Cationic technetium and rhenium complexes with pendant carbohydrates

Area of Science:

• Radiopharmaceutical Chemistry
• Coordination Chemistry
• Biomedical Imaging

Background:

• Dipicolylamine (DPA) derivatives are effective chelators for radiometals.
• Carbohydrate conjugation can influence the biodistribution and targeting of chelates.
• Development of novel radiotracers for diagnostic imaging requires careful design of chelating agents and radiometals.

Purpose of the Study:

• To synthesize and characterize novel carbohydrate-conjugated dipicolylamine chelators.
• To investigate the complexation of these chelators with technetium-99m (99mTc) and rhenium (Re).
• To evaluate the biological properties, including metabolism and biodistribution, of the resulting radiometal complexes.

Main Methods:

• Synthesis and characterization of three carbohydrate-conjugated dipicolylamine chelators (L(1), L(2), L(3)).
• Complexation of chelators with [M(CO)(3)](+) core (M=Tc, Re).
• Radiolabeling with [(99m)Tc(CO)(3)(H(2)O)(3)](+) and [(186)Re(CO)(3)(H(2)O)(3)](+).
• Assessment of hexokinase substrate potential.
• In vivo biodistribution studies of 99mTc complexes in animal models.

Main Results:

• Successful synthesis and characterization of chelators L(1), L(2), and L(3).
• High radiolabeling yields achieved for both 99mTc (>98%) and Re (>80%).
• Chelators and their Re-complexes were not metabolized by hexokinase.
• 99mTc complexes exhibited rapid clearance from most tissues, with >75% activity cleared from kidneys and liver within 2 hours post-injection.

Conclusions:

• Carbohydrate-conjugated dipicolylamine chelators efficiently complex with 99mTc and Re.
• The resulting radiometal complexes demonstrate favorable pharmacokinetic profiles with fast clearance.
• Lack of hexokinase metabolism suggests these complexes may avoid certain metabolic pathways, potentially useful for imaging applications.