The discovery and mechanism of action of letrozole

Regulation of aromatase in cancer

The regulation of aromatase, an enzyme involved in the biosynthesis of estrogen in normal and cancer cells, has been associated with growth factor signaling and immune response modulation. The tissue-specific regulatory roles of these factors are of particular importance as local aromatase expression is strongly linked to cancer development/progression and disease outcomes in patients. Therefore, aromatase has become a chemotherapeutic target and aromatase inhibitors (AIs) are used in the clinic for treating hormone-dependent cancers. Although AIs have shown promising results in the treatment of cancers, the emerging increase in AI-resistance necessitates the development of new and improved targeted therapies. This review discusses the role of tumor and stromal-derived growth factors and immune cell modulators in regulating aromatase. Current single-agent and combination therapies with or without AIs targeting growth factors and immune checkpoints are also discussed. This review highlights recent studies that show new connections between growth factors, mediators of immune response, and aromatase regulation.

Recent Discoveries of Macromolecule- and Cell-Based Biomarkers and Therapeutic Implications in Breast Cancer

Breast cancer is the most commonly diagnosed cancer type and the leading cause of cancer-related mortality in women worldwide. Breast cancer is fairly heterogeneous and reveals six molecular subtypes: luminal A, luminal B, HER2+, basal-like subtype (ER−, PR−, and HER2−), normal breast-like, and claudin-low. Breast cancer screening and early diagnosis play critical roles in improving therapeutic outcomes and prognosis. Mammography is currently the main commercially available detection method for breast cancer; however, it has numerous limitations. Therefore, reliable noninvasive diagnostic and prognostic biomarkers are required. Biomarkers used in cancer range from macromolecules, such as DNA, RNA, and proteins, to whole cells. Biomarkers for cancer risk, diagnosis, proliferation, metastasis, drug resistance, and prognosis have been identified in breast cancer. In addition, there is currently a greater demand for personalized or precise treatments; moreover, the identification of novel biomarkers to further the development of new drugs is urgently needed. In this review, we summarize and focus on the recent discoveries of promising macromolecules and cell-based biomarkers for the diagnosis and prognosis of breast cancer and provide implications for therapeutic strategies.

Suppressed estrogen supply via extra-ovarian progesterone receptor membrane component 1 in menopause

In post-menopausal women, intra-mammary estrogen, which is converted from extra-ovarian estrone (E1), promotes the growth of breast cancer. Since the aromatase inhibitor letrozole does not suppress 17β-estradiol (E2) production from E1, high intra-mammary E1 concentrations impair letrozole's therapeutic efficacy. Progesterone receptor membrane component 1 (Pgrmc1) is a non-classical progesterone receptor associated with breast cancer progression. In the present study, we introduced a Pgrmc1 heterozygous knockout (hetero KO) murine model exhibiting low Pgrmc1 expression, and observed estrogen levels and steroidogenic gene expression. Naïve Pgrmc1 hetero KO mice exhibited low estrogen (E2 and E1) levels and low progesterone receptor (PR) expression, compared to wild-type mice. In contrast, Pgrmc1 hetero KO mice that have been ovariectomized (OVX), including letrozole-treated OVX mice (OVX-letrozole), exhibited high estrogen levels and PR expression. Increased extra-ovarian estrogen production in Pgrmc1 hetero KO mice was observed with the induction of steroid sulfatase (STS). In MCF-7 cell, letrozole suppressed PR expression, but PGRMC1 knockdown increased PR and STS expression. Our presented results highlight the important role of Pgrmc1 in modulating estrogen production when ovary-derived estrogen is limited, thereby suggesting a potential therapeutic approach for letrozole resistance.

Aromatase Inhibitors for the Treatment of Breast Cancer: A Journey from the Scratch

Background:

Estrogens are essential for the growth of breast cancer in the case of premenopausal as well as in postmenopausal women. However, most of the breast cancer incidences are reported in postmenopausal women and the concurrent risk surges with an increase in age. Since the enzyme aromatase catalyses essential steps in estrogen biosynthesis, Aromatase Inhibitors (AIs) are effective targeted therapy in patients with Estrogen Receptor positive (ER+) breast cancer. AIs are more effective than Selective Estrogen Receptor Modulators (SERMs) because they block both the genomic and nongenomic activities of ER. Till date, first, second and third-generation AIs have been approved by the FDA. The third-generation AIs, viz. Letrozole, Anastrozole, Exemestane, are currently used in the standard treatment for postmenopausal breast cancer.

Methods:

Data were collected from Medline, PubMed, Google Scholar, Science Direct through searching of keywords: ‘aromatase’, ‘aromatase inhibitors’, ‘breast cancer’, ‘steroidal aromatase inhibitors’, ‘non-steroidal inhibitors’ and ‘generations of aromatase inhibitors’.

Results:

In the current scenario of breast cancer chemotherapy, AIs are the most widely used agents which reveal optimum efficacy along with the least side effects. Keeping in view the prominence of AIs in breast cancer therapy, this review covered the detailed description of aromatase including its role in the biosynthesis of estrogen, biochemistry, gene expression, 3D-structure, and information of reported AIs along with their role in breast cancer treatment.

Conclusion:

AIs are the mainstream solution of the ER+ breast cancer treatment regimen with the continuous improvement of human understanding of the importance of a healthy life of women suffering from breast cancer.

Inhibition of brain 17β-estradiol synthesis by letrozole induces cognitive decline in male and female rats

BACKGROUND

Hippocampal aromatase is responsible for local synthesis of 17β-estradiol (E2) that has much higher concentrations than serum levels in males and females. Letrozole, an aromatase inhibitor, passes through the brain barriers, distributes to the brain, and affects local E2 synthesis. Here, the effects of intra-cerebroventricular (ICV) letrozole administration in the presence and absence of gonads were examined on the cognitive abilities of male and female rats.

METHOD

Animals received intra-ICV injection of letrozole or vehicle for 14 consecutive days. Spatial working memory, novel object recognition memory, and anxiety-related behavior, were evaluated using Y-maze, object recognition test, and elevated plus maze, respectively. The E2 levels in the serum and hippocampal tissue were measured by the ELISA technique. RT-PCR was performed to assess the hippocampal estrogen receptors (ER) expression. Moreover, letrozole effect on neuronal activity of CA1 pyramidal neurons was studied by in vivo single-unit recording.

