Exemestane: a review of its use in postmenopausal women with advanced breast cancer

Encapsulation of exemestane in polycaprolactone nanoparticles: optimization, characterization, and release kinetics

This study was aimed at developing a polymeric drug delivery system for a steroidal aromatase inhibitor, exemestane (exe) intended for sustained targeted delivery of drug through intravenous route. Carboxylated polycaprolactone (cPCL) was synthesized by ring opening polymerization of caprolactone. Exe-loaded cPCL nanoparticles (NPs) were prepared by interfacial deposition of preformed polymer and characterized. A 3-factor, 3-level Box–Behnken design was used to derive a second-order polynomial equation and construct contour and response plots for maximized response of percentage drug entrapment (PDE) with constraints on particle size (PS). The independent variables selected were ratio of exe/cPCL, amount of cPCL, and volume of organic phase. Polymerization of caprolactone to cPCL was confirmed by Fourier transform infrared (FTIR) and gel permeation chromatography. The prepared NPs were evaluated for differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and in vitro release studies. Optimum formulation based on desirability (1.0) exhibited PDE of 83.96 % and PS of 180.5 nm. Check point analysis confirmed the role of the derived polynomial equation and contour plots in predicting the responses. Zeta potential of optimized formulation was −33.8 ± 2.1 mV. DSC studies confirmed the absence of any interaction between drug and polymer. TEM image showed non-aggregated and spherical shaped NPs. Drug release from NPs showed sustained release and followed Korsmeyer–Peppas model, indicating Fickian drug release. Thus, preparation of exe-loaded cPCL NPs with high PDE and desired PS suitable for providing passive targeting could be statistically optimized using Box–Behnken design.

Exemestane in early breast cancer: a review

The adjuvant treatment of women with endocrine-sensitive early breast cancer has been dominated for the last 40 years by tamoxifen. However, the side-effects associated with this therapy have prompted a search for safer and biochemically more selective endocrine agents and led to the development of the third-generation aromatase inhibitors (AIs) anastrozole, letrozole and exemestane. Promising results in advanced disease have paved the way for treating early breast cancer, and AIs are increasingly replacing tamoxifen in the adjuvant setting. Several large, randomized trials with AIs have been completed or are ongoing in women with early-stage breast cancer, documenting the significant impact that these drugs are making on the risk for recurrence of breast cancer. As a result, there is increasing and widespread use of AI therapy for the treatment of early-stage endocrine-responsive breast cancer. This review summarizes the data for exemestane in the adjuvant setting, showing that a switch to exemestane after 2 to 3 years of tamoxifen therapy is associated with a statistically significant survival benefit and is regarded as being sensitive by international and national experts.

In vitro cytochrome P450-mediated metabolism of exemestane

Exemestane is a potent and irreversible steroidal aromatase inhibitor drug used for the treatment of estrogen receptor-positive breast cancer. Our aim was to identify and assess the contribution of the specific cytochromes P450 (P450s) responsible for exemestane primary in vitro metabolism. With the use of high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry analytical techniques, 17-hydroexemestane (MI) formation and 6-hydroxymethylexemestane (MII) formation were found to be the predominant exemestane metabolic pathways. In a bank of 15 well characterized human liver microsomes with known P450 isoform-specific activities, the MI formation rate correlated significantly with CYP1A2 (Spearman r = 0.60, p = 0.02) and CYP4A11 (Spearman r = 0.67, p = 0.01) isoform-specific activities, whereas the MII production rate significantly correlated with CYP2B6 (Spearman r = 0.57, p = 0.03) and CYP3A (Spearman r = 0.76, p = 0.005) isoform-specific activities. Recombinant CYP1A1 metabolized exemestane to MI with a catalytic efficiency (Cl(int)) of 150 nl/pmol P450 × min that was at least 3.5-fold higher than those of other P450s investigated. Recombinant CYP3A4 catalyzed MII formation from exemestane with a catalytic efficiency of 840 nl/pmol P450 × min that was at least 4-fold higher than those of other P450s investigated. Among a panel of 10 chemical inhibitors tested, only ketoconazole and troleandomycin (CYP3A-specific chemical inhibitors) significantly inhibited the formation of MII by 45 and 95%, respectively. None of them markedly inhibited the formation of MI. In summary, exemestane seems to be metabolized to MI by multiple P450s that include CYP4A11 and CYP1A1/2, whereas its oxidation to MII is primarily mediated by CYP3A.

