Organic & Biomolecular Chemistry 2018-04-10

Synthesis of a C-functionalized TE1PA and comparison with analogues. Example of bioconjugation on 9E7.4 mAb for multiple myeloma 64Cu-PET imaging

Thomas Le Bihan, Anne-Sophie Navarro, Le Bris Nathalie, Patricia Le Saec, Sebastien Gouard, Ferid Haddad, Jean-Francois Gestin, Michel Cherel, Alain Faivre Chauvet, Raphael Tripier

Index: 10.1039/C8OB00499D

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Abstract

According to the excellent copper(II) and 64-copper(II) complexation of TE1PA ligand, a monopicolinate cyclam, in both aqueous medium and in vivo, we looked for a way to make it bifunctional, while keeping intact its chelating properties. Overcoming the already known drawback of a grafting by its carboxyl group, essential to the overall ligand assets, TE1PA bifunctional derivative bearing an additional isothiocyanate coupling function on a carbon atom of the macrocyclic ring was synthesized. This led to a comparable architecture of other bifunctional copper(II) chelators commercially available such as p-SCN-Bn-DOTA already used in clinical trials for 64Cu-immuno-PET imaging. The C functionalization of TE1PA on one carbon atom in β-N position of the cyclam backbone was successfully managed by adapting our patented methodology to the huge challenge to allow the regiospecific mono-N-functionalization of the unsymmetrical ligand. The so obtained ligand p-SCN-Bn-TE1PA was coupled to the 9E7.4 murine antibody (mAb), an IgG2a anti CD-138 for multiple myeloma (MM) targeting. The conjugation efficiency was checked by looking at the 64Cu radiolabeling and the radiopharmaceutical 64Cu-9E7.4-p-SCN-Bn-TE1PA immunoreactivity and especially by comparison with 9E7.4 p SCN-Bn-NOTA and 9E7.4-p-SCN-Bn-DOTA obtained respectively from commercially and presumed highly efficient chelators NOTA and DOTA. Results are quite clear, showing with p-SCN-Bn-TE1PA a coupling rate 5 times higher and an immunoreactivity of 1.5 to 2 times greater than its two competitors. p-SCN-Bn-TE1PA also outperforms TE1PA conjugated via its carboxylic function on the same antibody. A first 64Cu-immuno-PET preclinical study in a syngeneic model of MM was achieved confirming the high in vivo properties of 64Cu-9E7.4-p-SCN-Bn-TE1PA for PET imaging, looking at the high clearance already after 24 h and a particularly important tumor-to-liver ratio increasing at 48 h.