RESULTS

Letrozole (0.2, 0.4, and 0.8 µg) significantly decreased the hippocampal E2 levels compared to the vehicle group. Letrozole caused cognitive impairments in a dose-dependent manner in male and female rats in the presence or absence of gonads. Dose-response analysis revealed that the minimum effective dose of letrozole on the behavioral measures was 0.4 μg. Letrozole also caused an up-regulation of ERα and ERβ and a down-regulation of GPR30 gene expression. The firing rate of pyramidal neurons was reduced by letrozole in gonadal-intact animals.

CONCLUSION

The detrimental effects of letrozole treatment on cognitive abilities in the presence and absence of gonads indicate that local E2 synthesis in the hippocampus is a crucial factor in normal cognitive performance. The suppressive effect of letrozole on hippocampal neuronal firing might alter synaptic plasticity that is critical for memory formation. These data potentially suggest that memory deficits following letrozole administration should be monitored.

A review of the physiology behind letrozole applications in infertility: are current protocols optimal?

Letrozole is a targeted aromatase inhibitor which has primarily been used in post-menopausal women with breast cancer. Recently, it has been utilized in infertile pre-menopausal women because of its ability to enhance FSH production for ovulation induction. However, the ovarian follicle’s response to FSH is only a part of the endocrine events occurring in a developing follicle. The health of the small antral follicles is driven primarily by androgens, which contribute to granulosa cell mitosis, sensitivity to FSH, and resistance to atresia. In contrast, elevated androgens in the late antral to pre-ovulatory follicle have a negative impact on follicle health and lead to atresia and cystic follicle formation. This ovarian physiologic data suggests that current applications of letrozole to infertility may be squandering some of the primary benefits available in using letrozole to promote follicle development. Four applications of letrozole to infertility that have appeared in the medical literature are reviewed. Androgen-related benefits are reviewed and various questions put forward about how letrozole could be more effectively used to help patients in these settings.

Association between BMI, vitamin D, and estrogen levels in postmenopausal women using adjuvant letrozole: a prospective study

Studies have suggested that women with elevated BMI or 25-OH vitamin D levels may derive less benefit from AIs versus tamoxifen. We prospectively investigated whether high BMI or 25-OH vitamin D levels were associated with higher estrogen levels in post-menopausal women receiving standard adjuvant letrozole (2.5 mg/day). Furthermore, we evaluated whether an increased dose of letrozole resulted in lower serum estrogens in women with BMI > 25 kg/m2. Correlation between entry BMI and day 29 serum biomarkers (estrogens, 25-OH vitamin D, insulin, CRP, leptin) was assessed in all patients. On day 29, participants with BMI > 25 kg/m2 switched to letrozole 5 mg/day for 4-weeks and blood was drawn upon completion of the study. The change in serum estrogen levels was assessed in these patients (BMI > 25 kg/m2). 112 patients completed days 1-28. The Pearson correlations of estradiol and estrone with BMI or serum 25-OH vitamin D levels were near zero (-0.04 to 0.07, p = 0.48-0.69). Similar results were obtained for correlation with markers of obesity (insulin, CRP, and leptin) with estradiol and estrone (-0.15 to 0.12; p = 0.11-0.82). Thirty-one patients (BMI > 25 kg/m2) completed the interventional component; Increasing the dose of letrozole did not further reduce estradiol or estrone levels (change 0.1 and 0.4 pmol/L respectively; p = 0.74 and 0.36). There was no observed association between markers of obesity (BMI, insulin, leptin, and CRP), serum 25-OH vitamin D levels and estradiol or estrone levels. Additionally, an increased dose of letrozole did not further reduce estradiol or estrone levels compared to the standard dose.

Effect of Letrozole on sperm parameters, chromatin status and ROS level in idiopathic Oligo/Astheno/Teratozoospermia

BACKGROUND

This study investigates the effect of letrozole on hormone profiles, semen parameters, body mass index (BMI), degree of oxidative stress and sperm chromatin integrity in men with idiopathic oligo/astheno/teratozoospermia (iOAT) and T:E₂ ratio ≤ 10.

MATERIALS AND METHODS

This study is a longitudinal, prospective, interventional and open-labelled clinical trial. Semen samples were collected from 20 iOAT men with low serum testosterone (T) to estradiol (E₂) ratio (T:E₂ ratio ≤ 10). The participants were treated with 2.5 mg letrozole orally per day for 3 months. Then, sperm parameters, hormone profiles, BMI, chromatin integrity and intracellular reactive oxygen species (ROS) level were assessed pre- and post- treatment. The chromatin integrity was evaluated by assessment of DNA fragmentation (with TUNEL assay) and protamine deficiency (with Chromomycin A3, CMA3). Also, the intracellular ROS levels were investigated by 2', 7'-dichlorodihydrofluorescein diacetate (DCFH-DA) staining. Finally, the differences between the parameters evaluated before and after letrozole treatment were analyzed with the t-test and the Wilcoxon signed-rank test.

RESULTS

Sperm concentration, percentage of sperm motility and its normal morphology increased significantly after letrozole treatment. Moreover, serum testosterone level increased but estradiol level decreased significantly following treatment. The mean of T:E2 ratio improved 1600%. Also, letrozole treatment significantly reduced the percentage of sperm TUNEL positivity and sperm CMA3 positivity. While no significant difference was observed between intracellular ROS levels and BMI before and after treatment. Finally, as a notable result, four spontaneous pregnancies (20%) were achieved after treatment.

CONCLUSIONS

Letrozole treatment can effectively increase spontaneous pregnancies by improving sperm parameters and sperm chromatin integrity in men with iOAT and T:E2 ratio ≤ 10.

TRIAL REGISTRATION

Trial registration: IRCT, IRCT20191030045283N1. Registered 16 November 2019 - Retrospectively registered, https://fa.irct.ir/user/trial/43484/view.

