Exemestane's 17-hydroxylated metabolite exerts biological effects as an androgen

Menopausal symptoms in breast cancer survivors on adjuvant endocrine therapy compared with those of menopausal women

OBJECTIVES

To compare menopausal symptoms of breast cancer survivors on adjuvant endocrine therapy with those of menopausal women.

STUDY DESIGN

In a retrospective nested case-control study menopausal symptoms were compared of breast cancer survivors in pre-, peri- or post-menopause at the time of diagnosis, on tamoxifen or an aromatase inhibitor, plus a gonadotrophin-releasing hormone analogue, if pre- or peri-menopausal, and age-matched control women either in the late peri-menopause, or in surgical or in physiological post-menopause on no hormone replacement therapy. Differences between women on tamoxifen and those on aromatase inhibitors were also evaluated. Weighted and non-weighted t-tests, chi-square tests, and linear or logistic regressions were applied as appropriate.

MAIN OUTCOME MEASURES

Score on the Greene's Climacteric Scale and so of its subscales evaluating vasomotor, anxiety, depression, somatisation and sexuality symptoms.

RESULTS

A total of 99 breast cancer survivors (45 on tamoxifen, 54 on aromatase inhibitors) and 554 controls (173 in late perimenopause, 353 in natural and 28 in surgical menopause) were enrolled. The score on the Greene's Climacteric Scale was similar in cases and controls (means ± standard deviation) (21.3 ± 10.4 vs. 22.8 ± 11.5, p = 0.199), as were the subscale scores for vasomotor symptoms, anxiety, and somatisation. The depression score was lower (4.63 ± 3.3 vs. 5.98 ± 3.8; p = 0.001) in breast cancer survivors on adjuvant endocrine therapy, mainly due to a lower score of -2.132 (95 % confidence interval - 3.858/-0.407; p = 0.016) for users of aromatase inhibitors. The sexuality score was higher (1.76 ± 1.1 vs. 1.50 ± 1.1, p = 0.011) than in controls. Differences remained significant when corrected for age, menarche, body mass index, menopausal status (peri- or post-), type of menopause (natural, surgical), use of gonadotrophin-releasing hormone analogues, years of amenorrhea, smoking, alcohol use, and for breast radiotherapy, chemotherapy, tamoxifen or aromatase inhibitors. Among breast cancer survivors, women on aromatase inhibitors had lower scores for anxiety (5.75 ± 2.5vs.5.75 ± 2.5; p = 0.045) and depression (3.89 ± 2.5 vs. 5.13 ± 3.6; p = 0.046) than women on tamoxifen.

CONCLUSIONS

In breast cancer survivors, adjuvant therapy induces symptoms similar in type and intensity to those of symptomatic menopausal women. Compared with menopausal women, breast cancer survivors, particularly those on aromatase inhibitors, appear to experience less severe depressive symptoms.

Superior suppression of serum estrogens during neoadjuvant breast cancer treatment with letrozole compared to exemestane

PURPOSE

The aromatase inhibitor letrozole and the aromatase inactivator exemestane are two of the most pivotal cancer drugs used for endocrine treatment of ER-positive breast cancer in all phases of the disease. Although both drugs inhibit CYP19 (aromatase) and have been used for decades, a direct head-to-head, intra-patient-cross-over comparison of their ability to decrease estrogen synthesis in vivo is still lacking.

METHODS

Postmenopausal breast cancer patients suitable for neoadjuvant endocrine therapy were randomized to receive either letrozole (2.5 mg o.d.) or exemestane (25 mg o.d.) for an initial treatment period, followed by a second treatment period on the alternative drug (intra-patient cross-over study design). Serum levels of estrone (E1), estradiol (E2), letrozole, exemestane, and 17-hydroxyexemestane were quantified simultaneously using a novel, ultrasensitive LC-MS/MS method established in our laboratory.

RESULTS

Complete sets of serum samples (baseline and during treatment with letrozole or exemestane) were available from 79 patients, including 40 patients starting with letrozole (cohort 1) and 39 with exemestane (cohort 2). Mean serum estrone and estradiol levels in cohort 1 were 174 pmol/L and 46.4 pmol/L at baseline, respectively. Treatment with letrozole suppressed serum E1 and E2 to a mean value of 0.2 pmol/L and 0.4 pmol/L (P < 0.001). After the cross-over to exemestane, mean serum levels of E1 and E2 increased to 1.4 pmol/L and 0.7 pmol/L, respectively. In cohort 2, baseline mean serum levels of E1 and E2 were 159 and 32.5 pmol/L, respectively. Treatment with exemestane decreased these values to 1.8 pmol/L for E1 and 0.6 pmol/L for E2 (P < 0.001). Following cross-over to letrozole, mean serum levels of E1 and E2 were significantly further reduced to 0.1 pmol/L and 0.4 pmol/L, respectively. Serum drug levels were monitored in all patients throughout the entire treatment and confirmed adherence to the protocol and drug concentrations within the therapeutic range for all patients. Additionally, Ki-67 values decreased significantly during treatment with both aromatase inhibitors, showing a trend toward a stronger suppression in obese women.

CONCLUSION

To the best of our knowledge, we present here for the first time a comprehensive and direct head-to-head, intra-patient-cross-over comparison of the aromatase inhibitor letrozole and the aromatase inactivator exemestane concerning their ability to suppress serum estrogen levels in vivo. All in all, our results clearly demonstrate that letrozole therapy results in a more profound suppression of serum E1 and E2 levels compared to exemestane.

Letrozole delays acquisition of water maze task in female BALB/c mice: Possible involvement of anxiety

Letrozole, an aromatase inhibitor preventing estrogen synthesis from testosterone, is used as an adjuvant therapy in estrogen receptor-positive breast cancer patients. However, like other aromatase inhibitors, it induces many side effects, including impaired cognition. Despite its negative effect in humans, results from animal models are inconsistent and suggest that letrozole can either impair or improve cognition. Here, we studied the effects of chronic letrozole treatment on cognitive behavior of adult female BALB/c mice, a relevant animal model for breast cancer studies, to develop an appropriate animal model aimed at testing therapies to mitigate side effects of letrozole. In Morris water maze, letrozole 0.1 mg/kg impaired reference learning and memory. Interestingly, most of the letrozole 0.1 mg/kg-treated mice were able to learn the new platform position in reversal training and performed similar to control mice in a reversal probe test. Results of the reversal test suggest that letrozole did not completely disrupt spatial navigation, but rather delayed acquisition of spatial information. The delay might be related to increased anxiety as suggested by increased thigmotactic behavior during the reference memory training. The learning impairment was water maze-specific since we did not observe impairment in other spatial tasks such as in Y-maze or object location test. In contrast, the dose of 0.3 mg/kg did not have effect on water maze learning and facilitated locomotor habituation and recognition in novel object recognition test. The current study shows that letrozole dose-dependently modulates behavioral response and that its effects are task-dependent.

The effect of exemestane administration on the lipid profile in women: Meta-analysis of randomized controlled trials

OBJECTIVE

Postmenopausal women are prone to develop cardiovascular disorders. In addition, cardiovascular risk in women can be influenced by the long-term prescription of drugs that lead to estrogen deprivation, e.g., aromatase inhibitors, and that can cause dyslipidemia. Little is known about the impact of exemestane, an aromatase inhibitor, on serum lipids' concentration in women. Hence, we conducted a meta-analysis of randomized controlled trials (RCTs) to assess the influence of this pharmacological agent on the lipid profile in women.

METHODS

The Scopus, Web of Science, PubMed/Medline and EMBASE databases were searched by two surveyors for manuscripts published from the inception of these databases until April 3rd, 2023. No language restrictions were applied to the search. The random effects model was used to generate the combined results as weighted mean difference (WMD) and 95% confidence interval (CI).

