Formestane. A review of its pharmacological properties and clinical efficacy in the treatment of postmenopausal breast cancer

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.

Investigating hormone-induced changes in affective state using the affective bias test in male and female rats

Recent clinical and pre-clinical research suggests that affective biases may play an important role in the development and perpetuation of mood disorders. Studies in animals have also revealed that similar neuropsychological processes can be measured in non-human species using behavioural assays designed to measure biases in learning and memory or decision-making. Given the proposed links between hormones and mood, we used the affective bias test to investigate the effects of different hormone treatments in both male and female rats. Animals were pre-treated with acute doses of hormone or vehicle control prior to learning each of two independent substrate-reward associations. During a subsequent choice test, positive or negative biases were observed by animal's preference towards or away from the substrate learnt during drug treatment respectively. In both sexes, oestradiol and the oestrogen-like compound bisphenol A induced positive biases, whilst blockade of oestrogen hormones with formestane induced a negative bias. Progesterone induced a negative bias in both sexes, but testosterone only induced a negative bias in males. Blocking testosterone with flutamide induced a positive bias in both sexes at the higher dose (10 mg/kg). The oxytocin analogue, carbetocin induced positive biases in both sexes but the vasopressin analogue, desmopressin, induced a positive bias in male rats only. These results provide evidence that modulating levels of hormones using exogenous treatments can induce affective biases in rats. They also suggest that hormone-induced affective biases influence cognitive and emotional behaviour and could have longer-term effects in some mood disorders.

Repurposing steroidogenesis inhibitors for the therapy of neuropsychiatric disorders: Promises and caveats

Steroids exert a profound influence on behavioral reactivity, by modulating the functions of most neurotransmitters and shaping the impact of stress and sex-related variables on neural processes. This background - as well as the observation that most neuroactive steroids (including sex hormones, glucocorticoids and neurosteroids) are synthetized and metabolized by overlapping enzymatic machineries - points to steroidogenic pathways as a powerful source of targets for neuropsychiatric disorders. Inhibitors of steroidogenic enzymes have been developed and approved for a broad range of genitourinary and endocrine dysfunctions, opening to new opportunities to repurpose these drugs for the treatment of mental problems. In line with this idea, preliminary clinical and preclinical results from our group have shown that inhibitors of key steroidogenic enzymes, such as 5α-reductase and 17,20 desmolase-lyase, may have therapeutic efficacy in specific behavioral disorders associated with dopaminergic hyperfunction. While the lack of specificity of these effects raises potential concerns about endocrine adverse events, these initial findings suggest that steroidogenesis modulators with greater brain specificity may hold significant potential for the development of alternative therapies for psychiatric problems. This article is part of the Special Issue entitled 'Drug Repurposing: old molecules, new ways to fast track drug discovery and development for CNS disorders'.

Synthetic androgens as designer supplements

Anabolic androgenic steroids (AAS) are some of the most common performance enhancing drugs (PED) among society. Despite the broad spectrum of adverse effects and legal consequences, AAS are illicitly marketed and distributed in many countries. To circumvent existing laws, the chemical structure of AAS is modified and these designer steroids are sold as nutritional supplements mainly over the Internet. Several side effects are linked with AAS abuse. Only little is known about the pharmacological effects and metabolism of unapproved steroids due to the absence of clinical studies. The large number of designer steroid findings in dietary supplements and the detection of new compounds combined with legal loopholes for their distribution in many countries show that stricter regulations and better information policy are needed.

Synthesis and bioconversions of formestane

In an effort to generate new steroidal aromatase inhibitors, formestane (4-hydroxyandrost-4-ene-3,17-dione) (1) was biotransformed by Rhizopus oryzae to yield the known 4β,5α-dihydroxyandrostane-3,17-dione as the major product (5) and bioconverted by Beauveria bassiana to afford the known reduced 4,17β-dihydroxyandrost-4-en-3-one (6) and 3α,17β-dihydroxy-5β-androstan-4-one (7) and the new 4,11α,17β-trihydroxyandrost-4-en-3-one (8). All the metabolites showed more potent activities than their parent congener in the aromatase and MCF-7 breast cancer assays. The bioactivities and structural elucidation of these metabolites as well as the semisynthesis of formestane (1) from testosterone (2) are reported herein.

