Pharmacokinetics and tolerability of exemestane in combination with raloxifene in postmenopausal women with a history of breast cancer

Pharmacokinetic Drug Interaction Between Raloxifene and Cholecalciferol in Healthy Volunteers

Osteoporosis is a common skeletal disorder, often leading to fragility fracture. Combination therapy with raloxifene, a selective estrogen receptor modulator, and cholecalciferol (vitamin D₃) has been proposed to improve the overall efficacy and increase compliance of raloxifene therapy for postmenopausal osteoporosis. To our knowledge, there has been no report of any study on the pharmacokinetic interaction between raloxifene and cholecalciferol. This study aimed to evaluate the possible pharmacokinetic interactions between raloxifene and cholecalciferol in healthy adult male Korean volunteers. Twenty subjects completed this open‐label, randomized, single‐dose, 3‐period, 6‐sequence, crossover phase 1 study with a 14‐day washout period. Serial blood samples were collected from 20 hours before dosing to 96 hours after dosing. The plasma concentrations of raloxifene and cholecalciferol were determined using a validated method for high‐performance liquid chromatography with tandem mass spectrometry. The geometric mean ratios (90%CIs) for area under the plasma concentration–time curve from time 0 to the last quantifiable time point and maximum plasma concentration of raloxifene with or without cholecalciferol were 1.02 (0.87‐1.20) and 0.87 (0.70‐1.08), respectively. For baseline‐corrected cholecalciferol, geometric mean ratios (90%CIs) of area under the plasma concentration–time curve from time 0 to the last quantifiable time point and maximum plasma concentration with or without raloxifene were 1.01 (0.93‐1.09) and 0.99 (0.92‐1.06), respectively. Concurrent treatment with raloxifene and cholecalciferol was generally well tolerated. These results suggest that raloxifene and cholecalciferol have no clinically relevant pharmacokinetic drug‐drug interactions when administered concurrently. All treatments were well tolerated, with no serious adverse events.

Role of the UGT2B17 deletion in exemestane pharmacogenetics

Exemestane (EXE) is an aromatase inhibitor used for the prevention and treatment of breast cancer. The major metabolic pathway for EXE is reduction to form the active 17β-dihydro-EXE (17β-DHE) and subsequent glucuronidation to 17β-hydroxy-EXE-17-O-β-D-glucuronide (17β-DHE-Gluc) by UGT2B17. The aim of the present study was to determine the effects of UGT2B17 copy number variation on the levels of urinary and plasma 17β-DHE-Gluc and 17β-DHE in patients taking EXE. Ninety-six post-menopausal Caucasian breast cancer patients with ER+ breast tumors taking 25 mg EXE daily were recruited into this study. UGT2B17 copy number was determined by a real-time PCR copy number variant assay and the levels of EXE, 17β-DHE and 17β-DHE-Gluc were quantified by UPLC/MS in patients’ urine and plasma. A 39-fold decrease (P<0.0001) in the levels of creatinine-adjusted urinary 17β-DHE-Gluc was observed among UGT2B17 (*2/*2) subjects vs. subjects with the UGT2B17 (*1/*1) genotype. The plasma levels of 17β-DHE-Gluc was decreased 29-fold (P<0.0001) in subjects with the UGT2B17 (*2/*2) genotype vs. subjects with UGT2B17 (*1/*1) genotype. The levels of plasma EXE-adjusted 17β-DHE was 28% higher (P=0.04) in subjects with the UGT2B17 (*2/*2) genotype vs. subjects with the UGT2B17 (*1/*1) genotype. These data indicate that UGT2B17 is the major enzyme responsible for 17β-DHE-Gluc formation in vivo and that the UGT2B17 copy number variant may play a role in inter-individual variability in 17β-DHE levels in vivo.

Exemestane potency is unchanged by common nonsynonymous polymorphisms in CYP19A1: results of a novel anti-aromatase activity assay examining exemestane and its derivatives

