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

Topoisomerase IIα is a nuclear enzyme that regulates the tertiary structure of DNA. The influence of topoisomerase IIα 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 IIα 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 IIα levels, proliferation index, and HER2 expression were examined in 228 colorectal tumors by immunohistochemistry. Overexpression of topoisomerase IIα 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 IIα 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 IIα 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 IIα and HER2. In vitro, overexpression of topoisomerase IIα was associated with resistance to irinotecan (p = 0.001) and etoposide chemotherapy (p = 0.03), an effect mediated by inhibition of apoptosis.Topoisomerase IIα 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.