Cyclam with a phosphinate-bis(phosphonate) pendant arm is a bone-targeting carrier of copper radionuclides.

Ligands combining a bis(phosphonate) group with a macrocycle function as metal isotope carriers for radionuclide-based imaging and for treating bone metastases associated with several cancers. However, bis(phosphonate) pendant arms often slow down complex formation and decrease radiochemical yields. Nevertheless, their negative effect on complexation rates may be mitigated by using a suitable spacer between bis(phosphonate) and the macrocycle. To demonstrate the potential of bis(phosphonate) bearing macrocyclic ligands as a copper radioisotope carrier, we report the synthesis of a new cyclam derivative bearing a phosphinate-bis(phosphonate) pendant (H5te1PBP). The ligand showed a high selectivity to CuII over ZnII and NiII ions, and the bis(phosphonate) group was not coordinated in the CuII complex, strongly interacting with other metal ions in solution. The CuII complex formed quickly, in 1 s, at pH 5 and at a millimolar scale. The complexation rates significantly differed under a ligand or metal ion excess due to the formation of reaction intermediates differing in their metal-to-ligand ratio and protonation state, respectively. The CuII-te1PBP complex also showed a high resistance to acid-assisted hydrolysis (t1/2 2.7 h; 1 M HClO4, 25 °C) and was effectively adsorbed on the hydroxyapatite surface. H5te1PBP radiolabeling with [64Cu]CuCl2 was fast and efficient, with specific activities of approximately 30 GBq 64Cu per 1 µmol of ligand (pH 5.5, room temperature, 30 min). In a pilot experiment, we further demonstrated the excellent suitability of [64Cu]CuII-te1PBP for imaging active bone compartments by dedicated small animal PET/CT in healthy mice and subsequently in a rat femoral defect model, in direct comparison with [18F]fluoride. Moreover, [64Cu]CuII-te1PBP showed a higher uptake in critical bone defect regions. Therefore, our study highlights the potential of [64Cu]CuII-te1PBP as a PET radiotracer for evaluating bone healing in preclinical and clinical settings with a diagnostic value similar to that of [18F]fluoride, albeit with a longer half-life (12.7 h) than 18F (1.8 h), thereby enabling extended observation times.

Ynamide Click chemistry in development of triazole VEGFR2 TK modulators.

Structure novelty, chemical stability and synthetic feasibility attracted us to design 1,2,3-triazole compounds as potential inhibitors of VEGFR2 tyrosine kinase. Novel triazoles T1-T7 were proposed by oxazole (AAZ from PDB: 1Y6A)/1,2,3-triazole isosteric replacement, molecular modelling and docking. In order to enable synthesis of T1-T7 we developed a methodology for preparation of ynamide 22. Compound 22 was used for all Click chemistry reactions leading to triazoles T1-T3 and T6-T7. Among the obtained products, T1, T3 and T7 specifically bind VEGFR2 TK and modulate its activity by concentration dependent manner. Moreover predicted binding poses of T1-T7 in VEGFR2 TK were similar to the one known for the oxazole inhibitor AAZ (PDB: 1Y6A). Unfortunately the VEGFR2 inhibition by triazoles e.g. T3 and T7 is lower than that determined for their oxazole bioisosters T3-ox and AAZ, resp. Different electronic properties of 1,2,3-triazole/oxazole heterocyclic rings were proposed to be the main reason for the diminished affinity of T1-T3, T6 and T7 to an oxazole AAZ inhibitor binding site in VEGFR2 TK (PDB: 1Y6A or 1Y6B). Moreover T1-T3 and T6 were screened on cytotoxic activity against two human hepatocellular carcinoma cell lines. Selective cytotoxic activity of T2 against aggressive Mahlavu cells has been discovered indicating possible affinity of T2 to Mahlavu constitutionally active PI3K/Akt pathway.