Exemestane: a review of its use in postmenopausal women with breast cancer

Exemestane (Aromasin) is an orally active steroidal irreversible inactivator of the aromatase enzyme indicated as an adjuvant treatment in postmenopausal women with estrogen receptor-positive early-stage breast cancer following 2-3 years of adjuvant treatment with tamoxifen, and for the treatment of advanced breast cancer in postmenopausal women whose disease has progressed following tamoxifen or other antiestrogen therapy. Exemestane is effective for the treatment of postmenopausal women with early-stage or advanced breast cancer. In early-stage disease, switching to exemestane for 2-3 years after 2-3 years of adjuvant tamoxifen treatment was more effective in prolonging disease-free survival than continuing tamoxifen therapy, although it was not associated with an overall survival benefit, except in those with estrogen receptor-positive or unknown receptor status disease when nodal status, hormone replacement therapy (HRT) and chemotherapy use were adjusted for. Moreover, preliminary data suggest that the efficacy of exemestane is generally no different to that of tamoxifen in the primary adjuvant treatment of early-stage breast cancer, although exemestane may be better in prolonging the time to distant recurrence. In advanced disease, exemestane showed equivalent efficacy to megestrol in patients with disease refractory to tamoxifen and an efficacy not significantly different from that of fulvestrant in those refractory to a nonsteroidal aromatase inhibitor. Available data, some of which are limited, suggest exemestane is also effective in the first-line hormonal treatment of advanced breast cancer in postmenopausal women. Exemestane is generally well tolerated, although the potential bone fracture risk of the drug requires further investigation. Results from directly comparative trials indicating the efficacy, tolerability and bone fracture risk of exemestane relative to third-generation aromatase inhibitors and other agents in both early-stage and advanced disease, as well as the optimal sequence of endocrine therapies, are awaited with interest. In the meantime, switching to exemestane should be considered in postmenopausal women who have received 2-3 years of adjuvant tamoxifen treatment for early-stage breast cancer, and is an emerging treatment option for postmenopausal women with advanced breast cancer refractory to one or more antiestrogen therapies.

Clinical Evaluation of the Use of Exemestane as Further Hormonal Therapy after Nonsteroidal Aromatase Inhibitors in Postmenopausal Metastatic Breast Cancer Patients

OBJECTIVES

The aromatase inhibitors Anastrozole, Letrozole (type 2 nonsteroidal aromatase inhibitors: n-SAI) and Exemestane (type 1 steroidal aromatase inactivator) are used respectively as first- and second-line hormonal therapy in postmenopausal metastatic breast cancer women. Few clinical data are published on the sequential use of different classes of aromatase inhibitors.

METHODS

We report an analysis on 30 postmenopausal metastatic breast cancer women treated between January 2000 and May 2002 in 2 Italian Oncology Institutions with the hormonal sequence n-SAI (Anastrozole, Letrozole) --> Exemestane.

RESULTS

When receiving n-SAI (Anastrozole 8 patients and Letrozole 22 patients), 1 out of 30 women achieved a partial response, 20 of 30 patients no change (NC) > or =6 months. The analysis of the entire population treated with Exemestane showed an overall clinical benefit (CB) of 46.6 percent (14/30) with a median duration of 12 months (95%CI 6-25) and a median time to progression (TTP) of 4 months (95%CI 1-25).

CONCLUSIONS

These data confirm a partial lack of cross-resistance between n-SAI --> Exemestane given in sequence.

