Molecular pharmacology of aromatase and its regulation by endogenous and exogenous agents

Decoding the Role of CYP450 Enzymes in Metabolism and Disease: A Comprehensive Review

Cytochrome P450 (CYP450) is a group of enzymes that play an essential role in Phase I metabolism, with 57 functional genes classified into 18 families in the human genome, of which the CYP1, CYP2, and CYP3 families are prominent. Beyond drug metabolism, CYP enzymes metabolize endogenous compounds such as lipids, proteins, and hormones to maintain physiological homeostasis. Thus, dysregulation of CYP450 enzymes can lead to different endocrine disorders. Moreover, CYP450 enzymes significantly contribute to fatty acid metabolism, cholesterol synthesis, and bile acid biosynthesis, impacting cellular physiology and disease pathogenesis. Their diverse functions emphasize their therapeutic potential in managing hypercholesterolemia and neurodegenerative diseases. Additionally, CYP450 enzymes are implicated in the onset and development of illnesses such as cancer, influencing chemotherapy outcomes. Assessment of CYP450 enzyme expression and activity aids in evaluating liver health state and differentiating between liver diseases, guiding therapeutic decisions, and optimizing drug efficacy. Understanding the roles of CYP450 enzymes and the clinical effect of their genetic polymorphisms is crucial for developing personalized therapeutic strategies and enhancing drug responses in diverse patient populations.

Multifaceted 3D-QSAR analysis for the identification of pharmacophoric features of biphenyl analogues as aromatase inhibitors

Aromatase, a cytochrome P450 enzyme, is responsible for the conversion of androgens to estrogens, which fuel the multiplication of cancerous cells. Inhibition of estrogen biosynthesis by aromatase inhibitors (AIs) is one of the highly advanced therapeutic approach available for the treatment of estrogen-positive breast cancer. Biphenyl moiety aids lipophilicity to the conjugated scaffold and enhances the accessibility of the ligand to the target. The present study is focused on the investigation of, the mode of binding of biphenyl with aromatase, prediction of ligand-target binding affinities, and pharmacophoric features essential for favorable for aromatase inhibition. A multifaceted 3D-QSAR (SOMFA, Field and Gaussian) along with molecular docking, molecular dynamic simulations and pharmacophore mapping were performed on a series of biphenyl bearing molecules (1-33) with a wide range of aromatase inhibitory activity (0.15-920 nM). Among the generated 3D-QSAR models, the Force field-based 3D-QSAR model (R2 = 0.9151) was best as compared to SOMFA and Gaussian Field (R2=0.7706, 0.9074, respectively). However, all the generated 3D-QSAR models were statistically fit, robust enough, and reliable to explain the variation in biological activity in relation to pharmacophoric features of dataset molecules. A four-point pharmacophoric features with three acceptor sites (A), one aromatic ring (R) features, AAAR_1, were obtained with the site and survival score values 0.890 and 4.613, respectively. The generated 3D-QSAR plots in the study insight into the structure-activity relationship of dataset molecules, which may help in the designing of potent biphenyl derivatives as newer inhibitors of aromatase.Communicated by Ramaswamy H. Sarma.

Obesity and endocrine therapy resistance in breast cancer: Mechanistic insights and perspectives

The incidence of obesity, a recognized risk factor for various metabolic and chronic diseases, including numerous types of cancers, has risen dramatically over the recent decades worldwide. To date, convincing research in this area has painted a complex picture about the adverse impact of high body adiposity on breast cancer onset and progression. However, an emerging but overlooked issue of clinical significance is the limited efficacy of the conventional endocrine therapies with selective estrogen receptor modulators (SERMs) or degraders (SERDs) and aromatase inhibitors (AIs) in patients affected by breast cancer and obesity. The mechanisms behind the interplay between obesity and endocrine therapy resistance are likely to be multifactorial. Therefore, what have we actually learned during these years and which are the main challenges in the field? In this review, we will critically discuss the epidemiological evidence linking obesity to endocrine therapeutic responses and we will outline the molecular players involved in this harmful connection. Given the escalating global epidemic of obesity, advances in understanding this critical node will offer new precision medicine-based therapeutic interventions and more appropriate dosing schedule for treating patients affected by obesity and with breast tumors resistant to endocrine therapies.

Biomarker Modulation Study of Celecoxib for Chemoprevention in Women at Increased Risk for Breast Cancer: A Phase II Pilot Study

In preclinical studies, celecoxib has been associated with reduced risk of breast cancer. In this study, the aim was to assess the biomodulatory effect of celecoxib on blood and benign breast tissue biomarkers in women at increased risk for breast cancer. Women at increased risk for breast cancer [5-year Gail risk score of >1.67%, history of atypical hyperplasia, lobular carcinoma in situ, or previous estrogen receptor (ER)-negative breast cancer] were treated with celecoxib at 400 mg orally twice daily for 6 months. Participants underwent random periareolar fine needle aspiration and blood draw at baseline and at 6 months for analysis of biomarkers: serum levels of insulin-like growth factor 1 (IGF-1), IGF-binding protein 1 (IGFBP-1), and IGFBP-3; tissue expression of Ki-67 and ER; as well as cytology. Forty-nine patients were eligible for analysis. Median IGFBP-1 levels increased significantly from 6.05 ng/mL at baseline to 6.93 ng/mL at 6 months (P = 0.04), and median IGFBP-3 levels decreased significantly from 3,593 ng/mL to 3,420 ng/mL (P = 0.01). We also detected favorable changes in cytology of 52% of tested sites after 6 months of celecoxib therapy. No changes in tissue Ki-67 and ER expression levels were observed. No grade 3 or 4 toxicity was recorded. Celecoxib was well tolerated and induced favorable changes in serum biomarkers as well as cytology in this pilot phase II trial. A phase IIb placebo-controlled study with celecoxib could be considered for women at increased risk for breast cancer.

The dual role of tumor necrosis factor-alpha (TNF-α) in breast cancer: molecular insights and therapeutic approaches

BACKGROUND

Breast cancer is the most prevalent cancer among women worldwide and the fifth cause of death among all cancer patients. Breast cancer development is driven by genetic and epigenetic alterations, with the tumor microenvironment (TME) playing an essential role in disease progression and evolution through mechanisms like inflammation promotion. TNF-α is one of the essential pro-inflammatory cytokines found in the TME of breast cancer patients, being secreted both by stromal cells, mainly by tumor-associated macrophages, and by the cancer cells themselves. In this review, we explore the biological and clinical impact of TNF-α in all stages of breast cancer development. First of all, we explore the correlation between TNF-α expression levels at the tumor site or in plasma/serum of breast cancer patients and their respective clinical status and outcome. Secondly, we emphasize the role of TNF-α signaling in both estrogen-positive and -negative breast cancer cells. Thirdly, we underline TNF-α involvement in epithelial-to-mesenchymal transition (EMT) and metastasis of breast cancer cells, and we point out the contribution of TNF-α to the development of acquired drug resistance.

