Aromatase Inhibitors: Structural Features and Biochemical Characterization

Aromatase inhibitors for the treatment of breast cancer: An overview (2019-2023)

Aromatase inhibition is considered a legitimate approach for the treatment of ER-positive (ER+) breast cancer as it accounts for more than 70% of breast cancer cases. Aromatase inhibitor therapy has been demonstrated to be highly effective in decreasing tumour size, increasing survival rates, and lowering the chance of cancer recurrence. The present review deliberates the pathophysiology and the role of aromatase in estrogen biosynthesis. Estrogen biosynthesis, various androgens, and their function in the human body have also been discussed. The salient aspects of the aromatase active site, its mode of action, and AIs, along with their intended interactions with presently FDA-approved inhibitors, have been briefly discussed. It has been detailed how different reported AIs were designed, their SAR investigations, in silico analysis, and biological evaluations. Various AIs from multiple origins, such as synthetic and semi-synthetic, have also been discussed.

Adverse Event Profiles of the Third-Generation Aromatase Inhibitors: Analysis of Spontaneous Reports Submitted to FAERS

The third-generation aromatase inhibitors (AIs), represented by letrozole, anastrozole, and exemestane, have been used as a standard first-line adjuvant therapy for postmenopausal breast cancer patients with positive hormone receptor. However, their safety in the real world has not been systematically analyzed. We used the U.S. Food and Drug Administration Adverse Event Reporting System (FAERS) to investigate adverse event (AE) profiles of the three AIs, covering the period from Q1 2004 to Q3 2023. The time-to-event onset profiles and cumulative incidence were analyzed by Weibull shape parameter test and Kaplan-Meier method, respectively. The disproportionality analysis was utilized to assess drug toxicity risk. Based on the FAERS database, 18,035, 8242, and 7011 reports listing letrozole, anastrozole, and exemestane as primary suspected drugs were extracted, respectively. AEs associated with anastrozole displayed the latest onset (p < 0.0001); meanwhile, WSP test showed that all three AIs had early failure-type profiles. At the preferred term level, we acquired 95, 59, and 42 significant signals associated with letrozole, anastrozole, and exemestane, which involved 18, 13, and 15 system organ classes, respectively. The three AIs all reported that their strongest AE signal was trigger finger. Neutropenia was the most frequent AE for letrozole, while the highest occurrences of anastrozole and exemestane were arthralgia. We also found that interstitial lung disease, a rare but serious AE, showed strong signal intensity in all three AIs. Additionally, letrozole was also associated with lots of other rare but serious AEs in hematologic, respiratory, and hepatic systems, which were not recorded in the instructions. Our analysis of safety warning signals of the third-generation AIs from the FAERS database provided reference for clinical safe and rational drug use.

Influence of tumor microenvironment on the different breast cancer subtypes and applied therapies

Despite the significant improvements made in breast cancer therapy during the last decades, this disease still has increasing incidence and mortality rates. Different targets involved in general processes, like cell proliferation and survival, have become alternative therapeutic options for this disease, with some of them already used in clinic, like the CDK4/6 inhibitors for luminal A tumors treatment. Nevertheless, there is a demand for novel therapeutic strategies focused not only on tumor cells, but also on their microenvironment. Tumor microenvironment (TME) is a very complex and dynamic system that, more than surrounding and supporting tumor cells, actively participates in tumor development and progression. During the last decades, it has become clear that the cellular and acellular components of TME differ between the various breast cancer subtypes and shape the differences regarding their severity and prognosis. The pivotal role of the TME in controlling tumor growth and influencing responses to therapy represents a potential source for novel targets and therapeutic strategies. In this review, we present a description of the multiple therapeutic options used for different breast cancer subtypes, as well as the influence that the TME may exert on the development of the disease and on the response to the distinct therapies, which in some cases may explain their failure by the occurrence of relapses and resistance. Furthermore, the ongoing studies focused on the use of TME components for developing potential cancer treatments are described.

New 1,2,3-Triazole/1,2,4-triazole Hybrids as Aromatase Inhibitors: Design, Synthesis, and Apoptotic Antiproliferative Activity

A novel series of 1,2,3-triazole/1,2,4-triazole hybrids 5a, 5b, and 6a-i was designed and synthesized as antiproliferative agents targeting aromatase enzymes. The antiproliferative activity of the new hybrids against four cancer cells was studied using Erlotinib as a control. Compounds 6a and 6b demonstrated the highest antiproliferative activity among these hybrids, with GI50 values of 40 nM and 35 nM, respectively. Compound 6b was the most potent derivative, with a GI50 of 35 nM, comparable to Erlotinib's GI50 of 33 nM. Compound 6b inhibited all cancer cell lines with comparable efficacy to Erlotinib. Compounds 5a, 5b, and 6a-i were tested for inhibitory action against aromatase as a potential target for their antiproliferative activity. Results revealed that compounds 6a and 6b were the most potent aromatase inhibitors, with IC50 values of 0.12 ± 0.01 µM and 0.09 ± 0.01 µM, respectively, being more potent than the reference Ketoconazole (IC50 = 2.6 ± 0.20 µM) but less potent than Letrozole (IC50 = 0.002 ± 0.0002). These findings indicated that compounds 6a and 6b had significant aromatase inhibitory action and are potential antiproliferative candidates. The findings were further linked to molecular docking investigations, which gave models of strong interactions with the aromatase domain for inhibitors with high binding scores.

