First generation aromatase inhibitors--aminoglutethimide and testololactone

Bio-oxidation of progesterone by Penicillium oxalicum CBMAI 1185 and evaluation of the cytotoxic activity

We report the biotransformation of progesterone 1 by whole cells of Brazilian marine-derived fungi. A preliminary screening with 12 fungi revealed that the strains Penicillium oxalicum CBMAI 1996, Mucor racemous CBMAI 847, Cladosporium sp. CBMAI 1237, Penicillium oxalicum CBMAI 1185 and Aspergillus sydowii CBMAI 935 were efficient in the biotransformation of progesterone 1 in the first days of the reaction, with conversion values ranging from 75 % to 99 %. The fungus P. oxalicum CBMAI 1185 was employed in the reactions in quintuplicate to purify and characterize the main biotransformation products of progesterone 1. The compounds testololactone 1a, 12β-hydroxyandrostenedione 1b and 1β-hydroxyandrostenedione 1c were isolated and characterized by NMR, MS, [α]D and MP. In addition, the chromatographic yield of compound 1a was determined by HPLC-PDA in the screening experiments. In this study, we show a biotransformation pathway of progesterone 1, suggesting the presence of several enzymes such as Baeyer-Villiger monooxygenases, dehydrogenases and cytochrome P450 monooxygenases in the fungus P. oxalicum CBMAI 1185. In summary, the results obtained in this study contribute to the synthetic area and have environmental importance, since the marine-derived fungi can be employed in the biodegradation of steroids present in wastewater and the environment. The cytotoxic results demonstrate that the biodegradation products were inactive against the cell lines, in contrast to progesterone.

The crosstalk between ubiquitination and endocrine therapy

Endocrine therapy (ET), also known as hormone therapy, refers to the treatment of tumors by regulating and changing the endocrine environment and hormone levels. Its related mechanism is mainly through reducing hormone levels and blocking the binding of hormones to corresponding receptors, thus blocking the signal transduction pathway to stimulate tumor growth. However, with the application of ET, some patients show resistance to ET, which is attributed to abnormal accumulation of hormone receptors (HRs) and the production of multiple mutants of HRs. The targeted degradation of abnormal accumulation protein mediated by ubiquitination is an important approach that regulates the protein level and function of intracellular proteins in eukaryotes. Here, we provide a brief description of the traditional and novel drugs available for ET in this review. Then, we introduce the link between ubiquitination and ET. In the end, we elaborate the clinical application of ET combined with ubiquitination-related molecules. KEY MESSAGES: • A brief description of the traditional and novel drugs available for endocrine therapy (ET). • The link between ubiquitination and ET. • The clinical application of ET combined with ubiquitination-related molecules.

Novel pentacyclic derivatives and benzylidenes of the progesterone series cause anti-estrogenic and antiproliferative effects and induce apoptosis in breast cancer cells

The promising antitumor effects of progesterone derivatives have been identified in many studies. However, the specific mechanism of action of this class of compounds has not been fully described. Therefore, in this study, we investigated the antiproliferative and (anti)estrogenic activities of novel pentacyclic derivatives and benzylidenes of the progesterone series. The antiproliferative effects of the compounds were evaluated on hormone-dependent MCF7 breast cancer cells using the MTT test. Estrogen receptor α (ERα) activity was assessed by a luciferase-based reporter assay. Immunoblotting was used to evaluate the expression of signaling proteins. All benzylidenes demonstrated inhibitory effects with IC₅₀ values below 10 µM, whereas pentacyclic derivatives were less active. These patterns may be associated with the lability of the geometry of benzylidene molecules, which contributes to an increase in the affinity of interaction with the receptor. The selected compounds showed significant anti-estrogenic potency. Benzylidene 1d ((8 S,9 S,10R,13 S,14 S,17 S)-17-[(2E)-3-(4-fluorophenyl)prop-2-enoyl]-10,13-dimethyl-1,2,6,7,8,9,11,12,14,15-decahydrocyclopenta[a]phenanthren-3-one) was the most active in antiproliferative and anti-estrogenic assays. Apoptosis induced by compound 1d was accompanied by decreases in CDK4, ERα, and Cyclin D1 expression. Compounds 1d and 3d were characterized by high inhibitory potency against resistant breast cancer cells. Apoptosis induced by the leader compounds was confirmed by PARP cleavage and flow cytometry analysis. Compound 3d caused cell arrest in the G2/M phase. Further analysis of novel derivatives of the progesterone series is of great importance for medicinal chemistry, drug design, and oncology.

