Letrozole (CGS 20267)
For research use only.
CAS No. 112809-51-5
Letrozole (CGS 20267) 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 induces autophagy.
Selleck's Letrozole (CGS 20267) has been cited by 22 publications
Purity & Quality Control
Choose Selective Aromatase Inhibitors
|Description||Letrozole (CGS 20267) 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 induces autophagy.|
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|
|Step 2: Enter the in vivo formulation ()|
|% 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 μL 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.
2.Be sure to add the solvent(s) in order. You must ensure that the solution obtained, in the previous addition, is a clear solution before proceeding to add the next solvent. Physical methods such as vortex, ultrasound or hot water bath can be used to aid dissolving.
Calculate the mass, volume or concentration required for a solution. The Selleck molarity calculator is based on the following equation:
Mass (mg) = Concentration (mM) × Volume (mL) × Molecular Weight (g/mol)
*When preparing stock solutions, please always use the batch-specific molecular weight of the product found on the via label and MSDS / COA (available on product pages).
Calculate the dilution required to prepare a stock solution. The Selleck dilution calculator is based on the following equation:
Concentration (start) x Volume (start) = Concentration (final) x Volume (final)
This equation is commonly abbreviated as: C1V1 = C2V2 ( Input Output )
* When preparing stock solutions always use the batch-specific molecular weight of the product found on the vial label and MSDS / COA (available online).
Molecular Weight Calculator
Enter the chemical formula of a compound to calculate its molar mass and elemental composition:
Tip: Chemical formula is case sensitive. C10H16N2O2 c10h16n2o2
Instructions to calculate molar mass (molecular weight) of a chemical compound:
To calculate molar mass of a chemical compound, please enter its chemical formula and click 'Calculate'.
Definitions of molecular mass, molecular weight, molar mass and molar weight:
Molecular mass (molecular weight) is the mass of one molecule of a substance and is expressed in the unified atomic mass units (u). (1 u is equal to 1/12 the mass of one atom of carbon-12)
Molar mass (molar weight) is the mass of one mole of a substance and is expressed in g/mol.
Clinical Trial Information
|NCT Number||Recruitment||interventions||Conditions||Sponsor/Collaborators||Start Date||Phases|
|NCT04735367||Not yet recruiting||Drug: palbociclib plus letrozole||Breast Cancer||Pfizer||February 1 2021||--|
|NCT04002141||Recruiting||Drug: Placebo oral tablet|Drug: Letrozole||Endometriosis|Ovarian Hyperstimulation||University of California San Francisco||September 17 2019||Phase 2|
|NCT03900884||Recruiting||Drug: Venetoclax|Drug: Palbociclib|Drug: Letrozole||Breast Neoplasm Female||Peter MacCallum Cancer Centre Australia||September 25 2019||Phase 1|
|NCT04095364||Recruiting||Drug: Carboplatin|Drug: Letrozole|Drug: Paclitaxel||Low Grade Fallopian Tube Serous Adenocarcinoma|Low Grade Ovarian Serous Adenocarcinoma|Primary Peritoneal Low Grade Serous Adenocarcinoma|Stage II Fallopian Tube Cancer AJCC v8|Stage II Ovarian Cancer AJCC v8|Stage II Primary Peritoneal Cancer AJCC v8|Stage IIA Fallopian Tube Cancer AJCC v8|Stage IIA Ovarian Cancer AJCC v8|Stage IIA Primary Peritoneal Cancer AJCC v8|Stage IIB Fallopian Tube Cancer AJCC v8|Stage IIB Ovarian Cancer AJCC v8|Stage IIB Primary Peritoneal Cancer AJCC v8|Stage III Fallopian Tube Cancer AJCC v8|Stage III Ovarian Cancer AJCC v8|Stage III Primary Peritoneal Cancer AJCC v8|Stage IIIA Fallopian Tube Cancer AJCC v8|Stage IIIA Ovarian Cancer AJCC v8|Stage IIIA Primary Peritoneal Cancer AJCC v8|Stage IIIA1 Fallopian Tube Cancer AJCC v8|Stage IIIA1 Ovarian Cancer AJCC v8|Stage IIIA2 Fallopian Tube Cancer AJCC v8|Stage IIIA2 Ovarian Cancer AJCC v8|Stage IIIB Fallopian Tube Cancer AJCC v8|Stage IIIB Ovarian Cancer AJCC v8|Stage IIIB Primary Peritoneal Cancer AJCC v8|Stage IIIC Fallopian Tube Cancer AJCC v8|Stage IIIC Ovarian Cancer AJCC v8|Stage IIIC Primary Peritoneal Cancer AJCC v8|Stage IV Fallopian Tube Cancer AJCC v8|Stage IV Ovarian Cancer AJCC v8|Stage IV Primary Peritoneal Cancer AJCC v8|Stage IVA Fallopian Tube Cancer AJCC v8|Stage IVA Ovarian Cancer AJCC v8|Stage IVA Primary Peritoneal Cancer AJCC v8|Stage IVB Fallopian Tube Cancer AJCC v8|Stage IVB Ovarian Cancer AJCC v8|Stage IVB Primary Peritoneal 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.
Tel: +1-832-582-8158 Ext:3
If you have any other enquiries, please leave a message.