The excretion of five different 2-hydroxyoestrogen monomethyl ethers in human pregnancy urine

Synthesis of 3'-methoxy-E-diethylstilbestrol and its analogs as tumor angiogenesis inhibitors

3'-Methoxy-E-diethylstilbestrol (2), with the structural and original similarities to 2-methoxyestradiol (2-ME2, 1), was synthesized and screened against HUVEC and a series of human cancer cell lines including RL95-2, SKOV-3, MCF-7 and T-47D in vitro. The configuration of the title compound was determined via the single crystal X-ray diffraction of its benzoyl-ester derivative (10). The fact that 3'-methoxy-E-diethylstilbestrol and its analogues (8 and 11) showed potential antiangiogenesis and anti-tumor activities at a close level, whereas its ester derivative (10) did not display any cytotoxic activities on all the screening cell lines indicated that the core scaffold of 3'-methoxy-3,4-diphenylhexane and the exposed hydroxyl-groups in the structures are essential pharmacophores for their anti-tumor activities.

2-Methoxyestradiol blocks cell-cycle progression at the G2/M phase and induces apoptosis in human acute T lymphoblastic leukemia CEM cells

2-Methoxyestradiol (2-ME2) is an endogenous metabolite of 17beta-estradiol (E2) with estrogen receptor-independent anti-cancer activity. The current study sought to determine the mechanism of anti-cancer activity of 2-ME2 in human acute T lymphoblastic leukemia CEM cells. Results showed that 2-ME2 markedly suppressed proliferation of CEM cells in a time- and dose-dependent manner. 2-ME2-treated CEM cells underwent typical apoptotic changes. Exposure to 2-ME2 led to G(2)/M phase cell-cycle arrest, which preceded apoptosis characterized by the appearance of a sub-G(1) cell population. In addition, cytosolic cytochrome c release, increased procaspase-9 and -3 expressions, poly(ADP-ribose) polymerase (PARP) cleavage, and induced expression of caspase-8 were detected, suggesting that both the intrinsic apoptotic pathway and extrinsic apoptotic pathway were involved in 2-ME2-induced apoptosis. Moreover, the expression level of p21 protein was upregulated, whereas Bcl-2 and dysfunctional p53 protein were downregulated, which also contributed to 2-ME2-induced apoptosis. Our findings revealed that 2-ME2 might be a potent natural candidate for chemotherapeutic treatment of human acute T lymphoblastic leukemia when the precise effects of 2-ME2 were investigated further in other T leukemia cell lines and in primary T-cell leukemias.

2-methoxyestradiol-induced cell death in osteosarcoma cells is preceded by cell cycle arrest

2-Methoxyestradiol (2-ME), a naturally occurring mammalian metabolite of 17beta-Estradiol (E2), induces cell death in osteosarcoma cells. To further understand the molecular mechanisms of action, we have investigated cell cycle progression in 2-ME-treated human osteosarcoma (MG63, SaOS-2 and LM7 [corrected]) cells. At 5 microM, 2-ME induced growth arrest by inducing a block in cell cycle; 2-ME-treatment resulted in 2-fold increases in G1 phase cells and a decrease in S phase cells in MG63 and SaOS-2 osteosarcoma cell lines, compared to the appropriate vehicle controls. 2-ME-treatment induced a threefold increase in the G2 phase in LM7 [corrected] osteosarcoma cells. The results demonstrated steroid specificity, as the tumorigenic metabolite, 16alpha-hydroxyestradiol (16-OHE), did not have any effect on cell cycle progression in osteosarcoma cells. The cell cycle arrest coincided with an increase in expression of the cell cycle markers p21, p27 and p53 proteins in 2-ME-treated osteosarcoma cells. Also, MG63 cells, transiently transfected with cDNA for a 'loss of function mutant' RNA-dependent protein kinase (PKR) protein, were resistant to 2-ME-induced cell cycle arrest. These results suggest that 2-ME works in concert with factors regulating cell cycle progression, and cell cycle arrest precedes cell death in 2-ME-treated osteosarcoma cells.

Synthesis and in vivo antitumor evaluation of 2-methoxyestradiol 3-phosphate, 17-phosphate, and 3,17-diphosphate

A prodrug strategy was investigated to address the problem of limited aqueous solubility and the resulting limited bioavailability of the antitumor agent 2-methoxyestradiol. The 3-phosphate, 17-phosphate, and 3,17-diphosphate of 2-methoxyestradiol were synthesized. 2-methoxyestradiol 3-phosphate was metabolized more efficiently to the parent compound in vivo than 2-methoxyestradiol 17-phosphate, and it was also more cytotoxic in cancer cell cultures than either the 17-phosphate or the 3,17-diphosphate. These results agree with the in vivo anticancer activity of 2-methoxyestradiol 3-phosphate in a mouse Lewis lung carcinoma experimental metastasis model as opposed to the 17-phosphate and 3,17-diphosphate, both of which were inactive. The in vivo antitumor activity of 2-methoxyestradiol 3-phosphate at a dose of 200 mg/kg per day was comparable to that of a maximally tolerated dose of cyclophosphamide.