RESULTS

In total, 8 eligible RCTs were included in the meta-analysis. Overall results from the random effects model indicate that exemestane administration increases LDL-C (WMD: 4.42 mg/dL, 95 % CI: 0.44, 8.41, P = 0.02) and decreases HDL-C (WMD: -6.03 mg/dL, 95 % CI: -7.77, -4.29, P < 0.001) and TC (WMD: -5.40 mg/dL, 95 % CI: -9.95, -0.86, P = 0.02) levels, respectively. Moreover, exemestane prescription only lowered TG concentrations when it was administered for < 12 months (WMD: -14.60 mg/dL, 95 % CI: -23.57 to -5.62, P = 0.001).

CONCLUSION

Currently available evidence suggests that the administration of exemestane in females increases LDL-C values and reduces HDL-C, TC, and, when prescribed for less than 12 months, TG concentrations.

Structures and functions of human placental aromatase and steroid sulfatase, two key enzymes in estrogen biosynthesis

Cytochrome P450 aromatase (AROM) and steroid sulfatase (STS) are the two key enzymes for the biosynthesis of estrogens in human, and maintenance of the critical balance between androgens and estrogens. Human AROM, an integral membrane protein of the endoplasmic reticulum, is a member of the cytochrome P450 superfamily. It is the only enzyme to catalyze the conversion of androgens with non-aromatic A-rings to estrogens characterized by the aromatic A-ring. Human STS, also an integral membrane protein of the endoplasmic reticulum, is a Ca2+-dependent enzyme that catalyzes the hydrolysis of sulfate esters of estrone and dehydroepiandrosterone to the unconjugated steroids, the precursors of the most potent forms of estrogens and androgens, namely, 17β-estradiol, 16α,17β-estriol, testosterone and dihydrotestosterone. Expression of these steroidogenic enzymes locally within organs and tissues of the endocrine, reproductive, and central nervous systems is the key for maintaining high levels of the reproductive steroids. The enzymes have been drug targets for the prevention and treatment of diseases associated with steroid hormone excesses, especially in breast, endometrial and prostate malignancies. Both enzymes have been the subjects of vigorous research for the past six decades. In this article, we review the important findings on their structure-function relationships, specifically, the work that began with unravelling of the closely guarded secrets, namely, the 3-D structures, active sites, mechanisms of action, origins of substrate specificity and the basis of membrane integration. Remarkably, these studies were conducted on the enzymes purified in their pristine forms from human placenta, the discarded and their most abundant source. The purification, assay, crystallization, and structure determination methodologies are described. Also reviewed are their functional quaternary organizations, post-translational modifications and the advancements made in the structure-guided inhibitor design efforts. Outstanding questions that still remain open are summarized in closing.

Lack of cross-resistance between non-steroidal and steroidal aromatase inhibitors in breast cancer patients: the potential role of the adipokine leptin

PURPOSE

The aromatase inactivator exemestane may cause clinical disease stabilization following progression on non-steroidal aromatase inhibitors like letrozole in patients with metastatic breast cancer, indicating that additional therapeutic effects, not necessarily related to estrogen-suppression, may be involved in this well-known "lack of cross-resistance".

METHODS

Postmenopausal women with ER positive, HER-2 negative, locally advanced breast cancer were enrolled in the NEOLETEXE-trial and randomized to sequential treatment starting with either letrozole (2.5 mg o.d.) or exemestane (25 mg o.d.) followed by the alternative aromatase inhibitor. Serum levels of 54 cytokines, including 12 adipokines were assessed using Luminex xMAP technology (multiple ELISA).

RESULTS

Serum levels of leptin were significantly decreased during treatment with exemestane (p < 0.001), regardless whether exemestane was given as first or second neoadjuvant therapy. In contrast, letrozole caused a non-significant increase in serum leptin levels in vivo.

CONCLUSIONS

Our findings suggest an additional and direct effect of exemestane on CYP-19 (aromatase) synthesis presumably due to effects on the CYP19 promoter use that is not present during therapy with the non-steroidal aromatase inhibitor letrozole. Our findings provide new insights into the influence of clinically important aromatase inhibitors on cytokine levels in vivo that contribute to the understanding of the clinically observed lack of cross-resistance between non-steroidal and steroidal aromatase inhibitors in breast cancer patients.

TRIAL REGISTRATION

Registered on March 23rd 2015 in the National trial database of Norway (Registration number: REK-SØ-84-2015).

Three photoinitiators induce breast tumor growth in mouse xenografts with MCF-7 breast cancer cells

Photoinitiators are utilized in the production of a wide range of commonly used products. However, some photoinitiators exert toxic effects. We previously demonstrated the endocrine-disrupting effects of photoinitiators in vitro. The present study investigated the estrogenic activities of three photoinitiators: 1-hydroxycyclohexyl phenyl ketone (1-HCHPK), methyl 2-benzoylbenzoate (MBB), and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone (MTMP), which were subcutaneously injected into mouse xenografts with MCF-7 breast cancer cells. The results obtained showed that 1-HCHPK, MBB, and MTMP promoted breast tumor growth in these xenografts. A pretreatment with the estrogen receptor antagonist tamoxifen blocked the tumor growth-promoting effects of each photoinitiator. Collectively, the present results suggest that the three photoinitiators exhibit estrogenic agonist activities in vivo. Furthermore, as a factor for breast tumor growth, these photoinitiators potentially have estrogenic properties in vivo.

Challenges in Preventing Bone Loss Induced by Aromatase Inhibitors

CONTEXT

Aromatase inhibitors have become a mainstay in the adjuvant treatment regimen in postmenopausal women with hormone receptor-positive breast cancer. While many of these patients have an excellent long-term prognosis, adverse effects on bone represent an emerging complication of aromatase inhibitor treatment, resulting in substantial bone loss and fragility fractures. Treatment approaches to prevent aromatase inhibitor-induced bone loss typically consist of an antiresorptive approach with bisphosphonates or the RANKL antibody denosumab. However, different guidelines vary with respect to treatment thresholds, duration, and dosing. The choice of antiresorptive regime is further complicated by comorbidities and potential disease-modifying effects of individual agents.

OBJECTIVE

This review summarizes the evidence of how aromatase inhibitors affect bone health and provides an update of clinical approaches to preserve bone strength in affected women. (J Clin Endocrinol Metab XX: 0-0, 2020).

Changes in serum estrogenic activity during neoadjuvant therapy with letrozole and exemestane

The aromatase inhibitors (AIs), letrozole (Femar®/Femara®) and exemestane (Aromasin®), are widely used to treat estrogen receptor (ER) positive breast cancer in postmenopausal patients. In the setting of metastatic breast cancer, these drugs may be used after another causing new responses in selected patients after progressing on the first choice. The precise explanation for this "lack of cross resistance" is still missing. NEOLETEXE is a neoadjuvant, randomized, open-label, cross-over trial. Postmenopausal patients with ER-positive, HER-2 negative, locally advanced breast cancer were enrolled. All patients were randomized to treatment starting with either letrozole or exemestane for at least 2 months followed by another 2 months on the alternative AI. The total estrogenic activities in blood samples were determined using the AroER tri-screen assay developed in the Chen laboratory. Using this highly sensitive assay, estrogenic activity was detected at three time points for all patients. Importantly, a significantly higher total estrogenic activity was found during therapy with exemestane compared to letrozole in 21 out of 26 patients. When letrozole was included in the AroER tri-screen assay, the estrogenic activities in most samples collected during exemestane treatment were further reduced, suggesting that low levels of androgens remained in specimens obtained after exemestane treatment. Our results suggest the AroER tri-screen to be a very sensitive method to estimate the overall estrogen-mediated activity in human samples even during therapy with highly potent aromatase inhibitors. In the present study, serum estrogen activity was significantly higher during exemestane therapy when compared to letrozole therapy.

