Selective Non-steroidal Aromatase Inhibitor Research Articles

Development of Solid Lipid Nanoparticles with Letrozole for Breast Cancer Treatment: in-vitro and in-vivo evaluation

Breast cancer (BC) is the most common cancer in women worldwide. Letrozole (LTZ) is a third-generation selective nonsteroidal aromatase inhibitor and one of many anticancer drugs. Conventional LTZ therapies for BC are often administered orally or parenterally and frequently result in severe systemic side effects. To improve this situation, efforts have been made for an advanced drug delivery system that accurately releases the drug at the target site and increases therapeutic efficacy with minimal side effects. Here, we report the delivery system based on poloxomer 188 as a platform for LTZ-based solid lipid nanoparticles (SLNs) in cancer cells. The particle size, PDI, ZP, and DEE % of optimally selected LTZ -SLNs (pH 7.4) were 82.16 ± 7.24 nm, 0.287 ± 0.05, -15.0 ± 8.83 mV, and 57.89 ± 1.22 %, respectively. The SEM of LTZ -SLNs shows hexagonal phase stacking with a nanoflock morphology. The TEM image clearly shows that the introduced LTZ -SLN drugs contain LTZ drugs inside the particles. After 48 hours, it was reported that the percentage of LTZ release was 82.34%. LTZ-SLNs showed significant cytotoxic properties with an IC50 of 2.22ug/ml. The results of histopatholgical study confirmed that LTZ-SLNs can minimize the cytotoxicity of LTZ. Overall, the prepared nanoformulation offers great potential for BC treatment.

Analysis of 17β-estradiol (E2) role in the regulation of corpus luteum function in pregnant rats: Involvement of IGFBP5 in the E2-mediated actions.

BackgroundIn several species, considerably higher levels of estradiol-17 (E2) are synthesized in the CL. E2 has been suggested to participate in the regulation of luteal steroidogenesis and luteal cell morphology. In pregnant rats, several experiments have been carried out to examine the effects of inhibition of luteal E2 synthesis on CL structure and function.MethodsDuring days 12–15 of pregnancy in rats, luteal E2 was inhibited by way of daily oral administration of anastrozole (AI), a selective non-steroidal aromatase inhibitor, and experiments were also performed with E2 replacement i.e. AI+ E2 treatments. Luteal tissues from different treatment groups were subjected to microarray analysis and the differentially expressed genes in E2 treated group were further examined for expression of specific E2 responsive genes. Additional experiments were carried out employing recombinant growth hormone preparation and flutamide, an androgen receptor antagonist, to further address the specificity of E2 effects on the luteal tissue.ResultsMicroarray analysis of CL collected on day 16 of pregnancy post AI and AI+E2 treatments showed significantly lowered cyp19a1 expression, E2 levels and differential expression of a number of genes, and several of them were reversed in E2 replacement studies. From the differentially expressed genes, a number of E2 responsive genes were identified. In CL of AI pregnant rats, non-significant increase in expression of igf1, significant increase in igbp5, igf1r and decrease in expression of Erα were observed. In liver of AI treated rats, igf1 expression did not increase, but GH treatment significantly increased expression that was further increased with AI treatment. In CL of GH and AI+GH treated rats, expression of igfbp5 was higher. Administration of flutamide during days 12–15 of pregnancy resulted in non-significant increase in igfbp5 expression, however, combination of flutamide+AI treatments caused increased protein expression. Expression of few of the molecules in PI3K/Akt kinase pathway in different treatments was determined.ConclusionsThe results suggest a role for E2 in the regulation of luteal steroidogenesis, morphology and proliferation. igfbp5 was identified as one the E2 responsive genes with important role in the mediation of E2 actions such as E2-induced phosphorylation of PI3K/Akt kinase pathway.Electronic supplementary materialThe online version of this article (doi:10.1186/s12958-016-0153-1) contains supplementary material, which is available to authorized users.

