Preparation and biodistribution study of 99mTc-EC-Annexin-SPIO as a tracer of radiation induced apoptosis in mice model

Introduction: Apoptosis is a major consequence of ionizing radiation in proliferative tissues and quantification of the apoptotic cells could be helpful for noninvasive assessment and estimation of the radiation absorbed dose. Annexin V conjugated with super paramagnetic iron oxide nanoparticles (ANX-SPIO) is a biological probe for detection of apoptotic cells using magnetic resonance imaging. This study aimed at assessing the biodistribution alterations of the labeled ANXSPIO within the mice body shortly after exposure to different doses of ionizing radiation. Methods: 99mTc-EC-ANX-SPIO was prepared and its in vitro stability was tested. The binding affinity of radiocomplex to apoptotic cells was validated in vitro. Mice irradiated whole body with 2, 4 and 6 Gy (60Co gamma rays) and six hours later, radiocomplex was administrated intravenously and the biodistribution study was conducted 0.5, 1 and 2 hours later. Results: The radiochemical purity of radiocomplex was 94% ± 3.4% and it showed a good stability in PBS and serum. The radiocomplex maintained its efficacy for in vitro binding to apoptotic cells. radiocomplex accumulated in the bone marrow of all irradiated mice (p < 0.05). However, statistical analysis did not show significant correlation between the %ID/g of the femoral bones and the received radiation doses. Conclusion: Quantification of ANX-SPIO in bone marrow can be used as an indicator for radiation exposure but development and optimization of the assay are necessary for discrimination between different radiation doses.