Hybrid dual aromatase-steroid sulfatase inhibitors with exquisite picomolar inhibitory activity

Synthesis, in vitro and in silico anticancer evaluation of novel pyridin-2-yl estra-1,3,5(10)-triene derivatives

Aim: The aim of this study was the synthesis of steroid compounds with heterocyclic rings and good anticancer properties. Materials & methods: The synthesis, in silico and in vitro anticancer testing of novel pyridin-2-yl estra-1,3,5(10)-triene derivatives was performed. Results: All synthesized compounds have shown promising results for, antiproliferative activity, relative binding affinities for the ligand binding domains of estrogen receptors α, β and androgen receptor, aromatase binding potential, and inhibition of AKR1C3 enzyme. Conclusion: 3-Benzyloxy (17E)-pycolinilidene derivative 9 showed the best antitumor potential against MDA-MB-231 cell line, an activity that can be explained by its moderate inhibition of AKR1C3. Molecular docking simulation indicates that it binds to AKR1C3 in a very similar orientation and geometry as steroidal inhibitor EM1404.

Synthesis, biological evaluation, and stability studies of raloxifene mono- and bis-sulfamates as dual-targeting agents

All three possible sulfamate derivatives of the selective estrogen receptor modulator Raloxifene (bis-sulfamate 7 and two mono-sulfamates 8-9) were synthesized and evaluated as inhibitors of the clinical drug target steroid sulfatase (STS), both in cell-free and in cell-based assays, and also as estrogen receptor (ER) modulators. Bis-sulfamate 7 was the most potent STS inhibitor with an IC50 of 12.2 nM in a whole JEG3 cell-based assay, with the two mono-sulfamates significantly weaker. The estrogen receptor-modulating activities of 7-9 showed generally lower affinities compared to Raloxifene HCl, diethylstilbestrol and other known ligands, with mono-sulfamate 8 being the best ligand (Ki of 1.5 nM) for ERα binding, although 7 had a Ki of 13 nM and both showed desirable antagonist activity. The antiproliferative activities of the sulfamate derivatives against the T-47D breast cancer cell line showed 7 as most potent (GI50 = 7.12 µM), comparable to that of Raloxifene. Compound 7 also showed good antiproliferative potency in the NCI-60 cell line panel with a GI50 of 1.34 µM against MDA-MB-231 breast cancer cells. Stability testing of 7-9 showed that bis-sulfamate 7 hydrolyzed by desulfamoylation at a surprisingly rapid rate, initially leading selectively to 8 and finally to Raloxifene 3 without formation of 9. The mechanisms of these hydrolysis reactions could be extensively rationalized. Conversion of Raloxifene (3) into its bis-sulfamate (7) thus produced a promising drug lead with nanomolar dual activity as an STS inhibitor and ERα antagonist, as a potential candidate for treatment of estrogen-dependent breast cancer.

Dual aromatase-steroid sulfatase inhibitors (DASI's) for the treatment of breast cancer: a structure guided ligand based designing approach

Dual aromatase-steroid sulfatase inhibitors (DASIs) lead to significant deprivation of estrogen levels as compared to a single target inhibition and thereby exhibited an additive or synergistic effect in the treatment of hormone-dependent breast cancer (HDBC). Triazole-bearing DASI's having structural features of clinically available aromatase inhibitors are identified as lead structures for optimization as DASI's. To identify the spatial fingerprints of target-specific triazole as DASI's, we have performed molecular docking assisted Gaussian field-based comparative 3D-QSAR studies on a dataset with dual aromatase-STS inhibitory activities. Separate contours were generated for both aromatase and steroid sulphates showing respective pharmacophoric structural requirements for optimal activity. These developed 3D-QSAR models also showed good statistical measures with the excellent predictive ability with PLS-generated validation constraints. Comparative steric, electrostatic, hydrophobic, HBA, and HBD features were elucidated using respective contour maps for selective target-specific favourable activity. Furthermore, the molecular docking was used for elucidating the mode of binding as DASI's along with the MD simulation of 100 ns revealed that all the protease-ligand docked complexes are overall stable as compared to reference ligand (inhibitor ASD or Irosustat) complex. Further, the MM-GBSA study revealed that compound 24 binds to aromatase as well as STS active site with relatively lower binding energy than reference complex, respectively. A comparative study of these developed multitargeted QSAR models along with molecular docking and dynamics study can be employed for the optimization of drug candidates as DASI's.Communicated by Ramaswamy H. Sarma.

