Radiolabeled

Radiolabeled refers to a molecule that carries a radioactive nuclide, enabling its detection or therapeutic effect through emitted radiation. In medicine and research, radiolabeled compounds are used for diagnostic imaging, to track biological processes, and for targeted radiotherapy. The radiolabel is typically attached to a biological vector such as a peptide, antibody, nucleic acid, or small-molecule ligand, allowing the radiotracer to localize in specific tissues or receptors.

Labeling methods vary. Direct labeling introduces the radioactive atom during synthesis, while indirect labeling uses a chelator or prosthetic group to hold the radioisotope on the molecule. Common chelators for metal isotopes include DOTA, NOTA, and EDTA. Radiohalogens like iodine and astatine can be incorporated by halogenation chemistry, while positron-emitters such as fluorine-18 and copper-64 or zirconium-89 are often coordinated via chelators or specialized prosthetic groups. Radiolabeling aims for high radiochemical yield, purity, and in vivo stability to ensure accurate imaging or effective dose delivery.

Common isotopes include technetium-99m and iodine-123/131 for SPECT and thyroid or other organ imaging; fluorine-18, gallium-68, and zirconium-89 for PET imaging; and lutetium-177 or actinium-225 for radiotherapy. Well-known examples are [18F]fluorodeoxyglucose for PET imaging and radiolabeled monoclonal antibodies or peptides used in immuno-PET or peptide receptor radionuclide therapy.

Production and quality control reflect the intended use. Isotopes may be produced in cyclotrons or generators, and radiopharmaceuticals are manufactured under good manufacturing practice with stringent radiochemical purity, sterility, and apyrogenicity testing. Safety and regulatory frameworks govern handling, dosing, and disposal to protect patients and healthcare workers.