Downregulation of retinoblastoma protein is involved in the enhanced cytotoxicity of 4-hydroxytamoxifen plus mifepristone combination therapy versus antiestrogen monotherapy of human breast cancer

Patricia V Schoenlein, Min Hou, Julia S. Samaddar, Virgil Thomas Gaddy, Muthusamy Thangaraju, Jill Lewis, Maribeth H Johnson, Vadivel Ganapathy, Andre Kallab, John Thomas Barrett

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Abstract

In this study, human MCF-7 breast cancer cells, which express functional estrogen and progesterone receptors, were used to compare the efficacy of combined antiestrogen plus antiprogestin therapy to antiestrogen monotherapy. Cells were treated with the antiestrogen 4-hydroxytamoxifen (4-OHT) and/or the antiprogestin mifepristone (MIF) and effects on cell proliferation (cytostatic action), cell cycle phase, the phosphorylation state of the tumor suppressor retinoblastoma protein (Rb), and induction of active cell death (cytotoxic action) were determined. Combination hormonal therapy showed both increased cytostatic and cytotoxic activity as compared to either monotherapy. The increased cytostatic action was mediated by Rb activation; whereas, the cytotoxic (pro-apoptotic) action of combined hormonal therapy correlated to a significant reduction in Rb protein levels. To test the apparent role of Rb protein loss in the pro-apoptotic action of combined hormonal therapy, Rb was downregulated in MCF-7 cells using siRNA-targeting. The siRNA-mediated knockdown of Rb combined with 4-OHT therapy resulted in a pro-apoptotic action similar to that resulting from 4-OHT and MIF combination treatment, which included increased cell detachment from the monolayer, high-molecular-weight genomic DNA fragmentation, and cleavage of poly ADP-ribose polymerase (PARP) and lamin A. From these studies, we conclude that Rb protein downregulation is required for 4-OHT-treated, estrogen receptor positive (ER+) breast cancer cells to undergo active cell death. We discuss the potential of using an antiprogestin such as MIF plus antiestrogen treatment to more effectively downregulate Rb in ER+ breast cancer cells to increase the overall cytotoxic action of hormonal therapy.

Original languageEnglish (US)
Pages (from-to)643-655
Number of pages13
JournalInternational Journal of Oncology
Volume31
Issue number3
StatePublished - Sep 1 2007

Fingerprint

Mifepristone
Retinoblastoma Protein
Estrogen Receptor Modulators
Down-Regulation
Breast Neoplasms
Cytostatic Agents
Estrogen Receptors
Small Interfering RNA
Cell Death
Therapeutics
Lamin Type A
Tumor Suppressor Proteins
DNA Cleavage
Poly(ADP-ribose) Polymerases
MCF-7 Cells
DNA Fragmentation
Progesterone Receptors
afimoxifene
Cell Cycle
Molecular Weight

Keywords

  • Antiestrogen
  • Antiprogestin
  • Breast cancer
  • Cell death
  • MCF-7
  • Retinoblastoma protein

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

Cite this

@article{b1ffd59ae02147d8908f318bda403a8b,
title = "Downregulation of retinoblastoma protein is involved in the enhanced cytotoxicity of 4-hydroxytamoxifen plus mifepristone combination therapy versus antiestrogen monotherapy of human breast cancer",
abstract = "In this study, human MCF-7 breast cancer cells, which express functional estrogen and progesterone receptors, were used to compare the efficacy of combined antiestrogen plus antiprogestin therapy to antiestrogen monotherapy. Cells were treated with the antiestrogen 4-hydroxytamoxifen (4-OHT) and/or the antiprogestin mifepristone (MIF) and effects on cell proliferation (cytostatic action), cell cycle phase, the phosphorylation state of the tumor suppressor retinoblastoma protein (Rb), and induction of active cell death (cytotoxic action) were determined. Combination hormonal therapy showed both increased cytostatic and cytotoxic activity as compared to either monotherapy. The increased cytostatic action was mediated by Rb activation; whereas, the cytotoxic (pro-apoptotic) action of combined hormonal therapy correlated to a significant reduction in Rb protein levels. To test the apparent role of Rb protein loss in the pro-apoptotic action of combined hormonal therapy, Rb was downregulated in MCF-7 cells using siRNA-targeting. The siRNA-mediated knockdown of Rb combined with 4-OHT therapy resulted in a pro-apoptotic action similar to that resulting from 4-OHT and MIF combination treatment, which included increased cell detachment from the monolayer, high-molecular-weight genomic DNA fragmentation, and cleavage of poly ADP-ribose polymerase (PARP) and lamin A. From these studies, we conclude that Rb protein downregulation is required for 4-OHT-treated, estrogen receptor positive (ER+) breast cancer cells to undergo active cell death. We discuss the potential of using an antiprogestin such as MIF plus antiestrogen treatment to more effectively downregulate Rb in ER+ breast cancer cells to increase the overall cytotoxic action of hormonal therapy.",
keywords = "Antiestrogen, Antiprogestin, Breast cancer, Cell death, MCF-7, Retinoblastoma protein",
author = "Schoenlein, {Patricia V} and Min Hou and Samaddar, {Julia S.} and Gaddy, {Virgil Thomas} and Muthusamy Thangaraju and Jill Lewis and Johnson, {Maribeth H} and Vadivel Ganapathy and Andre Kallab and Barrett, {John Thomas}",
year = "2007",
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volume = "31",
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journal = "International Journal of Oncology",
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T1 - Downregulation of retinoblastoma protein is involved in the enhanced cytotoxicity of 4-hydroxytamoxifen plus mifepristone combination therapy versus antiestrogen monotherapy of human breast cancer

