Properties of estrogen and hydroxysteroid sulphotransferases in human mammary cancer

Recent insight on the control of enzymes involved in estrogen formation and transformation in human breast cancer

The great majority of breast cancers are in their early stage hormone-dependent and it is well accepted that estradiol (E2) plays an important role in the genesis and evolution of this tumor. Human breast cancer tissues contain all the enzymes: estrone sulfatase, 17beta-hydroxysteroid dehydrogenase, aromatase involved in the last steps of E2 bioformation. Sulfotransferases which convert estrogens into the biologically inactive estrogen sulfates are also present in this tissue. Quantitative data show that the 'sulfatase pathway', which transforms estrogen sulfates into the bioactive unconjugated E2, is 100-500 times higher than the 'aromatase pathway', which converts androgens into estrogens. The treatment of breast cancer patients with anti-aromatases is largely developed with very positive results. However, the formation of E2 via the 'sulfatase pathway' is very important in the breast cancer tissue. In recent years it was found that antiestrogens (e.g. tamoxifen, 4-hydroxytamoxifen), various progestins (e.g. promegestone, nomegestrol acetate, medrogestone, dydrogesterone, norelgestromin), tibolone and its metabolites, as well as other steroidal (e.g. sulfamates) and non-steroidal compounds, are potent sulfatase inhibitors. In another series of studies, it was found that E2 itself has a strong anti-sulfatase action. This paradoxical effect of E2 adds a new biological response of this hormone and could be related to estrogen replacement therapy in which it was observed to have either no effect or to decrease breast cancer mortality in postmenopausal women. Interesting information is that high expression of steroid sulfatase mRNA predicts a poor prognosis in patients with +ER. These progestins, as well as tibolone, can also block the conversion of estrone to estradiol by the inhibition of the 17beta-hydroxysteroid dehydrogenase type I (17beta-HSD-1). High expressison of 17beta-HSD-1 can be an indicator of adverse prognosis in ER-positive patients. It was shown that nomegestrol acetate, medrogestone, promegestone or tibolone, could stimulate the sulfotransferase activity for the local production of estrogen sulfates. This is an important point in the physiopathology of this disease, as it is well known that estrogen sulfates are biologically inactive. A possible correlation between this stimulatory effect on sulfotransferase activity and breast cancer cell proliferation is presented. In agreement with all this information, we have proposed the concept of selective estrogen enzyme modulators (SEEM). In conclusion, the blockage in the formation of estradiol via sulfatase, or the stimulatory effect on sulfotransferase activity in combination with anti-aromatases can open interesting and new possibilities in clinical applications in breast cancer.

The selective estrogen enzyme modulators in breast cancer: a review

It is well established that increased exposure to estradiol (E(2)) is an important risk factor for the genesis and evolution of breast tumors, most of which (approximately 95-97%) in their early stage are estrogen-sensitive. However, two thirds of breast cancers occur during the postmenopausal period when the ovaries have ceased to be functional. Despite the low levels of circulating estrogens, the tissular concentrations of these hormones are significantly higher than those found in the plasma or in the area of the breast considered as normal tissue, suggesting a specific tumoral biosynthesis and accumulation of these hormones. Several factors could be implicated in this process, including higher uptake of steroids from plasma and local formation of the potent E(2) by the breast cancer tissue itself. This information extends the concept of 'intracrinology' where a hormone can have its biological response in the same organ where it is produced. There is substantial information that mammary cancer tissue contains all the enzymes responsible for the local biosynthesis of E(2) from circulating precursors. Two principal pathways are implicated in the last steps of E(2) formation in breast cancer tissues: the 'aromatase pathway' which transforms androgens into estrogens, and the 'sulfatase pathway' which converts estrone sulfate (E(1)S) into E(1) by the estrone-sulfatase. The final step of steroidogenesis is the conversion of the weak E(1) to the potent biologically active E(2) by the action of a reductive 17beta-hydroxysteroid dehydrogenase type 1 activity (17beta-HSD-1). Quantitative evaluation indicates that in human breast tumor E(1)S 'via sulfatase' is a much more likely precursor for E(2) than is androgens 'via aromatase'. Human breast cancer tissue contains all the enzymes (estrone sulfatase, 17beta-hydroxysteroid dehydrogenase, aromatase) involved in the last steps of E(2) biosynthesis. This tissue also contains sulfotransferase for the formation of the biologically inactive estrogen sulfates. In recent years, it was demonstrated that various progestins (promegestone, nomegestrol acetate, medrogestone, dydrogesterone, norelgestromin), tibolone and its metabolites, as well as other steroidal (e.g. sulfamates) and non-steroidal compounds, are potent sulfatase inhibitors. Various progestins can also block 17beta-hydroxysteroid dehydrogenase activities. In other studies, it was shown that medrogestone, nomegestrol acetate, promegestone or tibolone can stimulate the sulfotransferase activity for the local production of estrogen sulfates. All these data, in addition to numerous agents which can block the aromatase action, lead to the new concept of 'Selective Estrogen Enzyme Modulators' (SEEM) which can largely apply to breast cancer tissue. The exploration of various progestins and other active agents in trials with breast cancer patients, showing an inhibitory effect on sulfatase and 17beta-hydroxysteroid dehydrogenase, or a stimulatory effect on sulfotransferase and consequently on the levels of tissular levels of E(2), will provide a new possibility in the treatment of this disease.

