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Oct 1, 2010 (Vol. 30, No. 17)

Protein Production Continues to Post Gains

Latest Advances Demonstrate that Biological Limits Have Yet to Be Achieved

  • Intestinal-Growth Promoting Peptide

    Nycomed focuses on pharmacological agents for the treatment of gastroenterological, respiratory, and inflammatory diseases as well as pain, osteoporosis, and tissue management. Dan Bach-Kristensen, Ph.D., a senior pharmaceutical scientist, will discuss his work with an intestinal growth promoting peptide at the meeting.

    “Teduglutide is a 33 amino acid long peptide analog of the naturally occurring glucagon-like peptide-2 that we are co-developing with NPS Pharmaceuticals for the treatment of small bowel syndrome,” Dr. Bach-Kristensen states. “The molecule has been modified by replacing an alanine at position 2 with a glycine, which considerably lengthened its in vivo half-life. It is a simple entity with no post-translational modifications.”

    According to Dr. Bach-Kristensen, an ordinary adult small intestine has the total surface area of a tennis court, whereas this is restricted to an area the size of a ping pong table in patients suffering from short bowel syndrome. This is usually the result of surgery for infection, inflammation, or as a result of cancer or trauma. The peptide stimulates the elongation of the intestinal villi, thereby increasing the overall surface area of the truncated bowel.

    Alternative treatments for short bowel syndrome are limited with no approved products available in the EU. “The FDA has approved the use of human growth hormone for this indication,” notes Dr. Bach-Kristensen, “but the effect is time-limited, and in the majority of trials patients rapidly return to their base-line state.”

    Research on teduglutide, which began in the late 1990s, included evaluation of different production processes. Originally the peptide was produced in a secreting mammalian cell line, but Dr. Bach-Kristensen says that production of the peptide by bacterial inclusion bodies is a viable alternative. The main purification challenge is the existence of isomers that can be separated by liquid chromatography and mass spectrometry. Electron-capture dissociation can be used to produce a set of fragments for characterization. In this platform, free radicals are produced that donate electrons to a series of fragments.

    “In clinical trials, patients experience increased absorption of nutrients and electrolytes and can see marked improvement in their quality of life,” Dr. Bach-Kristensen explains. “This means that they may be less dependent on parenteral nutrition and may in some cases be moved off of it entirely.”
    The studies on teduglutide have advanced to late Phase III trials.

  • Bispecific Antibodies Against Cancer

    According to Melvyn Little, Ph.D., CSO of Affimed Therapeutics, the company is getting ready for clinical trials with its tetravalent, bispecific antibodies. “An IND application was recently filed and approved with the FDA. Patient recruitment will start immediately.”

    These developments are a positive sign in the history of the tetravalent, bispecific therapeutic antibody technology (TandAb technology). Although investigators were designing these molecules as far back as the mid 1990s, it has taken years to move to the point at which Affimed is now positioned.

    TandAbs are constructed by joining together four antibody variable domains comprising the binding sites of two different antibodies. This four domain chain dimerizes with an identical chain in a head-to-tail fashion. They are expressed as a single polypeptide comprising four variable domains connected via amino-acid linkers varying in length. After translation in the endoplasmatic reticulum, the monomeric polypeptide pairs head-to-tail with another monomer, forming a functional homodimer TandAb® molecule.

    In one case, two of the sites are directed against CD3, part of the T-cell receptor, and the other ends of the molecules are directed against a tumor cell antigen. The result is a product that binds extremely tightly to both the T cell and the tumor cell, bringing about a rapid lysis of the target.

    In another permutation, the company has developed a product that is highly specific for the CD16A receptor on natural killer (NK) cells; two of its binding sites recruit NK cells and the other two binding sites target a tumor cell. The tight binding between the NK and tumor cells again leads to the demise of the malignant cells.

    The two foremost targets under scrutiny are Hodgkin lymphoma, using an anti-CD-30 antibody, and non-Hodgkin lymphoma, in which the antigenic target is CD-19. Affimed also has a daughter company, AbCheck, which is responsible for screening antibody libraries and developing antibodies against new antigens. 

    Part of the challenge for Affimed was to develop a robust GMP production process. The investigators began production with a secreting mammalian cell line. “Fortunately, there are no secondary post-translational modifications of the molecules to worry about, and we were able to develop the upstream and downstream purification process with little loss of product,” Dr. Little remarks. Now the firm is interested in producing future products in E. coli by purification from inclusion bodies.

    The lead product for clinical use is a lyophilizate in a low-salt formulation, which was found to be extremely stable, retaining activity for at least one year at 25° and even for six months at 40°C. These results are important since they establish that in the future such antibody therapeutics may be shipped at room temperature (or even sit in hot airplane shipping facilities) without loss of potency.

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