To develop novel 99mTc-labeled single-photon emission computed tomography (SPECT) radiotracers for imaging hypoxia, a novel HYNICNM ligand (6-hydrazinonicotinamide (HYNIC) 2-nitroimidazole derivative) was designed and synthesized. It was radiolabeled with technetium-99m using tricine/trisodium triphenylphosphine-3,3',3''-trisulfonate (TPPTS), tricine/sodium triphenylphosphine-3-monosulfonate (TPPMS) and tricine as co-ligands to obtain [99mTc]Tc-tricine-TPPTS-HYNICNM, [99mTc]Tc-tricine-TPPMS-HYNICNM, and [99mTc]Tc-(tricine)2-HYNICNM, respectively. The three technetium-99m complexes were radiolabeled in one step with a high yield (95%) and had good stability in saline and mouse serum. In vitro cellular uptake results showed that these complexes exhibited good hypoxic selectivity. The partition coefficient indicated that they were good hydrophilic complexes, and [99mTc]Tc-tricine-TPPTS-HYNICNM displayed the highest hydrophilicity (-3.02 ± 0.08). The biodistribution in mice bearing S180 tumors showed that [99mTc]Tc-tricine-TPPTS-HYNICNM exhibited higher tumor uptake (1.05 ± 0.27% IA/g); more rapid clearance from the liver, blood, muscle, and other non-target organs; and a higher tumor/non-target ratio, especially for the tumor/liver ratio (1.95), than [99mTc]Tc-tricine-TPPMS-HYNICNM and [99mTc]Tc-(tricine)2-HYNICNM. The results of single-photon emission computed tomography (SPECT) imaging studies of [99mTc]Tc-tricine-TPPTS-HYNICNM were in accordance with the biodistribution results, which suggested that [99mTc]Tc-tricine-TPPTS-HYNICNM is a promising agent for imaging tumor hypoxia.
Keywords: 2-nitroimidazole; HYNIC; hypoxia; technetium-99m; tumor.