Human immunoRNases as selective and non-immunogenic anticancer agents

G. D'Alessio, PhD, MD a C. De Lorenzo, PhD a, D. Palmer b, R. Piccoli a

a Dipartimento di Chimica Biologica, University of Naples Federico II, Napoli, Italy b Department of Immunology, Imperial College, London, U.K.

AIM: Most of conventional anticancer treatments are characterized by lack of tumor cell specificity. Immunotoxins (ITs ), made up of a monoclonal antibody (mAb) reactive to a tumor cell, fused to a cytotoxin, may still be aspecifically toxic and immunogenic. A new approach strategy is to prepare immunoRNases (IR), in which the toxin is replaced by a non-toxic RNase, and the mAb by an scFv. Upon directed internalization, the RNase becomes cytotoxic. Our aim is the preparation of murine/human and fully human, non-immunogenic, IRs directed to ErbB2, a transmembrane receptor highly expressed on several types of carcinomas. METHODS: To prepare a murine/human IR, the cDNA encoding a murine scFv from the anti-ErbB2 mAb MgR6 is fused to that encoding human pancreas RNase (HP-RNase). In the fully human IR, the cDNA encoding a human anti-ErbB2 scFv, isolated from a phage library through a double-selection strategy, is fused to the cDNA encoding HP-RNase. The recombinant proteins are expressed in E. coli. RESULTS: We found that the murine/human IR is active as an RNase, it specifically binds to ErbB2-positive cells, and selectively kills them. Interestingly, we found that the human anti-ErbB2 scFv we isolated is by itself an anti-tumor agent, as it binds, is internalized in, and selectively kills ErbB2 overexpressing target cells. The corresponding fully human IR is presently under test. CONCLUSIONS: Anti-ErbB2 IRs are capable to selectively recognize and kill ErbB2 overexpressing tumor cells. They have a high potential as innovative anti-cancer drugs.

KEY WORDS: scFv, immunotherapy, RNases.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Immunotherapy.