Preparation and evaluation of [67Ga]-DTPA-β-1-24- corticotrophin in normal rats

beta-1-24-corticotrophin was successively labeled with [Ga-67]-gallium chloride after residulation with freshly prepared cyclic DTPA-dianhydride. The best results of the conjugation were obtained by the addition of 1 ml of a beta-1-24-corticotrophin pharmaceutical solution (1mg/mL, pH = 6.5) to a glass tube pre-coated with DTPA-dianhydride (0.01 mg) at 25 degrees C with continuous mild stirring for 30 min. Radio-thin layer chromatography showed an overall radiochemical purity of > 90% at optimized conditions after labeling. HPLC showed a radiochemical purity more than 95% (specific activity = 300-500 MBq/mg, labeling efficiency 77%). The stability of the radioconjugate was tested in presence of human serum at 37 degrees C. Preliminary in vivo studies in normal rats were performed to determine the biodistribution of the radioirnmunoconjugate up to 30 min. Lungs showed to have the major tracer uptake which is consistent with the natural distribution of ACTH receptors in human body. Pretreatment of animals with cold peptide following labeled compound administration reduced lung uptake at least 10 and 3 times after 15 and 30 min, respectively, as well as significant decrease in adrenal uptake after 15 min. These data support the specific receptor binding of the radiolabeled compound. This tracer can be used in detection of ACTH receptor in lung and adrenal malignancies.