Radioliganden

Radioliganden, or radioligands, are ligands labeled with a radioactive isotope that are used for in vivo imaging or targeted radiotherapy. They combine a molecular targeting moiety with a radionuclide, allowing the compound to bind to a specific biological target such as a receptor, transporter, enzyme, or antigen. After administration, the radioligand accumulates at the target site, and the emitted radiation is detected by nuclear imaging systems to visualize and quantify target expression and function.

Imaging with radioligands relies on modalities such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Common PET isotopes include carbon-11 and fluorine-18, while gamma emitters like technetium-99m and iodine-123 are used for SPECT. Some radioligands are designed for therapeutic purposes as well, using beta or alpha emitters such as lutetium-177 or actinium-225, enabling theranostic applications where diagnosis and therapy are combined.

Applications span neurology, oncology, cardiology, and infectious disease research. In neurology, radioligands image neurotransmitter systems, for example via 11C-raclopride for dopamine D2 receptors. In oncology, tracers targeting somatostatin receptors (68Ga-DOTATATE) or PSMA (68Ga-PSMA-11) support diagnosis and treatment planning, with therapeutic counterparts such as 177Lu-PSMA-617. Other examples include 18F-FLT for cellular proliferation and 18F-FDOPA for dopaminergic function.

Radioligand development involves radiochemistry, pharmacokinetics, dosimetry, and regulatory approval. Production may require on-site cyclotrons or radionuclide generators, and safety considerations include radiation exposure and potential off-target binding. Radioligands are central to nuclear medicine and the expanding field of theranostics.