Human megakaryocytes cultured in vitro accumulate serotonin but not meta-iodobenzylguanidine whereas platelets concentrate both.

Objective: Thrombocytopenia is the major toxicity of radio-iodinated meta-iodobenzylguanidine (MIBG) therapy in patients with recurrent neuroblastoma. MIBG is taken up in platelets via the serotonin transporter. Given the delayed appearance and long duration of the thrombocytopenia, it seems likely that the precursor megakaryocytes are the primary targets of [131I]MIBG radiotoxicity.