Toshifumi Niwa

Separatory Determination of Bile Acid 3‐Sulfates by Liquid Chromatography/Electrospray Ionization Mass Spectrometry

A method for the separatory determination of bile acid 3-sulfates by liquid chromatography (LC)/electrospray ionization (ESI) mass spectrometry (MS) was developed. The sulfates were characterized by an abundant pseudomolecular ion [M - H] - with a doubly charged ion (M - 2H] 2- , and the ratio of these negative ions was markedly influenced by an acidic component of salt added to the mobile phase according to the pK a value of the conjugated form at C-24. The resolution into unconjugated and glycine-and taurine-conjugated cholic acid, chenodeoxycholic acid, deoxycholic acid, ursodeoxycholic acid and lithocholic acid 3-sulfates was achieved on a Capcell Pak C 18 column with 20 mM ammonium acetate-methanol (10:12, v/v) by selected ion monitoring, monitored with their corresponding pseudo-molecular ions. The combined use of stable isotope-labeled compounds as internal standards in LC/MS was applied to the determination of bile acid 3-sulfates in human urine.

Separation and Detection of Bile Acid 3-Glucuronides in Human Urine by Liquid Chromatography/Electrospray Ionization–Mass Spectrometry

A method for the separation and detection of bile acid 3-glucuronides by liquid chromatography (LC)/electrospray ionization (ESI)-mass spectrometry (MS) has been developed. On the ESI mode, glucuronides were characterized by an intense pseudo-molecular ion [M-h]- with a doubly charged ion [M-2H]2-, and the ratio of these negative ions were markedly influenced by an acidic component of salt added to a mobile phase, according to a pKa value of an acidic moiety at C-24. Bile acid 3-glucuronides in human urine were extracted with a SepPak C18 cartridge, followed by purification on lipophylic ion exchange gel, piperidinohydroxypropyl Sephadex LH-20. Subsequent resolution into unconjugated, glycine and taurine conjugated bile acid 3-glucuronides was attained by LC on a Develosil ODS-HG-5 column using 20 mM ammonium acetate (pH 7.0)-methanol (10:12, v/v) as a mobile phase, where 3-glucuronides were monitored with a characteristic negative ion [M-H]-. The newly developed method was applied to the quantitatiation of bile acid 3-glucuronides in human urine with satisfactory sensitivity and reliability.

Separation and Characterization of Carboxyl-linked Glucuronides of Bile Acids in Incubation Mixture of Rat Liver Microsomes

The carboxyl-linked 24-glucuronides of common bile acids have been identified by means of liquid chromatography (LC)/atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) in an incubation mixture with a male Wistar rat liver microsomal fraction. The authentic specimens of bile acid 24-glucuronide acetate-methyl esters were synthesized unequivocally using the Mitsunobu reaction, and the APCI-mass spectrometric properties of these glucuronide derivatives were also characterized. After incubation of common unconjugated bile acids with hepatic microsomes, glucuronides were extracted and purified with a Sep-Pak C18 cartridge and lipophilic ion exchange gel, piperidino-hydroxypropyl Sephadex LH-20, and then derivatized into the acetate-methyl esters. Subsequent resolution into alpha- and beta-isomers at the glucuronosyl linkage was attained by LC on Cosmosil 5C8 and Sumichiral OA-2500 columns using 200 mM ammonium acetate (pH 7.0)-methanol (1:4, v/v), where 24-glucuronides were monitored with characteristic positive ions [M + NH4]+. The 24-glucuronides of lithocholic, chenodeoxycholic, deoxycholic, ursodeoxycholic and cholic acid were definitely characterized, in contrast to no formation of corresponding 3-glucuronides.

Increased androgen receptor activity and cell proliferation in aromatase inhibitor-resistant breast carcinoma

Aromatase inhibitors (AI) are commonly used to treat postmenopausal estrogen-receptor (ER)-positive breast carcinoma. However, resistance to AI is sometimes acquired, and the molecular mechanisms underlying such resistance are largely unclear. Recent studies suggest that AI treatment increases androgen activity during estrogen deprivation in breast carcinoma, but the role of the androgen receptor (AR) in breast carcinoma is still a matter of controversy. The purpose of this study is to examine the potential correlation between the AR- and AI-resistant breast carcinoma. To this end, we performed immunohistochemical analysis of 21 pairs of primary breast carcinoma and corresponding AI-resistant recurrent tissue samples and established two stable variant cell lines from ER-positive T-47D breast carcinoma cell line as AI-resistance models and used them in in vitro experiments. Immunohistochemical analysis demonstrated that the expression of prostate-specific antigen (PSA) and Ki-67 were significantly higher and ER and progesterone receptor (PR) were lower in recurrent lesions compared to the corresponding primary lesions. Variant cell lines overexpressed AR and PSA and exhibited neither growth response to estrogen nor expression of ER. Androgen markedly induced the proliferation of these cell lines. In addition, the expression profile of androgen-induced genes was markedly different between variant and parental cell lines as determined by microarray analysis. These results suggest that in some cases of ER-positive breast carcinoma, tumor cells possibly change from ER-dependent to AR-dependent, rendering them resistant to AI. AR inhibitors may thus be effective in a selected group of patients.