2-methoxyestradiol induces apoptosis and cell cycle arrest in human chondrosarcoma cells

2-Methoxyestradiol (2ME) is an endogenous metabolite with estrogen receptor-independent anti-tumor activity. The current study seeks to determine the mechanism of anti-tumor activity of 2ME on human chondrosarcoma. 2ME caused a time- and dose-dependent cytotoxity in chondrosarcoma cells, while primary chondrocytes were minimally affected. Cells accumulated in G0/G1 phase in response to 2ME and DAPI stain indicated an induction of apoptosis. Bax, Cytochrome C, and Caspase-3 protein expression were increased, while p53 expression was decreased. A higher Bax/Bcl-2 ratio followed 2ME treatment. 2ME has a potentially promising role as a systemic therapy of chondrosarcoma when the mechanism of action is better delineated.

Double-stranded RNA-dependent protein kinase is involved in 2-methoxyestradiol-mediated cell death of osteosarcoma cells

We studied the involvement of interferon-regulated, PKR on 2-ME-mediated actions in human osteosarcoma cells. Our results show that PKR is activated by 2-ME treatment and is necessary for 2-ME-mediated induction of osteosarcoma cell death.

INTRODUCTION

Osteosarcoma is the most common primary bone tumor and most frequently develops during adolescence. 2-Methoxyestradiol (2-ME), a metabolite of 17beta-estradiol, induces interferon gene expression and apoptosis in human osteosarcoma cells. In this report, we studied the role of interferon-regulated double-stranded (ds)RNA-dependent protein kinase (PKR) protein on 2-ME-mediated cell death in human osteosarcoma cells.

MATERIALS AND METHODS

Western blot analyses were used to measure PKR protein and phosphorylation levels. Cell survival and apoptosis assays were measured using trypan blue exclusion and Hoechst dye methods, respectively. A transient transfection protocol was used to express the dominant negative PKR mutants.

RESULTS AND CONCLUSIONS

PKR was increased in 2-ME-treated MG63 cells, whereas 17beta-estradiol, 4-hydroxyestradiol, and 16alpha-hydroxyestradiol, which do not induce cell death, had no effect on PKR protein levels. Also, 2-ME treatment induced PKR kinase activity as indicated by increased autophosphorylation and phosphorylation of the endogenous substrate, eukaryotic initiation factor (eIF)-2alpha. dsRNA poly (I).poly (C), an activator of PKR protein, increased cell death when osteosarcoma cells were treated with a submaximal concentration of 2-ME. In contrast, a serine-threonine kinase inhibitor SB203580 and a specific PKR inhibitor 2-aminopurine (2-AP) blocked the 2-ME-induced cell death in MG63 cells. A dominant negative PKR mutant protein conferred resistance to 2-ME-induced cell death to MG63 osteosarcoma and 2-ME-mediated PKR regulation did not require interferon gene expression. PKR protein is activated in cell free extracts by 2-ME treatment, resulting in autophosphorylation and in the phosphorylation of the substrate eIF-2alpha. We conclude from these results that PKR is regulated by 2-ME independently of interferon and is essential for 2-ME-mediated cell death in MG63 osteosarcoma cells.

Distinct tumor stage-specific inhibitory effects of 2-methoxyestradiol in a breast cancer mouse model associated with Id-1 expression

2-Methoxyestradiol (2ME(2)), a metabolite of 17-beta-estradiol, inhibits angiogenesis and has additional antitumor activities. We have analyzed the tumor stage-specific effects of 2ME(2) in the C3(1)/Tag transgenic mouse model for breast cancer, which spontaneously develops estrogen receptor-negative mammary tumors following a predictable progression of lesion formation. When given either as a therapeutic agent in established tumors (late intervention study) or in mice with pre-invasive mammary lesions (early intervention study), tumor growth was reduced by 60% compared with untreated controls and was associated with an induction of apoptosis. In a prevention study, a significant reduction in mammary intraepithelial neoplasia (MIN) lesions was observed in animals beginning treatment at 6 weeks of age, before the appearance of histopathologic abnormalities. However, although 2ME(2) reduced the number of MIN lesions in the prevention study, a paradoxical increase in tumor multiplicity and growth rate was observed. This was associated with unusual cystic tumor formation, in which significant central necrosis was observed, surrounded by an outer region of proliferative tumor cell growth. The characteristics of the cystic tumor formation in mice treated with 2ME(2) at early ages are consistent with an impaired angiogenic response as observed in mice deficient for inhibitor of differentiation (Id-1). We further show that Id-1 expression is negatively regulated by 2ME(2), which may be an additional mechanism for the antiangiogenic effect of 2ME(2). Although 2ME(2) significantly reduced tumor growth at late stages, these results also suggest that altered tumor morphology and accelerated tumor growth may occur if 2ME(2) is administered in a prevention setting for prolonged periods.

