Topoisomerase II Inhibitors in Cancer Treatment

Topoisomerase II constitutes a family of nuclear enzymes essential to all living cells. These enzymes are capable of transferring one DNA double helix through a transient break in another DNA double helix. Type II topoisomerases play important roles in DNA metabolic processes, in which they are involved in DNA replication, transcription, chromosome condensation and de-condensation. Topoisomerase II is also the cellular target for a number of widely used anticancer agents currently in clinical use, such as the anthracyclines (daunorubicin and doxorubicin), the epipodophyllotoxins (etoposide and teniposide), and the aminoacridines. These agents stimulate the topoisomerase II-cleavable complex, which is a transient configuration of topoisomerase II on DNA in which topoisomerase II is covalently attached to DNA. This causes the accumulation of cytotoxic nonreversible DNA doublestrand breaks generated by the processing of such complexes by DNA metabolic processes. As of present, the clinical use of catalytic topoisomerase inhibitors as antineoplastic agents is limited to aclarubicin and MST-16. Both of these compounds are preferentially active toward hematological malignancies and show limited activity toward solid tumors. This review explains the role of topoisomerase inhibitors in cancer therapy.