Anticancer activity, apoptosis and a structure–activity analysis of a series of 1,4-naphthoquinone-2,3-bis-sulfides

We have previously reported on the synthesis of 1,4-naphthoquinone-sulfides and in this investigation we report on their anticancer activity against 6 human cancer cell lines to evaluate their cytostatic effects. The 1,4-naphthoquinone-2,3-bis-sulfides were most effective against melanoma (UACC62) (GI₅₀ = 6.5–10 μM) and prostate (PC3) (GI₅₀ = 5.51–8.53 μM) cancer cell lines. They exhibited better cytostatic effects than etoposide (GI₅₀ = 0.56–36.62 μM), parthenolide (GI₅₀ = 3.58–25.97 μM) and VK3 (GI₅₀ = 3.41–22.59 μM) against several of the cancer cell lines. These compounds are generally more selective for cancer cells than for normal human lung fetal fibroblasts (WI-38). One compound produces ROS which results in breast (MCF7) cancer cell death caused by apoptosis as evidenced by caspase 3/7 activation. Apoptosis was found to occur by a mitochondrial pathway and not by cell cycle arrest. Gene expression studies showed that p53 (a tumour suppressor), Mdm-2 (a p53 regulator) and Bcl-2 (apoptosis inhibitor) were up-regulated during apoptosis induction. These results encourage further research for potential application in cancer chemotherapy.