In-114m, a candidate for radionuclide therapy: Low-energy cyclotron production and labeling of DTPA-D-Phe(1)-octreotide

A method for production of carrier-free In-114m (half-life 49.5 days), whic h is a potential radionuclide for radionuclide therapy of slowly growing tu mors, is presented. A target consisting of five enriched cadmium (Cd-114) f oils, each 50 mu m thick, was irradiated by protons (from 12.6-6.5 MeV) giv ing a target yield of 0.8 MBq/mu Ah. A simple and cost-efficient thermal di ffusion method was used for the separation. The irradiated target foils wer e heated for 2 h at 306 degrees C and then etched in 0.05 M HC1. The obtain ed cadmium/indium solution was purified using a cation ion-exchange resin ( AG 1 x 8, Bio-Rad Laboratories, Hercules, CA USA). An overall yield of appr oximately 60% was obtained, whereas the loss of the target material was <1% per separation cycle. The In-114m production gave In-114m with high specif ic radioactivity and was successfully used to label diethylenetriamine pent aacetic acid (DTPA)-D-Phe(1)-octreotide. Furthermore, no difference in biod istribution between [In-114]- and [In-111]-DTPA-D-Phe(1)-octreotide in tumo r-bearing nude mice was seen. The high radionuclide uptake in the tumors in dicates a good receptor binding of the labeled octreotide. NUCL MED BIOL 27 ;2:183-188, 2000. (C) 2000 Elsevier Science Inc. All rights reserved.