Identification and Quantification of Novel Major Metabolites of the Steroidal Aromatase Inhibitor, Exemestane.

Exemestane (EXE) is an aromatase inhibitor used for the prevention and treatment of estrogen receptor-positive breast cancer. Although the known major metabolic pathway for EXE is reduction to form the active 17ß-dihydro-EXE (17ß-DHE) and subsequent glucuronidation to 17ß-hydroxy-EXE-17-O-ß-D-glucuronide (17ß-DHE-Gluc), previous studies have suggested that other major metabolites exist for exemestane. In the present study, a liquid chromatography-mass spectrometry (LC-MS) approach was used to acquire accurate mass data in MSE mode, in which precursor ion and fragment ion data were obtained simultaneously to screen novel phase II EXE metabolites in urine specimens from women taking EXE. Two major metabolites predicted to be cysteine conjugates of EXE and 17ß-DHE by elemental composition were identified. The structures of the two metabolites were confirmed to be 6-methylcysteinylandrosta-1,4-diene-3,17-dione (6-EXE-cys) and 6-methylcysteinylandrosta-1,4-diene-17ß-hydroxy-3-one (6-17ß-DHE-cys) after comparison with their chemically synthesized counterparts. Both underwent biosynthesis in vitro in three stepwise enzymatic reactions, with the first involving glutathione conjugation. The cysteine conjugates of EXE and 17ß-DHE were subsequently quantified by liquid chromatography-mass spectrometry in the urine and matched plasma samples of 132 subjects taking EXE. The combined 6-EXE-cys plus 6-17ß-DHE-cys made up 77% of total EXE metabolites in urine (vs. 1.7%, 0.14%, and 21% for EXE, 17ß-DHE, and 17ß-DHE-Gluc, respectively) and 35% in plasma (vs. 17%, 12%, and 36% for EXE, 17ß-DHE, and 17ß-DHE-Gluc, respectively). Therefore, cysteine conjugates of EXE and 17ß-DHE appear to be major metabolites of EXE in both urine and plasma.

Polymorphisms in ABCB1 and CYP19A1 genes affect anastrozole plasma concentrations and clinical outcomes in postmenopausal breast cancer patients.

AIMS: Anastrozole, an aromatase inhibitor widely used in breast cancer, has recently been indicated to be a P-glycoprotein (ABCB1) substrate. We have aimed to determine whether ABCB1 single-nucleotide polymorphisms (SNPs) can affect anastrozole plasma concentrations in these patients. In addition, we assessed the impact of SNPs in CYP19A1 and TCL1A on the development of arthralgia and cancer recurrence in our series. METHODS: This study included 110 postmenopausal women with hormone receptor-positive breast cancer. Anastrozole plasma levels were determined by a liquid chromatography-electrospray ionization-quadrupole-time-of-flight mass spectrometry system. Patients were genotyped for SNPs in the ABCB1, TCL1A and CYP19A1 genes to search for associations with pharmacokinetic and pharmacodynamics parameters using logistic regression models. RESULTS: Anastrozole concentrations showed an almost nine-fold interindividual variability (mean 26.95 ± 11.91 ng ml-1 ). The ABCB1 2677-TT genotype was associated with higher plasma levels (32.22 ± 12.82 vs. 25.86 ± 11.56 ng ml-1 for GG/GT subjects; 95% confidence interval: -12.3 to -0.40), whilst the 3435-TT genotype showed a protective effect on the risk of arthralgia (odds ratio = 0.32 [0.11-0.89]; P = 0.029). The CYP19A1 rs1008805 GG genotype was strongly and inversely associated with arthralgia (odds ratio = 0.24 [0.09-0.65], P = 0.004); however, SNPs near the TCL1A gene were not linked to this adverse effect. None of the patients who had cancer recurrence harboured the CYP19A1 rs727479 AA genotype, which, in contrast, was present in 38% of patients who did not relapse (P for trend = 0.031). CONCLUSION: Our findings indicate that variability in anastrozole plasma levels may be attributable to the status of the ABCB1 gene locus. Furthermore, genetic variants in CYP19A1 were associated with arthralgia and cancer recurrence in our patients.

