Triggering of Suicidal Erythrocyte Death by Topotecan

BACKGROUND/AIMS: The topoisomerase I inhibitor topotecan is used as treatment of various malignancies. The substance is effective by triggering tumor cell apoptosis. In analogy to apoptosis of nucleated cells, erythrocytes may enter eryptosis, a suicidal death characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the outer face of the erythrocyte membrane. Signaling leading to eryptosis include Ca(2+)-entry and ceramide formation. The present study explored, whether and how topotecan induces eryptosis. METHODS: Phosphatidylserine abundance at the erythrocyte surface was estimated from annexin V binding, cell volume from forward scatter, and ceramide abundance utilizing specific antibodies. RESULTS: A 48 hours exposure of human erythrocytes to topotecan significantly increased the percentage of annexin-V-binding cells and significantly decreased forward scatter. The effect of topotecan was paralleled by a significant increase of ceramide abundance. The effect of topotecan on annexin-V-binding was significantly blunted, but not abolished by removal of extracellular Ca2+. CONCLUSIONS: Topotecan stimulated cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect paralleled by increase of ceramide abundance and partially dependent on entry of extracellular Ca2+.