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.
Cited by 6 Publications
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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.
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.
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|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||0.5% CMC||10 mg/mL|
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Clinical Trial Information
|NCT Number||Recruitment||Conditions||Sponsor/Collaborators||Start Date||Phases|
|NCT02941926||Recruiting||Breast Cancer||Novartis Pharmaceuticals|Novartis||November 30, 2016||Phase 3|
|NCT00006174||Completed||McCune Albright Syndrome|Polyostotic Fibrous Dysplasia|Precocious Puberty||National Institute of Dental and Craniofacial Research (NIDCR)|National Institutes of Health Clinical Center (CC)||August 3, 2000||Phase 1|
|NCT03007979||Not yet recruiting||Breast Cancer|Breast Carcinoma|Cancer of Breast|Malignant Tumor of Breast||Washington University School of Medicine||February 28, 2017||Phase 2|
|NCT02907918||Not yet recruiting||Breast Cancer|Cancer of Breast|Breast Carcinoma||Washington University School of Medicine|Pfizer||February 28, 2017||Phase 2|
|NCT01872260||Recruiting||Breast Cancer||Novartis Pharmaceuticals|Novartis||October 22, 2013||Phase 1|
|NCT03008408||Not yet recruiting||Malignant Neoplasms of Female Genital Organs|Endometrial Carcinoma||M.D. Anderson Cancer Center|Novartis||April 2017||Phase 2|
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