Small cleavable adapters enhance the specific cytotoxicity of a humanized immunotoxin directed against CD64-positive cells.
The most potent immunotoxins (ITs) developed to date contain bacterial or plant cytotoxic components. As these are potentially immunogenic in man, human proteins are preferred for the long-term treatment of cancer. We have developed the first humanized IT for the treatment of CD64 malignancies such as acute myeloid leukemia. The bacterially expressed IT is composed of a humanized anti-CD64 single chain fragment [h22(scFv)] genetically fused to the human RNase angiogenin. As angiogenin lacks a dedicated translocation domain responsible for the higher potency of bacterial and plant-derived toxins, we have incorporated a recombinant adapter that contains a synthetic translocation domain flanked by proteolytically cleavable endosomal and cytosolic consensus sites. Although insertion of the adapter increased the cytotoxicity by up to 20-fold, serum stability was markedly reduced. Therefore, we designed a modified adapter variant with the endosomal-cleavable peptide deleted. The IT containing the truncated adapter showed significantly higher cytotoxicity than the adapter-free IT and superior serum stability to facilitate the potential applications in patients.
Hetzel
Christian
C
Fraunhofer IME, Department of Pharmaceutical Product, AACHEN, Germany. hetzel@molbiotech.rwth-aachen.de
Bachran
Christopher
C
Fischer
Rainer
R
Fuchs
Hendrik
H
Barth
Stefan
S
Stöcker
Michael
M
D049109:Cell Proliferation; D003602:Cytotoxicity, Immunologic; D000939:Epitopes; D005818:Genetic Engineering; D006801:Humans; D007128:Immunoglobulin Fragments / Q000235:genetics; D007167:Immunotherapy; D000922:Immunotoxins / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism; D049990:Membrane Transport Modulators / Q000276:immunology / Q000378:metabolism; D009369:Neoplasms / Q000276:immunology / Q000628:therapy; D011485:Protein Binding; D017452:Receptors, IgG / Q000276:immunology / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism; D012259:Ribonuclease, Pancreatic / Q000235:genetics; D020298:U937 Cells
D000939:Epitopes; D007128:Immunoglobulin Fragments; D000922:Immunotoxins; D049990:Membrane Transport Modulators; D017452:Receptors, IgG; D011993:Recombinant Fusion Proteins; C055966:immunoglobulin Fv; C046366:angiogenin; D012259:Ribonuclease, Pancreatic