Hormone receptor binding, selectivity and cytotoxicity of steroid D-homo lactone loaded chitosan nanoparticles for the treatment of breast and prostate cancer cells

Chemically modified steroids have a long history as anti-neoplastic drugs. Incorporation of a lactone moiety in the steroid nucleus, as in previously obtained 3β-acetoxy-17-oxa-17a-homoandrost-5-en-16-one (A) and 3β-hidroxy-17-oxa-17a-homoandrost-5-en-16-one (B), often results in enhanced anticancer properties. In this work, chitosan-based (Ch) nanoparticles were created and loaded with potent anticancer steroidal compounds, A and B. Changes to hormone receptor binding and cytotoxicity were then measured. In agreement with our previous results for A and B, A- and B-loaded Ch displayed cytotoxic properties against cancer cell lines. Both A-Ch and B-Ch showed activity toward estrogen negative breast cancer (MDA-MB-231) and androgen negative prostate cancer cell lines (PC-3). Greater selectivity toward cancer cells versus healthy lung fibroblast (MRC-5) was observed for B-Ch particles. Cell viability and cytotoxicity measurements after a recovery period indicate more robust recovery of healthy cells versus malignant cells. Compounds A and B or their Ch-encapsulated forms were shown to have negligible affinity for the ligand binding domain of estrogen receptor β or the androgen receptor in a fluorescent yeast screen, suggesting a lack of estrogenicity and androgenicity. Steroid-loaded chitosan nanoparticles display strong cytotoxicity towards MDA-MB-231 and PC-3 with a lack of hormone activity, indicating their safety and efficacy.

Tumor-targeted Drug Delivery by Nanocomposites

BACKGROUND

Tumor-targeted delivery by nanoparticles is a great achievement towards the use of highly effective drug at very low doses. The conventional development of tumor-targeted delivery by nanoparticles is based on enhanced permeability and retention (EPR) effect and endocytosis based on receptor-mediated are very demanding due to the biological and natural complications of tumors as well as the restrictions on the design of the accurate nanoparticle delivery systems.

METHODS

Different tumor environment stimuli are responsible for triggered multistage drug delivery systems (MSDDS) for tumor therapy and imaging. Physicochemical properties, such as size, hydrophobicity and potential transform by MSDDS because of the physiological blood circulation different, intracellular tumor environment. This system accomplishes tumor penetration, cellular uptake improved, discharge of drugs on accurate time, and endosomal discharge.

RESULTS

Maximum drug delivery by MSDDS mechanism to target therapeutic cells and also tumor tissues and sub cellular organism. Poorly soluble compounds and bioavailability issues have been faced by pharmaceutical industries, which are resolved by nanoparticle formulation.

CONCLUSION

In our review, we illustrate different types of triggered moods and stimuli of the tumor environment, which help in smart multistage drug delivery systems by nanoparticles, basically a multi-stimuli sensitive delivery system, and elaborate their function, effects, and diagnosis.

A review on diverse heterocyclic compounds as the privileged scaffolds in non-steroidal aromatase inhibitors

Breast cancer, emerging malignancy is common among women due to overexpression of estrogen. Estrogens are biosynthesized from androgens by aromatase, a cytochrome P450 enzyme complex, and play a pivotal role in stimulating cell proliferation. Therefore, deprivation of estrogen by blocking aromatase is considered as the effective way for the inhibition and treatment of breast cancer. In recent years, various non-steroidal heterocyclic functionalities have been extensively developed and studied for their aromatase inhibition activity. This review provides information about the structural-activity relationship of heterocycles (Type II) towards aromatase. This aids the medicinal chemist around the significance of different heterocyclic moieties and helps to design potent aromatase inhibitors.

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.

New A-homo lactam D-homo lactone androstane derivative: Synthesis and evaluation of cytotoxic and anti-inflammatory activities in vitro

This paper describes the synthesis of a new A-homo lactam D-homo lactone androstane derivative from dehydroepiandrosterone. To evaluate the impact of the introduction of nitrogen in the parental scaffold on biological activity, a new androstane enamide-type lactam derivative was prepared and characterized. The new compound as well as starting compounds were screened for cytotoxic, anti-angiogenic and anti-inflammatory activities using several human cancer cell lines (MCF-7, MDA-MB-231, PC3, CEM, G-361, HeLa), endothelial (HUVEC) and non-tumour (MRC-5 and BJ) cell lines. Strong cytotoxic and anti-inflammatory activity with a broad therapeutical window was demonstrated by the A-homo lactam D-homo lactone androstane derivative. The induction of apoptosis in treated PC3 cultures was confirmed using apoptotic morphology screening and a fluorescent double-staining method. New A-homo lactam D-homo lactone androstane derivative induced apoptosis more than the tested reference compounds, Formestane and Doxorubicin. An in silico ADME analysis showed that the compounds possess drug-like properties.

