Somatostatin Receptor Analogs ( 68 Ga-DOTATOC, 68 Ga-DOTANOC, 68 Ga-DOTATATE)

Neuroendocrine tumors (NETs) are rare neoplasms originating from neuroendocrine cells and characterized by the property of producing hormones and biogenic amines. NETs can present an indolent clinical course, thus diagnosis may be delayed when disease is at an advanced stage. A number of different techniques can be applied for NET diagnosis and localization: magnetic resonance, contrast-enhanced computed tomography, gastrointestinal endoscopy, and ultrasonography. Since NETs are known to overexpress somatostatin receptors, somatostatin receptor scintigraphy (SRS) with 111In-pentetreotide has been widely used for NET diagnosis, staging and monitoring response to treatment. Nevertheless, conventional scintigraphic approach presents some limitations due to poor spatial resolution. Positron emission tomography (PET) with 18F-fluorodeoxyglucose has a limited role for the imaging of NETs that are slow-growing neoplasms with reduced expression of glucose transporter receptors. To overcome these drawbacks, three different radiopharmaceuticals binding to somatostatin receptors have been introduced: 68Ga-DOTA-Phe1-Tyr3-Octreotide (TOC), 68Ga-DOTA-NaI3-Octreotide (NOC), and 68Ga-DOTA-Tyr3-Octreotate (TATE). This chapter is aimed to review these 68Ga-DOTA-compounds with particular emphasis on their synthesis, pharmacokinetic/pharmacodynamic properties and on the clinical application in NETs diagnosis and follow-up.