New estrogen receptor antagonists. 3,20-Dihydroxy-19-norpregna-1,3,5(10)-trienes: Synthesis, molecular modeling, and biological evaluation

Targeting hormone-resistant breast cancer cells with docetaxel: a look inside the resistance

Aim: The study aims to analyze the effect of long-term incubation of ERα-positive MCF7 breast cancer cells with 4-hydroxytamoxifen (HT) on their sensitivity to tubulin polymerization inhibitor docetaxel. Methods: The analysis of cell viability was performed by the MTT method. The expression of signaling proteins was analyzed by immunoblotting and flow cytometry. ERα activity was evaluated by gene reporter assay. To establish hormone-resistant subline MCF7, breast cancer cells were treated with 4-hydroxytamoxifen for 12 months. Results: The developed MCF7/HT subline has lost sensitivity to 4-hydroxytamoxifen, and the resistance index was 2. Increased Akt activity (2.2-fold) and decreased ERα expression (1.5-fold) were revealed in MCF7/HT cells. The activity of the estrogen receptor α was reduced (1.5-fold) in MCF7/HT. Evaluation of class III β-tubulin expression (TUBB3), a marker associated with metastasis, revealed the following trends: higher expression of TUBB3 was detected in triple-negative breast cancer MDA-MB-231 cells compared to hormone-responsive MCF7 cells (P < 0.05). The lowest expression of TUBB3 was found in hormone-resistant MCF7/HT cells (MCF7/HT < MCF7 < MDA-MB-231, approximately 1:2:4). High TUBB3 expression strongly correlated with docetaxel resistance: IC₅₀ value of docetaxel for MDA-MB-231 cells was greater than that for MCF7 cells, whereas resistant MCF7/HT cells were the most sensitive to the drug. The accumulation of cleaved PARP (a 1.6-fold increase) and Bcl-2 downregulation (1.8-fold) were more pronounced in docetaxel-treated resistant cells (P < 0.05). The expression of cyclin D1 decreased (2.8-fold) only in resistant cells after 4 nM docetaxel treatment, while this marker was unchanged in parental MCF7 breast cancer cells. Conclusion: Further development of taxane-based chemotherapy for hormone-resistant cancer looks highly promising, especially for cancers with low TUBB3 expression.

Photoswitchable Diazocine-Based Estrogen Receptor Agonists: Stabilization of the Active Form inside the Receptor

Photopharmacology is an emerging approach in drug design and pharmacological therapy. Light is used to switch a pharmacophore between a biologically inactive and an active isomer with high spatiotemporal resolution at the site of illness, thus potentially avoiding side effects in neighboring healthy tissue. The most frequently used strategy to design a photoswitchable drug is to replace a suitable functional group in a known bioactive molecule with azobenzene. Our strategy is different in that the photoswitch moiety is closer to the drug's scaffold. Docking studies reveal a very high structural similarity of natural 17β-estradiol and the E isomers of dihydroxy diazocines, but not their Z isomers, respectively. Seven dihydroxy diazocines were synthesized and subjected to a biological estrogen reporter gene assay. Four derivatives exhibit distinct estrogenic activity after irradiation with violet light, which can be shut off with green light. Most remarkably, the photogenerated, active E form of one of the active compounds isomerizes back to the inactive Z form with a half-life of merely several milliseconds in water, but nevertheless is active for more than 3 h in the presence of the estrogen receptor. The results suggest a significant local impact of the ligand-receptor complex toward back-isomerization. Thus, drugs that are active when bound but lose their activity immediately after leaving the receptor could be of great pharmacological value because they strongly increase target specificity. Moreover, the drugs are released into the environment in their inactive form. The latter argument is particularly important for drugs that act as endocrine disruptors.

Towards Unravelling the Role of ERα-Targeting miRNAs in the Exosome-Mediated Transferring of the Hormone Resistance

Hormone therapy is one of the most effective breast cancer treatments, however, its application is limited by the progression of hormonal resistance, both primary or acquired. The development of hormonal resistance is caused either by an irreversible block of hormonal signalling (suppression of the activity or synthesis of hormone receptors), or by activation of oestrogen-independent signalling pathways. Recently the effect of exosome-mediated intercellular transfer of hormonal resistance was revealed, however, the molecular mechanism of this effect is still unknown. Here, the role of exosomal miRNAs (microRNAs) in the transferring of hormonal resistance in breast cancer cells has been studied. The methods used in the work include extraction, purification and RNAseq of miRNAs, transfection of miRNA mimetics, immunoblotting, reporter analysis and the MTT test. Using MCF7 breast cancer cells and MCF7/T tamoxifen-resistant sub-line, we have found that some miRNAs, suppressors of oestrogen receptor signalling, are overexpressed in the exosomes of the resistant breast cancer cells. The multiple (but not single) transfection of one of the identified miRNA, miR-181a-2, into oestrogen-dependent MCF7 cells induced the irreversible tamoxifen resistance associated with the continuous block of the oestrogen receptor signalling and the activation of PI3K/Akt pathway. We suppose that the miRNAs-ERα suppressors may act as trigger agents inducing the block of oestrogen receptor signalling and breast cancer cell transition to an aggressive oestrogen-independent state.

