sestamibi

sestamibi is a coordination complex of the radioisotope technetium-99m used as a pharmaceutical agent in nuclear medicine. It is primarily employed as a myocardial perfusion imaging agent for the diagnosis of coronary artery disease and in parathyroid scintigraphy for locating hyperfunctioning parathyroid glands. The compound is marketed under the brand name Cardiolite by Lantheus Medical Imaging and is a cornerstone of non-invasive cardiac assessment.

Chemical properties and structure

The active component is the cationic complex technetium-99m hexakis(2-methoxyisobutylisonitrile). The central technetium atom is in the +1 oxidation state, coordinated by six isonitrile ligands derived from copper(I) tetrafluoroborate salts. This lipophilic, monovalent cation structure is critical for its biological behavior, allowing it to passively diffuse across cell membranes and accumulate within mitochondria. The synthesis involves the reaction of sodium pertechnetate with the ligand kit in the presence of a reducing agent like stannous chloride, a process standardized for clinical use by institutions like the Society of Nuclear Medicine and Molecular Imaging.

Medical applications

Its primary application is in single-photon emission computed tomography for evaluating blood flow to the myocardium. It is used in stress tests, often alongside exercise or pharmacological agents like adenosine or dipyridamole, to identify regions of ischemia or infarction caused by atherosclerosis. A major secondary use is in preoperative imaging for primary hyperparathyroidism, where it localizes adenomas or hyperplastic glands, guiding surgeons like those at the Mayo Clinic. It has also been investigated for imaging certain breast cancer tumors and multidrug resistance in oncology.

Mechanism of action

Following intravenous injection, the compound is rapidly extracted from the blood by tissues in proportion to regional blood flow. Its uptake into viable cells, particularly cardiomyocytes, is driven by the large negative transmembrane potential of the inner mitochondrial membrane. The lipophilic cation crosses the plasma membrane and is then sequestered within mitochondria, a process dependent on cellular adenosine triphosphate levels. In parathyroid tissue, uptake is linked to mitochondrial density and oxyphil cell content, with washout slowed in hyperfunctioning glands compared to the thyroid.

Pharmacokinetics and dosimetry

After injection, it clears rapidly from the bloodstream, with significant first-pass extraction by the heart, liver, and skeletal muscle. Hepatic clearance via the hepatobiliary system is the main excretion route, leading to gallbladder visualization. A typical administered activity for cardiac imaging is 740–1110 MBq, resulting in an effective dose of approximately 9 mSv. Dosimetry calculations are guided by models from the International Commission on Radiological Protection and data published in the Journal of Nuclear Medicine.

History and development

The development originated from research into technetium-based imaging agents at University of Cambridge laboratories. The isonitrile ligand family was pioneered by scientists including Alan Davison and Alun G. Jones. Clinical development for cardiac imaging was led by researchers at the Massachusetts General Hospital and DuPont, leading to Food and Drug Administration approval in 1990. Its utility in parathyroid imaging was discovered serendipitously at the University of Michigan and subsequently validated in studies at the National Institutes of Health.

Related compounds and alternatives

Other technetium-99m perfusion agents include tetrofosmin, marketed as Myoview by GE Healthcare. For parathyroid imaging, dual-tracer subtraction techniques using technetium-99m pertechnetate or iodine-123 are common. In cardiac positron emission tomography, alternatives include rubidium-82 chloride and ammonia N-13. Research into related complexes continues at institutions like Brookhaven National Laboratory, exploring agents for targeting different biological pathways. Category:Radiopharmaceuticals Category:Technetium compounds Category:Diagnostic agents