ANTITUMOR AGENTS .164. PODOPHENAZINE, 2'',3''-DICHLOROPODOPHENAZINE, BENZOPODOPHENAZINE, AND THEIR 4-BETA-P-NITROANILINE DERIVATIVES AS NOVEL DNA TOPOISOMERASE-II INHIBITORS

We report here the synthesis and biological evaluation of novel DNA to poisomerase II inhibitors, podophenazine (8), 2'',3''-dichloropodophen azine (9), and benzopodophenazine (10), and their 4 beta-p-nitroanilin e derivatives 13-15. Among these, 4'-O-demethyl-4 beta-(4'''-nitroanil ino)-4-desoxypodophenazine (13) and 4'-O-demethyl-2'',3''-dichloro-4 b eta-(4'''-nitroanilino)-4-desoxypodophenazine (14) were found to inhib it KB cells at sub-micromolar concentrations (IC50 = 0.11 +/- 0.03 and 0.48 +/- 0.17 mu M, respectively). Against KB/7d cells (a pleiotrophi c multiple drug-resistant subclone selected with etoposide which has r educed level of topoisomerase II), only compound 13 out of a target se ries maintained activity in the sub-micromolar concentration range wit h a IC50 value of 0.56 +/- 0.13 mu M. The differential toxicity ratio for 13 [IC50(KB/7d)/IC50(KB)] was similar to 5. Unlike etoposide and i ts congeners, compounds 13 and 14 were found to be weak inhibitors of the catalytic activity of topoisomerase II (IC100 = >100 and >150 mu M , respectively). In vitro protein-linked DNA complex formation assay r evealed that 13 and 14, respectively, induced marginal response (13 at 1 mu M, 320.3 +/- 124.5 cpm; 13 at 50 mu M, 308.8 +/- 139.9 cpm; 13 a t 100 mu M, 446.0 +/- 153.5 cpm) and no response (14 at 1 mu M, 104.9 +/- 52.6 cpm; 14 at 50 mu M, 103.3 +/- 42.6 cpm; 14 at 100 mu M, 101.4 +/- 35.2 cpm) compared to the enzyme control. On the basis of these r esults, we conclude that the mechanism of enzyme inhibition of these c ompounds is distinct from that of etoposide and its congeners. We are currently investigating the mechanism(s) of action of compounds 13 and 14 as well as synthesizing other derivatives in order to better chara cterize structure-activity relationships of this series of compounds.