Signaling pathways of apoptosis activated by aromatase inhibitors and antiestrogens

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Updated: Aug 30, 2026

Systems Biology of Metabolic Regulation by Estrogen Receptor Signaling in Breast Cancer
10:36

Systems Biology of Metabolic Regulation by Estrogen Receptor Signaling in Breast Cancer

Published on: March 17, 2016

Apinya Thiantanawat1, Brian J Long, Angela M Brodie

  • 1Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Health Science Facility, Room 580G, 685 West Baltimore Street, Baltimore, MD 21201, USA.

Cancer Research
|November 25, 2003
PubMed

Insights

Aromatase inhibitors like letrozole show greater effectiveness than tamoxifen in breast cancer treatment by inducing cell death and tumor regression. These inhibitors, along with estrogen withdrawal, effectively suppress tumor growth through specific molecular pathways.

Area of Science:

  • Oncology
  • Molecular Biology
  • Pharmacology

Background:

  • Aromatase inhibitors (AIs) are emerging as a superior treatment for breast cancer compared to antiestrogens like tamoxifen (Tam).
  • Understanding the precise molecular mechanisms of AIs is crucial for optimizing breast cancer therapy.

Purpose of the Study:

  • To investigate and compare the mechanisms of cell growth, cell cycle progression, and apoptosis induced by letrozole (Let), anastrozole, 4-hydroxyandrostenedione, estrogen withdrawal (E2W), tamoxifen (Tam), and faslodex.
  • To elucidate the signaling pathways involved in the efficacy of these treatments in estrogen-dependent human breast cancer cells (MCF-7Ca).

Main Methods:

  • Utilized estrogen-dependent human breast cancer cells (MCF-7Ca) stably transfected with aromatase.
  • Administered three aromatase inhibitors (letrozole, anastrozole, 4-hydroxyandrostenedione), estrogen withdrawal (E2W), and antiestrogens (tamoxifen, faslodex).
  • Assessed cell growth, cell cycle progression (G0-G1 arrest), apoptosis, protein expression (p53, p21, cyclin D1, c-myc, Bcl-2, Bax), and caspase activation (caspase-9, -6, -7, -3, -8) in vitro and in vivo tumor models.

Main Results:

  • All treatments induced growth suppression and G0-G1 cell cycle arrest, with increased p53 and p21, and decreased cyclin D1 and c-myc.
  • Aromatase inhibitors and E2W significantly increased apoptosis (4-7 fold), decreased Bcl-2, increased Bax, and activated caspases-9, -6, and -7.
  • Letrozole and E2W demonstrated tumor regression in vivo, unlike tamoxifen and faslodex, with letrozole showing the most significant anti-tumor effects.

Conclusions:

  • Aromatase inhibitors and estrogen withdrawal share similar molecular pathways for inducing cell cycle arrest and apoptosis in breast cancer.
  • Letrozole exhibits superior efficacy compared to estrogen withdrawal and antiestrogens, demonstrating significant tumor regression and cell growth inhibition.
  • The study highlights the potent anti-cancer effects of letrozole, supporting its role as a highly effective treatment for estrogen-dependent breast cancer.

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