Inhibition of rat liver microsomal estrogen 2-hydroxylase by 2-methoxyestrogens

Novel combination of 2-methoxyestradiol and cyclophosphamide enhances the antineoplastic and pro-apoptotic effects on S-180 ascitic tumour cells

Sarcoma 180 (S-180) tumour cell line is a stable murine tumour cell line with 98-99% stumour takes capacity in Swiss albino mouse - Mus musculus. 2 Methoxyestradiol (2ME) - a promising anti-neoplastic and anti-angiogenic agent, showed toxicity to host body in higher concentration. Cyclophosphamide (CP), the anti-neoplastic agent has long been used as a chemotherapeutic drug for treatment of different cancers. Our studies have shown that the combination effect of 2ME and CP on S-180 tumour cell line is anti-proliferative and less toxic. The treatment with lower concentrations of 2ME and CP (6.5 mg 2ME/kg body weight + 75 mg CP/kg body weight) antagonistically increased the life span of tumour bearing mice and synergistically inhibited the viable cell population. 2ME or CP treatment individually induces G2/M arrest. The combination treatment of 2ME + CP (6.5 mg 2ME/kg body weight + 75 mg CP/kg body weight) produced a significant increase of cells in the G0 which is the indication of cell arrest or apoptosis. Reduction of cell viability by 2ME + CP treatments is due to apoptotic cell death. This combination therapy produced a significant inhibitory effect of cell proliferation and augmentation of cell accumulation in the G0 phase (i.e. apoptosis). Apoptosis is validated by Fluorescence staining of control and treated S-180 tumour cells with Acridine Orange and EtBr dye. Moreover, a steady increase in the frequency of complex chromosomal aberrations (i.e. tri-, qudri-radial translocations) in tumour cells was noted in that particular concentration of combination therapy treated series along with the increase in dead cell frequency and tumour regression pattern. It is assumed that, these chromosomal abnormalities or damages recorded in higher frequency prevent the affected metaphases to enter into the next cell cycle through apoptosis or necrosis. This study introduces a novel combination, where this particular concentration of 2ME + CP (i.e. 6.5 mg 2ME/kg body weight + 75 mg CP/kg body weight) not only enhanced the life span of tumour bearing mouse and decreased the tumour volume antagonistically but also inhibited the viable cell population synergistically, which could serve as a potential effective regimen for cancer treatment.

Two faces of the estrogen metabolite 2-methoxyestradiol in vitro and in vivo

2-Methoxyestradiol (2-ME), an endogenous metabolite of 17β-estradiol (E2), interacts with estrogen receptors (ERs) and microtubules, however, 2-ME has a low affinity for ERs. Furthermore, 2‑ME has been identified as a potential novel antitumor agent, combining its anti‑proliferative effects on a variety of tumor cell types with its anti‑angiogenic action. Therefore, 2‑ME is of interest due to its potential anticancer therapeutic effects. In the current study, the estrogenic effect of 2‑ME on CaBP‑9k, ERα, and progesterone receptor (PR) mRNA levels in the absence and presence of E2 and progesterone (P4) in in vivo and in vitro models was examined. In GH3 cells, the mRNA level of CaBP‑9k was induced in the E2 treatment group (concentration, 10‑9 M), and the expression of CaBP‑9k was also upregulated in the 2‑ME‑treated group (concentration, 10‑7 M). Uterine lactoferrin (Ltf) mRNA expression was also increased in the 2‑ME group [dose, 40 mg/kg body weight (BW)], which was comparable to the response with E2 (dose, 40 µg/kg BW) observed in mice. As inhibitors of ER and PR activity, ICI 182,780 and mifepristone (RU486) were observed to reverse the E2 or 2‑ME mediated increase of CaBP‑9k and Ltf mRNA expression. In addition, it was found that 2‑ME significantly decreased the levels of ERα and increased PR transcripts. Consistent with the in vitro results, the mRNA levels revealed decreased ERα and increased PR in in vivo treatment of E2 and 2‑ME. These findings demonstrate that the expression of estrogenic markers, CaBP‑9k and Ltf, is regulated by 2‑ME in in vitro and in vivo models, therefore, estrogenic activi-ties of 2-ME may be increased in females during the estrous cycle via the ER and/or PR-mediated signaling pathway.

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.

