First clinical evidence that imaging with somatostatin receptor antagonists is feasible

Preclinical studies have indicated that somatostatin receptor (sst)-expressing tumors demonstrate higher uptake of radiolabeled sst antagonists than of sst agonists. In this study, we evaluated whether imaging with sst antagonists was feasible in patients. Methods: Biodistribution and tumor uptake of the sst antagonist ¹¹¹In-DOTA-pNO₂-Phe- c(DCys-Tyr-DTrp-Lys-Thr-Cys)DTyrNH₂ (¹¹¹In-DOTA-BASS) were studied in 5 patients with metastatic thyroid carcinoma or neuroendocrine tumors. Findings were compared with ¹¹¹In-pentetreotid ( ¹¹¹In-DTPA-octreotide) scan. Results: No adverse effects of ¹¹¹In-DOTA-BASS (20 μg) were observed. ¹¹¹In-DOTA-BASS detected 25 of 28 lesions, whereas ¹¹¹In-DTPA-octreotide detected only 17 of 28 lesions. In the same patient, ¹¹¹In-DOTA-BASS showed higher tumor and lower renal uptake than ¹¹¹In-DTPA-octreotide (3.5 ± 2.8 percentage injected activity [%IA] vs. 1.0 ± 0.99%IA and 1.5 ± 0.3%IA vs. 2.3 ± 0.7%IA) at 4 h after injection. Conclusion: Imaging of neuroendocrine tumors with sst antagonists is clinically feasible. The favorable human biodistribution data suggest that sst antagonists could significantly affect peptide receptor-mediated imaging and therapy.