catalysis of tamoxifen activation and covalent binding to rat and human liver microsomes. 800 Dec 26

The conversion of C19 steroids to estrogens occurs in a number of tissues, such as the ovary and placenta, and is catalyzed by aromatase P450 (P450arom; the product of the CYP19 gene). P450arom expression has also been detected in a number of uterine tumors, such as leiomyomas and endometrial cancer. On the other hand, P450arom expression was undetectable in normal endometrial and myometrial tissues. The present study was conducted to determine the presence or absence of aromatase expression in peritoneal endometriotic implants and in the eutopic endometrium of women with endometriosis. Endometriotic implants in pelvic peritoneum (n = 17; e.g. posterior culdesac, bladder, and anterior culdesac) and eutopic endometrial curettings (n = 11) of 14 patients with histologically documented pelvic endometriosis were obtained at the time of laparoscopy or laparotomy. Pelvic peritoneal biopsies distal to endometriotic implants as well as normal endometrial tissues (n = 7) from disease-free women were used as negative controls. We used competitive RT-PCR technology employing an internal standard to amplify P450arom transcripts in total ribonucleic acid (RNA) isolated from these tissues. P450arom transcripts were detected in all endometriotic implants and in all eutopic endometrial tissues from patients with endometriosis. P450arom messenger RNA species were not detectable in endometrial tissues from disease-free women or in endometriosis-free peritoneal tissues. The highest levels of transcripts were detected in an endometriotic implant that involved the full thickness of the anterior abdominal wall. The P450arom transcript level within the core of this endometriotic mass was 4-fold higher than that in the surrounding adipose tissue. It has been shown recently that aromatase expression in various human tissues is regulated by the use of tissue-specific promoters via alternative splicing. To analyze promoter usage, we amplified by RT-PCR the most likely promoter-specific untranslated 5'-termini of P450arom transcripts in 2 endometriotic implants. It appears that these endometriotic implants use both the adipose-type promoter I.4 and gonadal-type promoter II for aromatase expression. The use of promoter I.4 for aromatase expression in adipose tissue has been recently observed to be regulated by members of the interleukin-6 (IL-6) cytokine family. Based on these findings, we examined by RT-PCR, IL-6 and IL-11 messenger RNA expression in 5 endometriotic tissues and 1 eutopic endometrial sample from a patient with endometriosis. We detected IL-6 and IL-11 transcripts in all endometriotic tissues and in the eutopic endometrial tissue sample studied. Our findings indicate that both eutopic endometrial tissues and endometriotic implants from patients with endometriosis are biochemically different from normal endometrial tissues of disease-free women. The presence of aromatase expression in eutopic endometrial tissues from patients with endometriosis may be related to the capability of implantation of these tissues on peritoneal surfaces. Furthermore, the possibility of estrogen production in these implants may serve to promote their growth. Increased IL-6 and IL-11 expression in these tissues suggests that P450arom expression in endometriosis may be regulated in part by these cytokines.
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PMID:Aromatase expression in endometriosis. 855 Jul 48

Aromatase P450 (P450arom) is responsible for conversion of C19 steroids to estrogens in a number of human tissues, such as the placenta, gonads, adipose tissue, skin and the brain. Aromatase expression in human tissues is regulated by use of alternative promoters in the placenta (promoter I.1), adipose tissue (promoters I.4, I.3 and II) and gonads (promoter II). Aromatase expression is absent in the disease-free adult liver, adrenal and uterine tissues. Excessive or inappropriate aromatase expression in adipose fibroblasts and endometriosis-derived stromal cells, as well as in testicular, hepatic, adrenal and uterine tumors, is associated with abnormally high circulating estrogen levels and/or with increased local estrogen concentrations in these tissues. Whether systemically delivered or locally produced, elevated estrogen levels will in turn promote the growth of hormone-responsive tissues. We recently studied aromatase expression in testicular tumor and adipose tissue samples from prepubertal boys with gynecomastia, in hepatocellular cancer and adrenocortical tumor samples from adult men with gynecomastia, in breast adipose tissue samples proximal to breast tumors, and in endometrial cancer, leiomyoma and endometriosis tissues. Excessive aromatase activity and P450arom transcript levels were found in these tissue samples or in cultured cells derived from these tissues. In these neoplastic or non-neoplastic tissues or cells, the regulation of aromatase expression was studied in terms of alternative promoter use, both in vivo and in response to various hormonal stimuli. Our results were suggestive of a common metabolic abnormality associated with activation of a cyclic AMP-dependent signalling pathway that gives rise to transcriptional transactivation of aromatase expression via promoters I.3 and II in all of the above tissues. This article describes the common pathophysiological and molecular features of excessive aromatase expression in these disease states.
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PMID:Endocrine disorders associated with inappropriately high aromatase expression. 936 82

