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

2-Difluoromethoxy-Substituted Estratriene Sulfamates: Synthesis, Antiproliferative SAR, Antitubulin Activity, and Steroid Sulfatase Inhibition

2-Difluoromethoxyestratriene derivatives were designed to improve potency and in vivo stability of the drug candidate 2-methoxyestradiol (2ME2). Compound evaluation in vitro against the proliferation of MCF-7 and MDA MB-231 breast cancer cells, as inhibitors of tubulin polymerisation and also steroid sulfatase (STS) both in cell lysates and in whole cells, showed promising activities. In antiproliferative assays 2-difluoromethoxyestradiol was less potent than 2ME2, but its sulfamates were often more potent than their corresponding non-fluorinated analogues. The fluorinated bis-sulfamate is a promising antiproliferative agent in MCF-7 cells (GI50 0.28 μM) vs the known 2-methoxyestradiol-3,17-O,O-bissulfamate (STX140, GI50 0.52 μM), confirming the utility of our approach. Compounds were also evaluated in the NCI 60-cell line panel and the fluorinated bis-sulfamate derivative displayed very good overall activities with a sub-micromolar average GI50 . It was a very potent STS inhibitor in whole JEG-3 cells (IC50 3.7 nM) similar to STX140 (4.2 nM) and additionally interferes with tubulin assembly in vitro and colchicine binding to tubulin. An X-ray study of 2-difluoromethoxy-3-benzyloxyestra-1,3,5(10)-trien-17-one examined conformational aspects of the fluorinated substituent. The known related derivative 2-difluoromethyl-3-sulfamoyloxyestrone was evaluated for STS inhibition in whole JEG-3 cells and showed an excellent IC50 of 55 pM.

Efficient access to domain-integrated estradiol-flavone hybrids via the corresponding chalcones and their in vitro anticancer potential

Structural modification of the phenolic A-ring of estrogens at C-2 and/or C-3 significantly reduces or eliminates the hormonal effects of the compounds, thus the incorporation of other pharmacophores into these positions can provide biologically active derivatives suitable for new indications, without possessing unwanted side effects. As part of this work, A-ring integration of estradiol with chalcones and flavones was carried out in the hope of obtaining novel molecular hybrids with anticancer action. The syntheses were performed from 2-acetylestradiol-17β-acetate which was first reacted with various (hetero)aromatic aldehydes in a pyrrolidine-catalyzed reaction in DMSO. The chalcones thus obtained were then subjected to oxidative cyclization with I₂ in DMSO to afford estradiol-flavone hybrids in good yields. All newly synthesized derivatives were tested in vitro for cytotoxicity on human malignant cell lines of diverse origins as well as on a non-cancerous cell line, and the results demonstrated that estradiol-flavone hybrids containing a structure-integrated flavone moiety were the most active and cancer cell-selective agents. The minimal inhibitory concentration values (IC₅₀) were calculated for selected compounds (3c, 3d and 3e) and their apoptosis inducing capacity was verified by RT-qPCR (real-time quantitative polymerase chain reaction). The results suggest an important structure-activity relationship regarding estradiol-flavone hybrids that could form a promising synthetic platform and rationale for future drug developments.

Characterization of Signalling Pathways That Link Apoptosis and Autophagy to Cell Death Induced by Estrone Analogues Which Reversibly Depolymerize Microtubules

