Impact of estradiol structural modifications (18-methyl and/or 17-hydroxy inversion of configuration) on the in vitro and in vivo estrogenic activity

Synthesis of Estrone Heterodimers and Evaluation of Their In Vitro Antiproliferative Activity

Directed structural modifications of natural products offer excellent opportunities to develop selectively acting drug candidates. Natural product hybrids represent a particular compound group. The components of hybrids constructed from different molecular entities may result in synergic action with diminished side effects. Steroidal homo- or heterodimers deserve special attention owing to their potentially high anticancer effect. Inspired by our recently described antiproliferative core-modified estrone derivatives, here, we combined them into heterodimers via Cu(I)-catalyzed azide-alkyne cycloaddition reactions. The two trans-16-azido-3-(O-benzyl)-17-hydroxy-13α-estrone derivatives were reacted with 3-O-propargyl-D-secoestrone alcohol or oxime. The antiproliferative activities of the four newly synthesized dimers were evaluated against a panel of human adherent gynecological cancer cell lines (cervical: Hela, SiHa, C33A; breast: MCF-7, T47D, MDA-MB-231, MDA-MB-361; ovarian: A2780). One heterodimer (12) exerted substantial antiproliferative activity against all investigated cell lines in the submicromolar or low micromolar range. A pronounced proapoptotic effect was observed by fluorescent double staining and flow cytometry on three cervical cell lines. Additionally, cell cycle blockade in the G2/M phase was detected, which might be a consequence of the effect of the dimer on tubulin polymerization. Computational calculations on the taxoid binding site of tubulin revealed potential binding of both steroidal building blocks, mainly with hydrophobic interactions and water bridges.

Cytotoxic effect of 13α-estrane derivatives on breast, endometrial and ovarian cancer cell lines

Hormone-dependent cancers such as breast, uterine, and ovarian cancers account for more than 35% of all cancers in women. Worldwide, these cancers occur in more than 2.7 million women/year and account for 22% of cancer-related deaths/year. The generally accepted mechanism for the pathophysiology of estrogen-dependent cancers is estrogen receptor-mediated cell proliferation associated with an increased number of mutations. Therefore, drugs that can interfere with either local estrogen formation or estrogen action via estrogen receptors are needed. Estrane derivatives that have low or minimal estrogenic activity can affect both pathways. In this study, we investigated the effect of 36 different estrane derivatives on the proliferation of eight breast, endometrial, and ovarian cancer cell lines and the corresponding three control cell lines. Estrane derivatives 3 and 4_2Cl showed a stronger effect on the endometrial cancer cell lines KLE and Ishikawa, respectively, compared with the control cell line HIEEC, with IC50 values of 32.6 microM and 17.9 microM, respectively. Estrane derivative 4_2Cl was most active in the ovarian cancer cell line COV362 compared to the control cell line HIO80 with an IC50 value of 3.6 microM. In addition, estrane derivative 2_4I showed a strong antiproliferative effect on endometrial and ovarian cancer cell lines, while the effect on the control cell line was slight or absent. The addition of halogen at carbon 2 and/or 4 in estrane derivatives 1 and 2 increased the selectivity for endometrial cancer cells. Overall, these results suggest that single estrane derivatives are efficient cytotoxic agents for endometrial and ovarian cancer cell lines, and thus potential lead compounds for drug development.

Investigation of the Antineoplastic Effects of 2-(4-Chlorophenyl)-13α-Estrone Sulfamate against the HPV16-Positive Human Invasive Cervical Carcinoma Cell Line SiHa

Cervical carcinoma is one of the most frequent malignant gynecological cancers in women of reproductive age. Because of the poor tolerability of currently available chemotherapeutic agents, efforts have been focused on developing innovative molecules, including steroids, that exert antineoplastic effects with a better safety profile. In addition to their endocrine properties, certain estrogens exhibit additional biological activities, such as antiangiogenic and anticancer effects. Based on previous studies, the antineoplastic properties of 13α-estrone sulfamate derivatives (13AES1-3) were investigated, and the mechanism of action for the most promising compound 13AES3 was explored. Based on their effects on the viability of different human adherent gynecological cancer cells, the SiHa cervical cell line was used for mechanistic experiments. The most active analog 13AES3 was shown to exert considerable proapoptotic effects, as evidenced by a colorimetric caspase-3 assay and fluorescent double staining. It also elicited antimigratory and anti-invasive effects in a concentration-dependent manner, as evidenced by wound healing and Boyden chamber assays, respectively. Regarding their mechanism of action, 13AES derivatives were shown to inhibit tubulin polymerization, and computer simulations provided a possible explanation for the importance of the presence of the chlorophenyl ring on the estrane skeleton. 13AES3 is considered to be the first 13α-estrone derivative with a significant antineoplastic potency against SiHa cancer cells. Therefore, it might serve as a valuable lead molecule for the design of anticancer agents targeting cervical carcinomas.

Synthesis and Antiproliferative Activity of Steroidal Diaryl Ethers

Novel 13α-estrone derivatives have been synthesized via direct arylation of the phenolic hydroxy function. Chan-Lam couplings of arylboronic acids with 13α-estrone as a nucleophilic partner were carried out under copper catalysis. The antiproliferative activities of the newly synthesized diaryl ethers against a panel of human cancer cell lines (A2780, MCF-7, MDA-MB 231, HeLa, SiHa) were investigated by means of MTT assays. The quinoline derivative displayed substantial antiproliferative activity against MCF-7 and HeLa cell lines with low micromolar IC₅₀ values. Disturbance of tubulin polymerization has been confirmed by microplate-based photometric assay. Computational calculations reveal significant interactions of the quinoline derivative with the taxoid binding site of tubulin.

