Development of Technetium-99m-Labeled BODIPY-Based Probes Targeting Lipid Droplets Toward the Diagnosis of Hyperlipidemia-Related Diseases

Abstract

Hyperlipidemia causes systemic lipid disorder, which leads to hepatic steatosis and atherosclerosis. Thus, it is necessary to detect these syndromes early and precisely to improve prognosis. In the affected regions, abnormal formation and growth of lipid droplets is observed; therefore, lipid droplets may be a suitable target for the diagnosis of hyperlipidemia-related syndromes. In this study, we designed and synthesized [99mTc]Tc-BOD and [99mTc]Tc-MBOD composed of one technetium-99m and two BODIPY scaffolds with hydroxamamide (Ham) or N-methylated hydroxamamide (MHam) in radiochemical yields of 54 and 35%, respectively, with a radiochemical purity of over 95%. [99mTc]Tc-BOD showed significantly higher accumulation levels in foam cells than in non-foam cells (foam cells: 213.8 ± 64.8, non-foam cell: 126.2 ± 26.9 %dose/mg protein, p < 0.05) 2 h after incubation. In contrast, [99mTc]Tc-MBOD showed similar accumulation levels in foam cells and non-foam cells (foam cells: 92.2 ± 23.3, non-foam cell: 83.8 ± 19.8 %dose/mg protein). In normal mice, [99mTc]Tc-BOD exhibited gradual blood clearance (0.5 h: 4.98 ± 0.35, 6 h: 1.94 ± 0.12 %ID/g) and relatively high accumulation in the liver 6 h after administration (15.22 ± 1.72 %ID/g). Therefore, [99mTc]Tc-BOD may have potential as an imaging probe for detecting lipid droplets in disease lesions of hyperlipidemia.

Development of a hydroxamamide-based bifunctional chelating agent to prepare technetium-99m-labeled bivalent ligand probes

“…In general, the Ham group structure is known to have two tautomer, and thus the 99m Tc-Ham complex forms two tautomer which can be observed by RP-HPLC 7 . The chelation of Ham and 99m Tc was confirmed by the disappearance of the peak from 99m TcO 4 - (retention time: 2–4 min 11 ) and then the appearance of two peaks because it is difficult to synthesize the analogues of the rhenium-Ham complex 7 . To search for an appropriate 99m Tc radiolabeling reaction condition, we first evaluated the reaction of Ham-Cys and 99m TcO 4 - with different concentrations of Ham-Cys (final concentration: 10 and 20 mM) in different solvents [phosphate buffer (pH 7.4) and acetic acid/ethanol = 1/4].…”

“…We also evaluated the in vitro stability of 99m Tc-(Ham-RGD) 2 in mouse plasma; however, we found that the radiochemical purity decreased in a time dependent manner, and some unknown hydrophilic metabolites emerged (Figure S2 ). Given that other Ham-based 99m Tc radiolabeled compounds we developed previously 11 , 13 showed high stability in plasma and good blood clearance, it is suspected that those unknown metabolites affected the slow blood clearance. Although the metabolites and the reason of the instability is still unclear, the low stability of 99m Tc-(Ham-RGD) 2 in plasma is the limitation, and further study for redesigning the bifunctional chelate to improve the stability would be needed for use it in in vivo study.…”

Development of a Hydroxamamide-Based Bifunctional Chelating Agent to Prepare Technetium-99m-Labeled Bivalent Ligand Probes

“…In general, the Ham group structure is known to have two tautomer, and thus the 99m Tc-Ham complex forms two tautomer which can be observed by RP-HPLC 7 . The chelation of Ham and 99m Tc was con rmed by the disappearance of the peak from [ 99m Tc]NaTcO 4 (retention time: 2-4 min 11 ) and then the appearance of two peaks because it is di cult to synthesize the analogues of the rhenium-Ham complex 7 . To search for an appropriate 99m Tc radiolabeling reaction condition, we rst evaluated the reaction of Ham-Cys and [ 99m Tc]NaTcO 4 with different concentrations of Ham-Cys ( nal concentration: 10 and 20 mM) in different solvents [phosphate buffer (pH 7.4) and acetic acid/ethanol = 1/4].…”

“…To search for an appropriate 99m Tc radiolabeling reaction condition, we rst evaluated the reaction of Ham-Cys and [ 99m Tc]NaTcO 4 with different concentrations of Ham-Cys ( nal concentration: 10 and 20 mM) in different solvents [phosphate buffer (pH 7.4) and acetic acid/ethanol = 1/4]. In our previous study, we used an acetic acid/ethanol mixture as the solvent for 99m Tc radiolabeling reactions of compounds containing Ham [9][10][11][12][13] ; however, the radiochemical yields were low [10.4 ± 9.8% ( nal concentration of Ham-Cys:10 mM), 11.0 ± 5.0% (20 mM)] (Table 1) and the acquired 99m Tc-radiolabeled compound was unstable. On the other hand, 99m Tc radiolabeling reaction to give [ 99m Tc]Tc-(Ham-Cys) 2 in phosphate buffer (pH 7.4) proceeded with radiochemical yields of 68.7 ± 2.4% ( nal concentration of Ham-Cys: 10 mM) and 75.3 ± 4.5% (20 mM) (Table 1).…”

“…In addition, Ham makes it possible to easily produce 99m Tc-labeled compounds with a bivalent targeting scaffold because it forms 99m Tc-complexes with a metal-to-ligand ratio of 1:2 7 . Our group previously developed Ham-based 99m Tc radiolabeled SPECT imaging probes and demonstrated their properties for detecting their target biomolecules [9][10][11][12][13] . In these probes, the Ham group was directly incorporated into their chemical structures, that is to say, the reaction for induction of Ham group was not independent on the synthesis of those probes in most cases.…”