TOXICOLOGY AND PHARMACOKINETICS OF DT388-GM-CSF, A FUSION CONSISTING OF A TRUNCATED DIPHTHERIA-TOXIN (DT388) LINKED TO HUMAN GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR (GM-CSF) IN C57BL 6 MICE/

Because the majority of acute myeloid leukemia (AML) blasts express th e granulocyte-macrophage colony-stimulating factor (GMCSF) receptor, w e are developing a fusion toxin consisting of a truncated diphtheria t oxin (DT388) linked to human GM-CSF for multi-drug resistant AML, Our goal was to determine the toxicity and pharmacokinetics of DT388-GM-CS F in C57BL/6 mice, Because human GM-CSF does not cross-react with the mouse GM-GSF receptor, the toxicity observed should be nonspecific tox icity of DT388, We injected C57BL/6 mice ip with 0.1, 0.5, 1.0, 1.5, 1 75, 2.0, 3.5, 5.0, or 10 mu g/day of DT388-GM-CSF for 5 consecutive da ys. For pharmacokinetics, blood samples were drawn at 20, 40, 60, 120, and 180 min after ip administration of 81 mu g/kg of DT388-GM-CSF. In mice, the LD10 of DT388-GM-CSF is between 84.4 (1.5) and 104.4 (1.75) mu g/kg (mu g) when administered for 5 consecutive days. AU mice rece iving greater than or equal to 201 mu g/kg (3.5 mu g) for 5 consecutiv e days died, Histopathologic examination of morbid animals showed only renal toxicity with acute proximal tubular necrosis, DT388-GM-CSF is stable in vivo based on nonreducing SDS-PAGE gel of plasma samples of I-125-labeled DT388-GM-CSF injected ip, The peak concentration of DT38 8-GM-CSF was 3.3 x 10(-8) M at 40 min and exhibited a t 1/2 of 24 min. Based on its half-life, DT388-GM-CSF concentrations in :he plasma are above the concentration inhibiting 50% protein synthesis and inducing apoptosis in 50% of HL-60 cells (AML cell line) for 5.2 h. Only four of 17 mice developed a weak immune response (0.9-160 ng/mL) 3 weeks af ter treatment. DT388-GM-CSF exhibits a short t 1/2, but concentrations exceed those required in vitro to inhibit AML cell lines. (C) 1998 Ac ademic Press.