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)eth ylenediamine (TPEN) were investigated on cytotoxicity in clonal NG108-15 ne uroblastoma-glioma hybrid cells. Three min after addition of 100 mu M TPEN, cells began to retract their neurites and lose their characteristic multip olar shape; by 3-4 hr of exposure, most cells detached from the substrate, either singly or as variable-sized aggregates. Viability was assessed by mo nitoring uptake of calcein AM and propidium iodide, fluorescent dyes that s erved as markers for live and dead cells, respectively. Incubation of cultu res in 100 mu M TPEN led to a gradual decrease in the population exhibiting calcein fluorescence (viable cells) and a corresponding increase in the po pulation displaying propidium iodide fluorescence (nonviable cells). Loss o f cell viability reached 12% at 8 hr, 61% at 24 hr and 83% by 48 hr. Ultras tructural examination of TPEN-treated cells revealed condensed chromatin an d fragmented nuclei, characteristic of apoptosis, as well as plasma membran e defects and organelle swelling, generally associated with necrosis. Addit ion of an equimolar concentration of Zn2+ or Cu2+ but not Fe2+ or Mn2+ prev ented morphological abnormalities and cell death. (C)1999 Intox Press, Inc.