[Academic Detailing from the Viewpoint of Chemical Structural Formulas]

In order to implement academic detailing, it is extremely important to understand the pharmacological activity of drugs based on their chemical structures. To construct a database for academic detailing, a viewpoint for clinically utilizing the fundamental pharmacological features of a drug is required. These fundamental pharmacological features include chemical characteristics such as chemical structures, physical characteristics such as pharmaceutical formulations for efficient drug delivery to target organs, and a pharmacological viewpoint, which is a mechanism by which a drug is determined to be effective. In addition, in vivo kinetics are included in a drug's pharmacological features, i.e., a drug's excretion through urine and feces via the kidneys, its side effects due to differences in enzyme type when the drug is metabolized in the liver, as well as the capacity of the patient's current enzyme profile. This review describes academic detailing based on the chemical structure of drugs for breast cancer hormone therapy, as an example.

The beneficial androgenic action of steroidal aromatase inactivators in estrogen-dependent breast cancer after failure of nonsteroidal drugs

Direct treatment of ER (+) breast cancer with Formestane diminishes the tumor within weeks. This is unlikely due to lack of estrogens alone. We proposed that it is the negative influence of androgens on the growth of ER(+) breast cancer. We investigated the influence of Formestane and Exemestane and of their major androgenic metabolites 4-hydroxytestosterone and 17-hydroexemestane on the proliferation of MCF-7 cells and ZR-75-1 cells. Inhibitory effects could be prevented by antiandrogens and siRNA. Activation of the AR in MCF-7 and U2-OS cells was tested by reporter gene assays. In vivo androgenicity was evaluated using the Hershberger assay. Influence on the cell cycle was demonstrated by flow-cytometry. Influence of androgens on the activity of CCND1 was demonstrated by Chip-qPCR. Antitumor activity was determined by topical treatment of DMBA tumors. We found that breast cancer cells can metabolize Formestane and Exemestane to androgenic compounds which inhibit proliferation. This can be explained by hindering the accessibility of CCND1 by histone modification. Androgenic metabolites can abolish the growth of DMBA-tumors and prevent the appearance of new tumors. The lack of cross-resistance between steroidal and nonsteroidal aromatase inhibitors is due to inhibitory effects of androgenic steroidal metabolites on the production of cyclin D1. These sterols not only inhibit proliferation of cancer cells but can also stop the growth of DMBA cancers upon direct absorption into the tumor. The quick and considerable effect on ER(+) tumors may open a new avenue for neodjuvant treatment.

Outcomes in women with invasive ductal or invasive lobular early stage breast cancer treated with anastrozole or exemestane in CCTG (NCIC CTG) MA.27

BACKGROUND

Histological subtype, (invasive ductal breast cancer (IDBC)/invasive lobular breast cancer (ILBC)), might be a marker for differential response to endocrine therapy in breast cancer.

METHODS

Clinical trial MA.27 compared 5 years of adjuvant anastrozole or exemestane in postmenopausal patients with hormone receptor positive early breast cancer. We evaluated IDBC versus ILBC (based on original pathology reports) as predictor for event-free survival (EFS) and overall survival (OS).

RESULTS

A total of 5709 patients (5021 with IDBC and 688 with ILBC) were included (1876 were excluded because of missing or other histological subtype). Median follow-up was 4.1 years. Overall, histological subtype did not influence OS or EFS (HR (hazard ratio) 1.14, 95% confidence interval (CI) [0.79-1.63], P = 0.49 and HR 1.04, 95% CI [0.77-1.41], P = 0.81, respectively). There was no significant difference in OS between treatment with exemestane versus treatment with anastrozole in the IDBC group (HR = 0.92, 95% CI [0.73-1.16], P = 0.46). In the ILBC group, a marginally significant difference in favour of treatment with anastrozole was seen (HR = 1.79, 95% CI [0.98-3.27], P = 0.055). In multivariable analysis a prognostic effect of the interaction between treatment and histological subtype on OS (but not on EFS) was noted, suggesting a better outcome for patients with ILBC on anastrozole (HR 2.1, 95% CI [0.99-4.29], P = 0.05). After stepwise selection in the multivariable model, a marginally significant prognostic effect for the interaction variable (treatment with histological subtype) on OS (but not on EFS) was noted (Ratio of HR 2.1, 95% CI [1.00-4.31], P = 0.05).

CONCLUSION

Our data suggest an interaction effect between treatment and histology (P = 0.05) on OS. Here, patients with ILBC cancers had a better OS when treated with anastrozole versus exemestane, whereas no difference was noted for patients with IDBC.

CLINICAL TRIAL INFORMATION

NCT00066573.

Cognitive sequelae of endocrine therapy in women treated for breast cancer: a meta-analysis

PURPOSE

Evidence suggests anti-estrogen endocrine therapy (ET) is associated with adverse cognitive effects; however, findings are based on small samples and vary in the cognitive abilities affected. We conducted a meta-analysis to quantitatively synthesize the evidence.

METHODS

Electronic databases were searched in November 2016. Fourteen studies totaling 911 BC patients on aromatase inhibitors (AIs) or tamoxifen (TAM) and 911 controls (i.e., non-cancer controls and BC controls not using ET) were included. Neuropsychological tests were categorized into six domains. Effect sizes were computed to compare (1) ET patients versus controls and (2) TAM patients versus AI patients.

RESULTS

In cross-sectional comparisons, ET patients performed worse than control groups on verbal learning/memory, visual learning/memory, frontal executive function, and processing speed, but did not differ on psychomotor efficiency or visuospatial function. Subgroup analyses revealed that verbal learning/memory was the only domain where ET patients performed worse than both non-cancer and BC controls. In other domains, ET patients and BC controls performed equivalently. Regarding change from pre-treatment performance, ET patients did not differ from controls on any domain. TAM and AI patients did not from one another differ overall; however, subgroup analyses indicated that TAM patients performed better than non-steroidal AI patients on several domains, but showed few performance differences relative to steroidal AI patients.

CONCLUSIONS

Verbal learning/memory was the only domain where ET patients performed worse than both non-cancer and BC controls, suggesting specific adverse effects on this domain. Additional studies assessing change from pre-treatment performance and differences between steroidal and non-steroidal AIs are warranted.

Effect of aromatase inhibitors on learning and memory and modulation of hippocampal dickkopf-1 and sclerostin in female mice

BACKGROUND

There has been conflicting reports on the effect of third generation aromatase inhibitors on cognition in estrogen-deficient states. Since aromatase inhibitors themselves cause estrogen deprivation, the present work was designed to evaluate the comparative effect of three aromatase inhibitors on behavioral measures of learning and memory in female mice. Further, in view of the reports of estrogen and Wnt signaling pathway in cognition, the role of two Wnt signaling antagonists (dickkopf-1 and sclerostin) in mediation of cognitive effects of aromatase inhibitors was evaluated.

METHODS

Three behavioral paradigms were used for evaluating cognitive functions viz. Morris water maze, active avoidance learning and spontaneous alternation behavior following 10-15days of administration with aromatase inhibitors and the levels of dickkopf-1 and sclerostin were evaluated in hippocampus of female mice.

RESULTS

Anastrozole and letrozole (but not exemestane) impaired learning and memory as indicated by increase in escape latency and path length during spatial acquisition, reduction of % quadrant dwell time in Morris water maze, reduction of % avoidance and increase in escape responses in active avoidance learning and decrease in % alternation in a cross maze. The behavioral effects correlated well with the levels of dickkopf-1 and sclerostin in the mouse hippocampus. The highest impairment in learning and memory occurred with letrozole followed by anastrozole while exemestane was without such effects.

CONCLUSION

The present study demonstrates that aromatase inhibitors have adverse impact on cognition. Furthermore, modulation of Wnt signaling following estrogen depletion possibly contributed to observed effects in case of anastrozole and letrozole.