Breast Cancer MCF-7 Cell Spheroid Culture for Drug Discovery and Development

In vitro 3D cancer spheroids (tumoroids) exhibit a drug resistance profile similar to that found in solid tumors. 3D spheroid culture methods recreate more physiologically relevant microenvironments for cells. Therefore, these models are more appropriate for cancer drug screening. We have recently developed a protocol for MCF-7 cell spheroid culture, and used this method to test the effects of different types of drugs on this estrogen-dependent breast cancer cell spheroid. Our results demonstrated that MCF-7 cells can grow spheroid in medium using a low attachment plate. We managed to grow one spheroid in each well, and the spheroid can grow over a month, the size of the spheroid can grow over a hundred times in volume. Our targeted drug experimental results suggest that estrogen sulfotransferase, steroid sulfatase, and G protein-coupled estrogen receptor may play critical roles in MCF-7 cell spheroid growth, while estrogen receptors α and β may not play an essential role in MCF-7 spheroid growth. Organoids are the miniatures of in vivo tissues and reiterate the in vivo microenvironment of a specific organ, best fit for the in vitro studies of diseases and drug development. Tumoroid, developed from cancer cell lines or patients’ tumor tissue, is the best in vitro model of in vivo tumors. 3D spheroid technology will be the best future method for drug development of cancers and other diseases. Our reported method can be developed clinically to develop personalized drugs when the patient’s tumor tissues are used to develop a spheroid culture for drug screening.

Transition metal-catalysed A-ring C-H activations and C(sp2)-C(sp2) couplings in the 13α-oestrone series and in vitro evaluation of antiproliferative properties

Facile syntheses of 3-O-carbamoyl, -sulfamoyl, or -pivaloyl derivatives of 13α-oestrone and its 17-deoxy counterpart have been carried out. Microwave-induced, Ni-catalysed Suzuki-Miyaura couplings of the newly synthesised phenol esters with phenylboronic acid afforded 3-deoxy-3-phenyl-13α-oestrone derivatives. The carbamate and pivalate esters proved to be suitable for regioselective arylations. 2-(4-Substituted) phenyl derivatives were synthesised via Pd-catalysed, microwave-assisted C-H activation reactions. An efficient, one-pot, tandem methodology was elaborated for the introduction of the carbamoyl or pivaloyl group followed by regioselective C-2-arylation and subsequent removal of the directing group. The antiproliferative properties of the novel 13α-oestrone derivatives were evaluated in vitro on five human adherent cancer cell lines of gynaecological origin. 3-Sulfamate derivatives displayed substantial cell growth inhibitory potential against certain cell lines. The newly identified antiproliferative compounds having hormonally inactive core might be promising candidates for the design of more active anticancer agents.

Secosteroidal hydrazides: Promising scaffolds for anti-breast cancer agents

A convenient and selective approach to 13,17-secoestra-1,3,5(10)-trien-17-oic acid hydrazides and their N'-(het)arylmethylene derivatives was disclosed and these novel types of secosteroids were screened for cytotoxicity against hormone-dependent human breast cancer cell line MCF-7. A number of 13,17-secoestra-1,3,5(10)-trien-17-oic acid [N'-(het)arylmethylene]hydrazides show significant cytotoxic effect comparable or superior to that for reference drug cisplatin. Compound 3l exhibits the highest activity with the IC₅₀ value of about 2 μM and is 2.8 times more active than cisplatin. Hit 13,17-secoestra-1,3,5(10)-trien-17-oic acid [N'-(het)arylmethylene]hydrazides 3d, 3l and 3q are characterized by high cytotoxicity and good selectivity towards MCF-7 breast cancer cells. The synthesized secosteroids may be considered as new promising antitumor agents.

Solvent- and Wavelength-Dependent Photolysis of Estrone

The direct photolysis of estrone in solvents ranging from water to cyclohexane is reported. The photodegradation is dominated by lumiestrone, an epimer of estrone resulting from the inversion of the methyl group at carbon 13, regardless of solvent and photolysis wavelength in the range 254-320 nm. Solvent addition products are also observed in lesser amounts. The photodegradation rate in water is an order of magnitude slower than in nonaqueous solvents. Short wavelength excitation enhances photodegradation. Together, these results suggest complicated photophysics underlie the photochemistry with implications for the remediation of environmental estrogens.

Selective antiproliferative effect of C-2 halogenated 13α-estrones on cells expressing Organic anion-transporting polypeptide 2B1 (OATP2B1)

Organic anion-transporting polypeptide 2B1 (OATP2B1) is a multispecific transporter mediating the cellular uptake of steroids and numerous drugs. OATP2B1 is abundantly expressed in the intestine and is also present in various tumors. Increased steroid hormone uptake by OATP2B1 has been suggested to promote progression of hormone dependent tumors. 13α-estrones are effective inhibitors of endogenous estrogen formation and are potential candidates to inhibit proliferation of hormone dependent cancers. Recently, we have identified a variety of 13α/β-estrone-based inhibitors of OATP2B1. However, the nature of this interaction, whether these inhibitors are potential transported substrates of OATP2B1 and hence may be enriched in OATP2B1-overexpressing cells, has not yet been investigated. In the current study we explored the antiproliferative effect of the most effective OATP2B1 inhibitor 13α/β-estrones in control and OATP2B1-overexpressing A431 carcinoma cells. We found an increased antiproliferative effect of 3-O-benzyl 13α/β-estrones in both mock transfected and OATP2B1-overexpressing cells. However, C-2 halogenated 13α-estrones had a selective OATP2B1-mediated cell growth inhibitory effect. In order to demonstrate that increased sensitization can be attributed to OATP2B1-mediated cellular uptake, tritium labeled 2-bromo-13α-estrone was synthesized for direct transport measurements. These experiments revealed increased accumulation of [³H]2-bromo-13α-estrone due to OATP2B1 function. Our results indicate that C-2 halogenated 13α-estrones are good candidates in the design of anti-cancer drugs targeting OATP2B1.