Ferrozoles: Ferrocenyl derivatives of letrozole with dual effects as potent aromatase inhibitors and cytostatic agents

In the treatment of hormone-dependent cancers, aromatase inhibitors (AI) are receiving increased attention due to some undesirable effects such as the risk of endometrial cancer and thromboembolism of SERMs (selective estrogen receptor modulators). Letrozole is the most active AI with 99% aromatase inhibition. Unfortunately, this compound also exhibits some adverse effects such as hot flashes and fibromyalgias. Therefore, there is an urgent need to explore new types of AIs that retain the same-or even increased-antitumor ability. Inspired by the letrozole structure, a set of new derivatives has been synthesized that include a ferrocenyl moiety and different heterocycles. The derivative that contains a benzimidazole ring, namely compound 6, exhibits a higher aromatase inhibitory activity than letrozole and it also shows potent cytostatic behavior when compared to other well-established aromatase inhibitors, as demonstrated by dose-response, cell cycle, apoptosis and time course experiments. Furthermore, 6 promotes the inhibition of cell growth in both an aromatase-dependent and -independent fashion, as indicated by the study of A549 and MCF7 cell lines. Molecular docking and molecular dynamics calculations on the interaction of 6 or letrozole with the aromatase binding site revealed that the ferrocene moiety increases the van der Waals and hydrophobic interactions, thus resulting in an increase in binding affinity. Furthermore, the iron atom of the ferrocene fragment can form a metal-acceptor interaction with a propionate fragment, and this results in a stronger coupling with the heme group-a possibility that is consistent with the strong aromatase inhibition of 6.

Targeting the formation of estrogens for treatment of hormone dependent diseases-current status

Local formation and action of estrogens have crucial roles in hormone dependent cancers and benign diseases like endometriosis. Drugs that are currently used for the treatment of these diseases act at the receptor and at the pre-receptor levels, targeting the local formation of estrogens. Since 1980s the local formation of estrogens has been targeted by inhibitors of aromatase that catalyses their formation from androgens. Steroidal and non-steroidal inhibitors have successfully been used to treat postmenopausal breast cancer and have also been evaluated in clinical studies in patients with endometrial, ovarian cancers and endometriosis. Over the past decade also inhibitors of sulfatase that catalyses the hydrolysis of inactive estrogen-sulfates entered clinical trials for treatment of breast, endometrial cancers and endometriosis, with clinical effects observed primarily in breast cancer. More recently, inhibitors of 17beta-hydroxysteroid dehydrogenase 1, an enzyme responsible for formation of the most potent estrogen, estradiol, have shown promising results in preclinical studies and have already entered clinical evaluation for endometriosis. This review aims to provide an overview of the current status of the use of hormonal drugs for the major hormone-dependent diseases. Further, it aims to explain the mechanisms behind the -sometimes- observed weak effects and low therapeutic efficacy of these drugs and the possibilities and the advantages of combined treatments targeting several enzymes in the local estrogen formation, or drugs acting with different therapeutic mechanisms.