A unifying biology of sex steroid-induced apoptosis in prostate and breast cancers

Prostate and breast cancer are the two cancers with the highest incidence in men and women, respectively. Here, we focus on the known biology of acquired resistance to antihormone therapy of prostate and breast cancer and compare laboratory and clinical similarities in the evolution of the disease. Laboratory studies and clinical observations in prostate and breast cancer demonstrate that cell selection pathways occur during acquired resistance to antihormonal therapy. Following sex steroid deprivation, both prostate and breast cancer models show an initial increased acquired sensitivity to the growth potential of sex steroids. Subsequently, prostate and breast cancer cells either become dependent upon the antihormone treatment or grow spontaneously in the absence of hormones. Paradoxically, the physiologic sex steroids now kill a proportion of selected, but vulnerable, resistant tumor cells. The sex steroid receptor complex triggers apoptosis. We draw parallels between acquired resistance in prostate and breast cancer to sex steroid deprivation. Clinical observations and patient trials confirm the veracity of the laboratory studies. We consider therapeutic strategies to increase response rates in clinical trials of metastatic disease that can subsequently be applied as a preemptive salvage adjuvant therapy. The goal of future advances is to enhance response rates and deploy a safe strategy earlier in the treatment plan to save lives. The introduction of a simple evidence-based enhanced adjuvant therapy as a global healthcare strategy has the potential to control recurrence, reduce hospitalization, reduce healthcare costs and maintain a healthier population that contributes to society.

Ligand- and Structure-Based Drug Design of Non-Steroidal Aromatase Inhibitors (NSAIs) in Breast Cancer

Aromatase is a multienzyme complex overexpressed in breast cancer and responsible for estrogen production. It is the potential target for designing anti-breast cancer drugs. Ligand and Structure-Based Drug Designing approaches (LBDD and SBDD) are involved in development of active and more specific Nonsteroidal Aromatase Inhibitors (NSAIs). Different LBDD and SBDD approaches are presented here to understand their utility in designing novel NSAIs. It is observed that molecules should possess a five or six membered heterocyclic nitrogen containing ring to coordinate with heme portion of aromatase for inhibition. Moreover, one or two hydrogen bond acceptor features, hydrophobicity, and steric factors may play crucial roles for anti-aromatase activity. Electrostatic, van der Waals, and p-p interactions are other important factors that determine binding affinity of inhibitors. HQSAR, LDA-QSAR, GQSAR, CoMFA, and CoMSIA approaches, pharmacophore mapping followed by virtual screening, docking, and dynamic simulation may be effective approaches for designing new potent anti-aromatase molecules.

How far have we come in terms of estrogens in breast cancer? [Review]

Major advances in breast cancer treatment have almost always been linked to the actions of estrogen. Therefore, this review focused on estrogen actions in the breast, particularly the developments of the past 20 years, the present understanding of disease biology and possible future developments. Within these areas have focused on what is known about the underlying molecular biology and in particular integration of the bioinformatics revolution of the last 15 years with other facets of research. In addition, there will be an emphasis on the understanding brought about by a greater appreciation for the intracrinology of the breast.

Ligand- and Structure-Based Drug Design of Non-Steroidal Aromatase Inhibitors (NSAIs) in Breast Cancer

Aromatase is a multienzyme complex overexpressed in breast cancer and responsible for estrogen production. It is the potential target for designing anti-breast cancer drugs. Ligand and Structure-Based Drug Designing approaches (LBDD and SBDD) are involved in development of active and more specific Nonsteroidal Aromatase Inhibitors (NSAIs). Different LBDD and SBDD approaches are presented here to understand their utility in designing novel NSAIs. It is observed that molecules should possess a five or six membered heterocyclic nitrogen containing ring to coordinate with heme portion of aromatase for inhibition. Moreover, one or two hydrogen bond acceptor features, hydrophobicity, and steric factors may play crucial roles for anti-aromatase activity. Electrostatic, van der Waals, and p-p interactions are other important factors that determine binding affinity of inhibitors. HQSAR, LDA-QSAR, GQSAR, CoMFA, and CoMSIA approaches, pharmacophore mapping followed by virtual screening, docking, and dynamic simulation may be effective approaches for designing new potent anti-aromatase molecules.

The steroidogenic enzyme Cyp11a1 is essential for development of peanut-induced intestinal anaphylaxis

BACKGROUND

Cytochrome P450, family 11, subfamily A, polypeptide 1 (Cyp11a1), a cytochrome P450 enzyme, is the first and rate-limiting enzyme in the steroidogenic pathway, converting cholesterol to pregnenolone. Cyp11a1 expression is increased in activated T cells.

OBJECTIVES

We sought to determine the role of Cyp11a1 activation in the development of peanut allergy and TH cell functional differentiation.

METHODS

A Cyp11a1 inhibitor, aminoglutethimide (AMG), was administered to peanut-sensitized and challenged mice. Clinical symptoms, intestinal inflammation, and Cyp11a1 levels were assessed. The effects of Cyp11a1 inhibition on T(H)1, T(H)2, and T(H)17 differentiation were determined. Cyp11a1 gene silencing was performed with Cyp11a1-targeted short hairpin RNA.