Characterization of anastrozole effects, delivered by an intravaginal ring in cynomolgus monkeys.

STUDY QUESTION: Is it feasible to deliver anastrozole (ATZ), an aromatase inhibitor (AI), by a vaginal polymer-based drug delivery system in the cynomolgus monkey (Macaca fascicularis) to describe the pharmacokinetic profile? SUMMARY ANSWER: The present study showed the effective release of ATZ into the systemic circulation from intravaginal rings in cynomolgus monkeys. WHAT IS KNOWN ALREADY: ATZ is a marketed drug with well documented pharmacological and safety profiles for oral administration. Aromatase is the key enzyme catalyzing estrogen biosynthesis and is overexpressed in endometriotic lesions. AIs show therapeutic efficacy in endometriosis in exploratory clinical trials. STUDY DESIGN, SIZE, DURATION: The pharmacokinetics of the in vivo release and the pharmacodynamic activity of ATZ released by intravaginal rings (IVR) were investigated in healthy cycling female cynomolgus monkeys in three different dose groups (n = 5) for one menstrual cycle. PARTICIPANTS/MATERIALS, SETTING, METHODS: IVRs for the cynomolgus monkey, releasing three different doses of ATZ were designed and tested for in vitro/in vivo release for up to 42 days. For pharmacokinetic and pharmacodynamic evaluation, plasma samples were taken once daily from Day 1 to 3 and then every third day until menses occurred (17-42 days). MAIN RESULTS AND THE ROLE OF CHANCE: ATZ was shown to be compatible with the IVR drug delivery system. An average in vivo release of 277 µg/day/animal of ATZ for one menstrual cycle was effective in causing a decrease of systemic estradiol (E2) levels by ∼30% without inducing counter regulation such as the elevation of FSH or the formation of ovarian cysts. LIMITATIONS, REASONS FOR CAUTION: The study was limited to three dose groups in which only the highest dose decreased the E2 level. Hence, additional research with IVRs releasing higher amounts of ATZ is required to define the threshold for an ATZ-dependent ovarian stimulation in cynomolgus monkeys. WIDER IMPLICATIONS OF THE FINDINGS: The release rate administered from IVRs is sufficient and in a range that supports feasibility of IVR administration of ATZ as a new approach for long-term therapy of estrogen-dependent diseases such as endometriosis in human.

Sex-dependent influence of endogenous estrogen in pulmonary hypertension.

RATIONALE: The incidence of pulmonary arterial hypertension is greater in women, suggesting estrogens may play a role in the disease pathogenesis. Experimentally, in males, exogenously administered estrogen can protect against pulmonary hypertension (PH). However, in models that display female susceptibility, estrogens may play a causative role. OBJECTIVES: To clarify the influence of endogenous estrogen and sex in PH and assess the therapeutic potential of a clinically available aromatase inhibitor. METHODS: We interrogated the effect of reduced endogenous estrogen in males and females using the aromatase inhibitor, anastrozole, in two models of PH: the hypoxic mouse and Sugen 5416/hypoxic rat. We also determined the effects of sex on pulmonary expression of aromatase in these models and in lungs from patients with pulmonary arterial hypertension. MEASUREMENTS AND MAIN RESULTS: Anastrozole attenuated PH in both models studied, but only in females. To verify this effect was caused by reduced estrogenic activity we confirmed that in hypoxic mice inhibition of estrogen receptor α also has a therapeutic effect specifically in females. Female rodent lung displays increased aromatase and decreased bone morphogenetic protein receptor 2 and Id1 expression compared with male. Anastrozole treatment reversed the impaired bone morphogenetic protein receptor 2 pathway in females. Increased aromatase expression was also detected in female human pulmonary artery smooth muscle cells compared with male. CONCLUSIONS: The unique phenotype of female pulmonary arteries facilitates the therapeutic effects of anastrozole in experimental PH confirming a role for endogenous estrogen in the disease pathogenesis in females and suggests aromatase inhibitors may have therapeutic potential.