Exemestane (EXE) treats estrogen receptor positive (ER+) breast cancer in postmenopausal women by inhibiting the estrogen-synthesizing cytochrome P450 CYP19A1. Variability in the severity and incidence of side effects as well as overall drug efficacy may be partially explained by genetic factors, including nonsynonymous variation in CYP19A1, also known as aromatase. The present study identified phase I EXE metabolites in human liver microsomes (HLM) and investigated mechanisms that may alter the extent of systemic estrogen deprivation in EXE-treated women with breast cancer, including whether functional polymorphisms in aromatase cause differential inhibition by EXE and whether EXE metabolites possess anti-aromatase activity. The potency of EXE and ten of its derivatives was measured with HEK293-overexpressed wild type aromatase (CYP19A1*1) using a rapid novel UPLC tandem mass spectrometry method. Of the ten compounds assayed, five were poor inhibitors (IC ₅₀ ˃ 50 μmol/L) of wild type aromatase while five others, including the major metabolite, 17β-dihydroexemestane (17β-DHE), exhibited moderate potency, with IC ₅₀ values ranging between 1.2 and 7.1 μmol/L. The anti-aromatase activity of EXE was also tested with two common allozymes, aromatase^Thr201Met (CYP19A1*3) and aromatase^Arg264Cys (CYP19A1*4). Differential inhibition of variant aromatase is unlikely to account for variable clinical outcomes as EXE-mediated inhibition of aromatase^Thr201Met (IC ₅₀ = 0.86 ± 0.12 μmol/L) and aromatase^Arg264Cys (IC ₅₀ = 1.7 ± 0.65 μmol/L) did not significantly differ from wild type (IC ₅₀ = 0.92 ± 0.17 μmol/L). Although less potent than the parent drug, these results suggest that active metabolites may contribute to the therapeutic mechanism of EXE.

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.

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.

The use of raloxifene in osteoporosis treatment

INTRODUCTION

Osteoporosis is a common disease characterized by the occurrence of fragility fractures. Major osteoporotic fractures are associated with decreased quality of life and high costs.

AREAS COVERED

This review summarizes clinical data on raloxifene (RLX), a second generation selective estrogen-receptor modulator (SERM), currently approved for the treatment of postmenopausal osteoporosis. RLX has estrogen effects on bone and lipid profile, whereas it has anti-estrogen effects on uterus and breast cells. Its main side effects are hot flushes and venous thromboembolism. Literature searches were conducted to retrieve articles reporting RLX clinical trial data. For comparison of safety and efficacy, post-marketing studies on RLX were included.

EXPERT OPINION

RLX is effective in reducing vertebral fracture risk in osteoporotic women, it is safe and its ability to prevent breast cancer has to be considered in the analyses of cost/effect and of the ideal candidate to this treatment. RLX has to be avoided in patients with previous history of venous thromboembolism.

Ganitumab with either exemestane or fulvestrant for postmenopausal women with advanced, hormone-receptor-positive breast cancer: a randomised, controlled, double-blind, phase 2 trial

BACKGROUND

Insulin-like growth factors (IGF-1 and IGF-2) bind to the IGF-1 receptor (IGF-1R), increasing cell proliferation and survival. Ganitumab is a monoclonal IgG1 antibody that blocks IGF-1R. We tested the efficacy and safety of adding ganitumab to endocrine treatment for patients with hormone-receptor-positive breast cancer.

METHODS

We did this phase 2 trial in outpatient clinics and hospitals. We enrolled postmenopausal women with hormone-receptor-positive, locally advanced or metastatic breast cancer previously treated with endocrine treatment. They were randomly assigned (2:1) with a central randomisation schedule to receive intravenous ganitumab 12 mg per kg bodyweight or placebo in combination with open-label intramuscular fulvestrant (500 mg on day 1, then 250 mg on days 15, 29, and every 28 days) or oral exemestane (25 mg once daily) on a 28-day cycle. Patients, investigators, study monitors, and the sponsor staff were masked to treatment allocation. Response was assessed every 8 weeks. The primary endpoint was median progression-free survival in the intention-to-treat population. We analysed overall survival as one of our secondary endpoints. The study is registered at ClinicalTrials.gov, number NCT00626106.

FINDINGS

We screened 189 patients and enrolled 156 (106 in the ganitumab group and 50 in the placebo group). Median progression-free survival did not differ significantly between the ganitumab and placebo groups (3·9 months, 80% CI 3·6-5·3 vs 5·7 months, 4·4-7·4; hazard ratio [HR] 1·17, 80% CI 0·91-1·50; p=0·44). However, overall survival was worse in the the ganitumab group than in the placebo group (HR 1·78, 80% CI 1·27-2·50; p=0·025). With the exception of hyperglycaemia, adverse events were generally similar between groups. The most common grade 3 or higher adverse event was neutropenia-reported by six of 106 (6%) patients in the ganitumab group and one of 49 (2%) in the placebo group. Hyperglycaemia was reported by 12 of 106 (11%) patients in the ganitumab group (with six patients having grade 3 or 4 hyperglycaemia) and none of 49 in the placebo group. Serious adverse events were reported by 27 of 106 (25%) patients in the ganitumab group and nine of 49 (18%) patients in the placebo group.

INTERPRETATION

Addition of ganitumab to endocrine treatment in women with previously treated hormone-receptor-positive locally advanced or metastatic breast cancer did not improve outcomes. Our results do not support further study of ganitumab in this subgroup of patients.

FUNDING

Amgen.