RESULTS

Peanut sensitization and challenge resulted in diarrhea, inflammation, and increased levels of Cyp11a1, IL13, and IL17A mRNA in the small intestine. Inhibition of Cyp11a1 with AMG prevented allergic diarrhea and inflammation. Levels of pregnenolone in serum were reduced in parallel. AMG treatment decreased IL13 and IL17A mRNA expression in the small intestine without affecting Cyp11a1 mRNA or protein levels. In vitro the inhibitor decreased IL13 and IL17A mRNA and protein levels in differentiated T(H)2 and T(H)17 CD4 T cells, respectively, without affecting GATA3, retinoic acid-related orphan receptor γt (RORγt), or T(H)1 cells and IFNG and T-bet expression. Short hairpin RNA-mediated silencing of Cyp11a1 in polarized T(H)2 CD4 T cells significantly decreased pregnenolone and IL13 mRNA and protein levels.

CONCLUSION

Cyp11a1 plays an important role in the development of peanut allergy, regulating peanut-induced allergic responses through effects on steroidogenesis, an essential pathway in T(H)2 differentiation. Cyp11a1 thus serves as a novel target in the regulation and treatment of peanut allergy.

History of aromatase: saga of an important biological mediator and therapeutic target

Aromatase is the enzyme that catalyzes the conversion of androgens to estrogens. Initial studies of its enzymatic activity and function took place in an environment focused on estrogen as a component of the birth control pill. At an early stage, investigators recognized that inhibition of this enzyme could have major practical applications for treatment of hormone-dependent breast cancer, alterations of ovarian and endometrial function, and treatment of benign disorders such as gynecomastia. Two general approaches ultimately led to the development of potent and selective aromatase inhibitors. One targeted the enzyme using analogs of natural steroidal substrates to work out the relationships between structure and function. The other approach initially sought to block adrenal function as a treatment for breast cancer but led to the serendipitous finding that a nonsteroidal P450 steroidogenesis inhibitor, aminoglutethimide, served as a potent but nonselective aromatase inhibitor. Proof of the therapeutic concept of aromatase inhibition involved a variety of studies with aminoglutethimide and the selective steroidal inhibitor, formestane. The requirement for even more potent and selective inhibitors led to intensive molecular studies to identify the structure of aromatase, to development of high-sensitivity estrogen assays, and to "mega" clinical trials of the third-generation aromatase inhibitors, letrozole, anastrozole, and exemestane, which are now in clinical use in breast cancer. During these studies, unexpected findings led investigators to appreciate the important role of estrogens in males as well as in females and in multiple organs, particularly the bone and brain. These studies identified the important regulatory properties of aromatase acting in an autocrine, paracrine, intracrine, neurocrine, and juxtacrine fashion and the organ-specific enhancers and promoters controlling its transcription. The saga of these studies of aromatase and the ultimate utilization of inhibitors as highly effective treatments of breast cancer and for use in reproductive disorders serves as the basis for this first Endocrine Reviews history manuscript.

Novel chemical space exploration via natural products

Natural products (NPs) are a rich source of novel compound classes and new drugs. In the present study we have used the chemical space navigation tool ChemGPS-NP to evaluate the chemical space occupancy by NPs and bioactive medicinal chemistry compounds from the database WOMBAT. The two sets differ notably in coverage of chemical space, and tangible leadlike NPs were found to cover regions of chemical space that lack representation in WOMBAT. Property based similarity calculations were performed to identify NP neighbors of approved drugs. Several of the NPs revealed by this method were confirmed to exhibit the same activity as their drug neighbors. The identification of leads from a NP starting point may prove a useful strategy for drug discovery in the search for novel leads with unique properties.

Synthesis of some epoxy and/or N-oxy 17-picolyl and 17-picolinylidene-androst-5-ene derivatives and evaluation of their biological activity

Steroidal epoxy and/or N-oxy 17-picolyl and 17-picolinylidene-androst-5-ene derivatives have been prepared using 3beta,17beta-dihydroxy-17alpha-picolyl-androst-5-ene (1), 3beta-acetoxy-17-picolinylidene-androst-5-ene (2), and 3beta-hydroxy-17-picolinylidene-androst-5-ene (3) as synthetic precursors. The compounds 2 and/or 3 were reacted with m-chloroperoxybenzoic acid (MCPBA). The compounds synthesized from 2 were 17-picolinylidene-N-oxide 4, 5alpha,6alpha-epoxy and 5beta,6beta-epoxy-17-picolinylidene-N-oxide 5 and 6, and 5alpha,6alpha:17alpha,20alpha- and 5beta,6beta:17alpha,20alpha-diepoxy-N-oxide 7 and 8. Starting from compound 3, a mixture of 5alpha,6alpha-epoxy and 5beta,6beta-epoxy-17-picolinylidene 9 and 10, 5alpha,6alpha-epoxy and 5beta,6beta-epoxy-17-picolinylidene-N-oxide 11 and 12, and 5alpha,6alpha:17alpha,20alpha- and 5beta,6beta:17alpha,20alpha-diepoxy-N-oxide 13 and 14 were obtained. From compounds 15 and 18, obtained from 1 and 3 by the Oppenauer oxidation, the 4alpha,5alpha-epoxy and 4beta,5beta-epoxy derivatives 16, 17 and 20, 21 were prepared by oxidation with 30% H(2)O(2). Oxidation of 18 with MCPBA yielded only the N-oxide 19. The structures of compounds 15 and 18 were proved by the X-ray analysis. Compounds 1-6, 9, 15, 17, 18, and 21 were tested on activity against the enzyme aromatase. Antitumor activity against three tumor cell lines (human breast adenocarcinoma ER+, MCF-7, human breast adenocarcinoma ER-, MDA-MB-231, and prostate cancer PC3) was evaluated. Three tested compounds (1, 4, and 19) showed strong activity against PC3, the IC(50) values being in the range 0.55-10microM, whereas compound 17 showed strong activity against MDA-MB-231 (IC(50) 10.4microM).

