Structure-activity relationships of selective estrogen receptor modulators: modifications to the 2-arylbenzothiophene core of raloxifene

From Bones to Bugs: Structure-Based Development of Raloxifene-Derived Pathoblockers That Inhibit Pyocyanin Production in Pseudomonas aeruginosa

The human pathogen Pseudomonas aeruginosa is particularly notorious for its multiple resistance mechanisms. A new concept for anti-infectives is the "pathoblocker" approach, which targets virulence factors to disarm rather than kill pathogens and thus attenuates the development of resistance. Based on the estrogen receptor modulator raloxifene, which had previously been identified as a potential biosynthesis inhibitor of the virulence factor pyocyanin via in silico screening, analogues have been developed as pathoblockers against P. aeruginosa. These compounds reduce the production of pyocyanin by binding to the phenazine biosynthesis enzyme PhzB. Structure-activity relationships (SAR) were explored using nano differential scanning fluorimetry, isothermal titration calorimetry, and 12 X-ray cocrystal structures. Compared to raloxifene, congener 20c shows a 60-fold lower affinity for the human estrogen receptor with a 15-fold increase in pyocyanin inhibitory activity. The comprehensive structural information gathered in this study paves the way for the development of improved pathoblockers with increased potency and selectivity.

Synthesis Studies and the Evaluation of C6 Raloxifene Derivatives

Methodology is described for the synthesis of C6 derivatives of raloxifene, a prescribed drug for the treatment and prevention of osteoporosis. Studies have explored the incorporation of electron-withdrawing substituents at C6 of the benzothiophene core. Efficient processes are also examined to introduce hydrogen bond donor and acceptor functionality. Raloxifene derivatives are evaluated with in vitro testing to determine estrogen receptor (ER) binding affinity and gene expression in MC3T3 cells.

Endocrine disruption: the noise in available data adversely impacts the models' performance

This paper is devoted to the analysis of available experimental data and preparation of predictive models for binding affinity of molecules with respect to two nuclear receptors involved in endocrine disruption (ED): the oestrogen (ER) and the androgen (AR) receptors. The ED-relevant data were retrieved from multiple sources, including the CERAPP, CoMPARA, and the Tox21 projects as well as ChEMBL and PubChem databases. Data analysis performed with the help of generative topographic mapping revealed the problem of low agreement between experimental values from different sources. Collected data were used to train both classification models for ER and AR binding activities and regression models for relative binding affinity (RBA) and median inhibition concentration (IC50). These models displayed relatively poor performance in classification (sensitivities ER = 0.34, AR = 0.49) and in regression (determination coefficient r ² for the RBA and IC50 models in external validation varied from 0.44 to 0.76). Our analysis demonstrates that low models' performance resulted from misinterpreted experimental endpoints or wrongly reported values, thus confirming the observations reported in CERAPP and CoMPARA studies. Developed models and collected data sets included of 6215 (ER) and 3789 (AR) unique compounds, which are freely available.

Recent progress in selective estrogen receptor downregulators (SERDs) for the treatment of breast cancer

Selective estrogen receptor downregulators (SERDs) are a novel class of compounds capable of reducing the ERα protein level and blocking ER activity. Therefore, SERDs are considered as a significant therapeutic approach to treat ER+ breast cancer in both early stage and more advanced drug-resistant cases. After the FDA approval of a steroidal drug, fulvestrant, as a SERD for the treatment of breast cancer in patients who have progressed on antihormonal agents, several molecules with diverse chemical structures have been rapidly developed, studied and evaluated for selective estrogen receptor downregulation activity. Here we compile the promising SERDs reported in recent years and discuss the chemical structure and pharmacological profile of the most potent compound of the considered series. Because of the availability of only a limited number of effective drugs for the treatment of breast cancer, the quest for a potent SERD with respectable activity and bioavailability is still ongoing. The goal of this article is to make available to the reader an overview of the current progress in SERDs and provide clues for the future discovery and development of novel pharmacological potent SERDs for the treatment of breast cancer.

