Drug-induced apoptosis of erythroid precursor cells is mediated by caspase activation. (A) Chemotherapeutic agents activate caspases in immature erythroblasts. Erythroblasts at day 7 of differentiation were stimulated with 200 ng/mL camptothecin (CPT), 3 μg/mL cisplatin (CDDP), or 5 μM etoposide (VP-16) in the presence or absence of zVAD 40 μM, lysed after 8 hours, and analyzed by immunoblot with antibodies against caspase 3, caspase 7, and caspase 8. (B) zVAD inhibits apoptosis induced by chemotherapeutic agents. Day-7 erythroblasts were stimulated with 50 ng/mL camptothecin (CPT), 3 μg/mL cisplatin (CDDP), or 2 μM etoposide (VP-16) in the presence (□) or in the absence (▪) of zVAD 40 μM. After 24 hours the percentage of cell death was determined by ethidium bromide—acridine orange staining. A typical experiment of 5 performed with cells from different donors is shown.