Role of aromatase activation on sodium arsenite-induced proliferation, migration, and invasion of MDA-MB-231 and MDA-MB-453 breast cancer cell lines

Arsenic is an endocrine disruptor that promotes breast cancer (BCa) development. Estrogen synthesis, through aromatase activation, is essential for BCa promotion and progression through activating the G-coupled estrogen receptor 1 (GPER1), regulating rapid nongenomic effects involved in cell proliferation and migration of BCa cells. Herein, was studied the role of aromatase activation and the GPER1 pathway on sodium arsenite-induced promotion and progression of MDA-MB-231 and MDA-MB-453 BCa cell lines. Our results demonstrated that 0.1 μM of sodium arsenite induces cell proliferation, migration, invasion, and stimulates aromatase activity of BCa cell lines MDA-MB-231, MDA-MB-453, MCF-7, but not in a nontumorigenic breast epithelial cell line (MCF-12A). Using letrozole (an aromatase inhibitor) and G-15 (a GPER1-selective antagonist), we demonstrated that sodium arsenite-induced proliferation and migration is mediated by induction of aromatase enzyme and, at least in part, by GPER1 activation in MDA-MB-231 and MDA-MB-453 cells. Sodium arsenite induced phosphorylation of Src that participated in sodium arsenite-induced aromatase activity, and -cell proliferation of MDA-MB-231 cell line. Overall, data suggests that sodium arsenite induces a positive-feedback loop, resulting in the promotion and progression of BCa cells, through induction of aromatase activity, E2 production, GPER1 stimulation, and Src activation.

Hydrogen Isotope Exchange Catalyzed by Ru Nanocatalysts: Labelling of Complex Molecules Containing N-Heterocycles and Reaction Mechanism Insights

Ruthenium nanocatalysis can provide effective deuteration and tritiation of oxazole, imidazole, triazole and carbazole substructures in complex molecules using D₂ or T₂ gas as isotopic sources. Depending on the substructure considered, this approach does not only represent a significant step forward in practice, with notably higher isotope uptakes, a broader substrate scope and a higher solvent applicability compared to existing procedures, but also the unique way to label important heterocycles using hydrogen isotope exchange. In terms of applications, the high incorporation of deuterium atoms, allows the synthesis of internal standards for LC‐MS quantification. Moreover, the efficacy of the catalyst permits, even under subatmospheric pressure of T₂ gas, the preparation of complex radiolabeled drugs owning high molar activities. From a fundamental point of view, a detailed DFT‐based mechanistic study identifying undisclosed key intermediates, allowed a deeper understanding of C−H (and N−H) activation processes occurring at the surface of metallic nanoclusters.

The strength of evidence supporting luteal phase progestogen after assisted reproduction: A systematic review with reference to trial registration and pre-specified endpoints

OBJECTIVE

To measure the potential for outcome switching and selective reporting, in trials of luteal phase progestogen in assisted reproduction.

STUDY DESIGN

Trials identified through Medline and Embase in August 2017 using the MeSH term "assisted reproductive technology, luteal phase support" and associated text words. Randomised controlled trials (RCTs) comparing progestogen of any type, dose, and route of administration, with placebo or no treatment as luteal phase support in subfertile women undergoing in vitro fertilization (IVF) or intrauterine insemination (IUI). Eight trials after IVF and eleven after IUI, involving 1040 and 2764 participants respectively, were included.

RESULTS

None of the eight trials of progestogen therapy after IVF had been registered. Only 5/11 trials of progestogen after IUI had been registered, and only two of these prospectively. One of these had a registered primary outcome of "pregnancy sac plus heartbeat", but reported "pregnancy sac alone"; we judged this as an altered primary outcome. Three other trial had a registered primary outcome of "clinical pregnancy undefined" and reported "intra or extra-uterine pregnancy with a heartbeat"; we judged this alteration as minimal. That trial was negative. Overall, 26 different outcomes had been reported by the various trials. The three outcomes reported most often were pregnancy undefined (9/19), miscarriage (11/19) and clinical pregnancy (9/19). This suggests considerable potential for selective outcome reporting or outcome switching.

CONCLUSION

Apart from one negative trial, none of the evidence on luteal phase progestogen after assisted reproduction comes from prospectively registered trials: a slender reed indeed.

Effects of anastrozole on Ki-67 antigen expression in the vaginal epithelium of female rats in persistent estrus

OBJECTIVES

Aromatase inhibitors are the first-choice drugs for the treatment of hormone sensitive breast cancer. However, in addition to the scarcity of studies, there are controversies about their effects on vaginal epithelial cell proliferation in rats, especially those in persistent estrus.

METHODS

To investigate vaginal epithelial cell proliferation by Ki-67 antigen expression, persistent estrus was induced in 42 randomly selected rats. These rats were randomly divided into 2 groups: group I (control, n=21), which received 0.1 mL of propylene glycol (vehicle) daily, and group II (experimental, n=21), which received 0.5 mg/kg or 0.125 mg/day of anastrozole diluted with 0.1 mL of propylene glycol.

RESULTS

Light microscopy showed a higher concentration of cells with brown Ki-67 stained nuclei in the control compared to the experimental group. The mean percentage of Ki-67 stained nuclei per 500 cells in the vaginal epithelium was 68.64±2.64 and 30.46±2.00 [mean±standard error of the mean (SEM)] in the control and experimental groups, respectively (p<0.003).

CONCLUSION

This study showed that anastrozole, at the dose and treatment duration selected, significantly decreased cell proliferation in the vaginal mucosa of the rats in persistent estrus.

Aberrant Regulation of RAD51 Promotes Resistance of Neoadjuvant Endocrine Therapy in ER-positive Breast Cancer

Breast cancer is one of the most common malignant cancers affecting females. Estrogen receptor (ER)-positive breast cancer is responsive to endocrine therapy. Although current therapies offer favorable prospects for improving survival, the development of resistance remains a severe problem. In this study, we explored the resistance mechanisms of ER-positive breast cancer to neoadjuvant endocrine therapy. Microarray data of GSE87411 contained 109 pairs of samples from Z1031 trial, including untreated samples and post-treated samples with neoadjuvant aromatase inhibitor (AI) therapy. The differentially expressed genes (DEGs) were obtained from two different comparisons: untreated samples versus post-treated samples with AIs, and post-treated samples sensitive versus resistant to AIs. Multiple bioinformatic methods were applied to evaluate biological function, protein-protein network and potential binding between target protein and aromatase inhibitor. Then, regulation of gene expression, DNA methylation and clinicopathological factors of breast cancer were further analyzed with TCGA data. From GSE87411 dataset, 30 overlapped DEGs were identified. Cell division was found to be the main function of overlapped DEGs by functional enrichment and gene ontology (GO) analysis. RAD51 recombinase (RAD51), a key protein of homologous recombination, was detected to interact with BReast CAncer genes 2 (BRCA2). Moreover, according to the docking simulation, RAD51 might potentially bind to AIs. Overexpressed RAD51 was associated with hypermethylation of BRCA2, resistance to AIs and poor overall survival of patients with ER-positive breast cancer. Furthermore, RAD51 was found to be a better indicator than MKI67 for predicting resistance in neoadjuvant setting. The results indicated that methylation of BRCA2 led to incomplete suppression on RAD51, which caused an increased expression of RAD51, subsequently AI-resistance and poor prognosis in ER-positive breast cancer. RAD51 could be a new candidate used as a predicative marker and therapeutic target in neoadjuvant endocrine treatment.