Microwave-assisted Phospha-Michael addition reactions in the 13α-oestrone series and in vitro antiproliferative properties

Microwave-assisted phospha-Michael addition reactions were carried out in the 13α-oestrone series. The exocyclic 16-methylene-17-ketones as α,β-unsaturated ketones were reacted with secondary phosphine oxides as nucleophilic partners. The addition reactions furnished the two tertiary phosphine oxide diastereomers in high yields. The main product was the 16α-isomer. The antiproliferative activities of the newly synthesised organophosphorus compounds against a panel of nine human cancer cell lines were investigated by means of MTT assays. The most potent compound, the diphenylphosphine oxide derivative in the 3-O-methyl-13α-oestrone series (9), exerted selective cell growth-inhibitory activity against UPCI-SCC-131 and T47D cell lines with low micromolar IC₅₀ values. Moreover, it displayed good tumour selectivity property determined against non-cancerous mouse fibroblast cells.

Synthesis and evaluation of AKR1C inhibitory properties of A-ring halogenated oestrone derivatives

Enzymes AKR1C regulate the action of oestrogens, androgens, and progesterone at the pre-receptor level and are also associated with chemo-resistance. The activities of these oestrone halides were investigated on recombinant AKR1C enzymes. The oestrone halides with halogen atoms at both C-2 and C-4 positions (13β-, 13α-methyl-17-keto halogen derivatives) were the most potent inhibitors of AKR1C1. The lowest IC₅₀ values were for the 13α-epimers 2_2I,4Br and 2_2I,4Cl (IC₅₀, 0.7 μM, 0.8 μM, respectively), both of which selectively inhibited the AKR1C1 isoform. The 13α-methyl-17-keto halogen derivatives 2_2Br and 2_4Cl were the most potent inhibitors of AKR1C2 (IC₅₀, 1.5 μM, 1.8 μM, respectively), with high selectivity for the AKR1C2 isoform. Compound 1_2Cl,4Cl showed the best AKR1C3 inhibition, and it also inhibited AKR1C1 (Ki: AKR1C1, 0.69 μM; AKR1C3, 1.43 μM). These data show that halogenated derivatives of oestrone represent a new class of potent and selective AKR1C inhibitors as lead compounds for further optimisations.

Synthesis and evaluation of anticancer activities of 2- or 4-substituted 3-(N-benzyltriazolylmethyl)-13α-oestrone derivatives

2- or 4-Substituted 3-N-benzyltriazolylmethyl-13α-oestrone derivatives were synthesised via bromination of ring A and subsequent microwave-assisted, Pd-catalysed C(sp²)–P couplings. The antiproliferative activities of the newly synthesised brominated and phosphonated compounds against a panel of human cancer cell lines (A2780, MCF-7, MDA-MB 231) were investigated by means of MTT assays. The most potent compound, the 3-N-benzyltriazolylmethyl-4-bromo-13α-oestrone derivative exerted substantial selective cell growth-inhibitory activity against A2780 cell line with a submicromolar IC₅₀ value. Computational calculations reveal strong interactions of the 4-bromo derivative with both colchicine and taxoid binding sites of tubulin. Disturbance of tubulin function has been confirmed by photometric polymerisation assay.

Design, synthesis and biological evaluation of novel estrone phosphonates as high affinity organic anion-transporting polypeptide 2B1 (OATP2B1) inhibitors

Organic anion-transporting polypeptide 2B1 (OATP2B1) is a multispecific membrane transporter mediating the cellular uptake of various exo- and endobiotics, including drugs and steroid hormones. Increased uptake of steroid hormones by OATP2B1 may increase tumor proliferation. Therefore, understanding OATP2B1's substrate/inhibitor recognition and inhibition of its function, e.g., in hormone-dependent tumors, would be highly desirable. To identify the crucial structural features that correlate with OATP2B1 inhibition, here we designed modifications at four positions of the estrane skeleton. 13α- or 13β-estrone phosphonates modified at ring A or ring D were synthesized. Hirao and Cu(I)-catalyzed azide-alkyne click reactions served in the syntheses as key steps. 13β-Derivatives displayed outstanding OATP2B1 inhibitory action with IC₅₀ values in the nanomolar range (41-87 nM). A BODIPY-13α-estrone conjugate was additionally synthesized, modified at C-3-O of the steroid, containing a four-carbon linker between the triazole moiety and the BODIPY core. The fluorescent conjugate displayed efficient, submicromolar OATP2B1 inhibitory potency. The newly identified inhibitors and the structure-activity relationships specified here promote our understanding about drug recognition of OATP2B1.

Effects of neuro-adaptive electrostimulation therapy on pain and disability in fibromyalgia: A prospective, randomized, double-blind study

BACKGROUND

To evaluate the effectiveness of non-invasive neuro-adaptive electrostimulation (NAE) therapy for treating chronic pain and disability in patients with fibromyalgia.

METHOD/DESIGN

A prospective, randomized, sham-controlled study was conducted in 37 women with fibromyalgia. Participants were randomly assigned to receive either active NAE (n = 20) or stimulation with a sham device (n = 17). Participants in the experimental arm received eight 30-minute sessions over 4 weeks (2 sessions per week). The sham group received eight 30-minute sessions of sham stimulation. Therapeutic effects on pain relief, disability, and quality of life were evaluated using outcome measures at baseline, at 4 weeks, and after 3 months' follow-up.

