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Immunomedics and IBC Pharmaceuticals Report on a Novel Protein Engineering Platform Technology

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Immunomedics, Inc. and its wholly owned subsidiary, IBC Pharmaceuticals, Inc. have announced the development of a novel platform technology that can be used to generate multifunctional agents for diverse applications.

The on-line article entitled "Stably tethered multifunctional structures of defined composition made by the dock and lock method for use in cancer targeting," and authored by E.A. Rossi, D.M. Goldenberg, T.M. Cardillo, W.J. McBride, R.M. Sharkey and C.H. Chang, can be accessed online.

The print issue will be published in the Proceedings of the National Academy of Sciences of the USA on May 2, 2006.

This technology may enable the creation of virtually any multifunctional protein for diverse applications.

For example, one potential application is to connect multiple antibody fragments with toxic drugs or radioisotopes for disease therapy or imaging.

Another possibility is to increase the circulation time of hormones, hematopoietic growth factors, or cytokines in the body by linking them to polymers or albumin.

The method could also provide a novel means for selective targeting in gene therapy.

Termed the Dock and Lock (DNL) method, the technology is based on the exploitation of two alpha-helical peptides that are found in nature to bind specifically with each other.

By recombinantly fusing or chemically attaching each peptide to a constituent of interest, these helices provide a linker module for "docking" the two modified components into a quasi-stable structure, which is further "locked" into a stable complex.

"The DNL method can be applied to conjugate, quantitatively and site-specifically, various proteins or non-proteins into stably tethered complexes that retain the full functionalities of the individual components and are suitable for both in vitro and in vivo applications," commented Dr. Chien-Hsing Chang, Executive Vice President of Research at IBC Pharmaceuticals.

"A unique feature of the DNL method is that in its simplest format one of the two components is always provided with two copies, which can be very important for increased therapeutic efficacy."

"Suitable components for this technology include antibody fragments, peptide haptens, polyethylene glycols, human serum albumin, cytokines, DNA vaccines, small interfering RNAs, enzymes, fluorescent proteins and a variety of scaffold-based binding proteins," he added.

To prove the validity of the technology, a trivalent, bispecific protein, TF2, comprising three stably linked Fab fragments, was generated from two of Immunomedics' humanized antibodies, hMN-14, which binds specifically to carcinoembryonic antigen (CEA), and h679, which recognizes the peptide-hapten, histamine-succinyl-glycine (HSG).

By means of a 'pretargeting' method pioneered by IBC Pharmaceuticals, a bispecific antibody or fusion protein, derived from hMN-14 and h679, is first injected to target to the tumor, followed by giving an HSG-carrying radiotracer that binds selectively to the second arm of the bispecific antibody at the tumor site.

Pretargeting studies reported in this PNAS article using TF2 and a technetium-99m-labeled HSG-radiotracer in a CEA-expressing human colon cancer growing in mice demonstrated that 30% of injected radiotracer was bound to tumor within one hour.

As a result of the rapid tumor uptake tumor-to-nontumor ratios were achieved. At 0.5, 1, and 24 hours after the administration of the radiotracer, the tumor-to-blood ratios were 13, 66, and 395, respectively.

These data demonstrate that TF2 is stable and capable of in vivo applications. More importantly, other constructs made by the DNL method are also expected to be stable in vivo with retained biological properties.

"We believe the DNL method is superior, in at least five major aspects, to existing technologies that involve the conjugation of two or more biological entities: (1) The technology provides a convenient and facile way of constructing different proteins and non-proteins from modular subunits on demand; (2) the new method has shown good productivity of pure products with defined composition; (3) the resulting conjugates show high stability in vivo; (4) the multifunctional complexes produced can potentially have higher activity than each of their individual components; and (5) the technology generates potentially non-immunogenic molecules use as therapeutics," commented Cynthia L. Sullivan, President and Chief Executive Officer of Immunomedics.

"This exciting new technology is another testimony of our core strength in research and development. We continue to build on our strong track record of creating new and innovative products from our laboratories," further commented Ms. Sullivan.