Importance of local aromatase activity in hormone-dependent breast cancer: a review

The cytochrome P-450 enzyme complex aromatase is the rate-limiting step in the production of oestrogens. It catalyses the conversion of androgens to oestrogens. In the treatment of hormone-dependent breast cancer in postmenopausal women, aromatase is the target for treatment with aromatase inhibitors. Recently registered aromatase inhibitors like anastrozole, letrozole and exemestane have proven to be effective therapy for advanced breast cancer in postmenopausal patients failing to respond to treatment with tamoxifen. Intratumoural aromatase activity has predictive value for response to treatment with aromatase inhibitors. Attempts are being made to find an immunohistochemical technique to determine aromatase in tumour tissue, which may serve as a predictive factor. In situ oestrogen synthesis through local aromatase activity in the tumour and adjacent tissue is probably a very important growth-stimulating system in hormone-dependent breast cancer. This synthesis can be blocked with aromatase inhibitors. The regulation of aromatase activity and the cell types that contribute to this process are the subject of extensive research. There seems to be a complex interaction between malignant cells and adjacent cells in which factors such as IL-6 and its soluble receptor, TNF-alpha and prostaglandin E2 play an important role in stimulating aromatase activity.

Estrogen metabolism by conjugation

The involvement of estrogens in carcinogenic processes within estrogen-responsive tissues has been recognized for a number of years. Classically, mitogenicity associated with estrogen receptor-mediated cellular events was believed to be the mechanism by which estrogens contributed to carcinogenesis. Recently, the possibility that estrogens might contribute directly to mutagenesis resulting from DNA damage has been investigated. That damage is apparently a result of the formation of catechol estrogens that can be further oxidized to semiquinones and quinones. Those molecules represent reactive oxygen species and electrophilic molecules that can form depurinating DNA adducts, thus having the potential to result in permanent nucleotide mutation. Conjugation of parent estrogens to sulfate and glucuronide moieties; of catechol estrogens to methyl, sulfate, and glucuronide conjugates; and of catechol estrogen quinones to glutathione conjugates all represent potential "detoxification" reactions that may protect the cell from estrogen-mediated mitogenicity and mutagenesis. In this chapter, the biochemistry and molecular genetics of those conjugative reaction pathways are discussed. When applicable, the involvement of specific enzymatic isoforms is presented. Finally, the activity of many of these conjugative biotransformation reactions is subject to large interindividual variation--often due to the presence of common nucleotide polymorphisms within the genes encoding those enzymes. Functionally significant genetic polymorphisms that might contribute to variable conjugation of estrogens and catechol estrogens are also discussed.

Control of sulfatase and sulfotransferase activities by medrogestone in the hormone-dependent MCF-7 and T-47D human breast cancer cell lines