Benzoxazole-appended piperidine derivatives as novel anticancer candidates against breast cancer

Novel series of benzoxazole-appended piperidine derivatives were planned, synthesized and screened against two breast cancer cell lines. Considerable antiproliferative activity was observed for screened compounds (IC₅₀ = 33.32 ± 0.2 µM to 7.31 ± 0.43 µM and 1.66 ± 0.08 µM to 12.10 ± 0.57 µM) against MCF-7 and MDA-MB-231 cell lines respectively being more potent than doxorubicin (IC₅₀ = 8.20 ± 0.39 µM and 13.34 ± 0.63 µM respectively). Active compounds were submitted for enzyme inhibition assays when 4d and 7h demonstrated potent EGFR inhibition (0.08 ± 0.002 µM and 0.09 ± 0.002 µM respectively) compared to erlotinib (0.11 ± 0.003 µM). However, no one compound displayed effective ARO inhibition activity as tested compounds were less active than letrozole. Apoptosis inducing ability results implied that apoptosis was provoked by significant stimulation of caspase-9 protein levels (4.25-7.04-fold) upon treatment of MCF-7 cells with 4a, 7h, 9, 12e and 12f. Alternatively, MDA-MB-231 cells treated with 4d, 7a, 12b and 12c considerably increased caspase-9 levels (2.32-4.06-fold). Cell cycle arrest and annexin-V/Propidium iodide assays further confirmed apoptosis when tested compounds arrested cell cycle at various phases and demonstrated high annexin V binding affinity. Docking outcomes proved valuable binding affinities for compounds 4d and 7h to EGFR enzyme while compounds 4a and 12e, upon docking into the active site of ARO, failed to interact with heme, suggesting their inabilities to act as AIs. Therefore, these benzoxazoles can act as promising candidates exhibiting EGFR inhibition and apoptosis-promoting properties.

Letrozole as premedication of high intensity focused ultrasound treatment of uterine fibroids: A retrospective observation study

Background

No reports on Letrozole as a pretreatment before ablation of uterine fibroid with high intensity focused ultrasound (HIFU), so a retrospective observation study was performed to evaluate the response of different pre-HIFU medication.

Methods

We collected patients with single uterine fibroid receiving HIFU ablation from January 2018 to April 2021. All enrolled patients were classified into three group: group A (no pre-HIFU medication use), group B (Pre-HIFU letrozole use), group C (pre-HIFU gonadotrophin releasing hormone analog, GnRHa). Further associated clinical data and treatment response after HIFU treatment were reviewed and evaluated.

Results

A total of 39 patients including 21, 7, and 11 in group A, B, and C were collected respectively. After pre-HIFU medication, no difference of fibroid volume was found (A: 251.4, B: 360.6, C: 409.4 cm³, p = 0.250), and GnRHa group had significantly larger volume reduction than Letrozole users (38.6% vs. 16.4%, p = 0.007). The incidence of hypoestrogenic symptoms was higher in GnRHa group than in letrozole users (27.3% vs. 0, p = 0.170). GnRHa group had more sonication time (p = 0.001), treatment duration (p = 0.002), and ablated energy (p = 0.001) than group A and B. The treatment efficiency was higher in letrozole group than that in other 2 groups (4.52 vs. 2.39 vs. 2.34 cm³/min, p = 0.050). For patients with fibroid over 10 cm in diameter, letrozole group had even better energy efficiency (p = 0.067), treatment speed (p = 0.007), treatment efficiency (p = 0.001), NPV per energy (p = 0.005), and NPV per sonication (p = 0.004) than other 2 groups.

Conclusion

Letrozole as a pretreatment medication before HIFU treatment might increase the energy efficiency and treatment efficiency of its ablation of uterine leiomyoma, especially for fibroid over 10 cm. Future study of larger patient number is needed to confirm our results.

New benzothienopyrimidine derivatives as dual EGFR/ARO inhibitors: Design, synthesis, and their cytotoxic effect on MCF-7 breast cancer cell line

New cytotoxic agents based on benzothienopyrimidine scaffold were designed, synthesized, and evaluated against the MCF-7 breast cancer line in comparison to erlotinib and letrozole as reference drugs. Eight compounds demonstrated up to 20-fold higher anticancer activity than erlotinib, and five of these compounds were up to 11-fold more potent than letrozole in MTT assay. The most promising compounds were evaluated for their inhibitory activity against EGFR and ARO enzymes. Compound 12, which demonstrated potent dual EGFR and ARO inhibitory activity with IC₅₀ of 0.045 and 0.146 µM, respectively, was further evaluated for caspase-9 activation, cell cycle analysis, and apoptosis. The results revealed that the tested compound 12 remarkably induced caspase-9 activation (IC₅₀  = 16.29 ng/ml) caused cell cycle arrest at the pre-G₁ /G₁ phase and significantly increased the concentration of cells at both early and late stage of apoptosis. In addition, it showed a higher safety profile on normal MCF-10A cells, and higher antiproliferative activity on cancer cells (IC₅₀  = 8.15 µM) in comparison to normal cells (IC₅₀  = 41.20 µM). It also revealed a fivefold higher selectivity index than erlotinib towards MCF-7 cancer cells. Docking studies were performed to rationalize the dual inhibitory activity of compound 12.

The Role of Aromatase Enzyme in Hormone Related Diseases and Plant-Based Aromatase Inhibitors as Therapeutic Regimens

Medicinal plants have a long history of use as food and remedy in traditional and modern societies, as well as have been used as herbal drugs and sources of novel bioactive compounds. They provide a wide array of chemical compounds, many of which can not be synthesized via current synthesis methods. Natural products may provide aromatase inhibitory activity through various pathways and may act clinically effective for treating pathologies associated with excessive aromatase secretion including breast, ovarian and endometrial cancers, endometriosis, uterine fibroid, benign prostatic hyperplasia (BPH), prostate cancer, infertility, and gynecomastia. Recent studies have shown that natural products with aromatase inhibitory activity, could also be good options against secondary recurrence of breast cancer by exhibiting chemopreventive effects. Therefore, screening for new plant-based aromatase inhibitors may provide novel leads for drug discovery and development, particularly with increased clinical efficacy and decreased side effects.