Estrogen metabolites and systolic blood pressure in a population-based sample of postmenopausal women

CONTEXT

Lower systolic blood pressure (SBP) and lower rates of coronary heart disease among premenopausal women compared with similarly aged men and postmenopausal women suggest that female sex hormones may confer cardiovascular protection. 2-Hydroxyestradiol, a product of 17beta-estradiol oxidative metabolism, inhibits the proliferation of vascular smooth muscle cells in vitro. The other major product of 17beta-estradiol oxidative metabolism, 16alpha-hydroxyestradiol, does not demonstrate similar inhibitory effects. Concentrations of 2-hydroxyestrone (2-OHE) and 16alpha-hydroxyestrone (16-OHE) in urine reflect the relative activity of the 2- and 16alpha-hydroxylation pathways of 17beta-estradiol.

OBJECTIVE

The objective of this study was to determine the relationship between SBP and the ratio of 2-OHE to 16-OHE in urine.

DESIGN AND PARTICIPANTS

This was a cross-sectional study of 80 postmenopausal women living in Cook County, Illinois.

SETTING

This study was performed in an academic clinical laboratory.

MAIN OUTCOME MEASURE

The main outcome measure was SBP.

RESULTS

Women taking hormone replacement therapy had higher levels of urinary 2-OHE and 16-OHE, but their mean 2:16-OHE ratio and SBP did not differ from that of women not taking hormone replacement therapy. In a multivariate regression model that controlled for age, body mass index, race/ethnicity, and antihypertensive medication use, a sd increase in the 2:16-OHE ratio was associated with a 6.7-mm Hg decrease (P < 0.05) in SBP.

CONCLUSIONS

The ratio of urinary 2-OHE to 16-OHE is a significant predictor of SBP among postmenopausal women and may reflect the effects of 2-hydroxyestradiol, a potent inhibitor of vascular smooth muscle cell proliferation.

2-methoxyestradiol inhibits differentiation and is cytotoxic to osteoclasts

2-Methoxyestradiol (2-ME), a naturally occurring metabolite of 17beta-estradiol, is highly cytotoxic to a wide range of tumor cells but is harmless to most normal cells. However, 2-ME prevented bone loss in ovariectomized rats, suggesting it inhibits bone resorption. These studies were performed to determine the direct effects of 2-ME on cultured osteoclasts. 2-ME (2 microM) reduced osteoclast number by more than 95% and induced apoptosis in three cultured osteoclast model systems (RAW 264.7 cells cultured with RANKL, marrow cells co-cultured with stromal support cells, and spleen cells cultured without support cells in media supplemented with RANKL and macrophage colony stimulating factor (M-CSF)). The 2-ME-mediated effect was ligand specific; 2-hydroxyestradiol (2-OHE), the immediate precursor to 2-ME, exhibited less cytotoxicity; and 2-methoxyestrone (2-MEOE1) the estrone analog of 2-ME, was not cytotoxic. Co-treatment with ICI 182,780 did not antagonize 2-ME, suggesting that the cytotoxicity was not estrogen receptor-dependent. 2-ME-induced cell death in RAW 264.7 cells coincided with an increase in gene expression of cytokines implicated in inhibition of differentiation and induction of apoptosis. In addition, the 2-ME-mediated decrease in cell survival was partially inhibited by anti-lymphotoxin(LT)beta antibodies, suggesting that 2-ME-dependent effects involve LTbeta. These results suggest that 2-ME could be useful for treating skeletal diseases in which bone resorption is increased, such as postmenopausal osteoporosis and cancer metastasis to bone.