CONCLUSIONS

Collectively, these data reveal a pro-tumorigenic role of TNF-α during breast cancer progression and metastasis. We systemize the knowledge regarding TNF-α-related therapies in breast cancer, and we explain how TNF-α may act as both a target and a drug in different breast cancer therapeutic approaches. By corroborating the known molecular effects of TNF-α signaling in breast cancer cells with the results from several preclinical and clinical trials, including TNF-α-related clinical observations, we conclude that the potential of TNF-α in breast cancer therapy promises to be of great interest.

Effects of Celecoxib and Low-dose Aspirin on Outcomes in Adjuvant Aromatase Inhibitor-Treated Patients: CCTG MA.27

Background

Celecoxib and low-dose aspirin might decrease risk of breast cancer recurrence.

Methods

In the Canadian Cancer Trials Group MA.27, postmenopausal hormone receptor-positive breast cancer patients were randomly assigned (2 × 2) to adjuvant exemestane or anastrozole, and celecoxib or placebo. Low-dose aspirin of 81 mg or less was a stratification factor. Due to concerns about cardiac toxicity, celecoxib use was stopped in December 2004, while stratification by aspirin use was removed through protocol amendment. We examined the effects of celecoxib and low-dose aspirin on event-free survival (EFS), defined as time from random assignment to time of locoregional or distant disease recurrence, new primary breast cancer, or death from any cause; distant disease-free survival (DDFS); and overall survival (OS). All statistical tests were two-sided.

Results

Random assignment to celecoxib (n = 811, 50.0%) or placebo (n = 811, 50.0%) was discontinued after 18 months (n = 1622). At a median of 4.1 years' follow-up, among 1622 patients, 186 (11.5%) patients had an EFS event: 80 (4.9%) had distant relapse, and 125 (7.7%) died from any cause. Celecoxib did not statistically significantly impact EFS, DDFS, or OS in univariate analysis (respectively, P = .92, P = .55, and P = .56) or multivariable analysis (respectively, P = .74, P = .60, and P = .76). Low-dose aspirin use (aspirin users n = 476, 21.5%; non-aspirin users n = 1733, 78.5%) was associated in univariate analyses with worse EFS (hazard ratio [HR] = 1.48, 95% confidence interval [CI] = 1.12 to 1.96, P = 0.006) and worse OS (HR = 1.87, 95% CI = 1.35 to 2.61, P < .001). After adjusting for baseline characteristics and treatment arm, aspirin use showed no statistical association with EFS (P = .08) and DDFS (P = .82), but was associated with statistically worse OS (HR = 1.67, 95% CI = 1.13 to 2.49, P = .01).

Conclusion

Random assignment to short-term (≤18 months) celecoxib as well as use of low-dose aspirin showed no effect on DDFS and EFS in multivariable analysis. Low-dose aspirin increased "all-cause" mortality, presumably because of higher preexisting cardiovascular risks.

Comprehensive and Automated Linear Interaction Energy Based Binding-Affinity Prediction for Multifarious Cytochrome P450 Aromatase Inhibitors

Cytochrome P450 aromatase (CYP19A1) plays a key role in the development of estrogen dependent breast cancer, and aromatase inhibitors have been at the front line of treatment for the past three decades. The development of potent, selective and safer inhibitors is ongoing with in silico screening methods playing a more prominent role in the search for promising lead compounds in bioactivity-relevant chemical space. Here we present a set of comprehensive binding affinity prediction models for CYP19A1 using our automated Linear Interaction Energy (LIE) based workflow on a set of 132 putative and structurally diverse aromatase inhibitors obtained from a typical industrial screening study. We extended the workflow with machine learning methods to automatically cluster training and test compounds in order to maximize the number of explained compounds in one or more predictive LIE models. The method uses protein-ligand interaction profiles obtained from Molecular Dynamics (MD) trajectories to help model search and define the applicability domain of the resolved models. Our method was successful in accounting for 86% of the data set in 3 robust models that show high correlation between calculated and observed values for ligand-binding free energies (RMSE < 2.5 kJ mol-1), with good cross-validation statistics.

Investigation of antiaromatase activity using hepatic microsomes of Nile tilapia (Oreochromis niloticus)

Microsomal aromatase enzymes of humans and rats have been used in antiaromatase assays, but enzyme activity is species-specific. The current study extracted hepatic microsomes of Nile tilapia (Oreochromis niloticus) to investigate and compare the antiaromatase activity of chrysin, quercetin, and quercitrin. This activity was evaluated using a dibenzylfluorescein (DBF) assay. Results revealed that the age and body weight of Nile tilapia affected the yield of extracted microsomes. Extraction of hepatic microsomes of Nile tilapia was most effective when using a reaction medium with a pH of 8.0. A DBF assay using Nile tilapia microsomes revealed significant differences in levels of antiaromatase activity for chrysin, quercetin, and quercitrin. Chrysin was the most potent aromatase inhibitor, with an IC50 of 0.25 mg/mL. In addition, chrysin is an aromatase inhibitor that also inhibits the proliferation of cancer cells. Hepatic microsomes of Nile tilapia can be used to investigate and compare the antiaromatase activity of different compounds.

Theoretical Study of the Mechanism of Exemestane Hydroxylation Catalyzed by Human Aromatase Enzyme

Human aromatase (CYP19A1) aromatizes the androgens to form estrogens via a three-step oxidative process. The estrogens are necessary in humans, mainly in women, because of the role they play in sexual and reproductive development. However, these also are involved in the development and growth of hormone-dependent breast cancer. Therefore, inhibition of the enzyme aromatase, by means of drugs known as aromatase inhibitors, is the frontline therapy for these types of cancers. Exemestane is a suicidal third-generation inhibitor of aromatase, currently used in breast cancer treatment. In this study, the hydroxylation of exemestane catalyzed by aromatase has been studied by means of hybrid QM/MM methods. The Free Energy Perturbation calculations provided a free energy of activation for the hydrogen abstraction step (rate-limiting step) of 17 kcal/mol. The results reveal that the hydroxylation of exemestane is not the inhibition stage, suggesting a possible competitive mechanism between the inhibitor and the natural substrate androstenedione in the first catalytic subcycle of the enzyme. Furthermore, the analysis of the interaction energy for the substrate and the cofactor in the active site shows that the role of the enzymatic environment during this reaction consists of a transition state stabilization by means of electrostatic effects.

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.

