Esters and amides of 2,3-dimethoxy-8,9-methylenedioxy-benzo[i] phenanthridine-12-carboxylic acid: Potent cytotoxic and topoisomerase I-targeting agents

The exceptional topoisomerase I-targeting activity and antitumor activity of 5-(2-N,N-dimethylamino)ethyl-8,9-dimethoxy-2,3-methylenedioxy-5H-dibenzo[c,h] [1,6]naphthyridin-6-one (ARC-111, topovale) prompted studies on similarly substituted benzo[i]phenanthridine-12-carboxylic ester and amide derivatives. Among the benzo[i]phenanthridine-12-carboxylic esters evaluated, the 2-(N,N-dimethylamino)ethyl, 2-(N,N-dimethylamino)-1-methylethyl, and 2-(N,N-dimethylamino)-1,1-dimethylethyl esters possessed similar cytotoxicity, ranging from 30 to 55 nM in RPMI8402 and KB3-1 cells. Several of the carboxamide derivatives possess potent topoisomerase I-targeting activity and cytotoxicity. The 2-(N,N-dimethylamino)ethyl, 2-(N,N-diethylamino)ethyl, and 2-(pyrrolidin-1-yl)ethyl amides were among the more cytotoxic benzo[i]phenanthridine-12-carboxylic derivatives, with IC₅₀ values ranging from 0.4 to 5.0 nM in RPMI8402 and KB3-1 cells.