Exemestane and Its Active Metabolite 17-Hydroexemestane Induce UDP-Glucuronosyltransferase (UGT) 2B17 Expression in Breast Cancer Cells

Exemestane (EXE) is an aromatase inhibitor indicated for endocrine therapy of breast cancer in postmenopausal women. The primary active metabolite of EXE, 17-hydroexemestane (17-HE), is inactivated via glucuronidation, mainly by UDP-glucuronosyltransferase 2B17 (UGT2B17). UGT2B17 also has a primary role in inactivation of endogenous androgens testosterone and dihydrotestosterone and may play an important role in regulation of breast and prostate tumor intracrinology. We recently reported that UGT2B17 could be induced by both estrogenic and androgenic ligands in breast cancer cells via binding of the estrogen receptor α (ERα) or the androgen receptor (AR) to a complex regulatory unit in the proximal UGT2B17 promoter. In this study we show that both EXE and 17-HE increase UGT2B17 mRNA levels in breast cancer MCF-7 and MDA-MB-453 cells, and increase glucuronidation of UGT2B17 substrates, including 17-HE and androsterone. Using antagonists of ERα and AR as well as inhibition mediated by small interfering RNA (siRNA) we demonstrate that EXE and 17-HE induce UGT2B17 expression primarily via the AR. This result is consistent with previous reports that 17-HE can act as an AR ligand. In vitro studies suggest that multiple steroid-responsive DNA elements within the proximal promoter are involved in the response to 17-HE-liganded AR. The up-regulation of UGT2B17 by EXE and 17-HE in breast cancer cells might enhance the local metabolism of 17-HE as well as that of endogenous androgens, hence impacting potentially on treatment outcomes.

In vitro metabolism of exemestane by hepatic cytochrome P450s: impact of nonsynonymous polymorphisms on formation of the active metabolite 17β-dihydroexemestane

Exemestane (EXE) is an endocrine therapy commonly used by postmenopausal women with hormone‐responsive breast cancer due to its potency in inhibiting aromatase‐catalyzed estrogen synthesis. Preliminary in vitro studies sought to identify phase I EXE metabolites and hepatic cytochrome P450s (CYP450s) that participate in EXE biotransformation. Phase I metabolites were identified by incubating EXE with HEK293‐overexpressed CYP450s. CYP450s 1A2, 2C8, 2C9, 2C19, 2D6, 3A4, and 3A5 produce 17β‐dihydroexemestane (17β‐DHE), an active major metabolite, as well as two inactive metabolites. 17β‐DHE formation in pooled human liver microsomes subjected to isoform‐specific CYP450 inhibition was also monitored using tandem mass spectrometry. 17β‐DHE production in human liver microsomes was unaffected by isoform‐specific inhibition of CYP450s 2A6, 2B6, and 2E1 but decreased 12–39% following inhibition of drug‐metabolizing enzymes from CYP450 subfamilies 1A, 2C, 2D, and 3A. These results suggest that redundancy exists in the EXE metabolic pathway with multiple hepatic CYP450s catalyzing 17β‐DHE formation in vitro. To further expand the knowledge of phase I EXE metabolism, the impact of CYP450 genetic variation on 17β‐DHE formation was assessed via enzyme kinetic parameters. Affinity for EXE substrate and enzyme catalytic velocity were calculated for hepatic wild‐type CYP450s and their common nonsynonymous variants by monitoring the reduction of EXE to 17β‐DHE. Several functional polymorphisms in xenobiotic‐metabolizing CYP450s 1A2, 2C8, 2C9, and 2D6 resulted in deviant enzymatic activity relative to wild‐type enzyme. Thus, it is possible that functional polymorphisms in EXE‐metabolizing CYP450s contribute to inter‐individual variability in patient outcomes by mediating overall exposure to the drug and its active metabolite, 17β‐DHE.

Impact of nonsynonymous single nucleotide polymorphisms on in-vitro metabolism of exemestane by hepatic cytosolic reductases

OBJECTIVE

Exemestane (EXE) is a potent third-generation aromatase inhibitor used as endocrine therapy in breast cancer treatment and prevention. Characterization of its metabolic pathway is incomplete, with ambiguity existing in the identity of enzymes driving the production of its key metabolite, 17β-dihydroexemestane (17β-DHE). The impact of genetic variation on EXE metabolism is also unknown. This study aims to describe cytosolic reductase involvement in hepatic EXE metabolism and to assess the impact of functional polymorphisms on metabolite production.

MATERIALS AND METHODS

Phase I metabolites were identified in incubations of EXE with pooled human liver cytosol or recombinant protein for AKR1Cs and CBR1. Kinetic parameters characterizing EXE reduction were measured for purified wild-type enzymes, and nonsynonymous variants occurring at greater than 1% minor allele frequency using UPLC/MS/MS.

RESULTS

Human liver cytosol, CBR1, AKR1C1, AKR1C2, AKR1C3, and AKR1C4 reduce EXE to active primary metabolite 17β-DHE. The formation of a novel metabolite, 17α-DHE, was catalyzed by recombinant AKR1C4 and CBR1 in addition to hepatic cytosol. Variants AKR1C3 Arg258Cys and AKR1C4 Gly135Glu had significantly decreased affinity for EXE relative to their respective wild types. Five common AKR1C3 polymorphisms were associated with decreased rates of catalysis, whereas AKR1C4 Gly135Glu increased the velocity of EXE reduction.

CONCLUSION

AKR1Cs and CBR1 catalyze EXE reduction in vitro. These results imply that cytosolic ketosteroid reductases may participate in the EXE metabolic pathway in vivo. In addition, several common variants were associated with altered enzymatic activity, suggesting that functional polymorphisms could play an important role in overall EXE metabolism and activity by altering the extent and duration of 17β-DHE exposure.

Unravelling exemestane: From biology to clinical prospects

Aromatase inhibitors (AIs) are anti-tumor agents used in clinic to treat hormone-dependent breast cancer. AIs block estrogens biosynthesis by inhibiting the enzyme aromatase, preventing tumor progression. Exemestane, a third-generation steroidal AI, belongs to this class of drugs and is currently used in clinic to treat postmenopausal women, due to its high efficacy and good tolerability. Here, its pharmacological and biological aspects as well as its clinical applications and comparison to other endocrine therapeutic agents, are reviewed. It is also focused the benefits and risks of exemestane, drawbacks to be overcome and aspects to be explored.

The molecular mechanisms between metabolic syndrome and breast cancer

Metabolic syndrome, which is extremely common in developed and some developing countries, is a clustering of at least three of five of the following medical conditions: abdominal obesity, elevated blood pressure, elevated fasting plasma glucose, high serum triglycerides, and low high-density lipoprotein levels. It has been proved that there is a strong association between metabolic syndrome and breast cancer. Metabolic syndrome could increase the risk of breast cancer and influence the prognosis of the breast cancer patients. Some characteristic of metabolic syndrome such as obesity and lack of physical exercise are all risk factors for developing breast cancer. The metabolic syndrome mainly include obesity, type 2 diabetes, hypercholesterolemia and nonalcoholic fatty liver disease, and each of them impacts the risk of breast cancer and the prognosis of the breast cancer patients in different ways. In this Review, we focus on recently uncovered aspects of the immunological and molecular mechanisms that are responsible for the development of this highly prevalent and serious disease. These studies bring new insight into the complex associations between metabolic syndrome and breast cancer and have led to the development of novel therapeutic strategies that might enable a personalized approach in the management of this disease.

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

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

Impact of UGT2B17 Gene Deletion on the Pharmacokinetics of 17-Hydroexemestane in Healthy Volunteers

Exemestane is an aromatase inhibitor drug used for the treatment of hormone-dependent breast cancer. 17-Hydroexemestane, the major and biologically active metabolite of exemestane in humans, is eliminated via glucuronidation by the polymorphic UGT2B17 phase II drug-metabolizing enzyme. Previous microsomal studies have shown that UGT2B17 gene deletion affects the intrinsic hepatic clearances of 17-hydroexemestane in vitro. In this open-label study we set out to assess the effect of UGT2B17 gene deletion on the pharmacokinetics of 17-hydroexemestane in healthy female volunteers with and without UGT2B17. To achieve this goal, 14 healthy postmenopausal women (8 carriers of the homozygous UGT2B17 wild-type allele and 6 carriers of the homozygous UGT2B17 gene-deletion allele) were enrolled and invited to receive a single 25-mg oral dose of exemestane. Pharmacokinetics was assessed over 72 hours postdosing. Our results showed that there were statistically significant differences in plasma 17-hydroexemestane AUC0-∞ (P = .0007) and urine 17-hydroexemestane C24h (P = .001) between UGT2B17 genotype groups. Our data suggest that UGT2B17 gene deletion influences 17-hydroexemestane pharmacokinetics in humans.