Rapid and Sensitive LC-MS/MS Assay for Quantitation of Letrozole Using Solid-Phase Extraction from Human Blood Plasma and Its Application to Pharmacokinetic Studies

A validated assay for quantitation of letrozole (selective non-steroidal aromatase inhibitor) in human blood plasma using tandem LC-MS/MS was proposed. Biological samples were processed beforehand by solid-phase extraction over SOLA cartridges. The chromatographic separation used a Zorbax Bonus-RP column and mobile phase MeCN:HCO2H (0.2% aqueous) in a 70:30 vol% ratio at flow rate 0.3 mL/min. Letrozole was determined using an Agilent 6410 – 2K triple quadrupole mass spectrometer with electrospray ionization at +4000 V and multiple reaction monitoring (+MRM) for letrozole (286.1 > 217.1 m/z) and for internal standard olanzapine (313 > 256 m/z). A calibration curve for letrozole in the concentration range 0.25 – 100 ng/mL was linear (correlation coefficient R = 0.9998.95%; confidence interval, 0.9995 – 0.9976) with a lowest limit of quantitation of 0.25 ng/mL. Validation of the method indicated that it was highly sensitive, specific, accurate, and precise. The analyte was stable under various conditions. The assay was successfully applied to clinical pharmacokinetics studies.

Quantitative Determination of Anastrozole by Liquid Chromatography–Tandem Mass Spectrometry

Anastrozole is a potent and selective non-steroidal aromatase inhibitor and is used for therapy of postmenopausal women with hormone-receptor-positive breast cancer. This paper provides a detailed description of the determination of anastrozole in human plasma by liquid chromatography–mass spectrometry (LC–MS–MS). Plasma-sample pretreatment involved solid-phase extraction using Accubond SPE ODS-C18 cartridges. Chromatographic separation was carried out on a Zorbax Bonus-RP column with a mobile phase consisting of aqueous formic acid (0.2%) (eluent A) and MeOH (eluent B) with a ratio A:B = 30:70 (v/v) that was supplied at flow rate 0.2 mL/min. Detection was performed on an Agilent 6410-2K triple quadrupole tandem mass spectrometer by multiple reaction monitoring in the preset mass range 294.2 → 225.1 using atmospheric-pressure chemical ionization in positive-ion mode. A calibration curve for anastrozole was linear (R2 ≥ 0.97) over the concentration range 0.5 – 20.0 ng/mL with a lower detection limit of 0.5 ng/mL. The described procedures can be applied successfully to both therapeutic monitoring of anastrozole and drug bioequivalence studies.

DRUG PROFILE OF ANASTROZOLE: AN AROMATASE INHIBITOR

Anastrozole is a selective non-steroidal aromatase inhibitor and is the first drug approved by FDA in adjuvant hormonal therapy. Anastrozole was proved superior to tamoxifen for the treatment of hormoneresponsive breast cancer. In this review, we have highlighted the profile of this drug including its pharmacodynamics, pharmacokinetics, drug interactions, clinical studies and side effects.

Novel Highly Potent and Selective Nonsteroidal Aromatase Inhibitors: Synthesis, Biological Evaluation and Structure−Activity Relationships Investigation

In further pursuing our search for potent and selective aromatase inhibitors, a new series of molecules was designed and synthesized, exploring possible structural modifications of a previously identified xanthone scaffold. Among them, highly potent compounds, with inhibitory activity in the low nanomolar range, were found. In particular, substitution of the heterocyclic oxygen atom in the xanthone core by a sulfur atom and/or increase in structure flexibility seemed to be favorable for the interaction with the enzyme.

Drug-induced pruritic micropapular eruption: anastrozole, a commonly used aromatase inhibitor

Anastrozole, a selective nonsteroidal aromatase inhibitor is widely used as an adjuvant therapy for postmenopausal women with early hormone-sensitive breast cancer. There are few reports on cutaneous side effects of anastrozole. It may induce subacute cutaneous lupus erythematosus, erythema nodosum, cutaneous vasculitis, and nondescript skin eruptions. A 68-year-old woman was prescribed anastrozole after surgical removal of her breast cancer and adjuvant radiation therapy. Two months later she experienced a generalized pruritic micropapular eruption. History, clinical presentation, histology and inadvertent re-exposure to the drug confirmed that anastrozole triggered the exanthem. Pruritic micropapular eruption is a typical pattern for a drug hypersensitivity reaction. Anastrozole should be added to the list of medications able to induce not only non-specific eruptions but the type of exanthem typically triggered by drugs.

