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Query: UMLS:C0006142 (breast cancer)
 160,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Estrogen production by adipose tissue has been implicated in the etiology of such human cancers as endometrial and breast cancer. Estrogen production by adipose cells is subject to complex multifactorial regulation by a number of growth factors and cytokines, including those produced by breast cancer cells. In order to understand the mechanisms responsible for aromatase regulation, the structural gene encoding aromatase cytochrome P-450 (P-450AROM) was isolated from human genomic DNA. The gene spans at least 70 kb and is comprised of 10 exons, the first of which is untranslated. DNA sequence analysis indicates that the gene has a putative TATA (ATAAAA) sequence at -23 bp and putative CAAT binding sequences beginning at -41, -67, and -83 bp, that constitute a promoter region responsible for expression in placenta. However, this promoter does not appear to be responsible for expression in adipose, which may therefore be under the control of another, tissue-specific, promoter. Use of Polymerase Chain Reaction (PCR) technology has allowed for determination of expression of P-450AROM in samples of breast adipose. Preliminary results indicate that expression is highest in the upper lateral region, similar to the site of most frequent localization of tumors.
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PMID:The aromatase enzyme: from cloning to cancer. 213 92

Extraglandular conversion of C19 steroids to estrogens takes place primarily in the stromal cell component of adipose tissue and is catalyzed by aromatase cytochrome P450 (P450arom; the product of the CYP19 gene). CYP19 gene expression and aromatase activity in breast adipose stromal cells in culture are subject to complex hormonal regulation, which was recently found to be mediated in part by alternative use of tissue-specific promoters of the CYP19 gene. It has been proposed that increased local aromatase activity in breast adipose tissue may influence the growth of breast carcinomas. Using competitive RT-PCR, we quantified P450arom transcripts in breast adipose tissue from mastectomy specimens. In 10/15 patients, highest transcript levels were found in the quadrant where the tumor was located. We also found the highest proportions of adipose stromal cells versus adipocytes in those quadrants. Such findings suggest that regional differences in the relative proportions of the various histologic components give rise to locally elevated concentrations of estrogens. Although the initiating events are not known, once a neoplastic change has occurred, tumor growth may be promoted by the locally increased estrogen levels. We are currently investigating alternative promoter use for CYP19 gene transcription to explain this association. Our results underscore the importance of aromatase inhibitors as effective agents in treatment of hormone-responsive breast cancer, since aromatase inhibitors reduce local aromatase activity as well as blood estradiol levels.
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PMID:Aromatase gene expression in adipose tissue: relationship to breast cancer. 787 90

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

Extraglandular conversion of C19 steroids to estrogens takes place primarily in the stromal cell compartments of adipose tissue and is catalyzed by aromatase cytochrome P450 (P450arom, the product of the CYP19 gene). CYP19 gene expression and aromatase activity in breast adipose stromal cells in culture are subject to complex hormonal regulation, which was recently found to be mediated in part by alternative use of tissue-specific promoters of the CYP19 gene. It has been proposed that increased local aromatase activity in breast adipose tissue may influence the growth of breast carcinomas. Using competitive RT-PCR, we quantified P450arom transcripts in breast adipose tissue from mastectomy specimens. In 10 out of 15 patients, the highest transcript levels were found in the quadrant where the tumor was located. We also found the highest proportions of adipose stromal cells vs. adipocytes in these quadrants. These findings suggest that regional differences in the relative proportions of the histologic components give rise to local elevated concentrations of estrogens. Although the initiating events are not known, once a neoplastic change has occurred, tumor growth may be promoted by these locally increased estrogen levels. We are currently investigating alternative promoter use for CYP19 gene transcription to explain this association. Our results underscore the importance of aromatase inhibitors as effective agents in treatment of hormone-responsive breast cancer, since aromatase inhibitors reduce local aromatase activity as well as blood estradiol levels.
Breast Cancer Res Treat 1994
PMID:Regulation of aromatase expression in human tissues. 794 2

