Phenazine N,N′-dioxide scaffold as selective hypoxic cytotoxin pharmacophore. Structural modifications looking for further DNA topoisomerase II-inhibition activityElectronic supplementary information (ESI) available: Detailed experimental procedures and spectroscopic characterization of benzofuroxan (IV), Fig. 1S, 2S, 3S, and 4S. See DOI: 10.1039/c3md00022b

Phenazine-5,10-dioxides have been identified as prodrugs for antitumour therapy that undergo hypoxic-selective bioreduction, in the solid tumour cells, to form cytotoxic species. We investigated structural modifications of the phenazine-5,10-dioxide scaffold attempting to find new selective hypoxic cytotoxins with additional ability to inhibit DNA topoisomerase II. Four series of new phenazine-5,10-dioxides aryl-substituted connected by different linkers were prepared. The clonogenic survivals of V79 cells on aerobic and anaerobic conditions were determined, and studies of oxic DNA-interaction and hypoxic DNA topoisomerase II-inhibition, for the most relevant derivatives, were performed. Four new hypoxic-selective cytotoxins were identified at the assayed doses. In some of them were operative the DNA-interaction and/or the inhibition of DNA topoisomerase II. For one of the unselective cytotoxin biotransformation studies were performed on aerobic and anaerobic conditions, explaining the lack of selectivity. New phenazine N , N ′-dioxides with hypoxic-selective cytotoxicity and capability to inhibit, in hypoxia, DNA topoisomerase II were identified.