For research use only.
Catalog No.S1235 Synonyms: CGS 20267
Molecular Weight(MW): 285.3
Letrozole is a third generation inhibitor of aromatase with IC50 of 0.07-20 nM in cell-free assays.It has no effect on the plasma levels of 17α-OH progesterone, thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), or androstenedione and does not affect normal urine electrolyte excretion or thyroid function in clinical studies.
Selleck's Letrozole has been cited by 16 publications
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Uterus from mice treated with Letrozole. (A) 13 weeks old aP2-Cre/ERαflox/flox mice treated with vehicle have swollen abdomen while littermates treated with Letrozole for 17 days looks normal (B). (C) Uterus from vehicle treated aP2-/ERαflox/flox mice with severe hydrometra. (D) Uterus from Letrozole treated aP2-Cre/ERαflox/flox mice looks normal.
PLoS One 2014 9(1), e85581. Letrozole purchased from Selleck.
Effect of aromatase inhibitor letrozole on cellular proliferation marker Ki-67 expression in LNCaP tumor xenografts. A, Ki-67 immunostaining in transverse sections of xenograft tumors from C, C＋T, C＋T＋D, C＋T＋L, and C＋T＋D＋L mice 2 days after testosterone replacement. Panel B, Quantification of Ki-67–positive cells in LNCaP tumors at day 2 post testosterone replacement. Error bars represent SEM. Number of animals in each group is shown in parentheses. ***, P ＜.0001.
Endocrinology 2013 154, 2296-307. Letrozole purchased from Selleck.
Letrozole impairs object recognition and object placement memory consolidation. (A) Mice receiving bilateral dorsal hippocampal infusion of vehicle (n = 13), but not 0.005 μg (n = 9), 0.025 μg (n = 10), or 0.05 μg (n = 12) letrozole, immediately after training spent significantly more time with the novel object 24 h after training relative to chance (dashed line at 15 s). Vehicle-infused mice also spent significantly more time with the novel object than mice infused with 0.025 or 0.05 μg letrozole. These data suggest that the 0.025 and 0.05 μg doses of letrozole blocked object recognition memory consolidation. (B) Mice receiving bilateral dorsal hippocampal infusions of vehicle (n = 12) or 0.005 μg (n = 9) letrozole, but not 0.025 μg (n = 9) or 0.05 μg (n = 9) letrozole, immediately after training spent significantly more time than chance (*p < 0.05) with the moved object 4 h after training. Vehicle-infused mice also spent significantly more time with the moved object than mice infused with 0.025 or 0.05 μg letrozole, suggesting that the 0.025 and 0.05 μg doses of letrozole also blocked spatial memory consolidation. This effect was limited to within the first 2–3 h after training, as mice receiving a bilateral infusion of vehicle (n = 11) or 0.025 μg letrozole (n = 10) 3 h after OR training (C), or 2 h after OP training (vehicle: n = 13; letrozole: n = 9) (D), spent significantly more time than chance with the novel object (*p < 0.05), suggesting that the memory-impairing effects of letrozole are specific to the consolidation period immediately after training. *p < 0.05, **p < 0.01, ***p < 0.001 relative to chance; #p < 0.05 for between-group differences measured by Tukey's post hoc tests.
Horm Behav, 2016, 83:60-7. Letrozole purchased from Selleck.
Functional comparison of mono-cultured MCF7 cells and MCF7 cells co-cultured with CAFs before and after letrozole treatment. Cell invasion (a), migration (b), adhesion (c) and proliferation assays (d) revealed that MCF7 cells co-cultured with CAFs displayed increasing adhesion, invasion, migration and proliferation abilities compared with mono-cultured cells either with or without letrozole treatment. The invasion, migration and adhesion of co-cultured MCF7 cells were decreased after letrozole treatment (a–c). Letrozole had no effect on mono-cultured MCF7 cell migration, invasion, adhesion or proliferation (a–d). e–g Representative images of invasion, migration and adhesion assays (magnification: ×100). LET represents letrozole. MO and CO represents mono-cultured and co-cultured, respectively. Data are presented as the mean ± SD. *P < 0.05 and ***P < 0.001, as determined using the independent sample T test
Med Oncol, 2016, 33(7):64. Letrozole purchased from Selleck.