Identification of Novel Scaffolds with Dual Role as Antiepileptic and Anti-Breast Cancer

Aromatase inhibitors with an $\mathrm{IC}_{50}$ IC 50 value ranging from 1.4 to 49.7 µM are known to act as antiepileptic drugs besides being potential breast cancer inhibitors. The aim of the present study is to identify novel antiepileptic aromatase inhibitors with higher activity exploiting the ligand-based pharmacophore approach utilizing the experimentally known inhibitors. The resultant Hypo1 consists of four features and was further validated by using three different strategies. Hypo1 was allowed to screen different databases to identify lead molecules and were further subjected to Lipinski's Rule of Five and ADMET to establish their drug-like properties. Consequently, the obtained 68-screened molecules were subjected to molecular docking by GOLD v5.2.2. Furthermore, the compounds with the highest dock scores were assessed for molecular interactions. Later, the MD simulation was applied to evaluate the protein backbone stabilities and binding energies adapting GROMACS v5.0.6 and MM/PBSA which was followed by the density functional theory (DFT), to analyze their orbital energies, and further the energy gap between them. Eventually, the number of Hit molecules was culled to three projecting Hit1, Hit2, and Hit3 as the potential lead compounds based on their highest dock scores, hydrogen bond interaction, lowest energy gap, and the least binding energies and stable MD results.

Aromatisation of steroids in the bivalve Mytilus trossulus

In this study, we demonstrated the presence of the enzymatic complex able to perform aromatization (estrogen synthesis) in both, the microsomal and mitochondrial fractions of gills and gonads from Mytilus trossulus. Based on in vitro experiments, we highlighted the importance of temperature as the limiting factor of aromatisation efficiency (AE) in mussels. After testing range of temperatures (4–23 °C), the highest AE was found during incubation at 8 °C and pH 7.6 (41.66 pmol/h/mg protein in gills and 58.37 pmol/h/mg protein in gonads). The results were confirmed during field studies where the most efficient aromatisation occurred in bivalves collected in spring while the least effective in those collected in winter. During in vitro studies, AE turned out to be more intensive in female gonads than in male gonads. The process was also more intensive in mitochondrial fraction than in microsomal one (62.97 pmol/h/mg protein in male gills and 73.94 pmol/h/mg protein in female gonads). Enzymatic complex (aromatase-like enzyme) catalysing aromatisation in mussels was found to be insensitive to inhibitory effect of selective inhibitors of mammalian aromatase such as letrozole and anastrazole, suggesting its different structure from vertebrate aromatase. Further in vivo studies using ¹³C-labeled steroids at 8 °C temperature window confirmed that bivalves are able to uptake testosterone and androstenedione from the ambient environment and metabolise them to estrone and 17β-estradiol thus confirming endogenous estrogen’ synthesis.

Sex hormones and stroke: Beyond estrogens

Stroke risk and poor stroke outcomes in postmenopausal women have usually beeen attributed to decreased levels of estrogen. However, two lines of evidence suggest that this hormone may not be solely responsible for elevated stroke risk in this population. First, the increased risk for CVD and stroke occurs much earlier than menopause at a time when estrogen levels are not yet reduced. Second, estrogen therapy has not successfully reduced stroke risk in all studies. Other sex hormones may therefore also contribute to stroke risk. Prior to menopause, levels of the gonadotrophin Follicle Stimulating Hormone (FSH) are elevated while levels of the gonadal peptide inhibin are lowered, indicating an overall decrease in ovarian reserve. Similarly, reduced estrogen levels at menopause significantly increase the ratio of androgens to estrogens. In view of the evidence that androgens may be unfavorable for CVD and stroke, this elevated ratio of testosterone to estrogen may also contribute to the postmenopause-associated stroke risk. This review synthesizes evidence from different clinical populations including natural menopause, surgical menopause, women on chemotherapy, and preclinical stroke models to dissect the role of ovarian hormones and stroke risk and outcomes.

Sex hormones modulate pathogenic processes in experimental traumatic brain injury

Clinical and animal studies have revealed sex-specific differences in histopathological and neurological outcome after traumatic brain injury (TBI). The impact of perioperative administration of sex steroid inhibitors on TBI is still elusive. Here, we subjected male and female C57Bl/6N mice to the controlled cortical impact (CCI) model of TBI and applied pharmacological inhibitors of steroid hormone synthesis, that is, letrozole (LET, inhibiting estradiol synthesis by aromatase) and finasteride (FIN, inhibiting dihydrotestosterone synthesis by 5α-reductase), respectively, starting 72 h prior CCI, and continuing for a further 48 h after CCI. Initial gene expression analyses showed that androgen (Ar) and estrogen receptors (Esr1) were sex-specifically altered 72 h after CCI. When examining brain lesion size, we found larger lesions in male than in female mice, but did not observe effects of FIN or LET treatment. However, LET treatment exacerbated neurological deficits 24 and 72 h after CCI. On the molecular level, FIN administration reduced calpain-dependent spectrin breakdown products, a proxy of excitotoxicity and disturbed Ca²⁺ homeostasis, specifically in males, whereas LET increased the reactive astrocyte marker glial fibrillary acid protein specifically in females. Examination of neurotrophins (brain-derived neurotrophic factor, neuronal growth factor, NT-3) and their receptors (p75^NTR , TrkA, TrkB, TrkC) revealed CCI-induced down-regulation of TrkB and TrkC protein expression, which was reduced by LET in both sexes. Interestingly, FIN decreased neuronal growth factor mRNA expression and protein levels of its receptor TrkA only in males. Taken together, our data suggest a sex-specific impact on pathogenic processes in the injured brain after TBI. Sex hormones may thus modulate pathogenic processes in experimental TBI.