Aromatase inhibitors: past, present and future in breast cancer therapy

Estrogen has been implicated in promoting breast cancer in a majority of women. Endocrine therapy controlling estrogen production has been the guiding principle in treating breast cancer for more than a century. A greater understanding of this disease at a molecular level has led to the development of molecules that inhibit estrogen production by inhibiting the aromatase enzyme, that is the primary source of estrogen in postmenopausal women. This review examines the evolution of aromatase inhibitor (AI) based therapies over the past three decades. The third generation aromatase inhibitors (anastrozole, letrozole and exemestane), which have been found to be extremely specific and effective in an adjuvant/neoadjuvant/extended adjuvant setting are discussed from a biochemical and clinical perspective. A comprehensive discussion of the past, present, and future of aromatase inhibitors is conducted in this review.

Nanomolar concentrations of anabolic-androgenic steroids amplify excitotoxic neuronal death in mixed mouse cortical cultures

The use of anabolic-androgenic steroids (AASs) in the world of sport has raised a major concern for the serious, sometimes life-threatening, side effects associated with these drugs. Most of the CNS effects are of psychiatric origin, and whether or not AASs are toxic to neurons is yet unknown. We compared the effect of testosterone with that of the AASs, 19-nortestosterone (nandrolone), stanozolol, and gestrinone, on excitotoxic neuronal death induced by N-methyl-d-aspartate (NMDA) in primary cultures of mouse cortical cells. In the most relevant experiments, steroids were applied to the cultures once daily during the 4 days preceding the NMDA pulse. Under these conditions, testosterone amplified excitotoxic neuronal death only at very high concentrations (10 muM), whereas it was protective at concentrations of 10 nM and inactive at intermediate concentrations. Low concentrations of testosterone became neurotoxic in the presence of the aromatase inhibitors, i.e. anastrozole and aminoglutethimide, suggesting that the intrinsic toxicity of testosterone was counterbalanced by its aromatization into 17beta-estradiol. As opposed to testosterone, nortestosterone, stanozolol and gestrinone amplified NMDA toxicity at nanomolar concentrations; their action was insensitive to aromatase inhibitors, but was abrogated by the androgen receptor antagonist, flutamide. None of the AASs were toxic in the absence of NMDA. These data suggest that AASs increase neuronal vulnerability to an excitotoxic insult and may therefore facilitate neuronal death associated with acute or chronic CNS disorders.

Aromatase destabilizer: novel action of exemestane, a food and drug administration-approved aromatase inhibitor

Using Western blot as the major technique, we studied the effects of the three Food and Drug Administration (FDA)-approved aromatase inhibitors (AI) on aromatase protein stability in the aromatase-overexpressing breast cancer cell line MCF-7aro. We have found that exemestane treatment significantly reduces aromatase protein level. Exemestane induces aromatase degradation in a dose-responsive manner (25-200 nmol/L), and the effect can be seen in as early as 2 hours. Metabolic labeling with S(35)-methionine was used to determine the half-life (t(1/2)) of aromatase protein. In the presence of 200 nmol/L exemestane, the t(1/2) of aromatase was reduced to 12.5 hours from 28.2 hours in the untreated cells. Furthermore, exemestane-induced aromatase degradation can be completely blocked by 10 micromol/L MG132, indicating that the degradation is mediated by proteasome. We also examined the effect of exemestane on aromatase mRNA level using real-time reverse transcription-PCR. No significant changes in mRNA level were detected after 8 hours of treatment with exemestane (200 nmol/L). This is the first report on the evaluation of three FDA-approved AIs on the stability of the aromatase protein. We have found that exemestane, different from letrozole and anastrozole, can destabilize the aromatase protein.