Use of aromatase inhibitors to increase final height

During puberty in both sexes, the mechanism involved in epiphyseal fusion is mediated by the action of estrogen through a cascade of events including proliferation, differentiation, and apoptosis of chondrocytes. The enzyme P450 aromatase catalyzes the aromatization of C 19 androgens (androstenedione and testosterone) to C 18 estrogens (estrone and estradiol). Inhibition of estrogen action by aromatase inhibitors (AIs) appears to decelerate the process of growth plate fusion, and thus AIs may be used therapeutically to increase adult height. The clinical experience with AIs in the pediatric setting is limited to testolactone, fadrozole, letrozole, and anastrozole. Testolactone, a nonselective steroidal AI, has been used successfully as an adjunct to antiandrogen and gonadotropin-releasing hormone analogue (GnRHa), therapy for children with familial male-limited precocious puberty (FMPP) and congenital adrenal hyperplasia (CAH), and with some success in girls with McCune–Albright syndrome. The limitations of testolactone include its relatively low potency and the need for frequent dosing. Results of a randomized placebo-controlled trial in boys with delayed puberty treated with letrozole, a selective nonsteroidal AI, found that boys treated with letrozole + testosterone experienced delayed bone maturation and good growth response and achieved an increase in predicted adult height. In this study, only minor differences in bone density were seen between the placebo and letrozole treatment groups, both of which were receiving concomitant testosterone therapy. No adverse effects on testis size or inhibin B concentration were noted. The therapeutic value of AIs in growth promotion now remains to be substantiated in future controlled clinical trials.

The role of aromatase inhibitors in early breast cancer.

The role of hormonal therapy for the treatment of patients with early stage breast cancer has been evaluated in many studies. The results of these studies establish tamoxifen as the gold standard of hormonal therapy for the adjuvant treatment of hormone receptor-positive invasive breast cancer in pre- and postmenopausal women. Studies show tamoxifen reduces the risk of invasive breast cancer in women at increased risk for the disease, including women with ductal carcinoma in situ. Tamoxifen has adverse effects such as hot flashes, increased risk of uterine cancer in postmenopausal women, and rare occurrence of thromboembolic disease. Despite the multiple therapeutic roles of tamoxifen, alternatives are needed. Aromatase inhibitors (AI) are drugs with antiestrogenic activity. AIs function by inhibiting the peripheral conversion of adrenally synthesized androstenedione to estradiol through inhibition of the aromatase enzyme. AIs do not suppress estradiol synthesis by the ovary adequately. Therefore, AIs are effective in reducing circulating estradiol levels in postmenopausal women, but not premenopausal women. Selective nonsteroidal AIs, including anastrozole (Arimidex; AstraZeneca, Wilmington, DE) and letrozole (Femara; Novartis, East Hanover, NJ), and the steroidal AI exemestane (Aromasin; Pharmacia, Peapack, NJ) have been associated with increased specificity and improved therapeutic index compared to nonselective AIs such as aminoglutethamide. Nonsteroidal and steroidal AIs have demonstrated to be superior to megestrol acetate in second-line therapy of postmenopausal women with metastatic breast cancer, and selective nonsteroidal AIs have shown to be superior to tamoxifen in first-line therapy of postmenopausal women with metastatic breast cancer. The ATAC (Arimidex, tamoxifen, alone, or in combination) trial is the only published randomized trial comparing the efficacy of an AI to tamoxifen for the adjuvant treatment of women with early breast cancer. This large study showed that at a median follow-up time of 33 months, anastrozole alone results in significant improvement in disease-free survival rates, reduction in contralateral breast cancers, and increased tolerability, compared to tamoxifen in postmenopausal women. Although the long-term effects of AIs are not known, the early positive results of the ATAC trial led to the approval of anastrozole by the US Food and Drug Administration for use as adjuvant hormonal therapy for postmenopausal women with hormone receptor-positive invasive breast cancer. Thus, there is an alternative to tamoxifen for postmenopausal women with relative/absolute contraindications to tamoxifen use or patients who choose not to take tamoxifen because of its side-effect profile. New AIs may challenge the position of tamoxifen as the gold standard for the treatment of early stage breast cancer in postmenopausal women.

Anastrozole versus progestins/tamoxifen

Systemic therapy of breast cancer was introduced in 1896 by means of surgical ovariectomy [1]. Endocrine treatment is now widely accepted in advanced breast cancer with positive oestrogen or progesterone receptor status indicating endocrine dependency of the disease. Tamoxifen has been the treatment of choice for more than twenty years, due to it's favourable efficacy/tolerability ratio [2]. Several years ago, the third generation aromatase inhibitors have been introduced in the clinics [3]. Anastrozole is a potent selective non-steroidal aromatase inhibitor which can be administered orally as a once daily dose.