New thieno[3,2-d]pyrimidine-based derivatives: Design, synthesis and biological evaluation as antiproliferative agents, EGFR and ARO inhibitors inducing apoptosis in breast cancer cells

An array of newly synthesized thieno[3,2-d]pyrimidine-based derivatives and thienotriazolopyrimidines hybridized with some pharmacophoric anticancer fragments were designed, synthesized and assessed for their in vitro antiproliferative activity against MCF-7 and MDA-MB-231 breast cancer cell lines using erlotinib and pictilisib as reference standards in the MTT assay. In general, many compounds were endowed with considerable antiproliferative activity (IC₅₀ = 0.43-1.31 µM). Some of the tested compounds, namely 3c, 5b, 5c, 9d, 10, 11b and 13 displayed remarkable antiproliferative activity against both cell lines. Meanwhile, compounds 2c-e, 3b, 4a, 5a, 9c and 15b showed noticeable selectivity against MCF-7 cells while compounds 2b, 3a, 4b, 6a-c, 7, 8, 9b and 12 exhibited considerable selectivity against MDA-MB-231 cells. Further mechanistic evidences for their anticancer activities were provided by screening the most potent compounds against MCF-7 and/or MDA-MB-231 cells for EGFR and ARO inhibitory activities using erlotinib and letrozole as reference standards respectively. Results proved that, in general, tested compounds were better EGFRIs than ARIs. In addition, significant overexpression in caspase-9 level in treated MCF-7 breast cell line samples was observed for all tested compounds with the 4-fluorophenylhydrazone derivative 2d exhibiting the highest activation. In treated MDA-MB-231 breast cell line samples, 11b was found to highly induce caspase-9 level thereby inducing apoptosis. Cell cycle analysis and Annexin V-FITC/PI assay were also assessed for active compounds where results indicated that all tested compounds induced preG1 apoptosis and cell cycle arrest at G2/M phase. Compound 9d, as an inhibitor of ARO, was observed to downregulate the downstream signaling proteins HSP27 and p-ERK in MCF-7 cells. Furthermore, compound 11b downregulated EGFR expression as well as the downstream signaling protein p-AKT. Docking experiments on EGFR and ARO enzymes supported their in vitro results. Thus, the thienotriazolopyrimidines 11b and 12 showing good EGFR inhibition and the thieno[3,2-d]-pyrimidine derivatives 3b and 9d, eliciting the best ARO inhibition activity, can be considered as new candidates as anti-breast cancer agents that necessitate further development.

Computer-Aided Drug Design Applied to Secondary Metabolites as Anticancer Agents

Computer-Aided Drug Design (CADD) techniques have garnered a great deal of attention in academia and industry because of their great versatility, low costs, possibilities of cost reduction in in vitro screening and in the development of synthetic steps; these techniques are compared with highthroughput screening, in particular for candidate drugs. The secondary metabolism of plants and other organisms provide substantial amounts of new chemical structures, many of which have numerous biological and pharmacological properties for virtually every existing disease, including cancer. In oncology, compounds such as vimblastine, vincristine, taxol, podophyllotoxin, captothecin and cytarabine are examples of how important natural products enhance the cancer-fighting therapeutic arsenal. In this context, this review presents an update of Ligand-Based Drug Design and Structure-Based Drug Design techniques applied to flavonoids, alkaloids and coumarins in the search of new compounds or fragments that can be used in oncology. A systematical search using various databases was performed. The search was limited to articles published in the last 10 years. The great diversity of chemical structures (coumarin, flavonoids and alkaloids) with cancer properties, associated with infinite synthetic possibilities for obtaining analogous compounds, creates a huge chemical environment with potential to be explored, and creates a major difficulty, for screening studies to select compounds with more promising activity for a selected target. CADD techniques appear to be the least expensive and most efficient alternatives to perform virtual screening studies, aiming to selected compounds with better activity profiles and better "drugability".

Anti-estrogenic and anti-aromatase activities of citrus peels major compounds in breast cancer

Estrogen signaling is crucial for breast cancer initiation and progression. Endocrine-based therapies comprising estrogen receptor (ER) modulators and aromatase inhibitors remain the mainstay of treatment. This study aimed at investigating the antitumor potential of the most potent compounds in citrus peels on breast cancer by exploring their anti-estrogenic and anti-aromatase activities. The ethanolic extract of different varieties of citrus peels along with eight isolated flavonoids were screened against estrogen-dependent breast cancer cell lines besides normal cells for evaluating their safety profile. Naringenin, naringin and quercetin demonstrated the lowest IC_50s and were therefore selected for further assays. In silico molecular modeling against ER and aromatase was performed for the three compounds. In vivo estrogenic and anti-estrogenic assays confirmed an anti-estrogenic activity for the isolates. Moreover, naringenin, naringin and quercetin demonstrated in vitro inhibitory potential against aromatase enzyme along with anticancer potential in vivo, as evidenced by decreased tumor volumes. Reduction in aromatase levels in solid tumors was also observed in treated groups. Overall, this study suggests an antitumor potential for naringenin, naringin and quercetin isolated from citrus peels in breast cancer via possible modulation of estrogen signaling and aromatase inhibition suggesting their use in pre- and post-menopausal breast cancer patients, respectively.

Effect of GnRH-antagonist, mifepristone and letrozole on preventing ovarian hyperstimulation syndrome in rat model

RESEARCH QUESTION

Can luteolysis-targeted drugs, gonadotrophin-releasing hormone antagonist (GnRH-ant), mifepristone and letrozole, administered separately or in combination, prevent the progression of ovarian hyperstimulation syndrome (OHSS) in a rat model?

