Letrozole: a review of its use in the treatment of postmenopausal women with hormone-responsive early breast cancer

Pharmacokinetics of letrozole and effects of its increasing doses on gonadotropins in ewes during the breeding season

Letrozole is a non-steroidal, third-generation aromatase inhibitor used in humans. Although letrozole is not approved for use in animals, it is used off-label in cases of synchronization and infertility. The aim of this study was to determine the pharmacokinetics of letrozole after a single intravenous administration at three different doses in ewes during the breeding season and its effect on gonadotropins (luteinizing hormone (LH) and follicle-stimulating hormone (FSH)) at the beginning of proestrus. The study was carried out on 24 healthy Merino ewes. Ewes were randomly divided into four groups (n = 6) as control, 0.5, 1, and 2 mg/kg. Plasma concentrations of letrozole were measured using HPLC-UV and were analyzed by non-compartmental analysis. LH and FSH concentrations were measured with a commercial ELISA kit. The terminal elimination half-life (t1/2ʎz) was significantly prolonged from 11.82 to 18.44 h in parallel with the dose increase. The dose-normalized area under the concentration-time curve (AUC) increased, and total body clearance (ClT) decreased at the 1 and 2 mg/kg doses (0.05 L/h/kg) compared with the 0.5 mg/kg dose (0.08 L/h/kg). There were no differences in the volume of distribution at steady-state and initial (C0.083h) plasma concentration values between dose groups. The decreased ClT, prolonged t1/2ʎz, and increased AUC at increasing doses showed the nonlinear kinetic behavior of letrozole. Letrozole significantly reduced LH concentration without affecting FSH concentration at all doses. As a result, letrozole has the potential to be used in synchronization methods and manipulation of the follicular waves due to its effect on LH secretion.

Exemestane may be less detrimental than letrozole to bone health in women homozygous for the UGT2B17*2 gene deletion

PURPOSE

UGT2B17 gene deletion (UGT2B17*2) has been reported to affect bone health as well as the pharmacokinetics of aromatase inhibitor (AI) drugs such as exemestane. The goal of this study was to assess associations between UGT2B17 gene deletion and bone health prior to and after 24 months of AI treatment in postmenopausal women with hormone receptor positive (HR+) breast cancer.

METHODS

Bone health in women with HR+ breast cancer enrolled on the prospective randomized Exemestane and Letrozole Pharmacogenetics (ELPh) trial was determined by measuring bone turnover markers (BTM) and bone mineral density (BMD) pre-treatment and after 3 BTM and 24 BMD months of treatment with either the steroidal AI exemestane or the nonsteroidal AI letrozole. DNA samples were genotyped for UGT2B17*2.

RESULTS

Of the 455 subjects included in the analyses, 244 (53.6%) carried at least one copy of UGT2B17*2. UGT2B17*2 was associated with lower pre-treatment BMD at the hip (P = 0.01) and spine (P = 0.0076). Letrozole treatment was associated with a greater decrease in BMD of the hip (P = 0.03) and spine (P = 0.03) than exemestane. UGT2B17 genotype was not associated with changes in BMD from 24 months of AI treatment, though in UGT2B17*2 homozygous patients, there was a trend toward greater decreases in BMD of the spine from treatment with letrozole compared with exemestane (P = 0.05).

CONCLUSION

UGT2B17*2 may be associated with lower baseline BMD in women with HR+ breast cancer. Exemestane is less detrimental to bone health than letrozole in postmenopausal women treated with AI, and this effect may be confined to patients carrying UGT2B17*2, though this finding requires independent validation.

Impact of the OATP1B1 c.521T>C single nucleotide polymorphism on the pharmacokinetics of exemestane in healthy post-menopausal female volunteers

WHAT IS KNOWN AND OBJECTIVE

OATP1B1 mediates the transport of a diverse range of amphiphilic organic compounds that include bile acids, steroid conjugates and hormones. This retrospective pharmacogenetic study was conducted to assess the impact of the OATP1B1 c.521T>C single nucleotide polymorphism (SNP) on the pharmacokinetics of the steroidal aromatase inhibitor drug exemestane in healthy volunteers.

METHODS

Exemestane (25 mg) was administered orally to 14 healthy post-menopausal women. All of the 14 subjects were sampled for pharmacokinetic (PK) analyses and retrospectively genotyped for OATP1B1 c.521T>C (rs 4149056).

RESULTS AND DISCUSSION

Of the 14 subjects enrolled in the study, five were carriers of the minor C allele (OATP1B1 c.521TC+CC) and the remaining nine were carriers of the OATP1B1 c.521TT genotype. PK was assessed over 8 hours post-dosing. Our results showed statistically significant differences (P=.04) in the plasma exemestane AUC_0-8 between the OATP1B1 genotype groups. Our data also showed statistically significant differences (P=.04) in the plasma AUC_0-8 of 17-hydroexemestane (the major biologically active metabolite) between the OATP1B1 genotype groups.

WHAT IS NEW AND CONCLUSION

Our data suggest that the OAPTP1B1 c.521T>C SNP may influence exemestane pharmacokinetics in humans.

