131 I-Labeled Multifunctional Polyphosphazene Nanospheres for SPECT Imaging-Guided Radiotherapy of Tumors.

Design of theranostic nanoplatforms represents a major topic for current nanomedicine. Here, the preparation of multifunctional poly(cyclotriphosphazene-co-polyethylenimine) nanospheres (PNSs) labeled with radionuclide 131 I for single photon emission computed tomography (SPECT) imaging-guided radiotherapy of tumors is reported. In this work, PNSs are prepared using hexachlorocyclotriphosphazene as a crosslinker to crosslink branched polyethylenimine (PEI) via a nucleophilic substitution reaction, modified with 3-(4'-hydroxyphenyl) propionic acid-OSu (HPAO) for 131 I labeling, and reacted with 1,3-propane sulfonate (1,3-PS) to render the particles with antifouling property, followed by acetylation of the remaining surface amines and labeling with 131 I. The acquired PNS.NHAc-HPAO(131 I)-PS particles are well characterized. It is shown that the multifunctional PNSs with an average size of 184 ± 29.3 nm exhibit favorable antifouling properties, high 131 I labeling efficiency (76.05 ± 3.75%), and excellent radiostability and colloidal stability. With these properties owned, the developed PNS.NHAc-HPAO(131 I)-PS spheres enable much more efficient SPECT imaging and radiotherapy of a xenografted tumor model in vivo than the PEI counterpart material (PEI.NHAc-HPAO(131 I)-PS). The developed PNSs may be used as a versatile platform for further development of different forms of nanomedicine for various biomedical applications.