Preparation and characterization of two new forced degradation products of letrozole and development of a stability-indicating RP-LC method for its determination.

Two new hydrolytic products of letrozole were identified and proved to be true degradation products obtained by alkaline and acidic degradation of the drug. The acid and amide forms of the nitrile groups of letrozole were prepared and identified by IR and mass spectroscopic techniques. Subsequently, a simple, precise and selective stability-indicating RPLC method was developed and validated for the determination of letrozole in the presence of its degradation products. Letrozole was subjected to alkali and acid hydrolysis, oxidation, thermal degradation and photo-degradation. The degradation products were well isolated from letrozole. The chromatographic method was achieved using gradient elution of the drug and its degradation products on a reversed phase Zorbax Eclipse C18 column (100mm x 4.6mm, 3.5 µm) using a mobile phase consisting of 0.01M KH2PO4and methanol at a flow rate of 1 mL min⁻¹. Quantitation was achieved with UV detection at 230 nm. Linearity, accuracy and precision were found to be acceptable over the concentration range of 0.01-80 µgmL⁻¹. The proposed method was successfully applied to the determination of letrozole in bulk, plasma and in its pharmaceutical preparation.

Quantification of the aromatase inhibitor letrozole and its carbinol metabolite in mouse plasma by UHPLC-MS/MS.

A liquid chromatography - electrospray ionization-mass spectrometry (LC-ESI-MS) method was developed for the quantification of letrozole, a third-generation aromatase inhibitor, and its main carbinol metabolite (CM) in support of murine pharmacokinetic studies. Using polarity switching, simultaneous ESI-MS measurement of letrozole and CM was achieved in positive and negative mode, respectively. The assay procedure involved a one-step protein precipitation and extraction of all analytes from mouse plasma requiring only 5 µL of sample. Separation was optimized on an Accucore aQ column with gradient elution at a flow rate of 0.4 mL/min in 5 min. Two calibration curves per day over four consecutive measurement days showed satisfactory linear responses (r2 > 0.99) over concentration ranges of 5-1000 ng/mL and 20-2000 ng/mL for letrozole and CM, respectively. No matrix effect was found, and the mean extraction recoveries were 103-108 % for letrozole and 99.8-107 % for CM. Precision and accuracy within a single run and over four consecutive measurement days were verified to be within acceptable limits. Application of the developed method to preclinical pharmacokinetic studies in mice receiving oral letrozole at a dose 1 or 10 mg/kg revealed that the systemic exposure to letrozole was dose-, formulation-, and strain-dependent. These findings may inform the future design of preclinical studies aimed at refining the pharmacological profile of this clinically important drug.

Identification of non-adherence to adjuvant letrozole using a population pharmacokinetics approach in hormone receptor-positive breast cancer patients.

