177Lu-Labeled Eu-Doped Mesoporous SiO2 Nanoparticles as a Theranostic Radiopharmaceutical for Colorectal Cancer

Colorectal cancer is one of the most significant types of cancer, ranking second in the world's mortality cases. As colorectal cancer is often diagnosed at a late stage of disease progression, effective treatments are necessary. Therefore, radiotherapy has become a fundamental approach in the treatment of colorectal cancer, especially those based on the use of Lu-177. A potential approach to meet this challenge is the use of nanotechnology through the development of radionuclide-based nanomaterials. In this work, we investigated a SiO2-derived class of nanomaterials formed by the insertion of the coordination complex, based on Eu3+ and pyrimidine-2,6-dicarboxylic acid (DPA), into nanoparticles of amino-functionalized mesoporous silica (EuDPA/SiO2-NH2). The properties of the EuDPA/SiO2-NH2 nanoparticles were initially investigated by SEM, FT-IR, TGA, and luminescence. The cellular uptake of EuDPA/SiO2-NH2 nanoparticles into HT-29 cells was confirmed by fluorescence microscopy. Radioactivity was incorporated into the EuDPA/SiO2-NH2 nanoparticles by replacing a tracer quantity of Eu3+ sites with the lanthanide element Lu-177, which resulted in the composition of a dual-modality probe for both SPECT imaging and tumor radiotherapy. Analysis of Lu-177 loading into EuDPA/SiO2-NH2 particles showed efficient incorporation, up to 93% radioactivity into the final compound. The imaging potential of the Lu-177-EuDPA/SiO2-NH2 nanoparticles was investigated by SPECT/CT imaging, a subcutaneous HT-29 mouse model of colorectal cancer. Image analysis showed that tumor localization was maintained after intratumoral administration for up to 48 h. To evaluate the therapeutic potential of Lu-177-EuDPA/SiO2-NH2 nanoparticles, HT-29 xenografts were treated in vivo by direct intratumoral injection. Compared with control (PBS) treatment or treatment with unlabeled EuDPA/SiO2-NH2 nanoparticles, the treatment with Lu-177-EuDPA/SiO2-NH2 nanoparticles resulted in a significantly reduced tumor growth. Together, the results of this study results indicate that Lu-177-EuDPA/SiO2-NH2 is a promising agent for further development in SPECT imaging and clinical treatment of colorectal cancer.