Fluorescent somatostatin receptor probes for the intraoperative detection of tumor tissue with long-wavelength visible light
Related Experiment Video
Updated: Sep 30, 2026
Tissue-simulating Phantoms for Assessing Potential Near-infrared Fluorescence Imaging Applications in Breast Cancer Surgery
Published on: September 19, 2014
Walter Mier1, Barbro Beijer, Keith Graham
1Department of Nuclear Medicine, University of Heidelberg, INF 400, D-69120 Heidelberg, Germany. walter_mier@med.uni-heidelberg.de
Abstract:
Targeted fluorescent dyes are of substantial value for the intraoperative delineation of primary tumors and metastatic lesions. For this purpose long-wavelength red light (lambda=550-650 nm) offers advantages because of good tissue penetration and direct visibility. Since somatostatin receptors (SSTR) are overexpressed in a number of tumors, a series of potentially tumor-selective peptide-dye conjugates were synthesized by solid-phase peptide synthesis (SPPS). The octapeptides octreotate, Tyr(3)-octreotate and Tyr(3)-octreotide were employed and exhibited high affinity for somatostatin receptors (SSTR). The fluorescent dyes rhodamine 101, sulforhodamine B acid chloride, sulforhodamine 101 or rhodamine B isothiocyanate were conjugated either directly or via spacers, for example the peptidase-labile pentapeptide sequence Ala-Leu-Ala-Leu-Ala. The conjugates were completely assembled on the solid support: Fmoc-SPPS, cyclization via a disulfide linkage, N-terminal attachment of a spacer, and linkage to the fluorescent dye. An in vitro competition assay revealed that the conjugates bind to SSTRs with IC(50) values between 0.7 and 89 nM. The conjugates were generally stable to hydrolysis at pH 7-8 in buffer or serum. However, the rhodamine 101 conjugates revealed a loss of absorption at alkaline pH due to conversion to a neutral spirolactam form, as characterized by NMR.
Insights
New fluorescent peptide-dye conjugates targeting somatostatin receptors (SSTRs) show promise for intraoperative tumor detection. These novel compounds offer improved visibility for primary tumors and metastatic lesions during surgery.
Area of Science:
- Bioconjugation Chemistry
- Medical Imaging
- Oncology Diagnostics
Background:
- Intraoperative tumor delineation is crucial for surgical success.
- Targeted fluorescent dyes offer enhanced visualization of tumors and metastases.
- Somatostatin receptors (SSTRs) are frequently overexpressed in various cancers.
Purpose of the Study:
- To synthesize and characterize novel peptide-dye conjugates for SSTR-targeted tumor imaging.
- To evaluate the binding affinity and stability of these conjugates for potential clinical application.
Main Methods:
- Solid-phase peptide synthesis (SPPS) was used to create octapeptide conjugates (octreotate, Tyr(3)-octreotate, Tyr(3)-octreotide) with rhodamine dyes.
- Conjugation was achieved directly or via spacers, including a peptidase-labile sequence.
- In vitro competition assays assessed binding affinity to SSTRs; stability was evaluated at physiological pH.
Main Results:
- Synthesized peptide-dye conjugates demonstrated high affinity for SSTRs, with IC(50) values ranging from 0.7 to 89 nM.
- The conjugates exhibited good stability in buffer and serum at pH 7-8.
- Rhodamine 101 conjugates showed pH-dependent spectral changes due to spirolactam formation.
Conclusions:
- Novel SSTR-targeted peptide-dye conjugates are effective for potential tumor visualization.
- The developed conjugates possess favorable binding affinities and stability profiles.
- Further investigation into dye-specific stability is warranted for optimized imaging agents.
