Click chemistry has been employed for the assembly of novel and efficient triazole-based multidentate chelating systems while simultaneously attaching them to molecules of biological interest. The "click-to-chelate" approach offers a powerful new tool for the modification of (bio)molecules with metal chelators for potential diagnostic and therapeutic applications.
Purpose Neurotensin (NT) and its high affinity receptor (NTR1) are involved in several neoplastic processes. Thus, NT-based radiopharmaceuticals are potential tracers for targeted diagnosis and therapy of NTR-positive tumours. A new analogue based on NT(8-13), NT-XIX, with the three enzymatic cleavage sites stabilised, was synthesised and tested. Methods The synthesis was performed by Boc strategy. Labelling with 99m Tc/
188Re was performed using the tricarbonyl technique. Metabolic stability was tested in vitro and in vivo. NT-XIX was further characterised in vitro in HT-29 cells and in vivo in nude mice with HT-29 xenografts. Results NT-XIX showed much longer half-lives than nonstabilised analogues. Binding to NTR1 was highly specific, although the affinity was lower than that of natural NT. Bound activity rapidly internalised into HT-29 cells and 50% remained trapped after 24 h. In the time-course biodistribution, the highest uptake was found in the tumour at all p.i. times. In vivo uptake was specific, and accumulation of activity in the kidneys was low. Radioactivity clearance from healthy organs was faster than that from the tumour, resulting in improved tumour-to-tissue ratios and good SPECT/CT imaging. Treatment with 188 Re-NT-XIX (30 MBq, in three or four fractions) decreased tumour growth by 50% after 3 weeks. Conclusion The high in vivo stability and the favourable in vivo behaviour makes NT-XIX an excellent candidate for the imaging and therapy of NTR1-positive tumours.
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