RESULTS

The findings indicated a significant reduction of pain in the active NAE group compared with the sham group immediately post-intervention, with a difference on the Visual Analog Scale (VAS) of 3 points (P = .001), and at 3 months' follow-up (P = .02). There were significant intragroup differences between the groups (P < .05) at post-intervention. After the intervention, both groups presented significant reductions on the Fibromyalgia Impact Questionnaire (FIQ) with respect to baseline (P = .004), but not at the 3-month follow-up. In the conditioned pain modulation (CPM) in thumb variable we found significant differences between the groups at the 3-month follow-up (P = .02). No additional benefits for conditioned pain modulation and disability were observed between groups at the 3-month follow-up. Furthermore, anxiety/depression and catastrophizing improved in both groups, but no differences between groups were found.

CONCLUSIONS

In this fibromyalgia cohort, NAE therapy significantly improved pain and quality of life at 4 weeks, but not at 3-month follow-up, compared with the sham stimulation group. Future investigations are needed in larger populations to confirm these findings.

Pd-catalyzed Suzuki-Miyaura couplings and evaluation of 13α-estrone derivatives as potential anticancer agents

13α-Estrones are of great value owing to their potent multiple bioactivity, including anticancer activity. 3-OH or 3-OBn derivatives of 2- or 4-[(subst.) phenyl]-13α-estrone as potential antiproliferative agents have been synthesized via facile, microwave-induced, Pd-catalyzed Suzuki-Miyaura coupling. 2- or 4-Halogenated 13α-estrone derivatives have been reacted with (4-subst.)phenylboronic acids using Pd(PPh₃)₄ as catalyst. The nature of para substituents at the introduced phenyl group did not influence the outcome of couplings. Certain newly synthesized compounds displayed substantial antiproliferative action against human adherent cancer cell lines of gynecological origin. Important structure-activity relationships were revealed, which might be helpful in the design of potent and selective anticancer derivatives based on the hormonally inactive 13α-estrane core.

Structural dissection of 13-epiestrones based on the interaction with human Organic anion-transporting polypeptide, OATP2B1

Human OATP2B1 encoded by the SLCO2B1 gene is a multispecific transporter mediating the cellular uptake of large, organic molecules, including hormones, prostaglandins and bile acids. OATP2B1 is ubiquitously expressed in the human body, with highest expression levels in pharmacologically relevant barriers, like enterocytes, hepatocytes and endothelial cells of the blood-brain-barrier. In addition to its endogenous substrates, OATP2B1 also recognizes clinically applied drugs, such as statins, antivirals, antihistamines and chemotherapeutic agents and influences their pharmacokinetics. On the other hand, OATP2B1 is also overexpressed in various tumors. Considering that elevated hormone uptake by OATP2B1 results in increased cell proliferation of hormone dependent tumors (e.g. breast or prostate), inhibition of OATP2B1 can be a good strategy to inhibit the growth of these tumors. 13-epiestrones represent a potential novel strategy in the treatment of hormone dependent cancers by the suppression of local estrogen production due to the inhibition of the key enzyme of estrone metabolism, 17ß-hydroxysteroid-dehydrogenase type 1 (HSD17ß1). Recently, we have demonstrated that various phosphonated 13-epiestrones are dual inhibitors also suppressing OATP2B1 function. In order to gain better insights into the molecular determinants of OATP2B1 13-epiestrone interaction we investigated the effect of C-2 and C-4 halogen or phenylalkynyl modified epiestrones on OATP2B1 transport function. Potent inhibitors (with EC₅₀ values in the low micromolar range) as well as non-inhibitors of OATP2B1 function were identified. Based on the structure-activity relationship (SAR) of the various 13-epiestrone derivatives we could define structural elements important for OATP2B1 inhibition. Our results may help to understand the drug/inhibitor interaction profile of OATP2B1, and also may be a useful strategy to block steroid hormone entry into tumors.

Potent Anti-Ovarian Cancer with Inhibitor Activities on both Topoisomerase II and V600EBRAF of Synthesized Substituted Estrone Candidates

A series of 16-(α-alkoxyalkane)-17-hydrazino-estra-1(10),2,4-trien[17,16-c]-3-ol (3a-l) and estra-1(10),2,4-trien-[17,16-c]pyrazoline-3-ol derivatives (4a-d) were synthesized from corresponding arylidines 2a,b which was prepared from estrone 1 as starting material. Condensation of 1 with aldehydes gave the corresponding arylidine derivatives 2a,b which were treated with hydrazine derivatives in alcohols to give the corresponding derivatives 3a-l, respectively. Additionally, treatment of 2a,b with methyl- or phenylhydrazine in ethanolic potassium hydroxide afforded the corresponding N-substituted pyrazoline derivatives 4a-d, respectively. All these derivatives showed potent anti-ovarian cancer both in vitro and in vivo. The mechanism of anti-ovarian cancer was suggested to process via topoisomerase II and V600EBRAF inhibition.

Synthesis, Biological Evaluation and Docking Studies of 13-Epimeric 10-fluoro- and 10-Chloroestra-1,4-dien-3-ones as Potential Aromatase Inhibitors

Fluorination of 13-epimeric estrones and their 17-deoxy counterparts was performed with Selectfluor as the reagent. In acetonitrile or trifluoroacetic acid (TFA), 10β-fluoroestra-1,4-dien-3-ones were formed exclusively. Mechanistic investigations suggest that fluorinations occurred via SET in acetonitrile, but another mechanism was operative in TFA. Simultaneous application of N-chlorosuccinimide (NCS) and Selectfluor in TFA led to a 1.3:1 mixture of 10β-fluoroestra-1,4-dien-3-one and 10β-chloroestra-1,4-dien-3-one as the main products. The potential inhibitory action of the 10-fluoro- or 10-chloroestra-1,4-dien-3-one products on human aromatase was investigated via in vitro radiosubstrate incubation. The classical estrane conformation with trans ring anellations and a 13β-methyl group seems to be crucial for the inhibition of the enzyme, while test compounds bearing the 13β-methyl group exclusively displayed potent inhibitory action with submicromolar or micromolar IC50 values. Concerning molecular level explanation of biological activity or inactivity, computational simulations were performed. Docking studies reinforced that besides the well-known Met374 H-bond connection, the stereocenter in the 13 position has an important role in the binding affinity. The configuration inversion at C-13 results in weaker binding of 13α-estrone derivatives to the aromatase enzyme.

