Tamoxifen inhibits malignant peripheral nerve sheath tumor growth in an estrogen receptor-independent manner.

Abstract

Few therapeutic options are available for malignant peripheral nerve sheath tumors (MPNSTs), the most common malignancy associated with neurofibromatosis type 1 (NF1). Guided by clinical observations suggesting that some NF1-associated nerve sheath tumors are hormonally responsive, we hypothesized that the selective estrogen receptor (ER) modulator tamoxifen would inhibit MPNST tumorigenesis in vitro and in vivo. To test this hypothesis, we examined tamoxifen effects on MPNST cell proliferation and survival, MPNST xenograft growth, and the mechanism by which tamoxifen impeded these processes. We found that 1-5 μM 4-hydroxy-tamoxifen induced MPNST cell death, whereas 0.01-0.1 μM 4-hydroxy-tamoxifen inhibited mitogenesis. Dermal and plexiform neurofibromas, MPNSTs, and MPNST cell lines expressed ERβ and G-protein-coupled ER-1 (GPER); MPNSTs also expressed estrogen biosynthetic enzymes. However, MPNST cells did not secrete 17β-estradiol, exogenous 17β-estradiol did not stimulate mitogenesis or rescue 4-hydroxy-tamoxifen effects on MPNST cells, and the steroidal antiestrogen ICI-182,780 did not mimic tamoxifen effects on MPNST cells. Further, ablation of ERβ and GPER had no effect on MPNST proliferation, survival, or tamoxifen sensitivity, indicating that tamoxifen acts via an ER-independent mechanism. Consistent with this hypothesis, inhibitors of calmodulin (trifluoperazine, W-7), another known tamoxifen target, recapitulated 4-hydroxy-tamoxifen effects on MPNST cells. Tamoxifen was also effective in vivo, demonstrating potent antitumor activity in mice orthotopically xenografted with human MPNST cells. We conclude that 4-hydroxy-tamoxifen inhibits MPNST cell proliferation and survival via an ER-independent mechanism. The in vivo effectiveness of tamoxifen provides a rationale for clinical trials in cases of MPNSTs.

• Authors: Stephanie J Byer, Jenell M Eckert, Nicole M Brossier, Buffie J Clodfelder-Miller, Amy N Turk, Andrew J Carroll, John C Kappes, Kurt R Zinn, Jeevan K Prasain, Steven L Carroll
• Journal: Neuro-oncology (Neuro Oncol) Vol. 13 Issue 1 Pg. 28-41 (Jan 2011) ISSN: 1523-5866 [Electronic] England
• PMID: 21075781 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• ESR1 protein, human
• Estrogen Antagonists
• Estrogen Receptor alpha
• Estrogens
• RNA, Messenger
• Tamoxifen
• afimoxifene

Topics

• Animals
• Apoptosis (drug effects)
• Blotting, Western
• Cell Proliferation (drug effects)
• Estrogen Antagonists (pharmacology)
• Estrogen Receptor alpha (metabolism)
• Estrogens (metabolism)
• Humans
• Mice
• Nerve Sheath Neoplasms (drug therapy, metabolism, pathology)
• Neurofibroma, Plexiform (drug therapy, metabolism, pathology)
• Neurofibromatosis 1 (drug therapy, metabolism, pathology)
• RNA, Messenger (genetics)
• Reverse Transcriptase Polymerase Chain Reaction
• Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
• Tamoxifen (analogs & derivatives, pharmacology)
• Tumor Cells, Cultured
• Xenograft Model Antitumor Assays