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Cross-Species Quantitative Benchmarking of SSTR2 Radioligands in Fresh-Frozen Brain Sections: An Adaptable Framework
Caitlin McCutcheon1, Zachary Lawrence1, Marie James1
1Translational Sciences, Ratio Therapeutics, 19 Drydock Ave, Boston, MA, 02210, USA.
Molecular Imaging and Biology
|July 9, 2026
Summary
A new method accurately quantifies somatostatin receptor subtype 2 (SSTR2) binding across species. This platform aids in developing targeted radioligand therapies for cancers like neuroendocrine tumors.
Area of Science:
- Pharmacology
- Oncology
- Radiochemistry
Background:
- Somatostatin receptor subtype 2 (SSTR2) is overexpressed in various cancers, including neuroendocrine tumors, driving interest in SSTR2-targeted radioligand therapies.
- Clinical success of SSTR2 radioligand therapy necessitates advanced platforms for developing next-generation ligands.
- Quantitative cross-species binding data are crucial for translating preclinical findings to clinical radiotherapeutic applications.
Purpose of the Study:
- To develop and validate a quantitative platform for assessing SSTR2 ligand binding in native tissues across multiple species.
- To enable precise characterization of novel SSTR2 ligands and radiometal conjugates for radiotherapeutic development.
- To establish a reproducible method for comparing ligand affinities and densities, facilitating early-stage drug development decisions.
Main Methods:
- Utilized fresh-frozen tissue sections from mouse, rat, cynomolgus monkey, and human brain for SSTR2 binding assays.
- Employed high-affinity antagonist [177Lu]Lu-DOTA-LM3 with non-equilibrium kinetics and equilibrium binding methods.
- Applied section-wipe/gamma counting for absolute quantification without isotope standards; confirmed localization via autoradiography and immunohistochemistry.
Main Results:
- [177Lu]Lu-DOTA-LM3 demonstrated specific, saturable binding to a single class of high-affinity SSTR2 sites across all tested species.
- Autoradiography signals precisely co-localized with SSTR2-rich regions identified by immunohistochemistry.
- Radiometal conjugation impacted ligand properties, with lutetium preserving affinity while gallium significantly reduced it.
Conclusions:
- The developed native-tissue platform offers efficient, translatable, and reproducible absolute quantification of SSTR2 ligand binding.
- This method eliminates the need for tissue standards, streamlining the selection of chemotypes and radiometals.
- The platform supports informed species-bridging expectations, crucial for advancing SSTR2-targeted radiotherapies before in vivo studies.