Investigation of fluorinated and bifunctionalized 3-phenylchroman-4-one (isoflavanone) aromatase inhibitors

Fluorinated isoflavanones and bifunctionalized isoflavanones were synthesized through a one-step gold(I)-catalyzed annulation reaction. These compounds were evaluated for their in vitro inhibitory activities against aromatase in a fluorescence-based enzymatic assay. Selected compounds were tested for their anti-proliferative effects on human breast cancer cell line MCF-7. Compounds 6-methoxy-3-(pyridin-3-yl)chroman-4-one (3c) and 6-fluoro-3-(pyridin-3-yl)chroman-4-one (3e) were identified as the most potent aromatase inhibitors with IC₅₀ values of 2.5 μM and 0.8 μM. Therefore, these compounds have great potential for the development of pharmaceutical agents against breast cancer.

Molecular pathways: adipose inflammation as a mediator of obesity-associated cancer

The increasing rate of obesity worldwide is predicted to be associated with a surge in diseases. Notably, obesity has been linked to approximately 20% of cancer cases in the United States; obesity is associated with both increased risk and worse outcomes after diagnosis. Altered levels of circulating factors are strongly implicated, including insulin, insulin-like growth factor 1, leptin, adiponectin, and interleukin-6 (IL-6). In addition, increasing attention has focused on the consequences of local adipose inflammation. Inflammatory foci characterized by crown-like structures consisting of dead adipocytes encircled by macrophages occur in white adipose depots, including the breast tissue, of most overweight and obese women. Saturated fatty acids, released as a consequence of obesity-associated lipolysis, induce macrophage activation via Toll-like receptor 4, thereby stimulating NF-κB signaling. This, in turn, activates transcription of proinflammatory genes including COX-2, IL-6, IL-1β, and TNFα. Elevated levels of proinflammatory mediators cause both local and systemic effects. Of particular relevance with regard to breast cancer is increased transcription of the CYP19 gene encoding aromatase, the rate-limiting enzyme for estrogen synthesis. Notably, this obesity-inflammation-aromatase axis provides a plausible explanation for increased rates of postmenopausal, hormone receptor-positive breast cancer associated with obesity and hence may offer targets for interventions to attenuate risk or improve prognosis. Potential approaches include weight reduction, exercise, and suppression of obesity-driven signaling pathways using pharmaceutical or dietary agents. A key future goal is to identify biomarkers that accurately report adipose inflammation, both for identification of at-risk individuals and to assess the efficacy of interventions. Clin Cancer Res; 19(22); 6074-83. ©2013 AACR.

A comparative study for the evaluation of two doses of ellagic acid on hepatic drug metabolizing and antioxidant enzymes in the rat

The present study was designed to evaluate different doses of ellagic acid (EA) in vivo in rats for its potential to modulate hepatic phases I, II, and antioxidant enzymes. EA (10 or 30 mg/kg/day, intragastrically) was administered for 14 consecutive days, and activity, protein, and mRNA levels were determined. Although the cytochrome P450 (CYP) 2B and CYP2E enzyme activities were decreased significantly, the activities of all other enzymes were unchanged with the 10 mg/kg/day EA. In addition, western-blot and qRT-PCR results clearly corroborated the above enzyme expressions. On the other hand, while the NAD(P)H:quinone oxidoreductase 1 (NQO1), catalase (CAT), glutathione peroxidase (GPX), and glutathione S-transferase (GST) activities were increased significantly, CYP1A, 2B, 2C, 2E, and 19 enzyme activities were reduced significantly with 30 mg/kg/day EA. In addition, CYP2B, 2C6, 2E1, and 19 protein and mRNA levels were substantially decreased by the 30 mg/kg/day dose of EA, but the CYP1A protein, and mRNA levels were not changed. CYP3A enzyme activity, protein and mRNA levels were not altered by neither 10 nor 30 mg/kg/day ellagic acid. These results indicate that EA exerts a dose-dependent impact on the metabolism of chemical carcinogens and drugs by affecting the enzymes involved in xenobiotics activation/detoxification and antioxidant pathways.

Prostaglandin E2 stimulates estradiol synthesis in the cerebellum postnatally with associated effects on Purkinje neuron dendritic arbor and electrophysiological properties

Prostaglandins (PGs) are ubiquitous membrane-derived, lipid-signaling molecules with wide ranging effects throughout the body. In the brain, PGE(2) is the key regulator of fever after inflammation but is also implicated in neural development and synaptic plasticity. The steroid hormone estradiol is also a key regulator of neural development and synaptic plasticity. Recently, we showed that administering cyclooxygenase (COX) inhibitors to block PGE(2) production increased the total length of Purkinje cell dendrites, the number of dendritic spines, and the level of spinophilin protein, which is enriched in dendritic spines. Correspondingly, PGE(2) administration into the cerebellum decreased spinophilin protein content. We now report that PGE(2) stimulates estradiol synthesis in the immature rat cerebellum via enhanced activity of the aromatase enzyme. Treatment with cyclooxygenase inhibitors reduced cerebellar aromatase activity and estradiol content whereas PGE(2) administration increased both. Treatment with either PGE(2) or estradiol stunted Purkinje neuron dendritic length and complexity and produced a corresponding reduction in spinophilin content. Treatment with formestane to inhibit aromatase activity led to excessive sprouting of the dendritic tree, whereas elevated estradiol had the opposite effect. Electrophysiological measurements from Purkinje neurons revealed novel sex differences in input resistance and membrane capacitance that were abolished by estradiol exposure, whereas a sex difference in the amplitude of the afterhyperpolarization after an action potential was not. Correlated changes in action potential threshold suggest that prolonged alterations in neuronal firing activity could be a consequence of increased estradiol content during the second week of life. These findings reveal a previously unappreciated role for PG-stimulated steroidogenesis in the developing brain and a new potential route for inflammation-mediated disruption of neuronal maturation.

Development of a new class of aromatase inhibitors: design, synthesis and inhibitory activity of 3-phenylchroman-4-one (isoflavanone) derivatives

Aromatase (CYP19) catalyzes the aromatization reaction of androgen substrates to estrogens, the last and rate-limiting step in estrogen biosynthesis. Inhibition of aromatase is a new and promising approach to treat hormone-dependent breast cancer. We present here the design and development of isoflavanone derivatives as potential aromatase inhibitors. Structural modifications were performed on the A and B rings of isoflavanones via microwave-assisted, gold-catalyzed annulation reactions of hydroxyaldehydes and alkynes. The in vitro aromatase inhibition of these compounds was determined by fluorescence-based assays utilizing recombinant human aromatase (baculovirus/insect cell-expressed). The compounds 3-(4-phenoxyphenyl)chroman-4-one (1h), 6-methoxy-3-phenylchroman-4-one (2a) and 3-(pyridin-3-yl)chroman-4-one (3b) exhibited potent inhibitory effects against aromatase with IC(50) values of 2.4 μM, 0.26 μM and 5.8 μM, respectively. Docking simulations were employed to investigate crucial enzyme/inhibitor interactions such as hydrophobic interactions, hydrogen bonding and heme iron coordination. This report provides useful information on aromatase inhibition and serves as a starting point for the development of new flavonoid aromatase inhibitors.

