DNA topoisomerases are highly specialized nuclear enzymes that perform topological changes in DNA molecule in a very precise and unique fashion. Taking into account their fundamental roles in many events during DNA metabolism such as replication, transcription, recombination, condensation and segregation, it is no wonder that the last decade has witnessed an exponent ional interest on topoisomerases, mainly after the discovery of their potential role as targets in novel antitumour therapyThere are two isoenzymes of Topo II, topoisomerase α (topo II α) and topoisomerase β, during cell cycle there is a differential expression of the two isoforms thus indicating different functions. In normal tissue the level of topo II α is high during S/G2/M phase and low or not detectable in G0/G1 phase, while topo II β doesn’t change depending on cell cycle phase.