The conversion of androgens to estrogens occurs in a variety of cells and tissues, such as ovarian granulosa and testicular cells, placenta, adipose tissue, and various sites of the brain. The extragonadal synthesis of estrogens has great pathophysiological importance. Estrogens produced by, for example, adipose tissue have a role in the pathogenesis of certain forms of breast cancer and endometrial adenocarcinoma. The biosynthesis of estrogens is catalyzed by the aromatase, an enzyme localized in the endoplasmic reticulum that consists of two components: a cytochrome P450 (P450 Arom, P450 19 product of the CYP19 gene) and the NADPH cytochrome P450 reductase. The alignment of the amino acid sequences of human P450 19 with other mammalian P450s shows little sequence similarity, which indicates not only that P450 19 is a unique form of the P450 superfamily but also that the aromatase may be a good target for the development of selective P450 inhibitors. Aminoglutethimide (AG) is the pioneer drug of the reversible competitive nonsteroidal aromatase inhibitors. Since AG is a nonspecific aromatase inhibitor and presents some problems with tolerability, a number of structural analogues have been synthesized. For example, rogletimide is slightly less potent than AG but has the advantage of not inhibiting the cholesterol side-chain cleavage and is devoid of sedative action. Elongation of the ethyl substituent of AG and rogletimide leads to an increase in aromatase inhibition. Further studies led to the discovery of a new generation of much more potent aromatase inhibitors. An example is fadrozole. However, although fadrozole is a poor inhibitor of the cholesterol side-chain cleavage, it suppresses aldosterone release by ACTH-stimulated human adrenocortical cells. More selective aromatase inhibitors are the triazole derivatives. Examples are CGS 20267, CGS 47645, R 76 713, and ICI D1033. R 76 713's aromatase inhibitory effect is largely due to its (+)-S-enantiomer, vorozole. Computer modeling studies of the interaction of vorozole with part of the "I-helix" of P450 19 suggest that the chlorine-substituted phenyl ring of vorozole interacts with the gamma-carbonyl group of Glu-302. Thr-310, which corresponds to the highly conserved Thr-252 in P450 101, interacts with vorozole's triazole ring, and the 1-methyl-benzotriazole moiety binds near Asp-309.
Breast Cancer Res Treat 1994
PMID:Aromatase inhibitors--mechanisms for non-steroidal inhibitors. 794 4

Estrogen biosynthesis in adipose tissue has assumed great significance in terms of a number of estrogen-related diseases. Recent evidence suggests that estrogen synthesized locally in the breast is of singular significance in the development of breast cancer in elderly women. The biosynthesis of estrogen from C19 steroids is catalyzed by a specific form of cytochrome P450, namely aromatase cytochrome P450 (P450arom; the product of the CYP19 gene). The human CYP19 gene comprises nine coding exons, II-X, and its transcripts are expressed in the ovary, placenta, testes, adipose tissue, and brain. Tissue-specific expression of the CYP19 gene is determined, at least in part, by the use of tissue-specific promoters, which give rise to transcripts with unique 5'-noncoding termini. Transcripts in adipose tissue contain 5'-termini derived from specific untranslated exons, corresponding to expression derived from the proximal promoter II and its splice variant I.3, as well as a distal promoter, I.4. The object of the present study was to determine the distribution of these various exon-specific transcripts in breast adipose tissues from cancer-free women undergoing reduction mammoplasty and from patients with breast cancer, because this would provide important clues as to the nature of the factors regulating aromatase expression in these sites. To achieve this, we employed competitive RT-PCR, utilizing an internal standard for each exon-specific transcript of the CYP19 gene, as well as for the coding region, to evaluate total CYP19 gene transcripts. In cancer patients (n = 18), total CYP19 gene transcript levels were significantly higher in adipose tissue proximal to a tumor in comparison with adipose tissue distal to a tumor, in agreement with previous findings. Moreover, total transcript levels were higher in breast adipose tissue of cancer patients in comparison with those of cancer-free individuals (n = 9), even when the adipose tissue from the cancer patient was taken from a quadrant with no detectable tumor. We observed that exon I.4-specific transcripts were predominant in breast adipose obtained from cancer-free women. In this tissue, promoter-II-specific and exon I.3-specific transcripts were present in low copy number. On the other hand, in breast cancer patients, CYP19 gene transcripts from breast adipose tissue had primarily promoter-II-specific and exon I.3-specific sequence, whereas comparatively few transcripts had exon I.4-specific sequence at the 5'-terminus. We conclude that CYP19 gene transcription in breast adipose tissue of cancer-free individuals uses preferably promoter I.4, implicating a role of glucocorticoids and members of the IL-6 cytokine family in the regulation of this expression. On the other hand, the increased expression in breast adipose tissue bearing a carcinoma results from expression from promoters II and I.3, which are regulated by unknown factors acting via increased cAMP formation, which are presumably secreted by the tumor or associated cells.
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PMID:Use of alternative promoters to express the aromatase cytochrome P450 (CYP19) gene in breast adipose tissues of cancer-free and breast cancer patients. 892 26