Update on the use of aromatase inhibitors in breast cancer

Estrogens are biosynthesised from androgens by the CYP450 enzyme complex called aromatase. Aromatase is expressed in the ovary, placenta, brain, bone, adipose tissue and breast tissue. In breast cancer, intratumoural aromatase is the source for local estrogen production in the tissue. Inhibition of aromatase is an important approach for reducing growth stimulatory effects of estrogens in estrogen-dependent breast cancer. The potent and selective third-generation aromatase inhibitors anastrozole, letrozole and exemestane were introduced to the market as endocrine therapy in postmenopausal patients failing anti-estrogen therapy alone, or multiple hormonal therapies. Anastrozole and letrozole are both non-steroidal aromatase inhibitors that compete with the substrate for binding to the enzyme active site. Exemestane is a mechanism-based steroidal inhibitor that mimics the substrate, is converted by the enzyme to a reactive intermediate, and results in inactivation of aromatase. These third-generation aromatase inhibitors are currently approved as first-line therapy for the treatment of postmenopausal women with metastatic estrogen-dependent breast cancer. The use of an aromatase inhibitor as initial therapy, or after treatment with tamoxifen, is now recommended as adjuvant hormonal therapy for postmenopausal women with hormone-dependent breast cancer. Several clinical studies of aromatase inhibitors focus on the use of these agents in the adjuvant setting, for the treatment of early breast cancer. Recently published results show improved responses with these agents compared with tamoxifen.

Synthesis and study of some new N-substituted imide derivatives as potential anticancer agents

A new series of N-substituted imide derivatives have been synthesized by treating phthalic anhydride, naphthalic anhydride and their substituted derivatives with 2-hydrazino-1-imidazoline hydrobromide, various para-substituted aryl amines, aminoglutethimide and 2,4-dinitrophenyl hydrazine. Compounds 9, 10, 12, 18, 19, 23, 24 and 34-36 have been selected and screened for antineoplastic activity by National Cancer Institute, Bethesda, USA. Some newer aminoglutethimide derivatives 37-39 have also been prepared in order to study the effect of N-substitution on its pharmacological profile for the treatment of carcinoma. These compounds (37-39) have exhibited weak inhibition of human placental aromatase as compared to aminoglutethimide.

Aromatase inhibitors in the treatment of breast cancer

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

Testosterone amplifies excitotoxic damage of cultured oligodendrocytes

An overactivation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate receptors has been implicated in the pathophysiology of oligodendrocyte damage in demyelinating disorders of the CNS. We decided to examine the effect of testosterone on excitotoxic death of oligodendrocytes because a gender difference exists in the incidence and disease course of multiple sclerosis. Short-term pure cultures of oligodendrocytes (4 days in vitro) were exposed to a brief pulse with kainate or AMPA + cyclothiazide for the induction of excitotoxicity. Exposure to testosterone enantate was slightly toxic per se and amplified both AMPA and kainate toxicity. Testosterone treatment induced all gene targets of p53, and amplified the induction of these genes induced by kainate. The effect of testosterone was mediated by the activation of androgen receptors and was resistant to the aromatase inhibitors, dl-aminoglutethimide and 4-hydroxyandrost-4-ene-3,17-dione. Testosterone treatment also potentiated the stimulation of 45Ca2+ influx induced by AMPA + cyclothiazide or kainate without changing the expression of the glutamate receptor (GluR) 1, -2/3, and -4 subunits of AMPA receptors or the GluR6/7 subunits of kainate receptors. We conclude that testosterone amplifies excitotoxic damage of oligodendrocytes acting at an early step of the death cascade triggered by AMPA/kainate receptors.

Aromatase inhibitors in breast cancer therapy

Estrogens are involved in numerous physiological processes and have crucial roles in certain disease states, such as mammary carcinomas. Estradiol, the most potent endogenous estrogen, is biosynthesized from androgens by the cytochrome P450 enzyme complex called aromatase. Aromatase is found in breast tissue and the importance of intratumoral aromatase and local estrogen production is being unraveled. Inhibition of aromatase is an important approach for reducing growth stimulatory effects of estrogens in estrogen-dependent breast cancer. Steroidal and nonsteroidal aromatase inhibitors have shown clinical efficacy for the treatment of breast cancer. The initial nonselective nature of nonsteroidal inhibitors, such as aminoglutethimide, has been greatly reduced in the later generations of inhibitors, anastrozole and letrozole. Mechanism-based steroidal inhibitors, such as 4-hydroxyandrostenedione and exemestane produce potent aromatase inhibition in patients. The potent and selective third-generation aromatase inhibitors, anastrozole, letrozole and exemestane, are approved for clinical use as first-line endocrine therapy in postmenopausal women with metastatic hormone-dependent breast cancer and as second-line endocrine therapy in postmenopausal patients failing antiestrogen therapy alone or multiple hormonal therapies.

