It localizes to adrenergic tissue and thus can be used to identify the location of tumors such as pheochromocytomas and neuroblastomas.[4] With iodine-131 it can also be used to treat tumor cells that take up and metabolize norepinephrine.
MIBG is absorbed by and accumulated in granules of adrenal medullary chromaffin cells, as well as in pre-synaptic adrenergic neuron granules. The process in which this occurs is closely related to the mechanism employed by norepinephrine and its transporter in vivo.[5][6] The norepinephrine transporter (NET) functions to provide norepinephrine uptake at the synaptic terminals and adrenal chromaffin cells. MIBG, by bonding to NET, finds its roles in imaging and therapy.
Less than 10% of the administered MIBG gets metabolized into m-iodohippuric acid (MIHA), and the mechanism for how this metabolite is produced is unknown.[7]
Pheochromocytoma seen as dark sphere in center of the body (it is in the left adrenal gland). Image is by MIBG scintigraphy, with radiation from radioiodine in the MIBG. Two images are seen of the same patient from front and back. Note dark image of the thyroid due to unwanted uptake of iodide radioiodine from breakdown of the pharmaceutical, by the thyroid gland in the neck. Uptake at the side of the head are from the salivary glands. Radioactivity is also seen in the bladder, from normal renal excretion of iodide.
Iobenguane concentrates in presynaptic terminals of the heart and other autonomically innervated organs. This enables the possible non-invasive use as an in vivo probe to study these systems.[10][11]
Alternatives to imaging with 123I-MIBG, for certain indications and under clinical and research use, include the positron-emitting isotope iodine-124, and other radiopharmaceuticals such as 68Ga-DOTA and 18F-FDOPA for positron emission tomography (PET).[9][12][13]123I-MIBG imaging on a gamma camera can offer significantly higher cost-effectiveness and availability compared to PET imaging, and is particularly effective where 131I-MIBG therapy is subsequently planned, due to their directly comparable uptake.[14][9][15]
Thyroid blockade with (nonradioactive) potassium iodide is indicated for nuclear medicine scintigraphy with iobenguane/mIBG. This competitively inhibits radioiodine uptake, preventing excessive radioiodine levels in the thyroid and minimizing risk of thyroid ablation (in treatment with 131I). The minimal risk of thyroid cancer is also reduced as a result.[9][17]
The dosing regime for the FDA-approved commercial 123I-MIBG product Adreview is potassium iodideorLugol's solution containing 100 mg iodide, weight adjusted for children and given an hour before injection.[18]EANM guidelines, endorsed by the SNMMI, suggest a variety of regimes in clinical use, for both children and adults.[9][12]
Product labeling for diagnostic 131I iobenguane recommends giving potassium iodide one day before injection and continuing 5 to 7 days following.[19]131I iobenguane used for therapeutic purposes requires a different pre-medication duration, beginning 24–48 hours before iobenguane injection and continuing 10–15 days after injection.[16]
Iobenguane I 131, marketed under the trade name Azedra, has had a clinical trial as a treatment for malignant, recurrent or unresectable pheochromocytoma and paraganglioma, and the FDAapproved it on July 30, 2018. The drug is developed by Progenics Pharmaceuticals.[20][21]
^Scarsbrook AF, Ganeshan A, Statham J, Thakker RV, Weaver A, Talbot D, et al. (2007). "Anatomic and functional imaging of metastatic carcinoid tumors". Radiographics. 27 (2): 455–477. doi:10.1148/rg.272065058. PMID17374863.
^Beylergil V, Perez JA, Osborne JR (2016). "Molecular Imaging of Merkel Cell Carcinoma". In Hamblin MR, Avci P, Gupta GK (eds.). Imaging in dermatology. London. pp. 467–470. doi:10.1016/B978-0-12-802838-4.00033-9. ISBN978-0-12-802838-4. Metaiodobenzylguanidine (MIBG) is a radiolabeled analogue of guanethidine that enters the cells via the norepinephrine transporter and is either stored in the cytoplasm or in secretory granules{{cite book}}: CS1 maint: location missing publisher (link)
^Davidoff AM (2010). "Neuroblastoma". In Holcomb GW, Murphy JP, Ostlie DJ (eds.). Ashcraft's pediatric surgery (5th ed.). Philadelphia: Saunders/Elsevier. pp. 872–894. doi:10.1016/B978-1-4160-6127-4.00068-9. ISBN978-1-4160-6127-4. Metaiodobenzylguanidine (MIBG) is transported to and stored in the distal storage granules of chromaffin cells in the same way as norepinephrine.
^ abGiammarile F, Chiti A, Lassmann M, Brans B, Flux G (May 2008). "EANM procedure guidelines for 131I-meta-iodobenzylguanidine (131I-mIBG) therapy". European Journal of Nuclear Medicine and Molecular Imaging. 35 (5): 1039–1047. doi:10.1007/s00259-008-0715-3. PMID18274745. S2CID6884201.
^"AZEDRA® (iobenguane I 131". Billerica, MA: Progenics Pharmaceuticals Inc., a Lantheus company. July 2018. Archived from the original on 2019-08-17. Retrieved 2018-08-03.
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