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

The aromatase P450 (coded by the CYP19 gene) is responsible for the rate limiting step in the metabolism of C19 steroids to estrogens and is expressed in most breast carcinomas. A polymorphic tetranucleotide repeat (TTTA)n in intron 5, about 80 nucleotides downstream of exon 4 has previously been described. The allele frequencies of the polymorphic repeat were studied in series of 182 sporadic and 185 familial breast cancer patients as well as in 252 healthy control individuals. Five different alleles containing 7, 8, 9, 11 and 12-TTTA-repeats were detected. A relatively rare allele (A1) containing the longest repeat (TTTA)12 was found significantly more frequently in breast cancer patients than in control individuals. This indicates that individuals carrying the A1 allele of CYP19 may have an increased risk of developing breast cancer, OR 2.42 (95% confidence interval [CI] 1.03-5.80). The higher frequency was observed in both sporadic and familial patients, although when each of the groups was compared to the control group only a borderline significance was seen. A higher frequency of A1 allele carriers was also found in the group of patients with positive estrogen receptor and progesterone receptor positive tumors. These data suggest that the CYP19 gene may be involved as a low penetrance gene in breast cancer susceptibility.
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PMID:A rare CYP19 (aromatase) variant may increase the risk of breast cancer. 951 Nov 80

Estrogens play an important role in breast cancer development. Aromatase (CYP19), a cytochrome P450, is the enzyme that synthesizes estrogens. Aromatase is expressed at a higher level in human breast cancer tissue than in normal breast tissue using enzyme activity measurement, immunocytochemistry, and RT-PCR analysis. Cell culture, animal experiments using aromatase-transfected breast cancer cells, and transgenic mouse studies have demonstrated that in situ produced estrogen plays a more important role than circulating estrogens in breast tumor promotion. In addition, tumor aromatase has been shown to stimulate breast cancer growth in both an autocrine and a paracrine manner. RT-PCR and gene transcriptional studies have revealed that aromatase promoter switches from a glucocorticoid-stimulated promoter, I.4, in normal tissue to cAMP-stimulated promoters, I.3 and II, in cancereous tissue. Suppression of in situ estrogen biosynthesis can be achieved by the prevention of aromatase expression or by the inhibition of aromatase activity in breast tumors. While the control mechanism of aromatase expression in breast cancer tissue is not yet fully understood, aromatase-inhibitor therapy is considered for second-line treatment in patients who fail anti-estrogen therapy. Twenty to thirty percent of the patients who fail anti-estrogen treatment respond to aromatase-inhibitor treatment. Several potent and selective aromatase inhibitors have been developed and used to treat breast cancer. The binding nature of various aromatase inhibitors has been examined by computer modeling, site-directed mutagenesis of aromatase, and inhibition kinetics. The enzyme structure-function studies have led to the development of a computer model of the active site region of human aromatase. The model is used to evaluate the interaction of phytoestrogens such as flavones and isoflavones with aromatase. The study provides a molecular basis as to why isoflavones are significantly poorer inhibitors of aromatase than flavones. The phytoestrogen studies will help to determine which fruits and vegetables (those containing the appropriate phytoestrogens) should be included in the diet of postmenopausal women in order to reduce the incidence for breast cancer by inhibiting estrogen biosynthesis in breast tissue.
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PMID:Aromatase and breast cancer. 969 81

