STAT3 inhibition sensitizes colorectal cancer to chemoradiotherapy in vitro and in vivo.
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.
Department of General and Visceral Surgery, University Medicine Göttingen, Göttingen, Germany.
Melanie
M
Spitzner
Birte
B
Roesler
Christian
C
Bielfeld
Georg
G
Emons
Jochen
J
Gaedcke
Hendrik A
HA
Wolff
Margret
M
Rave-Fränk
Frank
F
Kramer
Tim
T
Beissbarth
Julia
J
Kitz
Jürgen
J
Wienands
B Michael
BM
Ghadimi
Reinhard
R
Ebner
Thomas
T
Ried
Marian
M
Grade
D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis; D015153:Blotting, Western; D049109:Cell Proliferation; D059248:Chemoradiotherapy; D015179:Colorectal Neoplasms / Q000378:metabolism / Q000473:pathology / Q000628:therapy*; D019008:Drug Resistance, Neoplasm; D005260:Female; D005472:Fluorouracil / Q000494:pharmacology*; D006801:Humans; D007124:Immunoenzyme Techniques; D066298:In Vitro Techniques; D051379:Mice; D008819:Mice, Nude; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
D000964:Antimetabolites, Antineoplastic; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D050796:STAT3 Transcription Factor; D005472:Fluorouracil
STAT3; chemoradiotherapy-resistance; chemoradiotherapy-sensitization; molecular target; rectal cancer