The search for novel anti-cancer compounds which can circumvent chemotherapeutic drug resistance and limit systemic toxicity remains a priority. 2-Ethyl-3-O-sulphamoyl-estra-1,3,5(10)15-tetraene-3-ol-17one (ESE-15-one) and 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) are sulphamoylated 2-methoxyestradiol (2-ME) analogues designed by our research team. Although their cytotoxicity has been demonstrated in vitro, the temporal and mechanistic responses of the initiated intracellular events are yet to be determined. In order to do so, assays investigating the compounds' effects on microtubules, cell cycle progression, signalling cascades, autophagy and apoptosis were conducted using HeLa cervical- and MDA-MB-231 metastatic breast cancer cells. Both compounds reversibly disrupted microtubule dynamics as an early event by binding to the microtubule colchicine site, which blocked progression through the cell cycle at the G₁/S- and G₂/M transitions. This was supported by increased pRB and p27^Kip1 phosphorylation. Induction of apoptosis with time-dependent signalling involving the p-JNK, Erk1/2 and Akt/mTOR pathways and loss of mitochondrial membrane potential was demonstrated. Inhibition of autophagy attenuated the apoptotic response. In conclusion, the 2-ME analogues induced a time-dependent cross-talk between cell cycle checkpoints, apoptotic signalling and autophagic processes, with an increased reactive oxygen species formation and perturbated microtubule functioning appearing to connect the processes. Subtle differences in the responses were observed between the two compounds and the different cell lines.

Multistep Synthesis and In Vitro Anticancer Evaluation of 2-Pyrazolyl-Estradiol Derivatives, Pyrazolocoumarin-Estradiol Hybrids and Analogous Compounds

Although the hormone independent cytotoxic activity of several estradiol derivatives endowed with a simple substituent at C-2 has been reported so far, 2-heterocyclic and 2,3-condensed analogs are less investigated from both synthetic and pharmacological points of view. Therefore, novel A-ring-connected 2-pyrazoles of estradiol and, for comparison, their structurally simplified non-steroidal pairs were synthesized from estradiol 3-methyl ether and 6-methoxy-1,2,3,4-tetrahydronaphthalene. Friedel-Crafts acetylation of the protected phenolic compounds and subsequent O-demethylation led to ortho-substituted derivatives regioselectively, which were converted to arylhydrazones with phenylhydrazine, 4-tolylhydrazine and 4-chloro-phenylhydrazine, respectively, under microwave conditions. The hydrazones were subjected to cyclization with the Vilsmeier-Haack reagent immediately after preparation and the ring closure/formylation sequence resulted in steroidal and non-steroidal 4'-formylpyrazoles in moderate to good yields. During reductive transformations, 4-hydroxymethyl-pyrazoles were obtained, while oxidative lactonization of the 4-formylpyrazole moiety with the phenolic OH in the presence of the Jones reagent afforded A-ring-integrated pyrazolocoumarin hybrids and related analogs. Steroidal pyrazoles, which were produced as C-17 acetates due to acetylation of C-17 OH during the primary Friedel-Crafts reaction, underwent deacetylation in alkaline methanol to furnish 2-heterocyclic estradiol derivatives. Pharmacological studies revealed the overall and cancer cell-specific cytotoxicity of the derivatives and the half maximal inhibitory concentrations were obtained for the most promising compounds.

Synthesis and Antitumor Evaluation of Novel Hybrids of Phenylsulfonylfuroxan and Estradiol Derivatives

Fifteen novel furoxan-based nitric oxide (NO) releasing hybrids of estradiol derivatives were synthesized and evaluated in vitro anti-proliferative activity in MDA-MB-231, A2780, Hela and HUVEC cell lines. Most of them displayed potent anti-proliferative effects. Among the compounds, 4-bromo-3-((phenylsulfonyl)-1,2,5-oxadiazole 2-oxide)-oxy-propoxy-estradiol (11 b) exhibited the best activity with IC50 values of 3.58-0.0008 μM. Preliminary pharmacological studies showed that 11 b induced apoptosis and hardly affected the cell cycle of MDA-MB-231 cell line. NO-releasing capacity and inhibition of ERK/MAPK pathway signaling might explain the potent antineoplastic activity of these compounds. The preliminary structure-activity relationship (SAR) showed that steroidal scaffolds with a linker in 3-position were favorable moieties to evidently increase the bioactivities of these hybrids. Overall, these results implied that 11 b merited to be further investigated as a promising anti-cancer candidate.

