114mIn, a candidate for radionuclide therapy: low-energy cyclotron production and labeling of DTPA-D-Phe-octreotide

Abstract

A method for production of carrier-free 114mIn (half-life 49.5 days), which is a potential radionuclide for radionuclide therapy of slowly growing tumors, is presented. A target consisting of five enriched cadmium ( 114Cd) foils, each 50 μm thick, was irradiated by protons (from 12.6–6.5 MeV) giving a target yield of 0.8 MBq/μAh. A simple and cost-efficient thermal diffusion method was used for the separation. The irradiated target foils were heated for 2 h at 306°C and then etched in 0.05 M HCl. The obtained cadmium/indium solution was purified using a cation ion-exchange resin (AG 1 × 8, Bio-Rad Laboratories, Hercules, CA USA). An overall yield of approximately 60% was obtained, whereas the loss of the target material was <1% per separation cycle. The 114mIn production gave 114mIn with high specific radioactivity and was successfully used to label diethylenetriamine pentaacetic acid (DTPA)-D-Phe-octreotide. Furthermore, no difference in biodistribution between [ 114mIn]- and [ 111In]-DTPA-D-Phe 1-octreotide in tumor-bearing nude mice was seen. The high radionuclide uptake in the tumors indicates a good receptor binding of the labeled octreotide.