DESIGN

Thirty-six female Wistar rats were randomly divided into six groups, including control group (OHSS group, ovarian hyperstimulation-induced OHSS); GnRH-ant group (OHSS with GnRH-ant treatment); mifepristone group (OHSS with mifepristone treatment); letrozole group (OHSS with letrozole treatment); combination group (OHSS with GnRH-ant, mifepristone and letrozole treatment in combination). The main outcomes were the alterations in OHSS-related indices, including ovarian weight, vascular permeability, serum oestradiol and progesterone levels, corpus luteum proportion and diameter, ovarian vascular endothelial growth factor (VEGF), interleukin 6 (IL-6), caspase-3 and cleaved caspase-3 levels.

RESULTS

No significant difference was found in body weight gain among the six groups. Compared with the control group, the OHSS group showed significant increases in all OHSS-related indices. GnRH-ant treatment showed decreases in vascular permeability, serum oestradiol level, corpus luteum diameter, ovarian VEGF /IL-6 mRNA levels, and increases in ovarian caspase-3 and cleaved caspase-3 levels. Mifepristone treatment demonstrated reduction in serum progesterone level and corpus luteum diameter, and elevation in ovarian caspase-3 and cleaved caspase-3 levels. Letrozole treatment displayed a decline in serum oestradiol level and corpus luteum diameter, and up-regulation in ovarian caspase-3 and cleaved caspase-3 levels. The combination treatment by GnRH-ant, mifepristone and letrozole showed enhanced synergistic effect on reducing OHSS-related indices.

CONCLUSIONS

GnRH-ant, mifepristone and letrozole are beneficial in preventing the progression of OHSS through different luteolytic mechanisms. Cocktail style treatment shows enhanced synergistic effect on preventing the progression of OHSS.

An attempt to potentiate the ovarian superstimulatory response in cattle by co-treatment with an aromatase inhibitor

Letrozole is used for the treatment of subfertility in women undergoing ovarian superstimulation, but the mechanism of action has not been investigated critically. The objective was to test the hypothesis that treatment with letrozole will potentiate the superstimulatory response following gonadotropin treatment by increasing the number of follicles present at ovarian follicular wave emergence in cattle. In Experiment 1, ovarian follicular wave emergence was synchronized among beef heifers (n = 8) by transvaginal ultrasound-guided follicle ablation. On Day 0 (wave emergence), a letrozole-releasing device (LRD) was placed intravaginally for 5 days, followed again by transvaginal follicle ablation on Day 5. The number of follicles ≥3 mm was recorded by transrectal ultrasonography on Days 0 and 6.5 (i.e., pre- vs. post-LRD treatment). In Experiment 2, non-lactating dairy cows were assigned randomly to one of two groups (n = 15/gp) after follicle ablation-induced synchronization of wave emergence (Day 0), and given either an LRD or sham device for 5 days. Superstimulatory treatment was initiated on Day 0, consisting of 8 doses of 50 mg of porcine FSH im at 12 h intervals, and luteolytic doses of prostaglandin on Days 3 and 3.5. The LRD/sham devices were removed on Day 3.5, GnRH was given im on Day 5, estrus response was determined on Days 5 and 6, and the ovarian response was recorded by ultrasonography on Days 0, 3.5, 5, 6.5, and 12. In Experiment 1, no difference was detected in the number of antral follicles at wave emergence pre- vs. post-LRD treatment (23.2 ± 3.2 vs. 23.5 ± 3.8 follicles; P = 0.67; mean ± SEM). In Experiment 2, the interval from prostaglandin treatment to estrus was longer (50.3 ± 1.1 vs. 40.7 ± 2.0 h; P < 0.001) and less variable (residuals: 3.1 ± 0.5 vs. 6.7 ± 0.9 h; P < 0.01) in the LRD vs. sham group. The proportion of ovulations (number of CL on Day 12 over the number of follicles ≥3 mm on Day 0) did not differ (0.65 ± 0.02 vs. 0.70 ± 0.02; P = 0.15) nor did the number of CL on Day 12 (15.9 ± 2.5 vs. 19.0 ± 2.0; P = 0.32) between the LRD and sham groups. In summary, treatment with letrozole did not increase the number of antral follicles at wave emergence or the superstimulatory response, but increased precision in the interval to estrus and may be useful for artificial insemination at a fixed time in superstimulatory protocols.

Estrogen receptor-positive (ER+) breast cancer treatment: Are multi-target compounds the next promising approach?

Endocrine therapy is currently the main therapeutic approach for estrogen receptor-positive (ER⁺) breast cancer, the most frequent subtype of breast cancer in women worldwide. For this subtype of tumors, the current clinical treatment includes aromatase inhibitors (AIs) and anti-estrogenic compounds, such as Tamoxifen and Fulvestrant, being AIs the first-line treatment option for post-menopausal women. Moreover, the recent guidelines also suggest the use of these compounds by pre-menopausal women after suppressing ovaries function. However, besides its therapeutic efficacy, the prolonged use of this type of therapies may lead to the development of several adverse effects, as well as, endocrine resistance, limiting the effectiveness of such treatments. In order to surpass this issues and clinical concerns, during the last years, several studies have been suggesting alternative therapeutic approaches, considering the function of aromatase, ERα and ERβ. Here, we review the structural and functional features of these three targets and their importance in ER⁺ breast cancer treatment, as well as, the current treatment strategies used in clinic, emphasizing the importance of the development of multi-target compounds able to simultaneously modulate these key targets, as a novel and promising therapeutic strategy for this type of cancer.

CYP19A1 gene polymorphism and colorectal cancer etiology in Saudi population: case-control study

BACKGROUND

Considerable interest is directed toward the enzyme aromatase (CYP19A1) and the development of cancer, due to CYP19A1's role in estrogen biosynthesis. Several cancers display excessive intra-tumor accumulation of estrogens, and aromatase inhibitors are used for treatment. The CYP19A1 gene exhibits polymorphism and mutations that can alter its expression or aromatase activity and influence estrogen production. We designed this study to investigate the link between CYP19A1 polymorphism and susceptibility to colorectal cancer (CRC) development in Saudis.