Dual Targeting of Steroid Sulfatase and 17β-Hydroxysteroid Dehydrogenase Type 1 by a Novel Drug-Prodrug Approach: A Potential Therapeutic Option for the Treatment of Endometriosis

A novel approach for the dual inhibition of steroid sulfatase (STS) and 17β-hydroxysteroid dehydrogenase type 1(17β HSD1) by a single drug was explored, starting from in-house 17β HSD1 inhibitors via masking their phenolic OH group with a sulfamate ester. The sulfamates were intentionally designed as drugs for the inhibition of STS and, at the same time, prodrugs for 17β-HSD1 inhibition ("drug-prodrug approach"). The most promising sulfamates 13, 16, 18-20, 22-24, 36, and 37 showed nanomolar IC₅₀ values for STS inhibition in a cellular assay and their corresponding phenols displayed potent 17β-HSD1 inhibition in cell-free and cellular assays, high selectivity over 17β-HSD2, reasonable metabolic stability, and low estrogen receptor α affinity. A close relationship was found between the liberation of the phenolic compound by sulfamate hydrolysis and 17β-HSD1 inactivation. These results showed that the envisaged drug-prodrug concept was successfully implemented. The novel compounds constitute a promising class of therapeutics for the treatment of endometriosis and other estrogen-dependent diseases.

Polypharmacology: The science of multi-targeting molecules

Polypharmacology is a concept where a molecule can interact with two or more targets simultaneously. It offers many advantages as compared to the conventional single-targeting molecules. A multi-targeting drug is much more efficacious due to its cumulative efficacy at all of its individual targets making it much more effective in complex and multifactorial diseases like cancer, where multiple proteins and pathways are involved in the onset and development of the disease. For a molecule to be polypharmacologic in nature, it needs to possess promiscuity which is the ability to interact with multiple targets; and at the same time avoid binding to antitargets which would otherwise result in off-target adverse effects. There are certain structural features and physicochemical properties which when present would help researchers to predict if the designed molecule would possess promiscuity or not. Promiscuity can also be identified via advanced state-of-the-art computational methods. In this review, we also elaborate on the methods by which one can intentionally incorporate promiscuity in their molecules and make them polypharmacologic. The polypharmacology paradigm of "one drug-multiple targets" has numerous applications especially in drug repurposing where an already established drug is redeveloped for a new indication. Though designing a polypharmacological drug is much more difficult than designing a single-targeting drug, with the current technologies and information regarding different diseases and chemical functional groups, it is plausible for researchers to intentionally design a polypharmacological drug and unlock its advantages.

Synthesis and Biological Evaluation of 1-(Diarylmethyl)-1H-1,2,4-triazoles and 1-(Diarylmethyl)-1H-imidazoles as a Novel Class of Anti-Mitotic Agent for Activity in Breast Cancer

We report the synthesis and biochemical evaluation of compounds that are designed as hybrids of the microtubule targeting benzophenone phenstatin and the aromatase inhibitor letrozole. A preliminary screening in estrogen receptor (ER)-positive MCF-7 breast cancer cells identified 5-((2H-1,2,3-triazol-1-yl)(3,4,5-trimethoxyphenyl)methyl)-2-methoxyphenol 24 as a potent antiproliferative compound with an IC₅₀ value of 52 nM in MCF-7 breast cancer cells (ER+/PR+) and 74 nM in triple-negative MDA-MB-231 breast cancer cells. The compounds demonstrated significant G₂/M phase cell cycle arrest and induction of apoptosis in the MCF-7 cell line, inhibited tubulin polymerisation, and were selective for cancer cells when evaluated in non-tumorigenic MCF-10A breast cells. The immunofluorescence staining of MCF-7 cells confirmed that the compounds targeted tubulin and induced multinucleation, which is a recognised sign of mitotic catastrophe. Computational docking studies of compounds 19e, 21l, and 24 in the colchicine binding site of tubulin indicated potential binding conformations for the compounds. Compounds 19e and 21l were also shown to selectively inhibit aromatase. These compounds are promising candidates for development as antiproliferative, aromatase inhibitory, and microtubule-disrupting agents for breast cancer.

