Several substituted dibenzo [c, h] cinnolines were synthesized and evaluated for their potential to target topoisomerase I and for their relative cytotoxic activity. Select benzo [i] phenanthridines are capable of stabilizing the cleavable complex formed with topoisomerase I and DNA. This study was initiated to examine whether dibenzo [c, h] cinnolines, which are in essence aza analogues of benzo [i] phenanthridines, possess ...