Preparation and preliminary biological evaluation of a 166Ho labeled polyazamacrocycle for possible use as an intravascular brachytherapy (IVBT) agent

166Ho can be considered as a potential radionuclide for intravascular brachytherapy (IVBT) using liquid-filled balloons owing to its suitable nuclear decay characteristics. The possibility of producing 166Ho with adequate specific activity using moderate flux reactors and natural holmium target makes it an attractive alternative of 188Re for developing IVBT agents. Keeping in mind the high thermodynamic stability of lanthanide complexes with polyazamacrocycles, 166Ho complex of 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA) was prepared and studied for its suitability as a possible agent for IVBT. 166Ho was produced with adequate specific activity and high radionuclidic purity by irradiating natural Ho2O3 powder. TETA was synthesized by a single step procedure using cyclam as the starting material. 166Ho–TETA complex was prepared with excellent radiochemical purity and the complex was found to retain its stability for 7 days at room temperature. Biodistribution studies carried out in Wistar rats showed major renal clearance of the injected activity with almost no retention in any of the vital organ/tissue.