DNA topoisomerases targeting anticancer agents and mechanism for acquirement of drug resistance

DNA topoisomerase(topo) I and II regulate the topological conformation and DNA molecules by catalyzing the concerted breakage of single or double strands. Topo I and II targeting anticancer agents such as camptothecins (CPT-II), epipodophyllotoxins (VP16 and VM26), and amsarcine are widely used in cancer chemotherapy. To enhance their therapeutic efficacies, one should understand how cellular sensitivities to these topo-targeting agents are regulated, and one should also understand what mechanisms or factors are involved in the appearance of tumor cells resistant to them. We will discuss if there is any marker useful for determining drug sensitivity to these topo-targeting agents in cancer cells.