A copper chelate of thiosemicarbazone NSC 689534 induces oxidative/ER stress and inhibits tumor growth in vitro and in vivo

In this study, a Cu²⁺ chelate of the novel thiosemicarbazone NSC 689534 was evaluated for in vitro and in vivo anti-cancer activity. Results demonstrated that NSC 689534 activity (low micromolar range) was enhanced four- to fivefold by copper chelation and completely attenuated by iron. Importantly, once formed, the NSC 689534/Cu²⁺ complex retained activity in the presence of additional iron or iron-containing biomolecules. NSC 689534/Cu ²⁺ mediated its effects primarily through the induction of ROS, with depletion of cellular glutathione and protein thiols. Pretreatment of cells with the antioxidant N-acetyl-l-cysteine impaired activity, whereas NSC 689534/Cu²⁺ effectively synergized with the glutathione biosynthesis inhibitor buthionine sulfoximine. Microarray analysis of NSC 689534/Cu ²⁺-treated cells highlighted activation of pathways involved in oxidative and ER stress/UPR, autophagy, and metal metabolism. Further scrutiny of the role of ER stress and autophagy indicated that NSC 689534/Cu ²⁺-induced cell death was ER-stress dependent and autophagy independent. Last, NSC 689534/Cu²⁺ was shown to have activity in an HL60 xenograft model. These data suggest that NSC 689534/Cu²⁺ is a potent oxidative stress inducer worthy of further preclinical investigation.