Direct labeling of proteins with 99mTc.

Area of Science:

• Bioconjugation Chemistry
• Radiopharmaceutical Chemistry
• Protein Chemistry

Background:

• Direct labeling of antibodies and antibody fragments with technetium-99m (99mTc) relies on forming stable bonds with protein sulfide groups.
• Optimizing 99mTc labeling requires sufficient reactive sulfides on the antibody protein for technetium metal ions.

Purpose of the Study:

• To optimize the direct labeling of antibodies and antibody fragments with 99mTc.
• To achieve high labeling yields and maintain immunoreactivity by controlling reactive sulfide availability and minimizing side reactions.

Main Methods:

• Reducing disulfide bridges in antibody proteins or using Fab' fragments to provide reactive sulfide groups.
• Protecting reactive sulfide groups with metal ions (e.g., tin, zinc) with lower binding affinity than technetium.
• Careful control of protein reduction and complete removal of reducing agents to minimize side reactions and impurities.

Main Results:

• Very high labeling yields of high-affinity-bonded 99mTc can be achieved without loss of immunoreactivity.
• Minimized radiochemical impurities, including low-affinity bound 99mTc, colloids, peptides, aggregates, or residual pertechnetate.
• Successful direct labeling methods are being rapidly introduced for clinical nuclear medicine studies.

Conclusions:

• Appropriate protein reduction and complete reducing agent removal are critical for minimizing side reactions in 99mTc antibody labeling.
• Direct labeling methods offer a common sequence of chemical reactions for preparing 99mTc-labeled antibodies and fragments.
• These methods are essential for advancing clinical nuclear medicine studies through improved radiolabeling techniques.