Inhibitory effect of luteolin on estrogen biosynthesis in human ovarian granulosa cells by suppression of aromatase (CYP19)

Inhibition of aromatase, the key enzyme in estrogen biosynthesis, is an important strategy in the treatment of breast cancer. Several dietary flavonoids show aromatase inhibitory activity, but their tissue specificity and mechanism remain unclear. This study found that the dietary flavonoid luteolin potently inhibited estrogen biosynthesis in a dose- and time-dependent manner in KGN cells derived from human ovarian granulosa cells, the major source of estrogens in premenopausal women. Luteolin decreased aromatase mRNA and protein expression in KGN cells. Luteolin also promoted aromatase protein degradation and inhibited estrogen biosynthesis in aromatase-expressing HEK293A cells, but had no effect on recombinant expressed aromatase. Estrogen biosynthesis in KGN cells was inhibited with differing potencies by extracts of onion and bird chili and by four other dietary flavonoids: kaempferol, quercetin, myricetin, and isorhamnetin. The present study suggests that luteolin inhibits estrogen biosynthesis by decreasing aromatase expression and destabilizing aromatase protein, and it warrants further investigation as a potential treatment for estrogen-dependent cancers.

The development of a whole-cell based medium throughput screening system for the discovery of human aldosterone synthase (CYP11B2) inhibitors: old drugs disclose new applications for the therapy of congestive heart failure, myocardial fibrosis and hypertension

Cytochrome P450 enzymes play an important role in steroid hormone biosynthesis of the human adrenal gland, e.g., the production of cortisol and aldosterone. Aldosterone, the most important human mineralocorticoid, is involved in the regulation of the salt and water homeostasis of the body and thus in the regulation of blood pressure, whereas cortisol is the most important glucocorticoid of the human body. CYP11B-dependent steroid hydroxylases are drug development targets, and since they are very closely related enzymes, the discovery of selective inhibitors has been subject to intense investigations for several years. Here we report the development of a whole-cell medium throughput screening technology for the discovery of CYP11B2 inhibitors. The new screening system displayed high reproducibility and was applied to investigate a library of pharmacologically active compounds. 1268 compounds were investigated during this study which revealed 5 selective inhibitors of CYP11B2 (after validation against CYP11B1). The new inhibitors of CYP11B2 are already existing drugs that could be used either in the treatment of hyperaldosteronism-related diseases or as lead compounds that could further be optimised to achieve safer and selective inhibitors of aldosterone synthase. Article from the Special issue on 'Targeted Inhibitors'.

Hormone therapy for breast cancer, with an emphasis on the pure antiestrogen fulvestrant: mode of action, antitumor efficacy and effects on bone health

Breast cancer is a major health problem in women of developed Western countries. Whereas estrogen receptor (ER) may be involved in many cases in breast carcinogenesis, its expression in breast tumors may predict a favorable response to hormone therapy. In this review, we report the role played by ER in breast cancer and compare the effects and mechanisms of action of partial (tamoxifen) and pure (fulvestrant) antiestrogens, as well as of aromatase inhibitors. Moreover, as ER also has a critical role in bone metabolism, we review the beneficial and adverse effects of breast cancer hormone therapy on bone health, with a particular emphasis on fulvestrant, the only pure antiestrogen recently approved by the FDA for Phase III clinical trials. We conclude that, because of its therapeutic efficacy and its seemingly minimal effect on bone integrity, fulvestrant represents a new option for the hormonal treatment of breast cancer that deserves further clinical evaluation.

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.

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.