PATIENTS AND METHODS

Blood samples from 100 CRC patients and 100 healthy controls were drawn for DNA extractions. Three polymorphic sites, rs4774585, rs936308, and rs4775936, were genotyped using Taqman genotyping by real-time polymerase chain reaction. Allelic and genotype frequencies were calculated and compared in the two groups.

RESULTS

All single nucleotide polymorphisms (SNPs) were polymorphic in Saudis, and comparison of allele frequencies showed several differences when compared to other populations. None of the SNPs were associated with the risk of CRC development in Saudis (P>0.05). Some gender and location (colon or rectal) differences were observed.

DISCUSSION

The results of this study highlighted the genetic heterogeneity existing between populations in the prevalence of different SNPs and their relation to disease state. It showed that, although rs4774585, rs936308, and rs4775936 are involved in CRC development in several populations, their role is not significant in the etiology of CRC in Saudis; however, some SNPs do increase susceptibility or resistance to CRC development as judged from the odds ratio. Further large-scale studies are warranted to clarify the role of the CYP19A1 development in CRC.

Anti-tumor efficacy of new 7α-substituted androstanes as aromatase inhibitors in hormone-sensitive and resistant breast cancer cells

The majority of breast cancer cases are estrogen receptor positive (ER⁺). Although, third-generation aromatase inhibitors (AIs) are used as first-line treatment in post-menopausal women, they cause endocrine resistance and bone loss, which limits their success. Therefore, there is a demand to discover new potent molecules, with less toxicity that can circumvent these drawbacks. Our group has previously demonstrated that new 7α-substituted steroidal molecules, 7α-(2ξ,3ξ-epoxypropyl)androsta-1,4-diene-3,17-dione (3), 7α-allylandrost-4-ene-3,17-dione (6), 7α-allylandrost-4-en-17-one (9), 7α-allyl-3-oxoandrosta-1,4-dien-17β-ol (10) and 7α-allylandrosta-1,4-diene-3,17-dione (12) are potent AIs in placental microsomes. In this work, it was investigated their anti-aromatase activity and in vitro effects in sensitive and resistant breast cancer cells. All the steroids efficiently inhibit aromatase in breast cancer cells, allowing to establish new structure-activity relationships for this class of compounds. Moreover, the new AIs can inhibit breast cancer cell growth, by causing cell cycle arrest and apoptosis. The effects of AIs 3 and 12 on sensitive cells were dependent on aromatase inhibition and androgen receptor (AR), while for AI 9 and AI 10 were AR- and ER-dependent, respectively. In addition, it was shown that all the AIs can sensitize resistant cancer cells being their behavior similar to the sensitive cells. In summary, this study contributes to the understanding of the structural modifications in steroidal scaffold that are translated into better aromatase inhibition and anti-tumor properties, providing important information for the rational design/synthesis of more effective AIs. In addition, allowed the discovery of new potent 7α-substituted androstane molecules to inhibit tumor growth and prevent endocrine resistance.

Cotargeting of CYP-19 (aromatase) and emerging, pivotal signalling pathways in metastatic breast cancer

Aromatase inhibition is one of the cornerstones of modern endocrine therapy of oestrogen receptor-positive (ER+) metastatic breast cancer (MBC). The nonsteroidal aromatase inhibitors anastrozole and letrozole, as well as the steroidal aromatase inactivator exemestane, are the preferred drugs and established worldwide in all clinical phases of the disease. However, although many patients suffering from MBC experience an initial stabilisation of their metastatic burden, drug resistance and disease progression occur frequently, following in general only a few months on treatment. Extensive translational research during the past two decades has elucidated the major pathways contributing to endocrine resistance and paved the way for clinical studies investigating the efficacy of novel drug combinations involving aromatase inhibitors and emerging drugable targets like mTOR, PI3K and CDK4/6. The present review summarises the basic research that provided the rationale for new drug combinations involving aromatase inhibitors and the main findings of pivotal clinical trials that have already started to change our way to treat hormone-sensitive MBC. The challenging situation of oestrogen receptor-positive and human epidermal growth factor receptor 2-positive (HER2+) MBC is also shortly reviewed to underline the complexity of the clinical scenario in the heterogeneous subgroups of hormone receptor-positive breast cancer patients and the increasing need for personalised medicine. Finally, we summarise some of the promising findings made with the combination of aromatase inhibitors with other potent endocrine treatment options like fulvestrant, a selective oestrogen receptor downregulator.

Unravelling exemestane: From biology to clinical prospects

Aromatase inhibitors (AIs) are anti-tumor agents used in clinic to treat hormone-dependent breast cancer. AIs block estrogens biosynthesis by inhibiting the enzyme aromatase, preventing tumor progression. Exemestane, a third-generation steroidal AI, belongs to this class of drugs and is currently used in clinic to treat postmenopausal women, due to its high efficacy and good tolerability. Here, its pharmacological and biological aspects as well as its clinical applications and comparison to other endocrine therapeutic agents, are reviewed. It is also focused the benefits and risks of exemestane, drawbacks to be overcome and aspects to be explored.

The implications of genetic variation for the pharmacokinetics and pharmacodynamics of aromatase inhibitors

INTRODUCTION

Breast cancer is the most common female cancer and remains a serious public health concern worldwide. Third-generation aromatase inhibitors (AIs) are widely used in postmenopausal women with estrogen receptor positive breast cancer. However, there is marked interindividual variability in terms of the efficacy and incidence of adverse events following treatment with AIs. Pharmacogenetics has the potential to predict clinical outcomes based on patients' genetic information, paving the way towards personalized treatment.