Purity & Quality Control
Choose Selective Aromatase Inhibitors
|Description||Letrozole is a third generation inhibitor of aromatase with IC50 of 0.07-20 nM in cell-free assays.It has no effect on the plasma levels of 17α-OH progesterone, thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), or androstenedione and does not affect normal urine electrolyte excretion or thyroid function in clinical studies.|
Letrozole potently inhibits aromatase derived from a variety of different sources including human placental microsomes, particulate fractions of human breast cancer, rat ovarian microsomes, MCF-7 cells transfected with aromatase (MCF-7Ca), JEG-3 human choriocarcinoma cells , CHO cells, hamster ovarian tissue, and particulate fractions of human breast cancer with IC50 of 11, 2, 7, 0.07, 0.07, 1.4, 20 and 0.8 nM. In the non-cellular systems, the IC50 of letrozole is calculated to be 1-13 nM.  Letrozole maximally inhibits estradiol production in vitro in LH-stimulated hamster ovarian tissue at 0.1 μM with an IC50 of 0.02 μM and does not significantly affect progesterone production up to 350 μM. In ACTH-stimulated rat adrenal tissue in vitro, aldosterone production is inhibited by with an IC50 of 210 μM.  Letrozole inhibits growth of the MCF-7 epithelial breast cancer cells in a dose-dependent way with IC50 of 1 nM. Inhibition can be observesed even at the very low concentrations tested (0.1 nM). Treatment of normal MCF-12A epithelial cells with letrozole did not affect their growth even when high letrozole concentrations (100 nM) or prolonged culture times. Letrozole (10 nM) signiﬁcantly suppressed the stimulatory effects of 4-androstene-3,17-dione (100 nM) or testosterone (100 nM) on MCF-7 cell proliferation. Concurrent administration of 17-β-estradiol with letrozole (10 nM) decreased the stimulatory effect of the enzymatic activity of MMP-2 and - 9 released by estradiol. 
|In vivo||Letrozole inhibits aromatase in vivo with ED50 of 1-3 μg/kg p.o..  Letrozole displays anti-endocrine effects. Letrozole inhibits androstenedione-induced uterine hypertrophy in immature rats with ED50 of 1-3 μg/kg. In the adult female rat, Letrozole (0.3-1 mg/kg daily p.o., 14 days) completely interrupts ovarian cyclicity and reduces uterine weight and serum estradiol (E2) concentrations to a similar extent to that seen after ovariectomy.  Letrozole induces dose-dependent regression of estrogen-dependent, 9,10-dimethylbenz-a-anthracene (DMBA)-induced mammary tumors in adult female rats. The ED50 for Letrozole is determined to be 10 - 30 µg/kg/day, with complete inhibition at a daily dose of 10 µg/day.  Letrozole produces dose-dependent inhibition of tumor growth of MCF-7 cells transfected with human aromatase gene (MCF-7Ca) implanted athymic nude mice, with complete inhibition at 20 mg/kg per day p.o.. |
Human placental aromatase activity:The assay is performed in a total volume of 1 mL at 37 ℃. Unless otherwise noted, the incubation mixture contains 11 nM [4- 14C] androstene-3, 17-dione ([4- 14C]A), 24 mM NADPH (tetrasodium salt Type III), the appropriate concentrations of the desired inhibitor, and 120 μg of microsomal protein. The (4- 14C)A is added as a solution in 1.7% ethanol in 0.05 M potassium phosphate buffer (pH 7.4), so that the final concentration of ethanol does not exceed 0.02% (v/v). The reaction is started by the addition of enzyme and stopped after 20 min by the addition of 7 vol of ethyl acetate. The mixture is agitated on a vortex mixer and centrifuged at 600 g for 5 min. The aqueous phase is re-extracted with 7 vol of ethyl acetate, and the combined extracts are evaporated to dryness using an Evapo-Mix. Over 99% of the radio- active of [4- 14C] added is recovered using this extraction system. The residue obtained is dissolved in 150 μL acetone, and 100 μL aliquots are chromatographed for 65 min on thin-layer plates precoated with silica gel 60 using ethyl: acetate: isooctane (140:60, v/v; system A) or toluene: chloroform: methanol (70:140:20; system B). The radioactive zones of the plate are located with a Berthold LB 2760 thin-layer scanner. The radioactive estradiol (E2) and estrone (E1) neaks are identified by comparison with authentic standards. The corresponding bonding band of silica gel is transferred to vials containing 10 mL of scintillation fluid, and counted with a 6880 Liquid Scintillation system.