BREAST CANCER: HIGH PREVALENCE AND RISING INCIDENCE: Breast cancer is the most common form of cancer among women in Europe, North and South America and Australasia; approximately 1 in 10 women in Western countries will develop breast cancer during their lifetime. It is estimated that the disease will affect five million women worldwide over the next decade, and the incidence of breast cancer is increasing on average by about 1% per year in industrialized countries and at a greater rate in developing countries. COMPLEX ETIOLOGY: Although the specific etiology of breast cancer remains unknown, a number of factors are recognized which increase a woman's risk of developing the disease. Genetic predisposition, or family history of breast cancer, is known to be responsible for 5% of all cases. However, the variation in incidence throughout populations, and changes relating to population migration and adoption of altered lifestyles, all point to the critical importance of nongenetic determinants. Such factors include early menarche, late menopause, late age at birth of first child or nulliparity, a history of benign breast disease, and diet. There is also evidence that hormones play a major role in the etiology of breast cancer, with the risk of developing malignancies related to the cumulative exposure of the breast to estrogen and progesterone, which stimulate the growth of tumor cells. TREATMENT FOR EARLY BREAST CANCER: SURGERY -/+ ADJUVANT THERAPY: At the time of diagnosis, approximately 50% of patients will be diagnosed with early breast cancer. This proportion is increasing as a consequence of the introduction of early detection programs. Surgery remains the primary treatment for early breast cancer, and the frequency of radical mastectomy has been replaced by breast conserving surgery. After surgery, other therapeutic modalities such as radiation, chemotherapy or endocrine therapy may be given in the adjuvant setting. Surgical cure rates vary for patients with early breast cancer; the US figure is approximately 40%, and there are no definitive means to predict those who will be cured and those who will have recurrent disease. As a result, following primary surgical treatment, adjuvant therapy is usually recommended to destroy any remaining cancer cells at the primary site, to control micrometastases and to prolong disease-free survival, with the ultimate aim of providing an overall survival benefit. Upon disease recurrence in the remaining 60% of patients, endocrine therapy and chemotherapy represent the two general classes of treatment. One of the principle decisions to be taken in advanced breast cancer is which therapy to select in order to maximize patient benefit. The choice is largely dependent upon prognostic factors and whether the patient is pre- or postmenopausal. ENDOCRINE THERAPY OR CHEMOTHERAPY IN ADVANCED BREAST CANCER: Unlike chemotherapy, endocrine therapy is not cytotoxic and is therefore better tolerated by the patient. A recent study comparing therapy for prognostically different groups showed that patients benefiting most from the use of sequential endocrine agents are those regarded as low risk. The preferred sequence of treatment has been suggested to be tamoxifen followed by selective aromatase inhibitor and then a progestin. ENDOCRINES AND ENZYMES OFFER NEW TREATMENTS FOR ADVANCED BREAST CANCER: ESTROGEN-DRIVEN BREAST CANCER: Since 1896, when Sir George Beatson demonstrated that ovariectomy induced regression of mammary tumors in women, the aim of endocrine breast cancer therapy has been to selectively deprive the body of estrogen. Ovariectomy accomplished this by removing the gland that is the predominant source of estrogens in premenopausal women. Since the avoidance of such surgery is preferable, emphasis is devoted to the pharmacological inhibitors of estrogen production. ENDOCRINE PATHWAY REVEALS "ACHILLES' HEEL": Like other steroid hormones, the two circulating estrogens-estrone and estradiol-are produced from cholesterol. Inhibiting the enzymes that are involved at earlier steps in the branching pathway of steroidogenesis could have an undesirable impact on the production of other physiologically important hormones such as aldosterone and cortisol. Since aromatase catalyzes the last step in estrogen production, it makes an ideal target for the development of selective and potent inhibitors (Fig. 1). STRUCTURE OF AROMATASE REVEALS SECRETS OF SELECTIVE INHIBITION: Aromatase is a cytochrome P450 enzyme, with both an iron-containing and a steroid-binding site. The substrate, androstenedione, sits in the enzyme's steroid-binding site, that site which otherwise catalyzes the formation of estrogen. From this structural relationship, there are, therefore, two reasonable ways to inhibit aromatase: * by occupying the steroid-binding site of the enzyme with a compound such as formestane (Lentaron®), or * by binding the iron with nitrogen-containing compounds such as aminoglutethimide (Orimeten®), the oldest aromatase inhibitor. AROMATASE INHIBITORS: STEROIDAL AND NON-STEROIDAL: Formestane (Lentaron®) is the only commercially available steroidal compound which inhibits aromatase and must be administered parenterally. Other new aromatase inhibitors such as fadrozole (Afema®) and letrozole (Femara®) are orally active nitrogen-containing compounds that bind the heme iron of aromatase. AMINOGLUTETHIMIDE VERSUS LETROZOLE: OLD VERSUS NEW: Although aminoglutethimide has long been used to treat advanced breast cancer, its aromatase inhibition is not selective. Consequently, aminoglutethimide also binds to and thereby inhibits several other cytochrome P450 enzymes in the steroidogenesis pathway. An ideal aromatase inhibitor would fit the catalytic site of aromatase optimally and would thus interact only with aromatase. The affinity of letrozole (Femara®) for the heme group of aromatase makes it a selective and potent inhibitor (Fig. 2). In fact, studies show that Femara® has little effect on the other adrenal steroids, and is the most selective aromatase inhibitor available today.
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PMID:Molecular Action and Clinical Relevance of Aromatase Inhibitors. 1038 95


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