Catalog No.S1235 Synonyms: CGS 20267

Letrozole Chemical Structure

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.

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4 Customer Reviews

  • 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.

  • 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.

    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

Biological Activity

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.
Aromatase [1]
(Cell-free assay)
0.07 nM-20 nM
In vitro

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. [1] 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. [2] 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. [3]

Cell Data
Cell Lines Assay Type Concentration Incubation Time Formulation Activity Description PMID
human MCF7a cells NUPKT2ZLS3m2b4TvfIlkcXS7IHHzd4F6 Ml7YR5l1d3SxeHnjbZR6KGGpYXnud5QhcHWvYX6gUWNHP2FiY3XscJMh\XiycnXzd4lv\yCWZYStc4ZnNTOkZYThTHNFOS2Dcn;tJIF{e2W|c3XkJIF{KGmwaHnibZRqd25ib3[gWHNVNXO2aX31cIF1\WRiY3XscEBxem:uaX\ldoF1cW:wIH3lZZN2emWmIHHmeIVzKDFyIHThfZMtKEWFNUC9OIUuODZizszN NHPjW|IzOjl3MUC3OC=>
human JEG3 cells NE\pTHBHfW6ldHnvckBie3OjeR?= NFy2fVBKdmirYnn0bY9vKG:oIHHyc41ifGG|ZTDhZ5Rqfmm2eTDpckBpfW2jbjDKSWc{KGOnbHzzMEBKSzVyPUCuNFAxQDlizszN M{jCclE5PTlyMkey
human MCF7 cells M4Hab2N6fG:2b4jpZ4l1gSCjc4PhfS=> NWr4TGRUPzJiaB?= MYTDfZRwfG:6aXPpeJkh[WejaX7zeEBme3S{b3flck1l\XCnbnTlcpQhcHWvYX6gUWNHPyClZXzsd{Bi\nSncjC3NkBpenNiYomgUXRVKGG|c3H5MEBKSzVyPUCuNFA4KM7:TR?= M1\TSFI1OzR3NEix
human MDA-MB-435 cells NIPDfoVIem:5dHigbY5pcWKrdHnvckBie3OjeR?= NEfHTGg1QCCq MX;Hdo94fGhiaX7obYJqfGmxbjDv[kBpfW2jbjDNSGEuVUJvNEO1JINmdGy|IHHmeIVzKDR6IHjyd{BjgSC|dXzmc5Jpd2SjbXnu[UBDKGG|c3H5MEBIUTVyPUCuNFY4KM7:TR?= NXe3copqOjB7NUC4PVg>
human IGROV1 cells NVj3[GpxT3Kxd4ToJIlvcGmkaYTpc44h[XO|YYm= M1rFR|Q5KGh? NXTGcFFmT3Kxd4ToJIlvcGmkaYTpc44hd2ZiaIXtZY4hUUeUT2[xJINmdGy|IHHmeIVzKDR6IHjyd{BjgSC|dXzmc5Jpd2SjbXnu[UBDKGG|c3H5MEBIUTVyPUCuNFk2KM7:TR?= NVHiUpAyOjB7NUC4PVg>
human MDA-MB-231 cells MXXHdo94fGhiaX7obYJqfGmxbjDhd5NigQ>? MYS0PEBp NVyxOVVtT3Kxd4ToJIlvcGmkaYTpc44hd2ZiaIXtZY4hVUSDLV3CMVI{OSClZXzsd{Bi\nSncjC0PEBpenNiYomgd5Vt\m:{aH;kZY1qdmViQjDhd5NigSxiR1m1NF0xNjF3IN88US=> MYGyNFk2ODh7OB?=
human T47D cells MU\Hdo94fGhiaX7obYJqfGmxbjDhd5NigQ>? NUD2VplZPDhiaB?= MVrHdo94fGhiaX7obYJqfGmxbjDv[kBpfW2jbjDUOFdFKGOnbHzzJIFnfGW{IES4JIhzeyCkeTDzeYxnd3Kqb3ThcYlv\SCEIHHzd4F6NCCJSUWwQVAvPDRizszN NUS1NGpEOjB7NUC4PVg>
human MCF7 cells NYT0V5VzT3Kxd4ToJIlvcGmkaYTpc44h[XO|YYm= MXe0PEBp MnHpS5Jwf3SqIHnubIljcXSrb36gc4YhcHWvYX6gUWNHPyClZXzsd{Bi\nSncjC0PEBpenNiYomgd5Vt\m:{aH;kZY1qdmViQjDhd5NigSxiR1m1NF0xNjdizszN MkLiNlA6PTB6OUi=
human OVCAR4 cells M3jrXmdzd3e2aDDpcohq[mm2aX;uJIF{e2G7 M{jSOVQ5KGh? NWfnSJdQT3Kxd4ToJIlvcGmkaYTpc44hd2ZiaIXtZY4hV1[FQWK0JINmdGy|IHHmeIVzKDR6IHjyd{BjgSC|dXzmc5Jpd2SjbXnu[UBDKGG|c3H5MEBIUTVyPUCuPFgh|ryP M4HZUFIxQTVyOEm4
human BT549 cells NIfLUJRIem:5dHigbY5pcWKrdHnvckBie3OjeR?= NYLwWG9EPDhiaB?= NViyRoFlT3Kxd4ToJIlvcGmkaYTpc44hd2ZiaIXtZY4hSlR3NEmgZ4VtdHNiYX\0[ZIhPDhiaILzJIJ6KHO3bH\vdohw\GGvaX7lJGIh[XO|YYmsJGdKPTB;MD64PUDPxE1? MWSyNFk2ODh7OB?=
human SKOV3 cells M3L0R2dzd3e2aDDpcohq[mm2aX;uJIF{e2G7 NIHXbpQ1QCCq M3PNc2dzd3e2aDDpcohq[mm2aX;uJI9nKGi3bXHuJHNMV1Z|IHPlcIx{KGGodHXyJFQ5KGi{czDifUB{fWyob4Loc4RidWmwZTDCJIF{e2G7LDDHTVUxRTFwMEmg{txO NGLKdnYzODl3MEi5PC=>
human NCI/ADR-RES cells Mo[xS5Jwf3SqIHnubIljcXSrb36gZZN{[Xl? NFrKWFU1QCCq MnHwS5Jwf3SqIHnubIljcXSrb36gc4YhcHWvYX6gUmNKN0GGUj3SSXMh[2WubIOgZYZ1\XJiNEigbJJ{KGK7IIP1cIZwemixZHHtbY5mKEJiYYPzZZktKEeLNUC9NU4yPiEQvF2= MnPQNlA6PTB6OUi=
human MDA-N cells M{LMcGdzd3e2aDDpcohq[mm2aX;uJIF{e2G7 NX\MRW5[PDhiaB?= M{faR2dzd3e2aDDpcohq[mm2aX;uJI9nKGi3bXHuJG1FSS2QIHPlcIx{KGGodHXyJFQ5KGi{czDifUB{fWyob4Loc4RidWmwZTDCJIF{e2G7LDDHTVUxRTFwNkGg{txO NETyWm4zODl3MEi5PC=>
human OVCAR5 cells MWjHdo94fGhiaX7obYJqfGmxbjDhd5NigQ>? M{nVTFQ5KGh? NGj2W3ZIem:5dHigbY5pcWKrdHnvckBw\iCqdX3hckBQXkODUkWgZ4VtdHNiYX\0[ZIhPDhiaILzJIJ6KHO3bH\vdohw\GGvaX7lJGIh[XO|YYmsJGdKPTB;MT62NkDPxE1? M{DMTVIxQTVyOEm4
human OVCAR8 cells MX3Hdo94fGhiaX7obYJqfGmxbjDhd5NigQ>? NWH2bIlrPDhiaB?= MlPrS5Jwf3SqIHnubIljcXSrb36gc4YhcHWvYX6gU3ZESVJ6IHPlcIx{KGGodHXyJFQ5KGi{czDifUB{fWyob4Loc4RidWmwZTDCJIF{e2G7LDDHTVUxRTRwNTFOwG0> MmOyNlA6PTB6OUi=