Recent progress in the development of steroid sulphatase inhibitors - examples of the novel and most promising compounds from the last decade

The purpose of this review article is to provide an overview of recent achievements in the synthesis of novel steroid sulphatase (STS) inhibitors. STS is a crucial enzyme in the biosynthesis of active hormones (including oestrogens and androgens) and, therefore, represents an extremely attractive molecular target for the development of hormone-dependent cancer therapies. The inhibition of STS may effectively reduce the availability of active hormones for cancer cells, causing a positive therapeutic effect. Herein, we report examples of novel STS inhibitors based on steroidal and nonsteroidal cores that contain various functional groups (e.g. sulphamate and phosphorus moieties) and halogen atoms, which may potentially be used in therapies for hormone-dependent cancers. The presented work also includes examples of multitargeting agents with STS inhibitory activities. Furthermore, the fundamental discoveries in the development of the most promising drug candidates exhibiting STS inhibitory activities are highlighted.

Synthesis and in vitro evaluation of piperazinyl-ureido sulfamates as steroid sulfatase inhibitors

Two new piperazinyl-ureido single ring aryl sulfamate-based inhibitor series were designed against the emerging oncology drug target steroid sulfatase (STS), for which there are existing potent steroidal and non-steroidal agents in clinical trials. 4-(Piperazinocarbonyl)aminosulfamates (5-31) were obtained by reacting 4-hydroxyarylamines with phenylchloroformate, subsequent sulfamoylation of the resulting hydroxyarylcarbamates and coupling of the product with 1-substituted piperazines. Pyrimidinyl-piperazinourea sulfamates (35-42) were synthesized by pyrimidine ring closure of 4-Boc-piperazine-1-carboxamidine with 3-(dimethylamino)propenones, deprotection and coupling with the sulfamoylated building block. Target ureidosulfamates 5-31 and 35-42 were evaluated both as STS inhibitors in vitro using a lysate of JEG-3 human placenta choriocarcinoma cell line and in a whole cell assay. SAR conclusions were drawn from both series. In series 35-42 the best inhibitory activity is related to the presence of a benzofuryl on the pyrimidine ring. In series 5-31 the best inhibitory activity was shown by the ureas bearing 4-chlorophenyl, 3,4-dichlorophenyl groups or aliphatic chains at the piperazino 4-nitrogen displaying IC₅₀ in the 33-94 nM concentration range. Final optimization to the low nanomolar level was achieved through substitution of the arylsulfamate ring with halogens. Four halogenated arylsulfamates of high potency were achieved and two of these 19 and 20 had IC₅₀ values of 5.1 and 8.8 nM respectively and are attractive for potential in vivo evaluation and further development. We demonstrate the optimization of this new series to low nanomolar potency, employing fluorine substitution, providing potent membrane permeant inhibitors with further development potential indicating piperazinyl-ureido aryl sulfamate derivatives as an attractive new class of STS inhibitors.

Rational Design of Multitarget-Directed Ligands: Strategies and Emerging Paradigms

Due to the complexity of multifactorial diseases, single-target drugs do not always exhibit satisfactory efficacy. Recently, increasing evidence indicates that simultaneous modulation of multiple targets may improve both therapeutic safety and efficacy, compared with single-target drugs. However, few multitarget drugs are on market or in clinical trials, despite the best efforts of medicinal chemists. This article discusses the systematic establishment of target combination, lead generation, and optimization of multitarget-directed ligands (MTDLs). Moreover, we analyze some MTDLs research cases for several complex diseases in recent years and the physicochemical properties of 117 clinical multitarget drugs, with the aim to reveal the trends and insights of the potential use of MTDLs.

