Recombinant complement receptor 2 radiolabeled with [99mTc(CO)3]+: a potential new radiopharmaceutical for imaging...

Area of Science:

• Bioconjugation Chemistry
• Molecular Imaging
• Immunology

Background:

• Activated complement plays a crucial role in various inflammatory and autoimmune diseases.
• Current imaging agents for complement activation have limitations in specificity and sensitivity.
• Complement Receptor 2 (CR2) binds C3d, a key marker of complement activation.

Purpose of the Study:

• To design and synthesize a novel Tc-99m labeled bioconjugate for imaging activated complement.
• To develop a site-specific radiolabeling strategy for recombinant CR2 (rCR2).
• To evaluate the binding characteristics and stability of the rCR2-Tc-99m conjugate.

Main Methods:

• Engineered recombinant CR2 (rCR2) with a hexahistidine tag for site-specific radiolabeling.
• Characterized rCR2 using N-terminal sequencing, SDS-PAGE, and size exclusion chromatography.
• Confirmed C3d binding via ELISA, flow cytometry, and surface plasmon resonance (SPR).
• Radiolabeled rCR2 with Tc-99m using [(99m)Tc(CO)(3)(OH(2))(3)](+).

Main Results:

• rCR2 demonstrated specific binding to C3d and C3d-positive red blood cells (RBCs).
• SPR analysis revealed an affinity (K(D)) of approximately 500 nM for rCR2 binding to C3d.
• Radiolabeling yielded >95% radiochemical yield with excellent stability.
• Site-specifically radiolabeled rCR2 showed specific binding to C3d(+) RBCs, inhibited by anti-C3d antibodies.

Conclusions:

• The rCR2-Tc-99m conjugate exhibits promising radiolabeling, stability, and C3d binding properties.
• This novel agent warrants further in vivo evaluation for imaging activated complement.
• The site-specific radiolabeling strategy ensures the integrity of the CR2 binding domain.