Antioxidative and antitumor activity of derivatives of 4-beta-amino-4'-demethylepipodophyllotoxin and their structure-activity relationship

The purpose of this study was to investigate antioxidative and antitumor activity of derivatives of 4-beta-amino-4'-demethylepipodophyllotoxin (DmePod) and to analyze their structure-activity relationship. Homogenates of liver, heart and kidney of rats were used to measure malondialdehyde (MDA) generation spontaneously formed or induced by a hydroxyl free radical generation system (Fe2+-ascorbic acid) using thiobarbituric acid (TBA) assay. H2O2-induced red blood cells (RBC) hemolysis was determined spectrophotometrically. Superoxide anion (O2-*) from zymosan-stimulated neutrophils of rats was evaluated by nitroblue tetrazolium (NBT) reduction assay. Microculture tetrazolium (MTT) assay was used to determine the antitumor effects on K562 and K562/DOX cells. The results showed that all the tested compounds strongly inhibited MDA formation from tissue homogenates in a concentration-dependent manner following the rank GP7OH > GP7 > VP16 and GP7H > DmePod > Pod. The potency of antihemolysis for DmePod, GP7, GP7OH, GP7H and VP16 was similar among them according to their IC50 values by 13.6, 8.6, 11.7, 10.3, and 9.47 micromol x L(-1), respectively, whereas the potency for Pod was the weakest (IC50 > 320 micromol x L(-1)). GP7, GP7OH and VP16 (160-320 micromol x L(-1)) significantly inhibited O2-* formation following the potency rank VP16 > GP7 > GP7OH. However, 320 micromol x L(-1) of DmePod, Pod or GP7H had no effect on O2-* formation. Meanwhile, all the tested compounds strongly inhibited K562 and K562/DOX cell proliferation for 96 h in a concentration-dependent manner. The resistance magnitude of GP7, GP7OH, VP16, and DmePod was 2.05, 2.21, 14.29, and 3.26, respectively, while antitumor activity of Pod and GP7H on K562/DOX cells was the weakest in all compounds. Taken together, the introduction of nitroxyl radical moieties into DmePod greatly enhances antioxidative and antitumor activity, and reverses drug resistance. Both NO* and NOH groups are essential active moieties.