Design, Synthesis, Anticancer Evaluation and Molecular Modeling of Novel Estrogen Derivatives

A series of estrone derivatives 3–8 was designed and synthesized using estrone arylmethylenes 2a,b as starting materials and their structures were confirmed by different spectral data and elemental analyses. All the newly synthesized compounds exhibited potent in vitro and in vivo cytotoxic activities against breast cancer cell lines. In addition, all compounds were subjected to in vitro and in vivo inhibition assays for EGFR and VEGFR-2 kinases as well as p53 ubiquitination activity to obtain more details about their mechanism of action. Based on the promising results, a molecular docking study was investigated for the most representative compound 5a against the two targets, EGFR and VEGFR-2 kinases, to assess its binding affinity, hoping to rationalize and obtain potent anticancer agents in the future.

Pd-Catalyzed microwave-assisted synthesis of phosphonated 13α-estrones as potential OATP2B1, 17β-HSD1 and/or STS inhibitors

Novel 2- or 4-phosphonated 13α-estrone derivatives were synthesized via the Hirao reaction. Bromo regioisomers (2- or 4-) of 13α-estrone and its 3-benzyl or 3-methyl ether were reacted with diethyl phosphite or diphenylphosphine oxide using Pd(PPh₃)₄ as catalyst under microwave irradiation. The influence of the new compounds on the transport function of the organic anion transporting polypeptide OATP2B1 was investigated by measuring Cascade Blue uptake. Derivatives bearing a 3-benzyl ether function displayed substantial submicromolar OATP2B1 inhibitory activity. The inhibitory effects of the compounds on human placental steroid sulfatase (STS) and 17β-hydroxysteroid dehydrogenase type 1 isozyme (17β-HSD1) were investigated by in vitro radiosubstrate incubation methods. None of the test compounds inhibited the STS markedly. The structure-activity relationship evaluation revealed that 2-substituted 3-hydroxy derivatives are able to inhibit the 17β-HSD1 enzyme with submicromolar IC₅₀ values. Dual OATP2B1 and 17β-HSD1 inhibitors have been identified.

Synthesis and structure-activity relationships of 2- and/or 4-halogenated 13β- and 13α-estrone derivatives as enzyme inhibitors of estrogen biosynthesis

Ring A halogenated 13α-, 13β-, and 17-deoxy-13α-estrone derivatives were synthesised with N-halosuccinimides as electrophile triggers. Substitutions occurred at positions C-2 and/or C-4. The potential inhibitory action of the halogenated estrones on human aromatase, steroid sulfatase, or 17β-hydroxysteroid dehydrogenase 1 activity was investigated via in vitro radiosubstrate incubation. Potent submicromolar or low micromolar inhibitors were identified with occasional dual or multiple inhibitory properties. Valuable structure–activity relationships were established from the comparison of the inhibitory data obtained. Kinetic experiments performed with selected compounds revealed competitive reversible inhibition mechanisms against 17β-hydroxysteroid dehydrogenase 1 and competitive irreversible manner in the inhibition of the steroid sulfatase enzyme.

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.

In Vitro and In Vivo Anti-Breast Cancer Activities of Some Synthesized Pyrazolinyl-estran-17-one Candidates

A series of estrone derivatives, 2–4, were synthesized from the corresponding arylidine estrone, 2a,b, as starting materials, which were prepared by condensation of estrone (3-hydroxy-estran-17-one, 1) with 4-bromobenzaldehyde and thiophene-2-aldehyde. Treating of 2a,b with hydrazine derivatives in acetic acid or propionic acid afforded pyrazoline derivatives, 3a–f and 4a–f, respectively. Furthermore, results proved the superiority of thienyl derivatives over 4-bromophenol derivatives in terms of cytotoxic effects on MCF-7 cancer cells. In vivo xenograft breast cancer animal model experiments revealed that the synthesized derivatives can be used for decreasing tumor volume, while the most potent derivative (4f) decreased the development of tumor volume by about 87.0% after 12 days.

Stereoselective synthesis of the four 16-hydroxymethyl-3-methoxy- and 16-hydroxymethyl-3-benzyloxy-13α-estra-1,3,5(10)-trien-17-ol isomers and their antiproliferative activities

The reduction of 16-hydroxymethylene-3-methoxy-13α-estra-1,3,5(10)-trien-17-one (14) and 16-hydroxymethylene-3-benzyloxy-13α-estra-1,3,5(10)-trien-17-one (16) yielded a mixture of two diastereomeric diols, the 16α-hydroxymethyl,17β-hydroxy and 16β-hydroxymethyl,17α-hydroxy isomers (17a-20a) in a ratio of 6:1. We describe a straightforward synthetic route to transform the isomers with trans functional groups attached to ring D (17a-20a) into isomers with cis functional groups (25a-28a). We determined the in vitro antiproliferative activities of compounds 17a-20a and 25a-28a by means of MTT assays against a panel of human adherent cancer cell lines HeLa, A2780, MCF-7, T47D, MDA-MB-231 and MDA-MB-361.

