Inhibition Of Aromatase Activity Research Articles

Synthesis of some novel androstanes as potential aromatase inhibitors

Novel pyrazole and isoxazole derivatives ( 6– 9) were synthesized as a aromatase inhibitors. Pyrazole was synthesized from hydrazine hydrate and isoxazoles from hydroxylamine hydrochloride under different conditions. Molecular docking studies were carried out for the synthesized compounds. The best score was obtained for the compound ( 9) followed by compound ( 6) while compound ( 8) afforded poorest of the score. Aromatase inhibitory activity for compound ( 6) having pyrazole ring at 2,3 position showed highest activity followed by nitrile derivative ( 9). Isomeric forms of isoxazole ( 7 and 8) showed very poor activity compared to fadrozole and aminoglutethimide. Preliminary kinetic studies have shown that both of the active compounds ( 6 and 9) are reversible inhibitors of the enzyme.

Synthesis and Biological Evaluation of 16E-Arylidenosteroids as Cytotoxic and Anti-aromatase Agents

Taking into consideration the structural requirements for cytotoxicity and aromatase inhibition, several new 16E-arylidenosteroidal derivatives have been prepared and evaluated for their cytotoxic and aromatase inhibitory activity. The new steroidal analogues 3, 5-8 and 11 exhibited significant cytotoxic effects when screened against three cancer cell lines, MCF-7 (breast), NCl-H460 (lung) and SF-268 central nervous system (CNS) at 100 µM and sensible cytotoxic effects subsequently in sixty cancer cell lines derived from nine cancers types (leukemia, lung, colon, CNS, melanoma, ovarian, renal, prostate and breast cancers). The imidazolyl substituted steroidal derivatives 5 and 7 exhibited strong inhibition of the aromatase enzyme with 16-[4-{3-(imidazol-1-yl)propoxy}-3-methoxybenzylidene]-5-androstene-3β,17β-diol (7) displaying 13 times more potency in comparison to aminoglutethimide.

Abstract S2-3: The Impact of Body Mass Index (BMI) on the Efficacy of Adjuvant Endocrine Therapy in Postmenopausal Hormone Sensitive Breast Cancer (BC) Patients; Exploratory Analysis from the TEAM Study

Abstract Background: Obesity is associated with an increased risk of breast cancer (BC) recurrence and decreased survival, also in case of adjuvant endocrine therapy. It is still not clear whether the activity of aromatase inhibitors and tamoxifen (T) given as adjuvant therapy is affected by body mass index (BMI), although both drugs are widely prescribed. In this analysis, we explored the outcome of TEAM patients (pts) treated with exemestane (E) versus T (2.75 yrs), and with E versus T followed by E (T/E) (5 yrs) in relation to BMI. Patients and Methods: The TEAM trial is a randomized, international phase III study in postmenopausal hormone sensitive early BC pts comparing the activity and safety of adjuvant E (25 mg daily) or the sequence of T (20 mg daily) followed by E (T/E), both regimens given for five years. WHO BMI definitions were used: normal 18.5-24.9 kg/m2, overweight 25-30 kg/m2, obese >30 kg/m2. Disease-free survival (DFS) and overall survival (OS) were calculated by Kaplan-Meier method; results were compared by using the log-rank test and Cox proportional hazard modelling adjusted for country. Results: Weight and height was known in 4741 pts. Mean BMI was 26.9 kg/m2 (SD 4.9); 39% had a normal BMI, 36.9% overweight, and 23.3% of pts was obese. Underweight pts (n=41, 0.9%) were excluded from further analysis. At 2.75 yrs (E vs T) disease relapse in normal weight, overweight and obese pts using E was observed in 8.1%, 6.8% and 7.5% respectively (p=0.57), and in 9.1%, 8.8%, and 12.5%, respectively (p=0.06) of pts using T. The hazard ratio (HR for risk of relapse on E vs T) in the three subgroups was 0.91 (95%CI 0.66-1.24), 0.78 (95%CI 0.55-1.089), and 0.57 (95%CI 0.39-0.84, p=0.004), respectively. At a median follow-up of 5.1 years, disease relapse in normal weight, overweight and obese pts using E occurred in 14.8%, 15.1% and 15.1%, respectively; and in pts using T in 17.0%, 16.9%, and 18.3%, respectively. Regarding DFS, the HR in normal weight, overweight, and obese pts was 0.87 (95%CI 0.69-1.10), 0.88 (95%CI 0.70-1.11), and 0.75 (95%CI 0.56-1.01, p=0.058), respectively, and with respect to OS 0.87 (95%CI 0.65-1.15, p= 0.32), 0.89 (95%CI 0.67-1.18, p= 0.43), and 0.71 (95% CI 0.51-1.01, p= 0.053), respectively. Conclusions: After 2.75 years more disease events were observed in obese women using tamoxifen, which was not seen in obese exemestane users, whereas at 5 years these differences in disease recurrences disappeared in this group. In contrast to recent reports, there seems to be a difference regarding the influence of a high BMI on recurrence rate between tamoxifen and the aromatase inhibitor exemestane. Further research on this topic is warranted. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr S2-3.