BACKGROUND: Letrozole, an aromatase inhibitor metabolised via CYP2A6 and CYP3A4/5 enzymes, is used as adjuvant therapy for women with hormone receptor (HR)-positive early breast cancer. The objective of this study was to quantify the impact of CYP2A6 genotype on letrozole pharmacokinetics (PK), to identify non-adherent patients using a population approach and explore the possibility of a relationship between non-adherence and early relapse. METHODS: Breast cancer patients enrolled in the prospective PHACS study (ClinicalTrials.gov NCT01127295) and treated with adjuvant letrozole 2.5 mg/day were included. Trough letrozole concentrations (Css,trough) were measured every 6 months for 3 years by a validated LC-MS/MS method. Concentration-time data were analysed using non-linear mixed effects modelling. Three methods were evaluated for identification of non-adherent subjects using the base PK model. RESULTS: 617 patients contributing 2534 plasma concentrations were included and led to a one-compartment PK model with linear absorption and elimination. Model-based methods identified 28 % of patients as non-adherent based on high fluctuations of their Css,trough compared to 3 % based on patient declarations. The covariate analysis performed in adherent subjects revealed that CYP2A6 intermediate (IM) and slow metabolisers (SM) had 21 % (CI95 % = 12 - 30 %) and 46 % (CI95 % = 41 - 51 %) lower apparent clearance, respectively, compared to normal and ultrarapid metabolisers (NM+UM). Early relapse (19 patients) was not associated with model-estimated, concentration-based or declared adherence in the total population (p = 0.41, p = 0.37 and p = 0.45, respectively). CONCLUSIONS: These findings will help future investigations focusing on the exposure-efficacy relationship for letrozole in adjuvant setting.

Reduced methadone clearance during aromatase inhibition.

Methadone is increasingly used in pain management and is a cornerstone in the treatment of opiate withdrawal. It is subject to highly variable clearance among patients. The complete metabolic disposition of methadone is likely to involve a number of enzymes, including specifically CYP2B6. Previous studies in vitro suggest that metabolism by aromatase may also contribute. Single-dose methadone pharmacokinetics (2 mg, intravenous) were studied in 15 healthy postmenopausal women in the presence and absence of a potent aromatase inhibitor, letrozole. A sequential design was used, involving a control period followed by treatment with letrozole (2.5 mg/d, 11 days), in which each subject served as her own control. On average, letrozole treatment reduced methadone systemic clearance by 22% (P = 0.001), increased methadone AUC by 23% (P = 0.007), and increased elimination half-life by 21% (P = 0.042). The plasma parent-to-metabolite ratio also increased (P = 0.009), and there was a linear relationship (R2 = 0.74) between change in this plasma ratio and change in methadone AUC0-∞. In contrast, there was no such association with change in apparent urinary methadone clearance. Letrozole did not change methadone distribution half-life or its volume of distribution. Overall, these data demonstrate a significant decrease in methadone clearance during coadministration of letrozole, consistent with decreased metabolism brought about by aromatase inhibition. An involvement of aromatase in the disposition of methadone may help explain the difficulty in methadone dosing and suggests a broader role for this catalyst of endogenous steroid metabolism in xenobiotic drug disposition.

Effects of a non-steroidal aromatase inhibitor on ovarian function in cattle.

Effects of the non-steroidal aromatase inhibitor letrozole on ovarian function in cattle were determined. The hypothesis that letrozole would arrest growth of the dominant follicle, resulting in emergence of a new follicular wave at a predictable post-treatment interval, was tested. Heifers were assigned randomly to four groups 4 days after follicular ablation (~2½ days after wave emergence) and given intravenous doses of 500 (n = 9), 250 (n = 10), or 125 µg kg⁻¹ (n = 10) letrozole or phosphate-buffered saline (controls; n = 10). Blood was collected and ovarian structures were monitored daily by transrectal ultrasonography. Plasma concentrations of LH and FSH were measured by radioimmunoassay; plasma concentrations of letrozole were determined by high-performance liquid chromatography tandem mass spectrometry. A single intravenous dose of letrozole did not induce regression of the dominant follicle present at the time of treatment, nor did it directly affect FSH release. Conversely, treatment with letrozole increased endogenous concentrations of LH and extended the lifespan of the dominant follicle, which delayed the next FSH surge and subsequent follicular wave emergence. Letrozole continues to have potential as a non-steroidal treatment for controlling ovarian function in cattle.

Population pharmacokinetic analysis of letrozole in Japanese postmenopausal women.

