STEFAN BARTH:  SATURDAY 01 APRIL 2006, 11:25

Novel recombinant immunotoxins for selective elimination of activated macrophages

Theo Thepen¹, Michael Huhn¹, Michael Stöcker², Mehmet K. Tur³, Stefan Barth^1,3
1Department of Pharmaceutical Product Development, Fraunhofer IME, Forckenbeckstr. 6, 52074 Aachen, Germany; ²Institute of Molecular Biotechnology at the RWTH Aachen, Worringerweg 1, 52974 Aachen, Germany; ³Helmholtz-Institute AME, Chair of Experimental Medicine and Immunotherapy, Pauwelsstr. 20, 52074 Aachen, Germany

Under pathological conditions, activated and dysregulated macrophages play a decisive role in the development of numerous inflammatory processes including progression of cancer.   Chronic inflammation is a high risk factor for a variety of epithelial cancers. Physical interaction of macrophages with malignant cells within the tumor microenvironment facilitates angiogenesis, breakdown of extra-cellular matrix, remodeling and promotion of tumor cell motility. Thus, macrophages are identified as an important target for immunotherapy. Characteristic for activated macrophages is specific and high expression of CD64, the high affinity receptor for IgG. The primary function of CD64 is internalization, which qualifies this receptor as a prime target for therapeutic intervention. To specifically target cell-receptors like CD64, monoclonal antibodies, or derivatives thereof are highly suitable. Using these ligands for selective elimination by combining them with e.g. a cytotoxic compound might result in potent therapeutics to treat CD64-expressing diseases. Proof of concept was provided by experiments targeting activated macrophages in chronic disease using chemically linked immunotoxins based on anti-CD64 antibody. There are however potential side effects, like immunogenicity and non-specific toxicity, associated with these classically constructed IT. Therefore, we designed a number of recombinant IT (rIT), consisting of either the bacterial toxin ETA or human granzyme B, and 1 or 2 single chain antibody fragments against CD64. This respectively resulted in both mono-valent h22(scFv) and bi-valent h22(scFv) 2 rIT. First data on efficacy of these constructs against CD64-positive target cells, both in vitro as well as in vivo will be presented. The results indicate requirement of cross-linking for CD64-mediated killing, which is achieved by both the bi-valent rIT and classical IT, but to a much lesser extend by the mono-valent rIT. The bi-valent recombinant immunotoxins are performing equal to the classically constructed anti-CD64 immunotoxins. This will demonstrates their potency not only for CD64-positive AML but also for the treatment of diseases tightly associated to chronic inflammation.

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