Effects of altering the electronics of 2-methoxyestradiol on cell proliferation, on cytotoxicity in human cancer cell cultures, and on tubulin polymerization

A series of new analogues of 2-methoxyestradiol (1) were synthesized to further elucidate the relationships between structure and activity. The compounds were designed to diminish the potential for metabolic deactivation at positions 2 and 17 and were analyzed as inhibitors of tubulin polymerization and for cytotoxicity. 17alpha-methyl-beta-estradiol (30), 2-propynyl-17alpha-methylestradiol (39), 2-ethoxy-17-(1'-methylene)estra-1,3,5(10)-triene-3-ol (50) and 2-ethoxy-17alpha-methylestradiol (51) showed similar or greater tubulin polymerization inhibition than 2-methoxyestradiol (1) and contained moieties that are expected to inhibit deactivating metabolic processes. All of the compounds tested were cytotoxic in the panel of 55 human cancer cell cultures, and generally, the derivatives that displayed the most activity against tubulin were also the most cytotoxic.

2-Methoxyestradiol exhibits a biphasic effect on VEGF-A in tumor cells and upregulation is mediated through ER-alpha: a possible signaling pathway associated with the impact of 2-ME2 on proliferative cells

2-Methoxyestradiol (2-ME2) was reported to elicit both stimulation and inhibition of tumor angiogenesis and growth depending on the dosage used. However, the mechanism(s) of the biphasic action of 2-ME2 has been elusive. Here we describe a regulatory role of vascular endothelial growth factor-A (VEGF-A) in the biphasic effects on estrogen receptor (ER)+ GH3 rat pituitary tumor cells and MCF-7 human breast tumor cells depending on the dosage of 2-ME2 used. We observed that acute exposure to 2-ME2, irrespective of dosage, did not alter cellular proliferation, but enhanced the VEGF-A mRNA level. As the treatment duration increased, biphasic effect was elicited. A concentration of 1 microM 2-ME2 increased both cell proliferation and VEGF-A levels in these cells, whereas higher doses exhibited reversed impact. A low dose of 2-ME2 also increased the VEGF-A mRNA expression in ER-alpha-transfected human mammary epithelial cells (HMECs). The effect was reversed in ER- cells. The enhanced expression of VEGF-A mRNA could be blocked by the pure estrogen antagonist, ICI 182,780, and reveal that the upregulation of VEGF-A expression by 2-ME2 is mediated through ER-alpha. Furthermore, the biphasic effect of 2-ME2 on cell proliferation can be modulated by administrating VEGF-A antibodies or VEGF-A proteins. Studies also demonstrate that the VEGF-A protein, induced by 2-ME2, is functionally active and upregulates the proliferation of adjacent endothelial cells.

2-methoxyestradiol strongly inhibits human uterine sarcomatous cell growth

OBJECTIVES

The objective was to test the hypothesis that uterine sarcomatous cells are hormone-sensitive. We included 2-methoxyestradiol, an endogenous metabolite of estradiol with antiproliferative properties.

METHODS

Proliferation assays assessed the effects of estradiol, progesterone, tamoxifen, raloxifen, [D-Trp(6)]leuteinizing hormone-releasing hormone (LHRH), ICI 182,780 (faslodex or fulvestrant), and 2-methoxyestradiol on cell growth of a cell line derived from uterine carcinosarcoma, but consisting solely of mesenchymal cells (SK-UT-1). Morphological changes of SK-UT-1 cells after exposure to 2-methoxyestradiol were evaluated and fluorescence immunohistochemistry for tubulin was used to detect changes in the mitotic spindle. Flow cytometry was used to assess the influence of 2-methoxyestradiol on the SK-UT-1 cell cycle as well as the role of p53 in apoptosis.

RESULTS

Cell proliferation analysis revealed that SK-UT-1 cells were stimulated by progesterone, tamoxifen, and [D-Trp(6)]LHRH. Cells were insensitive to estradiol, raloxifen, and ICI 182,780. Inhibition occurred after exposure to 2-methoxyestradiol and was accompanied by a threefold increase in the G2/M population, with a concomitant decrease in the G1 population, as shown by cell cycle analysis. SK-UT-1 cells exposed to 2-methoxyestradiol showed morphological changes indicative of apoptosis. Examination of signaling pathways that mediate 2-methoxyestradiol-induced apoptosis showed p53-independent growth inhibition. The inhibition of SK-UT-1 cell growth by arresting the cells during G2/M progression could be attributed to interference with the microtubule system, as determined by fluorescence immunohistochemistry.

CONCLUSIONS

The stimulatory effect of progesterone, tamoxifen, and [D-Trp(6)]LHRH suggests that uterine sarcomatous cells are hormone-sensitive. Our finding that 2-methoxyestradiol-mediated growth inhibition of uterine sarcomatous cells occurred in a p53-independent manner may have considerable clinical significance. The inadequate armature against uterine sarcomas and the limited toxicity of 2-methoxyestradiol may render these observations especially important.