An overview of the use of non-steroidal aromatase inhibitors in the treatment of breast cancer

A number of potent and selective non-steroidal aromatase inhibitors are now available for the treatment of advanced breast cancer in postmenopausal women. In particular, anastrozole represents a significant advantage over earlier agents, such as aminoglutethimide and formestane, in terms of both efficacy and tolerability. These agents are now established as the second-line therapy of choice in postmenopausal women with advanced disease progressing on tamoxifen and, furthermore, data are now available on the efficacy and tolerability of anastrozole as first-line treatment of advanced breast cancer compared with tamoxifen. The full potential of the new-generation aromatase inhibitors in the treatment of breast cancer is currently being investigated in a large programme of clinical trials, including evaluation as neoadjuvant treatment in postmenopausal women with newly-diagnosed locally-advanced or large operable breast cancers, as first-line treatment of advanced breast cancer in postmenopausal women. Aromatase inhibitors have been available for over 20 years; the ability of these compounds to reduce circulating oestradiol levels has been shown to produce clinical benefit in postmenopausal women with advanced breast cancer. Early aromatase inhibitors, however, such as aminoglutethimide and formestane, were not specific for the aromatase enzyme and resulted in significant side-effects.

Role of aromatase inhibitors in advanced breast cancer.

A number of potent and selective non-steroidal aromatase inhibitors are now available for treatment of advanced breast cancer in postmenopausal women, of which anastrozole and letrozole, in particular, represent a significant advantage over the earlier agents in terms of both efficacy and tolerability. These agents are rapidly becoming established as the second-line therapy of choice in postmenopausal women with advanced disease, progressing on tamoxifen, and data on their efficacy as first-line treatment compared with tamoxifen will be available in the near future. Exemestane, a new, steroidal aromatase inhibitor which potentially lacks cross-resistance with non-steroidal agents is still in clinical development. The full potential of the new-generation aromatase inhibitors in the treatment of breast cancer is currently being investigated in a large program of clinical trials evaluating their use as adjuvant treatment following surgery in postmenopausal patients with early disease.

New selective nonsteroidal aromatase inhibitors: Synthesis and inhibitory activity of 2,3 or 5-( α-azolylbenzyl)-1 H-indoles

Six azolyl substituted indoles were synthesized and tested for their activity to inhibit two P450 enzymes: P450 arom and P450 17α. It was observed that the introduction of α-imidazolylbenzyl chain at carbon 3 or 5 on indole nucleus led to very active molecules. Compounds 22, 23 and especially 33 demonstrate very high potential against P450 arom. Under our assay conditions of high substrate concentration the IC 50 are 0.057, 0.0785 and 0.041 μM, respectively. These compounds are moderate inhibitors against P450 17α.

The role of selective non-steroidal aromatase inhibitors in future treatment strategies.

The major role of endocrine therapy in the treatment of early and advanced breast cancer should not be forgotten as an increasing number of new and potentially more exciting agents are introduced. Endocrine therapy generally has a more powerful effect than cytotoxic therapy in the treatment of breast cancer. Alternatives to tamoxifen, such as anastrozole (Arimidex), are now being considered, both in advanced disease and as adjuvant therapy, whether as single agents or in combination. Anastrozole has a low side-effect profile and is becoming a drug of choice for second-line therapy in postmenopausal women with advanced breast cancer. The present use of anastrozole in postmenopausal women with advanced breast cancer includes second-line treatment after tamoxifen and first-line treatment after tamoxifen has been used as an adjuvant treatment. It may also be used when tamoxifen is not tolerated. The future potential of anastrozole is currently being investigated in a programme of clinical trials in postmenopausal women, including first-line treatment of advanced disease and as an adjuvant treatment for early breast cancer.

A randomised trial comparing two doses of the new selective aromatase inhibitor anastrozole (Arimidex) with megestrol acetate in postmenopausal patients with advanced breast cancer

