Preparation and biodistribution of [111In]-rHuEpo for erythropoietin receptor imaging

Human recombinant erythropoietin (EPO) was successively labeled with [111In]-indium chloride after conjugation with freshly prepared cyclic DTPA-dianhydride (ccDTPA). The best results of the conjugation were obtained by the addition of 100 i.u. of an EPO pharmaceutical solution (in phosphate buffer, pH 7.5) to a glass tube pre-coated with DTPA-dianhydride (0.01 mg) at 25 deg C with continuous mild stirring for 30 minutes. Radio thin layer chromatography (RTLC), instant thin layer chromatography (ITLC) and high performance liquid chromatography (HPLC) showed overall radiochemical purity of higher than 95% at optimized conditions (specific activity = 1.2-1.5 GBq/mg, labeling efficiency 80%). Preliminary in vivo studies in normal rat model was performed to determine the biodistribution of the radiotracer up to 1 hour using scarification. The high kidney uptake of the tracer was consistent with the reported EPO receptor distribution. (author)