Preparation and biodistribution study of Ga-gallium calcitonin

Introduction: In order to develop a radiolabeled calcitonin (CT) derivative for receptor imaging studies, CT was successively labeled with Ga-gallium chloride. Methods: The best results of the conjugation were obtained by the addition of 0.5 ml of a CT nasal pharmaceutical solution (1100 IU) to a glass tube pre-coated with DTPA-dianhydride (0.01 mg) at 25C with continuous mild stirring for 30 min. Results: After solid phase purification of the radiolabeled hormone, instant thin layer chromatography (ITLC) showed radiochemical purity of higher than 95 % at optimized conditions (specific activity =67-134 KBq/IU, labeling efficiency 70%). Ga-DTPA-CT mainly accumulates in the liver. Conclusion: Preliminary in vivo studies (ID/g%) in male wild-type rats showed significant liver uptake of the tracer after 24 hours. Ga-DTPA-CT can be a suitable probe for biodistribution study of CT receptors in various physiological as well as neoplastic lesions with over-expressed calcitonin receptors.