Sunitinib-sensitive Suicidal Erythrocyte Death

Abstract

Sunitinib, a multikinase inhibitor, stimulates apoptosis and is thus utilized for the treatment of malignancy. Even though lacking mitochondria and nuclei, critical elements in apoptosis of nucleated cells, erythrocytes may undergo eryptosis, an apoptosis-like suicidal death, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserineexposure at the cell surface. Triggers of eryptosis include activation of Ca²⁺ permeable cation channels with subsequent increase of cytosolic Ca²⁺-activity ([Ca²⁺]_i), ceramide formation, ATP-depletion, stimulation of p38 kinase and caspase activation. The present study explored, whether sunitinib stimulates eryptosis. [Ca²⁺]_iwas estimated from Fluo-3-fluorescence, cell volume from forward scatter, phosphatidylserine-exposure from annexin-V-binding, hemolysis from hemoglobin release, ceramide abundance from anti-ceramide antibody binding, and cytosolic ATP from luciferin–luciferase activity. A 48 h exposure to sunitinib (10 µM) significantly decreased forward scatter and increased annexin-V-binding, effects paralleled by significant increase of [Ca²⁺]_i. Sunitinib exposure was followed by a slight but significant increase of hemolysis. Sunitinib induced annexin-V-binding was slightly, but significantly blunted by removal of extracellular Ca²⁺, by p38 kinase inhibitor SB203580 (10 µM) and by the pancaspase inhibitor zVAD (10 µM). Sunitinib, however, did not significantly modify cytosolic ATP and ceramide abundance. The present observations reveal that sunitinib is able to trigger suicidal death in erythrocytes even in the absence of nuclei and mitochondria.