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 ANX-SPIO 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.