6'-Methoxy Raloxifene-analog enhances mouse bone properties with reduced estrogen receptor binding

Raloxifene (RAL) is an FDA-approved drug used to treat osteoporosis in postmenopausal women. RAL suppresses bone loss primarily through its role as a selective estrogen receptor modulator (SERM). This hormonal estrogen therapy promotes unintended side effects, such as hot flashes and increased thrombosis risk, and prevents the drug from being used in some patient populations at-risk for fracture, including children with bone disorders. It has recently been demonstrated that RAL can have significant positive effects on overall bone mechanical properties by binding to collagen and increasing bone tissue hydration in a cell-independent manner. A Raloxifene-Analog (RAL-A) was synthesized by replacing the 6-hydroxyl substituent with 6-methoxy in effort to reduce the compound's binding affinity for estrogen receptors (ER) while maintaining its collagen-binding ability. It was hypothesized that RAL-A would improve the mechanical integrity of bone in a manner similar to RAL, but with reduced estrogen receptor binding. Molecular assessment showed that while RAL-A did reduce ER binding, downstream ER signaling was not completely abolished. In-vitro, RAL-A performed similarly to RAL and had an identical concentration threshold on osteocyte cell proliferation, differentiation, and function. To assess treatment effect in-vivo, wildtype (WT) and heterozygous (OIM+/−) female mice from the Osteogenesis Imperfecta (OI) murine model were treated with either RAL or RAL-A from 8 weeks to 16 weeks of age. There was an untreated control group for each genotype as well. Bone microarchitecture was assessed using microCT, and mechanical behavior was assessed using 3-point bending. Results indicate that both compounds produced analogous gains in tibial trabecular and cortical microarchitecture. While WT mechanical properties were not drastically altered with either treatment, OIM+/− mechanical properties were significantly enhanced, most notably, in post-yield properties including bone toughness. This proof-of-concept study shows promising results and warrants the exploration of additional analog iterations to further reduce ER binding and improve fracture resistance.

Discovery of LSZ102, a Potent, Orally Bioavailable Selective Estrogen Receptor Degrader (SERD) for the Treatment of Estrogen Receptor Positive Breast Cancer

In breast cancer, estrogen receptor alpha (ERα) positive cancer accounts for approximately 74% of all diagnoses, and in these settings, it is a primary driver of cell proliferation. Treatment of ERα positive breast cancer has long relied on endocrine therapies such as selective estrogen receptor modulators, aromatase inhibitors, and selective estrogen receptor degraders (SERDs). The steroid-based anti-estrogen fulvestrant (5), the only approved SERD, is effective in patients who have not previously been treated with endocrine therapy as well as in patients who have progressed after receiving other endocrine therapies. Its efficacy, however, may be limited due to its poor physicochemical properties. We describe the design and synthesis of a series of potent benzothiophene-containing compounds that exhibit oral bioavailability and preclinical activity as SERDs. This article culminates in the identification of LSZ102 (10), a compound in clinical development for the treatment of ERα positive breast cancer.

Targeting protein quality control pathways in breast cancer

The efficient production, folding, and secretion of proteins is critical for cancer cell survival. However, cancer cells thrive under stress conditions that damage proteins, so many cancer cells overexpress molecular chaperones that facilitate protein folding and target misfolded proteins for degradation via the ubiquitin-proteasome or autophagy pathway. Stress response pathway induction is also important for cancer cell survival. Indeed, validated targets for anti-cancer treatments include molecular chaperones, components of the unfolded protein response, the ubiquitin-proteasome system, and autophagy. We will focus on links between breast cancer and these processes, as well as the development of drug resistance, relapse, and treatment.

Controlling Sulfuryl-Transfer Biology

In humans, the cytosolic sulfotransferases (SULTs) catalyze regiospecific transfer of the sulfuryl moiety (-SO3) from 3'-phosphoadenosine 5'-phosphosulfate to thousands of metabolites, including numerous signaling small molecules, and thus regulates their activities and half-lives. Imbalances in the in vivo set points of these reactions leads to disease. Here, with the goal of controlling sulfonation in vivo, molecular ligand-recognition principles in the SULT and nuclear receptor families are integrated in creating a strategy that can prevent sulfonation of a compound without significantly altering its receptor affinity, or inhibiting SULTS. The strategy is validated by using it to control the sulfonation and estrogen receptor (ER) activating activity of raloxifene (a US Food and Drug Administration-approved selective estrogen receptor modulator) and its derivatives. Preventing sulfonation is shown to enhance ER-activation efficacy 10(4)-fold in studies using Ishikawa cells. The strategy offers the opportunity to control sulfuryl transfer on a compound-by-compound basis, to enhance the efficacy of sulfonated drugs, and to explore the biology of sulfuryl transfer with unprecedented precision.