Glucose starvation greatly enhances antiproliferative and antiestrogenic potency of oligomycin A in MCF-7 breast cancer cells

Energy imbalance is one of the key properties of tumour cells, which in certain cases supports fast cancer progression and resistance to therapy. The simultaneous blocking of glycolytic processes and oxidative phosphorylation pathways seems to be a promising strategy for antitumor therapies. The study aimed to evaluate the effect of glucose starvation on the antiproliferative and antiestrogenic potency of oligomycin A against hormone-dependent breast cancer cells. Cell viability was assessed by the MTT test. Estrogen receptor alpha (ERα) activity was evaluated by reporter assay. mTOR, AMPK, Akt, and S6 kinase expression was assessed by immunoblotting. Glucose starvation caused multiple increases in the antiproliferative potency of oligomycin A in the hormone-dependent breast cancer MCF-7 cells, while its effect on the sensitivity of the second hormone-dependent cancer cell line, named T47D, was weak and limited. Glycolytic inhibitors, 3-bromopyruvate and 2-deoxyglucose, greatly enhanced the antiproliferative potency of oligomycin A in MCF-7 cells. Glucose starvation leads to remarkable activation of Akt in MCF-7 cells, whereas oligomycin A enhances its effect. The mTOR, S6 kinase, and AMPK signalling pathways are significantly modulated by oligomycin A under glucose starvation. Oligomycin A demonstrates more pronounced antiestrogenic effects under glucose starvation. Thus, glucose starvation and pharmacological inhibition of glycolysis are of interest for revealing the antitumor potential of macrolide oligomycin A against hormone-dependent breast cancers.

Radical Tandem Bicyclization Triggered by the α-Position of α,β-Unsaturated Ketones Bearing Nonterminal 1,6-Enynes: Synthesis of the 5H-Benzo[a]fluoren-5-one Skeleton

A novel method for the synthesis of 5H-benzo[a]fluoren-5-one from inactive nonterminal 1,6-alkynes through a free radical tandem bicyclization process has been established. This process achieved a continuous cyclization triggered rarely by the α-position of α,β-unsaturated ketones. The reaction constructed three C-C bonds in one step with the readily accessible substrates and excellent substrate compatibility.

Most recent strategies targeting estrogen receptor alpha for the treatment of breast cancer

Breast cancer is the most prominent, frequently diagnosed and leading cause of death among women. Estrogen is an agonist of estrogen receptor alpha (ER-α), expressed in mammary glands and is responsible for initiating many signalling pathways that lead to differentiation and development of breast tissue. Any mutations in these signalling pathways result in irregular growth of mammary tissue, leading to the development of tumour or cancer. All these observations attract the attention of researchers to antagonize ER-α receptor either by developing selective estrogen receptor modulators or by selective estrogen receptor degraders. Therefore, this article provides a brief overview of various factors that are responsible for provoking breast cancer in women and design strategies recently used by the various research groups across the world for antagonizing or demodulating ER-α.

In vivo study on biotransformation of pentacyclic analogs of progesterone: Identification of their metabolites by HPLC-MS method

Progesterone derivatives containing the D' additional cyclohexane ring in the 16α,17α-positions of steroid core (pregna-D'-pentaranes) exhibited high in vitro and in vivo selective progestogenic activity. The assessment of their biotransformation in the body, and the identification of possible metabolites are integral parts of a potential drug studies. Here we describe the results of in vivo metabolic transformation of 6α-methyl-16α,17α-cyclohexanopregn-4-ene-3,20-dione 1 and its 6-demethylated analog 2 and identification of their metabolites in rat urine. We synthesized and fully characterized (1D and 2D NMR, HRMS) 11 possible metabolites as the standards. Then we developed the LC-MS/MS assay including sample preparation and chromatography conditions for identification of the detected metabolites of 1 and 2. The 5α- and 5β-3,20-diketo-, 3β-hydroxy-20-keto-5α-, 3-keto-20(S)-hydroxy-5α-, 3β,20(S)-dihydroxy-5α-metabolites of compounds 1 and 2 were found in rat urine samples. The starting steroids 1 and 2, as well as both 3β,20(R)-dihydroxy metabolites were not detected in the examined biological urine samples. Thus, we demonstrate for the first time that exogenous progestines - pregna-D'-pentaranes - and endogenous progesterone follow similar metabolic pathways. Therefore, despite the presence of an additional ring D' and the methyl group in position 6, the main enzymatic transformations are similar to those of the natural hormone.