PURPOSE: Letrozole is an orally active aromatase inhibitor for the treatment of breast cancer. The objectives of this study were to examine the pharmacokinetic profile of letrozole in Japanese subjects and to identify factors that influence variability in the pharmacokinetics of letrozole using population pharmacokinetic (PPK) analysis. METHODS: Twenty-five healthy postmenopausal Japanese women were enrolled in the study and received 2.5 mg letrozole once daily for 14 or 28 days. A PPK model was developed using NONMEM software. Age, body weight (WT), AST, ALT, total bilirubin, serum creatinine (CRE), and genotype of CYP2A6 were studied as covariates. Estrone, estrone sulfate, and estradiol in plasma were measured as pharmacodynamic markers. RESULTS: CYP2A6 genotype, CRE, and AST were significant covariates for apparent systemic clearance (CL/F), and WT was a significant covariate for apparent distribution volume (Vd/F). Population mean estimates of CL/F and Vd/F in subjects without CYP2A6 mutation were 1.03 × (CRE/0.70)(-1.27) × (AST/17.5)(-0.793) L/h and 94.2 × (WT/51.1)(1.12) L respectively. CL/F in subjects possessing 1 and 2 CYP2A6 mutation alleles were 84.3% and 44.8% of the value in the subjects without mutation respectively. Estrogen levels fell to below detection limits in most subjects after letrozole administration. Three mild and transient adverse events (upper respiratory tract inflammation, arthralgia, and vomiting) were reported in the study. CONCLUSIONS: CYP2A6 genotype largely influences CL/F of letrozole. Genetic polymorphism of CYP2A6 and body weight will be causes of ethnic difference in PK. However, dose adjustment is not necessary, because of the wide therapeutic range.

Gender-based differences in brain and plasma pharmacokinetics of letrozole in sprague-dawley rats: Application of physiologically-based pharmacokinetic modeling to gain quantitative insights.

Based on the discovery that the estrogen synthase aromatase (CYP19A1) is abundantly expressed in high- grade gliomas, the aromatase inhibitor, letrozole is being investigated in pre-clinical models as a novel agent against this malignancy. Here, we investigated the systemic and brain pharmacokinetics of letrozole following single and steady state dosing in both male and female Sprague-Dawley rats. Furthermore, we employed physiologically-based pharmacokinetic (PBPK) modeling to gain quantitative insights into the blood-brain barrier penetration of this drug. Letrozole (4 mg/kg) was administered intraperitoneally daily for 5 days (for males) and 11 days (for females) and intracerebral microdialysis was performed for brain extracellular fluid (ECF) collection simultaneously with venous blood sampling. Drug levels were measured using HPLC and non-compartmental analysis was conducted employing WinNonlin®. Simcyp animal simulator was used for conducting bottom-up PBPK approach incorporating the specified multi-compartment brain model. Overall, marked gender-specific differences in the systemic and brain pharmacokinetics of letrozole were observed. Letrozole clearance was much slower in female rats resulting in markedly higher plasma and brain drug concentrations. At steady state, the plasma AUC 0-24 was 103.0 and 24.8 µg*h/ml and brain ECF AUC 0-12 was 24.0 and 4.8 µg*h/ml in female and male rats, respectively. The PBPK model simulated brain concentration profiles were in close agreement with the observed profiles. While gender-specific differences in letrozole PK are not observed in the clinical setting, these findings will guide the dose optimization during pre-clinical investigations of this compound. The PBPK model will serve as an important clinical translational tool.

Therapeutic Drug Monitoring of Oral Anti-Hormonal Drugs in Oncology.

