Novel angular benzophenazines: dual topoisomerase I and topoisomerase II inhibitors as potential anticancer agents

A series of substituted angular benzophenazines were prepared using a new synthetic route via a novel regiocontrolled condensation of 1,2-naphthoquinones and 2,3-diaminobenzoic acids. The synthesis and biological activity of this new series of substituted 8,9-benzo[a]phenazine carboxamide systems are described. The analogues were evaluated against the H69 parental human small cell lung carcinoma cell line and H69/LX4 resistant cell line which overexpresses P-glycoprotein. Selected analogues were evaluated against the COR-L23 parental human non small cell lung carcinoma cell line and the COR-L23/R resistant cell line which overexpresses multidrug resistance protein. This series of novel angular benzophenazines were potent cytotoxic agents in these cell lines and may be able to circumvent multidrug resistance mechanisms which result in the lack of efficacy of many drugs in cancer chemotherapy. These compounds show dual inhibition of topoisomerase I and topoisomerase II and thus target two key enzymes responsible for the topology of DNA that are active at different points in the cell cycle. The introduction of chirality into the carboxamide side chain of these novel benzophenazine carboxamides has resulted in the discovery of a potent enantiospecific series of cytotoxic agents, exemplified by 4-methoxy-benzo[a]phenazine-11-carboxylic acid (2-(dimethylamino)-1-(R)-methyl-ethyl)-amide, XR11576 ((R)-4j' '). In vivo activity has been demonstrated for 4-methoxy-benzo[a]phenazine-11-carboxylic acid (2-(dimethylamino)-1-(R)-methyl-ethyl)-amide, XR11576, after intravenous administration to female mice, and this compound has been selected as a development candidate for further evaluation.