Background: Somatostatin subtype 2 receptor (sst2)-targeted tumor imaging with [(111)In-DTPA0]octreotide is an established method for scintigraphic detection of neuroendocrine tumors. [99mTc]Demotide ([99mTc-N4-bzdg0, Tyr3]octreotide), presented herein, is a potential sst2-targeting radiotracer based on 99mTc.
Materials and methods: Demotide was synthesized in solution and labelled with 99mTc in alkaline medium. The in vitro properties of Demotide and [99mTc]Demotide were tested in sst2-expressing CA20948 cells and rat tissues, while biodistribution was studied in Lewis rats bearing CA20948 tumors.
Results: During labelling, [99mTc]Demotide was obtained in >98% yields and typical 1 mCi/nmol specific activities. Demotide showed in vitro sub-nM affinity for the sst2. While rapidly internalizing into CA20948 cells, [99mTc]Demotide localized effectively in CA20948 implants (2.2 +/- 1.1% ID/g at 1 h post injection) and in target organs in rats via a sst-mediated process and cleared rapidly via the kidneys.
Conclusion: The above favorable characteristics validate [99mTc]Demotide as a promising 99mTc-radiotracer for the targeted-imaging of sst2-positive tumors.