Strategies for improving quality of life in older patients with metastatic breast cancer

Given both the increase in the mean age of the population of Western countries and the high incidence of breast cancer beyond the age of 65 years, it is evident that breast cancer in older women will be a very common problem for the medical oncologist. Metastatic breast cancer is still not amenable to a cure; therefore quality of life during therapy is an important issue, which until recently has been poorly investigated. Similarly, despite recent advances in breast cancer therapy, physicians have been reluctant to enrol older patients in clinical trials, and there is a lack of data regarding this population. This review focuses on quality-of-life issues during metastatic breast cancer treatment in geriatric patients, comparing the standard therapeutic options and newer approaches. Although first-line endocrine therapy with tamoxifen remains a standard treatment, the newer third-generation aromatase inhibitors provide similar or better efficacy with fewer adverse effects and a better quality of life. It has been a common belief that chemotherapy impairs quality of life, but recent studies in advanced breast cancer have shown that this therapy has a positive effect on quality of life, at least in responders. Consequently, chemotherapy should not be denied to elderly patients with metastatic breast cancer, provided a prior geriatric assessment is performed to evaluate the risk-benefit ratio. New chemotherapy strategies, such as the taxanes and orally administered chemotherapy, represent a very attractive alternative for a better quality of life in elderly patients with metastatic breast cancer.

Gastric parietal cells: potent endocrine role in secreting estrogen as a possible regulator of gastro-hepatic axis

Estrogen, if it is produced in the gastrointestinal tract, may overflow into the systemic circulation in the case of increased portal-systemic shunting. This idea is in accord with a significant step-up in serum estradiol (E2) concentration in the portal vein of rats, compared with that in the artery. Gene expression of aromatase, estrogen synthetase, was demonstrated by RT-PCR in the gastric mucosa of male and female adult rats, equivalent to that in the ovary. Aromatase activity and production of E2 in the gastric mucosa were demonstrated by (3)H(2)O assay and gas chromatography-mass spectrometry, and they were inhibited by aromatase inhibitor, 4-hydroxyandrostenedione. Conversion of (14)C-androstenedione to (14)C-E2 through (14)C-testosterone in cultured gastric mucosa was also demonstrated. Parietal cells exhibited strong signals for aromatase mRNA and immunoreactive protein by in situ hybridization histochemistry and immunohistochemistry. Estrogen receptor alpha mRNA and immunoreactive protein were demonstrated in hepatocytes by RT-PCR, in situ hybridization histochemistry, and immunohistochemistry. Total gastrectomy reduced portal venous E2 concentration, without changing systemic E2 concentration, together with down-regulation of estrogen receptor alpha mRNA level in the liver. These findings indicate that gastric parietal cells play a potent endocrine role in secreting estrogen that may function as a regulator of the gastro-hepatic axis.

Aromatase inhibitors and inactivators for breast cancer therapy

Aromatase inhibitors and inactivators are increasingly important to the therapy of advanced breast cancer in postmenopausal women. These compounds are also currently being evaluated in the adjuvant setting and may have potential in breast cancer prevention. In addition to the recent clinical results, experimental research with development of aromatase 'knockout' mice as well as certain clinical observations in individuals lacking this enzyme have deepened our understanding of estrogens outside of the field of reproduction. Such information should help us to further develop this type of therapy in breast cancer and, in particular, extend our understanding of the lack of complete cross-resistance between aromatase inhibitors and inactivators. Clinically, third-generation aromatase inhibitors and inactivators have shown superiority compared with conventional treatment in advanced postmenopausal breast cancer with respect to second-line (tamoxifen failures) as well as first-line therapy. The fact that tamoxifen is noncurative in metastatic disease but improves long-term survival in the adjuvant setting suggests that even modest improvements in therapy of advanced disease may be translated into survival benefits in patients with early disease. In addition, these novel compounds with lack of complete cross-resistance extend the scope of using sequential treatment options to maximise the duration of optimal endocrine therapy in metastatic breast cancer disease.

