Recombinant anti-EGFR immunotoxin 425(scFv)-ETA' demonstrates anti-tumor activity against disseminated human pancreatic cancer in nude mice.

Pancreatic carcinoma is the fifth leading cause of cancer-related deaths in North America and Europe. Major reasons for the high mortality rate include the inability to detect pancreatic cancer at an early stage, extensive local invasion, and early formation of lymphatic and hematogenous metastases. Consequently, novel and effective therapies need to be developed urgently in order to improve the outcome of patients. Since overexpression of the epidermal growth factor receptor (EGFR) in pancreatic tumors correlates with advanced clinical staging, increased tumor size and reduced patient survival, this receptor represents an appropriate target for immunotherapy. We recently generated the recombinant immunotoxin 425(scFv)-ETA' by genetically fusing the anti-EGFR single chain variable fragment 425(scFv) to a truncated version of Pseudomonas aeroginosa exotoxin A (ETA'). The 425(scFv)-ETA' fusion protein was functionally expressed in the periplasmic space of Escherichia coli and was purified using a combination of metal-ion affinity and anion exchange chromatography. The protein showed specific binding to and toxicity against the EGFR-positive, metastatic pancreatic carcinoma cell line L3.6pl, but not to control cell systems. We report the anti-tumor activity of this recombinant immunotoxin in a disseminated human pancreatic cancer nude mouse model. After intravenous (i.v.) injection of L3.6pl cells into immunodeficient nude mice, both single (20 microg on day 1 after challenge) and repeated (10 microg on days 1, 2, 3 and 4 after tumor cell injection) i.v. administration of 425(scFv)-ETA' resulted in a significant reduction in the average number of lung metastases from 56.25 per animal in the control groups to 0.875 per animal (single injection) and 0.286 per animal (repeated injection), respectively, in the experimental groups. In summary, this is the first report showing an in vivo anti-tumor effect caused by the recombinant immunotoxin 425(scFv)-ETA' against disseminated growing metastatic human pancreatic carcinoma cells. Our data suggest that EGFR-specific antibody toxins could be suitable for further clinical investigation in the development of therapies for pancreatic carcinoma.