Elucidating the interaction of letrozole with human serum albumin by combination of spectroscopic and molecular modeling techniques

Human serum albumin (HSA) is the most abundant protein found in human blood and is extensively employed in clinical applications such as hypovolemic shock treatment. Also, there has been a lot of attempt to use HSA as a carrier to deliver various drugs to their specific targets. Thus, clarify of structure, dynamics, functions, and features of HSA-drug complexes play an important role from the viewpoint of pharmaceutical and/or biochemical sciences. In this study, the interaction of letrozole, as a non-steroidal aromatase inhibitor, with HSA has been studied by combining different techniques such as UV-Vis, fluorescence spectroscopy, and computational methods. The binding of letrozole quenches the serum albumin fluorescence intensities. A clear decrease in fluorescence intensities of letrozole-HSA complex with the increase in temperature showed the static mode of fluorescence quenching. The results of Stern-Volmer procedure analysis showed that letrozole is bound only to a site from the HSA. The results of thermodynamic analysis showed that reaction between HSA and letrozole is spontaneous and exothermic. Furthermore, by monitoring the intrinsic fluorescence and using site markers competitive measurement, the binding of letrozole in the neighborhood of Sudlow's site I of HSA has been proved. Finally, computational methods substantiated the experimental findings and it was revealed that letrozole was bound to Arg-209, Trp-214, Ala-350, and Gly-238 residues of subdomain IIA and IIIA of HSA, respectively.

Preclinical and phase I clinical studies of KW-2450, a dual IGF-1R/IR tyrosine kinase inhibitor, in combination with lapatinib and letrozole

Background:

KW-2450 is an oral dual insulin-like growth factor-1 receptor/insulin receptor tyrosine kinase inhibitor. We investigated the in vitro and in vivo preclinical activity of KW-2450 plus lapatinib and letrozole and conducted a phase I trial of the triple-drug combination in one male and 10 postmenopausal female patients with advanced/metastatic hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-positive breast cancer.

Methods:

A series of in vitro and in vivo animal studies was undertaken of KW-2450 in combination with lapatinib and hormonal agents. The phase I trial was conducted to establish the safety, tolerability, and recommended phase II dose (RP2D) of KW-2450 administered in combination with lapatinib and letrozole.

Results:

Preclinical studies showed KW-2450 and lapatinib act synergistically to induce in vitro apoptosis and inhibit growth of HER2-positive MDA-MB-361 and BT-474 breast cancer cell lines. This combined effect was confirmed in vivo using the MDA-MB-361 xenograft model. KW-2450 showed synergistic in vitro growth inhibition with letrozole and 4-hydroxytamoxifen in ER-positive MCF-7 breast cancer cells and MCF-7-Ac1 aromatase-transfected MCF-7 cells. In the phase I study, dose-limiting toxicity (DLT; grade 3 rash and grade 3 hyperglycemia, respectively) occurred in two of three patients at the dose of KW-2450 25 mg/day plus lapatinib 1500 mg/day and letrozole 2.5 mg/day. The RP2D of the triple-drug combination was established as KW-2450 25 mg/day, lapatinib 1250 mg/day, and letrozole 2.5 mg/day with no DLT at this dose level.

Conclusions:

The proposed phase II study of the RP2D for the triple-drug combination did not progress because of anticipated difficulty in patient enrollment and further clinical development of KW-2450 was terminated.

Clinical and molecular aspects of breast cancer: Targets and therapies

Breast Cancer is a complex disease characterized by the occurrence of multiple molecular alterations. Currently, some molecular markers are in use for breast cancer diagnostic, prognostic, and predictive purposes. Thus, genetic signatures are available for improving the decision-making. The biomarkers are also essential as therapeutic approaches, but many questions remain due to the lack of efficacy on breast cancer treatment, mainly for triple-negative breast cancer subtype. Since the genetic profile of breast cancer can also be related to different ethnic groups and geographic areas, the reference populations of the genetic assays and clinical trials need to include a broader population beyond the European and North American patients. In this review, we analyzed the current and potential molecular markers that could help to improve the strategies for breast cancer therapy.

Maternal fructose intake disturbs ovarian estradiol synthesis in rats

AIMS

Recent increases in fructose consumption have raised concerns regarding the potential adverse intergenerational effects, as maternal fructose intake may induce physiological dysfunction in offspring. However, no reports are available regarding the effect of excess maternal fructose on reproductive tissues such as the ovary. Notably, the maternal intrauterine environment has been demonstrated to affect ovarian development in the subsequent generation. Given the fructose is transferred to the fetus, excess fructose consumption may affect offspring ovarian development. As ovarian development and its function is maintained by 17β-estradiol, we therefore investigated whether excess maternal fructose intake influences offspring ovarian estradiol synthesis. Rats received a 20% fructose solution during gestation and lactation. After weaning, offspring ovaries were isolated.

KEY FINDINGS

Offspring from fructose-fed dams showed reduced StAR and P450(17α) mRNA levels, along with decreased protein expression levels. Conversely, attenuated P450arom protein level was found in the absence of mRNA expression alteration. Consistent with these phenomena, decreased circulating levels of estradiol were observed. Furthermore, estrogen receptor α (ERα) protein levels were also down-regulated. In accordance, the mRNA for progesterone receptor, a transcriptional target of ERα, was decreased. These results suggest that maternal fructose might alter ovarian physiology in the subsequent generation.

Variation in CYP2A6 Activity and Personalized Medicine

The cytochrome P450 2A6 (CYP2A6) enzyme metabolizes several clinically relevant substrates, including nicotine-the primary psychoactive component in cigarette smoke. The gene that encodes the CYP2A6 enzyme is highly polymorphic, resulting in extensive interindividual variation in CYP2A6 enzyme activity and the rate of metabolism of nicotine and other CYP2A6 substrates including cotinine, tegafur, letrozole, efavirenz, valproic acid, pilocarpine, artemisinin, artesunate, SM-12502, caffeine, and tyrosol. CYP2A6 expression and activity are also impacted by non-genetic factors, including induction or inhibition by pharmacological, endogenous, and dietary substances, as well as age-related changes, or interactions with other hepatic enzymes, co-enzymes, and co-factors. As variation in CYP2A6 activity is associated with smoking behavior, smoking cessation, tobacco-related lung cancer risk, and with altered metabolism and resulting clinical responses for several therapeutics, CYP2A6 expression and enzyme activity is an important clinical consideration. This review will discuss sources of variation in CYP2A6 enzyme activity, with a focus on the impact of CYP2A6 genetic variation on metabolism of the CYP2A6 substrates.

