Bis(phenazine-1-carboxamides):  Structure−Activity Relationships for a New Class of Dual Topoisomerase I/II-Directed Anticancer Drugs

Ring-substituted bis(phenazine-1-carboxamides), linked by a −(CH2)3NMe(CH2)3− chain, were prepared from the corresponding substituted phenazine-1-carboxylic acids by reaction of the intermediate imidazolides with bis(3-aminopropyl)methylamine. The compounds were evaluated for growth inhibitory activity in a panel of tumor cell lines, including P388 leukemia, Lewis lung carcinoma, and wild-type (JLC) and mutant (JLA and JLD) forms of human Jurkat leukemia. The latter mutant lines are resistant to topoisomerase (topo) II targeted agents because of lower levels of the enzyme. Analogues with small, lipophilic substituents (e.g., Me, Cl) at the 9-position were the most potent inhibitors, superior to the corresponding dimeric bis(acridine-4-carboxamides) (bis-DACA analogues). Several of the compounds were preferentially (up to 2-fold) more cytotoxic toward the mutant Jurkat lines than the wild-type. To test whether this selectivity was related to topoisomerase action, the most potent of the compounds (9-methyl) was evaluated in a cell-free system. It poisoned topo I at drug concentrations of 0.25 and 0.5 μM and inhibited the catalytic activity of both topo I and topo II at concentrations of 1 and 5 μM, respectively. Results from the NCI human tumor cell line panel showed the compounds had preferential activity toward colon tumor lines (on average 9.5-fold more active in the HT29 line than in the cell line panel as a whole). Several analogues produced significant growth delays in the relatively refractory subcutaneous colon 38 tumor model in vivo. In particular, the 9-methyl compound was substantially more potent in this tumor model than the clinical dual topo I/II poison DACA (total dose 90 versus 400 mg/kg) with comparable activity. The bis(phenazine-1-carboxamides) are a new and interesting class of dual topo I/II-directed anticancer drugs.