Steroidal pyrazolines evaluated as aromatase and quinone reductase-2 inhibitors for chemoprevention of cancer

The aromatase and quinone reductase-2 inhibition of synthesized heterocyclic pyrazole derivatives fused with steroidal structure for chemoprevention of cancer is reported herein. All compounds were interestingly less toxic than the reference drug (Cyproterone(®)). The aromatase inhibitory activities of these compounds were much more potent than the lead compound resveratrol, which has an IC(50) of 80 μM. In addition, all the compounds displayed potent quinone reductase-2 inhibition. Initially the acute toxicity of the compounds was assayed via the determination of their LD(50). The aromatase and quinone reductase-2 inhibitors resulting from this study have potential value in the treatment and prevention of cancer.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Screening for compounds with aromatase inhibiting activities from Atractylodes macrocephala Koidz

Ten compounds were isolated from the dichloromethane extract of Atractylodes macrocephala and their aromatase inhibiting activities were tested using an in vitro fluorescent-based aromatase assay. The results indicated that atractylenolide I (1), atractylenolide II (2) and atractylenolide III (3) had inhibition ratios of 94.56 ± 0.70%, 90.93 ± 1.41% and 86.31 ± 8.46%, respectively, at a concentration of 10 μM. We conclude from our results that atractylenolide and its derivates may serve as potential aromatase inhibitors (AIs) and thus merit continued study in the future.

The role of oestrogen in the pathogenesis of obesity, type 2 diabetes, breast cancer and prostate disease

A detailed review of the literature was performed in a bid to identify the presence of a common link between specific hormone interactions and the increasing prevalence of global disease. The synergistic action of unopposed oestrogen and leptin, compounded by increasing insulin, cortisol and xeno-oestrogen exposure directly initiate, promote and exacerbate obesity, type 2 diabetes, uterine overgrowth, prostatic enlargement, prostate cancer and breast cancer. Furthermore these hormones significantly contribute to the incidence and intensity of anxiety and depression, Alzheimer's disease, heart disease and stroke. This review, in collaboration with hundreds of evidence-based clinical researchers, correlates the significant interactions these hormones exert upon the upregulation of p450 aromatase, oestrogen, leptin and insulin receptor function; the normal status quo of their binding globulins; and how adduct formation alters DNA sequencing to ultimately produce an array of metabolic conditions ranging from menopausal symptoms and obesity to Alzheimer's disease and breast and prostate cancer. It reveals the way that poor diet, increased stress, unopposed endogenous oestrogens, exogenous oestrogens, pesticides, xeno-oestrogens and leptin are associated with increased aromatase activity, and how its products, increased endogenous oestrogen and lowered testosterone, are associated with obesity, type 2 diabetes, Alzheimer's disease and oestrogenic disease. This controversial break-through represents a paradigm shift in medical thinking, which can prevent the raging pandemic of diabetes, obesity and cancer currently sweeping the world, and as such, it will reshape health initiatives, reduce suffering, prevent waste of government expenditure and effectively transform preventative medicine and global health care for decades.

Anti-anxiety, cognitive, and steroid biosynthetic effects of an isoflavone-based dietary supplement are gonad and sex-dependent in rats

Isoflavone-rich diets are associated with reduced menopausal symptoms and lowered risk of cancers of reproductive tissues. Isoflavones may mimic some effects of estrogen by binding to estrogen receptors, and/or altering steroid availability. Despite their potential health benefits, neither the effects, nor mechanisms, of isoflavones are well understood. We hypothesized that isoflavones would alter behavior and physiology of rats in sex and/or gonad-dependent manner. An isoflavone-based, commercially-available, dietary supplement was administered via subcutaneous implantation to female and male, intact and gonadectomized Long-Evans rats. Affective (elevated plus-maze), cognitive (water-maze), and reproductive (sexual) behavior was examined. Weights of reproductive structures were measured, as an index of trophic effects. Steroid levels in circulation and brain regions associated with behavioral measures were evaluated by radioimmunoassay. The supplement increased anti-anxiety behavior of intact, but not gonadectomized, rats. The supplement enhanced visual-spatial performance of all rats, but this effect was most evident among proestrous female rats, which had the poorest spatial performance. There were neither effects of the supplement on sexual behavior, mass of reproductive tissues, nor plasma steroid levels. The supplement increased levels of 5α-androstane,17ß-diol-3α-diol (3α-diol) in the hippocampus (but not other brain regions) of gonadectomized females. Thus, the supplement altered anxiety and cognitive behavior and brain production of steroids; however, the anti-anxiety effects were limited to rats with an intact reproductive axis and effects on cognitive performance and neurosteriodogenesis were most evident among intact and gonadectomized, female rats respectively.

Molecular docking and QSAR study on steroidal compounds as aromatase inhibitors

In order to develop more potent, selective and less toxic steroidal aromatase (AR) inhibitors, molecular docking, 2D and 3D hybrid quantitative structure-activity relationship (QSAR) study have been conducted using topological, molecular shape, spatial, structural and thermodynamic descriptors on 32 steroidal compounds. The molecular docking study shows that one or more hydrogen bonds with MET374 are one of the essential requirements for the optimum binding of ligands. The QSAR model obtained indicates that the aromatase inhibitory activity can be enhanced by increasing SIC, SC_3_C, Jurs_WNSA_1, Jurs_WPSA_1 and decreasing CDOCKER interaction energy (ECD), IAC_Total and Shadow_XZfrac. The predicted results shows that this model has a comparatively good predictive power which can be used in prediction of activity of new steroidal aromatase inhibitors.

Antiangiogenic strategies in breast cancer management

Angiogenesis is considered one of the key mechanisms of tumour growth and survival. Therefore it represents an ideal pharmaceutical target. Many antiangiogenic agents have been developed so far in several solid tumours and also in breast cancer. Vascular endothelial growth factor (VEFG) is the main target and both monoclonal antibodies and small molecules belonging to the tyrosine kinase inhibitors directed against VEGF(R) have been developed. Some other therapeutic approaches have shown to exert some antiangiogenic activity, such as hormonal agents, metronomic chemotherapy, bisphosphonates and others. In this paper we provide an introduction of the current data supporting the angiogenesis in breast cancer and a review of the most relevant antiagiogenic therapies which have been investigated so far.

Design, synthesis, and biological evaluation of resveratrol analogues as aromatase and quinone reductase 2 inhibitors for chemoprevention of cancer

A series of new resveratrol analogues were designed and synthesized and their inhibitory activities against aromatase were evaluated. The crystal structure of human aromatase (PDB 3eqm) was used to rationalize the mechanism of action of the aromatase inhibitor 32 (IC50 0.59 microM) through docking, molecular mechanics energy minimization, and computer graphics molecular modeling, and the information was utilized to design several very potent inhibitors, including compounds 82 (IC50 70 nM) and 84 (IC50 36 nM). The aromatase inhibitory activities of these compounds are much more potent than that for the lead compound resveratrol, which has an IC50 of 80 microM. In addition to aromatase inhibitory activity, compounds 32 and 44 also displayed potent QR2 inhibitory activity (IC50 1.7 microM and 0.27 microM, respectively) and the high-resolution X-ray structures of QR2 in complex with these two compounds provide insight into their mechanism of QR2 inhibition. The aromatase and quinone reductase inhibitors resulting from these studies have potential value in the treatment and prevention of cancer.