Letrozole Determination by Capillary Zone Electrophoresis and UV Spectrophotometry Methods

Objective: Letrozole is a highly potent oral nonsteroidal aromatase inhibitor triazole derivative. The aim of this study was to quantify letrozole from bulk, pharmaceutical formulation, and spiked urine samples by developing a simple, rapid and cost effective capillary electrophoresis method. Methods: A capillary zone electrophoresis method was optimized and validated. Additionally, an UV spectrophotometry method was used for comparing results. Results:The capillary zone electrophoresis method using a 90 mM sodium tetraborate background electrolyte proved to be an efficient method for determination of letrozole in a very short time, less than 2 minutes, using 20 kV voltage, 50 mbar/2 seconds pressure and 50°C temperature as optimum parameters. Additionally, the UV spectrophotometry method proved to be simple and efficient to quantify letrozole from bulk material and pharmaceutical formulation with linearity of response between 5 to 20 μg·mL-1 concentrations. For both methods, validation parameters, including linearity, detection and quantification limits were determined. Also we proved that our electrophoretic method has potential in analyzing letrozole from biological samples, obtaining encouraging results on estimation of letrozole from spiked urine samples without any special treatment. Conclusions: To quantify letrozole from bulk material, pharmaceutical preparations, and spiked urine samples the capillary zone electrophoresis method using a tetraborate sodium background electrolyte has proven to be simple and appropriate. Also a simple UV spectrophotometric method has been developed and validated for the same purposes.

General and Mild Nickel-Catalyzed Cyanation of Aryl/Heteroaryl Chlorides with Zn(CN)2: Key Roles of DMAP

A new and general nickel-catalyzed cyanation of hetero(aryl) chlorides using less toxic Zn(CN)₂ as the cyanide source has been developed. The reaction relies on the use of inexpensive NiCl₂·6H₂O/dppf/Zn as the catalytic system and DMAP as the additive, allowing the cyanation to occur under mild reaction conditions (50-80 °C) with wide functional group tolerance. DMAP was found to be crucial for successful transformation, and the reaction likely proceeds via a Ni(0)/Ni(II) catalysis based on mechanistic studies. The method was also successfully extended to aryl bromides and aryl iodides.

Use of anastrozole in the chemoprevention and treatment of breast cancer: A literature review

Summary Aromatase inhibitors have emerged as an alternative endocrine therapy for the treatment of hormone sensitive breast cancer in postmenopausal women. The use of third-generation inhibitors represented by exemestane, letrozol and anastrozole is currently indicated. Anastrozole is a nonsteroidal compound and a potent selective inhibitor of the aromatase enzyme. Although a few studies have shown that its pharmacodynamic and pharmacokinetic properties may be affected by interindividual variability, this drug has been recently used in all configurations of breast cancer treatment. In metastatic disease, it is currently considered the first-line treatment for postmenopausal women with estrogen receptor-positive breast tumors. Anastrozole has shown promising results in the adjuvant treatment of early-stage breast cancer in postmenopausal women. It has also achieved interesting results in the chemoprevention of the disease. Therefore, due to the importance of anastrozole both for endocrine treatment and chemoprevention of hormone-sensitive breast cancer in postmenopausal women, we proposed the current literature review in the SciELO and PubMed database of articles published in the last 10 years.

Obesity and Breast Cancer Prognosis: Evidence, Challenges, and Opportunities

Purpose To summarize the evidence of an association between obesity and breast cancer prognosis. Methods We reviewed the literature regarding overweight and obesity and breast cancer survival outcomes, overall and with regard to breast cancer subtypes, breast cancer therapies, biologic mechanisms, and possible interventions. We summarize our findings and provide clinical management recommendations. Results Obesity is associated with a 35% to 40% increased risk of breast cancer recurrence and death and therefore poorer survival outcomes. This is most clearly established for estrogen receptor-positive breast cancer, with the relationship in triple-negative and human epidermal growth factor receptor 2-positive subtypes less well established. A range of biologic mechanisms that may underlie this association has been identified. Weight loss and lifestyle interventions, as well as metformin and other obesity-targeted therapies, are promising avenues that require further study. Conclusion Obesity is associated with inferior survival in breast cancer. Understanding the nature and mechanisms of this effect provides an important opportunity for interventions to improve the diagnosis, treatment, and outcomes of obese patients with breast cancer.

SPE-UPLC-MS/MS assay for determination of letrozole in human plasma and its application to bioequivalence study in healthy postmenopausal Indian women

A rapid and sensitive ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method is described for determination of letrozole in human plasma. Following solid phase extraction (SPE) of letrozole and letrozole-d4 on Orochem DVB-LP cartridges, chromatography was performed on Acquity UPLC BEH C₁₈ (50 mm×2.1 mm, 1.7 µm) column using methanol-0.1% formic acid in water (85:15, v/v) as the mobile phase. Detection was carried out on a triple quadrupole mass spectrometer with an electrospray source, operated under positive ionization mode. Quantitation of letrozole and letrozole-d4 was done using multiple reaction monitoring (MRM) following the transitions at m/z 286.2→217.0 and m/z 290.2→221.0, respectively. The calibration plots were linear through the concentration range of 0.10-100 ng/mL (r²≥0.9990) using 100 µL human plasma. The extraction recovery of letrozole ranged from 94.3% to 96.2% and the intra-batch and inter-batch precision was ≤5.2%. The method was successfully applied to a bioequivalence study of letrozole after oral administration of 2.5 mg tablet formulation to 16 healthy postmenopausal Indian women. The assay reproducibility was also established through incurred sample reanalysis (ISR) of 74 subject samples.

Acute inhibition of neurosteroid estrogen synthesis suppresses status epilepticus in an animal model

Status epilepticus (SE) is a common neurological emergency for which new treatments are needed. In vitro studies suggest a novel approach to controlling seizures in SE: acute inhibition of estrogen synthesis in the brain. Here, we show in rats that systemic administration of an aromatase (estrogen synthase) inhibitor after seizure onset strongly suppresses both electrographic and behavioral seizures induced by kainic acid (KA). We found that KA-induced SE stimulates synthesis of estradiol (E2) in the hippocampus, a brain region commonly involved in seizures and where E2 is known to acutely promote neural activity. Hippocampal E2 levels were higher in rats experiencing more severe seizures. Consistent with a seizure-promoting effect of hippocampal estrogen synthesis, intra-hippocampal aromatase inhibition also suppressed seizures. These results reveal neurosteroid estrogen synthesis as a previously unknown factor in the escalation of seizures and suggest that acute administration of aromatase inhibitors may be an effective treatment for SE.

