Development of Alginate-Based Biodegradable Radioactive Microspheres Labeled with Positron Emitter through Click Chemistry Reaction: Stability and PET Imaging Study

Biodegradable radioactive microspheres labeled with positron emitters hold significant promise for diagnostic and therapeutic applications in cancers and other diseases, including arthritis. The alginate-based polymeric microspheres offer advantages such as biocompatibility, biodegradability, and improved stability, making them suitable for clinical applications. In this study, we developed novel positron emission tomography (PET) microspheres using alginate biopolymer radiolabeled with gallium-68 (⁶⁸Ga) through a straightforward conjugation reaction. Polyethylenimine (PEI)-decorated calcium alginate microspheres (PEI-CAMSs) were fabricated and further modified using azadibenzocyclooctyne-N-hydroxysuccinimide ester (ADIBO-NHS). Subsequently, azide-functionalized NOTA chelator (N₃-NOTA) was labeled with [⁶⁸Ga]Ga to obtain [⁶⁸Ga]Ga-NOTA-N₃, which was then reacted with the surface-modified PEI-CAMSs using strain-promoted alkyne-azide cycloaddition (SPAAC) reaction to develop [⁶⁸Ga]Ga-NOTA-PEI-CAMSs, a novel PET microsphere. The radiolabeling efficiency and radiochemical stability of [⁶⁸Ga]Ga-NOTA-PEI-CAMSs were determined using the radio-instant thin-layer chromatography-silica gel (radio-ITLC-SG) method. The in vivo PET images were also acquired to study the in vivo stability of the radiolabeled microspheres in normal mice. The radiolabeling efficiency of [⁶⁸Ga]Ga-NOTA-PEI-CAMSs was over 99%, and the microspheres exhibited high stability (92%) in human blood serum. PET images demonstrated the stability and biodistribution of the microspheres in mice for up to 2 h post injection. This study highlights the potential of biodegradable PET microspheres for preoperative imaging and targeted radionuclide therapy. Overall, the straightforward synthesis method and efficient radiolabeling technique provide a promising platform for the development of theranostic microspheres using other radionuclides such as ⁹⁰Y, ¹⁷⁷Lu, ¹⁸⁸Re, and ⁶⁴Cu.