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Labeling of polypeptides with technetium-99m using a dextran spacer
A Holmberg1, M Marquez, J E Westlin
1Department of Oncology, University Hospital, Uppsala, Sweden.
Cancer Research
|December 1, 1995
Summary
This study enhances radioimmunoscintigraphy by coupling biomolecules like antibodies to dextran, enabling efficient technetium-99m labeling. This method preserves specific binding and significantly extends the in vivo half-life of agents like somatostatin.
Area of Science:
- Bioconjugation Chemistry
- Radiopharmaceutical Development
- Molecular Imaging
Background:
- Radioimmunoscintigraphy is crucial for cancer detection and evaluation.
- Technetium-99m (99mTc) is a preferred radionuclide for radiolabeling due to its availability and physical properties.
Purpose of the Study:
- To develop a method for labeling biomolecules with 99mTc using dextran as a linker.
- To evaluate the preservation of specific binding and in vivo stability of dextran-conjugated agents.
Main Methods:
- Coupling dextran to a monoclonal anticytokeratin antibody, epidermal growth factor, and somatostatin via stable amine bonds.
- Labeling the dextran moiety with 99mTc, achieving 60-94% labeling efficiency.
- Assessing specific binding of labeled conjugates to target cells or tissues and evaluating in vivo plasma half-life in rats.
Main Results:
- The dextranation process preserved >90% antibody activity and >90% specificity for epidermal growth factor binding to tumor cells.
- Somatostatin conjugates showed approximately 40% specific binding to rat adrenal homogenates.
- Somatostatin-dextran exhibited a significantly enhanced plasma half-life in rats, with a two-compartment profile of 4 and 8 hours.
Conclusions:
- Dextran conjugation is an effective strategy for 99mTc radiolabeling of biomolecules for imaging applications.
- This approach maintains the biological activity of the coupled molecules and improves their pharmacokinetic properties, particularly in vivo stability.