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 ( E CD), 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.

Retinol inhibits aromatase activity and expression in vitro

Aromatase converts androgens into estrogens and is thought to supply a local source of estrogen that facilitates the growth of hormone-responsive tumor cells. Inhibition of aromatase is therefore an important chemopreventive strategy. We investigated the effect of retinol and selected retinoids on the activity and expression of aromatase in two human carcinoma cell lines in vitro. Retinol (ROH) and all- trans retinoic acid (ATRA) significantly inhibited aromatase activity in a concentration-dependent manner in microsomes isolated from JEG-3 human placental carcinoma cells, whereas 9- cis and 13- cis retinoic acid had significant inhibitory activity only at the highest concentrations tested. Similar results were observed in an assay of cellular aromatase activity in MCF-7 human breast cancer cells. Enzyme kinetic studies by double-reciprocal plot demonstrated that ROH inhibited microsomal aromatase activity in a mixed manner. In addition, ROH suppressed both the basal and cAMP-induced expression of aromatase mRNA in MCF-7 cells and inhibited transcription controlled by a cAMP-responsive element. These results suggest that aromatase activity and expression are a molecular target of ROH and chemopreventive retinoids, an activity that may underlie, in part, their inhibitory effects on hormone-dependent cancer.

Effects of a nonsteroidal aromatase inhibitor on gonadal differentiation of bluegill sunfish Lepomis macrochirus

In the present study, the efficacy of Letrozole, a potent nonsteroidal aromatase inhibitor (AI), on gonadal sex differentiation and sex reversal was examined in bluegill sunfish (Lepomis macrochirus). In Experiment 1, using AI diet treatments (50, 150, 250 and 500 mg kg−1) from 30 to 90 days posthatch (dph), AI interrupted ovarian cavity formation at a dose of 500 mg kg1 diet and one intersex fish was identified in this group. The proportions of males in all the treated groups were significantly higher than those in the control group. In Experiment 2, using AI immersion treatments (250, 500 and 1000 μg L−1) during 30–50 dph, the treated groups of 500 and 1000 μg L−1 produced significantly more males than the control and 250 μg L−1 groups. Histological examination revealed no differences in ovary or testis tissue between control and AI-treated fish. There were no significant differences detected in body weight and length among the AI treated and control groups (P>0.05) for both experiments. The results from these two experiments suggest that inhibition of aromatase activity by AI could influence sex differentiation in bluegill sunfish.

Effect of aspirin and other NSAIDs on postmenopausal breast cancer incidence by hormone receptor status: results from a prospective cohort study

Aspirin and other non-aspirin non-steroidal anti-inflammatory drugs (NSAIDs) can inhibit aromatase activity and thus could selectively lower incidence of hormone receptor positive tumors. We assessed whether the association of aspirin and other NSAIDs with postmenopausal breast cancer risk differs by estrogen and progesterone receptor (ER and PR) status of the tumor. A population-based cohort of 26,580 postmenopausal women was linked to a SEER Cancer Registry to identify incident breast cancers. Regular use of aspirin and other NSAIDs was reported on a self-administered questionnaire mailed in 1992. Cox proportional hazards models were used to estimate multivariate relative risks (RRs) and 95% confidence intervals (CIs) of breast cancer incidence overall and by ER and PR status, adjusting for multiple breast cancer risk factors. Through 2005, 1,581 incident breast cancer cases were observed. Compared to aspirin never users, women who regularly consumed aspirin had a lower risk of breast cancer (RR = 0.80; 95% CI: 0.71-0.90), and there was evidence for lower risk with increasing frequency of use (RR = 0.71 for aspirin use 6 or more times/week vs. never use; P trend = 0.00001). Inverse associations for regular aspirin use were observed for ER+ (RR = 0.77; 95% CI 0.67-0.89), ER- (RR = 0.78; 95% CI 0.56-1.08), PR+ (RR = 0.79; 95% CI 0.68-0.92), and PR- (RR = 0.73; 95% CI 0.56-0.95) breast cancers. In contrast, use of other NSAIDs was not associated with breast cancer incidence overall (RR = 0.95, 95% CI: 0.85-1.07), or by ER or PR status. Aspirin, but not other NSAID use, was associated with about 20% lower risk of postmenopausal breast cancer and did not vary by ER or PR status of the tumor, suggesting that the hypothesized protective effects of aspirin may either be through cellular pathways independent of estrogen or progesterone signaling, or on tumor microenvironment.