Estrogen alpha receptor antagonists for the treatment of breast cancer: a review

Background

Cancer is at present one of the leading causes of death in the world. It accounts for 13% of deaths occurred worldwide and is continuously rising, with an estimated million of deaths up to 2030. Due to poor availability of prevention, diagnosis and treatment of breast cancer, the rate of mortality is at alarming level globally. In women, hormone-dependent estrogen receptor positive (ER+) breast cancer making up approximately 75% of all breast cancers. Hence, it has drawn the extensive attention of researchers towards the development of effective drugs for the treatment of hormone-dependent breast cancer. Estrogen, a female sex hormone has a vital role in the initiation and progression of breast malignancy. Therefore, estrogen receptor is the central target for the treatment of breast cancer.

Conclusion

In this review, we have studied various classes of antiestrogens that have been designed and synthesized with selective binding for estrogen alpha receptor (ER). Since estrogen receptor α is mainly responsible for the breast cancer initiation and progression, therefore there is need of promising strategies for the design and synthesis of new therapeutic ligands which selectively bind to estrogen alpha receptor and inhibit estrogen dependent proliferative activity.

3,20-Dihydroxy-13α-19-norpregna-1,3,5(10)-trienes. Synthesis, structures, and cytotoxic, estrogenic, and antiestrogenic effects

New 3,20-dihydroxy-13α-19-norpregna-1,3,5(10)-trienes were synthesized. The effects of these compounds on breast cancer cells and ERα activation were investigated. The scaffold of compounds containing the six-membered ring D' annulated at 16α,17α-positions was constructed via the Lewis acid catalyzed Diels-Alder reaction of butadiene with 3-methoxy-13α-19-norpregna-1,3,5(10),16-tetraen-20-one 5 under a pressure of 600 MPa. The hydrogenation of primary cyclohexene adduct 6 followed by the one-pot reduction-demethylation (DIBAH) gave target epimeric 3,20-dihydroxy steroids 8a and 8b. The Corey-Chaykovsky reaction of the same conjugated ketone 5 gave a 16α,17α-methylene-substituted compound. The reaction of the latter with DIBAH yielded 3,20(R,S)-dihydroxy-16α,17α-methyleno-13α-19-norpregna-1,3,5(10)-triene 10. The hydrogenation of the 16,17-double bond of compound 5 produced a mixture of 17α- and 17β-epimeric ketones, reduction-demethylation of which gave 3,20(S)-dihydroxy-13α,17α-19-norpregna-1,3,5(10)-triene 12a and 3,20(R)-dihydroxy-13α,17β-19-norpregna-1,3,5(10)-triene 12b. All compounds were fully characterized by 1D and 2D NMR, HRMS, and X-ray diffraction. All target compounds showed pronounced cytotoxic effect against MCF-7 breast cancer cells and NCI/ADR-RES doxorubicin-resistant cells at micromolar concentrations. The ERα-mediated luciferase reporter gene assay demonstrated that all compounds, except for compound 10, are ERα inhibitors, while cyclopropane compound 10 proved to be an ERα activator. Docking experiments showed that all compounds are well accommodated to LBD ERα but have some differences in the binding mode.

Structure-activity relationships of 2, 4-disubstituted pyrimidines as dual ERα/VEGFR-2 ligands with anti-breast cancer activity

Both ERα and VEGFR-2 are important targets for cancer therapies. Here a series of 2, 4-disubstituted pyrimidine derivatives were designed, synthesized and evaluated as dual ERα/VEGFR-2 ligands. Most of the derivatives exhibited potent activities in both enzymatic and cellular assays. Structure-activity relationship studies showed that a hydrogen-bonding interaction in the head section is important factors for the enhancement of ERα-binding affinity. The most potent compound II-9OH, an analog of 2-(4-hydroxylphenyl)pyrimidine, was 19-fold more efficacious than tamoxifen in MCF-7 cancer cells and exhibited the best ERα binding affinity (IC₅₀ = 1.64 μM) as well as excellent VEGFR-2 inhibition (IC₅₀ = 0.085 μM). Furthermore, this dual targeted compound II-9OH exerted significantly antiestrogenic property via suppressing the expression of progesterone receptor (PgR) mRNA in MCF-7 cells and also showed obvious in vivo angiogenesis inhibitory effects in CAM assay. An induction of apoptosis and a decrease in cell migration, accompanied by transduction inhibition of Raf-1/MAPK/ERK pathway, were observed in MCF-7 cells after treatment with II-9OH, suggesting that II-9OH is a promising candidate for the development of multifunctional agents targeting ERα and VEGFR-2 in the therapy of some breast cancers.