Advances in Endocrine Therapy for Breast Cancer: Considering Efficacy, Safety, and Quality of Life

Breast cancer is the most common cancer found in women in the United States. Endocrine therapy is the standard of care for most women with hormone receptor-positive tumors in adjuvant and metastatic settings. The selective estrogen response modifier tamoxifen has been the standard treatment for postmenopausal patients for many years. Numerous new endocrine therapy agents provide women with novel treatment options, including the nonsteroidal aromatase inhibitors anastrozole and letrozole, the steroidal aromatase inhibitor exemestane, and the estrogen receptor antagonist fulvestrant. Clinical trials have begun to define the role of these agents and their unique side-effect profiles. Nurses are vital in supporting patients in the decision-making process, managing side effects of treatment, and making observations to enhance understanding of the patient experience with new treatments. This article will assist nurses in educating patients about endocrine therapy options and their associated potential short- and long-term side effects, as well as treatment demands.

Dose adaptation of antineoplastic drugs in patients with liver disease

Dose adaptation for liver disease is important in patients treated with antineoplastic drugs because of the high prevalence of impaired liver function in this population and the dose-dependent, frequently serious adverse effects of these drugs. We classified the antineoplastic drugs marketed in Switzerland at the end of 2004 according to their bioavailability and/or hepatic extraction to predict their kinetic behaviour in patients with decreased liver function. This prediction was compared with kinetic studies carried out with these drugs in patients with liver disease. The studies were identified by a structured, computer-based literature search. Of the 69 drugs identified, 52 had a predominant extrarenal (in most cases hepatic) metabolism and/or excretion. For 49 drugs, hepatic extraction could be calculated and/or bioavailability data were available, allowing classification according to hepatic extraction. For 18 drugs, kinetic studies have been reported in patients with impaired liver function, with the findings generally resulting in quantitative recommendations for adaptation of the dosage. In particular, recommendations are precise for 16 drugs excreted by the bile (e.g. doxorubicin and derivatives and vinca alkaloids). Validation studies comparing such recommendations with kinetics and/or dynamics of antineoplastic drugs in patients with decreased liver function have not been published. We conclude that there are currently not enough data for safe use of cyctostatics in patients with liver disease. Pharmaceutical companies should be urged to provide kinetic data (especially hepatic extraction data) for the classification of such drugs and to conduct kinetic studies for drugs with primarily hepatic metabolism in patients with impaired liver function to allow quantitative advice to be given for dose adaptation.

Adjuvant aromatase inhibitor therapy for early breast cancer: A review of the most recent data

Tamoxifen is the established adjuvant treatment for postmenopausal women with hormone-sensitive early breast cancer. However, the side-effects associated with tamoxifen therapy have prompted a search for safer and potentially more effective endocrine agents. Results from randomized trials of the third-generation aromatase inhibitors, anastrozole, letrozole and exemestane, demonstrating improved efficacy compared with tamoxifen and favorable tolerability profiles, are discussed in this review.

A review of exemestane in the management of breast cancer

Breast cancer is a major health problem in developed countries. Endocrine therapy is a key component in the management of hormone receptor-positive disease. Although tamoxifen has historically been the gold standard in the first-line management of early and advanced breast cancer, the rise of third-generation aromatase inhibitors in the past decade has resulted in a major shift in endocrine therapy. Clinical trials of aromatase inhibitors including exemestane, an orally active steroidal aromatase inactivator, have demonstrated significant improvements in outcome measures compared with tamoxifen. In early breast cancer, key questions remain regarding the optimal sequence, duration and type of aromatase inhibitors, as well as their long-term safety.

A predictive model for exemestane pharmacokinetics/pharmacodynamics incorporating the effect of food and formulation

AIMS

Exemestane (Aromasin) is an irreversible aromatase inactivator used for the treatment of postmenopausal women with advanced breast cancer. The objective of this study was to evaluate the effect of formulation comparing a sugar-coated tablet (SCT) with a suspension and food on the pharmacokinetics (PK) and pharmacodynamics (PD) with respect to plasma estrone sulphate (E1S) concentrations of exemestane, using a PK/PD approach.

