R. Tecce et al., CHARACTERIZATION OF CYTOTOXIC ACTIVITY OF SAPORIN ANTI-GP185 HER-2 IMMUNOTOXINS/, International journal of cancer, 55(1), 1993, pp. 122-127
The oncogene HER-2/neu encodes a trans-membrane receptor of 185 kDa wi
th tyrosine-kinase activity. Over-expression of this molecule has been
reported in a significant proportion of human breast and ovarian carc
inomas, characterized by a poor clinical prognosis. Two monoclonal ant
ibodies (MAbs), recognizing distinct epitopes of the gp 185 extracellu
lar domain, have been utilized in the present study for the production
of immunotoxins (ITs) by conjugation to the type-1 RIP (ribosome-inac
tivating protein) plant toxin saporin 6 (SAP). These ITs have been sho
wn to retain tumor-specificity and specifically to inhibit protein syn
thesis in the gp185HER-2(+) SK-BR-3 breast-carcinoma cell line with IC
50 values lower then 1 nM. Kinetics of the cytotoxic activity of the I
Ts are characterized by a slow rate, since incubation times ranging fr
om 24 to 60 hr, depending on the different degree of expression of the
receptor, are required to determine > 90% inhibition in the incorpora
tion of radiolabeled leucine. However, the cytotoxic activity of these
ITs, as evaluated by a more sensitive clonogenic assay, appears highl
y 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 fro
m 1 to 5 x 10(-8) M. (C) 1993 Wiley-Liss, Inc.