AREAS COVERED

This article reviews pharmacogenetic studies of AIs, including pharmacokinetic and pharmacodynamic aspects, highlighting those studies where the efficacy and adverse events of AIs have been examined using both candidate gene and genome-wide approaches.

EXPERT OPINION

Pharmacogenetics is a promising approach to develop personalized medicine with AIs. However, the application of pharmacogenetics to predict therapeutic efficacy and adverse events in breast cancer patients is still far from implementation in routine clinical practice. Large, comprehensive, multicenter studies that simultaneously evaluate multiple genes and pathways, including rare variants, are warranted in order to produce reliable and informative results. The ultimate aim is to develop clinically-relevant guidelines for breast cancer therapy.

Comparison of the effects of letrozole and cabergoline on vascular permeability, ovarian diameter, ovarian tissue VEGF levels, and blood PEDF levels, in a rat model of ovarian hyperstimulation syndrome

OBJECTIVE

To evaluate the effects of letrozole and cabergoline in a rat model of ovarian hyperstimulation syndrome (OHSS).

STUDY DESIGN

In this prospective, controlled experimental study, the 28 female Wistar rats were divided into four subgroups (one non-stimulated control and three OHSS-positive groups: placebo, letrozole, and cabergoline). To induce OHSS, rats were injected with 10 IU of pregnant mare serum gonadotropin from day 29 to day 32 of life, followed by subcutaneous injection of 30 IU hCG on day 33. Letrozole rats received with a single dose of 0.1 mg/kg letrozole via oral gavage, on the hCG day. Cabergoline rats received with a single dose of 100 µg/kg cabergoline via oral gavage, on the hCG day. All animals were compared in terms of body weight, vascular permeability (VP), ovarian diameter, ovarian tissue VEGF expression (assessed via immunohistochemical staining), and blood pigment epithelium-derived growth factor (PEDF) levels.

RESULTS

The OHSS-positive placebo group (group 2) exhibited the highest VP, ovarian diameter, extent of VEGF staining, and lowest PEDF level, as expected. No significant difference was evident between the letrozole and cabergoline groups in terms of any of body weight; VP; PEDF level; ovarian diameter; or the staining intensity of, or percentage staining for, VEGF in ovarian tissues.

CONCLUSIONS

Letrozole and cabergoline were equally effective to prevent OHSS, reducing the ovarian diameter, VP, and PEDF and VEGF levels to similar extents.

Prevention and treatment of bone fragility in cancer patient

It is well known that fractures increase the risk of morbidity and mortality. The various mechanisms responsible for bone loss in cancer patients may have a different impact depending on the characteristics of the clinical case and correlates with the therapies used, or caused by the therapies used against cancer. Some hormonal treatments cause hypogonadism, event which contributes to the progressive loss of bone mass. This is detectable in patients with breast cancer receiving determines that estrogen-deprivation and in men with prostate cancer with therapies that determine androgen deprivation. Chemotherapy treatments used in cancer patients have reduced bone mass. In addition, low bone mass is detectable in patients with lymphoma treated with corticosteroids or radiation or alkylating agents. In premenopausal patients suffering from breast cancer, treatment with cytotoxic therapy or ablation of ovarian function, can lead to an 8% reduction in bone mineral density at the spine and 4% in the femur. With a chemotherapy regimen in CMF, the reduction of BMD is 6.5%; this bone loss is not recovered after discontinuation of therapy. Tamoxifen given for five years reduces bone remodeling and cause a 32% increase in the risk of osteoporotic fractures when used in premenopausal. After menopause, tamoxifen has a protective effect on bone mass, with a reduced risk of new fractures. Aromatase inhibitors in post-menopausal women, depending on the formulation can cause different effects on the reduction of BMD and fracture risk. We have in fact steroids, exemestane and nonsteroidal, letrozole and anastrozole. Patients at increased risk of fragility fractures should undergo preventive therapies as soon as possible after tests performed for the study of bone health. They can be used DEXA and the FRAX algorithm, which can define a secondary osteoporosis. Prevention and treatment of the increased risk of osteoporotic fracture is to maintain adequate levels of calcium and vitamin D. Bisphosphonates and denosumab are used for the management of bone remodeling and bone loss induced by cancer treatments. Bisphosphonates also have anti-tumor effects per se, which are expressed in potentially prevent the development of bone metastases. In men with metastatic prostate cancer and which is induced androgen deprivation, it is usefully used denosumab 120 mg monthly or zoledronic acid 4 mg monthly.

Treatment of aromatase (CYP19A1) inhibitor reduces fertility in porcine sperm

To ascertain whether aromatase (CYP19A1) expression is linked to sperm fertility of pigs, the present study determined the expression of the CYP19A1 gene in porcine sperm and its relationship with fertilization in vitro. First, to investigate its role in fertility, the presence of CYP19A1 of mRNA and protein expression in porcine sperm were confirmed by real-time (RT) or quantitative polymerase chain reaction (q-PCR) and by western blots. The expression levels were determined quantitatively using two sperm groups recovered by a Percoll gradient, which revealed that the sperm group with a low density had a higher penetration rate than that of the high-density group (P < 0.05). However, the expression level of CYP19A1 was not significantly different between the two groups. Secondly, to examine the effect of aromatase activity on fertilization, fresh semen was treated with a steroidal inhibitor, exemestane (50 μM for 0.5 h), followed by the dose- and time-dependent viability test. Our results clearly showed that an exemestane treatment effect (P < 0.05) was found for both the sperm-penetration rate and the oocyte cleavage rate. These results indicated that CYP19A1 could be involved in sperm fertility and its expression in sperm plays an important role in fertilization.