Possible role of the aromatase-independent steroid metabolism pathways in hormone responsive primary breast cancers

Aromatase inhibitors (AIs) exert antiproliferative effects by reducing local estrogen production from androgens in postmenopausal women with hormone-responsive breast cancer. Previous reports have shown that androgen metabolites generated by the aromatase-independent enzymes, 5α-androstane-3β, 17β-diol (3β-diol), androst-5-ene-3β, and 17β-diol (A-diol), also activate estrogen receptor (ER) α. Estradiol (E2) can also reportedly be generated from estrone sulfate (E1S) pooled in the plasma. Estrogenic steroid-producing aromatase-independent pathways have thus been proposed as a mechanism of AI resistance. However, it is unclear whether these pathways are functional in clinical breast cancer. To investigate this issue, we assessed the transcriptional activities of ER in 45 ER-positive human breast cancers using the adenovirus estrogen-response element-green fluorescent protein assay and mRNA expression levels of the ER target gene, progesterone receptor, as indicators of ex vivo and in vivo ER activity, respectively. We also determined mRNA expression levels of 5α-reductase type 1 (SRD5A1) and 3β-hydroxysteroid dehydrogenase type 1 (3β-HSD type 1; HSD3B1), which produce 3β-diol from androgens, and of steroid sulfatase (STS) and 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD type 1; HSD17B1), which produce E2 or A-diol from E1S or dehydroepiandrosterone sulfate. SRD5A1 and HSD3B1 expression levels were positively correlated with ex vivo and in vivo ER activities. STS and HSD17B1 expression levels were positively correlated with in vivo ER activity alone. Elevated expression levels of these steroid-metabolizing enzymes in association with high in vivo ER activity were particularly notable in postmenopausal patients. Analysis of the expression levels of steroid-metabolizing enzymes revealed positive correlations between SRD5A1 and HSD3B1, and STS and HSD17B1. These findings suggest that the SRD5A1-HSD3B1 as well as the STS-HSD17B pathways, could contributes to ER activation, especially postmenopause. These pathways might function as an alternative estrogenic steroid-producing, aromatase-independent pathways.

Estrogen signaling pathway and its imaging in human breast cancer

Recent remarkable progress in hormonal therapy has provided great benefit to breast cancer patients, but it also evokes novel issues: how accurately can the efficacy of each hormonal therapy be predicted and how can hormonal therapy–resistant patients be treated? These clinically important issues must be closely related to the biological events in each cancer, such as the alteration of intracellular multiple estrogen signaling pathways and the estrogen‐related cancer microenvironment, which has recently revealed by molecular biological studies on estrogen and its receptors. However, the estrogen signaling status in individual breast cancers has not been clarified yet. Here we present the context of these issues and introduce our study of new tools which enable the visualization of estrogen signals in individual cancers. The assessment of estrogen receptor (ER)‐α activity in individual cancers or ER‐activating ability of the cancer microenvironment in each breast cancer patient revealed several new findings and interesting observations. We hope that these approaches provide new clues about the estrogen‐dependent mechanisms of breast cancer development, and will be useful to advance the diagnosis and treatment of breast cancer patients. (Cancer Sci 2009; 100: 1773–1778)

Individual transcriptional activity of estrogen receptors in primary breast cancer and its clinical significance

To predict the efficacy of hormonal therapy at the individual‐level, immunohistochemical methods are used to analyze expression of classical molecular biomarkers such as estrogen receptor (ER), progesterone receptor (PgR), and HER2. However, the current diagnostic standard is not perfect for the individualization of diverse cases. Therefore, establishment of more accurate diagnostics is required. Previously, we established a novel method that enables analysis of ER transcriptional activation potential in clinical specimens using an adenovirus estrogen response element–green fluorescence protein (ERE‐GFP) assay system. Using this assay, we assessed the ERE transcriptional activity of 62 primary breast cancer samples. In 40% of samples, we observed that ER protein expression was not consistent with ERE activity. Comparison of ERE activity with clinicopathological information revealed that ERE activity was significantly correlated with the ER target gene, PgR, rather than ER in terms of both protein and mRNA expression. Moreover, subgrouping of Luminal A‐type breast cancer samples according to ERE activity revealed that ERα mRNA expression correlated with ER target gene mRNA expression in the high‐, but not the low‐, ERE‐activity group. On the other hand, the low‐ERE‐activity group showed significantly higher mRNA expression of the malignancy biomarker Ki67 in association with disease recurrence in 5% of patients. Thus, these data suggest that ER expression does not always correlate with ER transcriptional activity. Therefore, in addition to ER protein expression, determination of ERE activity as an ER functional marker will be helpful for analysis of a variety of diverse breast cancer cases and the subsequent course of treatment.