In the present study, we explored the effect of the progestin medrogestone on the sulfatase and sulfotransferase activities in the hormone-dependent MCF-7 and T-47D human breast cancer cell lines. After 24 h incubation at 37 degrees C of physiological concentrations of estrone sulfate ([3H]-E1S: 5x10(-9) mol/l), it was observed that this estrogen was converted in a great proportion to E2 in both cell lines. Medrogestone significantly inhibits this transformation, at all the concentrations tested (5x10(-8) to 5x10(-5) mol/l), in both cell lines. The IC50 values were 1.93 micromol/l and 0.21 micromol/l in MCF-7 and T-47D cells, respectively. In another series of studies, after 24 h incubation at 37 degrees C of physiological concentrations of estrone ([3H]-E1: 5x10(-9) mol/l), the sulfotransferase activity was detectable in both cell lines. Estrogen sulfates (ES) are found exclusively in the culture medium, which suggests that as soon as they are formed they are excreted into the medium. Medrogestone has a biphasic effect on sulfotransferase activity in both cell lines. At low doses: 5x10(-8) and 5x10(-7) mol/l, this compound stimulates the enzyme by +73.5 and 52.7%, respectively, in MCF-7, and by 84.5 and 62.6% in T-47D cells. At high concentrations: 5x10(-6) and 5x10(-5) mol/l, medrogestone has no effect on MCF-7 cells, but inhibits the sulfotransferase activity in T-47D cells by -31.4% at 5x10(-5) mol/l. In conclusion, the inhibitory effect provoked by medrogestone on the enzyme involved in the biosynthesis of E2 (sulfatase pathway) in estrogen-dependent breast cancer, as well as the stimulatory effect on the formation of the inactive ES, support a probable anti-proliferative effect of this progestin in breast tissue. Clinical applications of these findings can open new therapeutic possibilities for this disease.

Estrone sulfatase versus estrone sulfotransferase in human breast cancer: potential clinical applications

Estrone sulfate (E1S) is concentrated in high levels in human breast cancer tissue. The values are particularly high in postmenopausal women and many times those circulating in the plasma. Also, the tissular concentration of this conjugate are significantly higher in tumoural tissue than in the area of the breast considered as normal. The enzyme which hydrolyzes E1S: sulfatase, as well as the enzyme which biosynthesises this conjugate: sulfotransferase, are present in significant concentrations in breast cancer tissue. Consequently, E1S is a balance between the activities of the two enzymes. As breast cancer tissue has all the enzymes necessary for the synthesis of estradiol (E2), and the formation of E2 from E1S 'via sulfatase' is the main pathway, it was very attractive to explore inhibitory agents of this enzyme. It was observed that different substances including antiestrogens (4-hydroxytamoxifen, ICI 164,384) and various progestins (promegestone, nomegestrol acetate, medrogestone) as well as Org OD14 (tibolone) can block the sulfatase activity. In addition, it was demonstrated that different progestins (medrogestone, nomegestrol acetate, TX-525) and org OD14 can stimulate the sulfotransferase activity for the formation of the biologically inactive E1S. It is concluded that the inhibition of sulfatase and the stimulation of sulfotransferase activity can open interesting possibilities to explore these effects in patients with breast cancer.

Human estrogen sulfotransferase (hEST1) activities and its mRNA in various breast cancer cell lines. Effect of the progestin, promegestone (R-5020)

Using reverse transcriptase-polymerase chain reaction amplification it was possible to detect the presence of type 1 human estrogen sulfotransferase (hEST1) mRNA in the hormone-dependent: MCF-7 and T-47D, and hormone-independent: MDA-MB-231 and MDA-MB-468, human breast cancer cells. The expression of this mRNA is significantly higher in the MDA-MB-468 cells and a correlation of this mRNA expression with the enzymatic activity was observed. The progestin promegestone (R-5020) at a low concentration (5 x 10(-7) M) can significantly increase the estrogen sulfotransferase activity and its mRNA in the hormone-dependent MCF-7 and T-47D cells. As estrogen sulfates are biologically inactive, the stimulatory effect on sulfotransferase by promegestone may open attractive possibilities in the control of estradiol in human breast cancer.

Hydroxysteroid sulfotransferase activity in the rat brain and liver as a function of age and sex

