211At/64Cu labeled bivalent hapten in a two steps targetting approach (Affinity Enhancement System) – aRIT/ßPET

The work to be performed is divided into three parts:

- to develop C-functionalized macrocyclic ligands able to stably chelate copper-64 in vivo
- to use tin supported on ionic liquid for easy and rapid introduction of astatine
- to modify the Di-HSGL for the radiolabeling with these new ligands and to evaluate the radiolabelled hapten in vitro.

Partner 2 focused on the synthesis of bifunctional cyclam derivatives with C-functionalization known to form extremely stable complexes with copper. The result of this work has now provided access to four innovative bifunctional chelating azamacrocycles. A new family of ligands has also been developed by exploiting strong coordinating properties of picolinate arms. The unfonctionalized analogues of these cyclams and picolinates ligands were tested for radiolabelling with copper-64 by Partner 1. Furthermore, a new methodology for the synthesis of the di-HSGL has been developed by partner 2.
Partner 3 focused on the development of organotin reagents supported on ionic liquids for an easy and rapid radiolabeling with astatine, free of contaminants and high specific activity. The general synthesis methodology has been successfully developed and two stannic precursors supported on ionic liquids have already been radiolabelled successfully (partner 1).

The success of this project would lead to major innovations for alphaimmunotherapy and positon emission tomography of cancerous tumors. At the end of this projet, preclinical studies with the most promising candidates for the «AES« system will be considered.

Common work of the three partners has resulted in one publication (1), one oral communication (2) and a poster (3). A patent on the use of tin supported on ionic liquid is also pending.
(1) Roger L. Lima, M. Frindel, C. Platas-Iglesias, J.-F. Gestin, R. Delgado, V. Patinec, R. Tripe, 2013, Inorg. Chem ID: ic-2013-00174r, (2) Synthesis and study of novel bifunctional chelates for the vectorization of 64Cu for PET imaging.. R. Marion, M. Frindel, N. Camus, N. Le Bris, J.F. Gestin, A. Faivre-Chauvet, R. Tripe. Polyamines group GPOL 04, July 2012, Toulouse, (3) D. Faye M. Vybornyi, N. Louaisil, F. Boeda, H. Rajerison H, JF Gestin, S. Legoupy Tin Reagents Supported on Ionic Liquid: Design and Applications, 13th Belgian Organic Synthesis Symposium, July 2012, Leuven, Belgium.

Cancer diseases are the leading cause of death in France for the 2003-2007 period with 146 500 deaths and 357 700 new cases estimated in 2010 . Nuclear medicine is now opening new perspectives for diagnostic and functional imaging of tumors, for their characterization (phenotype, proliferation, response to treatment) and that of their environment (vascularization, hypoxia, inflammation, immune response), but also for therapy (vectorization and targeting of radionuclides emitting alpha or beta radiation for locoregional or systemic therapy).

Antibody-based imaging agents have been completely replaced by 18F-FDG, a broad spectrum PET imaging agent, with a reasonable specificity. In therapeutic applications, radiolabeled antibodies have shown limited efficacy in the case of solid tumors, which are less accessible and less radiosensitive than lymphomas.

Several avenues of research should permit to harness the full power of antibodies for medical imaging and for therapy such as development of new formats of antibodies, use of peptides…. Theses approaches may not be the best to deliver radionuclides because small proteins (or large peptides) do not diffuse as quickly as drugs or small peptides, but at the same time they have a limited residence time in the circulation. In addition, they generally show high to very high kidney uptake, which may not be so detrimental for imaging but is problematic for therapeutic applications.

Partner 1 have strongly participated in the development of another approach, called the "Affinity Enhancement System" (AES), approach which uses bispecific anti-tumor x anti-hapten antibodies and bivalent, radiolabeled, haptens.
This technology has proven its efficacy in cancer imaging (Barbet et al., 1998) and therapy, with the demonstration of increased overall survival in Medullary Thyroid Carcinoma patients treated with pretargeted AES radioimmunotherapy (Chatal et al., 2006 ).

Today this technology encounters some drawbacks due to the associated radionuclides used either for imaging or for therapy. half-life should be higher than 2h and less than 24h, specific activity is too low for RIT, associated energy of the common used radionuclide can be critical in terms of radioprotection either for the patient and for personnel and wastes management has to be considered also.

Therefore we propose in that project to use this really promising and innovative vectorisation technology (A.E.S.) associated with copper-64 (half-life: 12.7 hours) for pretargeted PET imaging and on astatine- 211 (half-life: 7.2 hours) for pretargeted alpha-immunotherapy. Our will his to open new perspectives for diagnostic and validation of tumors, for their characterization (phenotype, proliferation, response to treatment), but also for therapy (vectorization and targeting of radionuclides emitting alpha radiation for locoregional or systemic therapy).
The short half-lives of astate-211 and copper-64 and their low availability has been solved by the installation of the Arronax cyclotron in Nantes. This high energy cyclotron is dedicated for Nuclear Medicine and will produce theses radionuclides for preclinical and clinical uses.

The final objective of our project in to produce di-HSGL-copper-64 and di-HSGL-Astatine-211 with high specific activity and no tin contamination either for preclinical and clinical application. Therefore we propose to associate expertise and innovation in copper chelation chemistry (partner 2), in ionic liquids (partner 3), in bioconjugate chemistry, radiolabelling and in vitro evaluation (partner 1).

Our environment, academic and industrial (NUCSAN), provides us a very favorable field in order to transfer this innovative tool from bench to the clinic.
This project will also build on the strong potential of biomedical research in the Region “Pays de la Loire” and the “Pôle de Compétitivité Atlanpole Biotherapies”, the only one to display "radiopharmaceuticals" as keyword.