Letrozole

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Cat Number

API0232295

CAS Number

112809-51-5

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Product Detail Description Scientific Support Advanced Innovations Customer Q&A

CAS Number

112809-51-5

EINECS

675-034-8

Storage

Store at room temperature

Synonyms

Femara; Letrozol; CGS 20267; DTXSID4023202

Molecular Formula

C17H11N5

Molecular Weight

285.3

Smiles

C1=CC(=CC=C1C#N)C(C2=CC=C(C=C2)C#N)N3C=NC=N3

Appearance

White to off-white crystalline powder

Melting Point

181-183°C

Boiling Point

563.5±60.0°C at 760 mmHg (Predicted)

Relative Density

1.21±0.1 (Predicted)

General Description

Letrozole is a synthetic triazole derivative with a benzonitrile group, belonging to the class of non-steroidal aromatase inhibitors. Its chemical structure is 4,4'-(1H-1,2,4-triazol-1-ylmethylene)dibenzonitrile. Letrozole is a white to off-white crystalline powder, practically insoluble in water but soluble in organic solvents. It is a potent and selective inhibitor of the aromatase enzyme.

Mechanism of Action

Letrozole inhibits the aromatase enzyme, which is responsible for the conversion of androgens to estrogens in the peripheral tissues. By blocking this enzyme, it reduces the levels of circulating estrogens, which are essential for the growth of hormone receptor-positive breast cancer cells. The drug is highly selective for aromatase and does not affect other steroidogenic enzymes.

Application

Letrozole is indicated for the adjuvant treatment of early-stage hormone receptor-positive breast cancer in postmenopausal women, and for the treatment of advanced breast cancer. It is also used for the prevention of breast cancer in high-risk women. The drug is effective in reducing the risk of recurrence and improving survival.

In the PALOMA-2 trial final overall survival analysis of 666 postmenopausal women with ER+/HER2- advanced breast cancer, palbociclib plus letrozole did not significantly improve OS compared to letrozole alone. Median OS was 53.9 months vs 51.2 months (HR 0.96, 95% CI 0.78-1.18, P=0.34). An imbalance in unknown survival outcomes (13.3% vs 21.2%) limited interpretation. The PFS benefit did not translate into a statistically significant OS advantage, though the OS analysis was confounded by subsequent therapies and missing data.

Fig. 1 OS and time to chemotherapy. (Slamon DJ, et al., 2024)

References

Slamon DJ, et al. Overall Survival With Palbociclib Plus Letrozole in Advanced Breast Cancer. J Clin Oncol. 2024;42(9):994-1000.

In a letrozole‑induced rat model of polycystic ovary syndrome, letrozole increased body weight, disrupted estrous cyclicity, and reduced ovarian cystathionine β‑synthase (Cbs) mRNA and protein abundance at early time points. Betaine‑homocysteine S‑methyltransferase mRNA increased with age in letrozole‑treated rats. One‑carbon metabolism is altered in this PCOS model, with decreased CBS abundance in the early stages.

Fig. 2 Cumulative body weight gain of rats on letrozole and placebo across 8, 16, and 24 wk of age. (Bries AE, et al., 2021)

References

Bries AE, et al. Letrozole-Induced Polycystic Ovary Syndrome Attenuates Cystathionine-β Synthase mRNA and Protein Abundance in the Ovaries of Female Sprague Dawley Rats. J Nutr. 2021;151(6):1407-1415.

Does Letrozole require protection from light during long‑term storage?

Yes, it is photosensitive. Light exposure can cause photodegradation of the triazole ring. Store in light‑resistant containers, preferably amber glass.

What is the recommended storage temperature for Letrozole?

Store at controlled room temperature (15–25°C). Avoid excessive heat above 30°C, which can soften the powder and accelerate degradation.

Is Letrozole stable in tablet formulations with standard excipients?

Yes, when formulated with standard excipients and protected from moisture.

How is the impurity letrozole N‑oxide (an oxidative degradation product) monitored?

This degradation product is quantified using a stability‑indicating HPLC method, ensuring it remains within ICH qualification thresholds.