Current advances of tubulin inhibitors as dual acting small molecules for cancer therapy

Microtubule (MT)-targeting agents are highly successful drugs as chemotherapeutic agents, and this is attributed to their ability to target MT dynamics and interfere with critical cellular functions, including, mitosis, cell signaling, intracellular trafficking, and angiogenesis. Because MT dynamics vary in the different stages of the cell cycle, these drugs tend to be the most effective against mitotic cells. While this class of drug has proven to be effective against many cancer types, significant hurdles still exist and include overcoming aspects such as dose limited toxicities and the development of resistance. Newer generations of developed drugs attack these problems and alternative approaches such as the development of dual tubulin and kinase inhibitors are being investigated. This approach offers the potential to show increased efficacy and lower toxicities. This review covers different categories of MT-targeting agents, recent advances in dual inhibitors, and current challenges for this drug target.

3, 9-di-O-substituted coumestrols incorporating basic amine side chains act as novel apoptosis inducers with improved pharmacological selectivity

There is much interest in the use of phytoestrogens such as coumestrol in breast cancer intervention due to their antiestrogenic activity and multiple modes of tumor cell death. However, the clear beneficial effects of naturally occurring estrogen mimetic coumestrol remain controversial due to experimental evidence that it has been shown to stimulate MCF-7 cell proliferation via agonist effect on estrogen receptor at low concentration. Herein, to disconnect the ER interaction and apoptosis-specific mechanism of coumestrol, various 3, 9-di-O-substituted coumestrols (7a-7e) and their furan ring-opened analogs (5a-5e) were synthesized and assessed for antiproliferative properties. Attachment of a dimethylamine-containing side chain to 3-O of coumestrol led to the most promising compound 7e with improved antiproliferative activity (1.7-fold increase) against MCF-7 cells, decreased estrogen activity (>20 times weaker ERα binder) and a novel action to induce apoptosis. Mechanistic studies revealed that 7e is a tubulin polymerization inhibitor, which could arrest cell cycle at G2/M phase and induce apoptosis along with the decrease of mitochondrial membrane potential. In summary, such subtle modifications to the 3, 9-di-hydroxyl groups of coumestrol allow the generation of a novel apoptosis inducer with distinct pharmacological properties, providing an excellent starting point to future development of novel tumor-vascular disrupting agents targeting tubulin.

Tuning the Reactivity of Peroxo Anhydrides for Aromatic C-H Bond Oxidation

Phenol moieties are key structural motifs in many areas of chemical research from polymers to pharmaceuticals. Herein, we report on the design and use of a structurally demanding cyclic peroxide (spiro[bicyclo[2.2.1]heptane-2,4'-[1,2]dioxolane]-3',5'-dione, P4) for the direct hydroxylation of aromatic substrates. The new peroxide benefits from high thermal stability and can be synthesized from readily available starting materials. The aromatic C-H oxidation using P4 exhibits generally good yields (up to 96%) and appreciable regioselectivities.

Recent Advances in chemistry and pharmacology of 2-methoxyestradiol: An anticancer investigational drug

2-Methoxyestradiol (2ME2), an estrogen hormone metabolite is a potential cancer chemotherapeutic agent. Presently, it is an investigational drug under various phases of clinical trials alone or in combination therapy. Its anticancer activity has been attributed to its antitubulin, antiangiogenic, pro-apoptotic and ROS induction properties. This anticancer drug candidate has been explored extensively in last twenty years for its detailed chemistry and pharmacology. Present review is an update of its chemistry and biological activity. It also extends an assessment of potential of 2ME2 and its analogues as possible anticancer drug in future.

2ME2 increase radiation-induced apoptosis of keloid fibroblasts by targeting HIF-1α in vitro

BACKGROUND

Radiation therapy is considered to be a treatment for keloid scarring; however, radioresistance has been shown to be a serious impediment to treatment efficacy. There is therefore a need for the discovery of novel critical molecular targets whose inhibition might enhance the radiotherapeutic response. An elevated level of hypoxia inducible factor (HIF)-1α expression after radiation therapy in keloid fibroblasts has been demonstrated in our recent experiments. Therefore, we suggested there was a possible close relationship between HIF-1α and keloid radioresistance. The current study aimed to investigate whether target HIF-1α may enhance the radiotherapeutic efficacy of keloids.