Oral anti-hormonal drugs are essential in the treatment of breast and prostate cancer. It is well known that the interpatient variability in pharmacokinetic exposure is high for these agents and exposure-response relationships exist for many oral anti-hormonal drugs. Yet, they are still administered at fixed doses. This could lead to underdosing and thus suboptimal efficacy in some patients, while other patients could be overdosed resulting in unnecessary side effects. Therapeutic drug monitoring (TDM), individualized dosing based on measured blood concentrations of the drug, could therefore be a valid option to further optimize treatment. In this review, we provide an overview of relevant clinical pharmacokinetic and pharmacodynamic characteristics of oral anti-hormonal drugs in oncology and translate these into practical guidelines for TDM. For some agents, TDM targets are not well established yet and as a reference the median pharmacokinetic exposure could be targeted (exemestane: minimum plasma concentration (Cmin) 4.1 ng/mL and enzalutamide: Cmin 11.4 mg/L). However, for most drugs, exposure-efficacy analyses could be translated into specific targets (abiraterone: Cmin 8.4 ng/mL, anastrozole: Cmin 34.2 ng/mL, and letrozole: Cmin 85.6 ng/mL). Moreover, prospective clinical trials have shown TDM to be feasible for tamoxifen, for which the exposure-efficacy threshold of its active metabolite endoxifen is 5.97 ng/mL. Based on the available data, we therefore conclude that individualized dosing based on drug concentrations is feasible and promising for oral anti-hormonal drugs and should be developed further and implemented into clinical practice.

Anastrozole Aromatase Inhibitor Plasma Drug Concentration Genome-Wide Association Study: Functional Epistatic Interaction Between SLC38A7 and ALPPL2.

Anastrozole is a widely prescribed aromatase inhibitor for the therapy of estrogen receptor positive (ER+) breast cancer. We performed a genome-wide association study (GWAS) for plasma anastrozole concentrations in 687 postmenopausal women with ER+ breast cancer. The top single-nucleotide polymorphism (SNP) signal mapped across SLC38A7 (rs11648166, P = 2.3E-08), which we showed to encode an anastrozole influx transporter. The second most significant signal (rs28845026, P = 5.4E-08) mapped near ALPPL2 and displayed epistasis with the SLC38A7 signal. Both of these SNPs were cis expression quantitative trait loci (eQTL)s for these genes, and patients homozygous for variant genotypes for both SNPs had the highest drug concentrations, the highest SLC38A7 expression, and the lowest ALPPL2 expression. In summary, our GWAS identified a novel gene encoding an anastrozole transporter, SLC38A7, as well as epistatic interaction between SNPs in that gene and SNPs near ALPPL2 that influenced both the expression of the transporter and anastrozole plasma concentrations.

The growth-promoting action of individual women's sera on mammary carcinoma cells.

In vitro studies concerning the growth-stimulating effect of hormones, especially of estradiol and its metabolites, have mainly been performed using pure substances and breast cancer cell lines. In order to take into account the metabolism of inactive into active hormones or drugs and vice versa which occurs in several tissues, the influence of individual patients' sera on the growth of breast cancer cells in vitro was tested. Besides measuring the growth promoting action of several hormone replacement therapies, the antiestrogenic effect was determined by measuring the effect of 10(-10) M estradiol added to the culture medium (E2-sensitivity). Influence on proliferation and stimulatability was similar in MCF-7 and T47-D cells. Growth-promoting potential correlated significantly with patient age, being higher in young ladies than in older ones. The converse was true for E2 sensitivity. From the different steroid hormones tested, only higher estradiol levels were associated with increased growth stimulation and diminished E2 sensitivity. Hormone replacement therapy (HRT) of different types did not significantly increase growth potential of serum, however these results are preliminary. Treatment with tamoxifen of breast cancer patients led to a decrease of E2 sensitivity, whereas growth potential was not affected significantly. For the aromatase inhibitor Arimidex, a tendency towards growth inhibition and increased E2 sensitivity was observed. Our in vitro system allows identifying differences between individual persons and groups of women of different age or treatment with respect to stimulation of growth or influence on estrogen sensitivity of breast cancer cells by serum. It is speculated that results might reflect the personal risk or the risk under treatment to develop breast cancer.