Estrogen biosynthesis in adipose tissue increases with age and obesity, and has been implicated in the development of endometrial cancer and breast cancer. In normal human adipose tissue, expression of the CYP19 gene which encodes aromatase P450, the enzyme responsible for estrogen biosynthesis, is regulated by a distal promoter, namely promoter I.4. Stimulation of expression in adipose stromal cells by members of the type 1 cytokine family, i.e. interleukin (IL)-6, IL-11, leukemia inhibitory factor (LIF) and oncostatin M (OSM), is mediated via a Jak-STAT3 signaling pathway and a GAS element upstream of promoter I.4. In contrast, aromatase expression in breast adipose tissue proximal to tumor is increased three- to four-fold to the utilization of another promoter, namely promoter II, proximal to the translation initiation site. In the present report, we show that prostaglandin (PG) E2 is the most potent factor which stimulates aromatase expression via cyclic AMP and promoter II. PGE2 acts via EP1 and EP2 receptor subtypes to stimulate both the PKC and PKA pathways. The combined stimulation of both of these pathways results in the maximal expression of promoter II-specific CYP19 transcripts. Because PGE2 is a major secretory product both of breast tumor epithelial cells and fibroblasts, as well as of macrophages infiltrating the tumor site, then this could be the mechanism whereby estrogen biosynthesis is stimulated in breast sites adjacent to a tumor, leading in turn to increased growth and development of the tumor itself.
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PMID:Transcriptional regulation of CYP19 gene (aromatase) expression in adipose stromal cells in primary culture. 936 91

Although tamoxifen is approved for the treatment of hormone-dependent breast cancer as well as for the prevention of breast cancer in high-risk women, several studies in animal models have shown that tamoxifen is heptocarcinogenic, and in humans, tamoxifen has been associated with an increased risk of endometrial cancer. One potential mechanism of tamoxifen carcinogenesis could involve metabolism of tamoxifen to 3,4-dihydroxytamoxifen followed by oxidation to a highly reactive o-quinone which has the potential to alkylate and/or oxidize cellular macromolecules in vivo. In the study presented here, we synthesized the 3,4-dihydroxytamoxifen, prepared its o-quinone chemically and enzymatically, and studied the reactivity of the o-quinone with GSH and deoxynucleosides. The E (trans) and Z (cis) isomers of 3,4-dihydroxytamoxifen were synthesized using a concise synthetic pathway (four steps). This approach is based on the McMurry reaction between the key 4-(2-chloroethoxy)-3,4-methylenedioxybenzophenone and propiophenone, followed by selective removal of the methylenedioxy ring of (E, Z)-1-[4-[2-(N,N-dimethylamino)ethoxy]phenyl]-1-(3, 4-methylenedioxyphenyl)-2-phenyl-1-butene with BCl(3). Oxidation of 3,4-dihydroxytamoxifen by activated silver oxide or tyrosinase gave 3,4-dihydroxytamoxifen-o-quinone as a mixture of E and Z isomers. The resulting o-quinone has a half-life of approximately 80 min under physiological conditions. Reaction of the o-quinone with GSH gave two di-GSH conjugates and three mono GSH conjugates. Incubation of 3,4-dihydroxytamoxifen with GSH in the presence of microsomal P450 gave the same GSH conjugates which were also detected in incubations with human breast cancer cells (MCF-7). Reaction of 3, 4-dihydroxytamoxifen-o-quinone with deoxynucleosides gave only thymidine and deoxyguanosine adducts; neither deoxyadenosine nor deoxycytosine adducts were detected. Preliminary studies conducted with human breast cancer cell lines showed that 3, 4-dihydroxytamoxifen exhibited cytotoxic potency similar to that of 4-hydroxytamoxifen and tamoxifen in an estrogen receptor negative (ER(-)) cell line (MDA-MB-231); however, in the ER(+) cell line (MCF-7), the catechol metabolite was about half as toxic as the other two compounds. Finally, in the presence of microsomes and GSH, 4-hydroxytamoxifen gave predominantly quinone methide GSH conjugates as reported in the previous paper in this issue [Fan, P. W., et al. (2000) Chem. Res. Toxicol. 13, XX-XX]. However, in the presence of tyrosinase and GSH, 4-hydroxytamoxifen was primarily converted to o-quinone GSH conjugates. These results suggest that the catechol metabolite of tamoxifen has the potential to cause cytotoxicity in vivo through formation of 3,4-dihydroxytamoxifen-o-quinone.
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PMID:Synthesis and reactivity of a potential carcinogenic metabolite of tamoxifen: 3,4-dihydroxytamoxifen-o-quinone. 1064 67