Aromatase, aromatase inhibitors, and breast cancer

Estrogens are involved in numerous physiologic processes and have crucial roles in particular disease states, such as mammary carcinomas. Estradiol, the most potent endogenous estrogen, is biosynthesized from androgens by the cytochrome P-450 enzyme complex called aromatase. Aromatase is found in breast tissue, and the importance of intratumoral aromatase and local estrogen production is being unraveled. Inhibition of aromatase is an important approach for reducing growth stimulatory effects of estrogens in hormone-dependent breast cancer. Effective aromatase inhibitors have been developed as therapeutic agents for controlling estrogen-dependent breast cancer. Investigations into the development of aromatase inhibitors began in the 1970s and have expanded greatly in the past three decades. Competitive aromatase inhibitors are molecules that compete with the substrate androstenedione for noncovalent binding to the active site of the enzyme to decrease the amount of product formed. Steroidal inhibitors that have been developed to date build on the basic androstenedione nucleus and incorporate chemical substituents at varying positions on the steroid. The structure-activity relationships for steroidal inhibitors have become more refined in the past decade, and only some modifications can be made to the steroid and still keep its affinity for aromatase. Nonsteroidal aromatase inhibitors can be divided into three classes: aminoglutethimide-like molecules, imidazole/triazole derivatives, and flavonoid analogs. Mechanism-based aromatase inhibitors are inhibitors that mimic the substrate, are converted by the enzyme to a reactive intermediate, and result in the inactivation of aromatase. Aromatase inhibitors, both steroidal and nonsteroidal, have shown clinical efficacy for the treatment of breast cancer. The initial nonselective nature of nonsteroidal inhibitors such as aminoglutethimide has been greatly reduced in the later generations of inhibitors, anastrozole and letrozole. Mechanism-based steroidal inhibitors such as 4-hydroxyandrostenedione and exemestane produce prolonged aromatase inhibition in patients. The potent and selective third-generation aromatase inhibitors anastrozole, letrozole, and exemestane are approved for clinical use as second-line endocrine therapy in postmenopausal patients failing antiestrogen therapy alone or multiple hormonal therapies.

Constitutive expression of the steroid sulfatase gene supports the growth of MCF-7 human breast cancer cells in vitro and in vivo

Many human breast tumors are driven by high intratumor concentrations of 17beta-estradiol that appear to be locally synthesized. The role of aromatase is well established, but the possible contribution of the steroid sulfatase (STS), which liberates estrogens from their biologically inactive sulfates, has been inadequately assessed and remains unclear. To evaluate the role of STS further, we transduced estrogen-dependent MCF-7 human breast cancer cells with a retroviral vector directing the constitutive expression of the human STS gene. Gene integration was confirmed by Southern hybridization, production of the appropriately sized messenger RNA by Northern hybridization, and expression of functional protein by metabolism of [(3)H]estrone sulfate to [(3)H]estrone. Maximum velocity estimates of estrone formation are 64.2 pmol estrone/mg protein.h in STS-transduced cells (STS Clone 20), levels comparable to those seen in some human breast tumors. Lower levels of endogenous activity are seen in MCF-7 cells (13.0 pmol estrone/mg protein.h) and in cells transduced with vector lacking the STS gene (Vector 3 cells; 12.0 pmol estrone/mg protein.h). 17beta-Estradiol sulfate induces expression of the progesterone receptor messenger RNA only in STS Clone 20 cells, whereas estrone sulfate produces the greatest stimulation of anchorage-independent growth in these cells. STS Clone 20 cells retain responsiveness to antiestrogens, which block the ability of estrogen sulfate to increase the proportion of cells in both the S and G(2)/M phases of the cell cycle. Consistent with these in vitro observations, only STS Clone 20 cells exhibit a significant increase in the proportion of proliferating tumors in nude ovariectomized mice supplemented with 17beta-estradiol sulfate. The primary activity in vivo appears to be from intratumor STS, rather than hepatic STS. Surprisingly, 17beta-estradiol sulfate appears more effective than 17beta-estradiol when both are administered at comparable concentrations. This effect, which is seen only in STS Clone 20 cells, may reflect differences in the cellular pharmacology of exogenous estrogens compared with those released by the activity of intracellular STS. These studies directly demonstrate that intratumor STS activity can support estrogen-dependent tumorigenicity in an experimental model and may contribute to the promotion of human breast tumors.

New generation aromatase inhibitors in breast cancer. Weighing out potential costs and benefits

Endocrine therapy is the oldest and still one of the most effective forms of systemic therapy for breast cancer. Unfortunately, only one-third of all breast carcinomas respond to a strategy that modifies the activity of estrogen at the level of the tumour. Therefore, it is important that patients with cancer likely to respond are reliably identified. Substantial evidence indicates that tumour estrogen receptor level is the best predictor of response to hormonal therapy. Although antiestrogen therapy is still considered the endocrine modality of choice for all stages of breast cancer, there is renewed interest in finding new agents with improved therapeutic indices. The development of agents which selectively suppress aromatase, a key enzyme in estrogen biosynthesis, can be attributed not only to the importance of extraglandular aromatase activity, but also to the unparalleled success of tamoxifen. The present status, emerging roles and concerns of the new aromatase inhibitors are discussed in order to assess their potential costs and therapeutic merit.

