Lapatinib Induced Suicidal Death of Human Erythrocytes

Background/aims: The human epidermal growth factor receptors tyrosine kinase inhibitor lapatinib has been shown to trigger suicidal death or Apoptosis of tumor cells and is thus used for the treatment of malignancy. Side effects of lapatinib include anemia, which could, at least in theory, result from stimulation of eryptosis, the suicidal death of erythrocytes which is characterized by cell shrinkage and phospholipid scrambling of the cell membrane leading to phosphatidylserine translocation to the erythrocyte surface. Mechanisms involved in the triggering of eryptosis include oxidative stress, increase of cytosolic Ca2+ activity ([Ca2+]i), and ceramide. The present study explored, whether lapatinib induces eryptosis.

Methods: Phosphatidylserine exposure at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, [Ca2+]i from Fluo3-fluorescence, abundance of Reactive Oxygen Species (ROS) from DCFDA dependent fluorescence, and ceramide abundance utilizing labelled specific Antibodies.

Results: A 48 hours exposure of human erythrocytes to lapatinib (≥ 1 µg/ml) significantly increased the percentage of annexin-V-binding cells, and significantly decreased forward scatter. Lapatinib (7.5 µg/ml) did not significantly modify DCFDA fluorescence and ceramide abundance. Lapatinib slightly, but significantly decreased Fluo3-fluorescence (≥ 5 µg/ml). Lapatinib (7.5 µg/ml) enhanced the annexin-V-binding in the presence of the Ca2+ ionophore ionomycin (1 µM) without significantly modifying Fluo3 fluorescence in the presence of ionomycin. The effect of lapatinib on forward scatter but not on annexin-V-binding was significantly blunted by removal of extracellular Ca2+.

Conclusion: Lapatinib triggers cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect occurring despite decrease of cytosolic Ca2+ activity.