Natural Compounds with Aromatase Inhibitory Activity: An Update

Several synthetic aromatase inhibitors are currently in clinical use for the treatment of postmenopausal women with hormone-receptor positive breast cancer. However, these treatments may lead to untoward side effects and so the search for new aromatase inhibitors continues, especially those for which the activity is promoter-specific, targeting the breast-specific promoters I.3 and II. Recently, numerous natural compounds have been found to inhibit aromatase in noncellular, cellular, and IN VIVO studies. These investigations, covering the last two years, as well as additional studies that have focused on the evaluation of natural compounds as promoter-specific aromatase inhibitors or as aromatase inducers, are described in this review.

Synthesis and Antineoplastic Activity of O‐Alkylated Derivatives of 7‐Hydroximinoandrost‐5‐ene Steroids

Varied positioning of the hydroximino group on the parental steroid skeleton results in remarkable changes in the antineoplastic activity profile of the compounds. Here, the compound 7-oximino-5-androstene and its O-alkylated derivatives have been prepared and screened for cytotoxic and aromatase inhibitory activity. The steroidal 7-oximino ether derivatives exhibited insignificant cytotoxic effects when screened against three cancer cell lines, MCF-7 (breast), NCl-H460 (lung), and SF-268 (CNS) at 100 microM. However, the imidazolyl-substituted steroidal oxime ethers displayed moderate inhibition of cytochrome P450 aromatase.

4- and 6-( p-Sulphamoylphenyl)androstenediones: Studies of aromatase inhibitor-based oestrone sulphatase inhibition

4-( p-Sulphamoylphenyl)androstenedione ( 3) and 6α- p-sulphamoylphenyl analogues 12– 14 were synthesised and tested as aromatase inhibitors as well as oestrone sulphatase inhibitors in human placental microsomes. All of the p-sulphamoylphenyl compounds synthesised were powerful inhibitors of aromatase with apparent K i values ranging between 30 and 97 nM. In addition, the aromatase inhibitory activities of 6α- p-hydroxyphenyl compounds 9– 11, which may be produced from their respective sulphamoylphenyl compounds by action of oestrone sulphatase, were also high in a range of 23 and 75 nM of the K i values. On the other hand, all of the sulphamoylphenyl compounds were poor inhibitors of oestrone sulphatase with more than about 200 μM of IC 25 values. Although the present findings of the oestrone sulphatase inhibition are disappointing, such attempts may be valuable to develop a new class of drugs having a dual function, aromatase inhibitor and oestrone sulphatase inhibitor, for the treatment of oestrogen-dependent breast cancer.

Synthesis of some imidazolyl-substituted 2-benzylidene indanone derivatives as potent aromatase inhibitors for breast cancer therapy

The synthesis and aromatase inhibitory activity of a new series of 2-benzylidene indanones is presented. The imidazolyl-substituted indanones displayed potent aromatase inhibitory activity. The vanilloid-based derivative 2-[4-(3-imidazol-1-ylpropoxy)-3-methoxybenzylidene]-indan-1-one (26) exhibited maximum inhibition of human placental aromatase and was found to be 54 times more potent as compared to aminoglutethimide.

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 0.59μM) 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 70nM) and 84 (IC50 36nM). The aromatase inhibitory activities of these compounds are much more potent than that for the lead compound resveratrol, which has an IC50 of 80μM. In addition to aromatase inhibitory activity, compounds 32 and 44 also displayed potent QR2 inhibitory activity (IC50 1.7μM and 0.27μM, 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.