Free radical stress in chronic lymphocytic leukemia cells and its role in cellular sensitivity to ROS-generating anticancer agents

2-Methoxyestradiol (2-ME), a new anticancer agent currently in clinical trials, has been demonstrated to inhibit superoxide dismutase (SOD) and to induce apoptosis in leukemia cells through a free radical-mediated mechanism. Because the accumulation of superoxide (O(2)-) by inhibition of SOD depends on the cellular generation of O(2)-, we hypothesized that the endogenous production of superoxide may be a critical factor that affects the antileukemia activity of 2-ME. In the present study, we investigated the relationship between cellular O(2)- contents and the cytotoxic activity of 2-ME in primary leukemia cells from 50 patients with chronic lymphocytic leukemia (CLL). Quantitation of O(2)- revealed that the basal cellular O(2)- contents are heterogeneous among patients with CLL. The O(2)- levels were significantly higher in CLL cells from patients with prior chemotherapy. CLL cells with higher basal O(2)- contents were more sensitive to 2-ME in vitro than those with lower O(2)- contents. There was a significant correlation between the 2-ME-induced O(2)- increase and the loss of cell viability. Importantly, addition of arsenic trioxide, a compound capable of causing reactive oxygen species (ROS) generation, significantly enhanced the activity of 2-ME, even in the CLL cells that were resistant to 2-ME alone. These results suggest that the cellular generation of O(2)- plays an important role in the cytotoxic action of 2-ME and that it is possible to use exogenous ROS-producing agents such as arsenic trioxide in combination with 2-ME to enhance the antileukemia activity and to overcome drug resistance. Such a combination strategy may have potential clinical applications.

The effect of exchanging various substituents at the 2-position of 2-methoxyestradiol on cytotoxicity in human cancer cell cultures and inhibition of tubulin polymerization

A new set of estradiol derivatives bearing various substituents at the 2-position were synthesized in order to further elucidate the structural parameters associated with the antitubulin activity and cytotoxicity of 2-substituted estradiols. The potencies of the new compounds as inhibitors of tubulin polymerization were determined, and the cytotoxicities of the analogues in human cancer cell cultures were investigated. The substituents introduced into the 2-position of estradiol included E-3'-hydroxy-1'-propenyl, 2'-hydroxyethoxy, 3-N,N-dimethylaminoethylideneamino, 2'-hydroxyethylineneamino, (beta-3,4,5-trimethoxyphenyl)ethenyl, phenylethynyl, ethynly, 1'-propynyl, and cyano. The substituents conferring the ability to inhibit tubulin polymerization included E-3'-hydroxy-1'-propenyl, 2'-hydroxyethoxy, ethynyl, and 1'-propynyl. The remaining compounds were all inactive as inhibitors of tubulin polymerization when tested at concentrations of up to 40 microM. All of the compounds were cytotoxic in a panel of 55 human cancer cell cultures, and in general, the most cytotoxic compounds were also the most potent as inhibitors of tubulin polymerization. 2-(1'-Propynyl)estradiol displayed significant anticancer activity in the in vivo hollow fiber animal model.

2-methoxyestradiol induces interferon gene expression and apoptosis in osteosarcoma cells

2-Methoxyestradiol (2-ME), a naturally occurring mammalian metabolite of 17beta-estradiol, has been implicated as a physiological inhibitor of tumor cell proliferation. In this study, the effects of 2-ME on cultured osteosarcomatous cells were investigated. Dose-dependent growth inhibition was observed in MG63 and TE85 human osteosarcoma cells exposed to 2-ME. The cell killing by 2-ME was ligand-specific; the immediate precursor (2-hydroxyestradiol), the parent compound (17beta-estradiol), and the equivalent metabolite of estrone (2-methoxyestrone) exhibited less potency and efficacy. Furthermore, 2-ME was similarly effective at killing immortalized human fetal osteoblastic cells (hFOB) with and without estrogen receptor-alpha and -beta and rat osteosarcoma cells (ROS17/2.8). The cytotoxicity of 2-ME was selective to transformed and immortalized osteoblastic cells; 2-ME (2 microm) had no effect on the proliferation of primary cultures of human osteoblasts. Co-treatment with the potent estrogen receptor ligand, ICI-182,780, did not reduce 2-ME-induced osteosarcoma cell death, implying that this action is not mediated by conventional estrogen receptors. The expression levels of bone matrix protein genes, type 1 collagen and osteonectin, were transiently reduced after 2-ME treatment, suggesting that the surviving cells are capable of producing bone matrix. The 2-ME-mediated killing of osteosarcoma cells was due to the induction of apoptosis; treatment induced expression of interferon genes within 12 h and histological evidence of apoptosis within 48 h of 2-ME treatment. Thus, our results demonstrate that 2-ME is highly cytotoxic to osteosarcoma cells but not normal osteoblasts. These findings suggest that further study of 2-ME as a potential intervention for treatment of osteosarcoma is warranted.