METHODS

This was an open, three-period, randomized, crossover study. Twelve healthy postmenopausal women received single oral doses of 25 mg exemestane as a SCT after fasting or food and as a suspension after fasting. Exemestane and E1S concentrations were determined before and up to 14 days after drug administration. Population analysis was performed in two steps: (i) a compartmental PK model was selected incorporating the effect of food and formulation; (ii) conditional on the PK model, a PD model was developed employing indirect response models. Model selection was performed using standard statistical tests. Validation and assessment of the predictive capability of the selected model was performed using real test data sets obtained from the literature.

RESULTS

A three-compartment model with first-order elimination rate best described exemestane disposition (k12 0.454, k21 0.158, k13 0.174, k31 0.016 and k 0.738 h(-1)). Absorption was described by a mono-exponential function [ka 2.3 (SCT after fasting), 1.1 (SCT after food) and 7.6 h(-1) (suspension); lag time 0.2 h]. The PD model assumed that E1S plasma concentrations are determined by a zero-order synthesis rate (6.5 pg ml(-1) h(-1)) and a first-order elimination constant (0.032 h(-1)). Exemestane inhibited E1S synthesis with a C50 value of 22.1 pg ml(-1). The mean population estimates were used to simulate the administration of different doses of the drug (0.5, 1, 2.5, 5 and 25 mg day(-1)). The model predictions were in agreement with historical data.

CONCLUSIONS

Exemestane absorption is influenced by the formulation of the drug and by food, but its disposition is independent of both. PK differences do no translate into clinically important differences in the PD. The PK/PD model developed was able to predict successfully the response to different doses and administration schedules with respect to oestrogen suppression.

Pharmacokinetics and dose finding of a potent aromatase inhibitor, aromasin (exemestane), in young males

Suppression of estrogen, via estrogen receptor or aromatase blockade, is being investigated in the treatment of different conditions. Exemestane (Aromasin) is a potent and selective irreversible aromatase inhibitor. To characterize its suppression of estrogen and its pharmacokinetic (PK) properties in males, healthy eugonadal subjects (14-26 yr of age) were recruited. In a cross-over study, 12 were randomly assigned to 25 and 50 mg exemestane daily, orally, for 10 d with a 14-d washout period. Blood was withdrawn before and 24 h after the last dose of each treatment period. A PK study was performed (n = 10) using a 25-mg dose. Exemestane suppressed plasma estradiol comparably with either dose [25 mg, 38% (P <or= 0.002); 50 mg, 32% (P <or= 0.008)], with a reciprocal increase in testosterone concentrations (60% and 56%; P <or= 0.003 for both). Plasma lipids and IGF-I concentrations were unaffected by treatment. The PK properties of the 25-mg dose showed the highest exemestane concentrations 1 h after administration, indicating rapid absorption. The terminal half-life was 8.9 h. Maximal estradiol suppression of 62 +/- 14% was observed at 12 h. The drug was well tolerated. In conclusion, exemestane is a potent aromatase inhibitor in men and an alternative to the choice of available inhibitors. Long-term efficacy and safety will need further study.

An overview of the pharmacology and pharmacokinetics of the newer generation aromatase inhibitors anastrozole, letrozole, and exemestane

BACKGROUND

The newer generation, nonsteroidal aromatase inhibitors (AIs) anastrozole and letrozole have shown superior efficacy compared with tamoxifen as first-line treatments and compared with megestrol acetate as second-line therapy in postmenopausal women with advanced breast carcinoma. In an open-label, Phase II trial, it was reported that exemestane showed numerical superiority compared with tamoxifen for objective response and clinical benefit. Because these agents ultimately may be administered for periods of up to 5 years in the adjuvant setting, it is of increasing importance to assess their tolerability and pharmacologic profiles.