Functional genetic polymorphisms in the aromatase gene CYP19 vary the response of breast cancer patients to neoadjuvant therapy with aromatase inhibitors

Aromatase (CYP19) is a critical enzyme in estrogen biosynthesis and aromatase inhibitors (AI) are employed widely for endocrine therapy in postmenopausal women with breast cancer. We hypothesized that single nucleotide polymorphisms (SNPs) in the CYP19 gene may alter the effectiveness of AI therapy in the neoadjuvant setting. Genomic DNA was obtained for sequencing from 52 women pre-AI and post-AI treatment in this setting. Additionally, genomic DNA obtained from 82 samples of breast cancer and 19 samples of normal breast tissue was subjected to resequencing. No differences in CYP19 sequence were observed between tumor and germ-line DNA in the same patient. A total of 48 SNPs were identified including 4 novel SNPs when compared with previous resequencing data. For genotype-phenotype association studies, we determined the levels of aromatase activity, estrone, estradiol, and tumor size in patients pre-AI and post-AI treatment. We defined two tightly linked SNPs (rs6493497 and rs7176005 in the 5'-flanking region of CYP19 exon 1.1) that were significantly associated with a greater change in aromatase activity after AI treatment. In a follow-up study of 200 women with early-stage breast cancer who were treated with adjuvant anastrozole, these same two SNPs were also associated with higher plasma estradiol levels in patients pre-AI and post-AI treatment. Electrophoretic mobility shift and reporter gene assays confirmed likely functional effects of these two SNPs on transcription of CYP19. Our findings indicate that two common genetic polymorphisms in the aromatase gene CYP19 vary the response of breast cancer patients to aromatase inhibitors.

Synthesis and antiproliferative activity of coumarin-estrogen conjugates against breast cancer cell lines

The syntheses and cytotoxic activity of coumarin-estrogen conjugates are described. In vitro results indicated that conjugates 10, 11 and 13 show growth inhibitory activities at 5-dose concentration (100, 10, 1, 0.1, 0.01 muM) against the following NCI-7- human breast cancer cell lines: BT-549, HS 578T, MCF 7, MDA-MB-231/ATCC, MDA-MB-435, NCI/ADR-RES, and thus serve as new leads for further development of antibreast cancer agent.

Synergistic up-regulation of prostaglandin E synthase expression in breast cancer cells by 17beta-estradiol and proinflammatory cytokines

Inflammatory mediators, such as cytokines and prostaglandins, play a fundamental role in estrogen-dependent breast cancer through their ability to up-regulate aromatase expression and subsequent local production of estrogens in the breast. To study the link between estrogens and inflammation further, we examined the regulation of prostaglandin E synthase (PTGES), a key enzyme in the production of prostaglandin E2. We found that 17beta-estradiol (E2) rapidly and robustly up-regulates PTGES mRNA and protein levels in estrogen receptor (ER)-positive breast cancer cells through ER recruitment to an essential estrogen response element located in the 5' flanking region of the PTGES gene. PTGES is also up-regulated by the proinflammatory cytokines TNFalpha or IL-1beta. Surprisingly, the combination of E2 and cytokines leads to a synergistic up-regulation of PTGES in an ER and nuclear factor-kappaB (NFkappaB)-dependent manner. This is in contrast to the mutual transrepression between ER and NFkappaB that has been well characterized in other cell types. Furthermore, we found enhanced recruitment of ERalpha as well as the NFkappaB family member, p65, to the PTGES estrogen response element by the combination of E2 and TNFalpha compared with either E2 or TNFalpha alone. The synergistic up-regulation of PTGES may result in enhanced prostaglandin E2 production, which in turn may further enhance aromatase expression and production of local estrogens. Our findings suggest that a finely tuned positive feedback mechanism between estrogens and inflammatory factors may exist in the breast and contribute to hormone-dependent breast cancer growth and progression.

Pharmacophore mapping of flavone derivatives for aromatase inhibition

Aromatase, which catalyses the final step in the steroidogenesis pathway of estrogen, has been target for the design of inhibitor in the treatment of hormone dependent breast cancer for postmenopausal women. The extensive SAR studies performed in the last 30 years to search for potent, selective and less toxic compounds, have led to the development of second and third generation of non-steroidal aromatase inhibitors (AI). Besides the development of synthetic compounds, several naturally occurring and synthetic flavonoids, which are ubiquitous natural phenolic compounds and mediate the host of biological activities, are found to demonstrate inhibitory effects on aromatase. The present study explores the pharmacophores, i.e., the structural requirements of flavones (Fig. 1) for inhibition of aromatase activity, using quantitative structure activity relationship (QSAR) and space modeling approaches. The classical QSAR studies generate the model (R (2) = 0.924, Q (2) = 0.895, s = 0.233) that shows the importance of aromatic rings A and C, along with substitutional requirements in meta and para positions of ring C for the activity. 3D QSAR of Comparative Molecular Field Analysis (CoMFA, R (2) = 0.996, R(2)(cv) = 0.791) and Comparative Molecular Similarity Analysis (CoMSIA, R (2) = 0.992, R(2)(cv) = 0.806) studies show contour maps of steric and hydrophobic properties and contribution of acceptor and donor of the molecule, suggesting the presence of steric hindrance due to ring C and R''-substituent, bulky hydrophobic substitution in ring A, along with acceptors at positions 11, and alpha and gamma of imidazole ring, and donor in ring C favor the inhibitory activity. Further space modeling (CATALYST) study (R = 0.941, Delta( cost ) = 96.96, rmsd = 0.876) adjudge the presence of hydrogen bond acceptor (keto functional group), hydrophobic (ring A) and aromatic rings (steric hindrance) along with critical distance among features are important for the inhibitory activity.

Flavan-3-ols: nature, occurrence and biological activity

Representing the most common flavonoid consumed in the American diet, the flavan-3-ols and their polymeric condensation products, the proanthocyanidins, are regarded as functional ingredients in various beverages, whole and processed foods, herbal remedies and supplements. Their presence in food affects food quality parameters such as astringency, bitterness, sourness, sweetness, salivary viscosity, aroma, and color formation. The ability of flavan-3-ols to aid food functionality has also been established in terms of microbial stability, foamability, oxidative stability, and heat stability. While some foods only contain monomeric flavan-3-ols [(-)-epicatechin predominates] and dimeric proanthocyanidins, most foods contain oligomers of degree of polymerization values ranging from 1-10 or greater than 10. Flavan-3-ols have been reported to exhibit several health beneficial effects by acting as antioxidant, anticarcinogen, cardiopreventive, antimicrobial, anti-viral, and neuro-protective agents. This review summarizes the distribution and health effects of these compounds.