... Click to View More Cell Line Experimental Data

In vivo Letrozole inhibits aromatase in vivo with ED50 of 1-3 μg/kg p.o.. [2] 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. [1] 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. [4] 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.. [5]


Kinase Assay:


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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.
Cell Research:


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  • Cell lines: Human breast cancer cells MCF-7
  • Concentrations: ~100 nM
  • Incubation Time: 1 days
  • Method:

    Cells are seeded in duplicate at 5,000 to 10,000 cells per well in 24-well plates. The day after plating, different concentrations of Letrozole are added. At the end of incubation, cells are trypsinizated and placed in Isotone solution and counted immediately using a Coulter particle-counter.

    (Only for Reference)
Animal Research:


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  • Animal Models: Human breast carcinoma xenografts MCF-7 with human aromatase gene (MCF-7Ca)
  • Formulation: 0.5% (w/v) solution of carboxymethylcellulos
  • Dosages: 20 mg/kg/day
  • Administration: orally administered by gavage once every 2 days
    (Only for Reference)

Solubility (25°C)

In vitro DMSO 57 mg/mL (199.78 mM)
Water Insoluble
Ethanol Insoluble
In vivo Add solvents individually and in order:
0.5% CMC Na

* 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.

Chemical Information

Molecular Weight 285.3


CAS No. 112809-51-5
Storage powder
Synonyms CGS 20267

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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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Cell Lines Assay Type Concentration Incubation Time Formulation Activity Description PMID