Temsirolimus enhances the efficacy of cetuximab in colon cancer through a CIP2A-dependent mechanism.
OBJECTIVE
A dozen clinical trials examining a combination of temsirolimus and cetuximab in treating metastatic colon cancer are currently underway. We investigated the role of cancerous inhibitor of protein phosphatase 2A (CIP2A) in the synergism between temsirolimus and cetuximab in colon cancer.


METHODS
Five colon cancer cell lines were used for in vitro studies. Signal transduction pathways were assessed by immunoblotting. The synergism between studied drugs was analyzed with combination indexes. Gene silencing was performed using small interfering RNAs. The efficacies of temsirolimus and cetuximab were tested in nude mice with colon cancer xenografts. Transcriptional activity was assessed using a reporter assay. The inhibitors leupeptin, chloroquine, and MG132 were used to assess protein degradation. The association between CIP2A, clinicopathological parameters, and survival was examined by immunohistochemical staining using a tumor tissue microarray.


RESULTS
Temsirolimus decreased the resistance of cells to cetuximab by both inhibiting transcription of CIP2A and increasing degradation of CIP2A through the lysosomal-autophagy pathway. The mammalian target of rapamycin (mTOR) protein immunoprecipitated along with CIP2A. Temsirolimus decreased expression of phosphorylated extracellular regulated protein kinase (pErk) and phosphorylated v-akt murine thymoma viral oncogene (pAKT) and decreased the interaction of CIP2A and mTOR in cell lines without the K-ras codon 12 mutation. CIP2A was a prognostic marker only in colon cancer patients with weak expression of pErk or pAKT.


CONCLUSIONS
Temsirolimus decreases cellular resistance to cetuximab by regulating CIP2A expression in colon cancer cells. Potential biomarkers for CIP2A inhibitors include pErk and pAKT.
National Yang-Ming University School of Medicine, Taipei, Taiwan.
Hsei-Wei
HW
Wang
Shung-Haur
SH
Yang
Guan-Da
GD
Huang
Jen-Kou
JK
Lin
Wei-Shone
WS
Chen
Jeng-Kai
JK
Jiang
Yuan-Tzu
YT
Lan
Chun-Chi
CC
Lin
Wei-Lun
WL
Hwang
Cheng-Hwai
CH
Tzeng
Anna Fen-Yau
AF
Li
Chueh-Chuan
CC
Yen
Hao-Wei
HW
Teng
D000818:Animals; D061067:Antibodies, Monoclonal, Humanized / Q000008:administration & dosage; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001324:Autoantigens / Q000235:genetics / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000378:metabolism*; D015153:Blotting, Western; D049109:Cell Proliferation / Q000187:drug effects; D000068818:Cetuximab; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D020123:Sirolimus / Q000008:administration & dosage / Q000031:analogs & derivatives
D061067:Antibodies, Monoclonal, Humanized; D001324:Autoantigens; D014408:Biomarkers, Tumor; C500266:CIP2A protein, human; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D034741:RNA, Small Interfering; C401859:temsirolimus; D051057:Proto-Oncogene Proteins c-akt; D000068818:Cetuximab; D020123:Sirolimus