A New Fluorine-18 Somatostatin Tracer for PET Imaging of Neuroendocrine Tumors

A new fluorine-18-labeled somatostatin analog ([Al18F]NODA-MPAA-HTA) was synthesized with 60–80% radiochemical yield and >95% purity. It binds all five somatostatin receptor subtypes and showed a binding affinity of 8.77 nM for SSTR2. In mice bearing SSTR2-positive tumors, the tracer achieved tumor-to-muscle uptake ratios greater than 5-fold, producing high-contrast PET images with no defluorination detected in vivo.

The researchers designed a peptide-based radiotracer by conjugating fluorine-18 to a modified KE108 somatostatin analog using aluminum-fluoride chelation chemistry. They tested its stability in saline and bovine serum, measured cellular uptake and receptor binding affinity in SSTR2-expressing cells, and performed micro-PET imaging and biodistribution studies in tumor-bearing mice.

Current PET imaging of neuroendocrine tumors primarily uses gallium-68-labeled somatostatin analogs, but fluorine-18 has advantages — its longer half-life (110 minutes vs. 68 minutes) and easier production could make these scans more widely available. This new tracer targets all five somatostatin receptor subtypes rather than just SSTR2, potentially improving detection of tumors that express different receptor profiles.

Peptide-based radiotracers are central to the 'theranostics' revolution in oncology, where the same peptide scaffold is used for both imaging and targeted radiation therapy. Developing fluorine-18 versions of somatostatin analogs could democratize PET imaging for neuroendocrine tumors by reducing dependence on cyclotron-adjacent gallium-68 generators, making these critical scans available at more hospitals.

This is a preclinical study conducted only in cell lines and mice — no human imaging data were collected. The tumor model used cells engineered to overexpress SSTR2, which may not reflect the heterogeneous receptor expression found in actual patient tumors. Long-term toxicity and pharmacokinetics in larger animal models were not assessed.