Estrogen signaling: An emanating therapeutic target for breast cancer treatment

Breast cancer, a most common malignancy in women, was known to be associated with steroid hormone estrogen. The discovery of estrogen receptor (ER) gave us not only a powerful predictive and prognostic marker, but also an efficient target for the treatment of hormone-dependent breast cancer with various estrogen ligands. ER consists of two subtypes i.e. ERα and ERβ, that are mostly G-protein-coupled receptors and activated by estrogen, specially 17β-estradiol. The activation is followed by translocation into the nucleus and binding with DNA to modulate activities of different genes. ERs can manage synthesis of RNA through genomic actions without directly binding to DNA. Receptors are tethered by protein-protein interactions to a transcription factor complex to communicate with DNA. Estrogens also exhibit nongenomic actions, a characteristic feature of steroid hormones, which are so rapid to be considered by the activation of RNA and translation. These are habitually related to stimulation of different protein kinase cascades. Majority of post-menopausal breast cancer is estrogen dependent, mostly potent biological estrogen (E2) for continuous growth and proliferation. Estrogen helps in regulating the differentiation and proliferation of normal breast epithelial cells. In this review we have investigated the important role of ER in development and progression of breast cancer, which is complicated by receptor's interaction with co-regulatory proteins, cross-talk with other signal transduction pathways and development of treatment strategies viz. selective estrogen receptor modulators (SERMs), selective estrogen receptor down regulators (SERDs), aromatase and sulphatase inhibitors.

Radical Anions of Aromatic Carbonitriles as Reagents for Arylation of Fluorinated Benzonitriles

The first example of phenylation of fluorobenzonitriles with the sodium salt of a benzonitrile radical anion in liquid ammonia is presented. The reaction regioselectivity corresponds to the ortho- and para-fluorine atom substitution in fluorobenzonitrile with the phenyl moiety of the benzonitrile radical anion and affords 2- and 4-cyanobiphenyls in 40-90% yields. 3-Methoxybenzonitrile as well as 1-cyanonaphthalene radical anions were also successfully subjected to this interaction forming 3'-methoxycyanobiphenyls and (1-naphthyl)benzonitriles, respectively. The radical anion acts as an ipso-C-nucleophile with consequent loss of the cyano group. The revealed new type of radical anion reactivity opens up the prospect of developing a general approach to fluorinated cyanobisarenes on the basis of an interaction of the cyanoarene radical anion with fluorinated substrates activated to aromatic nucleophilic substitution.

Polypharmacology by Design: A Medicinal Chemist's Perspective on Multitargeting Compounds

Multitargeting compounds comprising activity on more than a single biological target have gained remarkable relevance in drug discovery owing to the complexity of multifactorial diseases such as cancer, inflammation, or the metabolic syndrome. Polypharmacological drug profiles can produce additive or synergistic effects while reducing side effects and significantly contribute to the high therapeutic success of indispensable drugs such as aspirin. While their identification has long been the result of serendipity, medicinal chemistry now tends to design polypharmacology. Modern in vitro pharmacological methods and chemical probes allow a systematic search for rational target combinations and recent innovations in computational technologies, crystallography, or fragment-based design equip multitarget compound development with valuable tools. In this Perspective, we analyze the relevance of multiple ligands in drug discovery and the versatile toolbox to design polypharmacology. We conclude that despite some characteristic challenges remaining unresolved, designed polypharmacology holds enormous potential to secure future therapeutic innovation.

SULFATION PATHWAYS: Steroid sulphatase inhibition via aryl sulphamates: clinical progress, mechanism and future prospects