An overview of benzo[b]thiophene-based medicinal chemistry

Among sulfur containing heterocycles, benzothiophene and its derivatives are at the focus as these candidates have structural similarities with active compounds to develop new potent lead molecules in drug design. Benzo[b]thiophene scaffold is one of the privileged structures in drug discovery as this core exhibits various biological activities allowing them to act as anti-microbial, anti-cancer, anti-inflammatory, anti-oxidant, anti-tubercular, anti-diabetic, anti-convulsant agents and many more. Further, numerous benzothiophene-based compounds as clinical drugs have been extensively used to treat various types of diseases with high therapeutic potency, which has led to their extensive developments. Due to the wide range of biological activities of benzothiophene, their structure activity relationships (SAR) have generated interest among medicinal chemists, and this has culminated in the discovery of several lead molecules against numerous diseases. The present review is endeavoring to highlight the progress in the various pharmacological activities of benzo[b]thiophene derivatives. It is hoped that this review will be helpful for new thoughts in the quest for rational designs of more active and less toxic benzothiophene-based medicinal drugs, as well as more effective diagnostic agents and pathologic probes. Also, SAR studies that highlight the chemical groups responsible for evoking the potential activities of benzothiophene derivatives are studied and compared.

Antiestrogens: structure-activity relationships and use in breast cancer treatment

About 70% of breast tumors express estrogen receptor alpha (ERα), which mediates the proliferative effects of estrogens on breast epithelial cells, and are candidates for treatment with antiestrogens, steroidal or non-steroidal molecules designed to compete with estrogens and antagonize ERs. The variable patterns of activity of antiestrogens (AEs) in estrogen target tissues and the lack of systematic cross-resistance between different types of molecules have provided evidence for different mechanisms of action. AEs are typically classified as selective estrogen receptor modulators (SERMs), which display tissue-specific partial agonist activity (e.g. tamoxifen and raloxifene), or as pure AEs (e.g. fulvestrant), which enhance ERα post-translational modification by ubiquitin-like molecules and accelerate its proteasomal degradation. Characterization of second- and third-generation AEs, however, suggests the induction of diverse ERα structural conformations, resulting in variable degrees of receptor downregulation and different patterns of systemic properties in animal models and in the clinic.

Design and synthesis of novel selective estrogen receptor degradation inducers based on the diphenylheptane skeleton

Estrogen receptors (ERs) are a family of nuclear receptors (NRs) that regulate physiological effects such as reproduction and bone homeostasis. It has been reported that approximately 70% of human breast cancers are hormone-dependent and ERα-positive. Recently, novel anti-breast cancer drugs based on different mechanisms of action have received significant attention. In this article, we have designed and synthesized a selective ER degradation inducer based on the diphenylheptane skeleton. Western blotting analysis revealed that PBP-NC10 degraded ERα through the ubiquitin-proteasome system. We also performed computational docking analysis to predict the binding mode of PBP-NC10 to ERα.

Visible-light-induced tandem cyclization of 2-alkynylanilines with disulfides: a convenient method for accessing benzothiophenes under transition-metal-free and photocatalyst-free conditions

An efficient route to benzothiophenes via visible-light induced cyclization of 2-alkynylanilines with disulfides under transition-metal-free and photocatalyst-free conditions was developed.

A practical synthesis of benzothiophenes via visible-light-promoted cyclization of disulfides and alkynes

Visible-light-promoted radical cyclization of disulfides and alkynes provided benzothiophenes in good yields.

Raloxifene: A Selective Estrogen Receptor Modulator for Reducing the Risk of Invasive Breast Cancer in Postmenopausal Women