2-Methoxyestradiol, an endogenous estradiol metabolite, differentially inhibits granulosa and endothelial cell mitosis: a potential follicular antiangiogenic regulator

2-Methoxyestradiol (2-ME) is an estradiol metabolite with antiangiogenic and antitumor activity. It is formed by granulosa cell (GC) catechol-O-methyltransferase activity and is present in the normal follicle at high concentrations. In this unique microenvironment, it may regulate selected cell types via autocrine and/or paracrine action. To assess the possibility that 2-ME or estradiol might exert differential mitotic and/or apoptotic effects on endothelial cells and GCs, we compared their actions on primary cultures of hormone- and/or growth factor-stimulated porcine GCs (pGCs) as well as two types of endothelial cells, primary cultures of porcine endothelial cells (pECs), and a spontaneously transformed rabbit endothelial vascular cell (REVC) line. The 2-ME, but not estradiol, dose dependently suppressed tritiated thymidine ((3)H-T) incorporation into epidermal growth factor (EGF)-stimulated REVCs and EGF/insulin (INS)-stimulated pECs. In contrast, 2-ME did not attenuate incorporation in FSH/INS-stimulated pGCs. It reduced incorporation by approximately 50% in EGF/INS-stimulated pGCs, indicating that responsiveness to 2-ME in normal cells can be modulated by hormone and growth factor treatment. Estradiol was not antimitotic to pGCs. As indicated by 4',6-diamido-2-phenylindole hydrochloride nuclear staining, estradiol was nonapoptotic in either cell type, and 2-ME significantly increased apoptosis of REVCs, but not of pGCs. In a cell migration assay, REVC movement was attenuated by 2-ME, but not by estradiol. In summary, the results show that antimitotic as well as proapoptotic responses to 2-ME vary with cell type and, in the case of pGC antimitotic activity, with the regulatory microenvironment. Thus, they provide a rationale for autocrine and/or paracrine action of 2-ME at its site of production in vivo, and they strongly support the concept of 2-ME as a candidate ovarian angiogenesis inhibitor.

Male predominance in hepatocellular carcinoma: new insight and a possible therapeutic alternative

Hepatocellular carcinoma is one of the most common cancers in the world. The male to female ratio is 3-6 to 1 in patients with hepatocellular carcinoma. Although steroid hormones and receptors have been examined extensively for their role in the growth regulation of hepatocellular carcinoma, the direct stimulation of hepatocellular carcinoma by steroid hormones still awaits elucidation. On the other hand, clinical trials using antagonists for steroid hormones to treat hepatocellular carcinoma were found to be mostly ineffective. Recently it has been found that 2-methoxyestradiol - an estrogen metabolite - is effective in growth inhibition of various tumor cells as well as in angiogenesis inhibition. Since estrogen is metabolized in the liver, it is conceivable that females with menstruation cycles have more estrogen metabolized in their liver, consequently more 2-methoxyestradiol produced which could inhibit tumor growth in situ. We propose that the low incidence and mortality of hepatocellular carcinoma found in females may have resulted from the high levels of 2-methoxyestradiol produced in the liver during their reproductive years. Consequently, the growth of hepatocellular carcinoma in females is delayed significantly as compared to males. The potential of using 2-methoxyestradiol for treatment of patients with hepatocellular carcinoma after resection of tumor should be explored.

2-Methoxyestradiol, an endogenous metabolite of 17beta-estradiol, inhibits adipocyte proliferation

The effects of 2-methoxyestradiol (2ME), a naturally occurring mammalian metabolite of 17beta-estradiol, on adipocyte growth has been investigated in mouse brown adipose tissue precursor cells developed in primary culture. 2ME inhibits brown adipocyte proliferation in a dose-response manner (IC50 = 1.7 x 10(-6) M for DNA synthesis), with much higher potency than its hormone precursor 17beta-estradiol, and cells acquire the typical differentiated morphology--more round with a higher content of triglycerides. 2ME causes similar effects in the immortal brown adipocyte tumor-derived hibernoma cell line HIB 1B and the immortal 3T3-F442A white adipocyte line. These findings suggest a possible role for 2ME in adipocyte proliferation, and probably in the differentiation process, entering the cells in the adipogenic program.