A comparison of the efficacy of two doses of letrozole alone or with continuous recombinant follicle-stimulating hormone for ovulation induction in anovulatory women

AIMS

To determine the efficacy of letrozole alone or with recombinant follicle-stimulating hormone (rFSH) for ovarian induction in anovulatory women.

METHODS

A total of 322 patients undergoing intrauterine insemination (IUI) were included in this retrospective study. Letrozole (2.5 or 5.0 mg) was administered from days 5 to 9 of menses, alone or followed with rFSH started on day 9 until the day of human chorionic gonadotropin administration. A single IUI was performed 24 h after ovulation.

RESULTS

The number of follicles, endometrial thickness and serum estradiol levels were significantly higher in the letrozole + rFSH groups than in the letrozole-alone groups (p < 0.05), but no significant difference was found between the two doses of letrozole, whether alone or with rFSH. Women treated with 5.0 mg/day of letrozole + rFSH required a total dose of rFSH similar to women treated with 2.5 mg/day of letrozole + rFSH (230.77 ± 118.29 vs. 258.55 ± 130.13 IU, respectively; p = 0.205). There was no significant difference in pregnancy rates between the two doses of letrozole, whether alone or with rFSH.

CONCLUSION

Treatment with letrozole + rFSH was more efficacious than letrozole alone for pregnancy in the IUI program; however, the effect of 5.0 mg/day of letrozole versus 2.5 mg/day of letrozole on ovulation was equivalent, regardless of whether rFSH was used.

Effects of steroidal aromatase inhibitors on sensitive and resistant breast cancer cells: aromatase inhibition and autophagy

Several therapeutic approaches are used in estrogen receptor positive (ER(+)) breast cancers, being one of them the use of aromatase inhibitors (AIs). Although AIs demonstrate higher efficacy than tamoxifen, they can also exhibit de novo or acquired resistance after prolonged treatment. Recently, we have described the synthesis and biochemical evaluation of four steroidal AIs, 3β-hydroxyandrost-4-en-17-one (1), androst-4-en-17-one (12), 4α,5α-epoxyandrostan-17-one (13a) and 5α-androst-2-en-17-one (16), obtained from modifications in the A-ring of the aromatase substrate, androstenedione. In this study, it was investigated the biological effects of these AIs in different breast cancer cell lines, an ER(+) aromatase-overexpressing human breast cancer cell line (MCF-7aro cells), an estrogen-receptor negative (ER(-)) human breast cancer cell line (SK-BR-3 cells), and a late stage of acquired resistance cell line (LTEDaro cells). The effects of an autophagic inhibitor (3-methyladenine) plus AIs 1, 12, 13a or exemestane in LTEDaro cells were also studied to understand the involvement of autophagy in AI acquired resistance. Our results showed that these steroids inhibit aromatase of MCF-7aro cells and decrease cell viability in a dose- and time-dependent manner. The new AI 1 is the most potent inhibitor, although the AI 12 demonstrates to be the most effective in decreasing cell viability. Besides, and in advantage over exemestane, AIs 12 and 13a also reduced LTEDaro cells viability. The use of the autophagic inhibitor allowed AIs to diminish viability of LTEDaro cells, presenting a similar behavior to the sensitive cells. Thus, inhibition of autophagy may sensitize hormone-resistant cancer cells to anti-estrogen therapies.

7-Meth-oxy-2-phenyl-chroman-4-one

In the title compound, C(16)H(14)O(3), the ring O atom and the two adjacent non-fused C atoms, as well as the attached phenyl ring, exhibit static disorder [occupancy ratio 0.559 (12):0.441 (12)]. The crystal packing features π-π [centroid-centroid distance = 3.912 (1) Å] and C-H⋯π inter-actions.

Aromatase, estrone sulfatase, and 17β-hydroxysteroid dehydrogenase: structure-function studies and inhibitor development

Aromatase, estrone sulfatase, and 17β-hydroxysteroid dehydrogenase type 1 are involved in the key steps of 17β-estradiol biosynthesis. Structure-function studies of aromatase, estrone sulfatase and 17β-hydroxysteroid dehydrogenase type 1 are important to evaluate the molecular basis of the interaction between these enzymes and their inhibitors. Selective and potent inhibitors of the three enzymes have been developed as antiproliferative agents in hormone-dependent breast carcinoma. New treatment strategies for hormone-dependent breast cancer are discussed.

Inflammatory osteoarthritis which was precipitated by Arimidex and resolved with tamoxifen

We report the case of a 51-year-old woman who presented with an inflammatory flare of osteoarthritis of the small joints of her hands occurring in a temporal relationship with the commencement of Arimidex, prescribed to reduce systemic oestrogen levels to treat breast cancer. Following the cessation of Arimidex and the initiation of tamoxifen, a specific oestrogen receptor antagonist, this flare resolved. It has long been observed that during the menopause, as oestrogen levels decline, many women develop osteoarthritis or experience progression of the disease. However, this theory of oestrogen-dependent osteoarthritis has not been consistently demonstrated in animal models. As far as the authors are aware, this is the first case in which systemic oestrogen reduction has resulted in a severe osteoarthritis flare but targeted oestrogen receptor blockade led to a resolution of symptoms. These findings may inform the pathophysiological process underlying oestrogen-dependent osteoarthritis, although further series are needed.

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.

Letrozole administration during the luteal phase after ovarian stimulation impacts corpus luteum function: a randomized, placebo-controlled trial

OBJECTIVE

To investigate the effect of letrozole-an oral aromatase inhibitor-on E(2), P, and LH levels when administered during the luteal phase after oocyte retrieval in IVF/intracytoplasmic sperm injection (ICSI) cycles.

DESIGN

Prospective, randomized, placebo controlled trial.

SETTING

University-affiliated private reproductive medicine center.

PATIENT(S)

Thirty oocyte donors undergoing standardized controlled ovarian hyperstimulation (COH) protocols.