Overview of the pharmacology of the aromatase inactivator exemestane

One third of all breast cancers and two thirds of postmenopausal breast cancers are estrogen dependent. Antiestrogen strategies, such as inhibition of estrogen-receptor binding and estrogen deprivation, are effective for the management of hormone-dependent breast cancer. Although currently available agents are effective, the development of more potent and selective agents continues. Both steroidal and nonsteroidal inhibitors of aromatase have been developed for clinical uses. A novel class of steroidal irreversible antiaromatase agents demonstrates a high degree of specificity for the aromatase enzyme and exhibits a unique pharmacokinetic profile. The ability of these agents to inactivate aromatase may explain their high degree of potency and lengthy duration of action. Exemestane, an orally active aromatase inactivator, has demonstrated excellent selectivity and tolerability and broad-based efficacy in the treatment of postmenopausal breast cancer. Current findings suggest that exemestane will be a valuable alternative for women with breast cancer, not only for those progressing on other hormonal therapies but in earlier stages of the disease and prevention.

Nonsteroidal aromatase inhibitors: recent advances

Aromatase is the cytochrome P450 enzyme responsible for the last step of estrogen biosynthesis, and aromatase inhibitors constitute an important class of drugs in clinical use for the treatment of breast cancer. Nonsteroidal aromatase inhibitors (NSAIs) are competitive inhibitors of aromatase, which bind to the enzyme active site by coordinating the iron atom present in the heme group of the P450 protein. Presently, third generation NSAIs are in use, and research efforts are being carried out both to identify new molecules of therapeutic interest and to clarify the mechanism of action. In this article, we present a survey of the compounds that have been recently reported as NSAIs, to provide a broad view on the general structure-activity relationships of the class. Moreover, starting from the current knowledge of the mechanistic aspects of aromatase action and from recent theoretical work on the molecular modeling of both enzyme and inhibitors, we try to indicate a way to integrate these different studies in view of a more general understanding of the aromeatase-inhibitor system. Finally, some aspects regarding the possible future development of the field are considered briefly.

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.

Phase III, multicenter, double-blind, randomized study of letrozole, an aromatase inhibitor, for advanced breast cancer versus megestrol acetate

PURPOSE

To compare two doses of letrozole (0.5 mg and 2.5 mg every day) and megestrol acetate (40 mg qid) as endocrine therapy in postmenopausal women with advanced breast cancer previously treated with antiestrogens.

PATIENTS AND METHODS

This double-blind, randomized, multicenter, multinational study enrolled 602 patients, all of whom were included in the primary analysis in the protocol. Patients had advanced or metastatic breast cancer with evidence of disease progression while receiving continuous adjuvant antiestrogen therapy, had experienced relapse within 12 months of stopping adjuvant antiestrogen therapy given for at least 6 months, or had experienced disease progression while receiving antiestrogen therapy for advanced disease. Tumors were required to be estrogen receptor- and/or progesterone receptor-positive or of unknown status. Confirmed objective response rate was the primary efficacy variable. Karnofsky Performance Status and European Organization for Research and Treatment of Cancer quality-of-life assessments were collected for 1 year.

RESULTS

There were no statistically significant differences among the three treatment groups for overall objective tumor response. Patients treated with letrozole 0.5 mg had improvements in disease progression (P =.044) and a decreased risk of treatment failure (P =.018), compared with patients treated with megestrol acetate. Letrozole 0.5 mg showed a trend (P =.053) for survival benefit when compared with megestrol acetate. Megestrol acetate was more likely to produce weight gain, dyspnea, and vaginal bleeding, and the letrozole groups were more likely to experience headache, hair thinning, and diarrhea.

CONCLUSION

Given a favorable tolerability profile, once-daily dosing, and evidence of clinically relevant benefit, letrozole is equivalent to megestrol acetate and should be considered for use as an alternative treatment of advanced breast cancer in postmenopausal women after treatment failure with antiestrogens.

