Bone scintigraphy with 99mTechnetium-methylenediphosphonate (99mTc-MDP) or 99mTechnetium-hydroxymethylenediphosphonate (99mTc-HMDP) presents several limitations, namely low specificity, uncertainty in the radiopharmaceutical's molecular structure and long acquisition time after injection. Aiming to find bone-seeking radiotracers based on the core fac-[99mTc(CO)3]+ with improved chemical and biological properties, we synthesized new conjugates (pz-PAM and pz-ALN), comprising a pyrazolyl-diamine chelating unit (pz: N,N,N donor atom set) for metal stabilization and a pendant pamidronate (PAM) or alendronate (ALN) moiety for bone targeting. The reaction of the conjugates with fac-[99mTc(CO)3]+ yielded (> 95%) the stable complexes fac-[99mTc(CO)3(pz-PAM)]− (2a) and fac-[99mTc(CO)3(pz-ALN)]− (3a), which have been characterized by comparing their HPLC gamma-traces with the UV-vis traces of the Re surrogates 2 and 3, respectively. 2a and 3a bind strongly onto hydroxyapatite. The biodistribution studies in Balb-c mice have shown that 2a and 3a presented an high bone uptake (2a 18.3 ± 0.6% I.D./g, 3a 17.3 ± 6.1% I.D./g, at 1 h post injection), similar to 99mTc-MDP (17.1 ± 2.4% I.D./g, at 1 h post injection), with comparable clearance from most tissues and increased total excretion (2a 66% I.D., 3a 67% I.D. and 99mTc-MDP 49% I.D., at 1 h post injection). The bone-to-blood (2a 86.2, 3a 74.7) and the bone-to-muscle ratios (2a 77.7, 3a 79.0) are higher than the ones found for 99mTc-MDP (70.9, 47.9), at 4 h post injection. Planar whole-body gamma camera images of the rats injected with the 99mTc(CO)3-labeled pamidronate (2a) and alendronate (3a) confirmed the overall adequate biological profile of the new radiotracers for bone imaging.
SCHEDULED MAINTENANCE
Please wait while we load your content...