INTERVENTION(S)

Patients were randomized after successful egg retrieval to receive either 2.5 mg of letrozole (Femara; Novartis, Barcelona, Spain) or a placebo (folic acid tablets). All donors were under intrauterine device (IUD) contraception.

MAIN OUTCOME MEASURE(S)

Serum E(2), P, and LH the day of hCG administration and days +4, +7 and +10 after ovum pick-up.

RESULT(S)

Donors had a comparable serum E(2) level on the day of hCG administration (1,858 vs. 2,143 pg/mL). Interestingly, levels dramatically dropped 4 days after egg retrieval, reaching a statistically significant lower level in those receiving letrozole (279 vs. 1,586 pg/mL). Again, at the next time points serum E(2) levels were significantly lower (day +7: 240 vs. 855 pg/mL and day +10: 40 vs. 448 pg/mL). No significant differences were observed in P levels, but LH serum concentrations were lower in the control group on day +7 (0.18 vs. 0.02 mIU/mL and day +10 (0.40 vs. 0.16 mIU/mL), when serum E(2) levels were higher.

CONCLUSION(S)

The administration of 2.5 mg of letrozole during the luteal phase has an impact on corpus luteum (CL) function. It reduces serum E(2) levels, which allows a faster recovery of LH concentration. This may be of interest not only for egg donors, but also in patients at high risk of ovarian hyperstimulation syndrome (OHSS) who freeze all their embryos or who cancel hCG administration to reduce the potential risk that high E(2) levels pose.

A 3D QSAR model of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core applying molecular dynamics simulations and ligand-protein docking

The 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) enzyme plays a crucial role in female hormonal regulation by catalysing the NADPH-dependent reduction of the less potent estrone E1 into the biologically active estradiol E2. Because 17beta-HSD1 is a key enzyme in E2 biosynthesis, it has emerged as an attractive drug target for inhibitor development. Herein we report the plausible binding modes and a 3D QSAR model of 17beta-HSD1 inhibitors based on a (di)cycloalkenothieno[2,3-d]pyrimidin-4(3H)-one core. Two generated enzyme complexes with potent inhibitors were subjected to molecular dynamics simulation to mimic the dynamic process of inhibitor binding. A set of 17beta-HSD1 inhibitors based on the thieno[2,3-d]pyrimidin-4(3H)-one core were docked into the resulting active site, and a CoMFA model employing the most extensive training set to date was generated. The model was validated with an external test set. Active site residues involved in inhibitor binding and CoMFA fields for steric and electrostatic interactions were identified. The model will be used to guide structural modifications of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core in order to improve the biological activity as well as in the design of novel 17beta-HSD1 inhibitors.

Effect of letrozole at 2.5 mg or 5.0 mg/day on ovarian stimulation with gonadotropins in women undergoing intrauterine insemination

OBJECTIVE

To determine the effect of combined therapy of letrozole (2.5 mg or 5.0 mg) with recombinant follicle-stimulating hormone (FSH) in comparison with the administration of recombinant FSH alone in an intrauterine insemination (IUI) program.

DESIGN

Retrospective study.

SETTING

Assisted fertilization program in a specialized infertility center.

PATIENT(S)

110 women undergoing IUI and gonadotropin therapy.

INTERVENTION(S)

Recombinant FSH alone administered from day 3 or combined with letrozole, 2.5 or 5.0 mg/day, on days 3 to 7, and gonadotropins starting on day 7 of the menstrual cycle. Transvaginal ultrasound examinations were done until the dominant follicle reached 18 mm in diameter. Ovulation was triggered with 10,000 IU of human chorionic gonadotropin (hCG), and IUI performed 30 to 40 hours later.

MAIN OUTCOME MEASURE(S)

Recombinant FSH dose required, number of follicles greater than 14 mm and 18 mm, endometrial thickness, pregnancy rates, miscarriages, and characteristics of newborns.

RESULT(S)

Women treated with FSH and 5.0 mg/day of letrozole required a lower dose of FSH than the group cotreated with 2.5 mg/day of letrozole or with FSH alone. Throughout most of the follicular phase, the endometrial thickness was statistically significantly less in both letrozole cotreatment groups compared with the FSH control group. By the day of hCG administration, the endometrial thickness was comparable among all the groups. The pregnancy rates were the same with recombinant FSH alone or combined with letrozole.

CONCLUSION(S)

In terms of cost-effectiveness, 5.0 mg/day of letrozole is more effective than the 2.5 mg/day in cotreatment with no adverse effect on pregnancy rate or outcome.

New experimental models for aromatase inhibitor resistance

Clinical trials have demonstrated the importance of aromatase inhibitor (AI) therapy in the effective treatment of hormone-dependent breast cancers. In contrast to tamoxifen, an antagonist of the estrogen receptor (ER), AIs have shown to be better tolerated along with decreased recurrence rates of the disease. Currently, three third-generation AIs are being used: exemestane, letrozole, and anastrozole. Our laboratory is attempting to understand several aspects of AI functionality. In this paper, we first review recent findings from our structure-function studies of aromatase as well as the molecular characterization of the interaction between AIs and aromatase. Based on these studies, we propose new evidence for the interaction of letrozole and exemestane with aromatase. In addition, we will discuss recent results generated from our AI-resistant cell lines. Our laboratory has generated MCF-7aro cells that are resistant to letrozole, anastrozole, exemestane, and tamoxifen. Basic functional characterization of aromatase and ERalpha in these resistant cell lines has been done and microarray analysis has been employed in order to better understand the mechanism responsible for AI resistance on a genome-wide scale. The results generated so far suggest the presence of at least four types of resistant cell lines. Overall, the information presented in this paper supplements our understanding of AI function, and such information can be valuable for the development of treatment strategies against AI resistant breast cancers.