Evaluation of K(HYNIC)2 as A Bifunctional Chelator for 99mTc-Labeling of Small Biomolecules

摘要

This study sought to evaluate K(HYNIC)2 (K = lysine and HYNIC = 6-hydrazinonicotinyl) as a bifunctional chelator for ^99mTc-labeling of biomolecule. In this study, four K(HYNIC)2–conjugated cyclic RGD peptides, K(HYNIC)2-RGD2 (RGD2 = E[c(RGDfK)]2), K(HYNIC)2-3G-RGD2 (3G-RGD2 = Gly-Gly-Gly-E[Gly-Gly-Gly-c(RGDfK)]2), K(HYNIC)2-2P-RGD2 (2P-RGD2 = E[PEG4-c(RGDfK)]2, and PEG4 = 15-amino-4,7,10,13-tetraoxapentadecanoic acid), and K(HYNIC)₂-3P-RGD₂ (3P-RGD₂ = PEG₄-E[PEG₄-c(RGDfK)]₂) were prepared, and evaluated for their integrin α_vβ₃ binding affinity. IC₅₀ values were determined to be 47 ± 2, 35 ± 2, 37 ± 2, 85 ± 2 and 422 ± 15 nM for K(HYNIC)₂-2P-RGD₂, K(HYNIC)₂-3P-RGD₂, K(HYNIC)₂-3G-RGD₂, K(HYNIC)₂-RGD₂ and c(RGDyK), respectively, against ¹²⁵I-echistatin bound to U87MG cells. Macrocyclic complexes [^99mTc(K(HYNIC)₂-RGD₂)(tricine)] (>1), [^99mTc(K(HYNIC)₂-3G-RGD₂)(tricine)] (>2), [^99mTc(K(HYNIC)₂-2P-RGD₂)(tricine)] (>3), and [^99mTc(K(HYNIC)₂-3P-RGD₂)(tricine)] (>4) were prepared, and evaluated in athymic nude mice bearing U87MG glioma xenografts for their tumor targeting capability and biodistribution. It was found that >1 – >4 all had high solution stability and more than two isomers, as evidenced by the presence of multiple radiometric peaks in their radio-HPLC chromatograms. The tumor uptake of >1 – >4 was 3.78 ± 0.81, 7.46 ± 1.68, 9.74 ± 1.65 and 8.59 ± 1.52 %ID/g, respectively, which was completely consistent with trend of integrin α_vβ₃ binding affinity for cyclic RGD peptides. Replacing [^99mTc(HYNIC)(tricine)(TPPTS)] (TPPTS = trisodium triphenylphosphine-3,3′,3″-trisulfonate) with [^99mTc(K(HYNIC)₂)(tricine)] had little impact on radiotracer tumor uptake; but it had significant effect on the uptake of radiotracer in kidneys, lungs and spleen. The tumor was clearly visualized by SPECT/CT with excellent contrast in a glioma-bearing mouse administered with >4. K(HYNIC)₂ would be particularly useful for ^99mTc-labeling of small biomolecules with one or more disulfide linkages.