Raloxifene hydrochloride is a selective estrogen receptor modulator that has antiestrogenic effects on breast and endometrial tissue and estrogenic effects on bone, lipid metabolism and blood clotting. Tamoxifen is the prototypical selective estrogen receptor modulator and reduces the risk of both in situ and invasive breast cancers by half when compared with placebo. The limitations on the use of tamoxifen for breast cancer risk reduction relate to its well-known, but rare, side effects. A number of clinical trials have established the benefit of raloxifene on osteoporosis and fracture. Raloxifene significantly improves serum lipids and serum markers of cardiovascular disease risk, but has no significant effect on the risk of primary coronary events. In several osteoporosis trials and the Raloxifene Use for The Heart (RUTH) trial, raloxifene decreased the risk of estrogen receptor-positive breast cancer by 44–90%. In the Study of Tamoxifen And Raloxifene (STAR) trial, the effect of raloxifene on invasive breast cancer was equivalent to that of tamoxifen, with more favorable effects on uterine malignancy and clotting events. Symptomatic side effects are acceptable. In total, the available data indicate that raloxifene represents an acceptable alternative to tamoxifen for the reduction of the risk of postmenopausal breast cancer in high-risk women. The potential market for a compound shown to reduce the risk of breast cancer in postmenopausal women who are at increased risk for breast cancer is more than 10 million women in the USA alone.

Synthesis and evaluation of raloxifene derivatives as a selective estrogen receptor down-regulator

Estrogen receptors (ERs) play a major role in the growth of human breast cancer cells. A selective estrogen receptor down-regulator (SERD) that acts as not only an inhibitor of ligand binding, but also induces the down-regulation of ER, would be useful for the treatment for ER-positive breast cancer. We previously reported that tamoxifen derivatives, which have a long alkyl chain, had the ability to down-regulate ERα. With the aim of expanding range of the currently available SERDs, we designed and synthesized raloxifene derivatives, which had various lengths of the long alkyl chains, and evaluated their SERD activities. All compounds were able to bind ERα, and RC10, which has a decyl group on the amine moiety of raloxifene, was shown to be the most potent compound. Our findings suggest that the ligand core was replaceable, and that the alkyl length was important for controlling SERD activity. Moreover, RC10 showed antagonistic activity and its potency was superior to that of 4,4'-(heptane-4,4-diyl)bis(2-methylphenol) (18), a competitive antagonist of ER without SERD activity. These results provide information that will be useful for the development of promising SERDs candidates.

Design and synthesis of novel flexible ester-containing analogs of tamoxifen and their evaluation as anticancer agents

Background: Tamoxifen (TAM) is metabolized to the more active 4-hydroxytamoxifen by CYP2D6 enzyme. Due to the genetic polymorphisms in CYP2D6, clinical outcomes of TAM treatment vary. Novel flexible TAM analogs with altered activation pathway were synthesized and were tested for their antiproliferative action on MCF-7 cell lines and their binding affinity for ERα and ERβ. Results: All compounds showed better antiproliferative activity than TAM. Compound 3 showed 80-times more ERα binding than TAM, 900-times more selectivity toward ERα. Compound 3 was tested on the entire National Cancer Institute cancerous cell lines; results indicated a broad spectrum anticancer activity. Conclusion: The novel analogs were more potent than TAM with higher selectivity toward ERα and with potential metabolic stability toward CYP2D6.

Design and synthesis of novel tamoxifen analogues that avoid CYP2D6 metabolism

Tamoxifen (TAM) is a widely used drug in the prophylaxis and treatment of breast cancer. TAM is metabolized to the more active 4-hydroxytamoxifen (4-OH-TAM) and endoxifen by cytochrome P450 (CYP) mainly CYP2D6 and CYP3A4 enzymes. Due to the genetic polymorphisms in CYP2D6 genes, high variation in the clinical outcomes of TAM treatment is observed among women of different populations. To address this issue, novel TAM analogues with possible altered activation pathways were synthesized. These analogues were tested for their antiproliferative action on MCF-7 breast cancer cell lines as well as their binding affinity for estrogen receptor (ER) ER-α and ER-β receptors. These entire novel compounds showed better antiproliferative activity than did TAM on the MCF-7 cells. Moreover, compound 10 exhibited a half maximal growth inhibition (GI50) that was 1000 times more potent than that of TAM (GI50 < 0.005 μM vs 1.58 μM, respectively). Along with a broad spectrum activity on various cancer cell lines, all the TAM analogues showed considerable activity on the ER-negative breast cancer cell line. For further study, compound 10 was incubated in human liver microsomes (HLM), human hepatocytes (hHEP) and CYP2D6 supersomes. The active hydroxyl metabolite was detected after incubation in HLM and hHEP, implicating the involvement of other enzymes in its metabolism. These results prove that this novel series of TAM analogues might provide improved clinical outcomes for poor 2D6 metabolizers.