Estrogen Response element-GFP (ERE-GFP) introduced MCF-7 cells demonstrated the coexistence of multiple estrogen-deprivation resistant mechanisms

The acquisition of estrogen-deprivation resistance and estrogen receptor (ER) signal-independence in ER-positive breast cancer is one of the crucial steps in advancing the aggressiveness of breast cancer; however, this has not yet been elucidated in detail. To address this issue, we established several estrogen-deprivation-resistant (EDR) breast cancer cell lines from our unique MCF-7 cells, which had been stably transfected with an ERE-GFP reporter plasmid. Three cell lines with high ER activity and another 3 cell lines with no ER activity were established from cell cloning by monitoring GFP expression in living cells. The former three ERE-GFP-positive EDR cell lines showed the overexpression of ER and high expression of several ER-target genes. Further analysis of intracellular signaling factors revealed a marked change in the phosphorylation status of ERα on Ser167 and Akt on Thr308 by similar mechanisms reported previously; however, we could not find any changes in MAP-kinase factors. Comprehensive phospho-proteomic analysis also indicated the possible contribution of the Akt pathway to the phosphorylation of ERα. On the other hand, constitutive activation of c-Jun N-terminal kinase (JNK) was observed in ERE-GFP-negative EDR cells, and the growth of these cells was inhibited by a JNK inhibitor. An IGF1R-specific inhibitor diminished the phosphorylation of JNK, which suggested that a novel signaling pathway, IGF1R-JNK, may be important for the proliferation of ER-independent MCF-7 cells. These results indicate that ER-positive breast cancer cells can acquire resistance by more than two mechanisms at a time, which suggests that multiple mechanisms may occur simultaneously. This finding also implies that breast cancers with different resistance mechanisms can concomitantly occur and mingle in an individual patient, and may be a cause of the recurrence of cancer.

Studies on steroids : CCXXIX. Separation and characterization of catechol oestrogen glucuronides in urine of pregnant women by high-performance liquid chromatography

The separation and characterization of catechol oestrogen glucuronides in the urine of pregnant women by high-performance liquid chromatography with electrochemical detection is described. The urine samples from pregnant women were passed through Amberlite XAD-2 and Sep-Pak C18 columns and subsequented to ion-exchange chromatography on piperidinohydroxypropyl Sephadex LH-20 to isolate the oestrogen glucuronide fraction. The subsequent resolution into individual oestrogen glucuronides was achieved by high-performance liquid chromatography on a reversed-phase column. 2-Hydroxyoestrone 2-glucuronide and 4-hydroxyoestrone 4-glucuronide were identified on the basis of their behaviour in high-performance liquid chromatography with three different mobile phases. Derivatization of two glucuronides with 2-ferrocenylethylamine, followed by chromatographic separation and measurement of hydrodynamic voltammograms with an electrochemical detector was carried out for unequivocal identification. Enzymatic cleavage of the glucuronoside linkage followed by the identification of deconjugated catechol oestrogens by high-performance liquid chromatography with electrochemical detection further supported the structural assignment of these metabolites. The ratio between the amounts of 2-hydroxyoestrone 2-glucuronide and 4-hydroxyoestrone 4-glucuronide excreted in the urine of pregnant women was found to be ca. 5:1.

Contribution of Estrone Sulfate to Cell Proliferation in Aromatase Inhibitor (AI) -Resistant, Hormone Receptor-Positive Breast Cancer

Aromatase inhibitors (AIs) effectively treat hormone receptor-positive postmenopausal breast cancer, but some patients do not respond to treatment or experience recurrence. Mechanisms of AI resistance include ligand-independent activation of the estrogen receptor (ER) and signaling via other growth factor receptors; however, these do not account for all forms of resistance. Here we present an alternative mechanism of AI resistance. We ectopically expressed aromatase in MCF-7 cells expressing green fluorescent protein as an index of ER activity. Aromatase-overexpressing MCF-7 cells were cultured in estrogen-depleted medium supplemented with testosterone and the AI, letrozole, to establish letrozole-resistant (LR) cell lines. Compared with parental cells, LR cells had higher mRNA levels of steroid sulfatase (STS), which converts estrone sulfate (E1S) to estrone, and the organic anion transporter peptides (OATPs), which mediate the uptake of E1S into cells. LR cells proliferated more in E1S-supplemented medium than did parental cells, and LR proliferation was effectively inhibited by an STS inhibitor in combination with letrozole and by ER-targeting drugs. Analysis of ER-positive primary breast cancer tissues showed a significant correlation between the increases in the mRNA levels of STS and the OATPs in the LR cell lines, which supports the validity of this AI-resistant model. This is the first study to demonstrate the contribution of STS and OATPs in E1S metabolism to the proliferation of AI-resistant breast cancer cells. We suggest that E1S metabolism represents a new target in AI-resistant breast cancer treatment.