Design and synthesis of antibody mimics – Mimobody

Firstly we determined the minimal peptide sequences allowing the recognition of the antibody with its target (epitope). To do it, hundreds of peptide fragments (corresponding to the consensus sequence of the antibody) were synthesized on cellulose membranes. The membranes were then incubated with the epitope made fluorescent to select affine fragments. The selected peptide fragments (antibody mimetics) were synthesized then toperform physico-chemical and biological studies allowing the validation of their affinity and their selectivity. The affinity of the antibody mimetics for the various epitopes (CD20, EGFR) was characterized by surface plasmon resonance and by quartz crystal microbalance. The selectivity of mimetics was directly studied on lymphoma expressing CD20 and on animal models.

We identified the key residues involved in the recognition of the antibody Rituximab with the CD20 epitope.
Concerning Cetuximab, we have identified the potential sequences involved in the recognition with the EGFR.
We developed a new method of macromolecular assembly which allows preparing polyfunctional compounds.
We identified a compound which targets non-Hodgkin’s lymphoma with low affinity. Derivatives of this compound are currently synthesized to improve its affinity and its specificity.

If the project is successful, pharmaceutical companies might be undoubtedly interested in our models for cancer diagnostic or drug-delivery agent. Our experience with previous drug-delivery system in term of intellectual property and results exploitation will facilitate the development of MIMOBODY project.

This project gave rise to 3 scientific publications (Chem. Eur. J. 2015, 21, 6022 ; ChemBioChem 2016, 17, 515 ; J. Mat. Chem. B 2017. DOI: 10.1039/C7TB00630F), 1 conference (10/2016, CEA, Saclay) and several communications by poster during national and international congresses (20ème congrès du GFPP in Arcachon, journée de printemps de la Société Chimique de France section Rhône-Alpes in Chambéry, 2ème journée plénière du GDR bio-ingénierie des interfaces in Bordeaux, 12èmes Journées du Cancéropôle Grand Sud-Ouest in La Grande Motte, 2nd European conference on physical chemistry in Borgo).

Since the nineties, monoclonal antibodies (mAb) have emerged as a promising class of pharmaceuticals for the treatment of many human diseases including cancer. MAbs such as IgG (immunoglobulin G) are proteins that comprise two essential domains: an epitope recognition part that is composed of the complementary-determining regions (CDRs), and the Fc region that activates the immune system. These mAbs can block tumor growth, activate tumor lysis by immunoactivation or by coupling to toxins. However, few mAbs are being used in human therapy a quarter century after their discovery. They are widely used as diagnostic and research reagents but their introduction into human therapy has been much slower: today, only 11 mAbs were marketed and used in oncology. Manufacture of mAbs requires a special handling and a costly biotech production procedure. The cost of mAb therapy is a major limiting factor with annual costs of about US$ 100,000 per patient leading to serious concerns about its economical pertinence. Beside this problem however, like most of proteins, many factors, such aggregation, large size, and immunogenicity, limit their use for therapy. Consequently, there is a pressing need for new molecular systems that integrate mAb properties. This challenge can be achieved by designing small antibody mimics by using an entire synthetic approach. Previously, our laboratory has designed and synthesized biomolecular systems based on cyclopeptide scaffolds endowed with tumor-targeting functions that enable the specific delivery of toxic molecules, or imaging probes, or a combination thereof, to malignant tissues. To have access to such sophisticated biomolecular compounds, we have developed new chemical strategies for the synthesis of well-defined biomolecular assemblies using orthogonal chemoselective ligations. In the Mimobody project, we propose to capitalize on these previous studies to prepare small synthetic antibody mimics (named Mimobody), through two IgG examples: Rituximab (Rituxan®) indicated for the treatment of patients with non-Hodgkin's lymphoma, and Cetuximab (Erbitux®) indicated for treatment of carcinoma. It is conceivable to design antibody mimics based on the analysis of the crystal structure of the mAb in complex with its epitope. By transferring the recognition domain (CDR fragments) from the mAb to a synthetic scaffold, it is possible to provide a new class of pharmaceuticals and an alternative to antibodies.