Complex agonist-like properties of ICI 182,780 (Faslodex) in human breast cancer cells that predominantly express progesterone receptor-B: Implications for treatment resistance

Jianbo Wu, Yayun Liang, Zafar Nawaz, Salman M. Hyder

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

ICI 182,780 (Faslodex), considered a pure antiestrogen, is approved for treatment of post-menopausal breast cancer patients who fail to respond to tamoxifen therapy. We recently reported that, like mifepristone, ICI 182,780 exhibits anti-progestin activity, blocking the progestin-dependent increase in endogenous vascular endothelial growth factor (VEGF) mRNA and protein release. Some anti-progestins have partial agonist-like activity in breast cancer cells expressing high levels of progesterone receptor B (PRB). Our results show that ICI 182,780 can also induce reporter activity from a plasmid containing a simple progestin responsive element (PRE) in these cells. Using small interfering RNA, we determined that induction is dependent on the presence of PR, estrogen receptor and SRC-1. Regulation of more complex progestin-responsive promoters was contextdependent; induction was observed from the MMTV promoter but not from the VEGF promoter. In contrast, ICI 182,780 increased the release of angiogenically active VEGF from cells expressing elevated levels of PRB. This effect was dependent on the phosphatidylinositol-3 kinase and ERK7MAPK signaling pathways. We hypothesize that these agonist-like properties of ICI 182,780 (one genomic and one non-genomic) may contribute to the acquisition of drug resistance, suggesting that both anti-hormonal and anti-angiogenic treatment may be appropriate in these patients.

Original languageEnglish (US)
Pages (from-to)1647-1659
Number of pages13
JournalInternational journal of oncology
Volume27
Issue number6
StatePublished - Dec 1 2005

Keywords

  • Anti-estrogen
  • Estrogen receptor
  • Faslodex
  • Progesterone receptor
  • Progestin
  • VEGF

ASJC Scopus subject areas

  • Cancer Research
  • Oncology

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