Selective Human Estrogen Receptor Partial Agonists (ShERPAs) for Tamoxifen-Resistant Breast Cancer

Almost 70% of breast cancers are estrogen receptor α (ERα) positive. Tamoxifen, a selective estrogen receptor modulator (SERM), represents the standard of care for many patients; however, 30-50% develop resistance, underlining the need for alternative therapeutics. Paradoxically, agonists at ERα such as estradiol (E2) have demonstrated clinical efficacy in patients with heavily treated breast cancer, although side effects in gynecological tissues are unacceptable. A drug that selectively mimics the actions of E2 in breast cancer therapy but minimizes estrogenic effects in other tissues is a novel, therapeutic alternative. We hypothesized that a selective human estrogen receptor partial agonist (ShERPA) at ERα would provide such an agent. Novel benzothiophene derivatives with nanomolar potency in breast cancer cell cultures were designed. Several showed partial agonist activity, with potency of 0.8-76 nM, mimicking E2 in inhibiting growth of tamoxifen-resistant breast cancer cell lines. Three ShERPAs were tested and validated in xenograft models of endocrine-independent and tamoxifen-resistant breast cancer, and in contrast to E2, ShERPAs did not cause significant uterine growth.

Structural features underlying raloxifene's biophysical interaction with bone matrix

Raloxifene, a selective estrogen receptor modulator (SERM), reduces fracture risk at least in part by improving the mechanical properties of bone in a cell- and estrogen receptor-independent manner. In this study, we determined that raloxifene directly interacts with the bone tissue. Through the use of multiple and complementary biophysical techniques including nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR), we show that raloxifene interacts specifically with the organic component or the organic/mineral composite, and not with hydroxyapatite. Structure-activity studies reveal that the basic side chain of raloxifene is an instrumental determinant in the interaction with bone. Thus, truncation of portions of the side chain reduces bone binding and also diminishes the increase in mechanical properties. Our results support a model wherein the piperidine interacts with bone matrix through electrostatic interactions with the piperidine nitrogen and through hydrophobic interactions (van der Waals) with the aliphatic groups in the side chain and the benzothiophene core. Furthermore, in silico prediction of the potential binding sites on the surface of collagen revealed the presence of a groove with sufficient space to accommodate raloxifene analogs. The hydroxyl groups on the benzothiophene nucleus, which are necessary for binding of SERMs to the estrogen receptor, are not required for binding to the bone surface, but mediate a more robust binding of the compound to the bone powder. In conclusion, we report herein a novel property of raloxifene analogs that allows them to interact with the bone tissue through potential contacts with the organic matrix and in particular collagen.

Identification of GDC-0810 (ARN-810), an Orally Bioavailable Selective Estrogen Receptor Degrader (SERD) that Demonstrates Robust Activity in Tamoxifen-Resistant Breast Cancer Xenografts

Approximately 80% of breast cancers are estrogen receptor alpha (ER-α) positive, and although women typically initially respond well to antihormonal therapies such as tamoxifen and aromatase inhibitors, resistance often emerges. Although a variety of resistance mechanism may be at play in this state, there is evidence that in many cases the ER still plays a central role, including mutations in the ER leading to constitutively active receptor. Fulvestrant is a steroid-based, selective estrogen receptor degrader (SERD) that both antagonizes and degrades ER-α and is active in patients who have progressed on antihormonal agents. However, fulvestrant suffers from poor pharmaceutical properties and must be administered by intramuscular injections that limit the total amount of drug that can be administered and hence lead to the potential for incomplete receptor blockade. We describe the identification and characterization of a series of small-molecule, orally bioavailable SERDs which are potent antagonists and degraders of ER-α and in which the ER-α degrading properties were prospectively optimized. The lead compound 11l (GDC-0810 or ARN-810) demonstrates robust activity in models of tamoxifen-sensitive and tamoxifen-resistant breast cancer, and is currently in clinical trials in women with locally advanced or metastatic estrogen receptor-positive breast cancer.

