DMNQ-S17 inhibits constitutive NF-kappaB activation leading to induction of apoptosis through the activation of caspase-3 in human myeloid leukemia U937 cells

Through cytotoxicity screening with naphthoquinone derivatives, a novel compound 6-(1-oxoallkyl)-5,8-dimethoxy-1,4-naphthoquinone-S17 (DMNQ-S17) showed its potency against human myeloid leukemia U937 cells. Thus, to elucidate the apoptotic mechanism of DMNQ-S17, this study was performed in myeloid leukemia U937 cells by 2,3-bis [2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide (XTT) assay, eletrophoretic mobility shift assay (EMSA), terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay, 4′,6-diamidino-2-phenylindole (DAPI) staining, and Western blotting. In the present study, DMNQ-S17 inhibited constitutive NF κB activation and its transcriptional activity in U937 cells. In addition, DMNQ-S17 induced apoptotic features such as apoptotic bodies, cell shrinkage and chromatin condensation in U937 cells. Consistently, flow cytometric analysis showed that DMNQ-S17 increased sub-G1 portion and TUNEL positive cells in a concentration-dependent manner. Furthermore, DMNQ-S17 effectively attenuated mitochondrial membrane potential, released cytochrome C, activated caspase-3 expression, and cleaved poly (ADP-ribose) polymerase (PARP). Reversely, caspase-3 and -9 inhibitors also blocked the DMNQ-S17 induced caspase-3 activation and PARP cleavage in U937 cells. Taken together, these findings suggest that DMNQ-S17 can be a potent anticancer candidate for myeloid leukemias by the suppression of NF-κB activation leading to the activation of caspase-3 in human myeloid leukemia U937 cells.