Development and validation of an improved high-throughput method for the determination of anastrozole in human plasma by LC-MS/MS and atmospheric pressure chemical ionization.

In the present study, an automated, 96-well format LC-MS/MS method for the determination of anastrozole in human plasma was developed and fully validated. Within method development procedure, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) were compared in terms of sensitivity and specificity, with the former proven to be more appropriate and thus being chosen for analyte ionization. In addition, the effect of declustering potential (DP) and collision energy (CE) in sensitivity was, as well, studied and compared between APCI and ESI source employment. Samples were treated with an acetonitrile (ACN) protein precipitation step followed by liquid-liquid extraction (LLE) with methyl t-butyl ether (MTBE) as the organic solvent, using omeprazole as the internal standard (IS). The statistical evaluation for the APCI protocol revealed excellent linearity, accuracy and precision values for the range of concentrations 0.100-100 ng/mL. The method proposed involves the lowest plasma volume so far reported (190 microL), as well as the shortest run time (1.6 min) and along with the employment of two robotic liquid handling systems enabled the rapid and reliable determination of anastrozole in a bioequivalence study (>1000 plasma samples) after per os administration of 1mg tablet within a 4-day period of time.

Anastrozole quantification in human plasma by high-performance liquid chromatography coupled to photospray tandem mass spectrometry applied to pharmacokinetic studies.

A rapid, sensitive and specific method for quantifying the aromatase inhibitor (anastrozole) in human plasma using dexchlorpheniramine as the internal standard (I.S.) is described herein. The analyte and the I.S. were extracted from 200 microl of human plasma by liquid-liquid extraction using a mixture of diethyl ether:dichloromethane (70:30, v/v) solution. Extracts were removed and dried in the organic phase then reconstituted with 200 microl of acetonitrile:water (50:50; v/v). The extracts were analyzed by high performance liquid chromatography coupled with photospray tandem mass spectrometry (HPLC-MS-MS). Chromatography was performed isocratically on a Genesis, C18 4 microm analytical column (100 mm x 2.1mm i.d.). The method had a chromatographic run time of 2.5 min and a linear calibration curve ranging from 0.05-10 ng ml(-1). The limit of quantification (LOQ) was 0.05 ng ml(-1). This HPLC-MS-MS procedure was used to assess pharmacokinetic studies.

Falsely elevated serum oestradiol due to exemestane therapy.

In this study, we present a case of falsely elevated oestradiol (E2) concentration, determined by two immunoassays, in a breast cancer patient receiving exemestane therapy. The positive bias of immunochemical measurements was revealed using liquid chromatography tandem mass spectrometry which showed undetectable E2 concentration. The discrepancy is expected to be a consequence of the structural resemblance of E2 and exemestane sharing the same steroidal backbone. Inaccurate laboratory findings in therapy monitoring, as in this case, may lead to unnecessary changes of therapy.

Exploratory study of drug plasma levels during bicalutamide 150 mg therapy co-administered with tamoxifen or anastrozole for prophylaxis of gynecomastia and breast pain in men with prostate cancer.

