Production of multimeric prostate-specific membrane antigen small-molecule radiotracers using a solid-phase 99mTc...

Area of Science:

• Radiochemistry and Nuclear Medicine
• Oncology and Cancer Imaging
• Molecular Imaging Probes

Background:

• Prostate-specific membrane antigen (PSMA) targeted small-molecule ligands show promise for prostate cancer imaging.
• Challenges exist in labeling highly charged ligands with technetium-99m (99mTc) and achieving high purity.
• An adamantane-trimerized small molecule with nanomolar PSMA binding and 12 negative charges was developed.

Purpose of the Study:

• To develop a clinically viable SPECT diagnostic agent for PSMA-positive prostate cancer.
• To establish a simple, rapid, and efficient method for radiolabeling PSMA-targeting molecules with 99mTc.
• To overcome the limitations of labeling highly charged ligands and purification.

Main Methods:

• A cartridge-based, solid-phase prelabeling strategy was developed to convert 99mTc-pertechnetate.
• The strategy produces a chemically pure 99mTc-N-hydroxysuccinimide (NHS) ester intermediate in neat organic solvent within 25 minutes.
• This intermediate enables one-step labeling of amine-containing molecules with 99mTc, achieving high specific activity without HPLC.

Main Results:

• Solid-phase conversion yielded 99mTc-MAS3-NHS with >99% radiochemical purity in 25 minutes.
• The intermediate was conjugated to an adamantane-trimerized PSMA-targeting molecule (GPI) with >95% yield, eliminating the need for HPLC.
• The final 99mTc-labeled molecule demonstrated specific binding to PSMA-expressing human prostate cancer cells.

Conclusions:

• A simple, cartridge-based method efficiently converts 99mTc-pertechnetate to a preloaded NHS ester intermediate (>99% purity, 25 min prep time).
• This chemistry facilitates the production of high-specific-activity, 99mTc-labeled, PSMA-targeted small molecules.
• Successful gamma-ray radioscintigraphic imaging of living human prostate cancer cells was achieved, validating the approach.