METHODS

2-methoxyestradiol (2ME2) was applied to inhibit HIF-1α expression, and the treatment results were assessed by cell proliferation, apoptosis and radiosensitivity. A lentivirus-mediated small interfering RNA (siRNA) transduction method was used to block the expression of HIF-1α gene.

RESULTS

Both mRNA and protein levels can be effectively inhibited after the knockdown of HIF-1α, leading to a significant increase of radiation-induced apoptosis in keloid fibroblasts. Our experiment also demonstrated that 2ME2 could effectively inhibit the protein expression of HIF-1α, which significantly increased the late stage of radiation-induced apoptosis of keloid fibroblasts.

CONCLUSIONS

The present study indicates that HIF-1α might serve as a therapeutic target for keloids. Furthermore, suppression of HIF-1α by 2ME2 may be a promising therapeutic adjuvant in radiation therapy for keloids.

Synthesis of sex hormone-derived modified steroids possessing antiproliferative activity

During recent years intensive research has been focused on the synthesis of structurally modified steroid hormones in order to obtain compounds with beneficial biological activity such as cell-growth inhibition. Experimental results have revealed that some steroidal derivatives possess direct cytostatic effect on cancer cells in a hormone receptor-independent manner. After a brief account on the most important biological function and characteristics of the naturally occurring sex hormones in physiological and pathological conditions, structural modifications of estrane and androstane scaffolds are discussed in detail. The review covers literature publications (from 2002 to 2012) relating to the synthesis and antiproliferative activity of semisynthetic sex hormone-derived molecules containing simple or heterocyclic substituents. The compounds reviewed are divided into three main categories according to their sterane framework and the nature of substitution. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Molecular crosstalk between apoptosis and autophagy induced by a novel 2-methoxyestradiol analogue in cervical adenocarcinoma cells

Background

2-Methoxyestradiol has been shown to induce both autophagy and apoptosis in various carcinogenic cell lines. Although a promising anti-cancer agent, it has poor bioavailability and rapid in vivo metabolism which decreases its efficiency. In order to improve 2-methoxyestradiol’s anti-proliferative properties, a novel 2-methoxyestradiol analogue, 2-ethyl-3-O-sulphamoyl-estra-1,3,5 (10)16-tetraene (ESE-16), was previously in silico-designed in our laboratory. This study investigated ESE-16 for its anti-proliferative potential on a cervical adenocarcinoma cell (HeLa) cell line. Additionally, the possible intracellular crosstalk mechanisms between the two types of cell death were investigated.

Methods and results

HeLa cells exposed to 0.5 μM ESE-16 for 24 hours showed morphological evidence of both apoptotic and autophagic death pathways as assessed by polarization-optical transmitted light differential interference contrast microscopy, fluorescent microscopy and transmission electron microscopy. Flow cytometric cyclin B1 quantification revealed induction of programmed cell death after halting cell cycle progression in metaphase. Confocal microscopy demonstrated that ESE-16 caused microtubule fragmentation. Flow cytometric analysis of cell cycle progression and phosphatidylserine flip determination confirmed induction of apoptosis. Moreover, an increase in aggresome formation and microtubule-associated protein light chain, LC3, was demonstrated indicative of autophagy. Both caspase 8 and 3 were upregulated in a spectrophotometric analysis, indicating the involvement of the extrinsic pathway of apoptotic induction.

Conclusions

We conclude that the novel in silico-designed compound, ESE-16, exerts its anti-proliferative effect on the tumorigenic human epithelial cervical (HeLa) cells by sequentially targeting microtubule integrity, resulting in a metaphase block, causing induction of both autophagic and apoptotic cell death via a crosstalk mechanism that involves the extrinsic pathway. Future investigations will expand on signal transduction pathways involved in both apoptosis and autophagy for assessment of ESE-16 effects on microtubule dynamic instability parameters.

