Gallium in Nuclear Medicine and Oncology

Gallium is a calcium resorption inhibitor. It works by inhibiting the usual release of calcium from the bone into the blood. Gallium is used for treating high calcium levels in the blood caused by cancer in patients who do not respond to proper fluid intake or fluid injected into the vein.

Gallium has long been known to concentrate in skeletal tissue, particularly regions of bone deposition and remodeling. Elemental gallium is a potent inhibitor of bone resorption that acts to maintain or restore bone mass. There are several medically useful gallium radionuclides that have made extensive contribution in both the diagnosis and therapy of diseases. A huge variety of monofunctional and bifunctional chelators have been developed that allow the formation of stable 68Ga(III) complexes and convenient coupling to biomolecules such as amino acids, peptides, nanoparticles, or even whole cells. Gallium pharmaceuticals can be divided into two groups according to radioactivity, i.e., radiopharmaceuticals – using radioactive Ga(III) isotopes, and conventional pharmaceuticals – using non-radioactive Ga(III) ion. The pharmaceuticals can also be divided according to the target site of a drug, i.e., those having an impact on soft tissue (most of the drugs) and hard tissue (bones and bone metastasis). In oncology and nuclear medicine, gallium and its compounds have been applied for imaging as well as therapy.

Following are abstracts of interest:

Radiopharmaceuticals

Fred A. MettlerJr. MD, MPH, Milton J. Guiberteau MD, FACR, FACNM, in Essentials of Nuclear Medicine and Molecular Imaging (Seventh Edition), 2019

Gallium-67 has a physical half-life of 78.3 hours and decays by electron capture, emitting gamma radiation. When injected intravenously, most 67Ga is immediately bound to plasma proteins, primarily transferrin. During the first 12 to 24 hours, excretion from the body is primarily through the kidneys, with 20% to 25% of the administered dose being excreted by 24 hours. After that time, the intestinal mucosa becomes the major route of elimination. 

Gallium-67 Tumor Imaging

in Oncology In Nuclear Medicine (Fourth Edition), 2014

Gallium-67 (Ga-67) was initially used as a bone-imaging agent and is still sometimes used for the assessment of infection. Ga-67 is sensitive for many cancers, including hepatocellular cancer, sarcomas, and lung cancer. For years, Ga-67 was primarily used in the assessment of lymphoma. Eventually, CT became the primary imaging modality in lymphoma, with Ga-67 used as a problem-solving tool. Recently, Ga-67 has become relatively obsolete for tumor imaging.

Although its biodistribution is complex, Ga-67 has a biological behavior similar to that of iron. It is carried in the blood by iron transport proteins, such as transferrin. Excretion of 15% to 25% of the dose occurs through the kidneys in the first 24 hours, with the bowel becoming the major route of excretion after that. 

More information: Gallium: Indications, Side Effects, Warnings - Drugs.com

Gallium 69 Sesquioxide (Gallium-69) is the stable (non-radioactive) isotope of Gallium. It is both naturally occurring and produced by fission.