Radioisotope carrying polyethylene oxide-polycaprolactone copolymer micelles for targetable bone imaging

The aim of this research is to develop polymeric micelle system as a targetable bone imaging carriers without nonspecific phagocytosis which is made of polyethylene oxide (PEO) and polycaprolactone (PCL). Diamino-PEO, which has two amino groups in its structure, was used to conjugate both PCL and ligand for specific radioisotope. PCL was conjugated to one amino group of diamino-PEO by using diaminohexyl cyclocarbodiimide (DCC), coupling agent. Hydroxyphenylpropionic acid (HPP), diethylenetriamine pentaacetic acid (DTPA) and mercaptoacetyl glycine glycidyl glycine (MAG3), as ligands for specific radioisotopes, were coupled to the rest of amino group of diamino-PEO by the same method as described. Formation of ligand-conjugated block copolymers, critical micelle concentration (CMC) of the copolymers, hydrodynamic radii, and morphology of the micelles were investigated. Besides, 125I-labelling efficiency and biodistribution of the micelles were examined. PEO-PCL block copolymer micelles demonstrated CMC of 25 mg/l and size of 60 nm, which may be adequate for blood vessel and bone imaging. 125I-labelling efficiency was above 90%, and was more stable at human serum for 24 h. 125I-labelled polymeric micelles showed higher blood maintenance and bone uptake when compared to stannous colloid, used as a control. A noticeable decrease in liver or spleen uptake could be achieved by the micelles. Therefore, radioisotope carrying PEO-PCL micelle system was suggested as a useful tool for effective diagnostic bone targeting and imaging.