Pharmacokinetics and metabolism of formestane in breast cancer patients

Formestane (Lentaron(R), 4-hydroxyandrostenedione) is a steroidal aromatase inhibitor used for treatment of advanced breast cancer. Clinically, it is administered as a depot form once fortnightly by intramuscular (i.m.) injection. To investigate the pharmacokinetics, bioavailability and metabolism of the drug, seven patients received single 250 mg i.m. doses of commercial formestane on Days 0, 21, 35, 49 and 63 of this trial. On Day 63, three of the patients received an additional single intravenous (i.v.) pulse dose of 1 mg of 14C-labelled formestane. The plasma kinetics after i.m. dosing confirmed a sustained release of formestane from the site of injection. Within 24-48 h of the first dose, the circulating drug reached a C(max) of 48.0+/-20.9 nmol/l (mean+/-S.D.; N=7). At the end of the dosing interval, after 14 days, the plasma concentration was still at 2.3+/-1.8 nmol/l. The kinetic variables did not significantly change during prolonged treatment. Intramuscular doses appear to be fully bioavailable. Following i.v. injection of 14C-formestane, the unchanged drug disappeared rapidly from plasma, the terminal elimination half-life being 18+/-2 min (N=3). Plasma clearance, CL was 4.2+/-1.3 l/(h kg) and the terminal distribution volume V(z) was 1.8+/-0.5 l/kg. The drug is mainly eliminated by metabolism, renal excretion of metabolites accounting for 95% of dose. The excretory balance of 14C-compounds in urine and faeces totals up to 98.9+/-0.8% of the i.v. dose after 168 h. The 14C-compounds in plasma and urine were separated by HPLC, and three major metabolites were submitted to structural analysis by MS, NMR and UV spectroscopy. One of the metabolites is the direct 4-O-glucuronide of formestane. The other two represent 3-O-sulfates of the exocons 3beta,4beta-dihydroxy-5alpha-androstane-17-one and 3alpha,4beta-dihydroxy-5alpha-androstane-17-one, their ratio being 7:3. These exocons are formed by stereoselective 3-keto reduction, accompanied by reduction of the 4,5-enol function. The exocons do not inhibit human placental aromatase activity in vitro.

Is there a growing role for endocrine therapy in the treatment of breast cancer?

Novel biochemical findings on the molecular mechanisms of estrogen actions may help us to understand some of the unexplained observations seen in breast cancer treatment and suggest new therapeutic opportunities. Thus, apart from the challenge of improving the clinical treatment of patients with advanced disease, results from trials in this setting may reveal new therapeutic principles that may be evaluated in the adjuvant setting. The role of endocrine therapy in metastatic as well as early breast cancer is increasing, and the possibility of improving cure rates for breast cancer by implementing therapy with novel aromatase inhibitors in the adjuvant setting is exciting. While the results from prevention trials are most interesting, suggesting the possibility of reducing breast cancer incidence in high-risk groups, more data are needed before we can decide whether such interventions are warranted in women at high risk of developing breast cancer.

Steroidal aromatase inhibitors in elderly patients

The choice of treatment for elderly breast cancer patients needs particular care because the presence of physiological functional impairments can modify the drug bioavailability in an unpredictable manner. Hormonal treatment remains one of the choices and, although tamoxifen has proved to be effective in any setting, the use of selective aromatase inhibitors is arousing. Depending on their chemical structure, aromatase inhibitors are either steroidal (such as exemestane and formestane) or non-steroidal (such as letrozole, vorozole and anastrozole). Formestane has been studied in elderly patients with breast cancer and has been found to induce an overall response rate of 51% (95% CI, 35-67%). The drug suppresses estradiol (E2) levels, and changes in other hormones (FSH, LH and SHBG) are observed, but with poor clinical significance, thus confirming its selectivity and potency. Formestane has also been demonstrated to be as effective as tamoxifen. Exemestane and non-steroidal aromatase inhibitors appear to be very promising drugs.