Microbial transformation of anti-cancer steroid exemestane and cytotoxicity of its metabolites against cancer cell lines

Background

Microbial transformation of steroids has been extensively used for the synthesis of steroidal drugs, that often yield novel analogues, not easy to obtain by chemical synthesis. We report here fungal transformation of a synthetic steroidal drug, exemestane, used for the treatment of breast cancer and function through inhibition of aromatase enzyme.

Results

Microbial transformation of anti-cancer steroid, exemestane (1), was investigated by using two filamentous fungi. Incubation of 1 with fungi Macrophomina phaseolina, and Fusarium lini afforded three new, 11α-hydroxy-6-methylene-androsta-1, 4-diene-3,17-dione (2), 16β, 17β-dihydroxy-6-methylene-androsta-1, 4-diene-3-one (3), and 17β-hydroxy-6-methylene-androsta-1, 4-diene-3, 16-dione (4), and one known metabolites, 17β-hydroxy-6-methylene-androsta-1, 4-diene-3-one (5). Their structures were deduced spectroscopically. Compared to 1 (steroidal aromatase inactivator), the transformed metabolites were also evaluated for cytotoxic activity by using a cell viability assay against cancer cell lines (HeLa and PC3). Metabolite 2 was found to be moderately active against both the cell lines.

Conclusions

Biotransformation of exemestane (1) provides an efficient method for the synthesis of new analogues of 1. The metabolites were obtained as a result of reduction of double bond and hydroxylation. The transformed product 2 exhibited a moderate activity against cancer cell lines (HeLa and PC3). These transformed products can be studied for their potential as drug candidates.

Effect of everolimus on bone marker levels and progressive disease in bone in BOLERO-2

BACKGROUND

Breast Cancer Trials of Oral Everolimus 2 (BOLERO-2), a phase III study in postmenopausal women with estrogen receptor-positive breast cancer progressing despite nonsteroidal aromatase inhibitor therapy, showed statistically significant benefits with adding everolimus to exemestane. Moreover, in preclinical studies, mammalian target of rapamycin inhibition was associated with decreased osteoclast survival and activity. Exploratory analyses in BOLERO-2 evaluated the effect of everolimus on bone marker levels and progressive disease in bone.

METHODS

Patients were treated with exemestane (25mg/day) and randomized (2:1) to everolimus (10mg/day; combination) or placebo (exemestane only). Exploratory endpoints included changes in bone turnover marker levels vs baseline and progressive disease in bone, defined as unequivocal progression of a preexisting bone lesion or the appearance of a new bone lesion.

RESULTS

Baseline disease characteristics were well balanced between arms (N = 724); baseline bisphosphonate use was not (43.9% combination vs 54.0% exemestane only). At a median of 18 months of follow-up, median progression-free survival (primary endpoint) was statistically significantly longer with the combination vs exemestane only (Cox proportional hazard ratio = 0.45, 95% confidence interval = 0.38 to 0.54; log-rank, 1-sided P < .0001). Bone marker levels at 6 and 12 weeks increased with exemestane only, as expected, but decreased with the combination. The cumulative incidence rate of progressive disease in bone was lower in the combination arm. Bone-related adverse events occurred with similar frequency in both arms (3.3% combination vs 4.2% exemestane only).

CONCLUSION

These exploratory analyses suggest that everolimus has beneficial effects on bone turnover and progressive disease in bone in patients receiving exemestane for hormone receptor-positive breast cancer progressing during/after nonsteroidal aromatase inhibitor therapy.

The epidemiology and molecular mechanisms linking obesity, diabetes, and cancer

The worldwide epidemic of obesity is associated with increasing rates of the metabolic syndrome and type 2 diabetes. Epidemiological studies have reported that these conditions are linked to increased rates of cancer incidence and mortality. Obesity, particularly abdominal obesity, is associated with insulin resistance and the development of dyslipidemia, hyperglycemia, and ultimately type 2 diabetes. Although many metabolic abnormalities occur with obesity and type 2 diabetes, insulin resistance and hyperinsulinemia appear to be central to these conditions and may contribute to dyslipidemia and altered levels of circulating estrogens and androgens. In this review, we will discuss the epidemiological and molecular links between obesity, type 2 diabetes, and cancer, and how hyperinsulinemia and dyslipidemia may contribute to cancer development. We will discuss how these metabolic abnormalities may interact with estrogen signaling in breast cancer growth. Finally, we will discuss the effects of type 2 diabetes medications on cancer risk.

Progesterone-inducible cytokeratin 5-positive cells in luminal breast cancer exhibit progenitor properties

Progestins play a deleterious role in the onset of breast cancer, yet their influence on existing breast cancer and tumor progression is not well understood. In luminal estrogen receptor (ER)- and progesterone receptor (PR)-positive breast cancer, progestins induce a fraction of cells to express cytokeratin 5 (CK5), a marker of basal epithelial and progenitor cells in the normal breast. CK5(+) cells lose expression of ER and PR and are relatively quiescent, increasing their resistance to endocrine and chemotherapy compared to intratumoral CK5(-)ER(+)PR(+) cells. Characterization of live CK5(+) cells has been hampered by a lack of means for their direct isolation. Here, we describe optical (GFP) and bioluminescent (luciferase) reporter models to quantitate and isolate CK5(+) cells in luminal breast cancer cell lines utilizing the human KRT5 gene promoter and a viral vector approach. Using this system, we confirmed that the induction of GFP(+)/CK5(+) cells is specific to progestins, is dependent on PR, can be blocked by antiprogestins, and does not occur with other steroid hormones. Progestin-induced, fluorescence-activated cell sorting-isolated CK5(+) cells had lower ER and PR mRNA, were slower cycling, and were relatively more invasive and sphere forming than their CK5(-) counterparts in vitro. Repeated progestin treatment and selection of GFP(+) cells enriched for a persistent population of CK5(+) cells, suggesting that this transition can be semi-permanent. These data support that in PR(+) breast cancers, progestins induce a subpopulation of CK5(+)ER(-)PR(-) cells with enhanced progenitor properties and have implications for treatment resistance and recurrence in luminal breast cancer.

Novel aromatase inhibitors by structure-guided design

Human cytochrome P450 aromatase catalyzes with high specificity the synthesis of estrogens from androgens. Aromatase inhibitors (AIs) such as exemestane, 6-methylideneandrosta-1,4-diene-3,17-dione, are preeminent drugs for the treatment of estrogen-dependent breast cancer. The crystal structure of human placental aromatase has shown an androgen-specific active site. By utilization of the structural data, novel C6-substituted androsta-1,4-diene-3,17-dione inhibitors have been designed. Several of the C6-substituted 2-alkynyloxy compounds inhibit purified placental aromatase with IC(50) values in the nanomolar range. Antiproliferation studies in a MCF-7 breast cancer cell line demonstrate that some of these compounds have EC(50) values better than 1 nM, exceeding that for exemestane. X-ray structures of aromatase complexes of two potent compounds reveal that, per their design, the novel side groups protrude into the opening to the access channel unoccupied in the enzyme-substrate/exemestane complexes. The observed structure-activity relationship is borne out by the X-ray data. Structure-guided design permits utilization of the aromatase-specific interactions for the development of next generation AIs.

