Induction of Necroptosis in Cancer Stem Cells using a Nickel(II)-Dithiocarbamate Phenanthroline Complex.

The cytotoxic properties of a series of nickel(II)-dithiocarbamate phenanthroline complexes is reported. The complexes 1-6 kill bulk cancer cells and cancer stem cells (CSCs) with micromolar potency. Two of the complexes, 2 and 6, kill twice as many breast cancer stem cell (CSC)-enriched HMLER-shEcad cells as compared to breast CSC-depleted HMLER cells. Complex 2 inhibits mammosphere formation to a similar extent as salinomycin (a CSC-specific toxin). Detailed mechanistic studies suggest that 2 induces CSC death by necroptosis, a programmed form of necrosis. Specifically, 2 triggers MLKL phosphorylation, oligomerization, and translocation to the cell membrane. Additionally, 2 induces necrosome-mediated propidium iodide (PI) uptake and mitochondrial membrane depolarisation, as well as morphological changes consistent with necroptotosis. Strikingly, 2 does not evoke necroptosis by intracellular reactive oxygen species (ROS) production or poly(ADP) ribose polymerase (PARP-1) activation.