Phase I trial of exemestane in combination with metformin and rosiglitazone in nondiabetic obese postmenopausal women with hormone receptor-positive metastatic breast cancer

PURPOSE

Obese women with breast cancer have worse prognosis than women with normal body mass index. Endocrine therapy resistance is in part mediated by insulin resistance in obese women with breast cancer. We investigated the tolerability and pharmacokinetics of exemestane in combination with metformin and rosiglitazone in nondiabetic overweight and obese postmenopausal women with hormone receptor-positive metastatic breast cancer.

METHODS

Patients had previously received chemotherapy and endocrine therapy for breast cancer. Exemestane was given as 25 mg orally per day. Metformin (M) and rosiglitazone (R) were given twice daily. Dose level 1 consisted of M 1,500 mg/day and R 6 mg/day. Dose level 2 consisted of M 2,000 mg/day and R 8 mg/day. Plasma concentrations of exemestane were measured on days 1, 8, and 15.

RESULTS

Twenty patients were enrolled. Fourteen patients received exemestane, metformin, and rosiglitazone. Six patients received exemestane with metformin only (2,000 mg/day). Both regimens were well tolerated at the highest doses tested, and there were no notable changes in plasma exemestane levels. Six patients (30%) had stable disease for 6 months or longer.

CONCLUSIONS

Oral daily administration of exemestane (25 mg) and metformin (2,000 mg) with and without rosiglitazone (8 mg) daily was well tolerated. Exemestane pharmacokinetics were not altered by metformin and rosiglitazone.

[Hormone therapy and breast cancer]

The nuclear estrogen receptors (ER) are the major targets for endocrine treatment of hormone-dependent breast cancers. Hormone therapy blocked endogenous estrogen activation of ER, either by competitive inhibition of endogenous estrogens (selective estrogen receptor modulators - SERM or selective estrogen receptor down regulators - SERD) or by inhibition of estrogen synthesis (aromatase inhibitors) from adrenal androgens in post-menopausal women. The efficacy of these treatments has been shown on large series of breast cancer patients. However de novo or acquired resistance to treatment occurs. The better knowledge of the mechanism of action of such treatment may help to better understand them, and also for the determinism of adverse side effects of the different class of molecules.

Enhanced bioavailability of exemestane via proliposomes based transdermal delivery

Exemestane, a novel steroidal aromatase inactivator used in the treatment of advanced breast cancer has limited bioavailability (42%) due to poor solubility, extensive first-pass metabolism, and also the absorption is dependent on formulation type and food. The present study is aimed to evaluate the feasibility of proliposomes for transdermal delivery of exemestane. The prepared proliposomes were characterized for size, zeta potential, and entrapment efficiency. The size of the vesicles was found to be between 440 and 700 nm with high entrapment efficiency for the formulation containing greater amounts of phosphatidylcholine. Differential scanning calorimetry and Fourier transform infrared studies were performed to understand the phase transition behavior and mechanism for skin permeation, respectively. The drug release across cellophane membrane follows zero-order kinetics by diffusion. Ex vivo permeation enhancement assessed from flux, permeability coefficient, and enhancement ratio were significantly higher for proliposome gels compared with control. A significant improvement in the bioavailability (2.4-fold) was observed from optimized proliposome gel compared with control (oral suspension). The stability data reveal that the formulations are more stable when stored at 4°C. In conclusion, proliposomal gels offer potential and prove to be efficient carriers for improved and sustained transdermal delivery of exemestane.

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.

Dissolution improvement and the mechanism of the improvement from cocrystallization of poorly water-soluble compounds

PURPOSE

To demonstrate improvement in the dissolution of exemestane and megestrol acetate from cocrystallization using various particle sizes and to investigate the mechanism of the improved dissolution.

METHODS

Cocrystal screening was performed by slurry crystallization. The cocrystals were identified and characterized by powder X-ray diffraction, thermal analysis, and single crystal X-ray diffraction. Different particle sizes of each cocrystal were prepared from organic solutions. Solubility and dissolution rates were evaluated using dissolution tests. Transformation behavior of the cocrystals in suspension was analyzed by PXRD and polarization microscopy.

RESULTS

Two novel cocrystals were obtained: exemestane (EX)/maleic acid (MAL) (cocrystal 1) and megestrol acetate (MA)/saccharin (SA) (cocrystal 2). Cocrystal 1 showed a high dissolution rate even with large particles. Cocrystal 2 showed supersaturation with fine particles. The transformation from cocrystal 1 to EX was observed within 1 min in suspension. Cocrystal 2 was transformed to MA within 2-4 h.

CONCLUSIONS

Cocrystallizations of EX and MA improved initial dissolution rates compared to the respective original crystals. The mechanism of dissolution enhancement varied. With cocrystal 1, fine particle formation resulted in enhancement, whereas with cocrystal 2, enhancement was due to the maintenance of the cocrystal form and rapid dissolution before transformation to the original crystal.