The development, application and limitations of breast cancer cell lines to study tamoxifen and aromatase inhibitor resistance

Estrogen plays important roles in hormone receptor-positive breast cancer. Endocrine therapies, such as the antiestrogen tamoxifen, antagonize the binding of estrogen to estrogen receptor (ER), whereas aromatase inhibitors (AIs) directly inhibit the production of estrogen. Understanding the mechanisms of endocrine resistance and the ways in which we may better treat these types of resistance has been aided by the development of cellular models for resistant breast cancers. In this review, we will discuss what is known thus far regarding both de novo and acquired resistance to tamoxifen or AIs. Our laboratory has generated a collection of AI- and tamoxifen-resistant cell lines in order to comprehensively study the individual types of resistance mechanisms. Through the use of microarray analysis, we have determined that our cell lines resistant to a particular AI (anastrozole, letrozole, or exemestane) or tamoxifen are distinct from each other, indicating that these mechanisms can be quite complex. Furthermore, we will describe two novel de novo AI-resistant cell lines that were generated from our laboratory. Initial characterization of these cells reveals that they are distinct from our acquired AI-resistant cell models. In addition, we will review potential therapies which may be useful for overcoming resistant breast cancers through studies using endocrine resistant cell lines. Finally, we will discuss the benefits and shortcomings of cell models. Together, the information presented in this review will provide us a better understanding of acquired and de novo resistance to tamoxifen and AI therapies, the use of appropriate cell models to better study these types of breast cancer, which are valuable for identifying novel treatments and strategies for overcoming both tamoxifen and AI-resistant breast cancers.

Comparison of changes in the lipid profile of postmenopausal women with early stage breast cancer treated with exemestane or letrozole

Effects of aromatase inhibitor (AI) therapy on the plasma lipid profile are not clear. Here the authors describe changes in fasting lipids (total cholesterol, high-density lipoprotein [HDL], low-density lipoprotein [LDL], and triglycerides) before and after 3 months of exemestane or letrozole treatment. HDL was reduced in the entire cohort (P < .001) and in the exemestane group (P < .001) but unchanged in the letrozole group (P = .169). LDL was increased in the entire cohort (P = .005) and in the letrozole group (P = .002) but unchanged in the exemestane group (P = .361). This effect was at least partially attributable to washout of tamoxifen as only patients with prior use of tamoxifen experienced a significant increase in LDL. Baseline HDL was an independent predictor of the change in HDL (r(2) = -0.128, P < .001), and prior tamoxifen use was associated with greater increases in LDL (r(2) = 0.057, P < .001). Use of lipid-altering medications did not protect against the exemestane-induced drop in HDL or the increase in LDL observed in women with prior use of tamoxifen taking letrozole. In conclusion, AI treatment and/or washout of tamoxifen induced detrimental changes in the lipid profile of postmenopausal women with breast cancer.

Estrogen carcinogenesis in breast cancer

Many studies have reported a correlation between elevated estrogen blood levels and breast cancer and this observation has raised controversy concerning the long-term use of hormonal replacement therapy. This review will not address further this controversial topic; but rather, this review focuses on the role of estrogen signaling in first, the normal development of the breast and second, how alterations of this signaling pathway contribute to breast cancer.

Breast cancer medications and vision: effects of treatments for early-stage disease

This review concerns the effects on vision and the eye of medications prescribed at three phases of treatment for women with early-stage breast cancer (BC): (1) adjuvant cytotoxic chemotherapy, (2) adjuvant endocrine therapy, and (3) symptomatic relief. The most common side effects of cytotoxic chemotherapy are epiphora and ocular surface irritation, which can be caused by any of several different regimens. Most notably, the taxane docetaxel can lead to epiphora by inducing canalicular stenosis. The selective-estrogen-receptor-modulator (SERM) tamoxifen, long the gold-standard adjuvant-endocrine-therapy for women with hormone-receptor-positive BC, increases the risk of posterior subcapsular cataract. Tamoxifen also affects the optic nerve head more often than previously thought, apparently by causing subclinical swelling within the first 2 years of use for women older than ∼50 years. Tamoxifen retinopathy is rare, but it can cause foveal cystoid spaces that are revealed with spectral-domain optical coherence tomography (OCT) and that may increase the risk for macular holes. Tamoxifen often alters the perceived color of flashed lights detected via short-wavelength-sensitive (SWS) cone response isolated psychophysically; these altered perceptions may reflect a neural-response sluggishness that becomes evident at ∼2 years of use. The aromatase inhibitor (AI) anastrozole affects perception similarly, but in an age-dependent manner suggesting that the change of estrogen activity towards lower levels is more important than the low estrogen activity itself. Based on analysis of OCT retinal thickness data, it is likely that anastrozole increases the tractional force between the vitreous and retina. Consequently, AI users, myopic AI users particularly, might be at increased risk for traction-related vision loss. Because bisphosphonates are sometimes prescribed to redress AI-induced bone loss, clinicians should be aware of their potential to cause scleritis and uveitis occasionally. We conclude by suggesting some avenues for future research into the visual and ocular effects of AIs, particularly as relates to assessment of cognitive function.

Histologic and cytologic detection of endocrine and reproductive tract effects of exemestane in female rats treated for up to twenty-eight days

The objective of this study was to determine the shortest period of time necessary to detect histologic evidence of estrous cycle disruption in Sprague-Dawley rats treated for up to 28 days with the aromatase inhibitor exemestane at 1,000 mg/kg. Rats were evaluated on day 5, 8, 15, or 29. Vaginal mucification, uterine and cervical epithelial atrophy, uterine luminal epithelial vacuolation, decreased uterine granulocytes, and hypertrophy/hyperplasia of mammary ducts and alveoli were noted by day 5 and persisted throughout the study. From day 8 to day 29, absence of recent basophilic corpora lutea, increased atresia of antral follicles, interstitial cell hyperplasia, and increased luteinized follicles were present in the ovaries of treated rats. Vaginal smears detected persistent diestrus, confirming estrous cycle disruption between days 5 and 8. Ovary and uterine weights were largely unaffected. Serum hormone levels were not useful due to the study design employed. Other effects of exemestane included decreased adrenal weights and decreased cell size in both the adrenal zona fasciculata and the pituitary pars distalis. While early histologic changes were evident on day 5, only after 8 days of treatment were findings considered sufficient to clearly identify exemestane-induced estrous cycle disruption using microscopy alone.

Molecular Docking of Aromatase Inhibitors

Aromatase is an enzyme that plays a critical role in the development of estrogen receptor positive breast cancer. As aromatase catalyzes the aromatization of androstenedione to estrone, a naturally occurring estrogen, it is a promising drug target for therapeutic management. The undesirable effects found in aromatase inhibitors (AIs) that are in clinical use necessitate the discovery of novel AIs with higher selectivity, less toxicity and improving potency. In this study, we elucidate the binding mode of all three generations of AI drugs to the crystal structure of aromatase by means of molecular docking. It was demonstrated that the docking protocol could reliably reproduce the interaction of aromatase with its substrate with an RMSD of 1.350 Å. The docking study revealed that polar (D309, T310, S478 and M374), aromatic (F134, F221 and W224) and non-polar (A306, A307, V370, L372 and L477) residues were important for interacting with the AIs. The insights gained from the study herein have great potential for the design of novel AIs.

Do aromatase inhibitors have adverse effects on cognitive function?

Aromatase inhibitors are an important component of treatment for most postmenopausal women with hormone receptor-positive, early-stage breast cancer. Women taking aromatase inhibitors experience very low levels of circulating estrogen. This might be expected to result in cognitive dysfunction given the important relationship between estrogen and cognition in the basic science literature. Several studies have examined the cognitive effects of aromatase inhibitors, including two within large randomized trials which were adequately powered to detect moderate (but not small) effects. With this caveat, the available data do not support the hypothesis that aromatase inhibitors adversely affect cognitive function or that aromatase inhibitors might have a more adverse effect on cognitive function in comparison with tamoxifen. Further research is needed for confirmation.