Testolactone-associated high androgen levels, a pharmacologic effect or a laboratory artifact?

Testolactone, an aromatase inhibitor, blocks conversion of androgens to estrogens. In familial male precocious puberty, slowing of pubertal progression and growth velocity occurs with testolactone and spironolactone. Girls with McCune-Albright syndrome, given testolactone, respond similarly. A 2-yr-old female (case 1) on testolactone for non-McCune-Albright gonadotropin independent precocious puberty had marked elevations of androstenedione (18 ng/mL, normal: 0.2-3.1) and testosterone (3.6 ng/mL, normal < 0.2) but no virilization. Investigations were undertaken to determine whether elevations in testosterone and androstenedione were caused by interference in these RIAs. After a single oral dose of testolactone (5 mg/kg in case 1; 4 mg/kg in case 2, a 3-yr-old boy with familial male precocious puberty; 10 mg/kg in a healthy postmenopausal control), serum testosterone and androstenedione were measured serially by RIA for 24 h. Androstenedione went from normal to a mean peak of 45.4 ng/mL at 1-2 h and returned to baseline by 24 h. Testosterone, undetectable at baseline (case 1 and control) or 1.8 ng/mL (case 2) rose to a mean peak of 6.9 ng/mL and returned to baseline by 24 h. Testolactone, in serial dilutions, cross-reacted in the testosterone assay. Testolactone significantly interferes in these serum RIAs, making their use unreliable in follow-up of patients treated with testolactone.

Fadrozole HCL (CGS-16949A) versus megestrol acetate treatment of postmenopausal patients with metastatic breast carcinoma: results of two randomized double blind controlled multiinstitutional trials

BACKGROUND

Breast cancer patients with prior response to endocrine therapy achieve subsequent benefit from additional endocrine therapies. The efficacy and safety of an aromatase inhibitor, fadrozole HCL, were compared with megestrol acetate in post menopausal patients who had disease progression after receiving antiestrogen therapy either for metastatic disease or as adjuvant therapy.

METHODS

In 2 multiinstitutional prospective trials, 683 postmenopausal patients were randomized to receive either fadrozole HCL, 1 mg twice daily, or megestrol acetate, 40 mg 4 times daily, in a double blind fashion after progression on first-line hormonal therapy. Objective response rates, time to progression, survival and safety of the two regimens were compared.

RESULTS

Results of intent-to-treat analyses are presented in this study. No significant differences were detected between the two treatment groups in time to progression, objective response rates, duration of response, and survival in either trial. There were no clinically meaningful differences between the treatment groups in the incidence and severity of adverse experiences, except that weight gain, fluid retention, and dyspnea were observed in more patients in the megestrol acetate group compared with those receiving fadrozole HCL, whereas nausea and vomiting were observed in more patients in the fadrozole HCL group compared with those receiving megestrol acetate.

CONCLUSIONS

Fadrozole HCL was as efficacious as megestrol acetate in postmenopausal patients with metastatic breast carcinoma after one hormonal therapy. Adverse experiences were mild with both therapies, but megestrol acetate was associated wiht a higher frequency of weight gain, fluid retention and dyspnea, whereas fadrozole HCL was associated with a higher frequency of nausea and vomiting.

Letrozole, a new oral non-steroidal aromastase inhibitor in treating postmenopausal patients with advanced breast cancer. A pilot study

PURPOSE

To evaluate the endocrine effects as well as the pharmacokinetic parameters, efficacy and safety of letrozole, a new fourth-generation non-steroidal aromatase inhibitor.

PATIENTS AND METHODS

Fourteen postmenopausal women with progressive metastatic breast cancer, previously treated with endocrine therapy and/or chemotherapy for advanced disease, were treated with 0.5 mg daily doses of letrozole, orally. Endocrine and pharmacokinetic measurements were made before treatment and on days 14, 28, 56, and 84 of therapy.

RESULTS

Letrozole induced a >86% decrease in plasma estrone and a approximately 67% reduction in circulating estradiol from day 14 on. There was a statistically significant decrease in plasma cortisol, which appeared clinically irrelevant since all values remained within the normal range. No significant changes in aldosterone concentration were noted. One patient achieved a complete response (CR) and 4 patients a partial response (PR), with an objective response rate of 36% (95% CI 13% to 65%). Median duration of response was 24 months, ranging from 4 to 44 months. No toxic effects attributable to letrozole were noted in any patient.

CONCLUSION

Letrozole appears to be a very promising new antiaromatase drug. The characteristics of the patients more likely to respond, taking into account prior systemic treatment, should be defined by future studies. Further phase II and phase III studies comparing letrozole to other available second or even first-line endocrine-therapy agents, are warranted.