Elsevier

PET Clinics

Volume 4, Issue 1, January 2009, Pages 39-47
PET Clinics

PET Imaging of Hypoxia

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Hypoxia imaging has applications in functional recovery in ischemic events such as stroke and myocardial ischemia, but especially in tumors in which hypoxia can be predictive of treatment response and overall prognosis. Recently, there has been development of imaging agents using PET for non-invasive imaging of hypoxia. Many of these PET agents have come to the forefront of hypoxia imaging. Halogenated PET nitroimidazole imaging agents labeled with 18F (t1/2 = 110 m) and 124I (t1/2 = 110 m) have been under investigation for the last 25 years, with radiometal agents (64Cu-ATSM) being developed more recently. This article focuses on these PET imaging agents for hypoxia.

Section snippets

Radiolabled 2-nitroimidazoles as markers for hypoxia

Nitroimidazoles first were proposed as reducible hypoxia markers in 1979.23 These compounds enter cells by passive diffusion and undergo reduction forming a reactive intermediate species. In the presence of oxygen, the molecule is reoxidized, and the nitroimidazole diffuses back out of the cell. Under hypoxic conditions, however, further reduction occurs, forming covalent bonds with intracellular macromolecules, thus trapping the compound inside the cell.24 This mechanism is shown in Fig. 2.

[60,61,62,64Cu ]copper(II)-diacetyl-bis(N4-methylthiosemicarbazone)

Dithiosemicarbazones were discovered to possess antitumor properties in the 1960s. This led to the development of this class of ligands as radiopharmaceuticals because of the simplicity of the chemistry and the availability of copper positron- emitting isotopes.47 [60,61,62,64Cu ]copper(II)-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) is a neutral lipophilic molecule that is highly membrane-permeable and undergoes reduction and becomes trapped in the cell. This complex has been

Summary

A recent review concluded “PET imaging with specific hypoxia tracers is becoming a must in radiation therapy planning.”10 With the developments of new therapies in phase 3 clinical trials to overcome hypoxia in tumors, the testing of predictive assays that can identify patient populations that can benefit from these treatments is necessary.57 In addition, it has been suggested that dynamic hypoxia measurements during oxygen-modifying treatments could aid in the determination of responding and

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