Tubulin as a target for anticancer drugs: agents which interact with the mitotic spindle

Tubulin is the biochemical target for several clinically used anticancer drugs, including paclitaxel and the vinca alkaloids vincristine and vinblastine. This review describes both the natural and synthetic agents which are known to interact with tubulin. Syntheses of the more complex agents are referenced and the potential clinical use of the compounds is discussed. This review describes the biochemistry of tubulin, microtubules, and the mitotic spindle. The agents are discussed in relation to the type of binding site on the protein with which they interact. These are the colchicine, vinca alkaloid, rhizoxin/maytansine, and tubulin sulfhydryl binding sites. Also included are the agents which either bind at other sites or unknown sites on tubulin. The literature is reviewed up to October 1997.

Synthesis of analogs of 2-methoxyestradiol with enhanced inhibitory effects on tubulin polymerization and cancer cell growth

A new series of estradiol analogs was synthesized in an attempt to improve on the anticancer activity of 2-methoxyestradiol, a naturally occurring mammalian tubulin polymerization inhibitor. The compounds were evaluated as inhibitors of tubulin polymerization and the binding of [3H]colchicine to tubulin, as well as for in vitro cytotoxicity in human cancer cell cultures. Overall, the most potent of the new compounds were 2-(2',2',2'-trifluoroethoxy)-6-oximinoestradiol, 2-ethoxy-6-oximinoestradiol, and 2-ethoxy-6-methoximinoestradiol. These agents lacked significant affinity for the estrogen receptor. The cytotoxicities of the compounds correlated in general with their abilities to inhibit tubulin polymerization, thus supporting inhibition of tubulin polymerization as the primary mechanism causing inhibition of cell growth.

2-Methoxyestradiol, an endogenous estrogen metabolite, induces apoptosis in endothelial cells and inhibits angiogenesis: possible role for stress-activated protein kinase signaling pathway and Fas expression

2-Methoxyestradiol (2-ME) is an endogenous metabolite of estradiol-17beta and the oral contraceptive agent 17-ethylestradiol. 2-ME was recently reported to inhibit endothelial cell proliferation. The current study was undertaken to explore the mechanism of 2-ME effects on endothelial cells, especially whether 2-ME induces apoptosis, a prime mechanism in tissue remodeling and angiogenesis. Cultured bovine pulmonary artery endothelial cells (BPAEC) exposed to 2-ME showed morphological (including ultrastructural) features characteristic of apoptosis: cell shrinkage, cytoplasmic and nuclear condensation, and cell blebbing. 2-ME-induced apoptosis in BPAEC was a time- and concentration-dependent process (EC50 = 0.45 +/- 0.09 microM, n = 8). Nucleosomal DNA fragmentation in BPAEC treated with 2-ME was identified by agarose gel electrophoresis (DNA ladder) as well as in situ nick end labeling. Under the same experimental conditions, estradiol-17beta and two of its other metabolites, estriol and 2-methoxyestriol (< or =10 microM), did not have an apoptotic effect on BPAEC. 2-ME activated stress-activated protein kinase (SAPK)/c-Jun amino-terminal protein kinase in BPAEC in a concentration-dependent manner. The activity of SAPK was increased by 170 +/- 27% and 314 +/- 22% over the basal level in the presence of 0.4 and 2 microM 2-ME (n = 3-6), respectively. The activation of SAPK was detected at 10 min, peaked at 20 min, and returned to basal levels at 60 min after exposure to 2-ME. Inhibition of SAPK/c-Jun amino-terminal protein kinase activation by basic fibroblast growth factor, insulin-like growth factor, or forskolin reduced 2-ME-induced apoptosis. Immunohistochemical analysis of BPAEC indicated that 2-ME up-regulated expression of both Fas and Bcl-2. In addition, 2-ME inhibited BPAEC migration (IC50 = 0.71 +/- 0.11 microM, n = 4) and basic fibroblast growth factor-induced angiogenesis in the chick chorioallantoic membrane model. Taken together, these results suggest that promotion of endothelial cell apoptosis, thereby inhibiting endothelial cell proliferation and migration, may be a major mechanism by which 2-ME inhibits angiogenesis.

Interactions of 2-methoxyestradiol, an endogenous mammalian metabolite, with unpolymerized tubulin and with tubulin polymers