Tetrahydrofurandiol stimulation of phospholipase A2, lipoxygenase, and cyclooxygenase gene expression and MCF-7 human breast cancer cell proliferation

BACKGROUND

We characterized an endocrine disruptor from ground corncob bedding material that interferes with male and female sexual behavior and ovarian cyclicity in rats and stimulates estrogen receptor (ER)-positive and ER-negative breast cancer cell proliferation. The agents were identified as an isomeric mixture of tetrahydrofurandiols (THF-diols; 9,12-oxy-10,13-dihydroxy-octadecanoic acid and 10,13-oxy-9,12-dihydroxyoctadecanoic acid). Synthetic THF-diols inhibited rat male and female sexual behavior at oral concentrations of 0.5-1 ppm, and stimulated MCF-7 human breast cancer cell proliferation in vitro.

OBJECTIVES

Because THF-diols are derived from lipoxygenase and cyclooxygenase pathways, we suspected that these compounds may regulate cell proliferation by modulating specific enzymatic sites involved in linoleic acid metabolism including phospholipase A(2) (PLA2), lipoxygenases (LOX-5 and LOX-12), cyclooxygenases (COX-1 and COX-2), and closely coupled enzymes including aromatase (AROM).

METHODS

MCF-7 human breast cancer cells were treated with inhibitors for PLA2 (quinacrine), lipoxygenases (LOX-5 and LOX-12; baicalein, REV-5091, nordihydroguaiaretic acid), cyclooxygenases (COX-1, COX-2, indomethacin), and AROM (formestane). The effects of these enzyme inhibitors on cell proliferation in response to THF-diols or estradiol (E(2)) were assessed. THF-diol modulation of the expression (RNA and protein) of these enzymes was also evaluated by quantitative real-time PCR (QPCR) and Western blot analyses.

RESULTS

The enzyme inhibition and gene expression (RNA and protein) studies identified PLA2, LOX-5, LOX-12, COX-2, and perhaps AROM as likely sites of THF-diol regulation in MCF-7 cells. COX-1 was not affected by THF-diol treatment.

DISCUSSION

THF-diol stimulation of MCF-7 cell proliferation is mediated through effects on the expression of the PLA2, COX-2, LOX-5, and LOX-12 genes and/or their respective enzyme activities. The products of these enzymes, including prostaglandins, hydroxyeicosatetraenoic acids (HETEs) and hydroxyoctadecenoic acids (HODEs), are well-established mitogens in normal and malignant cells. Therefore, it is likely that these compounds are involved in the mechanism of action of THF-diols in breast cancer cells. Although the formestane inhibition studies suggested that AROM activity might be modulated by THF-diols, this was not confirmed by the gene expression studies.

Prevention of breast cancer: current state of the science and future opportunities

Despite significant progress in breast cancer treatment, mammary tumours still represent the second most frequent cause of cancer-related death in women in the US, with > 211,000 new cases in 2005; however, an expanding range of options for early diagnosis and more reliable risk assessment offers new alternatives for disease control by cancer prevention. Completed large studies with the classical selective estrogen receptor modulator (SERM) tamoxifen have demonstrated that preventing breast cancer pharmacologically is now possible. Novel SERMs, aromatase inhibitors and gonadotropin-releasing hormone agonists targeting hormonal pathways are being tested in clinical trials, revealing the potential for dramatic reductions in tumour incidence with minimal side effects; however, SERMs and aromatase inhibitors are effective only against estrogen receptor-positive tumours, thus chemopreventive drugs targeting other critical signalling pathways (such as retinoids, selective COX inhibitors and tyrosine kinase inhibitors) may provide a means to prevent estrogen receptor-negative breast cancer. In the future, hormonal and estrogen receptor-independent agents may be combined to prevent the development of all mammary tumours. This article reviews the current and novel strategies for breast cancer prevention.

Virtual screen for ligands of orphan G protein-coupled receptors

This paper describes a virtual screening methodology that generates a ranked list of high-binding small molecule ligands for orphan G protein-coupled receptors (oGPCRs), circumventing the requirement for receptor three-dimensional structure determination. Features representing the receptor are based only on physicochemical properties of primary amino acid sequence, and ligand features use the two-dimensional atomic connection topology and atomic properties. An experimental screen comprised nearly 2 million hypothetical oGPCR-ligand complexes, from which it was observed that the top 1.96% predicted affinity scores corresponded to "highly active" ligands against orphan receptors. Results representing predicted high-scoring novel ligands for many oGPCRs are presented here. Validation of the method was carried out in several ways: (1) A random permutation of the structure-activity relationship of the training data was carried out; by comparing test statistic values of the randomized and nonshuffled data, we conclude that the value obtained with nonshuffled data is unlikely to have been encountered by chance. (2) Biological activities linked to the compounds with high cross-target binding affinity were analyzed using computed log-odds from a structure-based program. This information was correlated with literature citations where GPCR-related pathways or processes were linked to the bioactivity in question. (3) Anecdotal, out-of-sample predictions for nicotinic targets and known ligands were performed, with good accuracy in the low-to-high "active" binding range. (4) An out-of-sample consistency check using the commercial antipsychotic drug olanzapine produced "active" to "highly-active" predicted affinities for all oGPCRs in our study, an observation that is consistent with documented findings of cross-target affinity of this compound for many different GPCRs. It is suggested that this virtual screening approach may be used in support of the functional characterization of oGPCRs by identifying potential cognate ligands. Ultimately, this approach may have implications for pharmaceutical therapies to modulate the activity of faulty or disease-related cellular signaling pathways. In addition to application to cell surface receptors, this approach is a generalized strategy for discovery of small molecules that may bind intracellular enzymes and involve protein-protein interactions.

Human aromatase: gene resequencing and functional genomics

Aromatase [cytochrome P450 19 (CYP19)] is a critical enzyme for estrogen biosynthesis, and aromatase inhibitors are of increasing importance in the treatment of breast cancer. We set out to identify and characterize genetic polymorphisms in the aromatase gene, CYP19, as a step toward pharmacogenomic studies of aromatase inhibitors. Specifically, we "resequenced" all coding exons, all upstream untranslated exons plus their presumed core promoter regions, all exon-intron splice junctions, and a portion of the 3'-untranslated region of CYP19 using 240 DNA samples from four ethnic groups. Eighty-eight polymorphisms were identified, resulting in 44 haplotypes. Functional genomic studies were done with the four nonsynonymous coding single nucleotide polymorphisms (cSNP) that we observed, two of which were novel. Those cSNPs altered the following amino acids: Trp39Arg, Thr201Met, Arg264Cys, and Met364Thr. The Cys264, Thr364, and double variant Arg39Cys264 allozymes showed significant decreases in levels of activity and immunoreactive protein when compared with the wild-type (WT) enzyme after transient expression in COS-1 cells. A slight decrease in protein level was also observed for the Arg39 allozyme, whereas Met201 displayed no significant changes in either activity or protein level when compared with the WT enzyme. There was also a 4-fold increase in apparent K(m) value for Thr364 with androstenedione as substrate. Of the recombinant allozymes, only the double mutant (Arg39Cys264) displayed a significant change from the WT enzyme in inhibitor constant for the aromatase inhibitors exemestane and letrozole. These observations indicate that genetic variation in CYP19 might contribute to variation in the pathophysiology of estrogen-dependent disease.

