Somatostatin receptor subtype 2-mediated uptake of radiolabelled somatostatin analogues in the human kidney

Purpose Renal irradiation is a dose-limiting factor in peptide receptor radionuclide therapy using radiolabelled somatostatin analogues. This irradiation is mainly caused by reabsorption of radiolabelled peptides in the proximal tubule. In the human kidney, somatostatin receptors are expressed in the vasa recta, tubuli and glomeruli. It is not clear to what extent these receptors contribute to the total kidney radioactivity uptake. Methods Retrospectively, ¹¹¹In-DTPA⁰]octreotide scans of ten selected patients with carcinoids (well-differentiated gastrointestinal endocrine tumour) with liver metastases were evaluated. For each patient, two scans were obtained: one scan was performed without (control) and one during treatment with unlabelled octreotide. Kidney, tumour, spleen and liver uptake was measured in both scans. Results The interval between the two scans per patient varied from 50 to 397 days. Octreotide treatment substantially lowered kidney ¹¹¹In-DTPA⁰]octreotide uptake in eight out of ten patients. Kidney uptake in all patients was reduced to 82%±15% of control, (p < 0.01). A correlation between kidney uptake and spleen uptake was found (r=0.67, p < 0.05). Serum creatinine was unchanged. Surprisingly, tumour and liver ¹¹¹In-DTPA⁰]octreotide uptake was not significantly influenced by unlabelled octreotide therapy, but spleen uptake was significantly lowered by treatment (30.6% of control, p < 0.002). Conclusion We conclude that the somatostatin receptor plays a role in the total renal uptake of radiolabelled somatostatin analogues. The long interval between scans might explain the finding that tumour and liver metastasis uptake of ¹¹¹In-DTPA⁰]octreotide was unchanged. Further studies are needed to confirm and eludicate the results of this study.