Positron emission tomography study on pancreatic somatostatin receptors in normal and diabetic rats with 68Ga-DOTA-octreotide: A potential PET tracer for beta cell mass measurement

Diabetes mellitus (DM) is a metabolic disorder characterized by hyperglycemia, and the loss or dysfunction of pancreatic beta cells has been reported before the appearance of clinical symptoms and hyperglycemia. To evaluate beta cell mass (BCM) for improving the detection and treatment of DM at earlier stages, we focused on somatostatin receptors that are highly expressed in the pancreatic beta cells, and developed a positron emission tomography (PET) probe derived from octreotide, a metabolically stable somatostatin analog. Octreotide was conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), a chelating agent, and labeled with 68Gallium (68Ga). After intravenous injection of 68Ga-DOTA-octreotide, a 90-min emission scan of the abdomen was performed in normal and DM model rats. The PET studies showed that 68Ga-DOTA-octreotide radioactivity was highly accumulated in the pancreas of normal rats and that the pancreatic accumulation was significantly reduced in the rats administered with an excess amount of unlabeled octreotide or after treatment with streptozotocin, which was used for the chemical induction of DM in rats. These results were in good agreement with the ex vivo biodistribution data. These results indicated that the pancreatic accumulation of 68Ga-DOTA-octreotide represented specific binding to the somatostatin receptors and reflected BCM. Therefore, PET imaging with 68Ga-DOTA-octreotide could be a potential tool for evaluating BCM.