Leukotoxin diols from ground corncob bedding disrupt estrous cyclicity in rats and stimulate MCF-7 breast cancer cell proliferation

Previous studies in our laboratory demonstrated that high-performance liquid chromatography (HPLC) analysis of ground corncob bedding extracts characterized two components (peak I and peak II) that disrupted endocrine function in male and female rats and stimulated breast and prostate cancer cell proliferation in vitro and in vivo. The active substances in peak I were identified as an isomeric mixture of 9,12-oxy-10,13-dihydroxyoctadecanoic acid and 10,13-oxy-9,12-dihydroxyoctadecanoic acid, collectively designated tetrahydrofurandiols (THF-diols). Studies presented here describe the purification and identification of the HPLC peak II component as 9,10-dihydroxy-12-octadecenoic acid (leukotoxin diol; LTX-diol), a well-known leukotoxin. A synthetic mixture of LTX-diol and 12,13-dihydroxy-9-octadecenoic acid (iso-leukotoxin diol; i-LTX-diol) isomers was separated by HPLC, and each isomer stimulated (p < 0.001) MCF-7 cell proliferation in an equivalent fashion. The LTX-diol isomers failed to compete for [3H]estradiol binding to the estrogen receptor or nuclear type II sites, even though oral administration of very low doses of these compounds (>> 0.8 mg/kg body weight/day) disrupted estrous cyclicity in female rats. The LTX-diols did not disrupt male sexual behavior, suggesting that sex differences exist in response to these endocrine-disruptive agents.

Dietary flavonoids: effects on xenobiotic and carcinogen metabolism

Flavonoids are present in fruits, vegetables and beverages derived from plants (tea, red wine), and in many dietary supplements or herbal remedies including Ginkgo Biloba, Soy Isoflavones, and Milk Thistle. Flavonoids have been described as health-promoting, disease-preventing dietary supplements, and have activity as cancer preventive agents. Additionally, they are extremely safe and associated with low toxicity, making them excellent candidates for chemopreventive agents. The cancer protective effects of flavonoids have been attributed to a wide variety of mechanisms, including modulating enzyme activities resulting in the decreased carcinogenicity of xenobiotics. This review focuses on the flavonoid effects on cytochrome P450 (CYP) enzymes involved in the activation of procarcinogens and phase II enzymes, largely responsible for the detoxification of carcinogens. A number of naturally occurring flavonoids have been shown to modulate the CYP450 system, including the induction of specific CYP isozymes, and the activation or inhibition of these enzymes. Some flavonoids alter CYPs through binding to the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, acting as either AhR agonists or antagonists. Inhibition of CYP enzymes, including CYP 1A1, 1A2, 2E1 and 3A4 by competitive or mechanism-based mechanisms also occurs. Flavones (chrysin, baicalein, and galangin), flavanones (naringenin) and isoflavones (genistein, biochanin A) inhibit the activity of aromatase (CYP19), thus decreasing estrogen biosynthesis and producing antiestrogenic effects, important in breast and prostate cancers. Activation of phase II detoxifying enzymes, such as UDP-glucuronyl transferase, glutathione S-transferase, and quinone reductase by flavonoids results in the detoxification of carcinogens and represents one mechanism of their anticarcinogenic effects. A number of flavonoids including fisetin, galangin, quercetin, kaempferol, and genistein represent potent non-competitive inhibitors of sulfotransferase 1A1 (or P-PST); this may represent an important mechanism for the chemoprevention of sulfation-induced carcinogenesis. Importantly, the effects of flavonoids on enzymes are generally dependent on the concentrations of flavonoids present, and the different flavonoids ingested. Due to the low oral bioavailability of many flavonoids, the concentrations achieved in vivo following dietary administration tend to be low, and may not reflect the concentrations tested under in vitro conditions; however, this may not be true following the ingestion of herbal preparations when much higher plasma concentrations may be obtained. Effects will also vary with the tissue distribution of enzymes, and with the species used in testing since differences between species in enzyme activities also can be substantial. Additionally, in humans, marked interindividual variability in drug-metabolizing enzymes occurs as a result of genetic and environmental factors. This variability in xenobiotic metabolizing enzymes and the effect of flavonoid ingestion on enzyme expression and activity can contribute to the varying susceptibility different individuals have to diseases such as cancer. As well, flavonoids may also interact with chemotherapeutic drugs used in cancer treatment through the induction or inhibition of their metabolism.

Potential use of COX-2-aromatase inhibitor combinations in breast cancer

Cyclooxygenase-2 (COX-2) is overexpressed in several epithelial tumours, including breast cancer. Cyclooxygenase-2-positive tumours tend to be larger, higher grade, node-positive and HER-2/neu-positive. High COX-2 expression is associated with poor prognosis. Cyclooxygenase-2 inhibition reduces the incidence of tumours in animal models, inhibits the development of invasive cancer in colorectal cancer and reduces the frequency of polyps in familial adenomatous polyposis (FAP). These effects may be as a result of increased apoptosis, reduced angiogenesis and/or proliferation. Studies of COX-2 inhibitors in breast cancer are underway both alone and in combination with other agents. There is evidence to suggest that combining COX-2 inhibitors with aromatase inhibitors, growth factor receptor blockers, or chemo- or radiotherapy may be particularly effective. Preliminary results from combination therapy with celecoxib and exemestane in postmenopausal women with advanced breast cancer showed that the combination increased the time to recurrence. Up to 80% of ductal carcinomas in situ (DCISs) express COX-2, therefore COX-2 inhibition may be of particular use in this situation. Cyclooxygenase-2 expression correlates strongly with expression of HER-2/neu. As aromatase inhibitors appear particularly effective in patients with HER-2/neu-positive tumours, the combination of aromatase inhibitors and COX-2 inhibitors may be particularly useful in both DCIS and invasive cancer.

