Cytotoxic actions of the heavy metal chelator TPEN on NG108-15 neuroblastoma-glioma cells.

Effects of the heavy metal chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) were investigated on cytotoxicity in clonal NG108-15 neuroblastoma-glioma hybrid cells. Three min after addition of 100 microM TPEN, cells began to retract their neurites and lose their characteristic multipolar shape; by 3-4 hr of exposure, most cells detached from the substrate, either singly or as variable-sized aggregates. Viability was assessed by monitoring uptake of calcein AM and propidium iodide, fluorescent dyes that served as markers for live and dead cells, respectively. Incubation of cultures in 100 microM TPEN led to a gradual decrease in the population exhibiting calcein fluorescence (viable cells) and a corresponding increase in the population displaying propidium iodide fluorescence (nonviable cells). Loss of cell viability reached 12% at 8 hr, 61% at 24 hr and 83% by 48 hr. Ultrastructural examination of TPEN-treated cells revealed condensed chromatin and fragmented nuclei, characteristic of apoptosis, as well as plasma membrane defects and organelle swelling, generally associated with necrosis. Addition of an equimolar concentration of Zn2+ or Cu2+ but not Fe2+ or Mn2+ prevented morphological abnormalities and cell death.