An "omics" approach to determine the mechanisms of acquired aromatase inhibitor resistance

Aromatase inhibitors (AIs) are the major types of drugs to treat hormone-dependent breast cancer. Although these drugs work effectively, cancer still recurs in many patients after treatment as a result of acquired resistance to the AIs. To characterize the resistant mechanisms, a set of MCF-7aro cell lines that acquired resistance to the AIs was generated. Through an "Omics" approach, we found that the resistance mechanisms of the three AIs (anastrozole, letrozole, and exemestane) differ and activation of estrogen receptor alpha (ERα) is critical for acquired AI resistance. Our results reveal that growth factor/signal transduction pathways are upregulated after ERα-dependent pathways are suppressed by AIs, and ERα can then be activated through different crosstalk mechanisms.

Characterization of 17-dihydroexemestane glucuronidation: potential role of the UGT2B17 deletion in exemestane pharmacogenetics

OBJECTIVE

Exemestane is a third-generation aromatase inhibitor used in the treatment of breast cancer in postmenopausal women. Reduction to form 17-dihydroexemestane and subsequent glucuronidation to exemestane-17-O-glucuronide is a major pathway for exemestane metabolism. The goal of this study was to analyze 17-dihydroexemestane anti-aromatase activity, characterize the 17-dihydroexemestane glucuronidation pathway, and determine whether the functional polymorphisms in active UGTs could play a role in altered 17-dihydroexemestane glucuronidation.

METHODS

Homogenates from a HEK293 aromatase-overexpressing cell line (HEK293-aro) were used to examine exemestane versus 17-dihydroexemestane anti-aromatase activities. UGT-overexpressing cell lines and a panel (n=110) of human liver microsome (HLM) were screened for glucuronidation activity against 17-dihydroexemestane. UGT2B17 genotyping and liver mRNA expression were performed by real-time PCR.

RESULTS

The inhibition of estrone formation from androst-4-ene-3,17-dione in HEK293-aro cell homogenates was similar for 17-dihydroexemestane (IC(50)=2.3±0.83 μmol/l) and exemestane (IC(50)=1.4±0.42 μmol/l). UGTs 2B17 and 1A4 were high-expression hepatic UGTs that exhibited activity against 17-dihydroexemestane, with UGT2B17 exhibiting a 17-fold higher V(max)/K(M) than UGT1A4. The rate of exemestane-17-O-glucuronide formation was shown to be significantly (P<0.001) decreased (14-fold) in HLMs exhibiting the UGT2B17(*2/*2) deletion genotype versus wild-type UGT2B17(*1/*1) HLMs; a 36-fold lower V(max)/K(M) (P=0.023) was observed in UGT2B17(*2/*2) versus UGT2B17(*1/*1) HLMs. A significant (P<0.0001, R(2)=0.72) correlation was observed between HLM exemestane-17-O-glucuronide formation and liver UGT2B17 expression.

CONCLUSION

These data suggest that 17-dihydroexemestane is an active metabolite of exemestane and that the UGT2B17 deletion polymorphism could play an important role in determining levels of excretion of 17-dihydroexemestane and overall exemestane metabolism.

Disruption of androgen and estrogen receptor activity in prostate cancer by a novel dietary diterpene carnosol: implications for chemoprevention

Emerging data are suggesting that estrogens, in addition to androgens, may also be contributing to the development of prostate cancer (PCa). In view of this notion, agents that target estrogens, in addition to androgens, may be a novel approach for PCa chemoprevention and treatment. Thus, the identification and development of nontoxic dietary agents capable of disrupting androgen receptor (AR) in addition to estrogen receptor (ER) could be extremely useful in the management of PCa. Through molecular modeling, we found that carnosol, a dietary diterpene, fits within the ligand-binding domain of both AR and ER-alpha. Using a time-resolved fluorescence resonance energy transfer assay, we found that carnosol interacts with both AR and ER-alpha and additional experiments confirmed that it functions as a receptor antagonist with no agonist effects. LNCaP, 22Rv1, and MCF7 cells treated with carnosol (20-40 mumol/L) showed decreased protein expression of AR and ER-alpha. Oral administration of carnosol at 30 mg/kg 5 days weekly for 28 days to 22Rv1 PCa xenografted mice suppressed tumor growth by 36% (P = 0.028) and was associated with a decrease in serum prostate-specific antigen by 26% (P = 0.0042). These properties make carnosol unique to any known antiandrogen or antiestrogen investigated thus far for the simultaneous disruption of AR and ER-alpha. We suggest that carnosol may be developed or chemically modified through more rigorous structure-activity relationship studies for a new class of investigational agents-a dual AR/ER modulator.

Cognitive changes associated with endocrine therapy for breast cancer

Endocrine therapy in the setting of breast cancer has undoubtedly advanced clinical outcomes in this disease, but treatment with endocrine therapy is accompanied by a wide spectrum of side effects. It is of prime importance to understand and characterize these toxicities to facilitate clinical decision-making. Somewhat surprisingly, there is a relative paucity of data pertaining to cognitive changes associated with endocrine therapy. In this article we review cognitive associated with two classes of endocrine therapy: (1) selective estrogen receptor modulators (SERMs; tamoxifen and raloxifene) and (2) aromatase inhibitors (AIs; anastrozole, letrozole, and exemestane). Companion studies to the Multiple Outcome of Raloxifene Evaluation (MORE), the Study of Tamoxifen and Raloxifene (STAR) and National Surgical Adjuvant Breast and Bowel Project (NSABP) P-1 trials provide relevant data to understand the effect of SERMs on cognition. In contrast, substudies of the Arimidex, Tamoxifen Alone or in Combination (ATAC), Tamoxifen and Exemestane Adjuvant Multinational (TEAM) and Breast International Group (BIG) 1-98 trials juxtapose cognitive effects of AIs against those of tamoxifen. These and other studies are examined herein to provide a comprehensive overview of the effect of endocrine therapy on cognition.

Exemestane as first-line therapy in postmenopausal women with recurrent or metastatic breast cancer

Antiestrogen therapies generally offer significant disease control to hormone receptor-positive recurrent or metastatic breast cancer patients and are substantially better tolerated than standard chemotherapy regimens, thus representing an attractive first treatment option. The steroidal aromatase inhibitor (AI) exemestane exhibits antitumor effects by lowering full-body estrogen production in postmenopausal women and is an established treatment option for metastatic breast cancer. We review data from 2 recent phase III clinical trials that have confirmed exemestane activity in the first-line metastatic breast cancer setting, with moderate improvements in median progression-free survival (10-12 months) and objective response rates (37%-46%) compared with tamoxifen. The activity of first-line exemestane is comparable with other antiestrogen therapies, including fulvestrant and the nonsteroidal AIs letrozole and anastrozole. Additional findings demonstrating the clinical benefits of exemestane in women who previously progressed on nonsteroidal AIs highlight a partial lack of cross-resistance between these therapies and reinforce the opportunity to use multiple antiestrogen treatments sequentially. Future therapeutic developments in hormone receptor-positive metastatic breast cancer could include combinations with other targeted compounds plus AIs or other antiestrogen-based combinations and the identification of new strategies to evaluate differences among antiestrogen therapies to help optimize the treatment sequence and potential combinations.

Effects of tamoxifen and exemestane on cognitive functioning of postmenopausal patients with breast cancer: results from the neuropsychological side study of the tamoxifen and exemestane adjuvant multinational trial

PURPOSE

To evaluate the influence of adjuvant tamoxifen and exemestane on cognitive functioning in postmenopausal patients with breast cancer (BC).

PATIENTS AND METHODS

Neuropsychological assessments were performed before the start (T1) and after 1 year of adjuvant endocrine treatment (T2) in Dutch postmenopausal patients with BC, who did not receive chemotherapy. Patients participated in the international Tamoxifen and Exemestane Adjuvant Multinational trial, a prospective randomized study investigating tamoxifen versus exemestane as adjuvant therapy for hormone-sensitive BC.