AU - Schoenlein, Patricia V

AU - Hou, Min

AU - Samaddar, Julia S.

AU - Gaddy, Virgil Thomas

AU - Thangaraju, Muthusamy

AU - Lewis, Jill

AU - Johnson, Maribeth H

AU - Ganapathy, Vadivel

AU - Kallab, Andre

AU - Barrett, John Thomas

PY - 2007/9/1

Y1 - 2007/9/1

N2 - In this study, human MCF-7 breast cancer cells, which express functional estrogen and progesterone receptors, were used to compare the efficacy of combined antiestrogen plus antiprogestin therapy to antiestrogen monotherapy. Cells were treated with the antiestrogen 4-hydroxytamoxifen (4-OHT) and/or the antiprogestin mifepristone (MIF) and effects on cell proliferation (cytostatic action), cell cycle phase, the phosphorylation state of the tumor suppressor retinoblastoma protein (Rb), and induction of active cell death (cytotoxic action) were determined. Combination hormonal therapy showed both increased cytostatic and cytotoxic activity as compared to either monotherapy. The increased cytostatic action was mediated by Rb activation; whereas, the cytotoxic (pro-apoptotic) action of combined hormonal therapy correlated to a significant reduction in Rb protein levels. To test the apparent role of Rb protein loss in the pro-apoptotic action of combined hormonal therapy, Rb was downregulated in MCF-7 cells using siRNA-targeting. The siRNA-mediated knockdown of Rb combined with 4-OHT therapy resulted in a pro-apoptotic action similar to that resulting from 4-OHT and MIF combination treatment, which included increased cell detachment from the monolayer, high-molecular-weight genomic DNA fragmentation, and cleavage of poly ADP-ribose polymerase (PARP) and lamin A. From these studies, we conclude that Rb protein downregulation is required for 4-OHT-treated, estrogen receptor positive (ER+) breast cancer cells to undergo active cell death. We discuss the potential of using an antiprogestin such as MIF plus antiestrogen treatment to more effectively downregulate Rb in ER+ breast cancer cells to increase the overall cytotoxic action of hormonal therapy.

AB - In this study, human MCF-7 breast cancer cells, which express functional estrogen and progesterone receptors, were used to compare the efficacy of combined antiestrogen plus antiprogestin therapy to antiestrogen monotherapy. Cells were treated with the antiestrogen 4-hydroxytamoxifen (4-OHT) and/or the antiprogestin mifepristone (MIF) and effects on cell proliferation (cytostatic action), cell cycle phase, the phosphorylation state of the tumor suppressor retinoblastoma protein (Rb), and induction of active cell death (cytotoxic action) were determined. Combination hormonal therapy showed both increased cytostatic and cytotoxic activity as compared to either monotherapy. The increased cytostatic action was mediated by Rb activation; whereas, the cytotoxic (pro-apoptotic) action of combined hormonal therapy correlated to a significant reduction in Rb protein levels. To test the apparent role of Rb protein loss in the pro-apoptotic action of combined hormonal therapy, Rb was downregulated in MCF-7 cells using siRNA-targeting. The siRNA-mediated knockdown of Rb combined with 4-OHT therapy resulted in a pro-apoptotic action similar to that resulting from 4-OHT and MIF combination treatment, which included increased cell detachment from the monolayer, high-molecular-weight genomic DNA fragmentation, and cleavage of poly ADP-ribose polymerase (PARP) and lamin A. From these studies, we conclude that Rb protein downregulation is required for 4-OHT-treated, estrogen receptor positive (ER+) breast cancer cells to undergo active cell death. We discuss the potential of using an antiprogestin such as MIF plus antiestrogen treatment to more effectively downregulate Rb in ER+ breast cancer cells to increase the overall cytotoxic action of hormonal therapy.

KW - Antiestrogen

KW - Antiprogestin

KW - Breast cancer

KW - Cell death

KW - MCF-7

KW - Retinoblastoma protein

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M3 - Article

VL - 31

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JO - International Journal of Oncology

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