COX2 induction: a mechanism of endocrine breast cancer resistance?

PURPOSE

Urine prostaglandin E2 (PGE2) levels have shown to be a risk factor of breast cancer, and the use of nonsteroidal anti-inflammatory drugs (NSAIDs) is known to be beneficial in preventing breast cancer risk and/or recurrence with or without aromatase inhibitors. We hypothesized that the use of an aromatase inhibitor triggers the activation of the inflammatory pathway via release of PGE2.

METHODS

A single oral 25 mg dose of an aromatase inhibitor (exemestane) was given to 14 healthy postmenopausal female volunteers. Blood and urine samples were collected between 0 and 72 h post-dosing for pharmacokinetic and pharmacodynamic analysis.

RESULTS

Our findings showed that urine PGE2 levels were markedly increased 72 h after exemestane administration (average pre-dosing PGE2 levels, 4061.1 pg/mL vs. post-dosing average PGE2 levels, 10732.5 pg/mL, P = 0.001, Wilcoxon Rank Test). Out of 14 subjects enrolled in the study, one subject showed no change in PGE2; another showed a 23-fold decreased in PGE2; and the remaining 12 showed an average of 8.4-fold increase in PGE2 levels (range 1.3-30.5, standard deviation 9.2) after exemestane administration. We found no statistically significant correlations between fold increase in urine PGE2 levels and the pharmacokinetics of either exemestane or 17-hydroexemestane (major in vivo metabolite of exemestane).

CONCLUSION

Our results indicate that one of the pharmacological effects to aromatase inhibitors (e.g., exemestane) involves the activation of the inflammatory pathway via release of PGE2. Further in vitro mechanistic and in vivo translational studies designed to elucidate the role of this newly discovered effect are now warranted.

SPE-UPLC-MS/MS assay for determination of letrozole in human plasma and its application to bioequivalence study in healthy postmenopausal Indian women

A rapid and sensitive ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method is described for determination of letrozole in human plasma. Following solid phase extraction (SPE) of letrozole and letrozole-d4 on Orochem DVB-LP cartridges, chromatography was performed on Acquity UPLC BEH C₁₈ (50 mm×2.1 mm, 1.7 µm) column using methanol-0.1% formic acid in water (85:15, v/v) as the mobile phase. Detection was carried out on a triple quadrupole mass spectrometer with an electrospray source, operated under positive ionization mode. Quantitation of letrozole and letrozole-d4 was done using multiple reaction monitoring (MRM) following the transitions at m/z 286.2→217.0 and m/z 290.2→221.0, respectively. The calibration plots were linear through the concentration range of 0.10-100 ng/mL (r²≥0.9990) using 100 µL human plasma. The extraction recovery of letrozole ranged from 94.3% to 96.2% and the intra-batch and inter-batch precision was ≤5.2%. The method was successfully applied to a bioequivalence study of letrozole after oral administration of 2.5 mg tablet formulation to 16 healthy postmenopausal Indian women. The assay reproducibility was also established through incurred sample reanalysis (ISR) of 74 subject samples.

Drug Use Evaluation of Letrozole in Breast Cancer Patients at Regional Cancer Hospitals in Thailand

BACKGROUND

Medication policy development in Thailand is continually promoting rational drug use. Letrozole, an endocrine therapy drug, is usually prescribed for post-menopausal status early and advanced stage breast cancer. After Ministry of Public Health announced Letrozole as compulsory licensed drug in 2009, more breast cancer patients can access to this drug at low cost especially those within universal coverage schemes. To ensure that Letrozole is rationally prescribed, the drug utilization study was conducted.

OBJECTIVES

The aim of this study was to describe the appropriate use of Letrozole in breast cancer and the relationship between appropriate use and health benefit schemes.

MATERIALS AND METHODS

A retrospective study to evaluate use of Letrozole in breast cancer patients was performed for six months between January - June 2010 in seven regional cancer hospitals, Thailand. All prescriptions of Letrozole were identified from pharmacy dispensing databases and prescription papers. A medical record review was also performed to evaluate appropriate use referring to the drug use evaluation criteria. The approved criterion of this study was referred from the guideline of Thai National Formulary version 2010.

RESULTS

There were 681 prescriptions of Letrozole for 254 breast cancer patients with an average age of 58.6 ± 10.0 years. The patients in universal coverage scheme (UCS), civil servant medication benefit scheme (CSMBS) and social security scheme (SSS) were 77.7%, 18.5% and 8.7% respectively. 10.6% were prescribed Letrozole for the first time. Letrozole were prescribed by oncologists (82.8%). The average number of tablets per prescription was 58 ± 10. Calcium supplements were prescribed concomitant with Letrozole for 19.4%. To assess drug use evaluation criteria, 45 prescriptions were excluded because of uncompleted clinical data, 636 prescriptions were evaluated. The study showed 86 prescriptions (13.5%) with inappropriate use including 6 (0.9%) not prescribed for estrogen receptor (ER) and/or progesterone receptor (PR) positive, 31 (4.9%) not prescribed for post-menopausal and 49 (7.7%) not prescribed for an appropriate duration. Appropriate use percentages in different health benefit schemes were similar, 85.7% of CSMBS, 86.4% of SSS and 86.7% of UCS. The relationship between health benefit scheme and appropriate use of Letrozole was not significantly different, χ2 (2, N = 636) = 0.081, p > 0.05.

