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Characterization of cytotoxic activity of saporin anti‐gp185/HER‐2 immunotoxins
Author(s) -
Tecce R.,
Digiesi G.,
Savarese A.,
Trizio D.,
Natali P. G.
Publication year - 1993
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.2910550122
Subject(s) - immunotoxin , cytotoxic t cell , saporin , microbiology and biotechnology , clonogenic assay , epitope , monoclonal antibody , cytotoxicity , tyrosine kinase , biology , cell culture , extracellular , ribosome inactivating protein , antibody , chemistry , receptor , in vitro , biochemistry , immunology , ribosome , rna , gene , genetics
The oncogene HER‐2/ neu encodes a trans‐membrane receptor of 185 kDa with tyrosine‐kinase activity. Over‐expression of this molecule has been reported in a significant proportion of human breast and ovarian carcinomas, characterized by a poor clinical prognosis. Two monoclonal antibodies (MAbs), recognizing distinct epitopes of the gp 185 extracellular domain, have been utilized in the present study for the production of immunotoxins (ITs) by conjugation to the type‐1 RIP (ribosome‐inactivating protein) plant toxin saporin 6 (SAP). These ITs have been shown to retain tumor‐specificity and specifically to inhibit protein synthesis in the gp 185 HER‐2(+) SK‐BR‐3 breast‐carcinoma cell line with IC 50 values lower then I nM. Kinetics of the cytotoxic activity of the ITs are characterized by a slow rate, since incubation times ranging from 24 to 60 hr, depending on the different degree of expression of the receptor, are required to determine > 90% inhibition in the incorporation of radiolabeled leucine. However, the cytotoxic activity of these ITs, as evaluated by a more sensitive clonogenic assay, appears highly potent, since we have observed that 3 to 4 logs of cells are killed upon exposure to the ITs for short times at concentrations ranging from 1 to 5 × 10 −8 M. © 1993 Wiley‐Liss, Inc.