Structure-activity relationships of 2-, 4-, or 6-substituted estrogens as aromatase inhibitors

Aromatase, which is responsible for the conversion of androgens to estrogens, is a potential therapeutic target for the selective lowering of estrogen levels in patients with estrogen-dependent breast cancer. To develop a novel class of aromatase inhibitors, we tested series of 2- and 4-substituted (halogeno, methyl, formyl, methoxy, nitro, and amino) estrones (7 and 9), as well as series of 6alpha- and 6beta-substituted (alkyl, phenalkyl, and alkoxy) estrones (13 and 14), and their estradiol analogs (8, 10, 11, and 12) as aromatase inhibitors. All of the inhibitors examined blocked the androstenedione aromatization in a competitive manner. Introduction of halogeno and methyl functions at C-2 of estrone as well as that of a phenalkyl or methyl function at the C-6alpha or C-6beta position markedly increased affinity to aromatase (apparent K(i) value=0.10-0.66 microM for the inhibitors versus 2.5 microM for estrone). 6alpha-Phenylestrone (13c) was the most powerful inhibitor among the estrogens studied, and its affinity was comparable to that of the androgen substrate androstenedione. Estradiol analogs were much weaker inhibitors than the corresponding estrone compounds in each series, indicating that the 17-carbonyl group plays a critical role in the formation of a thermodynamically stable enzyme-inhibitor complex.

Aromatase inhibitors in the treatment of breast cancer

Estradiol, the most potent endogenous estrogen, is biosynthesized from androgens by the cytochrome P450 enzyme complex called aromatase. Aromatase is present in breast tissue, and intratumoral aromatase is the source of local estrogen production in breast cancer tissues. Inhibition of aromatase is an important approach for reducing growth-stimulatory effects of estrogens in estrogen-dependent breast cancer. Steroidal inhibitors that have been developed to date build upon the basic androstenedione nucleus and incorporate chemical substituents at varying positions on the steroid. Nonsteroidal aromatase inhibitors can be divided into three classes: aminoglutethimide-like molecules, imidazole/triazole derivatives, and flavonoid analogs. Mechanism-based aromatase inhibitors are steroidal inhibitors that mimic the substrate, are converted by the enzyme to a reactive intermediate, and result in the inactivation of aromatase. Both steroidal and nonsteroidal aromatase inhibitors have shown clinical efficacy in the treatment of breast cancer. The potent and selective third-generation aromatase inhibitors, anastrozole, letrozole, and exemestane, were introduced into the market as endocrine therapy in postmenopausal patients failing antiestrogen therapy alone or multiple hormonal therapies. These agents are currently approved as first-line therapy for the treatment of postmenopausal women with metastatic estrogen-dependent breast cancer. Several clinical studies of aromatase inhibitors are currently focusing on the use of these agents in the adjuvant setting for the treatment of early breast cancer. Use of an aromatase inhibitor as initial therapy or after treatment with tamoxifen is now recommended as adjuvant hormonal therapy for a postmenopausal woman with hormone-dependent breast cancer.

Design, synthesis, and 3D QSAR of novel potent and selective aromatase inhibitors

The design, synthesis, and biological evaluation of a series of new aromatase inhibitors bearing an imidazole or triazole ring linked to a fluorene (A), indenodiazine (B), or coumarin scaffold (C) are reported. Properly substituted coumarin derivatives displayed the highest aromatase inhibitory potency and selectivity over 17-alpha-hydroxylase/17-20 lyase. The modeling of the aromatase inhibition data by Comparative Molecular Field Analysis (CoMFA/GOLPE 3D QSAR approach) led to the development of a PLS model with good fitting and predictive powers (n = 22, ONC = 3, r(2) = 0.949, s = 0.216, and q(2) = 0.715). The relationship between aromatase inhibition and the steric and electrostatic fields generated by the examined azole inhibitors enables a clear understanding of the nature and spatial location of the main interactions modulating the aromatase inhibitory potency.

The role of COX-2 inhibition in breast cancer treatment and prevention

Several studies have suggested that cyclooxygenase-2 (COX-2) expression is associated with parameters of aggressive breast cancer, including large tumor size, positive axillary lymph node metastases, and HER2-positive tumor status. Studies of mammary tumors in mice and rats have indicated that moderate to high COX-2 expression is related to the genesis of mammary tumors that are sensitive to treatment with nonspecific and specific COX-2 inhibitors. Moreover, these studies also suggest that mammary tumors are associated with high prostaglandin levels and induction of aromatase, a cytochrome P450 enzyme that catalyses estrogen production. Mechanistically, lack of apoptosis and increased angiogenesis and invasiveness have been implicated as mechanisms of tumor growth in COX-2-dependent mammary tumors. Based on these observations, clinical trials are evaluating adjunctive therapy with a selective COX-2 inhibitor, celecoxib, in combination with several regimens used in the metastatic and adjuvant or neoadjuvant settings of breast cancer. In addition, proof-of-principle trials are being conducted to ascertain the effects of celecoxib on known markers of proliferation, angiogenesis, and apoptosis. Finally, based on the apparent synergy between celecoxib and the aromatase inhibitor exemestane, the National Cancer Institute of Canada Clinical Trials Group is launching a phase III trial comparing exemestane with or without celecoxib against placebo in postmenopausal women with elevated risk of breast cancer. Results of these trials will help to define the role of celecoxib in the management and prevention of breast cancer. Epidemiologic evidence suggests the incidence of breast, colon, and lung cancers is inversely related to the use of aspirin and nonsteroidal anti-inflammatory drugs, which are nonspecific inhibitors of COX. COX-1 and COX-2 are enzymes that generate prostaglandins and thromboxanes from free arachidonic acid. Genetic approaches pursued in animal models and biochemical evidence obtained from human tumor cell lines have strongly implicated COX-2, an inducible enzyme, in many preinvasive and invasive human tumors. In this article we will first review data that point to COX-2 as an important indicator in the genesis of breast cancer and discuss planned and ongoing clinical trials evaluating specific COX-2 inhibitors in the treatment and prevention of breast cancer.

Novel sensitizing agents: Potential Contribution of COX-2 inhibitor for endocrine therapy of breast cancer

Enhancement of the therapeutic effect of conventional drugs is currently an active treatment strategy for breast cancer, as shown in the clinical application of trastuzumab with chemotherapeutic agents, which prolonged survival even for metastatic disease. Cyclo-oxygenase 2(COX-2)inhibitors, which are chemoprevention agents for familial polyposis coli, are now contributing to this strategy in combination with chemotherapeutic and endocrine drugs. As an endocrine application, overexpression of COX-2 contributes to increased expression of aromatase in the breast tumor. In addition, it is also known to promote rich micro-vessels within the tumor through up-regulation of prostaglandin E2(PGE2), which can induce vascular endothelial growth factor(VEGF)and basic fibroblast growth factor(bFGF)in cancer cells, and can directly modulate endothelial cell proliferation. Since both rich vasculature and accelerated estrogen synthesis are thought to contribute to unfavorable conditions for the response to endocrine therapy, inhibiting COX-2 with COX-2 inhibitors is a promising strategy to potentiate endocrine therapy.