Antiproliferative effect of normal and 13-epi-D-homoestrone and their 3-methyl ethers on human reproductive cancer cell lines

The possibility of the therapeutic use of estrogens emerged following the recognition that certain estradiol analogs, and particularly metabolites (e.g. the A-ring metabolite 2-hydroxyestrone, etc.) inhibit the differentiation of diverse tumor cell lines. Until recently, despite the investigation of numerous synthetic d-ring-substituted estrone derivatives, no analysis had been published on the effects of D-ring expansion of estrone on its tumor-suppressing activity. The aim of the present study was to characterize the antiproliferative effects of normal and 13-epi-D-homoestrone and their 3-methyl ethers (1-4) on human reproductive cancer cell lines. The antitumor activities of the two epimer pairs on HeLa, MCF-7 and Ishikawa cells were determined. Normal D-homoestrone exerted the greatest cytostatic effect on HeLa cells (IC(50)=5.5 μM) and was subjected to further investigations to elucidate its mechanism of action on apoptosis induction. Morphological changes detected by Hoechst 33258-propidium iodide double staining, the cell cycle arrest at phase G2/M and the subsequent increase in the proportion of the subG1 fraction determined by flow cytometric analysis and the significant increase in the activity of caspase-3 confirmed the induction of apoptosis in HeLa cells treated with D-homoestrone. D-Homoestrone was also tested on a non-cancerous human lung fibroblast cell line (MRC-5) to determine its selective toxicity. The concentration in which it inhibited cell proliferation by 50% was at least six times higher for the fibroblast cells than for cervical cancer cells. No significant in vivo estrogenic activity was observed as concerns the uterus weight of gonadectomized rats after a 7-day treatment with normal D-homoestrone. These results led to the conclusion that normal D-homoestrone is a novel antitumor compound with a similar activity on HeLa cells as that of the reference agent cisplatin, but its selectivity toward non-cancerous cells is significantly higher than that of cisplatin. It may be considered to be a basic lead molecule for the preclinical development of potential anticancer agents.

An overview of tubulin inhibitors that interact with the colchicine binding site

Tubulin dynamics is a promising target for new chemotherapeutic agents. The colchicine binding site is one of the most important pockets for potential tubulin polymerization destabilizers. Colchicine binding site inhibitors (CBSI) exert their biological effects by inhibiting tubulin assembly and suppressing microtubule formation. A large number of molecules interacting with the colchicine binding site have been designed and synthesized with significant structural diversity. CBSIs have been modified as to chemical structure as well as pharmacokinetic properties, and tested in order to find a highly potent, low toxicity agent for treatment of cancers. CBSIs are believed to act by a common mechanism via binding to the colchicine site on tubulin. The present review is a synopsis of compounds that have been reported in the past decade that have provided an increase in our understanding of the actions of CBSIs.

Synthesis of 2-substituted 17β-hydroxy/17-methylene estratrienes and their in vitro cytotoxicity in human cancer cell cultures

Synthesis of various types of 2-(alkylaminomethyl) and 2-(aroyl) 17β-estradiol analogs are reported. The synthesis of similar types of 2-substituted 17-methylene estratriene analogs was also achieved. Synthesis of chalcone derivatives of 17β-estradiol and 17-methylene estratriene were also realized. All these 2-substituted estratrienes were tested for their antiproliferative activity by using four different cell lines from colon, lung, glioma and breast cancers. Among the various 2-substituted estratrienes, the compounds 10d, 14a-h and 17e were found to have in vitro antiproliferative activity comparable to that of parent analogs 1-4. Comparison of the SAR pattern of these 2-susbtituted estratriene derivatives confirmed that relatively, 17-methylene estratrienes are more active than that of 17β-estradiol analogs.

Silanol: a traceless directing group for Pd-catalyzed o-alkenylation of phenols

A silanol-directed, Pd(II)-catalyzed C-H alkenylation of phenols is reported. This work features silanol, as a novel traceless directing group, and a directed o-C-H alkenylation of phenols. This new method allows for efficient synthesis of diverse alkenylated phenols, including an estrone derivative.

