Synthesis, radiolabelling and biodistribution of HYNIC-Tyr3 octreotide: a somatostatin receptor positive tumour imaging agent

In vivo imaging of tumours using radiolabelled somatostatin (SST) analogues has become an accepted clinical tool in oncology. HYNIC-Tyr(3) octreotide and Tyr(3) octreotide were synthesized by FMOC solid-phase peptide synthesis using a semi-automated synthesizer. These were analyzed and purified by RP-HPLC, mass spectroscopy, IR spectroscopy, H-1 NMR and C-13 NMR. The prochelator 6-BOC-HYNIC was also synthesised and characterised indigenously. HYNIC-Tyr(3) octreotide was labelled with Tc-99m using Tricine and EDDA as coligand by SnCl2 method. Labelling with Tc-99m was performed at 100 A degrees C for 15 min and radiochemical analysis by ITLC and HPLC methods. The radiochemical purity of the complex was over 98% and log p value was found to be -1.27 +/- A 0.12. The stability of radiolabelled peptide complex was checked at 37 A degrees C up to 24 h. Blood clearance and protein-binding study was also performed. In vivo biodistribution studies in rat showed uptake of Tc-99m-HYNIC-TOC in kidney than any other organs. The blood clearance was faster with rapid excretion through kidneys and relatively low uptake in liver.