Sensitivity of cancer cells to truncated diphtheria toxin.
BACKGROUND
Diphtheria toxin (DT) has been utilized as a prospective anti-cancer agent for the targeted delivery of cytotoxic therapy to otherwise untreatable neoplasia. DT is an extremely potent toxin for which the entry of a single molecule into a cell can be lethal. DT has been targeted to cancer cells by deleting the cell receptor-binding domain and combining the remaining catalytic portion with targeting proteins that selectively bind to the surface of cancer cells. It has been assumed that "receptorless" DT cannot bind to and kill cells. In the present study, we report that "receptorless" recombinant DT385 is in fact cytotoxic to a variety of cancer cell lines.


METHODS
In vitro cytotoxicity of DT385 was measured by cell proliferation, cell staining and apoptosis assays. For in vivo studies, the chick chorioallantoic membrane (CAM) system was used to evaluate the effect of DT385 on angiogenesis. The CAM and mouse model system was used to evaluate the effect of DT385 on HEp3 and Lewis lung carcinoma (LLC) tumor growth, respectively.


RESULTS
Of 18 human cancer cell lines tested, 15 were affected by DT385 with IC(50) ranging from 0.12-2.8 microM. Furthermore, high concentrations of DT385 failed to affect growth arrested cells. The cellular toxicity of DT385 was due to the inhibition of protein synthesis and induction of apoptosis. In vivo, DT385 diminished angiogenesis and decreased tumor growth in the CAM system, and inhibited the subcutaneous growth of LLC tumors in mice.


CONCLUSIONS
DT385 possesses anti-angiogenic and anti-tumor activity and may have potential as a therapeutic agent.
Zhang
Yi
Y
Departments of Biochemistry and Molecular Biology and Pathology, Dalhousie University, Halifax, Nova Scotia, Canada.
Schulte
Wendy
W
Pink
Desmond
D
Phipps
Kyle
K
Zijlstra
Andries
A
Lewis
John D
JD
Waisman
David Morton
DM
D000818:Animals; D002417:Cattle; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002642:Chick Embryo; D049033:Chorioallantoic Membrane / Q000187:drug effects / Q000378:metabolism; D004167:Diphtheria Toxin / Q000494:pharmacology*; D004705:Endocytosis / Q000187:drug effects; D006801:Humans; D051379:Mice; D050505:Mutant Proteins / Q000494:pharmacology*; D009369:Neoplasms / Q000098:blood supply / Q000473:pathology*; D009389:Neovascularization, Pathologic / Q000378:metabolism / Q000473:pathology; D014176:Protein Biosynthesis / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
D004167:Diphtheria Toxin; D050505:Mutant Proteins
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