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

Hydroxamamide (Ham) is a thiol-free chelating agent that forms technetium-99m (99mTc)-complexes with a metal-to-ligand ratio of 1:2 under moderate reaction conditions. Therefore, Ham-based chelating agents will produce 99mTc-labeled compounds with a bivalent targeting scaffold. For their universal usage, we developed a novel Ham-based bifunctional chelating agent, “Ham-Mal”, with a maleimide group that can easily conjugate with a thiol group, for to preparing 99mTc-labeled bivalent ligand probes. Ham-Mal was synthesized by a four-step reaction, and then reacted with cysteine or c(RGDfC) to produce Ham-Cys or Ham-RGD. These precursors were reacted with 99mTcO4- for 10 min under room temperature to obtain 99mTc-(Ham-Cys)2 and 99mTc -(Ham-RGD)2. The cellular uptake level of 99mTc-(Ham-RGD)2 by U87MG (high Integrin ɑvβ3 expression) cells was significantly higher than that by PC3 (low Integrin ɑvβ3 expression) cells at 60 min after the incubation, and the uptake was significantly suppressed by pre-treatment for 15 min with excess c(RGDfK) peptide. In the in vivo study with U87MG/PC3 dual xenografted BALB/c-nu mice, the radioactivity of U87MG tumor tissue was significantly higher than that of PC3 tumor tissue at 360 min after the administration of 99mTc-(Ham-RGD)2. These results suggest Ham-Mal may have potential as a bifunctional chelating agent for 99mTc-labeled bivalent ligand probes.

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

Hydroxamamide (Ham) is a thiol-free chelating agent that forms technetium-99m (99mTc)-complexes with a metal-to-ligand ratio of 1:2 under moderate reaction conditions. Therefore, Ham-based chelating agents will produce 99mTc-labeled compounds with a bivalent targeting scaffold. For their universal usage, we developed a novel Ham-based bifunctional chelating agent, “Ham-Mal”, with a maleimide group that can easily conjugate with a thiol group, for to preparing 99mTc-labeled bivalent ligand probes. Ham-Mal was synthesized by a four-step reaction, and then reacted with cysteine or c(RGDfC) to produce Ham-Cys or Ham-RGD. These precursors were reacted with [99mTc]TcO4− for 10 min under room temperature to obtain [99mTc]Tc-(Ham-Cys)2 and [99mTc]Tc-(Ham-RGD)2. The cellular uptake level of [99mTc]Tc-(Ham-RGD)2 by U87MG (high Integrin ɑvβ3 expression) cells was significantly higher than that by PC3 (low Integrin ɑvβ3 expression) cells at 60 min after the incubation, and the uptake was significantly suppressed by pre-treatment for 15 min with excess c(RGDfK) peptide. In the in vivo study with U87MG/PC3 dual xenografted Balb/c-nu mice, the radioactivity of U87MG tumor tissue was significantly higher than that of PC3 tumor tissue at 360 min after the administration of [99mTc]Tc-(Ham-RGD)2. These results suggest Ham-Mal may have potential as a bifunctional chelating agent for 99mTc-labeled bivalent ligand probes.

Synthesis of a DOTA-C-glyco bifunctional chelating agent and preliminary in vitro and in vivo study of [68Ga]Ga-DOTA-C-glyco-RGD

A carbohydrate containing [68Ga]Ga-DOTA-RGD tracer was designed and demonstrated promising results for cancer diagnosis by positron emission tomography imaging.

Synthesis of novel technetium-99m tricarbonyl-HBED-CC complexes and structural prediction in solution by density functional theory calculation

HBED-CC ( N,N' -bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylene diamine- N,N' -diacetic acid, L 1 ) is a common bifunctional chelating agent in preparation of 68 Ga-radiopharmaceuticals. Due to its high stability constant for the Ga 3+ complex (logK GaL = 38.5) and its acyclic structure, it is well known for a rapid and efficient radiolabelling at ambient temperature with Gallium-68 and its high in vivo stability. [ 99m Tc][Tc(CO) 3 (H 2 O) 3 ] + is an excellent precursor for radiolabelling of biomolecules. The aim of this study was to develop a novel preparation method of 99m Tc-HBED-CC complexes. In this study, HBED-CC-NI (2,2'-(ethane-1,2-diylbis((2-hydroxy-5-(3-((2-(2-nitro-1H-imidazol-1-yl)ethyl)amino)-3-oxopropyl)benzyl)-azanediyl))-diacetic acid, L 2 ), a derivative of HBED-CC, was designed and synthesized. Both L 1 and L 2 were radiolabelled by [ 99m Tc][Tc(CO) 3 (H 2 O) 3 ] + successfully for the first time. In order to explore the coordination mode of metal and chelates, non-radioactive Re(CO) 3 L 1 and Re(CO) 3 L 2 were synthesized and characterized spectroscopically. Tc(CO) 3 L 1 and Tc(CO) 3 L 2 in solution were calculated by density functional theory and were analysed with radio-HPLC chromatograms. It showed that [ 99m Tc]Tc(CO) 3 L 2 forms two stable diastereomers in solution, which is similar to those of [ 68 Ga]Ga-HBED-CC complexes. Natural bond orbital analysis through the natural population charges revealed a charge transfer between [ 99m Tc][Tc(CO) 3 ] + and L 1 or L 2 . The experimental results showed that tricarbonyl technetium might form stable complex with HBED-CC derivatives, which is useful for the future application of using HBED-CC as a bifunctional chelating agent in developing new 99m Tc-radiopharmaceuticals as diagnostic imaging agents.

MANOTA: a promising bifunctional chelating agent for copper-64 immunoPET

A comparison of four bifunctional chelating agents showed superior behaviour of a new NOTA derivative for 64Cu labelling of antibody fragments.