Effects of endocrine disruptors on steroidogenic enzymes gene expression and on aromatase activity in two human cell lines

Endocrine disruptors are chemicals that can alter functions of the endocrine system by several ways. In the present study, we have evaluated the effects of several endocrine disruptors and of some of their metabolites on the last step of steroidogenesis in two cell line models. Two enzymes are implicated in this step: aromatase (CYP19A1), which plays a central role by catalyzing the irreversible conversion of androgens to estrogens, and 17beta-hydroxysteroid dehydrogenase (HSD17B), which catalyses the conversion of inactive sexual hormones to active ones in different steroidogenic organs. We have screened the selected chemicals for their ability to modulate the expression of steroidogenic enzymes and aromatase activity in the human choriocarcinoma JEG-3 cell line and in the human adrenocortical H295R cell line after both short (4 h) and long exposure (24 h). All chemicals were tested at concentrations that did not cause cytotoxicity after 24h of exposure, as tested by the MTT viability assay. Gene expression profile was assessed by real-time RT-PCR and aromatase activity was assessed by the method of tritiated water. Treatments of JEG-3 cells by atrazine, methoxychlor and the vinclozolin metabolite M2 resulted in an increase of CYP19A1 mRNA levels. In contrast, Bisphenol-A and the methoxychlor metabolite HPTE down-regulated the expression of CYP19A1 mRNA. Methoxychlor and HPTE decreased the amount of HSD17B1 mRNAs. In H295R cells, atrazine up-regulated CYP19A1 mRNA expression, HPTE increased HSD17B1 mRNA levels and methoxychlor increased HSD17B1 and HSD17B5 mRNA levels. Concerning the aromatase activity, treatment of H295R cells by atrazine induced aromatase activity. Furthermore, exposure of these cells to either bisphenol A or HPTE inhibited aromatase activity. In JEG-3 cells, which display higher basal aromatase expression than H295R cells, the pattern of aromatase activity regulation was similar but less pronounced. Taken together, these initial results contribute to a better characterization of the action of endocrine disrupting chemicals and their metabolites on the steroidogenic pathways, which needs to be considered when assessing their effects on human health.

Roles of 17 -Estradiol Involve Regulation of Reelin Expression and Synaptogenesis in the Dentate Gyrus

Studies on the role of 17β-estradiol (E2) in the hippocampus have mainly focused on CA1 and CA3 regions, whereas in dentate gyrus (DG), its role is largely unknown. Here, we examined potential functions of E2 in DG, particularly during development. Immunohistochemistry and in situ hybridization revealed abundance of estrogen receptor (ER)α, but not ERβ, expression in DG. Similar to CA1, analysis of synapse densities revealed a reduction in spine synapse number in DG molecular layer of immature rats and adult mice after inhibition of estradiol synthesis using letrozole. Interestingly, strong expression of ERα was found in Cajal-Retzius (CR) cells, which regulate neuronal migration and synaptogenesis via the extracellular matrix protein reelin. Immunoreactivity of aromatase, the final enzyme of estradiol synthesis, was strongest in mature granule cells. In hippocampal slice cultures, exogenous application of E2 caused an increase in reelin expression in CR cells, which was abolished after blockade of ERs using ICI182,780. Vice versa, inhibition of aromatase activity by letrozole resulted in reduced reelin expression, suggesting that E2 deriving from hippocampal sources contributes to the regulation of reelin as well as to the maintenance of spine synapses in DG. E2 further regulated Notch1, a signaling protein involved in neuronal differentiation.

Docking and 3D-QSAR studies of diverse classes of human aromatase (CYP19) inhibitors