The first Pd-catalyzed Buchwald-Hartwig aminations at C-2 or C-4 in the estrone series

A facile Pd-catalyzed C(sp²)–N coupling to provide a range of 2- or 4-[(subst.)phenyl]amino-13α-estrone derivatives has been achieved under microwave irradiation. The reactions were mediated with the use of Pd(OAc)₂ as a catalyst and KOt-Bu as a base in the presence of X-Phos as a ligand. The desired products have been obtained in good to excellent yields. The nature and the position of the aniline substituent at the aromatic ring influenced the outcome of the couplings. 2-Amino-13α-estrone was also synthesized in a two-step protocol including an amination of 2-bromo-13α-estrone 3-benzyl ether with benzophenone imine and subsequent hydrogenolysis.

Synthesis of novel 13α-estrone derivatives by Sonogashira coupling as potential 17β-HSD1 inhibitors

Novel 13α-estrone derivatives were synthesized by Sonogashira coupling. Transformations of 2- or 4-iodo regioisomers of 13α-estrone and its 3-methyl ether were carried out under different conditions in a microwave reactor. The 2-iodo isomers were reacted with para-substituted phenylacetylenes using Pd(PPh₃)₄ as catalyst and CuI as a cocatalyst. Coupling reactions of 4-iodo derivatives could be achieved by changing the catalyst to Pd(PPh₃)₂Cl₂. The product phenethynyl derivatives were partially or fully saturated. Compounds bearing a phenolic OH group furnished benzofurans under the conditions used for the partial saturation. The inhibitory effects of the compounds on human placental 17β-hydroxysteroid dehydrogenase type 1 isozyme (17β-HSD1) were investigated by an in vitro radiosubstrate incubation method. Certain 3-hydroxy-2-phenethynyl or -phenethyl derivatives proved to be potent 17β-HSD1 inhibitors, displaying submicromolar IC₅₀ values.

Impact of androstane A- and D-ring inversion on 17β-hydroxysteroid dehydrogenase type 3 inhibitory activity, androgenic effect and metabolic stability

17β-Hydroxysteroid dehydrogenase type 3 (17β-HSD3) is a major player in human endocrinology, being one of the most important enzymes involved in testosterone production. To capitalize on the discovery of RM-532-105, a steroidal 17β-HSD3 inhibitor, we explored the effect of its backbone configuration on inhibitory activity, androgenic profile, and metabolic stability. Two modifications that greatly alter the natural shape of steroids, i.e. inversion of the methyl on carbon 13 (13α-CH₃ instead of 13β-CH₃) and inversion of the hydrogen on carbon 5 (5β-H instead of 5α-H), were tested after the syntheses in 6 steps of 2 isomeric forms (5α/13α-RM-532-105 (6a) and 5β/13β-RM-532-105 (6b), respectively) of the 17β-HSD3 inhibitor RM-532-105 (5α/13β-configurations). For compound 6b, a cis/trans junction of the A/B rings did not significantly alter the inhibitory activity on 17β-HSD3 (IC₅₀=0.15μM) as well as the liver microsomal stability (16.6% of 6b remaining after 1h incubation) compared to RM-532-105 (IC₅₀=0.11μM and 14.1% remaining). In contrast, a trans/cis junction of C/D rings reduced the inhibitory activity on 17β-HSD3 (IC₅₀=1.09μM) but increased the metabolic stability with 29.4% of compound 6a remaining after incubation. The structural modifications represented by compounds 6a and 6b did not change the non-androgenicity profile of an androsterone derivative such as RM-532-105, but slightly increased its cytotoxic activity.

Crystalline arrays of side chain modified bile acids derivatives. Two novel self-assemblies based on π-π and belly-to-belly interactions

Crystalline derivatives of side chain modified bile acids were efficiently prepared from the naturally occurring steroids by palladium-catalyzed cross coupling reaction as a key step. The solvent-free crystalline bile acids derivatives 2b-e are readily accessed by slow evaporation from selected solvents. A variety of steroidal scaffolds were found and elucidated by SXRD studies. The crystal packing of the title compounds are dominated by hydrogen-bonding interactions established between differently positioned acetyl protecting groups, which in the case of 2b and 2e take advantage of the facial amphiphilicity producing two novel steroidal supramolecular self-assemblies combining π-π and strong facial interactions. Thus, these crystalline arrays of side chain modified bile acids represent promising scaffolds for research and implementation in biomolecular materials or inclusion phenomena.

Synthesis and Biological Evaluation of Triazolyl 13α-Estrone-Nucleoside Bioconjugates

2′-Deoxynucleoside conjugates of 13α-estrone were synthesized by applying the copper-catalyzed alkyne–azide click reaction (CuAAC). For the introduction of the azido group the 5′-position of the nucleosides and a propargyl ether functional group on the 3-hydroxy group of 13α-estrone were chosen. The best yields were realized in our hands when the 3′-hydroxy groups of the nucleosides were protected by acetyl groups and the 5′-hydroxy groups were modified by the tosyl–azide exchange method. The commonly used conditions for click reaction between the protected-5′-azidonucleosides and the steroid alkyne was slightly modified by using 1.5 equivalent of Cu(I) catalyst. All the prepared conjugates were evaluated in vitro by means of MTT assays for antiproliferative activity against a panel of human adherent cell lines (HeLa, MCF-7 and A2780) and the potential inhibitory activity of the new conjugates on human 17β-hydroxysteroid dehydrogenase 1 (17β-HSD1) was investigated via in vitro radiosubstrate incubation. Some protected conjugates displayed moderate antiproliferative properties against a panel of human adherent cancer cell lines (the protected cytidine conjugate proved to be the most potent with IC₅₀ value of 9 μM). The thymidine conjugate displayed considerable 17β-HSD1 inhibitory activity (IC₅₀ = 19 μM).

Synthesis and biological evaluation of 13α-estrone derivatives as potential antiproliferative agents

13α-Estrone derivatives containing various substituents on C-3 and C-17 were synthesized, and evaluated by means of MTT assays for in vitro antiproliferative activity against a panel of human adherent cancer cell lines (HeLa, MCF-7, A2780 and A431). Compounds with N-benzyltriazolylmethoxy moieties on C-3 proved to be more potent than their 3-hydroxy or 3-ether counterparts. Some triazoles exerted substantial cytostatic effects against particular tumor cell lines, with submicromolar IC50 values.

