Human DNA topoisomerase II is an important target in anticancer therapy. Despite the clinical success of drugs that target topoisomerase II, the development of resistant cancer cells can limit their clinical efficacy. To maximize the therapeutic potential of anticancer drugs, combination therapies and multi-target drugs have been suggested in many studies, where the use of multi-target drugs is advantageous from the pharmacokinetics point of view. There are various different options for the preparation of dual-target or multiple-target inhibitors, as topoisomerase II is both structurally (e.g., topoisomerase I, Hsp90, kinases) and functionally (e.g., histone deacetylases, proteasome) connected to many validated anticancer targets. In this article, we discuss the scientific background behind targeting topoisomerase II together with a number of other targets important in cancer therapy, we review the present status and discuss further options in the field.

Introduction: The bacterial topoisomerases DNA gyrase and topoisomerase IV are validated targets for development of novel antibacterial agents. Fluoroquinolones inhibit the catalytic GyrA and/or ParC(GrlA) subunit and have been commonly used, although these have toxicity liabilities that restrict their use. The ATPase GyrB and ParE(GrlB) subunits have been much less explored and after withdrawal of their inhibitor novobiocin, there are no further marketed inhibitors to date. ATP-competitive inhibitors of GyrB and/or ParE(GrlB) are of special interest, as this target has been validated, and it is expected that many of the problems associated with fluoroquinolones can be avoided. Areas covered: This review summarises the development of ATP-competitive inhibitors of GyrB and/or ParE(GrlB) as novel antibacterial agents over the last 10 years. Structural features of the new inhibitors and their optimisation strategies are highlighted. Expert opinion: The development of novel ATP-competitive inhibitors of GyrB and/or ParE(GrlB) is ongoing in industrial and academical research. Development of resistance is one of the most problematic issues, but GyrB/ParE(GrlB) inhibitors do not show cross-resistance with fluoroquinolones. Other common issues, such as low solubility, high protein binding, development of off-target resistance (e.g., via bacterial efflux pumps), are related to the structures of the inhibitors themselves, which is thus a main focus of design strategies. With some now in early clinical development, there is reasonable expectation that novel ATP-competitive inhibitors of GyrB/ParE(GrlB) will reach the market in the near future.