Letrozole: Scientific Profile
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Third-generation type II aromatase inhibitor for selective research of the hormonal axis. It blocks the conversion of androgens to estrogens through the competitive inhibition of the aromatase enzyme complex.
Letrozole is a highly potent non-steroidal aromatase inhibitor, classified among the third-generation compounds for use in endocrine research. Its main function resides in the reversible binding to the heme group of the cytochrome P450 that composes the aromatase enzyme (CYP19A1). Unlike other modulators, Letrozole does not affect the biosynthesis of other adrenal steroids such as cortisol or aldosterone, maintaining high pharmacological selectivity in study models.
In biomedical research settings, this compound has been documented to be capable of reducing circulating serum estradiol concentrations by up to 95-98% in experimental models. This characteristic makes it a critical tool for studying the negative feedback on luteinizing hormone (LH) and follicle-stimulating hormone (FSH). It is also used to analyze the modulation of bone mineral density and induced gynecomastia in settings of androgenic imbalance.
The scientific literature highlights its usefulness in protocols simulating inverted hypogonadotropic hypogonadism and in research on the induction of ovulation in animal models through the stimulation of gonadotropin secretion. Its pharmacokinetic profile presents a bioavailability above 99%, which facilitates precision in dosing within controlled laboratory settings.
Mechanism of action
The compound acts through a reversible competitive inhibition of the aromatase enzyme. It binds specifically to the iron atom of the heme group of the cytochrome P450 subunit, preventing the transformation of androgenic substrates (such as androstenedione and testosterone) into estrogens (estrone and estradiol). This blockade interrupts the peripheral synthesis of estrogens in adipose, hepatic and muscle tissues, consequently raising gonadotropin levels through the reduction of estrogenic inhibition in the hypothalamus.
Mechanism summary
Competitive and reversible inhibition of cytochrome P450 (CYP19) that blocks the peripheral biosynthesis of estrogens from androgenic precursors.
Estudios Clínicos (10)
- Letrozol bør være førstevalgspræparat til kvinder med anovulatorisk subfertilitet i Danmark (Hedegaard M · Ugeskrift for laeger · 2019) PMID 31538576.
- Letrozole (2006) PMID 29999996.
- Letrozole (Femara) (Gerken P · Clinical journal of oncology nursing · 2004) PMID 15208828.
- Palbociclib and Letrozole in Advanced Breast Cancer. (Finn RS, et al. · N Engl J Med · 2016) PMID 27959613.
- Overall Survival with Ribociclib plus Letrozole in Advanced Breast Cancer. (Hortobagyi GN, et al. · N Engl J Med · 2022) PMID 35263519.
- Updated results from MONALEESA-2, a phase III trial of first-line ribociclib plus letrozole versus placebo plus letrozole in hormone receptor-positive, HER2-negative advanced breast cancer. (Hortobagyi GN, et al. · Ann Oncol · 2018) PMID 29718092.
- Letrozole Compared With Clomiphene Citrate for Polycystic Ovarian Syndrome: A Systematic Review and Meta-analysis. (Liu Z, et al. · Obstet Gynecol · 2023) PMID 36735392.
- Letrozole and Infertility Among Males With Spermatogenic Failure: A Randomized Clinical Trial. (Sun Y, et al. · JAMA Netw Open · 2026) PMID 42313386.
- Efficacy and safety of letrozole or anastrozole in the treatment of male infertility with low testosterone-estradiol ratio: A meta-analysis and systematic review. (Guo B, et al. · Andrology · 2022) PMID 35438843.
- Letrozole normalizes serum testosterone in severely obese men with hypogonadotropic hypogonadism. (de Boer H, et al. · Diabetes Obes Metab · 2005) PMID 15811136.
Warnings
Letrozole is a compound exclusively for research use (RUO); the following warnings and handling considerations apply to its use in the laboratory:
- Exclusive use in laboratory and research settings
- May cause fetal harm in embryological development models
- Requires strict monitoring of serum estradiol levels
- Handle with personal protective equipment to avoid accidental absorption
- Models with preexisting severe hepatic insufficiency
- Research subjects in a pre-pubertal state
- Known hypersensitivity to triazole-derived compounds
- Presence of preexisting osteoporosis in the study model
Technical data
- CAS
- 112809-51-5
- Molecular formula
- C17H11N5
- Molecular weight
- 285.3 Da
- Compound type
- hormone
- Storage
- 15-30°C in a cool, dry place
- Shelf life (lyophilized)
- 36 months
- Shelf life (reconstituted)
- Not applicable (solid formulation)
- Light-sensitive
- No
Frequently asked questions about Letrozole
What is Letrozole?
Third-generation type II aromatase inhibitor for selective research of the hormonal axis. It blocks the conversion of androgens to estrogens through the competitive inhibition of the aromatase enzyme complex.
What is the mechanism of action of Letrozole?
Competitive and reversible inhibition of cytochrome P450 (CYP19) that blocks the peripheral biosynthesis of estrogens from androgenic precursors.
What is Letrozole investigated for?
In preclinical research, Letrozole is studied mainly in: Systemic modulation of the hypothalamic-pituitary-gonadal axis; Research on the reduction of androgen aromatization; Study of the induction of endogenous LH and FSH secretion. Material exclusively for scientific research.
What are the chemical properties of Letrozole?
Molecular formula C17H11N5; molecular weight 285.3 Da; CAS number 112809-51-5.
How is Letrozole stored?
Storage conditions: 15-30°C in a cool, dry place; lyophilized stability: 36 months; once reconstituted: Not applicable (solid formulation).
What routes of administration are studied for Letrozole?
In the research models the following are described: Oral (Research), Intraperitoneal (Animal models). Use is exclusively for scientific research.