Comparative investigation of the in vitro inhibitory potencies of 13-epimeric estrones and D-secoestrones towards 17β-hydroxysteroid dehydrogenase type 1

The inhibitory effects of 13-epimeric estrones, D-secooxime and D-secoalcohol estrone compounds on human placental 17β-hydroxysteroid dehydrogenase type 1 isozyme (17β-HSD1) were investigated. The transformation of estrone to 17β-estradiol was studied by an in vitro radiosubstrate incubation method. 13α-Estrone inhibited the enzyme activity effectively with an IC₅₀ value of 1.2 μM, which indicates that enzyme affinity is similar to that of the natural estrone substrate. The 13β derivatives and the compounds bearing a 3-hydroxy group generally exerted stronger inhibition than the 13α and 3-ether counterparts. The 3-hydroxy-13β-D-secoalcohol and the 3-hydroxy-13α-D-secooxime displayed an outstanding cofactor dependence, i.e. more efficient inhibition in the presence of NADH than NADPH. The 3-hydroxy-13β-D-secooxime has an IC₅₀ value of 0.070 μM and is one of the most effective 17β-HSD1 inhibitors reported to date in the literature.

Impact of structural modifications at positions 13, 16 and 17 of 16β-(m-carbamoylbenzyl)-estradiol on 17β-hydroxysteroid dehydrogenase type 1 inhibition and estrogenic activity

The chemical synthesis of four stereoisomers (compounds 5a-d) of 16β-(m-carbamoylbenzyl)-estradiol, a potent reversible inhibitor of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1), and two intermediates (compounds 3a and b) was performed. Assignment of all nuclear magnetic resonance signals confirmed the stereochemistry at positions 13, 16 and 17. Nuclear overhauser effects showed clear correlations supporting a C-ring chair conformation for 5a and b and a C-ring boat conformation for 5c and d. These compounds were tested as 17β-HSD1 inhibitors and to assess their proliferative activity on estrogen-sensitive breast cancer cells (T-47D) and androgen-sensitive prostate cancer cells (LAPC-4). Steroid derivative 5a showed the best inhibitory activity for the transformation of estrone to estradiol (95, 82 and 27%, at 10, 1 and 0.1μM, respectively), but like the other isomers 5c and d, it was found to be estrogenic. The intermediate 3a, however, was weakly estrogenic at 1μM, not at all at 0.1μM, and showed an interesting inhibitory potency on 17β-HSD1 (90, 59 and 22%, at 10, 1 and 0.1μM, respectively). As expected, no compound showed an androgenic activity. The binding modes for compounds 3a and b, 5a-d and CC-156 were evaluated from molecular modeling. While the non-polar interactions were conserved for all the inhibitors in their binding to 17β-HSD1, differences in polar interactions and in binding conformational energies correlated to the inhibitory potencies.

Synthesis and in Vitro Antiproliferative Evaluation of C-13 Epimers of Triazolyl-d-Secoestrone Alcohols: The First Potent 13α-d-Secoestrone Derivative

The syntheses of C-13 epimeric 3-[(1-benzyl-1,2,3-triazol-4-yl)methoxy]-d-secoestrones are reported. Triazoles were prepared from 3-(prop-2-inyloxy)-d-secoalcohols and p-substituted benzyl azides via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The antiproliferative activities of the products and their precursors were determined in vitro against a panel of human adherent cervical (HeLa, SiHa and C33A), breast (MCF-7, MDA-MB-231, MDA-MB-361 and T47D) and ovarian (A2780) cell lines by means of MTT assays. The orientation of the angular methyl group and the substitution pattern of the benzyl group of the azide greatly influenced the cell growth-inhibitory potential of the compounds. The 13β derivatives generally proved to be more potent than their 13α counterparts. Introduction of a benzyltriazolylmethyl group onto the 3-OH position seemed to be advantageous. One 13α compound containing an unsubstituted benzyltriazolyl function displayed outstanding antiproliferative activities against three cell lines.

Synthesis of A-ring halogenated 13α-estrone derivatives as potential 17β-HSD1 inhibitors

13α-Estrone and its 3-methyl or benzyl ether were halogenated in ring A with N-bromo- or N-iodosuccinimide or 1,3-dibromo-5,5-dimethylhydantoin as electrophile triggers. The chemo- and regioselectivities of the reactions depended greatly on the nature of the substituent on C-3. Bromination of the ethers led to 2- and 4-regioisomers. Bis-halogenation occurred only in the case of the phenolic derivative. Iodination and bromination resulted in similar products, except that the 3-benzyl ether could not be iodinated under the applied conditions. The potential inhibitory action of the new halogenated 13α-estrones on human 17β-hydroxysteroid dehydrogenase 1 activity was investigated via in vitro radiosubstrate incubation. Some compounds proved to be effective inhibitors, with IC50 values in the submicromolar range.

Synthesis and in vitro pharmacological evaluation of N-[(1-benzyl-1,2,3-triazol-4-yl)methyl]-carboxamides on d-secoestrone scaffolds

An efficient synthesis of several N-[(1-benzyl-1,2,3-triazol-4-yl)methyl]carboxamides in the 13β- and 13α-d-secoestrone series is reported. Novel triazoles were synthesized via the Cu(I)-catalyzed azide-alkyne cycloaddition of steroidal alkynyl carboxamides and p-substituted benzyl azides. Each of the products was evaluated in vitro by means of MTT assays for antiproliferative activity against a panel of human adherent cancer cell lines (HeLa, MCF-7, A431 and A2780). Some of them exhibited activities similar to those of the reference agent cisplatin. On change of the substitution pattern of the benzyl group of the azide, great differences in the cell growth-inhibitory properties were observed. The p-alkylbenzyl-substituted triazoles selectively exerted high cytostatic action against A2780 cells, with IC50 values of 1 µM. We investigated the potential inhibitory action exerted on the human 17β-HSD1 activity of the new secosteroids. Three triazoles effectively suppressed the estrone to 17β-estradiol conversion with IC50 values in low micromolar range.