Aromatase (cytochrome 19) inhibitors have emerged as promising candidates for treatment of breast cancer. In search of potent aromatase inhibitors, docking and three-dimensional quantitative structure-activity relationship (3D-QSAR) studies using molecular shape, spatial, electronic, structural and thermodynamic descriptors have been performed on a diverse set of compounds having human aromatase inhibitory activities. An attempt has also been made to include two-dimensional (2D) descriptors in the QSAR studies. The chemometric tools used for model development are genetic function approximation (GFA) and genetic partial least squares (G/PLS). The docking study shows that the important interacting amino acids in the active site cavity are Met374, Arg115, Ile133, Ala306, Thr310, Asp309, Val370 and Ser478. One or more hydrogen bond formation with Met374 is one of the essential requirements for the ligands for optimum aromatase inhibition. The binding is further stabilized by van der Waals interactions with a few non-polar amino acid residues in the active site. The developed QSAR models indicate the importance of different shape, Jurs parameters, structural parameters, topological branching index and E-state index for different fragments. The results obtained from the QSAR analysis are supported by our docking observations. There should be one or two hydrogen bond acceptor groups (like -NO2, -CN) and optimal hydrophobicity for ideal aromatase inhibitors. A GFA model with spline option obtained using 3D descriptors was found to be the best model based on internal validation (Q2=0.668) while the best (externally) predictive model was a GFA model with spline option using combined set (2D and 3D) descriptors (Rpred2=0.687). Based on rm2(overall) criterion, the best model was a G/PLS model (using 3D descriptors) with spline option (rm2(overall)=0.606).

Transferrin-conjugated lipid-coated PLGA nanoparticles for targeted delivery of aromatase inhibitor 7α-APTADD to breast cancer cells

Transferrin (Tf)-conjugated lipid-coated poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles carrying the aromatase inhibitor, 7α-(4′-amino)phenylthio-1,4-androstadiene-3,17-dione (7α-APTADD), were synthesized by a solvent injection method. Formulation parameters including PLGA-to-lipid, egg PC-to-TPGS, and drug-to-PLGA ratios and aqueous-to-organic phase ratio at the point of synthesis were optimized to obtain nanoparticles with desired sizes and drug loading efficiency. The optimal formulation had a drug loading efficiency of 36.3 ± 3.4%, mean diameter of 170.3 ± 7.6 nm and zeta potential of −18.9 ± 1.5 mV. The aromatase inhibition activity of the nanoparticles was evaluated in SKBR-3 breast cancer cells. IC 50 value of the Tf-nanoparticles was ranging from 0.77 to 1.21 nM, and IC 50 value of the nanoparticles was ranging from 1.90 to 3.41 nM ( n = 3). The former is significantly lower than the latter ( p < 0.05). These results suggested that the aromatase inhibition activity of the Tf-nanoparticles was enhanced relative to that of the non-targeted nanoparticles, which was attributable to Tf receptor (TfR) mediated uptake. In conclusion, Tf-conjugated lipid-coated PLGA nanoparticles are potential vehicles for improving the efficiency and specificity of therapeutic delivery of aromatase inhibitors.

Abstract A68: Aromatase inhibition and chemopreventive potential of novel resveratrol derivatives

Abstract Resveratrol, a naturally occurring stilbene found in the human diet, has been shown to mediate a host of biological activities. It has been reported to display both estrogenic and anti-estrogenic activities, depending on cell type and conditions, but inhibition of aromatase activity is weak (IC50 = 25 µM). We have conducted a systematic study in which about 60 substituted stilbenes were synthesized and evaluated for biologic potential. Several of these synthetic derivatives were found to inhibit aromatase activity with IC50 values in the sub-micromolar range. Within the series, structure-activity relationships demonstrated substitution of an amine group produced greater inhibition than a nitro group, and the position of these groups was of greater importance than the number and position of methoxy groups. Compound 1 [(E)-4-(3,5-dimethoxystyryl)aniline] was one of the most potent inhibitors, with an IC50 of 0.31 µM, which is comparable to that of aminoglutethimide (IC50 = 0.2 µM). In addition, crystallographic analysis revealed compound 1 binds to quinone reductase 2 in an orientation similar to that of resveratrol, but demonstrates greater inhibitory potency. Compound 1 has been synthesized on a multigram scale, oral administration with laboratory animals indicates excellent absorption and good metabolic stability, and more advanced testing is underway. (Supported by program project P01 CA48112 awarded by the National Cancer Institute) Citation Information: Cancer Prev Res 2010;3(1 Suppl):A68.

Inhibition of aromatase activity in MCF-7aro human breast cancer cells by the natural androgens testosterone and androstenedione.