Estrogen metabolism in microsomal, cell, and tissue preparations of kidney and liver from Syrian hamsters

The estrogen-treated golden Syrian hamster has been used as an experimental model for estrogen-induced and estrogen-dependent cancers, but pathways to neoplastic transformation remain unknown in this animal. Metabolism of estrogens to activated or reactive compounds, followed by subsequent oxidative damage to the target tissue, remains a potential step in the tumorigenic process. In this study, the extent of estrogen metabolism is compared in three different in vitro preparations from untreated and estrogen-treated Syrian hamsters, primary kidney cell cultures, microsomal preparations, and freshly prepared tissue kidney slices. In primary kidney cell cultures, the amount of catechol estrogens decreased upon increasing estrogen (DES) treatment period, and completely disappeared after about 6 months treatment. This decrease is not a result of formation of less amounts of catechol estrogens, but rather reflects the presence of the enzyme systems to further metabolize any formed catechol estrogens, since the amount of catechol estrogens formed, as detected by 3H2O release, is unchanged. The polar metabolites a, b and c increased with estrogen treatment, and metabolite c appeared only after DES treatment. The appearance of polar metabolite c only in kidney preparations from DES-treated animals implies that it may serve as a marker of cellular transformation. Estriol and estrone were detected, but were not affected by DES treatment, while no methoxyestrogens were isolated. Studies of estradiol metabolism in microsomal preparations showed a very low rate of metabolism, compared to the primary kidney cell cultures. In contrast, estrogen metabolism was extensive in kidney slices from untreated hamsters, with only approx. 30% of the substrate estradiol remaining unmetabolized after 6 h of incubation. While no catechol estrogens were detected, a small quantity of estriol, and a large amount of estrone and methoxyestrogens were isolated. The polar metabolite a was the main polar metabolite detected, with very little of metabolite b and no metabolite c. In kidney slices from 4 month DES-treated hamsters, a much higher amount of polar metabolites was detected, and metabolite c appeared after 6 h incubation. Mass spectrometric analysis and HPLC data of metabolite c indicate that this metabolite is 15 alpha-hydroxyesteradiol. This metabolite may serve as a biomarker for changes occurring in the hamster kidney cells under continuous estrogen exposure. Finally, formation of water soluble conjugates was demonstrated in both kidney slices and liver slices from Syrian hamsters, with glucuronide, sulfate and thioether conjugates of estrone and estradiol and glucuronides of catechol estrogens detected.(ABSTRACT TRUNCATED AT 400 WORDS)

Enzymatic O-methylation of catechol estrogens in red blood cells: differences in animal species and strains

Enzymatic O-methylation of catechol estrogens in red blood cells has been investigated with respect to species difference. In the presence of S-adenosylmethionine, 2- or 4-hydroxyestradiol (2-OHE2 or 4-OHE2) was incubated with blood lysate obtained from rats (five strains), guinea pigs, mice, rabbits, dogs, monkeys, and humans, respectively. The yielded guaiacols and unchanged substrate were determined by gas chromatography/mass spectrometry in a selected ion monitoring mode employing the corresponding 2H4-labeled compounds as internal standards. The total amounts of guaiacols formed from 2-OHE2 and 4-OHE2 were different, being the highest (79.6% and 38.1%) in monkeys and the lowest (5.1% and 1.9%) in humans. The ratios of isomeric guaiacols formed from 4-OHE2 (4Me/3Me) were 7.6-71, while those from 2-OHE2 (2Me/3Me) were 1.4-3.2. Thus, marked differences in O-methylation of catechol estrogens were observed among animal species, but no significant strain difference was detected in rats.

Determination of catechol and guaiacol estrogens in urine by capillary gas chromatography/mass spectrometry

A gas chromatographic (GC)/mass spectrometric method for the simultaneous determination in urine of 2- and 4-hydroxyestrones and hydroxyestradiols, and their monomethyl ethers, is described. Separation of these catechol and guaiacol estrogens was achieved by derivatization into their trimethylsilyl and tert-butyldimethylsilyl ethers, followed by capillary GC on a DB-1 column. The calibration graphs were satisfactorily constructed for these estrogen metabolites by selected ion monitoring at the respective molecular ions using 2-bromoestrone and 4-hydroxyestradiol-d3 3-methyl ether as internal standards. The extraction and purification of the desired estrogens in biological fluids were effected by the combined use of Extrelut-3 and ion exchange columns. The sensitivity and reliability obtained by the newly developed method has proved to be satisfactory for the quantitation of catechol and guaiacol estrogens in human urine.