Synthesis of trans-16-triazolyl-13α-methyl-17-estradiol diastereomers and the effects of structural modifications on their in vitro antiproliferative activities

Novel 16-triazoles in the 13α-estrone series were synthesized via Cu(I)-catalyzed azide-alkyne cycloaddition of the two diastereomeric (on C-16 and on C-17) 16-azido-13α-estra-1,3,5(10)-trien-17-ol 3-benzyl ethers with substituted phenylacetylenes. The new heterocyclic derivatives were evaluated in vitro by means of MTT assays for antiproliferative activity against a panel of human adherent cancer cell lines (HeLa, MCF-7, A431, A2780, T47D, MDA-MB-231 and MDA-MB-361). The inversion of the configurations at C-16 and C-17 selectively affected the growth-inhibitory properties of the tested compounds. The 16β,17α isomers generally proved to be potent on all cell lines, with IC50 values comparable to those of the reference agent cisplatin. Change of the substitution pattern of the phenyl group of the acetylene led to great differences in antiproliferative properties. Exclusively the p-phenyl-substituted triazoles exerted high cytostatic effects. One of the most potent compounds activated caspase-3 and caspase-9 without influencing caspase-8, confirming the induction of apoptosis via the intrinsic pathway.

Synthesis and in vitro antiproliferative evaluation of d-secooxime derivatives of 13β- and 13α-estrone

d-Secooximes were synthesized from the d-secoaldehydes in the 13β- and 13α-estrone series. The oximes were modified at three sites in the molecule: the oxime function was transformed into an oxime ether, oxime ester or nitrile group, the propenyl side-chain was saturated and the 3-benzyl ether was removed in order to obtain a phenolic hydroxy function. Triazoles were formed via Cu(I)-catalysed azide-alkyne cycloaddition (CuAAC) from 3-(prop-2-yniloxy)-d-secooximes and benzyl azides. All the products were evaluated in vitro by means of MTT assays for antiproliferative activity against a panel of human adherent cell lines (HeLa, MCF-7, A2780 and A431). Some of them exhibited activities with submicromolar IC50 values, better than that of the reference agent cisplatin. The structural modifications led to significant differences in the cytostatic properties. Flow cytometry indicated that one of the most potent agents resulted in a cell cycle blockade.

Cycloaddition of steroidal cyclic nitrones to C=N dipolarophiles: stereoselective synthesis and antiproliferative effects of oxadiazolidinones in the estrone series

Cyclic nitrones of estrone 3-methyl or 3-benzyl ether were reacted with phenyl isocyanate or nonsubstituted phenyl isocyanates as reactive CN dipolarophiles, yielding condensed homosteroidal oxadiazolidinones. These dipolar cycloadditions were carried out under conventional heating or microwave irradiation. The chemo- and stereoselectivities of the reactions and the effects of the aromatic substituents on the reaction rates and yields were investigated and compared. The structures of the new products were determined by NMR (one- and two-dimensional) and MALDI-MS techniques, with C70 fullerenes as matrix in the latter case. The antiproliferative properties of the synthetized compounds were determined on a panel of human adherent cell lines (HeLa, MCF7, A2780 and A431) by means of MTT assays. Some of them exhibited activities comparable to that of the reference agent cisplatin. Flow cytometry indicated that one of the most potent agents (11a) resulted in a cell cycle blockade.

Separation of dansylated 17β-estradiol, 17α-estradiol, and estrone on a single HPLC column for simultaneous quantitation by LC-MS/MS

We show here that baseline separation of dansylated estrone, 17β-estradiol, and 17α-estradiol can be done, contrary to previous reports, within a short run time on a single RP-LC analytical column packed with particles bonded with phenyl-hexyl stationary phase. The chromatographic method coupled with isotope dilution tandem MS offers a simple assay enabling the simultaneous analysis of these analytes. The method employs (13)C-labeled estrogens as internal standards to eliminate potential matrix effects arising from the use of deuterated estrogens. The assay also offers adequate accuracy and sensitivity to be useful for biological samples. The practical applicability of the validated method is demonstrated by the quantitative analyses of in vivo samples obtained from rats treated with Premarin®.

"All in the mind"? Brain-targeting chemical delivery system of 17β-estradiol (Estredox) produces significant uterotrophic side effect

Here we revisit the peculiarly named redox chemical delivery system concept. This unique prodrug approach has long been claimed to be capable of targeting 17β-estradiol (E2), which has numerous beneficial central effects, into the brain without detrimental peripheral hormonal exposure. Using a well-established protocol to monitor E2's antidepressant-like effect, we show that the administration of this chemical delivery system incorporated into hydroxypropyl-β-cyclodextrin (i.e., Estredox), indeed, triggers a transient antidepressant-like behavior in ovariectomized mice. At the same time, even an acute dose of the carefully purified chemical delivery system produces significant circulating E2 levels and uterotrophic side effects for several days after drug administration. For the first time, we also unequivocally show by liquid chromatography coupled with tandem mass spectrometry that the uterus of the Estredox-treated animals contains a large quantity of E2 compared to that of the control group. These thus far unexposed yet consequential peripheral side effects brought about by Estredox call for a thorough and unbiased reassessment of the extent of brain-targeting of the hormone via the chemical delivery system approach.