The high concentrations of dehydroepiandrosterone sulfate and pregnenolone sulfate in the mammalian brain, despite the blood-brain barrier's impermeability to these compounds, and the apparent independence of these concentrations from those in plasma prompted us to investigate whether enzymatic sulfation of dehydroepiandrosterone was detectable in the rat brain. Low hydroxysteroid sulfotransferase activities were detectable in in vitro incubations of homogenates from all rat brain regions except the cerebellum, being highest in the hypothalamus and pons. This activity was not ascribable to enzyme in brain capillary blood. The activity was mainly cytosolic, although there was also significant activity in the partially purified nuclear fraction. The enzyme had different properties from those of hepatic isozymes, with a pH optimum of 6.5 and a high Km of approximately 2 mM for dehydroepiandrosterone. The enzyme was also active with pregnenolone as substrate. Activities in the brain were approximately 300-fold lower than in the liver but, as in the liver, these were higher in females than in males. The variations in brain activity as a function of age did not parallel those in the liver. Relatively high activities were found in the fetal brain and declined at birth, while activities were insignificant in the fetal liver and rose following birth. There was a major peak in activity in pubertal female brains, but this peak was less important, and later, in males. No evidence was found to indicate that the low brain enzyme activities and high Km were attributable either to the presence of an inhibitor or to the steroid sulfation actually being a secondary activity of another brain sulfotransferase. We discuss whether the sulfotransferase activities found are adequate to synthesize the dehydroepiandrosterone and pregnenolone sulfate found in brain.

Steroid sulfation by expressed human cytosolic sulfotransferases

The human cytosolic sulfotransferases (STs), dehydroepiandrosterone sulfotransferase (DHEA-ST) and the phenol-sulfating form of phenol sulfotransferase, (P-PST), have been expressed in bacteria and used to investigate the ability of the cloned enzymes to conjugate steroids and related compounds. DHEA-ST was capable of sulfating all of the 3-hydroxysteroids, testosterone and estrogens tested as substrates. The 3-hydroxysteroids, androsterone, epiandrosterone and androstenediol, were conjugated at 50-60% of the rate of DHEA. Of the steroids tested, P-PST was capable of conjugating only the estrogens. The catechol estrogens, 2-hydroxyestradiol, 4-hydroxyestradiol and 4-hydroxyestrone, and compounds with estrogenic activity such as 17 alpha-ethynyl-estradiol and trans-4-hydroxytamoxifen, were also tested as substrates. DHEA-ST showed little or no sulfation activity with these compounds; however, all of these compounds were sulfated by P-PST. These results indicate that the expressed human STs are valuable in analyzing the overlapping substrate specificities of these enzymes and that P-PST may have an important role in the metabolism of estrogens and estrogenic compounds in human tissues.

Cloning and expression of cDNA encoding human placental estrogen sulfotransferase

Using two oligoprimers derived from the bovine placental estrogen sulfotransferase sequence, we amplified a probe for human placental estrogen sulfotransferase. Using this probe to screen a human placental cDNA library constructed in lambda gt11, we isolated a cDNA clone of 1.3 kb encoding human estrogen sulfotransferase. DNA analysis predicts a protein of 295 amino acids with a calculated molecular weight of 34,199. Alignment of the amino acid sequence with other sulfotransferases indicates that human placental estrogen sulfotransferase shares 68.6, 68.2 and 65.9% similarity with bovine placental, guinea pig adrenocortical, and rat liver estrogen sulfotransferase, respectively. It shows also 95.6, 57.6, 85.3, and 54.2% similarity to human phenol, human DHEA, rat phenol, and rat hydroxysteroid sulfotransferase, respectively. Transfection of expression vectors encoding human estrogen sulfotransferase and dehydroepiandrosterone (DHEA) sulfotransferase in human adrenal adenocarcinoma SW-13 cells indicates that estrogen sulfotransferase transforms estrone more specifically, whereas DHEA sulfotransferase is more specific for DHEA and pregnenolone.

Identification and characterization of cytosolic sulfotransferase activities in MCF-7 human breast carcinoma cells

MCF-7 human mammary carcinoma cells have been reported to possess beta-estradiol and dehydroepiandrosterone sulfotransferase activities. These steroid sulfotransferase activities may be important in the metabolism and activity of different steroids in these cells. This report describes and characterizes both the enzymatic activity of three cytosolic sulfotransferases found in MCF-7 cells and the corresponding immunoblot analysis of these enzymes with specific anti-sulfotransferase antibodies. Two cytosolic sulfotransferases have been purified and characterized from human tissues which are capable of sulfating estrogens. These are the phenol-sulfating form of phenol sulfotransferase (P-PST) and the hydroxysteroid sulfotransferase, dehydroepiandrosterone sulfotransferase (DHEA-ST). The results of this study show that P-PST is the major cytosolic sulfotransferase found in MCF-7 cytosol and is responsible for most of the beta-estradiol sulfation in these cells. Although DHEA-ST activity was found in MCF-7 cytosol, this activity was only about 3% of the P-PST activity. Immunoblot analysis of MCF-7 cytosol detected both P-PST and lower levels of the monoamine-sulfating form of PST; however DHEA-ST could not be detected apparently because of low levels of expression. Human liver P-PST was expressed in Cos-7 Green monkey kidney fibroblasts and the ability of the cloned enzyme to sulfate beta-estradiol was investigated. This study indicates that P-PST is the prevalent cytosolic sulfotransferase in MCF-7 cytosol and is responsible for the majority of beta-estradiol sulfation in these cells.

