Preparation and biodistribution of [67Ga]-insulin for SPECT purposes

Human recombinant insulin was successively labeled with [67Ga]-gallium chloride after conjugation with freshly prepared cyclic DTPA-dianhydride (ccDTPA). The best results of the conjugation were obtained by the addition of 0.5 ml of an insulin pharmaceutical solution (5 mg/ml, in phosphate buffer, pH = 8) to a glass tube precoated with DTPA-dianhydride (0.01 mg) at 25°C with continuous mild stirring for 30 min. Radiothin-layer chromatography (RTLC), instant thin-layer chromatography (ITLC) and high-performance liquid chromatography (HPLC) showed overall radiochemical purity higher than 96% in optimized conditions (specific activity = 300 500 MBq/mg, labeling efficiency 77%). Preliminary in vivo studies with normal rats were performed to determine the biodistribution of the radiotracer up to 110 h. They showed a high liver uptake of the tracer which is consistent with other reported radiolabeled insulins.