DOI:http://dx.doi.org/10.7554/eLife.12917.001

Seizures occur when connected groups of cells in the brain become over-active and fire together. Current anti-seizure medications work by reducing brain activity generally. Although this is often effective in controlling seizures, it can also lead to negative side effects like drowsiness, dizziness or difficulty concentrating. A better alternative would be to target a factor that promotes activity especially during seizures.

Most people think of estrogens as being female sex hormones. However, estrogens are also made in the brain of both sexes, where they could promote activity during seizures. Sato and Woolley therefore set out to test a two-part hypothesis: that seizures stimulate the production of estrogen in the brain, and that inhibiting this production process just as seizures begin would make seizures less severe.

Sato and Woolley studied male and female rats and found that in both sexes, seizures stimulate the production of estrogens in the hippocampus – a part of the brain that is often involved in seizures. Because estrogens are known to increase the activity of cells in the hippocampus, this suggested that estrogens that are produced in the brain during seizures could make seizures worse. Sato and Woolley tested this by injecting rats with a drug that inhibits estrogen production, called an aromatase inhibitor, shortly after seizures began. The drug strongly suppressed seizures, whereas control rats that did not receive the injection continued to have seizures.

Overall, Sato and Woolley show that the production of estrogen in the brain escalates seizure activity, and suggest that aromatase inhibitors may be useful for controlling seizures. Several questions remain that require further study. How does seizure activity lead to estrogen being made in the brain? How do estrogen levels go back down after a seizure? What circumstances other than seizures stimulate brain estrogen production, and what roles does this production process play in activity that is not related to seizures?

DOI:http://dx.doi.org/10.7554/eLife.12917.002

The ALTERNATE trial: assessing a biomarker driven strategy for the treatment of post-menopausal women with ER+/Her2- invasive breast cancer

The Alliance for Clinical Trials in Oncology cooperative group has designed a phase III neoadjuvant clinical trial (ALTERNATE trial) which randomizes women with cT2-4 N0-3 M0 ER+/Her2- invasive breast cancer to either anastrozole, fulvestrant or its combination to assess a biomarker-driven treatment strategy to identify women with a low risk of disease recurrence. This strategy incorporates the findings that: higher expression of the proliferation marker, Ki67, after 2 weeks of neoadjuvant endocrine therapy (ET), is associated with poor recurrence-free survival, and that patients with surgical findings of pT1/2, pN0 disease, Ki67 ≤2.7% and ER Allred score of 3-8 after neoadjuvant ET have extremely low recurrence rates. We present a description and rationale for the design of this trial.

DFT computations on the hydrogen bonding interactions between methacrylic acid-trimethylolpropane trimethacrylate copolymers and letrozole as drug delivery systems

The hydrogen bonding interactions between letrozole (Let) anticancer drug and three copolymers of methacrylic acid-trimethylolpropane trimethacrylate (M1–M3 as molecular imprinted polymers) were studied using density functional theory (DFT) at both B3LYP and B3PW91 levels. The binding energies were corrected for the basis set superposition error (BSSE) and zero-point vibrational energies (ZPVE) so that the most negative [Formula: see text] were measured for compounds 7 and 8 formed between M1 copolymer and endocyclic N1 and N2 atoms of drug, respectively. Also, among complexes 13–15 in which two copolymers were contributed in the formation of O–H[Formula: see text]N bonds with the drug, compound 13 (containing two M1 copolymers) showed the highest [Formula: see text] value. The interactions of all copolymers with drug were exergonic (spontaneous interaction) and exothermic. The QTAIM data supported the covalent character of the C–N, C–H, N–N, C–O, O–H and O–H[Formula: see text]N bonds, the intermediate nature of C[Formula: see text]N and C[Formula: see text]O bonds while the electrostatic character of C–H[Formula: see text]O, HC[Formula: see text]HC and CH[Formula: see text]N interactions. According to the [Formula: see text], [Formula: see text] and [Formula: see text] values, it was suggested that t complexes 7 and 8 (among two particles systems) as well as complex 13 (among three particles systems) can be the most promising drug delivery systems.

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

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

Development and validation of a rapid LC-MS/MS method to quantify letrozole in human plasma and its application to therapeutic drug monitoring

A selective, rapid, and sensitive liquid chromatography-tandem mass spectrometry(LC-MS/MS) method was developed and validated for the determination of letrozole (LTZ) in human plasma, using anastrozole as internal standard (IS). Sample preparation was performed by one-step protein precipitation with methanol. The analyte and IS were chromatographed on a reversed-phase YMC-ODS-C18 column (2.0 × 100 mm i.d., 3 µm) with a flow rate of 0.3 mL/min. The mobile phase consisted of water containing 0.1% formic acid (v/v) and methanol containing 0.1% formic acid (v/v). The mass spectrometer was operated in selected reaction monitoring mode through electrospray ionization ion mode using the transitions of m/z 286.2 → 217.1 for LTZ and m/z 294.1 → 225.1 for IS, respectively. The method was validated for selectivity, linearity, lower limit of quantitation, precision, accuracy, matrix effects and stability in accordance with the US Food and Drug Administration guidelines. Linear calibration curves were 1.0-60.0 ng/mL. Intra- and inter-batch precision (CV) for LTZ were <9.34%, and the accuracy ranged from 97.43 to 105.17%. This method was successfully used for the analysis of samples from patients treated with LTZ in the dose of 2.5 mg/day. It might be suitable for therapeutic drug monitoring of these patients and contribute to predict the risk of adverse reactions.

Progesterone levels in letrozole associated controlled ovarian stimulation for fertility preservation in breast cancer patients

STUDY QUESTION

Are progesterone levels after letrozole-associated controlled ovarian stimulation (COS) for fertility preservation in breast cancer patients, lower than after standard in vitro fertilization (IVF) cycles?

SUMMARY ANSWER

During the luteal phase of letrozole-associated COS cycles (triggered with human chorionic gonadotrophin (hCG)) progesterone levels are similarly elevated to those obtained after standard COS without letrozole.

WHAT IS KNOWN ALREADY

Current fertility preservation strategies for breast cancer patients include association of COS with the aromatase inhibitor letrozole to harvest several mature oocytes while maintaining low estradiol levels. Data on progesterone levels are however lacking despite growing evidence of the role of progesterone in breast tumorigenesis.