(Arene)Cl₂Ru(II) complexes with N-coordinated estrogen and androgen isonicotinates: interaction with sex hormone binding globulin and anticancer activity

(Arene)dichloridoruthenium(II) complexes with N-coordinated isonicotinates of androgens (6) and estrogens (9) were prepared and tested for affinity to the estrogen receptor (ERα) and sex hormone binding globulin (SHBG), as well as for cytotoxicity in cancer cells. None of the new complexes bound noticeably to the ER and most of them also bound less strongly to SHBG than the corresponding unmetallated steroids 7. In MTT assays the Ru(p-cymene) complexes 9 of 2-substituted estrones were equally or even more cytotoxic than the metal-free steroids against hormone-dependent (MCF-7 breast and KB-V1 cervix carcinomas) and hormone-independent (518A2 melanoma) cells. The addition of external SHBG to MTT assays lowered the cytotoxicities of the complexes 9 and distinctly more so those of some steroids 7, probably by the way of sequestration and reduction of the cellular uptake. In the absence of SHBG the estrogen complexes 9 were internalized by 518A2 melanoma cells and ruthenated their DNA as quantified by ICP-OES. They also ruthenated salmon sperm DNA but did not change the topology of plasmid DNA in EMSA experiments. In addition, the Ru(p-cymene) complex of 2-ethoxyestrone (9c) was shown to reduce the motility of 518A2 melanoma cells in a wound-healing assay.

Docking, synthesis, and in vitro evaluation of antimitotic estrone analogs

In the present study, Autodock 4.0 was employed to discover potential carbonic anhydrase IX inhibitors that are able to interfere with microtubule dynamics by binding to the Colchicine binding site of tubulin. Modifications at position 2' of estrone were made to include moieties that are known to improve the antimitotic activity of estradiol analogs. 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10),15-tetraen-3-ol-17-one estronem (C9) and 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (C12) were synthesized and tested in vitro. Growth studies were conducted utilizing spectrophotometrical analysis with crystal violet as DNA stain. Compounds C9 and C12 were cytotoxic in MCF-7 and MDA-MB-231 tumorigenic and metastatic breast cancer cells, SNO non-keratinizing squamous epithelium cancer cells and HeLa cells after 48 h exposure. Compounds C9 inhibited cell proliferation to 50% of the vehicle-treated controls from 110 to 160 nm and C12 at concentrations ranging from 180 to 220 nm. Confocal microscopy revealed abnormal spindle morphology in mitotic cells. Cell cycle analysis showed an increase in the number of cells in the G(2) /M fraction after 24 h and an increase in the number of cell in the sub-G(1) fraction after 48 h, indicating that the compounds are antimitotic and able to induce apoptosis.

Synthesis of antimicrobial natural products targeting FtsZ: (+)-totarol and related totarane diterpenes

An efficient, convergent synthesis of totarol by a diastereoselective epoxide/alkene/arene bicyclization is described. The reported synthesis enables the preparation of related diterpenes totaradiol and totarolone as well as previously unavailable derivatives that exhibit comparable inhibition of the bacterial cell division protein FtsZ.

Chemistry of the cortistatins--a novel class of anti-angiogenic agents

Synthetic efforts culminating the construction of several highly advanced intermediates, and completed syntheses of the recently disclosed cortistatin family of anti-proliferative agents are described in this perspective.

Synthesis and antitumor activities of 3-modified 2-methoxyestradiol analogs

The syntheses of 2-methoxyestradiol analogs with modifications at the 3-position are described. The analogs were assessed for their antiproliferative, antiangiogenic, and estrogenic activities. Several lead substituents were identified with similar or improved antitumor activities and reduced metabolic liability compared to 2-methoxyestradiol.

Synthesis of 2- and 17-substituted estrone analogs and their antiproliferative structure-activity relationships compared to 2-methoxyestradiol

A novel series of 17-modified and 2,17-modified analogs of 2-methoxyestradiol (2ME2) were synthesized and characterized. These analogs were designed to retain or potentiate the biological activities of 2ME2 and have diminished metabolic liability. The analogs were evaluated for antiproliferative activity against MDA-MB-231 breast tumor cells, antiangiogenic activity in HUVEC, and estrogenic activity on MCF-7 cell proliferation. Several analogs were evaluated for metabolic stability in human liver microsomes and in vivo in a rat cassette dosing model. This study lead to several 17-modified analogs of 2ME2 that have similar or improved antiproliferative and antiangiogenic activity, lack estrogenic properties and have improved metabolic stability compared to 2ME2.

