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A Practical Guide for the Production and PET/CT Imaging of 68Ga-DOTATATE for Neuroendocrine Tumors in Daily Clinical Practice
Published on: April 17, 2019
Vapreotide labeled with Tc-99m for imaging tumors
1THOMAS JEFFERSON UNIV,DEPT RADIOL,DIV NUCL MED,PHILADELPHIA,PA 19107. VET AFFAIRS MED CTR,ENDOCRINE POLYPEPTIDE & CANC INST,NEW ORLEANS,LA 70146. TULANE UNIV,SCH MED,DEPT MED,NEW ORLEANS,LA 70146.
Abstract:
Vapreotide (RC-160), an octapeptide analog of somatostatin, has a high affinity for somatostatin receptor subtypes SSTR2 and SSTR5. Vapreotide binds differently to the tumors of the breast, ovary, exocrine pancreas, prostate and colon, than octreotide another octapeptide analog of somatostatin. Vapreotide was labeled with Tc-99m, a radionuclide highly suitable for scintigraphic imaging. The labeling procedure was simple, produced >70% yields and could be applicable to label other peptides containing a cystine bridge. HPLC analysis showed that the tracer was stable when Tc-99m-RC-160 was challenged with 100 fold molar excess DTPA (diethylenetriaminepentaacetic acid), HSA (human serum albumin) or cysteine and incubated at 37 degrees C for 4 h. HPLC analysis of urine samples obtained from mice that received Tc-99m-RC-160 showed that the preparation was stable in vivo. Rat brain cortex membrane receptor displacement assays showed that the Kd values for Tc-99m-RC-160 (71x10(-9) M) and Tc-99m-octreotide (86x10(-9) M) (Sandostatin(R)) were in nM range, and were similar to that for I-125-RC-160 (46x10(-9) M). High binding affinity of Tc-99m-RC-160 for human breast tumor cells SKBR-3 was also observed. These results suggest that Tc-99m-RC-160 is worthy of evaluation as an agent for scintigraphic imaging of tumors rich in somatostatin receptor subtypes SSTR2 and SSTR5.
Insights
Technetium-99m-labeled vapreotide (Tc-99m-RC-160) shows high affinity for somatostatin receptors SSTR2 and SSTR5. This agent is stable and suitable for scintigraphic imaging of tumors expressing these receptors.
Area of Science:
- Nuclear Medicine
- Radiopharmaceutical Chemistry
- Oncology
Background:
- Somatostatin analogs are crucial in diagnosing and treating neuroendocrine tumors.
- Vapreotide (RC-160) is an octapeptide analog with high affinity for somatostatin receptor subtypes SSTR2 and SSTR5.
- Targeting somatostatin receptors is a key strategy for tumor imaging.
Purpose of the Study:
- To develop and evaluate technetium-99m-labeled vapreotide (Tc-99m-RC-160) as a scintigraphic imaging agent.
- To assess the stability and binding characteristics of Tc-99m-RC-160.
Main Methods:
- Simple radiolabeling of vapreotide with Tc-99m achieved high yields (>70%).
- High-performance liquid chromatography (HPLC) was used to confirm tracer stability in vitro and in vivo.
- Receptor binding assays (Kd values) were performed using rat brain cortex membranes and human breast tumor cells (SKBR-3).
Main Results:
- Tc-99m-RC-160 demonstrated high binding affinity (nM range) for somatostatin receptors, comparable to octreotide.
- The radiotracer exhibited excellent stability in vitro when challenged with DTPA, HSA, or cysteine.
- In vivo stability was confirmed by HPLC analysis of urine samples from mice.
- High binding affinity was observed for human breast tumor cells (SKBR-3).
Conclusions:
- Tc-99m-RC-160 is a stable and effective radiotracer for scintigraphic imaging.
- Its high affinity for SSTR2 and SSTR5 makes it a promising agent for visualizing tumors expressing these receptors.
- Further evaluation of Tc-99m-RC-160 for clinical tumor imaging is warranted.
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