Increasing anticarcinoma activity of an anti-erbB2 recombinant immunotoxin by the addition of an anti-EpCAM sFv.
OBJECTIVE
erbB2, the product of the Her2-neu gene, is a well-established therapeutic target for antibody-based biologicals, but anti-erbB2 antibody-toxin fusion proteins are limited in their activity. The goal of this study was to determine if genetically adding an sFv targeting epithelial cell adhesion molecule (EpCAM) to an anti-Her2 sFv immunotoxin would result in enhanced antitumor activity.


METHODS
In vitro studies were done in which the new bispecific immunotoxin DTEpCAM23 was compared with monospecific immunotoxins (DTEpCAM and DT23) to quantitate immunotoxin activity. Mixtures of monospecific immunotoxins were tested to determine if they were as effective as the bispecific immunotoxin. Binding and internalization studies were also done. In vivo, bispecific immunotoxins were given i.t. to athymic nude mice bearing HT-29 human colon cancer flank tumors and i.p. to mice with i.p. tumors.


RESULTS
DTEpCAM23 bispecific immunotoxins showed far greater activity than monospecific immunotoxin (sometimes over 2,000-fold) against most tumor lines. Bispecific immunotoxin was superior and selective in its activity against different carcinoma cell lines. Bispecific immunotoxin had greater activity than monospecific immunotoxin indicating an advantage of having both sFv on the same single-chain molecule. Binding and internalization studies did not explain the differences between bispecific immunotoxin and monospecific immunotoxin activity. Orientation of the sFvs on the molecule had a significant effect on in vitro and in vivo properties. The bispecific immunotoxins were more effective than the monospecific immunotoxin in the flank tumor mouse model.


CONCLUSIONS
The synthesis of bispecific immunotoxin created a new biological agent with superior in vitro and in vivo activity (over monospecific immunotoxin), more broad reactivity, more efficacy against tumors in vivo, and diminished toxic effects in mice.
Stish
Brad J
BJ
Department of Therapeutic Radiology-Radiation Oncology, University of Minnesota Cancer Center, Minneapolis, Minnesota 55455, USA.
Chen
Hua
H
Shu
Yanqun
Y
Panoskaltsis-Mortari
Angela
A
Vallera
Daniel A
DA
D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics; D002277:Carcinoma / Q000188:drug therapy*; D015815:Cell Adhesion Molecules / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000494:pharmacology / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy*; D000071858:Epithelial Cell Adhesion Molecule; D006801:Humans; D000922:Immunotoxins / Q000494:pharmacology / Q000627:therapeutic use*; D051379:Mice; D008819:Mice, Nude; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000494:pharmacology / Q000627:therapeutic use*
D000951:Antigens, Neoplasm; D015815:Cell Adhesion Molecules; D000071858:Epithelial Cell Adhesion Molecule; D000922:Immunotoxins; D018719:Erb-b2 Receptor Tyrosine Kinases; D011993:Recombinant Fusion Proteins; C521812:DTEpCAM23 immunotoxin