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.