Volume 134, Issue 4 pp. 997-1007
Cancer Therapy

STAT3 inhibition sensitizes colorectal cancer to chemoradiotherapy in vitro and in vivo

Melanie Spitzner

Melanie Spitzner

Department of General and Visceral Surgery, University Medicine Göttingen, Göttingen, Germany

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Birte Roesler

Birte Roesler

Department of General and Visceral Surgery, University Medicine Göttingen, Göttingen, Germany

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Christian Bielfeld

Christian Bielfeld

Department of General and Visceral Surgery, University Medicine Göttingen, Göttingen, Germany

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Georg Emons

Georg Emons

Department of General and Visceral Surgery, University Medicine Göttingen, Göttingen, Germany

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Jochen Gaedcke

Jochen Gaedcke

Department of General and Visceral Surgery, University Medicine Göttingen, Göttingen, Germany

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Hendrik A. Wolff

Hendrik A. Wolff

Department of Radiotherapy and Radiooncology, University Medicine Göttingen, Göttingen, Germany

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Margret Rave-Fränk

Margret Rave-Fränk

Department of Radiotherapy and Radiooncology, University Medicine Göttingen, Göttingen, Germany

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Frank Kramer

Frank Kramer

Department of Medical Statistics, University Medicine Göttingen, Göttingen, Germany

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Tim Beissbarth

Tim Beissbarth

Department of Medical Statistics, University Medicine Göttingen, Göttingen, Germany

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Julia Kitz

Julia Kitz

Department of Pathology, University Medicine Göttingen, Göttingen, Germany

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Jürgen Wienands

Jürgen Wienands

Department of Cellular and Molecular Immunology, University Medicine Göttingen, Göttingen, Germany

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B. Michael Ghadimi

B. Michael Ghadimi

Department of General and Visceral Surgery, University Medicine Göttingen, Göttingen, Germany

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Reinhard Ebner

Reinhard Ebner

Genetics Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD

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Thomas Ried

Thomas Ried

Genetics Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD

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Marian Grade

Corresponding Author

Marian Grade

Department of General and Visceral Surgery, University Medicine Göttingen, Göttingen, Germany

Correspondence to: Marian Grade, Department of General and Visceral Surgery, University Medicine Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany. Tel.: +49-551-39-6944; Fax: +49-551-39-12550; E-mail: [email protected]Search for more papers by this author
First published: 12 August 2013
Citations: 110

Abstract

Increased activity of signal transducer and activator of transcription 3 (STAT3) is common in human malignancies, including colorectal cancers (CRCs). We have recently reported that STAT3 gene expression correlates with resistance of CRC cell lines to 5-fluorouracil (5-FU)-based chemoradiotherapy (CT/RT). This is of considerable clinical importance, because a large proportion of rectal cancers are resistant to preoperative multimodal treatment. To test whether STAT3 contributes to CT/RT-resistance, we first confirmed that STAT3 protein expression correlated positively with increasing resistance. While STAT3 was not constitutively active, stimulation with interleukin-6 (IL-6) resulted in remarkably higher expression levels of phosphorylated STAT3 in CT/RT-resistant cell lines. A similar result was observed when we determined IL-6-induced expression levels of phosphorylated STAT3 following irradiation. Next, STAT3 was inhibited in SW480 and SW837 using siRNA, shRNA and the small-molecule inhibitor STATTIC. Successful silencing and inhibition of phosphorylation was confirmed using Western blot analysis and a luciferase reporter assay. RNAi-mediated silencing as well as STATTIC treatment resulted in significantly decreased clonogenic survival following exposure to 3 µM of 5-FU and irradiation in a dose-dependent manner, with dose-modifying factors of 1.3–2.5 at a surviving fraction of 0.37. Finally, STAT3 inhibition led to a profound CT/RT-sensitization in a subcutaneous xenograft model, with a significantly delayed tumor regrowth in STATTIC-treated mice compared with control animals. These results highlight a potential role of STAT3 in mediating treatment resistance and provide first proof of concept that STAT3 represents a promising novel molecular target for sensitizing resistant rectal cancers to CT/RT.

Abstract

What's new?

A considerable percentage of rectal cancers are resistant to preoperative chemoradiotherapy, which exposes patients to the potential side effects of both irradiation and chemotherapy without clear benefits. In this study, IL-6-stimulated expression levels of phosphorylated STAT3 were remarkably higher in chemoradiotherapy-resistant colorectal cancer cell lines. RNAi- and small molecule-mediated STAT3 inhibition sensitized to chemoradiotherapy in vitro in a dose-dependent manner, which led to a profound chemoradiotherapy-sensitization in a subcutaneous xenograft model. These results highlight a potential role of STAT3 in treatment resistance, and provide first proof of concept that STAT3 represents a promising novel molecular target for sensitizing resistant rectal cancers to chemoradiotherapy.

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