Topoisomerase II alpha expression and cytotoxicity of anthracyclines in human neoplastic cells

Topoisomerase II is ATP dependent enzyme that catalyzes DNA strand passage, the pivotal process in replication, transcription, recombination etc. As part of this breakage and religation process the intermediate generated is a cleavable complex between DNA and topoisomerase II. This complex is the target for topoisomerase II inhibitors like epipodophyllotoxins, actinomycin D or anthracyclines. Stabilization of cleavable complexes by the topoisomerase II inhibitors leading to DNA lesions and next to apoptosis is the most common mechanism of drug resistance reflected in reduced formation of the complexes due to decreased amounts and/or activity of topoisomerase II. The aim of this study was to characterize human melanoma and human cervix carcinoma cells differing in sensitivity to doxorubicin and anthracycline analogs, annamycin and WP903 for topoisomerase IIα protein and gene expression with use of Western blot and RT- PCR. As shown, no significant differences in topoisomerase IIα protein level were noted between the cell lines tested. These results were confirmed at the gene expression level. The current study points to the fact that topoisomerase IIα protein or gene expression are not the reliable marker of cell sensitivity to anthracyclines but these observations do not exclude the potential mutations in topoisomerase IIα gene or some postranslational changes in that protein which requires further studies.