Steroid sulfation Current concepts

Formation of steroid sulfates is catalyzed by sulfotransferase enzymes that are widely distributed and frequently of high specificity. Steroid sulfates cannot be described as being active hormones, but some serve in tissue sites as precursors of active steroids formed by enzymic cleavage of the sulfate group by sulfatase enzymes. There is increasing evidence that intracellular sulfation and desulfation can play a role in regulating the availability of active steroid hormones near target sites. There are strong indications for this regulation in the uterine compartment, in the liver, and in mammary cancer cells.

Regulation of estrogen sulfotransferase by estrogen in MCF-7 human mammary cancer cells

The importance of the steroid hormone microenvironment within cells is now recognised in studies on endocrine-related neoplasms such as breast cancer. This focuses attention on enzymes which control the intracellular levels of estradiol-17 beta (E2). One such enzyme, estrogen sulfotransferase, which converts E2 to inactive E2-3 sulfate, has now been shown to be regulated by estrogen in MCF-7 human mammary cancer cells. Hydroxysteroid sulfotransferase, which sulfurylates the adrenal-derived estrogen 5-androstene-3 beta,17 beta-diol, is also under estrogen control. Evidence is provided which shows that one function of these enzymes may involve elimination of estrogen from the cell following processing of the ligand-charged estrogen receptor (ER).

Comparison of estrogen sulfotransferase and pregnenolone sulfotransferase of guinea pig

Guinea pig adrenal estrogen sulfotransferase from either sex was eluted as a single peak, irrespective of buffer salt concentration, when subjected to fast protein liquid chromatography on gel filtration columns. The same enzyme was consistently eluted in two distinct peaks during chromatofocusing. Adrenal pregnenolone sulfotransferase was eluted during gel filtration in a heterogeneous pattern, dependent on salt concentration. These properties have made possible almost complete separation of the two sulfotransferases in one step, although adrenal estrogen sulfotransferase may possess a minute intrinsic ability to catalyze sulfation of pregnenolone. Pregnenolone sulfotransferase had no measurable activity toward estrone. Pregnenolone sulfotransferase from both sexes yielded variable elution patterns during chromatofocusing. Estrogen sulfotransferase from the adrenal, as well as that of guinea pig chorion, was strongly inhibited by N-ethylmaleimide and to a lesser degree by iodoacetamide and iodoacetate. Adrenal and chorion estrogen sulfotransferases were thermolabile and were activated, although not protected from the effect of heat, by binding to 3'-phosphoadenosine 5'-phosphosulfate. Adrenal pregnenolone sulfotransferase was inhibited only by high concentrations of N-ethylmaleimide and not at all by iodoacetamide or iodoacetate. It was more thermostable than the estrogen sulfotransferase and was not activated by binding to 3'-phosphoadenosine 5'-phosphosulfate.

Enzymatic regulation of estradiol-17 beta concentrations in human breast cancer cells

Estradiol-17 beta is known to be involved in both the etiology and maintenance of growth of breast cancer. However, blood levels of the hormone do not reflect those found within the cells due to a number of transformations catalysed by enzymes which may be under metabolite and/or hormonal regulation. Recognition of the importance of the hormone microenvironment within the cell focuses attention on these enzymes and provides the subject for this review. An interplay between the sex hormones, estrogen and progestin, can control estradiol-17 beta concentrations in breast cancer cells at the level of key transforming enzymes. In addition, some enzymes catalyse production of biologically inert derivatives which are rapidly eliminated from the cell. Other enzymes catalyse the formation of derivatives which are exclusively intracellular and can act as reserve forms of the hormone. Yet others lead to estradiol-17 beta metabolites which are cytotoxic. An improved understanding of the enzymes and the role of the related metabolites can provide the opportunity for the development of new therapeutic agents.