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Preparation and Evaluation of 99mTc-labeled Tridentate Chelates for Pre-targeting Using Bioorthogonal Chemistry
Published on: February 4, 2017
99mTc(CO)3-labeled pamidronate and alendronate for bone imaging
Elisa Palma1, João D G Correia, Bruno L Oliveira
1Unidade de Ciências Químicas e Radiofarmacêuticas, ITN, Estrada Nacional 10, 2686-953 Sacavém, Portugal.
Dalton Transactions (Cambridge, England : 2003)
|February 9, 2011
Summary
New technetium-based radiotracers show high bone uptake and improved targeting for bone imaging. These novel agents offer better bone-to-tissue ratios compared to (99m)Tc-MDP.
Area of Science:
- Radiochemistry
- Nuclear Medicine
- Biomedical Imaging
Background:
- Current bone scintigraphy agents like (99m)Technetium-methylenediphosphonate ((99m)Tc-MDP) have limitations including low specificity and long acquisition times.
- Development of novel bone-seeking radiotracers with improved properties is crucial for enhanced diagnostic accuracy.
Purpose of the Study:
- To synthesize and evaluate new fac-[(99m)Tc(CO)(3)](+)-based radiotracers for bone imaging.
- To improve chemical stability, bone targeting, and pharmacokinetic profiles compared to existing agents.
Main Methods:
- Synthesis of novel conjugates (pz-PAM and pz-ALN) with a pyrazolyl-diamine chelator and pamidronate or alendronate moieties.
- Radiolabeling with fac-[(99m)Tc(CO)(3)](+) to form stable complexes fac-[(99m)Tc(CO)(3)(pz-PAM)](-) (2a) and fac-[(99m)Tc(CO)(3)(pz-ALN)](-) (3a).
- In vitro hydroxyapatite binding assays and in vivo biodistribution studies in Balb-c mice and rats.
Main Results:
- High radiochemical yields (>95%) and stability of the new complexes (2a and 3a).
- Strong binding of 2a and 3a to hydroxyapatite, indicating bone affinity.
- Comparable high bone uptake (18.3 ± 0.6% I.D./g for 2a, 17.3 ± 6.1% I.D./g for 3a at 1h) similar to (99m)Tc-MDP (17.1 ± 2.4% I.D./g).
- Increased total excretion (66% I.D. for 2a, 67% I.D. for 3a at 1h) compared to (99m)Tc-MDP (49% I.D.).
- Higher bone-to-blood and bone-to-muscle ratios for 2a and 3a compared to (99m)Tc-MDP at 4h post-injection.
- Gamma camera imaging confirmed adequate biological profiles for bone imaging.
Conclusions:
- The novel fac-[(99m)Tc(CO)(3)](+)-based radiotracers (2a and 3a) demonstrate excellent chemical and biological properties for bone imaging.
- These new agents exhibit high bone uptake, strong hydroxyapatite binding, and favorable pharmacokinetic profiles, including increased excretion and improved bone-to-tissue ratios.
- The developed radiotracers represent promising alternatives to (99m)Tc-MDP for enhanced bone scintigraphy.