The aim of this study was to compare the efficacy and tolerability of the new aromatase inhibitor ‘ARIMIDEX’ (anastrozole) with megestrol acetate in the treatment of advanced breast cancer in postmenopausal women. Anastrozole is a new potent and highly selective non-steroidal aromatase inhibitor. We conducted a prospective randomised trial comparing two doses of anastrozole (1 and 10 mg orally once daily) with megestrol acetate (40 mg orally four times daily) in postmenopausal patients with advanced breast cancer who progressed after prior tamoxifen therapy. All patients were analysed for efficacy as randomised (intention to treat) and for tolerability as per treatment received. Of the 378 patients who entered the study, 135 were randomised to anastrozole 1 mg, 118 to anastrozole 10 mg, and 125 patients to megestrol acetate. After a median follow-up of 192 days, response rate which included complete response, partial response and patients who had disease stabilisation for 6 months or more was 34% for anastrozole 1 mg, 33.9% for anastrozole 10 mg and 32.8% for megestrol acetate. There were no statistically significant differences between either dose of anastrozole and megestrol acetate in terms of objective response rate, time to objective progression of disease or time to treatment failure. The three treatments were generally well tolerated, but more patients on megestrol acetate reported weight gain, oedema and dyspnoea as adverse events while more patients on anastrozole reported gastro-intestinal disorders, usually in the form of mild transient nausea. Patients on anastrozole did not report higher incidences of oestrogen withdrawal symptoms. Anastrozole is an effective and well tolerated treatment for postmenopausal patients with advanced breast cancer. The higher 10 mg dose did not result in additional clinical benefit, but was well tolerated reflecting the good therapeutic margin with anastrozole. Based on this data, anastrozole 1 mg should be the recommended therapeutic dose.

Development of Steroidal and Nonsteroidal Inhibitors of Aromatase for the Treatment of Hormone-Dependent Breast Cancer

Abstract: Aromatase (estrogen synthase) is an enzyme complex responsible for the conversion of androgens to estrogens in the final step in steroidogenesis. Estrogens play important roles in both normal physiology and reproduction and in certain estrogen-responsive disease states, such as hormone-dependent breast cancer. Approximately two-thirds of newly diagnosed breast cancer cases are hormone-dependent breast cancer, and estrogens have potent mitogenic effects on this type of breast cancer. Decreasing circulating estrogen levels could result in effective therapy for hormone-dependent breast cancer. Since aromatase is the rate limiting step for the biosynthesis of estrogens, it is an appropriate target for inhibition. Over the past two decades, both steroidal and nonsteroidal aromatase inhibitors have been developed that are very potent compounds and very selective for aromatase versus other steroidogenic cytochrome P450 enzymes. The steroidal inhibitor 4-hydroxyandrostenedione has demonstrated clinical efficacy in the treatment of hormone-dependent breast cancer in postmenopausal women and is currently available in Europe. Several potent and selective nonsteroidal aromatase inhibitors are now undergoing extensive Phase II and Phase Ill clinical trials and should become available within the next few years for the treatment of breast cancer in postmenopausal women.

Open dose-finding study of a new potent and selective nonsteroidal aromatase inhibitor, CGS 20 267, in healthy male subjects.

The aim of this open, dose-finding study was to evaluate the effects of single dose CGS 20 267, a new oral nonsteroidal aromatase inhibitor, on the inhibition of estrogen production and also on the production of adrenal and testicular steroids in healthy male subjects. Nine dose levels ranging from 0.02-30 mg and placebo were tested, each dose being given to 3 subjects only. A total of 18 subjects were included; 12 of them received 2 single administration, the remaining 6 were exposed only once to one of the 2 highest dose levels. A reduction in serum estrogen levels when compared to baseline was already observed after 2 h, reaching maximum suppression between 10 and 48 h after administration. After 24 h, a suppression of estrone levels by 60-85% from baseline was achieved with all tested doses. A reduction in estradiol levels by about 30% from baseline was observed at the lowest dose (0.02 mg). This reduction was further enhanced dose dependently to a maximum of about 90% from baseline at 24 h after administration of the highest dose (30 mg). With the higher doses (10 and 30 mg), estrogen suppression was maintained up to 3 days. A dose-dependent increase of testosterone, LH, and FSH was observed and was most pronounced in the 10- and 30-mg dose groups, which can be considered as a consequence of the long-lasting aromatase inhibition achieved with these high doses. No effect on serum cortisol and aldosterone levels was observed up to the highest dose. No clinically relevant changes were observed in blood chemistry and hematology tests. The systemic and subjective tolerability of CGS 20 267 was good at all doses. This study has shown that CGS 20 267 is a well tolerated, potent, selective, and long-acting inhibitor of the aromatase enzyme after single administration.

Open dose-finding study of a new potent and selective nonsteroidal aromatase inhibitor, CGS 20 267, in healthy male subjects

Open dose-finding study of a new potent and selective nonsteroidal aromatase inhibitor, CGS 20 267, in healthy male subjects