Diphtheria toxin fused to granulocyte-macrophage colony-stimulating factor and Ara-C exert synergistic toxicity against human AML HL-60 cells.
Human granulocyte-macrophage colony-stimulating factor fused to truncated diphtheria toxin (DT388-GM-CSF) sensitized wild-type and Bcl2-overexpressing HL60 human leukemia cells to intoxication by Ara-C based on proliferation and clonogenic assays. The toxin/drug combination showed dramatic synergistic toxicity with combination indices of < 0.1. Synergy was not seen with two other protein synthesis inhibiting drugs--ricin and cycloheximide nor with GMCSF alone. No changes in Ara-C incorporation into cellular DNA or cell cycle occupancy were seen. As compared to exposure to DT388-GM-CSF or Ara-C alone, co-treatment produced significant increases in cytosolic accumulation of cytochrome c, a higher percentage of cells with loss of mitochondrial membrane potential and an increase in reactive oxygen species and morphologic changes of apoptosis, and a greater induction of poly(ADP-ribose) polymerase (PARP) and DNA fragmentation factor 45 (DFF45) cleavage activities of caspase 3. Co-treatment did not significantly alter Bcl2, Bcl-xL, Bax or Fas receptor (FasR), but modestly increased Fas ligand (FasL) protein. These finding suggest that co-treatment with DT388-GM-CSF may lead to a lowered apoptotic threshold and clonogenic survival of human AML blasts due to Ara-C. These observations also suggest that clinical trials of combination therapy may be warranted in patients with AML.
Kim
C N
CN
Department of Medicine, Emory University School of Medicine, Atlanta, GA, USA.
Bhalla
K
K
Kreitman
R J
RJ
Willingham
M C
MC
Hall
P
P
Tagge
E P
EP
Jia
T
T
Frankel
A E
AE
D000208:Acute Disease; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D003561:Cytarabine / Q000627:therapeutic use*; D004167:Diphtheria Toxin / Q000737:chemistry / Q000627:therapeutic use*; D004357:Drug Synergism; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000737:chemistry / Q000627:therapeutic use*; D018922:HL-60 Cells; D006801:Humans; D007951:Leukemia, Myeloid / Q000188:drug therapy*; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects; D011500:Protein Synthesis Inhibitors / Q000627:therapeutic use; D011993:Recombinant Fusion Proteins / Q000627:therapeutic use*
D000970:Antineoplastic Agents; D004167:Diphtheria Toxin; D011500:Protein Synthesis Inhibitors; D011993:Recombinant Fusion Proteins; D003561:Cytarabine; D016178:Granulocyte-Macrophage Colony-Stimulating Factor