RESULTS

Participants included 80 tamoxifen users (mean age, 68.7 years; range 51 to 84), 99 exemestane users (mean age, 68.3 years; range, 50 to 82), and 120 healthy controls (mean age, 66.2 years; range, 49 to 86). At T2, after adjustment for T1 performance, exemestane users did not perform statistically significantly worse than healthy controls on any cognitive domain. In contrast, tamoxifen users performed statistically significantly worse than healthy controls on verbal memory (P < .01; Cohen's d = .43) and executive functioning (P = .01; Cohen's d = .40), and statistically significantly worse than exemestane users on information processing speed (P = .02; Cohen's d = .36). With respect to visual memory, working memory, verbal fluency, reaction speed, and motor speed, no significant differences between the three groups were found.

CONCLUSION

After 1 year of adjuvant therapy, tamoxifen use is associated with statistically significant lower functioning in verbal memory and executive functioning, whereas exemestane use is not associated with statistically significant lower cognitive functioning in postmenopausal patients with BC. Our results accentuate the need to include assessments of cognitive effects of adjuvant endocrine treatment in long-term safety studies.

A liquid chromatography-tandem mass spectrometry method for the simultaneous determination of exemestane and its metabolite 17-dihydroexemestane in human plasma

A simple and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the quantitation of exemestane (Exe) and its main metabolite 17-dihydroexemestane (DhExe) in human plasma. The analytes were extracted by protein precipitation with acetonitrile, containing stable 13C-labelled Exe (13C3-Exe) as internal standard, and measured by LC-MS/MS. The best chromatographic separation of the analytes from the interferences was achieved by using a Phenyl column operating under isocratic regime conditions. The total chromatographic runtime was 5.0 min and the elution of Exe and DhExe occurred at 2.5 min and 2.9 min, respectively. Quantitation was performed by employing the positive electrospray ionization (ESI) technique and multiple reaction monitoring mode (MRM). The monitored precursor to product-ion transitions for Exe, DhExe and 13C3-Exe internal standard were m/z 297.0 --> 120.8, m/z 299.1 --> 134.9 and m/z 300.0 --> 123.2, respectively. The lower limit of quantitation (LLOQ) was 0.1 ng/ml for DhExe and 0.2 ng/ml for Exe. The method was linear up to 36-51 ng/ml with r2 > or = 0.998. The intra- and inter-assay precision were < or = 7.7% and 5.1% for Exe and < or = 8.1 and 4.9% for DhExe while deviations from nominal values were in the 1.5-13.2% and - 9.0-5.8% ranges for Exe and DhExe, respectively. The analytical method resulted robust and suitable for pharmacokinetic monitoring of Exe and its main metabolite during adjuvant therapy in patients with breast cancer.

Cancer treatment-related bone disease

Bone health may be impaired in many patients being treated for cancer. Primary tumors that reside in or form metastases to bone can result in compromised skeletal integrity. It has also been increasingly recognized that patients undergoing therapies for treatment of cancer are at higher risk of bone loss. These include androgen-deprivation therapy for prostate cancer and aromatase inhibitor therapy for breast cancer, among others. Hypogonadism induced by many of these cancer treatments results in bone loss and increases the risk of osteoporosis and fractures. Progress has been made in identifying the role of oral and intravenous bisphosphonates to prevent bone loss in these patients. This review discusses bone loss associated with cancer treatments, with a focus on breast cancer, prostate cancer, and survivors of childhood malignancies.

Lack of complete cross-resistance between different aromatase inhibitors; a real finding in search for an explanation?

While third-generation aromatase inhibitors (anastrozole, letrozole and exemestane) are successfully implemented as adjuvant and first-line therapy for hormone-sensitive breast cancer in postmenopausal women, important questions remain to be addressed. An issue of particular interest is the question about lack of complete cross-resistance between steroidal and non-steroidal compounds. Although the studies reporting this phenomenon in general contain a small number of patients, the findings across the different reports seem consistent. While several potential mechanisms have been suggested, so far we lack scientific proof what mechanisms may be responsible for this finding. Finally, we do not know whether lack of cross-resistance actually signals an improved efficacy for certain compounds or may be due to alternative mechanisms of action. Neither do we know whether some tumours are more sensitive to particular drugs. This paper summarizes clinical findings up to now with respect to lack of cross-resistance and discuss potential mechanisms involved.

Aromatase inhibitors: are there differences between steroidal and nonsteroidal aromatase inhibitors and do they matter?

Aromatase inhibitors (AIs) are approved for use in both early- and advanced-stage breast cancer in postmenopausal women. Although the currently approved "third-generation" AIs all powerfully inhibit estrogen synthesis, they may be subdivided into steroidal and nonsteroidal inhibitors, which interact with the aromatase enzyme differently. Nonsteroidal AIs bind noncovalently and reversibly to the aromatase protein, whereas steroidal AIs may bind covalently and irreversibly to the aromatase enzyme. The steroidal AI exemestane may exert androgenic effects, but the clinical relevance of this has yet to be determined. Switching between steroidal and nonsteroidal AIs produces modest additional clinical benefits, suggesting partial noncrossresistance between the classes of inhibitor. In these circumstances, the response rates to the second AI have generally been low; additional research is needed regarding the optimal sequence of AIs. To date, clinical studies suggest that combining an estrogen-receptor blocker with a nonsteroidal AI does not improve efficacy, while combination with a steroidal AI has not been evaluated. Results from head-to-head trials comparing steroidal and nonsteroidal AIs will determine whether meaningful clinical differences in efficacy or adverse events exist between the classes of AI. This review summarizes the available evidence regarding known differences and evaluates their potential clinical impact.

Characterization of the weak estrogen receptor alpha agonistic activity of exemestane

Third generation aromatase inhibitors (AI) have shown good clinical efficacy in comparison to the anti-estrogen tamoxifen. The steroidal AI, exemestane (EXE) has previously been shown to act as an androgen, but this report demonstrates the estrogen-like activity of EXE. Based on genome-wide microarray analysis, high correlation was seen between EXE-Only (EXE O, hormone-free) and hormone-containing AI-resistant lines. In addition, the top regulated genes in the EXE O lines were mostly estrogen-responsive genes. This estrogen-like activity of EXE was further validated using estrogen receptor (ER) activity assays, where in comparison to 17beta-estradiol (E2), EXE was able to induce ER activity, though at a higher concentration. Also, this EXE-mediated ER activity was blocked by the ER antagonist ICI as well as the ERalpha-specific antagonist methyl-piperidino-pyrazole (MPP). Similarly, EXE was able to induce proliferation of breast cancer cell lines, MCF-7 and MCF-7aro, as well as activate transcription of known estrogen-responsive genes, i.e., PGR, pS2 and AREG. These results suggest that EXE does have weak estrogen-like activity.

Molecular signatures of neoadjuvant endocrine therapy for breast cancer: characteristics of response or intrinsic resistance

Approximately 30% of patients with estrogen receptor (ER) positive breast cancers exhibit de novo or intrinsic resistance to endocrine therapies. The purpose of this study was to define genes that distinguish ER+ resistant from ER+ responsive tumors, prior to the start of hormone therapies. Previously untreated post-menopausal patients with ER+ breast cancers were treated for 4 months in a neoadjuvant setting with the aromatase inhibitor exemestane alone, or in combination with the antiestrogen tamoxifen. Matched pre- and post-treatment tumor samples from the same patient, were analyzed by gene expression profiling and were correlated with response to treatment. Genes associated with tumor shrinkage achieved by estrogen blockade therapy were identified, as were genes associated with resistance to treatment. Prediction Analysis of Microarrays (PAM) identified 50 genes that can predict response or intrinsic resistance to neoadjuvant endocrine therapy of ER+ tumors, 8 of which have been previously implicated as useful biomarkers in breast cancer. In summary, we identify genes associated with response to endocrine therapy that may distinguish ER+, hormone responsive breast cancers, from ER+ tumors that exhibit intrinsic or de novo resistance. We suggest that the estrogen signaling pathway is aberrant in ER+ tumors with intrinsic resistance. Lastly, the studies show upregulation of a "lipogenic pathway" in non-responsive ER+ tumors that may serve as a marker of intrinsic resistance. This pathway may represent an alternative target for therapeutic intervention.