Comparison of in vitro and in vivo Properties of HYNIC- [βAla7-Tle12] Neurotensin (5-13) Labeled with 99mTc using Two Co-ligand Systems

Abstract

Background and purpose: The selection of co-ligand has a profound effect on the labeling efficiency, biodistribution, and tumor-targeting ability of 99mTc-labeled HYNIC-conjugated peptides. This study compared the in-vitro and in-vivo properties from the 99mTc-labeling of 6-Hydrazinonicotinamide-conjugated neurotensin (HYNIC-[βAla7-Tle12] NT (5-13)) by Tricine/EDDA and Tricine as two co-ligand systems. Materials and methods: After radiolabeling, cellular specific binding, affinity and internalization were evaluated toward the HT-29 cell line, as neurotensin overexpressing cells for both of them. Finally, the biodistribution studies were performed on HT-29 xenografted tumor-bearing nude mice, and the imaging was performed using a gamma camera. Results: The radiochemical purity of 99mTc labeled peptide with tricine and tricine/EDDA as co-ligands was found over 95%, and they showed desirable saline and serum stability up to 24 h. The dissociation constant (Kd) value for radiolabeled peptide with tricine and tricine/EDDA toward NT receptors were determined as 50.41 ± 9.76 and 32.66 ± 4.00, respectively. Internalization of radiolabeled peptide with tricine/EDDA was reported almost 2-fold more than radiolabeled peptide with tricine as co-ligand for HT-29 cell line after 4 h incubation. In biodistribution and imaging, the tumor/muscle activity ratio was 2.30 and 4.20, 1.74 and 2.28 at 2 h post-injection with tricine and tricine/EDDA, respectively. Conclusion: Despite relatively similar radiochemical properties of both peptide radio-complexes with 99mTc, the complex labeled with a mixture of tricine/EDDA as co-ligands showed more suitable in vivo properties than tricine.

Keywords

• ht-29
• hynic
• imaging
• neurotensin
• 99mtc
• tricine