Identification of a potent 5-phenyl-thiazol-2-ylamine-based inhibitor of FLT3 with activity against drug resistance-conferring point mutations

Numerous FLT3 inhibitors have been explored as a viable therapy for the treatment of acute myeloid leukemia (AML). However, clinical data have been underwhelming due to incomplete inhibition of FLT3 or the emergence of resistant mutations treated with these older agents. We previously developed a series of 3-phenyl-1H-5-pyrazolylamine derivatives as highly potent and selective FLT3 inhibitors with good in vivo efficacy using an intravenous (IV) route. However, the poor bioavailability of these pyrazole compounds limits the development of these promising antileukemic compounds for clinical use. Herein, we describe a novel class of 5-phenyl-thiazol-2-ylamine compounds that are multi-targeted FLT3 inhibitors. From this class of compounds, compound 7h was very potent against AML cell lines and exhibited excellent oral efficacy in AML xenograft models. In addition, further studies demonstrated that compound 7h exhibited potent in vitro and in vivo activities against clinically relevant AC220 (3)-resistant kinase domain mutants of FLT3-ITD.

One-pot synthesis of 2,3-substituted benzo[b]thiophenes via Cu(i) catalysed intramolecular cyclisation from dithioesters

The novel route involves CuI catalyzed C–S bond formation using dithioesters. This approach is valuable for synthesis of rolaxifene analogues.

Novel selective estrogen mimics for the treatment of tamoxifen-resistant breast cancer

Endocrine-resistant breast cancer is a major clinical obstacle. The use of 17β-estradiol (E2) has reemerged as a potential treatment option following exhaustive use of tamoxifen or aromatase inhibitors, although side effects have hindered its clinical usage. Protein kinase C alpha (PKCα) expression was shown to be a predictor of disease outcome for patients receiving endocrine therapy and may predict a positive response to an estrogenic treatment. Here, we have investigated the use of novel benzothiophene selective estrogen mimics (SEM) as an alternative to E2 for the treatment of tamoxifen-resistant breast cancer. Following in vitro characterization of SEMs, a panel of clinically relevant PKCα-expressing, tamoxifen-resistant models were used to investigate the antitumor effects of these compounds. SEM treatment resulted in growth inhibition and apoptosis of tamoxifen-resistant cell lines in vitro. In vivo SEM treatment induced tumor regression of tamoxifen-resistant T47D:A18/PKCα and T47D:A18-TAM1 tumor models. T47D:A18/PKCα tumor regression was accompanied by translocation of estrogen receptor (ER) α to extranuclear sites, possibly defining a mechanism through which these SEMs initiate tumor regression. SEM treatment did not stimulate growth of E2-dependent T47D:A18/neo tumors. In addition, unlike E2 or tamoxifen, treatment with SEMs did not stimulate uterine weight gain. These findings suggest the further development of SEMs as a feasible therapeutic strategy for the treatment of endocrine-resistant breast cancer without the side effects associated with E2.

Bone cell-independent benefits of raloxifene on the skeleton: a novel mechanism for improving bone material properties

Raloxifene is an FDA approved agent used to treat bone loss and decrease fracture risk. In clinical trials and animal studies, raloxifene reduces fracture risk and improves bone mechanical properties, but the mechanisms of action remain unclear because these benefits occur largely independent of changes to bone mass. Using a novel experimental approach, machined bone beams, both from mature male canine and human male donors, were depleted of living cells and then exposed to raloxifene ex vivo. Our data show that ex vivo exposure of non-viable bone to raloxifene improves intrinsic toughness, both in canine and human cortical bone beams tested by 4-point bending. These effects are cell-independent and appear to be mediated by an increase in matrix bound water, assessed using basic gravimetric weighing and sophisticated ultrashort echo time magnetic resonance imaging. The hydroxyl groups (OH) on raloxifene were shown to be important in both the water and toughness increases. Wide and small angle X-ray scattering patterns during 4-pt bending show that raloxifene alters the transfer of load between the collagen matrix and the mineral crystals, placing lower strains on the mineral, and allowing greater overall deformation prior to failure. Collectively, these findings provide a possible mechanistic explanation for the therapeutic effect of raloxifene and more importantly identify a cell-independent mechanism that can be utilized for novel pharmacological approaches for enhancing bone strength.