METHODS

In the absence of data from direct clinical comparisons, the published literature was reviewed for the clinical pharmacology, pharmacokinetic characteristics, and selectivity profiles of anastrozole, letrozole, and exemestane.

RESULTS

At clinically administered doses, the plasma half-lives of anastrozole (1 mg once daily), letrozole (2.5 mg once daily), and exemestane (25 mg once daily) were 41-48 hours, 2-4 days, and 27 hours, respectively. The time to steady-state plasma levels was 7 days for both anastrozole and exemestane and 60 days for letrozole. Androgenic side effects have been reported only with exemestane. Anastrozole treatment had no impact on plasma lipid levels, whereas both letrozole and exemestane had an unfavorable effect on plasma lipid levels. In indirect comparisons, anastrozole showed the highest degree of selectivity compared with letrozole and exemestane in terms of a lack of effect on adrenosteroidogenesis.

CONCLUSIONS

All three AIs demonstrated clinical efficacy over preexisting treatments. However, there were differences in terms of pharmacokinetics and effects on lipid levels and adrenosteroidogenesis. The long-term clinical significance of these differences remains to be elucidated.

Fulvestrant (Faslodex): current status in the therapy of breast cancer

Fulvestrant (Faslodex, formerly ICI 182,780) is a potent steroidal antiestrogen that mediates its effects by estrogen receptor downregulation. It appears to act as a pure antiestrogen and exhibits none of the negative side effects associated with the partial agonist activity of tamoxifen. It has been shown to be as effective as the oral aromatase inhibitor anastrozole in postmenopausal women with advanced breast cancer who have progressed on prior endocrine therapy, principally tamoxifen. It therefore provides the clinician with an alternative therapeutic strategy following the development of tamoxifen resistance. Fulvestrant might also have potential as a follow-on therapy after tamoxifen in an adjuvant setting and help alleviate some of the concerns surrounding long-term (up to 5 years) tamoxifen therapy.

A summary of second-line randomized studies of aromatase inhibitors

The new generation of selective aromatase inhibitors (anastrozole, letrozole and exemestane) offer a significant efficacy and safety advantage over both older agents in this class (aminoglutethimide) and the progestins (megestrol acetate (MA)), as second-line treatment for postmenopausal women with advanced hormone-dependent breast cancer who have failed on tamoxifen therapy. Exemestane, a steroidal aromatase inhibitor, has been shown to have activity after failure with the non-steroidal aromatase inhibitors, anastrozole and letrozole, and could be used as third-line treatment. Although the newer aromatase inhibitors belong to the same class and appear, from indirect comparisons, to have similar efficacy compared with the older therapies, they have different pharmacokinetic and pharmacodynamic profiles, suggesting the potential for clinical differences. Compared with exemestane and letrozole, anastrozole shows greater selectivity for aromatase, as it lacks any evidence of an effect on adrenal steroidogenesis and has no androgenic effects. Therefore, it is clear that these agents should not be considered to be similar in all respects. In summary, the introduction of the aromatase inhibitors represents a significant step forward in the treatment of advanced breast cancer in postmenopausal women. Studies in the adjuvant setting will ultimately determine whether the differences in pharmacokinetics and phamacodynamics will be of clinical relevance.

Anastrozole: pharmacological and clinical profile in postmenopausal women with breast cancer

A significant proportion of breast cancers are estrogen-dependent and are therefore amenable to endocrine therapy. Although tamoxifen has been the mainstream of endocrine treatment for over 20 years, new agents have entered the clinic, which have potentially superior activity and an improved safety profile. The development of orally-active, potent and selective third-line aromatase inhibitors represents a major advantage in the management of hormone-sensitive breast cancer. Anastrozole (Arimidex) was the first of these agents to become available and is currently widely indicated for both first- and second-line treatment for postmenopausal women with breast cancer. This review focuses on the biochemical properties and clinical efficacy of anastrozole, providing an overview of the current clinical status and possible future applications.