STUDY DESIGN, SIZE, DURATION

This is a prospective observational study comparing estradiol and progesterone levels of 21 breast cancer patients undergoing letrozole-associated COS with 21 infertile patients undergoing standard COS for IVF and/or intra cytoplasmic sperm injection (ICSI).

PARTICIPANTS/MATERIALS, SETTING, METHODS

All patients underwent COS with a GnRH antagonist protocol. In the fertility preservation group, ovulation induction was started in the follicular or luteal phase depending on the chemotherapy schedule and in 10 cases a GnRH antagonist was administered during luteal phase to induce luteolysis. Final oocyte maturation was induced by hCG in all patients. Estradiol and progesterone levels were measured on the day of hCG, at oocyte retrieval, and on days 3 and 8 after oocyte retrieval. Hormone levels in fertility preservation patients were compared with those observed in infertility patients.

MAIN RESULTS AND THE ROLE OF CHANCE

While estradiol levels were significantly lower in the fertility preservation group compared with the control group (P < 0.001), progesterone levels were similar at all times, including patients receiving a GnRH antagonist during the luteal phase.

LIMITATIONS, REASONS FOR CAUTION

The studied populations (breast cancer and infertile patients) are different, which may induce selection bias. The small sample size limits the study's statistical power and the possibility to perform multivariate analysis. Recruitment of the study and control patients was completed at the same time; however, enrollment of controls started at a later time.

WIDER IMPLICATIONS OF THE FINDINGS

While the use of letrozole in fertility preservation patients has a favorable effect on estrogen levels, no benefit is seen for progesterone levels which are high and comparable with progesterone levels after standard COS in IVF patients. As progesterone has been associated with tumor cell proliferation, caution is mandatory. Modified protocols including GnRH agonist triggering should be investigated.

Predicting the reactivity of nitrile-carrying compounds with cysteine: a combined computational and experimental study

Here, we report on a mechanistic investigation based on DFT calculations and kinetic measures aimed at determining the energetics related to the cysteine nucleophilic attack on nitrile-carrying compounds. Activation energies were found to correlate well with experimental kinetic measures of reactivity with cysteine in phosphate buffer. The agreement between computations and experiments points to this DFT-based approach as a tool for predicting both nitrile reactivity toward cysteines and the toxicity of nitriles as electrophile agents.

Computational studies on the anastrozole and letrozole, effective chemotherapy drugs against breast cancer

In this paper, computational studies were carried out on anastrozole and letrozole, chemotherapy drugs used against breast cancer. Optimization and frequency calculations were performed at B3LYP/6-31G (d) basis set and vibrational frequencies were assignment. Single point calculations were performed at DFT method with a hybrid functional B3LYP/6-311G (d, p) basis set. Theoretical NMR data were obtained at DFT method with a hybrid functional B3LYP/6-311G++ (2d, p) with GIAO (Gauge-Independent Atomic Orbital). IEF-PCM method was used as solvation model. NBO calculations were performed by the same basis set and calculation method with single point calculation. Global and localized reactivity parameters; fukui indices (f) chemical hardness (η), softness (S), chemical potential (μ), electronegativity (χ) and electrophilicity index (ω) were calculated. All computational parameters were compared with the experimental results obtained from the literature.

Optimum duration of neoadjuvant letrozole to permit breast conserving surgery

The aim of this multicenter, prospective, longitudinal phase IV study was to establish the optimal duration of neoadjuvant letrozole that would allow breast conservation surgery (BCS) in patients with early breast cancer who were initially unsuitable. Primary, invasive, estrogen-receptor- and/or progesterone-receptor-positive breast cancer patients, with large tumors (≥T2 i.e., >20 mm) not initially suitable for BCS, received 2.5 mg letrozole p.o. daily. Patients continued treatment until they became eligible for BCS, progressed, failed to meet criteria for BCS and withdrew for scheduled mastectomy, withdrew for other reasons, or completed 12 months of letrozole treatment without a BCS decision being made. A total of 146 patients were enrolled; seven patients who did not have a valid postbaseline tumor assessment were excluded from the final efficacy analysis. At study closure, 69 % of patients (96 of 139) were eligible for BCS. The median time to achieve a tumor response sufficient to allow BCS with neoadjuvant letrozole was 7.5 months (95 % CI 6.3-8.5 months). Letrozole was well tolerated, and most adverse events were mild-to-moderate (grade 1-2). The results from this trial suggest that extended letrozole therapy in the neoadjuvant setting (7.5 months), as opposed to conventional treatment of 4 months, is optimal to achieve maximum reduction in tumor volume sufficient for BCS.

Role of aromatase in sex-specific cerebrovascular endothelial function in mice

Stroke risk and outcome are strongly modified by estrogen. In addition to ovaries, estrogen is produced locally in peripheral tissue by the enzyme aromatase, and extragonadal synthesis becomes the major source of estrogen after menopause. Aromatase gene deletion in female mice exacerbates ischemic brain damage after stroke. However, it is not clear which cell type is responsible for this effect, since aromatase is expressed in multiple cell types, including cerebrovascular endothelium. We tested the hypothesis that cerebrovascular aromatase contributes to sex differences in cerebrovascular endothelial function. Cerebrocortical microvascular responses to the endothelium-dependent vasodilator ACh were compared between male and female wild-type (WT) and aromatase knockout (ArKO) mice by measuring laser-Doppler perfusion in vivo through a closed cranial window. Additional studies were performed in WT mice treated with the aromatase inhibitor fadrozole or vehicle. WT female mice had significantly greater responses to ACh compared with WT males (P < 0.001), which was associated with higher aromatase expression in female compared with male cerebral vessels (P < 0.05). ACh responses were significantly lower in ArKO compared with WT females (P < 0.05) and in WT females treated with fadrozole versus vehicle (P < 0.001). Conversely, ACh responses were significantly higher in ArKO versus WT males (P < 0.05). Levels of phosphorylated endothelial nitric oxide synthase (eNOS) were lower in ArKO versus WT female brains, but were not altered by aromatase deletion in males. We conclude that cerebrovascular endothelial aromatase plays an important and sexually dimorphic role in cerebrovascular function and that aromatase inhibitors in clinical use may have cardiovascular consequences in both males and females.

Chopping unfunctionalized carbon–carbon bonds: a new paradigm for the synthesis of organonitriles

Chopping of carbon–carbon bonds was very recently shown to be an efficient new strategy for the synthesis of organonitriles, as developed in this Highlight.