Steroid sulphatase is an emerging drug target for the endocrine therapy of hormone-dependent diseases, catalysing oestrogen sulphate hydrolysis to oestrogen. Drug discovery, developing the core aryl O-sulphamate pharmacophore, has led to steroidal and non-steroidal drugs entering numerous clinical trials, with promising results in oncology and women's health. Steroidal oestrogen sulphamate derivatives were the first irreversible active-site-directed inhibitors and one was developed clinically as an oral oestradiol pro-drug and for endometriosis applications. This review summarizes work leading to the therapeutic concept of sulphatase inhibition, clinical trials executed to date and new insights into the mechanism of inhibition of steroid sulphatase. To date, the non-steroidal sulphatase inhibitor Irosustat has been evaluated clinically in breast cancer, alone and in combination, in endometrial cancer and in prostate cancer. The versatile core pharmacophore both imbues attractive pharmaceutical properties and functions via three distinct mechanisms of action, as a pro-drug, an enzyme active-site-modifying motif, likely through direct sulphamoyl group transfer, and as a structural component augmenting activity, for example by enhancing interactions at the colchicine binding site of tubulin. Preliminary new structural data on the Pseudomonas aeruginosa arylsulphatase enzyme suggest two possible sulphamate-based adducts with the active site formylglycine as candidates for the inhibition end product via sulphamoyl or sulphonylamine transfer, and a speculative choice is suggested. The clinical status of sulphatase inhibition is surveyed and how it might develop in the future. Also discussed are dual-targeting approaches, development of 2-substituted steroidal sulphamates and non-steroidal derivatives as multi-targeting agents for hormone-independent tumours, with other emerging directions.

Steroid metabolism in breast cancer: Where are we and what are we missing?

It is well-known that breast cancer is hormone-dependent and that steroid hormones exert their mitogenic effects by binding to estrogen, progesterone and androgen receptors. Vital to our understanding and treatment of this malignancy, is the local metabolism of steroid hormones in breast cancer tissue. This review summarises our current knowledge on steroid producing pathways in the adrenal, ovary and breast, while focussing on the availability of specific circulating hormone precursors and steroidogenic enzymes involved in the local synthesis and metabolism of steroid hormones in the breast. Consequently, we highlight alternate pathways that may be instrumental in the etiology of breast cancer.

Synergistic effects of inhibiting the MNK-eIF4E and PI3K/AKT/ mTOR pathways on cell migration in MDA-MB-231 cells

The study of eukaryotic initiation factor 4E (eIF4E) is a key focus in cancer research due to its role in controlling the translation of tumour-associated proteins, that drive an aggressive migratory phenotype. eIF4E is a limiting component of the eIF4F complex which is a critical determinant for the translation of mRNAs. Mitogen-activated protein kinase interacting protein kinases (MNK1/2) phosphorylate eIF4E on Ser209, promoting the expression of oncogenic proteins, whereas mTORC1 phosphorylates and de-activates the eIF4E inhibitor, 4E-BP1, to release translational repression. Here we show that inhibiting these pathways simultaneously effectively slows the rate of cell migration in breast cancer cells. However, a molecular hybridisation approach using novel, cleavable dual MNK1/2 and PI3K/mTOR inhibiting hybrid agents was less effective at slowing cell migration.

Recent Progress in the Discovery of Next Generation Inhibitors of Aromatase from the Structure-Function Perspective

Human aromatase catalyzes the synthesis of estrogen from androgen with high substrate specificity. For the past 40 years, aromatase has been a target of intense inhibitor discovery research for the prevention and treatment of estrogen-dependent breast cancer. The so-called third generation aromatase inhibitors (AIs) letrozole, anastrozole, and the steroidal exemestane were approved in the U.S. in the late 1990s for estrogen-dependent postmenopausal breast cancer. Efforts to develop better AIs with higher selectivity and lower side effects were handicapped by the lack of an experimental structure of this unique P450. The year 2009 marked the publication of the crystal structure of aromatase purified from human placenta, revealing an androgen-specific active site. The structure has reinvigorated research activities on this fascinating enzyme and served as the catalyst for next generation AI discovery research. Here, we present an account of recent developments in the AI field from the perspective of the enzyme's structure-function relationships.

