Increased topoisomerase IIα expression in colorectal cancer is associated with advanced disease and chemotherapeutic resistance via inhibition of apoptosis

Topoisomerase II alpha is a nuclear enzyme that regulates the tertiary structure of DNA. The influence of topoisomerase II alpha gene (TOP2A) or protein alterations on disease progression and treatment response in colorectal cancer (CRC) is unknown. The study investigated the clinical relevance of topoisomerase II alpha in CRC using in vivo and in vitro models. Differentially expressed genes in early and late-stage CRC were identified by array comparative genomic hybridization (CGH). Cellular location of gene amplifications was determined by fluorescence in situ hybridization (FISH). Topoisomerase II alpha levels, proliferation index, and HER2 expression were examined in 228 colorectal tumors by immunohistochemistry. Overexpression of topoisomerase II alpha in vitro was achieved by liposome-based transfection. Cell growth inhibition and apoptosis were quantified using the crystal violet assay and flow cytometry, respectively, in response to drug treatment. Amplification of TOP2A was identified in 3 (7.7%) tumors using array CGH and confirmed using FISH. At the protein level, topoisomerase II alpha staining was observed in 157 (69%) tumors, and both staining and intensity levels were associated with an aggressive tumor phenotype (p values 0.04 and 0.005, respectively). Using logistic regression analysis, topoisomerase II alpha remained significantly associated with advanced tumor stage when corrected for tumor proliferation (p = 0.007) and differentiation (p = 0.001). No association was identified between topoisomerase II alpha and HER2. In vitro, overexpression of topoisomerase II alpha was associated with resistance to irinotecan (p = 0.001) and etoposide chemotherapy (p = 0.03), an effect mediated by inhibition of apoptosis. Topoisomerase II alpha overexpression is significantly associated with alterations in tumor behavior and response to drug treatment in CRC. Our results suggest that gene amplification may represent an important mechanism underlying these changes. (C) 2008 Elsevier Ireland Ltd. All rights reserved.