OBJECTIVE: A randomized multicenter (14 centers) trial was conducted in 114 men with prostate cancer to determine whether the antiestrogen tamoxifen ('Nolvadex') 20 mg or the aromatase inhibitor anastrozole ('Arimidex') 1 mg prevent gynecomastia and breast pain during treatment with the non-steroidal antiandrogen bicalutamide ('Casodex') 150 mg, without compromising efficacy, safety, or quality of life. Plasma samples were collected in a subgroup of these patients to investigate whether trough (pre-dose) concentrations of bicalutamide 150 mg are influenced by concomitant administration of tamoxifen 20 mg or anastrozole 1 mg; the results of this pilot study are reported in this article. METHODS: A subpopulation of patients from a randomized placebo-controlled trial evaluating tamoxifen 20 mg and anastrozole 1 mg for the prevention of gynecomastia and breast pain in men receiving bicalutamide 150 mg for early or recurrent prostate cancer were selected on a voluntary basis from three of the trial centers. Plasma samples were collected on days 7, 14, 28, and 84 of therapy and analyzed to determine the plasma concentrations of (R)-bicalutamide and (S)-bicalutamide. In addition, plasma concentrations of tamoxifen, N-desmethyltamoxifen, and anastrozole were determined. RESULTS: A total of 21 patients were selected. There was no significant difference between treatment groups with respect to the trough plasma concentrations of either bicalutamide enantiomer at any point during the study. Plasma concentrations of the enantiomers, and the relative proportion of the (R))- and (S)-enantiomers, were consistent with those reported in previous studies. Plasma concentrations of tamoxifen, N-desmethyltamoxifen, and anastrozole were also similar to those described elsewhere in the literature. CONCLUSIONS: The findings of this pilot study suggest that trough plasma concentrations of bicalutamide enantiomers following administration of bicalutamide 150 mg are not markedly influenced by concomitant administration of tamoxifen 20 mg or anastrozole 1 mg. However, an effect of tamoxifen on bicalutamide pharmacokinetics can not be completely excluded due to the size of this study. Further studies are needed to clarify the effect of tamoxifen on bicalutamide pharmacokinetics and prostate cancer control in bicalutamide-treated patients. 'Arimidex', 'Casodex', and 'Nolvadex' are trademarks of the AstraZeneca group of companies.

Potent 11ß-hydroxylase inhibitors with inverse metabolic stability in human plasma and hepatic S9 fractions to promote wound healing.

Topical application of CYP11B1 inhibitors to reduce cutaneous cortisol is a novel strategy to promote healing of chronic wounds. Pyridyl substituted arylsulfonyltetrahydroquinolines were designed and synthesized resulting in a strong inhibitor 34 (IC50 = 5 nM). It showed no inhibition of CYP17 and CYP19 and no mutagenic effects. It exhibited inverse metabolic stability in plasma (t1/2 ≫ 150 min), which is similar to wound fluid in composition, and in liver S9 fractions (t1/2 = 16 min).

Does obesity interfere with anastrozole treatment? Positive association between body mass index and anastrozole plasma levels.

INTRODUCTION: The efficacy of adjuvant endocrine treatment with aromatase inhibitors (AIs), inhibiting the conversion of androgens to estrogen in adipose tissue, might depend on the overall volume of adipose tissue. However, little evidence is available regarding the pharmacokinetic behavior of AIs in women with obesity. The aim of this study was to investigate the interaction between body mass index (BMI) and anastrozole treatment as well as estrogenic activity. PATIENTS AND METHODS: A total of 216 postmenopausal patients with early-stage breast cancer who were receiving AI treatment with anastrozole constituted the final sample included in the analysis. During a regular 3-month after-care check-up, sociodemographic and clinical data and BMI were assessed. Blood samples were collected during routine blood testing. Measurement of AI plasma levels was performed by liquid chromatography-tandem mass spectrometry. Follicle stimulating hormone (FSH) and estradiol were measured within the routine blood examination. RESULTS: A median anastrozole plasma concentration of 34.7 ng/mL (mean, 37.4), with a large interindividual variability, was observed (SD, 15.1; range, 5.4-86.5). After age adjustment, it was found that anastrozole plasma concentrations significantly increased with BMI (r = 0.241; P = .001). Anastrozole serum concentrations in women with obesity (BMI ≥ 30) exceeded those of women with normal weight (BMI ≤ 25) by 25%. Women with excess weight had lower mean FSH levels, indicating higher estrogenic activity, compared with women with normal weight. CONCLUSION: This study indicates that BMI is a vital factor in anastrozole metabolism, as measured by anastrozole plasma concentration and FSH levels. Further research is mandatory to clarify results on the association of obesity and AI treatment efficacy to allow adapting AI treatment accordingly.