Salinomycin, a polyether
ionophore antibiotic effective against a variety of pathogens, has been shown to trigger apoptosis of
cancer cells and cancer stem cells. The substance is thus considered for the treatment of
malignancy.
Salinomycin compromises tumour cell survival at least in part by interference with mitochondrial function. Erythrocytes lack mitochondria but may undergo apoptosis-like suicidal cell death or eryptosis, which is characterized by scrambling of the cell membrane with
phosphatidylserine exposure at the erythrocyte surface. Signalling involved in the triggering of eryptosis includes activation of
oxidant-sensitive Ca(2+) permeable
cation channels with subsequent increase in cytosolic Ca(2+) activity ([Ca(2+)]i). This study explored whether
salinomycin stimulates eryptosis.
Phosphatidylserine-exposing erythrocytes were identified by measurement of
annexin-V binding, cell volume was estimated from forward scatter,
haemolysis determined from haemoglobin release, [Ca(2+)]i quantified utilizing Fluo3-fluorescence and oxidative stress from 2',7' dichlorodihydrofluorescein diacetate (
DCFDA) fluorescence in flow cytometry. A 48-hr exposure to
salinomycin (5-100 nM) was followed by a significant increase in Fluo3-fluorescence,
DCFDA fluorescence and
annexin-V binding, as well as a significant decrease in forward scatter (at 5-10 nM, but not at 50 and 100 nM). The
annexin-V binding after
salinomycin treatment was significantly blunted but not abrogated in the nominal absence of extracellular Ca(2+) or in the presence of
antioxidant n-acetyl
cysteine (1 mM).
Salinomycin triggers cell membrane scrambling, an effect at least partially due to oxidative stress and entry of extracellular Ca(2+).