Discovery and Development of the Aryl O-Sulfamate Pharmacophore for Oncology and Women's Health

In 1994, following work from this laboratory, it was reported that estrone-3-O-sulfamate irreversibly inhibits a new potential hormone-dependent cancer target steroid sulfatase (STS). Subsequent drug discovery projects were initiated to develop the core aryl O-sulfamate pharmacophore that, over some 20 years, have led to steroidal and nonsteroidal drugs in numerous preclinical and clinical trials, with promising results in oncology and women's health, including endometriosis. Drugs have been designed to inhibit STS, e.g., Irosustat, as innovative dual-targeting aromatase-steroid sulfatase inhibitors (DASIs) and as multitargeting agents for hormone-independent tumors, such as the steroidal STX140 and nonsteroidal counterparts, acting inter alia through microtubule disruption. The aryl sulfamate pharmacophore is highly versatile, operating via three distinct mechanisms of action, and imbues attractive pharmaceutical properties. This Perspective gives a personal view of the work leading both to the therapeutic concepts and these drugs, their current status, and how they might develop in the future.

Estrogen O-sulfamates and their analogues: Clinical steroid sulfatase inhibitors with broad potential

Estrogen sulfamate derivatives were the first irreversible active-site-directed inhibitors of steroid sulfatase (STS), an emerging drug target for endocrine therapy of hormone dependent diseases that catalyzes inter alia the hydrolysis of estrone sulfate to estrone. In recent years this has stimulated clinical investigation of the estradiol derivative both as an oral prodrug and its currently ongoing exploration in endometriosis. 2-Substituted steroid sulfamate derivatives show considerable potential as multi-targeting agents for hormone-independent disease, but are also potent STS inhibitors. The steroidal template has spawned nonsteroidal STS inhibitors one of which, Irosustat, has been evaluated clinically in breast cancer, endometrial cancer and prostate cancer and there is potential for innovative dual-targeting approaches. This review surveys the role of estrogen sulfamates, their analogues and current status.

Recent developments in steroidal and nonsteroidal aromatase inhibitors for the chemoprevention of estrogen-dependent breast cancer

Aromatase, a cytochrome P450 enzyme complex present in breast tissues, plays a significant role in the biosynthesis of important endogenous estrogens from androgens. The source of estrogen production in breast cancer tissues is intra-tumoral aromatase, and inhibition of aromatase may inhibit the growth stimulation effect of estrogens in breast cancer tissues. Consequently, aromatase is considered a useful therapeutic target in the treatment and prevention of estrogen-dependent breast cancer. Recently, different natural products and synthetic compounds have been rapidly developed, studied, and evaluated for aromatase inhibitory activity. Aromatase inhibitors are classified into two categories on the basis of their chemical structures, i.e., steroidal and nonsteroidal aromatase inhibitors. This review highlights the synthetic steroidal and nonsteroidal aromatase inhibitors reported in the literature in the last few years and will aid medicinal chemists in the design and synthesis of novel and pharmacologically-potent aromatase inhibitors for the treatment of breast cancer.

Discovery of a novel series of phenyl pyrazole inner salts based on fipronil as potential dual-target insecticides

A series of novel phenyl pyrazole inner salt derivatives based on fipronil were designed and synthesized in the search for dual-target insecticides. These compounds were designed to target two families of nicotinic acetylcholine receptors and γ-aminobutyric acid receptors. The insecticidal activities of the new compounds against diamondback moth (Plutella xylostella) were evaluated. The results of bioassays indicated that most of the inner salts showed moderate to high activities, of which the phenyl pyrazole inner salts containing quinoline had excellent biological activity. Previous structure-activity relationship studies revealed that a suitable structure of the quaternary ammonium salts was critical for the bioactivity of phenyl pyrazole inner salts, which contribute to exposing the cationic nitrogen to bind to the receptor (for instance, nicotinic acetylcholine receptors) and possibly interact with the receptor via hydrogen bonding and cooperative π-π interaction. The present work demonstrates that the insecticidal potency of phenyl pyrazole inner salts holds promise for the development new dual-target phenyl pyrazole insecticides.

Synthesis of hybrid anticancer agents based on kinase and histone deacetylase inhibitors

A HDAC, kinase inhibitor hybrid, (Z)-N1-(3-((1H-pyrrol-2-yl)methylene)-2-oxoindolin-5-yl)-N8-hydroxyoctanediamide, 6, showed impressive anticancer action in a number of biochemical and cell-based assays.