Computational study of estrogen receptor-alpha antagonist with three-dimensional quantitative structure-activity relationship, support vector regression, and linear regression methods

Human estrogen receptor (ER) isoforms, ERα and ERβ, have long been an important focus in the field of biology. To better understand the structural features associated with the binding of ERα ligands to ERα and modulate their function, several QSAR models, including CoMFA, CoMSIA, SVR, and LR methods, have been employed to predict the inhibitory activity of 68 raloxifene derivatives. In the SVR and LR modeling, 11 descriptors were selected through feature ranking and sequential feature addition/deletion to generate equations to predict the inhibitory activity toward ERα. Among four descriptors that constantly appear in various generated equations, two agree with CoMFA and CoMSIA steric fields and another two can be correlated to a calculated electrostatic potential of ERα.

The discovery and development of selective estrogen receptor modulators (SERMs) for clinical practice

Selective estrogen receptor modulators (SERMs) are structurally different compounds that interact with intracellular estrogen receptors in target organs as estrogen receptor agonists or antagonists. These drugs have been intensively studied over the past decade and have proven to be a highly versatile group for the treatment of different conditions associated with postmenopausal women's health, including hormone responsive cancer and osteoporosis. Tamoxifen, a failed contraceptive is currently used to treat all stages of breast cancer, chemoprevention in women at high risk for breast cancer and also has beneficial effects on bone mineral density and serum lipids in postmenopausal women. Raloxifene, a failed breast cancer drug, is the only SERM approved internationally for the prevention and treatment of postmenopausal osteoporosis and vertebral fractures. However, although these SERMs have many benefits, they also have some potentially serious adverse effects, such as thromboembolic disorders and, in the case of tamoxifen, uterine cancer. These adverse effects represent a major concern given that long-term therapy is required to prevent osteoporosis or prevent and treat breast cancer. The search for the 'ideal' SERM, which would have estrogenic effects on bone and serum lipids, neutral effects on the uterus, and antiestrogenic effects on breast tissue, but none of the adverse effects associated with current therapies, is currently under way. Ospemifene, lasofoxifene, bazedoxifene and arzoxifene, which are new SERM molecules with potentially greater efficacy and potency than previous SERMs, have been investigated for use in the treatment and prevention of osteoporosis. These drugs have been shown to be comparably effective to conventional hormone replacement therapy in animal models, with potential indications for an improved safety profile. Clinical efficacy data from ongoing phase III trials are available or are awaited for each SERM so that a true understanding of the therapeutic potential of these compounds can be obtained. In this article, we describe the discovery and development of the group of medicines called SERMs. The newer SERMs in late development: ospemifene, lasofoxifene, bazedoxifene, are arzoxifene are described in detail.

Discovery of 3-phenyl-1H-5-pyrazolylamine derivatives containing a urea pharmacophore as potent and efficacious inhibitors of FMS-like tyrosine kinase-3 (FLT3)

Preclinical investigations and early clinical trials suggest that FLT3 inhibitors are a viable therapy for acute myeloid leukemia. However, early clinical data have been underwhelming due to incomplete inhibition of FLT3. We have developed 3-phenyl-1H-5-pyrazolylamine as an efficient template for kinase inhibitors. Structure-activity relationships led to the discovery of sulfonamide, carbamate and urea series of FLT3 inhibitors. Previous studies showed that the sulfonamide 4 and carbamate 5 series were potent and selective FLT3 inhibitors with good in vivo efficacy. Herein, we describe the urea series, which we found to be potent inhibitors of FLT3 and VEGFR2. Some inhibited growth of FLT3-mutated MOLM-13 cells more strongly than the FLT3 inhibitors sorafenib (2) and ABT-869 (3). In preliminary in vivo toxicity studies of the four most active compounds, 10f was found to be the least toxic. A further in vivo efficacy study demonstrated that 10f achieved complete tumor regression in a higher proportion of MOLM-13 xenograft mice than 4 and 5 (70% vs 10% and 40%). These results show that compound 10f possesses improved pharmacologic and selectivity profiles and could be more effective than previously disclosed FLT3 inhibitors in the treatment of acute myeloid leukemia.

Application of 4D-QSAR studies to a series of raloxifene analogs and design of potential selective estrogen receptor modulators

Four-dimensional quantitative structure-activity relationship (4D-QSAR) analysis was applied on a series of 54 2-arylbenzothiophene derivatives, synthesized by Grese and coworkers, based on raloxifene (an estrogen receptor-alpha antagonist), and evaluated as ERa ligands and as inhibitors of estrogen-stimulated proliferation of MCF-7 breast cancer cells. The conformations of each analogue, sampled from a molecular dynamics simulation, were placed in a grid cell lattice according to three trial alignments, considering two grid cell sizes (1.0 and 2.0 Å). The QSAR equations, generated by a combined scheme of genetic algorithms (GA) and partial least squares (PLS) regression, were evaluated by "leave-one-out" cross-validation, using a training set of 41 compounds. External validation was performed using a test set of 13 compounds. The obtained 4D-QSAR models are in agreement with the proposed mechanism of action for raloxifene. This study allowed a quantitative prediction of compounds' potency and supported the design of new raloxifene analogs.