MR 20492 and MR 20494: two indolizinone derivatives that strongly inhibit human aromatase

In this study, we describe the synthesis of a new family of indolizinone derivatives designed to fit an extrahydrophobic pocket within the active site of aromatase and to strongly inhibit human aromatase. This could help improve the specificity of the inhibitors. Equine aromatase, very well characterized biochemically, is used as a comparative model. Indeed, in a previous comparison between both human and equine aromatases, we described the importance of the interaction between the inhibitor and this pocket for the indane derivative MR 20814. MR 20492 and MR 20494 are more potent inhibitors of human aromatase (Ki/Km: 1.0+/-0.3 and 0.5+/-0.3, respectively). The Ki/Km for MR 20494 is slightly higher than that obtained for fadrozole (0.1+/-0.0) and Ki/Km for both indolizinone derivatives are lower than those obtained for 4-hydroxyandrostenedione (1.9+/-0.8) and MR 20814 (8.1+/-.7). These new compounds are not enzyme inactivators. Moreover, as indicated by the higher Ki/Km values obtained with equine enzyme (9.0+/-0.6 and 6.1+/-1.6 for MR 20492 and MR 20494, respectively), both human and equine aromatase active sites appear to be structurally different. Difference absorption spectra study (350-500 nm) revealed that MR20492 and MR20494 were characterized by a combination of type-I and -II spectra with both enzymes. This result could be due to the isomerization of the molecule in polar solvent (Z and E forms). The evaluation of these new molecules, as well as 4-hydroxyandrostenedione and fadrozole, on aromatase activity in transfected 293 cell cultures evidenced a strong inhibition (IC50: 0.20+/-0.03 microM, 0.20+/-0.02 microM and 0.50+/-0.40 microM for MR 20494, fadrozole and 4-OHA, respectively) except for MR 20492 (3.9+/-0.9 microM) and MR 20814 (10.5+/-0.6 microM). These results proved that these molecules formed part of a promising family of potent inhibitors and that they penetrate 293 cells, without evidencing any cytotoxicity in Hela cells with MTT assay. This is thus encouraging for the development of new drugs for the treatment of estrogen-dependent cancers, these molecules also constitute new tools for understanding the aromatase active site.

Anastrozole. A review of its use in the management of postmenopausal women with advanced breast cancer

Anastrozole is a new oral nonsteroidal aromatase inhibitor indicated for the second-line endocrine treatment of postmenopausal women with advanced breast cancer. In postmenopausal women, anastrozole significantly reduces plasma estrogen levels; maximal suppression is achieved at dosages > or = 1 mg/day and levels remain suppressed during long term therapy. In two phase III clinical trials, anastrozole 1 or 10 mg/day showed similar clinical efficacy to that of oral megestrol (megestrol acetate) 160 mg/day in postmenopausal women with advanced breast cancer. Primary end-points [including time to disease progression (120 to 170 days) and overall response rates (complete and partial response and stable disease lasting > or = 24 weeks: 29 to 37%)] and secondary end-points [time to treatment failure (115 to 168 days) and duration of response (257 to 261 days)] did not differ significantly between treatment groups. However, a significant survival advantage was observed in patients treated with anastrozole 1 mg/day compared with megestrol in a follow-up combined analysis of patients enrolled in both studies (median time to death 26.7 vs 22.5 months). Quality of life parameters were generally improved to a similar extent in all treatment groups. Anastrozole is generally well tolerated in the majority of patients, the most common adverse events being gastrointestinal (GI) disturbances (incidence 29 to 33%). These events are generally mild or moderate and transient. Other adverse events reported with anastrozole include headache (< or = 18%), asthenia (< or = 16%), pain (< or = 15%), hot flushes and bone pain (both < or = 12%), back pain and dyspnoea (both < or = 11%) and peripheral oedema (< or = 9%). GI disturbance tended to be more common with anastrozole than megestrol, particularly at the 10 mg/day dosage; however, compared with megestrol, anastrozole is less frequently associated with weight gain.

CONCLUSIONS

Anastrozole, with its apparent survival advantage versus megestrol (demonstrated in a combined analysis of phase III studies), convenient once daily oral administration and acceptable short term tolerability profile, is a second-line treatment option for postmenopausal patients with tamoxifenrefractory advanced breast cancer. The results of ongoing comparative trials with tamoxifen will determine the relative efficacy of anastrozole as first-line endocrine therapy for advanced breast cancer and as adjuvant therapy for early disease. In addition, direct comparative studies are required to determine the efficacy of anastrozole relative to that of other oral aromatase inhibitors such as letrozole and vorozole.