-  Haynes BP, et al. J Steroid Biochem Mol Biol, 2003, 87(1), 35-45.
-  Bhatnagar AS, et al. J Steroid Biochem Mol Biol, 1990, 37(6), 1021-1027.
-  Mitropoulou TN, et al. Int J Cancer, 2003, 104(2), 155-160.
|In vitro||DMSO||57 mg/mL (199.78 mM)|
|In vivo||Add solvents to the product individually and in order(Data is from Selleck tests instead of citations):
0.5% CMC Na
For best results, use promptly after mixing.
* Please note that Selleck tests the solubility of all compounds in-house, and the actual solubility may differ slightly from published values. This is normal and is due to slight batch-to-batch variations.
In vivo Formulation Calculator (Clear solution)
|Step 1: Enter information below (Recommended: An additional animal making an allowance for loss during the experiment)|
|Dosage||mg/kg||Average weight of animals||g||Dosing volume per animal||ul||Number of animals|
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|% DMSO % % Tween 80 % ddH2O|
Working concentration： mg/ml；
Method for preparing DMSO master liquid: ： mg drug pre-dissolved in μL DMSO (Master liquid concentration mg/mL，)
Method for preparing in vivo formulation：Take DMSO master liquid, next addμL PEG300， mix and clarify, next addμL Tween 80，mix and clarify, next add μL ddH2O，mix and clarify.
1.Please make sure the liquid is clear before adding the next solvent.
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Clinical Trial Information
|NCT Number||Recruitment||interventions||Conditions||Sponsor/Collaborators||Start Date||Phases|
|NCT04227327||Recruiting||Drug: Abemaciclib|Drug: Aromatase Inhibitors||Advanced Breast Cancer||University of Milano Bicocca||January 7 2020||Phase 2|
|NCT03870919||Suspended||Drug: Palbociclib|Other: locoregional treatment||Breast Cancer Stage IV|Radiotherapy|Surgery||UNICANCER|Pfizer||October 23 2019||Not Applicable|
|NCT04002141||Recruiting||Drug: Placebo oral tablet|Drug: Letrozole||Endometriosis|Ovarian Hyperstimulation||University of California San Francisco||September 17 2019||Phase 2|
|NCT03900884||Not yet recruiting||Drug: Venetoclax|Drug: Palbociclib|Drug: Letrozole||Breast Neoplasm Female||Peter MacCallum Cancer Centre Australia||September 2019||Phase 1|
|NCT04095364||Recruiting||Drug: Carboplatin|Drug: Letrozole|Drug: Paclitaxel||Low Grade Ovarian Serous Adenocarcinoma|Primary Peritoneal Low Grade Serous Adenocarcinoma|Stage II Ovarian Cancer AJCC v8|Stage IIA Ovarian Cancer AJCC v8|Stage IIB Ovarian Cancer AJCC v8|Stage III Ovarian Cancer AJCC v8|Stage IIIA Ovarian Cancer AJCC v8|Stage IIIA1 Ovarian Cancer AJCC v8|Stage IIIA2 Ovarian Cancer AJCC v8|Stage IIIB Ovarian Cancer AJCC v8|Stage IIIC Ovarian Cancer AJCC v8|Stage IV Ovarian Cancer AJCC v8|Stage IVA Ovarian Cancer AJCC v8|Stage IVB Ovarian Cancer AJCC v8||NRG Oncology|National Cancer Institute (NCI)||August 26 2019||Phase 3|
Answers to questions you may have can be found in the inhibitor handling instructions. Topics include how to prepare stock solutions, how to store inhibitors, and issues that need special attention for cell-based assays and animal experiments.
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