3-Phenyl-1H-5-pyrazolylamine-based derivatives as potent and efficacious inhibitors of FMS-like tyrosine kinase-3 (FLT3)

A new class of FLT3 inhibitors has been identified based on the 3-phenyl-1H-5-pyrazolylamine scaffold. The structure-activity relationships led to the discovery of two carbamate series, and some potent compounds within these two series exhibited better growth inhibition of FLT3-mutated MOLM-13 cells than FLT3 inhibitors sorafenib (2) and ABT-869 (3). In particular, compound 8d exhibited the ability to regress tumors in mouse xenograft model using MOLM-13 cells.

Hydrophobic Interactions Improve Selectivity to ERα for Ben-zothiophene SERMs

The discovery, pharmacology, and biophysical characterization of an ERα selective benzothiophene (BTPα) is described. BTPα (4) is a high affinity ligand with 140-fold greater selectivity for ERα (K(i)=0.25 nM) over ERbeta (K(i)=35 nM). In rodent models of estrogen action, BTPα blocks the effects of estrogen in the uterus but mimics the effects estrogen on bone. The basis of ERα selectivity for BTPα was evaluated by using protein crystallography and hydrogen/deuterium exchange (HDX) mass spectrometry. HDX data supports that the n-butyl chain of BTPα stabilizes helix 7 in ERα relative to that of ERβ which we propose leads to an enhancement of affinity to the alpha receptor sub-type.

A scaffold-independent subcellular event-based analysis: characterization of significant structural modifications

General and singular subcellular events within the ligand-dependent receptor-mediated cellular response were separated by using the Jurs and the electrotopological state (ES) descriptors, allowing characterization of the significant structural modifications in a given set of collected peroxisome proliferator-activated receptor γ (PPARγ) agonists. The identified Jurs descriptor is the integrated function of all the general events but is scaffold-dependent. The top captured ES descriptors stand for significant structural modifications, i.e., singular events. To further elucidate the descriptor-event relationship, three biological data sets show that the Jurs descriptor can be further divided into three important descriptors, the log D, polar surface area, and shape-like descriptor. The identification of the essential descriptors for general events is the first regression, and the prioritization of all the possible structural modifications of the 46 collected thiazolidinedione PPARγ agonists is the second regression. As results, the top captured ES symbols can correspond to the singular ligand--receptor interactions as highlighted in the X-ray crystallographic image of rosiglitazone--PPARγ complex.

Integrating medicinal chemistry, organic/combinatorial chemistry, and computational chemistry for the discovery of selective estrogen receptor modulators with Forecaster, a novel platform for drug discovery

As part of a large medicinal chemistry program, we wish to develop novel selective estrogen receptor modulators (SERMs) as potential breast cancer treatments using a combination of experimental and computational approaches. However, one of the remaining difficulties nowadays is to fully integrate computational (i.e., virtual, theoretical) and medicinal (i.e., experimental, intuitive) chemistry to take advantage of the full potential of both. For this purpose, we have developed a Web-based platform, Forecaster, and a number of programs (e.g., Prepare, React, Select) with the aim of combining computational chemistry and medicinal chemistry expertise to facilitate drug discovery and development and more specifically to integrate synthesis into computer-aided drug design. In our quest for potent SERMs, this platform was used to build virtual combinatorial libraries, filter and extract a highly diverse library from the NCI database, and dock them to the estrogen receptor (ER), with all of these steps being fully automated by computational chemists for use by medicinal chemists. As a result, virtual screening of a diverse library seeded with active compounds followed by a search for analogs yielded an enrichment factor of 129, with 98% of the seeded active compounds recovered, while the screening of a designed virtual combinatorial library including known actives yielded an area under the receiver operating characteristic (AU-ROC) of 0.78. The lead optimization proved less successful, further demonstrating the challenge to simulate structure activity relationship studies.