[Targeted toxin therapy in the treatment of leukemia]

A chimeric toxin in which the cell surface binding domain of Pseudomonas exotoxin was replaced with mature human granulocyte colony-stimulating factor (G-CSF) was produced in Escherichia coli, partially purified and tested for its biological activity on a G-CSF-dependent murine myeloid leukemia cell line, NFS60. This fusion protein, termed as G-CSF-PE40, can displace [125I] G-CSF binding to its receptor. After 48 hrs incubation in the presence of G-CSF, G-CSF-PE40 inhibited protein synthesis and revealed cytotoxicity in NFS60 cells in a concentration dependent manner. The half maximal dose of G-CSF-PE40 for protein synthesis inhibition (ID50) in NFS60 cells was estimated at around 100pM. Additionally, relatively low concentration of G-CSF-PE40 stimulated DNA synthesis in NFS60 cells after 16 hrs' incubation in the absence of G-CSF, suggesting that G-CSF-PE40 also can transduce a transient mitogenic signal. Thus, G-CSF-PE40 may be useful in the selective elimination of myeloid cells expressing G-CSF receptors, especially in combination with chemotherapeutic agents like cytosine arabinoside.