The human breast contains all the enzymes responsible for local bioformation of estradiol (E2). Two principal pathways are implicated in the last steps of E2 formation: the 'aromatase' which transforms androgens into estrogens, and the 'sulfatase' which converts estrogen sulfates into active unconjugated estrogens; activities found in both normal and cancerous breast. Aromatase inhibition by anti-aromatase agents is largely used with very positive results in the treatment of breast cancer patients. In this study, the effects of the natural androgens androstenedione and testosterone were explored on aromatase activity in a stable aromatase-expressing estrogen receptor-positive human breast cancer cell line MCF-7aro. The cells were incubated with physiological concentrations of [3H]-testosterone (5nmol/L) alone or in the presence of either testosterone or androstenedione (0.5 and 50μmol/L) 24h at 37°C. Cellular radioactivity uptake was determined. [3H]-E2 was characterized by thin-layer chromatography. The MCF-7aro cells have a very high aromatase activity because conversion of [3H]-testosterone to [3H]-E2 was 3.02±0.17pmol/mg DNA in non-treated cells. Testosterone, at concentrations of 0.5 and 50μmol/L, provoked inhibition of E2 formation of 36% and 79%, respectively. The effect of androstenedione at 0.5 and 50μmol/L was 56% and 76%, respectively. In breast cancer cells, the natural androgens testosterone and androstenedione, have the capacity to control bioformation of estradiol by blocking aromatase activity. The data can provide important information on the control mechanism of estrogen intratumoral levels and open new possibilities in breast cancer treatment.

Pomegranate Ellagitannin–Derived Compounds Exhibit Antiproliferative and Antiaromatase Activity in Breast Cancer Cells In vitro

Estrogen stimulates the proliferation of breast cancer cells and the growth of estrogen-responsive tumors. The aromatase enzyme, which converts androgen to estrogen, plays a key role in breast carcinogenesis. The pomegranate fruit, a rich source of ellagitannins (ET), has attracted recent attention due to its anticancer and antiatherosclerotic properties. On consumption, pomegranate ETs hydrolyze, releasing ellagic acid, which is then converted to 3,8-dihydroxy-6H-dibenzo[b,d]pyran-6-one ("urolithin") derivatives by gut microflora. The purpose of this study was to investigate the antiaromatase activity and inhibition of testosterone-induced breast cancer cell proliferation by ET-derived compounds isolated from pomegranates. A panel of 10 ET-derived compounds including ellagic acid, gallagic acid, and urolithins A and B (and their acetylated, methylated, and sulfated analogues prepared in our laboratory) were examined for their ability to inhibit aromatase activity and testosterone-induced breast cancer cell proliferation. Using a microsomal aromatase assay, we screened the panel of ET-derived compounds and identified six with antiaromatase activity. Among these, urolithin B (UB) was shown to most effectively inhibit aromatase activity in a live cell assay. Kinetic analysis of UB showed mixed inhibition, suggesting more than one inhibitory mechanism. Proliferation assays also determined that UB significantly inhibited testosterone-induced MCF-7aro cell proliferation. The remaining test compounds also exhibited antiproliferative activity, but to a lesser degree than UB. These studies suggest that pomegranate ET-derived compounds have potential for the prevention of estrogen-responsive breast cancers.

Mechanism-based categorization of aromatase inhibitors: a potential discovery and screening tool

Cytochrome P450 aromatase is a key steroidogenic enzyme that converts androgens to estrogens in vertebrates. There is much interest in aromatase inhibitors (AIs) both because of their use as pharmaceuticals in the treatment of estrogen-sensitive breast cancers, and because a number of environmental contaminants can act as AIs, thereby disrupting endocrine function in humans and wildlife through suppression of circulating estrogen levels. The goal of the current work was to develop a mechanism-based structure–activity relationship (SAR) categorization framework highlighting the most important chemical structural features responsible for inhibition of aromatase activity. Two main interaction mechanisms were discerned: steroidal and non-steroidal. The steroid scaffold is most prominent when the structure of the target chemical is similar to the natural substrates of aromatase – androstenedione and testosterone. Chemicals acting by non-steroidal mechanism(s) possess a heteroatom (N, O, S) able to coordinate the heme iron of the cytochrome P450, and thus interfere with steroid hydroxylation. The specific structural boundaries controlling AI for both analyzed mechanisms were defined, and a software tool was developed that allowed a decision tree (profile) to be built discriminating AIs by mechanism and potency. An input chemical follows a profiling path and the structure is examined at each step to decide whether it conforms with the structural boundaries implemented in the decision tree node. Such a system would aid drug discovery efforts, as well as provide a screening tool to detect environmental contaminants that could act as AIs.