Nuclear Uptake and Dosimetry of 64Cu-Labeled Chelator–Somatostatin Conjugates in an

64Cu radiopharmaceuticals have shown tumor growth inhibition in tumor-bearing animal models with a relatively low radiation dose that may be related to nuclear localization of the 64Cu in tumor cells. Here we address whether the nuclear localization of 64Cu from a 64Cu-labeled chelator–somatostatin conjugate is related to the dissociation of the radio-copper from its chelator. The 64Cu complex of 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA) has demonstrated instability in vivo, whereas 64Cu-CB-TE2A (CB-TE2A is 4,11-bis(carboxy-methyl)-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane) was highly stable. Methods: Receptor binding, nuclear uptake, internaliza-tion, and efflux assays were performed to characterize the inter-action with the somatostatin receptor and the intracellular fate of 64Cu-labeled chelator–peptide conjugates in A427-7 cells. From these data, the absorbed dose to cells was calculated. Results