Synthesis, antiproliferative, and pharmacokinetic properties of 3- and 17-double-modified analogs of 2-methoxyestradiol

The syntheses of 21 analogs of 2-methoxyestradiol are presented, including ENMD-1198 which was selected for advancement into Phase 1 clinical trials in oncology. These analogs were evaluated for antiproliferative activity using breast tumor MDA-MB-231 cells, for antiangiogenic activity in HUVEC proliferation assays, and for estrogenic activity in MCF-7 cell proliferation. The most active analogs were evaluated for iv and oral pharmacokinetic properties via cassette dosing in rat and in mice pharmacokinetic models.

Specific reaction of alpha,beta-unsaturated carbonyl compounds such as 6-shogaol with sulfhydryl groups in tubulin leading to microtubule damage

6-Shogaol and 6-gingerol are ginger components with similar chemical structures. However, while 6-shogaol damages microtubules, 6-gingerol does not. We have investigated the molecular mechanism of 6-shogaol-induced microtubule damage and found that the action of 6-shogaol results from the structure of alpha,beta-unsaturated carbonyl compounds. alpha,beta-Unsaturated carbonyl compounds such as 6-shogaol react with sulfhydryl groups of cysteine residues in tubulin, and impair tubulin polymerization. The reaction with sulfhydryl groups depends on the chain length of alpha,beta-unsaturated carbonyl compounds. In addition, alpha,beta-unsaturated carbonyl compounds are more reactive with sulfhydryl groups in tubulin than in 2-mercaptoethanol, dithiothreitol, glutathione and papain, a cysteine protease.

Synthesis and structure-activity relationships of 16-modified analogs of 2-methoxyestradiol

A series of 16-modified 2-methoxyestradiol analogs were synthesized and evaluated for antiproliferative activity toward HUVEC and MDA-MB-231 cells, and for susceptibility to conjugation. In addition, the estrogenicity of these analogs was accessed by measuring cell proliferation of the estrogen-dependent cell line MCF7 in response to compound treatment. It was observed that antiproliferative activity dropped as the size of the 16 substituent increased. Selected analogs tested in glucuronidation assays had similar rates of clearance to 2-methoxyestradiol, but had enhanced clearance in sulfonate conjugation assays.

3,17-disubstituted 2-alkylestra-1,3,5(10)-trien-3-ol derivatives: synthesis, in vitro and in vivo anticancer activity

Estradiol-3,17-O,O-bis-sulfamates inhibit steroid sulfatase (STS), carbonic anhydrase (CA), and, when substituted at C-2, cancer cell proliferation and angiogenesis. C-2 Substitution and 17-sulfamate replacement of the estradiol-3,17-O,O-bis-sulfamates were explored with efficient and practical syntheses developed. Evaluation against human cancer cell lines revealed the 2-methyl derivative 27 (DU145 GI(50) = 0.38 microM) as the most active novel bis-sulfamate, while 2-ethyl-17-carbamate derivative 52 (GI(50) = 0.22 microM) proved most active of its series (cf. 2-ethylestradiol-3,17-O,O-bis-sulfamate 4 GI(50) = 0.21 microM). Larger C-2 substituents were deleterious to activity. 2-Methoxy-17-carbamate 50 was studied by X-ray crystallography and was surprisingly 13-fold weaker as an STS inhibitor compared to parent bis-sulfamate 3. The potential of 4 as an orally dosed anti-tumor agent is confirmed using breast and prostate cancer xenografts. In the MDA-MB-231 model, dramatic reduction in tumor growth or regression was observed, with effects sustained after cessation of treatment. 3-O-Sulfamoylated 2-alkylestradiol-17-O-carbamates and sulfamates have considerable potential as anticancer agents.