Tamoxifen is a major drug used for adjuvant chemotherapy of breast cancer; however, its use has been associated with a small but significant increase in risk of endometrial cancer. In rats, tamoxifen is a hepatocarcinogen, and DNA adducts have been observed in both rat and human tissues. Tamoxifen has been shown previously to be metabolized to reactive products that have the potential to form protein and DNA adducts. Previous studies have suggested a role for P450 3A4 in protein adduct formation in human liver microsomes, via a catechol intermediate; however, no clear correlation was seen between P450 3A4 content of human liver microsomes and adduct formation. In the present study, we investigated the P450 forms responsible for covalent drug-protein adduct formation and the possibility that covalent adduct formation might occur via alternative pathways to catechol formation. Recombinant P450 3A4 catalyzed adduct formation, and this correlated with the level of uncoupling in the P450 incubation, consistent with a role of reactive oxygen species in potentiating adduct formation after enzymatic formation of the catechol metabolite. Whereas P450s 1A1, 2D6, and 3A5 generated catechol metabolite, no covalent adduct formation was observed with these forms. By contrast, P450 2B6, 2C19, and rat liver microsomes catalyzed drug-protein adduct formation but not catechol formation. Drug protein adducts formed specifically with P450 3A4 in incubations using membranes isolated from bacteria expressing P450 3A4 and reductase, as well as in reconstitutions of purified 3A4, suggesting that the electrophilic species reacted preferentially with the P450 enzymes concerned.
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PMID:Bioactivation of tamoxifen by recombinant human cytochrome p450 enzymes. 1201 81

To investigate expression of steroidogenic enzymes involved in androgen and estrogen synthesis in the stroma of postmenopausal ovaries.Ovarian stromal tissue samples were obtained at hysterectomy from postmenopausal women who had hysterectomy and oophorectomy. Tissues were frozen immediately in liquid nitrogen and kept frozen until RNA was extracted. Total RNA was examined by Northern blot analysis using (32)P-labeled cDNA probes encoding human P450 side chain cleavage (P450(SSC)), P450(17alpha), and cytochrome P450 aromatase (P450(arom)). Concentrations of mRNA encoding cytochrome P450(SSC), cytochrome P450 17alpha-hydroxylase (CYP17), and P450(arom) were determined in the ovarian stroma. We detected P450(SSC) mRNA in all postmenopausal ovaries studied. P450(SSC) mRNA was increased threefold in the ovarian stroma of postmenopausal women with endometrial cancer and endometrial hyperplasia. CYP17 mRNA was detected in the ovarian stroma of all women with endometrial cancer. P450(arom) mRNA was not detected in the ovaries studied. Postmenopausal ovaries possess enzymes for initiation of steroidogenesis. Enzymes essential for androgen synthesis were expressed in the ovarian stroma of postmenopausal women with endometrial cancer or hyperplasia.
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PMID:Expression of messenger ribonucleic acid encoding steroidogenic enzymes in postmenopausal ovaries. 1251 92

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