TOP1 gene copy numbers in colorectal cancer samples and cell lines and their association to in vitro drug sensitivity

Abstract

Objective. A positive relationship between topoisomerase-1 (TOP1) protein and sensitivity toward the TOP1 inhibitor irinotecan has been reported in patients with metastatic colorectal cancer (mCRC). In this study, we analyzed TOP1 gene copy number variation in tumor tissue from CRC patients and CRC cell lines with different sensitivities to the TOP1 inhibitor SN-38 and oxaliplatin. Material and methods. A TOP1 gene probe with a chromosome 20 centromere (CEN-20) reference probe was applied on normal mucosa and on tumor tissue from 50 stage III CRC patients. Additionally, associations between TOP1/CEN-20 ratio and in vitro sensitivity to SN-38 (irinotecan) and oxaliplatin were tested on 10 CRC cell lines. Results. In the malignant epithelium, 84% of the samples demonstrated an increased TOP1 gene copy number and 64% had an increased TOP1/CEN-20 ratio compared with the non-affected mucosa. Sixteen (32%) of the tumors had a ratio of ≥1.5 and 9 (18%) of these had a ratio of ≥2.0. A positive association was observed between the TOP1 gene copy number and the TOP1/CEN-20 ratio and in vitro sensitivity toward SN-38, but not toward oxaliplatin. Conclusions. A large fraction of the clinical samples demonstrated increased TOP1 gene copy number and increased TOP1/CEN-20 ratio. The cell line study suggested an association between TOP1 gene copy number or TOP1/CEN-20 ratio and sensitivity to irinotecan but not oxaliplatin.

Key Words::

• biomarker
• colorectal cancer
• irinotecan and oxaliplatin sensitivity
• TOP1 copy number

Acknowledgments

We would like to thank the RanX05 study group for collecting clinical samples and Ms. Annette Bartels for the preparation of the histological samples. Grant support: IMK Almene Foundation, Kathrine og Vigo Skovgaards Foundation, Tømrermester Johannes Fog Foundation, Fabrikant Einar Willumsens Memorial Trust, The Obelske Family Trust, Danish Cancer Society, The Kornerup Foundation, The Aage and Johanne Louis-Hansen Foundation, The Aase and Ejnar Danielsen Fund, The Medical Research Council, Sawmill owner Jeppe Juhl and Wife Ovita Juhl Foundation and The Danish Council for Strategic Research.

Declaration of interest: Kirsten Vang Nielsen and Sven Müller are employees at DAKO A/S and Nils Brünner is Medical Advisor to DAKO A/S. The other authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.