2-substituted estradiol bis-sulfamates, multitargeted antitumor agents: synthesis, in vitro SAR, protein crystallography, and in vivo activity

The anticancer activities and SARs of estradiol-17-O-sulfamates and estradiol 3,17-O,O-bis-sulfamates (E2bisMATEs) as steroid sulfatase (STS) inhibitors and antiproliferative agents are discussed. Estradiol 3,17-O,O-bis-sulfamates 20 and 21, in contrast to the 17-O-monosulfamate 11, proved to be excellent STS inhibitors. 2-Substituted E2bisMATEs 21 and 23 additionally exhibited potent antiproliferative activity with mean graph midpoint values of 18-87 nM in the NCI 60-cell-line panel. 21 Exhibited antiangiogenic in vitro and in vivo activity in an early-stage Lewis lung model, and 23 dosed p.o. caused marked growth inhibition in a nude mouse xenograft tumor model. Modeling studies suggest that the E2bisMATEs and 2-MeOE2 share a common mode of binding to tubulin, though COMPARE analysis of activity profiles was negative. 21 was cocrystallized with carbonic anhydrase II, and X-ray crystallography revealed unexpected coordination of the 17-O-sulfamate of 21 to the active site zinc and a probable additional lower affinity binding site. 2-Substituted E2bisMATEs are attractive candidates for further development as multitargeted anticancer agents.

SAR studies of 2-methoxyestradiol and development of its analogs as probes of anti-tumor mechanisms

The major estrogen metabolite 2-methoxyestradiol (2ME) has been shown to target tumor cells without severe side effects and is currently being evaluated in clinical trials for several types of cancer. Despite its promise for use in clinical setting, the mechanism(s) by which 2ME exerts its anti-tumor activity is not clearly defined at this time. Employing organic chemistry tools, we synthesized 2ME analogs with which 2ME affinity column was prepared, enabling us to detect a protein that selectively interacts with 2ME. This 2ME analog will be useful as a probe to identify the biological target(s) of 2ME and study their functions in tumor cells.

Steroids: partial synthesis in medicinal chemistry

This article reviews the progress in the chemistry of the steroids that was published between January and December 2004. The reactions and partial synthesis of estrogens, androgens, pregnanes, cholic acid derivatives, cholestanes and vitamin D analogues are covered. There are 127 references.

A-ring-substituted estrogen-3-O-sulfamates: potent multitargeted anticancer agents

Efficient and flexible syntheses of 2-substituted estrone, estradiol and their 3-O-sulfamate (EMATE) derivatives have been developed using directed ortho-lithiation methodology. 2-Substituted EMATEs display a similar antiproliferative activity profile to the corresponding estradiols against a range of human cancer cell lines. 2-Methoxy (3, 4), 2-methylsulfanyl (20, 21) and 2-ethyl EMATEs (32, 33) proved the most active compounds with 2-ethylestradiol-3-O-sulfamate (33), displaying a mean activity over the NCI 55 cell line panel 80-fold greater than the established anticancer agent 2-methoxyestradiol (2). 2-Ethylestradiol-3-O-sulfamate (33) was also an effective inhibitor of angiogenesis using three in vitro markers, and various 2-substituted EMATEs also proved to be inhibitors of steroid sulfatase (STS), a therapeutic target for the treatment of hormone-dependent breast cancer. The potential of this novel class of multimechanism anticancer agents was confirmed in vivo with good activity observed in the NCI hollow fiber assay and in a MDA-MB-435 xenograft mouse model.

A common pharmacophore for a diverse set of colchicine site inhibitors using a structure-based approach

Modulating the structure and function of tubulin and microtubules is an important route to anticancer therapeutics, and therefore, small molecules that bind to tubulin and cause mitotic arrest are of immense interest. A large number of synthetic and natural compounds with diverse structures have been shown to bind at the colchicine site, one of the major binding sites on tubulin, and inhibit tubulin assembly. Using the recently determined X-ray structure of the tubulin:colchicinoid complex as the template, we employed docking studies to determine the binding modes of a set of structurally diverse colchicine site inhibitors. These binding models were subsequently used to construct a comprehensive, structure-based pharmacophore that in combination with molecular dynamics simulations confirms and extends our understanding of binding interactions at the colchicine site.