A recombinant immunotoxin derived from a humanized epithelial cell adhesion molecule-specific single-chain antibody fragment has potent and selective antitumor activity.
OBJECTIVE
Epithelial cell adhesion molecule (Ep-CAM) is a tumor-associated antigen overexpressed in many solid tumors but shows limited expression in normal epithelial tissues. To exploit this favorable expression pattern for targeted cancer therapy, an Ep-CAM-specific recombinant immunotoxin was developed and its antitumor activity investigated.


METHODS
The immunotoxin 4D5MOCB-ETA was developed by genetically fusing a truncated form of Pseudomonas aeruginosa exotoxin A (ETA) (ETA(252-608)KDEL) to the highly stable humanized single-chain antibody fragment (scFv) 4D5MOCB. Cytotoxicity of 4D5MOCB-ETA was measured in cell growth and leucine incorporation assays in vitro. Tumor localization and antitumor activity were assessed in athymic mice bearing established human tumor xenografts.


RESULTS
Fusion of the toxin moiety to the scFv did neither affect its thermal stability nor its antigen-binding affinity. In vitro, 4D5MOCB-ETA potently and specifically inhibited protein synthesis and reduced the viability of Ep-CAM-positive carcinoma cells of diverse histological origins with IC(50)s ranging from 0.005 to 0.2 pM. Upon systemic administration in mice, 4D5MOCB-ETA showed similar organ distribution as the scFv 4D5MOCB and preferentially localized to Ep-CAM-positive tumor xenografts with a tumor:blood ratio of 5.4. The potent antitumor activity of 4D5MOCB-ETA was demonstrated by its ability to strongly inhibit the growth and induce regression of relatively large tumor xenografts derived from lung, colon, or squamous cell carcinomas.


CONCLUSIONS
We describe for the first time the development of a fully recombinant Ep-CAM-specific immunotoxin and demonstrate its potent activity against solid tumors of various histological origins. 4D5MOCB-ETA is currently being evaluated in a Phase I study in patients with refractory squamous cell carcinoma of the head and neck.
Di Paolo
Claudio
C
Clinic and Policlinic for Oncology, University Hospital, CH-8044 Zürich, Switzerland.
Willuda
Jörg
J
Kubetzko
Susanne
S
Lauffer
Ikar
I
Tschudi
Dominique
D
Waibel
Robert
R
Plückthun
Andreas
A
Stahel
Rolf A
RA
Zangemeister-Wittke
Uwe
U
D036002:ADP Ribose Transferases / Q000737:chemistry; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001427:Bacterial Toxins / Q000737:chemistry / Q000494:pharmacology*; D015815:Cell Adhesion Molecules; D002455:Cell Division; D045744:Cell Line, Tumor; D002850:Chromatography, Gel; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000378:metabolism*; D005098:Exotoxins / Q000737:chemistry; D005260:Female; D005434:Flow Cytometry; D005822:Genetic Vectors; D006801:Humans; D007128:Immunoglobulin Fragments / Q000737:chemistry* / Q000494:pharmacology*; D000922:Immunotoxins / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D051379:Mice; D008810:Mice, Inbred C57BL; D008819:Mice, Nude; D008958:Models, Molecular; D009368:Neoplasm Transplantation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000494:pharmacology*; D013997:Time Factors; D037521:Virulence Factors / Q000737:chemistry; D000097668:Pseudomonas aeruginosa Exotoxin A
D036002:ADP Ribose Transferases; D000970:Antineoplastic Agents; D001427:Bacterial Toxins; D015815:Cell Adhesion Molecules; D005098:Exotoxins; D007128:Immunoglobulin Fragments; D000922:Immunotoxins; D011994:Recombinant Proteins; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A; C483831:immunotoxin 4D5MOCB-ETA