Molecular simulations of aromatase reveal new insights into the mechanism of ligand binding

CYP19A1, also known as aromatase or estrogen synthetase, is the rate-limiting enzyme in the biosynthesis of estrogens from their corresponding androgens. Several clinically used breast cancer therapies target aromatase. In this work, explicitly solvated all-atom molecular dynamics simulations of aromatase with a model of the lipid bilayer and the transmembrane helix are performed. The dynamics of aromatase and the role of titration of an important amino acid residue involved in aromatization of androgens are investigated via two 250-ns long simulations. One simulation treats the protonated form of the catalytic aspartate 309, which appears more consistent with crystallographic data for the active site, while the simulation of the deprotonated form shows some notable conformational shifts. Ensemble-based computational solvent mapping experiments indicate possible novel druggable binding sites that could be utilized by next-generation inhibitors. In addition, the effects of protonation on the ligand positioning and channel dynamics are investigated using geometrical models that estimate the opening width of critical channels. Significant differences in channel dynamics between the protonated and deprotonated trajectories are exhibited, suggesting that the mechanism for substrate and product entry and the aromatization process may be coupled to a "locking" mechanism and channel opening. Our results may be particularly relevant in the design of novel drugs, which may be useful therapeutic treatments of cancers such as those of the breast and prostate.

Synthesis and structure-activity relationship studies of derivatives of the dual aromatase-sulfatase inhibitor 4-{[(4-cyanophenyl)(4H-1,2,4-triazol-4-yl)amino]methyl}phenyl sulfamate

4-{[(4-Cyanophenyl)(4H-1,2,4-triazol-4-yl)amino]methyl}phenyl sulfamate and its ortho-halogenated (F, Cl, Br) derivatives are first-generation dual aromatase and sulfatase inhibitors (DASIs). Structure-activity relationship studies were performed on these compounds, and various modifications were made to their structures involving relocation of the halogen atom, introduction of more halogen atoms, replacement of the halogen with another group, replacement of the methylene linker with a difluoromethylene linker, replacement of the para-cyanophenyl ring with other ring structures, and replacement of the triazolyl group with an imidazolyl group. The most potent in vitro DASI discovered is an imidazole derivative with IC50 values against aromatase and steroid sulfatase in a JEG-3 cell preparation of 0.2 and 2.5 nM, respectively. The parent phenol of this compound inhibits aromatase with an IC50 value of 0.028 nM in the same assay.

Synthesis and evaluation of analogues of estrone-3-O-sulfamate as potent steroid sulfatase inhibitors

Estrone sulfamate (EMATE) is a potent irreversible inhibitor of steroid sulfatase (STS). In order to further expand SAR, the compound was substituted at the 2- and/or 4-positions and its 17-carbonyl group was also removed. The following general order of potency against STS in two in vitro systems is observed for the derivatives: The 4-NO(2) > 2-halogens, 2-cyano > EMATE (unsubstituted)>17-deoxyEMATE > 2-NO(2) > 4-bromo>2-(2-propenyl), 2-n-propyl > 4-(2-propenyl), 4-n-propyl > 2,4-(2-propenyl)= 2,4-di-n-propyl. There is a clear advantage in potency to place an electron-withdrawing substituent on the A-ring with halogens preferred at the 2-position, but nitro at the 4-position. Substitution with 2-propenyl or n-propyl at the 2- and/or 4-position of EMATE, and also removal of the 17-carbonyl group are detrimental to potency. Three cyclic sulfamates designed are not STS inhibitors. This further confirms that a free or N-unsubstituted sulfamate group (H(2)NSO(2)O-) is a prerequisite for potent and irreversible inhibition of STS as shown by inhibitors like EMATE and Irosustat. The most potent derivative synthesized is 4-nitroEMATE (2), whose IC(50)s in placental microsomes and MCF-7 cells are respectively 0.8 nM and 0.01 nM.