2-Methoxyestradiol (2ME) is an endogenous mammalian catabolite of estradiol with antimitotic activity. Although it is a competitive inhibitor of the binding of colchicine to tubulin, it has unusual effects on glutamate-induced tubulin polymerization. Polymer that was little changed in morphology assembled at a reduced rate and was relatively cold stable. We have now examined interactions of [4-3H]-2ME with unpolymerized tubulin and polymer. The [3H]2ME binds avidly to tubulin even on ice, and it is readily displaced by other colchicine site drugs. An association rate constant on ice of 1.9 x 10(2) M-1s-1 was obtained. Scatchard analysis indicated a single class of binding site and an association equilibrium constant of 5.7 x 10(5) M-1. These values lead to a calculated dissociation rate constant of 3.3 x 10(-4) s-1. In glutamate-induced tubulin assembly, a reaction that requires GTP and leads to the formation of sheets of parallel protofilaments, increasing amounts of [3H]2ME were incorporated into polymer, reaching near-stoichiometry with tubulin at 100 microM 2ME. Equivalent binding of [3H]2ME occurred when the drug was added to preformed polymer, but binding of [3H]2ME to polymer was not readily inhibited by colchicine site drugs. Significant amounts of [3H]2ME were also incorporated into microtubule polymer formed with microtubule-associated proteins, glycerol, or 4-morpholineethanesulfonate buffer, but the stoichiometry was substantially lower than that in the sheet polymer induced by either glutamate or 1,4-piperazineethanesulfonate buffer. The structural differences between the microtubule and sheet polymers leading to these differences in apparent affinity for 2ME are unknown, but presumably interaction of the estrogen metabolite with cellular microtubules has functional significance related to the antimitotic properties of the compound.

2-Methoxyestradiol, an endogenous mammalian metabolite, inhibits tubulin polymerization by interacting at the colchicine site

A metabolite of estradiol, 2-methoxyestradiol (2ME), inhibits angiogenesis in the chicken embryo chorioallantoic membrane assay. Since 2ME causes mitotic perturbations, we examined its interactions with tubulin. In our standard 1.0 M glutamate system (plus 1.0 mM MgCl2 at 37 degrees C), superstoichiometric concentrations (relative to tubulin) of 2ME inhibited the nucleation and propagation phases of tubulin assembly but did not affect the reaction extent. Although polymer formed in the presence of 2ME was more cold-stable than control polymer, morphology was little changed. Under suboptimal reaction conditions (0.8 M glutamate/no MgCl2 at 26 degrees C), substoichiometric 2ME totally inhibited polymerization. No other estrogenic compound was as effective as 2ME as an inhibitor of polymerization or of the binding of colchicine to tubulin. Inhibition of colchicine binding was competitive (Ki, 22 microM). Thus, a mammalian metabolite of estradiol binds to the colchicine site of tubulin and, depending on reaction conditions, either inhibits assembly or seems to be incorporated into a polymer with altered stability properties.

Serum concentration and urinary excretion of "classical" estrogens, catecholestrogens and 2-methoxyestrogens in normal human pregnancy

Catecholestrogens, 2-methoxyestrogens and "classical" estrogens (estrone, estradiol, estriol) were measured simultaneously in serum and urine samples of 220 pregnant women from the 8th week of pregnancy until to delivery. From these data we established the central 0.80 centile intervals as time specified reference intervals for each substance analyzed. Serum and urinary estradiol rise steadily during the progress of pregnancy, whereas estrone, catecholestrogens and 2-methoxyestrogens reach a plateau during the last trimester. These observations support the hypothesis, that the amount of the latter compounds may be regulated by separate mechanisms. The values of concentration and excretion of 2- and 4-substituted estrogens varied widely throughout pregnancy. Even very high or very low concentrations of these substances had no recognizable relation to the outcome of pregnancy. This supports the assumption that catecholestrogens and their methylethers are metabolites without any regulatory function in pregnancy.

Coordinated induction of estrogen hydroxylase and catechol-O-methyl transferase by xenobiotics in first trimester human placental explants

The estrogen phenol A-ring metabolism was investigated in the first trimester placenta using radioenzymatic techniques. In untested explants cultured for 16 h, estrogen hydroxylase (EH) but not catechol-O-methyl transferase (COMT) activity was increased significantly 1.8-fold (P less than 0.05). Cultures made in the presence of chemoprotectors, 25 microM of 1-phenylazo-2-naphthol (Sudan I) and coumarin but not 2(3)-tert-butyl-4-hydroxyanisole (BHA) caused a significant increase in EH activity, 1.8- and 2.2-fold, respectively (P less than 0.05). This was coupled with a significant, P less than 0.05, increase in the COMT activity by 25 microM of all three chemoprotectors, BHA, Sudan I, and coumarin, 2.7-, 2.3-, and 2-fold respectively. The carcinogens benzo(a)pyrene and 20-methylcholanthrene at 50 microM concentration, however, had no effect upon both enzymes' activity. Finally, the two enzymes's activities were correlated under the experimental conditions tested. Except for zero time where no correlation was found (r2 = 0.3), in all other experimental conditions, a significant (r2 = 0.75) correlation was observed. In conclusion, EH and COMT enzyme activities appear to undergo a coordinated induction in cultured placental explants in the first trimester. The implications of catechol metabolism for embryonal development are discussed.