Synthesis of 18F-labelled quinoline derivatives for a novel pretargeting approach to image therapeutic monoclonal antibodies.

67 Objectives: Biological therapeutics, especially monoclonal antibodies (mAbs), accounted for 50% of the top selling drugs in 2018.1 To analyze the location and binding of mAbs in vivo using PET, typically mAbs are labeled with a long-lived radionuclides, such as Zr-89, allowing for sufficient time for binding and clearance from circulation.2,3 The patients are scanned several days after injection, exposing the subject to higher doses of radiation than using short-live isotopes.4 To overcome this limitation, pretargeting approaches using click-chemistry have been developed.5 To further increase biocompatibility, we are investigating a novel pretargeting approach that consists in adding a short peptide to the mAb engineered to bind a drug-like radiolabeled small molecule. This allows the mAb to be administered to the patient without radiation present and after a designated time, the radiotracer can be administered to image the antibody’s location. The small molecule will bind non-covalently with the mAb as opposed to having reaction groups that need to click together to form a covalent bond.6 Methods: Small molecule selection: Around 40 possible drug-like fluorine-containing small molecule candidates were computationally screened for desired properties. From this group, two small molecules (6-fluoro-4-aminoquinoline, 6F4AQ, and 6-fluoro-3-aminoquinoline, 6F3AQ) were immobilized on a gold-plated glass surfaces using an alkenothyolate linker and EDC/NHS coupling reagent for peptide binding experiments.7Peptide selection: A commercial phage display peptide library (E811L, New England BioLabs) containing 109 unique dodecapeptides was used to screen for peptides recognizing the small molecules.8Radiolabeling of small molecules: The corresponding aryl boronic ester and iodonium salt precursors were synthesized from the bromo- and iodo-precursor, respectively. Known Cu-mediated methods were used to incorporate the fluorine-18 on the scaffolds.9,10 Results: 6F4AQ and 6F3AQ were selected for having favorable predicted properties (logP, PSA), being amenable to radiolabeling with fluorine-18 and having commercially available authentic products and precursors. [18F]6F4AQ and [18F]6F3AQ were radiochemically synthesized in sufficient yields, molar activity, and radiochemical purity from the iodonium and boronic ester precursors. After six rounds of panning, the six most abundant peptides from the phage display screen were selected for future experiments. Future work includes investigating the binding of the radiolabeled small molecules to the peptides in vitro and in vivo. Conclusions: The development of a two-component system to image therapeutic mAbs using PET can potentially be used to predict patient response in a shorter timeframe and provide invaluable information for diagnosis, therapy monitoring, and mAb development. Research support: R00EB0020075, T32EB013180 References: (1) Philippidis, A. Top 15 Best-Selling Drugs of 2018 http://www.genengnews.com/a-lists/top-15-best-selling-drugs-of-2018/ (accessed Oct 14, 2019). (2) Clark, J.; O’Hagan, D. J. Fluor. Chem.2017, 203, 31-46. (3) McKnight, B. N.; Viola‐Villegas, N. T J. Label. Compd. Radiopharm.2018, 61, 727-738. (4) Boros, E.; Holland, J. P. J. Label. Compd. Radiopharm.2018, 61, 652-671. (5) Rondon, A.; Degoul, F. Bioconjug. Chem.2019. ASAP, DOI: 10.1021/acs.bioconjchem.9b00761. (6) Vaidyanathan, G.; Zalutsky, M. R. Nat. Protoc.2006, 1, 1655-1661. (7) Lahiri, J.; Isaacs, L.; Tien, J.; Whitesides, G. M. Anal. Chem.1999, 71, 777-790. (8) Sawada, T.; Okeya, Y.; Hashizume, M.; Serizawa, T. Chem. Commun.2013, 49, 5088-5090. (9) Mossine, A. V.; Brooks, A. F.; Makaravage, K. J.; et al. Org. Lett.2015, 17, 5780-5783. (10) Preshlock, S.; Tredwell, M.; Gouverneur, V. Chem. Rev.2016, 116, 719-766.