CONCLUSIONS

The study showed inappropriate use in breast cancer patients because of non-compliance with duration, menopausal status and hormone receptor requirements. To prescribe appropriate indication did not referred to the appropriate practice along the treatment. Drug use evaluation proved very useful for detecting the sign of inappropriate use and allows immediate feedback to the stakeholder for developing medication policy in the future. Importantly, there was no significantly difference in appropriate use of Letrozole across health benefit schemes.

Plasma estrone sulfate concentrations and genetic variation at the CYP19A1 locus in postmenopausal women with early breast cancer treated with letrozole

Estrogen synthesis suppression induced by aromatase inhibitors in breast cancer (BC) patients may be affected by single nucleotide polymorphisms (SNPs) of the gene encoding aromatase enzyme, CYP19A1. We assessed the association between plasma estrone sulfate (ES), letrozole treatment, and four SNPs of CYP19A1 gene (rs10046 C>T, rs4646 G>T, rs749292 C>T, rs727479 T>G) which seem to be related to circulating estrogen levels. Patients were enrolled into a prospective, Italian multi-center clinical trial (Gruppo Italiano Mammella, GIM-5) testing the association of CYP19A1 SNPs with the efficacy of letrozole adjuvant therapy, in postmenopausal early BC patients. SNPs were identified from peripheral blood cell DNA. Plasma ES concentrations were evaluated by Radio Immuno Assay. Blood samples were obtained immediately before letrozole therapy (N = 204), at 6-weeks (N = 178), 6 (N = 152) and 12-months (N = 136) during treatment. Medians (IQR) of ES were 160 pg/mL (85–274) at baseline, 35 pg/mL (12–64) at 6-weeks, 29 pg/mL (17–48) at 6 months and 25 pg/mL (8–46) after 12 months treatment. No statistically significant association was evident between polymorphisms and ES circulating levels during letrozole therapy. Letrozole suppression of the aromatase enzyme function is not affected by polymorphisms of CYP19A1 gene in postmenopausal BC patients.

Cardiotoxicity of molecularly targeted agents

Cardiac toxicity of molecularly targeted cancer agents is increasingly recognized as a significant side effect of chemotherapy. These new potent therapies may not only affect the survival of cancer cells, but have the potential to adversely impact normal cardiac and vascular function. Unraveling the mechanisms by which these therapies affect the heart and vasculature is crucial for improving drug design and finding alternative therapies to protect patients predisposed to cardiovascular disease. In this review, we summarize the classification and side effects of currently approved molecularly targeted chemotherapeutics.

Aromatase inhibition: a potential target for the management of recurrent or metastatic endometrial cancer by letrozole: more questions than answers?

INTRODUCTION

Endometrial cancer generally presents as early and resectable disease, but about 20% of patients present with either incurable or recurrent/metastatic disease. Patients with good performance status will be treated with hormonal agents, including progestins and tamoxifen, followed by cytotoxic chemotherapy. The options are restricted to hormonal agents for those with multiple comorbidities and older age. Therefore, there is a need to identify novel hormonal agents and other targeted therapeutics with improved therapeutic window in this setting.

AREA COVERED

Clinical trials of letrozole in localized and metastatic settings are reviewed. In the localized setting, limited by the small sample size, preliminary and conflicting clinical activities were observed. Despite the selection of Type I endometrial cancer, which is more estrogen-dependent for its growth, modest clinical activity was observed in the metastatic setting. Thus far, no biomarkers for efficacy have been identified.

EXPERT OPINION

Further understanding of the relevance of aromatase and estrogen receptor and their interplay with other growth pathways will be necessary to guide further development of letrozole. It is premature to declare letrozole a therapeutic option in recurrent/metastatic endometrial cancer.

An integrated microfluidic cell array for apoptosis and proliferation analysis induction of breast cancer cells

In vitro sensitivity testing of tumor cells could rationalize and improve the choice of chemotherapy and hormone therapy. In this report, a microfluidic device made from poly(dimethylsiloxane) and glass was developed for an assay of drug induced cytotoxicity. We evaluated the apoptotic and proliferation-inhibitory effects of anticancer drugs mitomycin C (MMC) and tamoxifen (TAM) using MCF-7 breast cancer cells. MMC and TAM both induced apoptosis and inhibited proliferation of MCF-7 cells in a concentration-dependent manner. MMC caused the expression of antiapoptotic protein Bcl-2 a dose-dependent reduction in MCF-7 cells. The expression of Bcl-2 did not change significantly in MCF-7 cells treated by TAM. The results in the microfluidic device were correlated well with the data obtained from the parallel experiments carried out in the conventional culture plates. The developed microfluidic device could be a potential useful tool for high content screening and high throughput screening research.