DNA topoisomerases (Topo) are ubiquitous enzymes in eukaryotic cell and prokaryotic cell. They are crucial for cellular genetic processes, such as replication, recombination, transcription, chromosome condensation, and the maintenance of genome stability by catalyzing the passage of individual DNA strands (topoisomerase Ⅰ) or double helices (topoisomerase Ⅱ) through one another. In accordance, topoisomerases are over expressed in cancer cell growth and thus are important cellular targets for anticancer drugs. The structures and biological functions of topoisomerases are discussed in this review. Moreover, some recent progresses of organic compounds and metal complexes as DNA topoisomerase inhibitors are discussed in detail.

Contents
1 Introduction
2 Structures and mechanisms of DNA topoisomerases
2.1 Structures of DNA topoisomerases
2.2 Mechanisms of DNA topoisomerases
3 Biological functions of DNA topoisomerases
3.1 Regulation of topological states of DNA
3.2 Role of DNA topoisomerases in recombination and repair
4 DNA topoisomerases inhibitors
4.1 Mechanisms of DNA topoisomerase inhibition
4.2 Organic compounds as DNA topoisomerase inhibitors
4.3 Metal complexes as DNA topoisomerase inhibitors
5 Perpective