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