DC3: ALFONSO FUMANAL IDOCIN (SP)
Partner of attachment: CEA (French Alternative Energies and Atomic Energy Commission) FR
Supervisor: Dr. Simon SPECKLIN
University of Attachment: UPSAC (University Paris-Saclay) FR
Director of Thesis : Dr. Bertrand KUHNAST

Biological molecules such as peptides and antibodies are interesting for in vivo imaging. Fluor 18, a beta emisor radioisotope, is the most used radioisotope for PET scan. It has a half-life of 109 min meaning that the labelling strategies of biologics need to be fast to avoid loss of radioactivity. In order to improve the purity and speed of the labelling of biologics, we propose a new approach, combining a solid support and a linker molecule that contains an imino sydnone group. Imino sydnones are mesoionic heterocyclic betaines that can undergo click reactions with internal alkynes such as DBCO. This way we propose to develop an imino sydnone linker that serves as union between the biological molecule and the solid support. Upon addition of DBCO carrying the 18F atom, the linker cleaves and the biological molecule now labelled is released. This way we increase the purity of labelled biologics and reduce the time of reaction, leading to higher molar activities.
We have successfully synthesized a suitable linker in 6 steps with 15% total yield. This linker contains an urea group attached to the imino sydnone that allows for faster kineticts in the DBCO click reaction, which needs to be as fast as possible to avoid losing radioactivity from the 18F. The molecule presents two ends, one designed to be attached to a solid support and another to the biological molecule. Thanks to a terminal amine, we can graft the linker onto a solid support that presents activated ester groups. Two different commercial solid supports have been tested, agarose and tentagel, both NHS activated. Both of them have proven to be very efficient on the grafting. Next, we conducted a CuAAC click reaction to add on the azide end of the linker an NHS group that reacts with an amine of the biological molecule. The terminal azide is easily tunable via CuAAC, meaning that we could adjust a more suitable coupling group depending on the biological molecule. We have tested the DBCO “click and release” of the linker on both steps so far, and we confirm that the is the only product detected ion both cases is the click product. This means that we have been successful on grafting the linker to the resin and performing a CuAAC on it, and releasing the linker on both cases. The DBCO “click and release” strategy proovfed to be a selective strategy to cleave the linker off the resin and hinted to be very fast. This result allows us to move forward onto the coupling of small amines before the testing with larger biological molecules. Radiolabeling will start soon after that.
We have proven that a “click and release” strategy is possible with an imino sydnone linker and hinted to be fast enough to be used on 18F radiolabeling. Both tentagel and agarose resins proofed to be suitable solid support resins, being agarose the one presenting faster reactions times for the grafting. We were able to perform a CuAAC on the linker directly after being grafted on the resin, allowing us to introduce on the azide end of the linker functional groups to better fit the biological molecule to be labeled. As DBCO “click and release” reaction was successful, we are moving forward to the coupling with small amines and we are planning on performing the first radiolabeling test soon. By the end of the year we are expecting to achieve a first proof of concept of the “click and release” strategy with larger biological molecules.
