Inhibitory effect on ovarian cancer ALDH plus stem-like cells by Disulfiram and Copper treatment through ALDH and ROS modulation

Background: Disulfiram (DSF) is a drug used for treatment of alcoholism that has also displayed promising anticancer activity. It unfolds its effects by inhibiting the enzyme activity of aldehyde dehydrogenase (ALDH) isoforms. Methods: MIT assay, spheroid formation, clonogenicity assay, qRT-PCR, and ALDH enzyme activity analysis were performed using ovarian cancer cell lines IGROV1, SKOV3 and SKOV3IP1. Cell cycle analyses and measurement of intracellular reactive oxygen species (ROS) were carried out by flow cytometry. ALDH + and ALDH - cells were isolated by FACS sorting. Results: ALDH activity was inhibited in ovarian cancer stem cells (the proportion of ALDH + cells was reduced from 21.7% to 0.391%, 8.4% to 0%, 6.88% to 0.05% in cell lines IGROV1, SKOV3, and SKOV3IP1, respectively). DSF with or without the cofactor copper (Cu2+) exhibited cytotoxicity dose- and time-dependent and enhanced cisplatin-induced apoptosis. DSF + Cu2+ increased intracellular ROS levels triggering apoptosis of ovarian cancer stem cells (CSC). Significantly more colony and spheroid formation was observed in ALDH + compared with ALDH- cells (P < 0.01). Moreover, ALDH + cells were more resistant to cisplatin treatment compared with ALDH-cells (P < 0.05) and also exhibited a lower basal level of ROS. However, no significant difference in ROS accumulation nor in cellular viability was observed in ALDH + cells in comparison to ALDH- cells after pretreatment with DSF (0.08 mu M). Conclusion: Our findings provide evidence that DSF might be employed as a novel adjuvant chemotherapeutic agent in combination with cisplatin for treatment of ovarian cancer.