Radiolabeling of biodegradable polymeric microspheres with [99mTc(CO)3]+ and in vivo biodistribution evaluation using MicroSPECT/CT imaging.

Poly(L-lactide) (PLA) microspheres tailored with a tridentate chelating group were radiolabeled with [(99m)Tc(H(2)O)(3)(CO)(3)](+) and optimized for labeling efficiency and stability. Various ligand-polymer blend compositions with commercial PLA (from 2% to 100%) were evaluated. Labeling efficiencies over 95% were achieved in a 5 min reaction using 100% of the ligand-polymer or within 15 min using a 5% ligand-polymer blend. The addition of 1.5% of PEGylated copolymer to the blend did not affect the labeling efficiency of these particles but changed their in vivo behavior. MicroSPECT/CT imaging showed significant uptake of non-PEGylated microspheres by the murine lung, while only the liver and spleen took up PEGylated microspheres. Such (99m)Tc radiolabeled biodegradable microspheres will be useful diagnostic imaging agents for visualization of the functioning reticuloendothelial system (RES). Similarly, other sizes of the same microspheres will allow imaging of lung perfusion, bone marrow, lymph and inflammation scintigraphy, and radioembolization therapy.