New PET scanning probe offers tantalizing capabilities
Researchers plan to begin human studies soon
In the next few months, researchers at the University of California at Los Angeles' (UCLA's) Jonsson Comprehensive Cancer Center will begin human studies on a new probe for Positron Emission Tomography (PET) that they believe will provide clinicians and researchers with a powerful new window on the immune system, as well as enable them to gauge early patient response to therapies.
The discovery of the new probe was first reported in the online edition of Nature Medicine.1
Scientists created the probe, FAC (fluoroarabinofuranosyl cytosine), by slightly altering the molecular structure of the chemotherapy drug, gemcitabine, and then adding a radiolabel so that cells that take in the probe are visible during PET scanning. Ultimately, scientists hope to use the probe to monitor the body in 3D — not only for response to therapies, but also to gain new insights on immune system disorders such as inflammatory bowel disease and rheumatoid arthritis.
"Another potential [application] — and this might be even more exciting than monitoring treatment — is that we hope that we can use this probe to stratify patients even before starting treatment," says Caius Radu, MD, an assistant professor of molecular and medical pharmacology at Jonsson Cancer Center and the lead author of the study. "First we have to know more about what diseases this probe would be best used for, and I think that mouse studies give us a clue, but we now have to actually do the human research."
No toxic effects
For each type of disease, scientists need to set up a collaborative study, and Radu says they are doing that right now.
"There is quite a diverse group of people who are interested," says Radu, noting that they range from drug developers and cancer researchers to practicing clinicians. He notes that studies on the probe can be launched quickly.
"This is not a drug, so it doesn't have to go through the same sort of approval process as a drug would have to go through," says Radu. "And whenever you do a PET imaging study, you only have to inject very small amounts of the probe, which has no toxic effects."
Radu explains that a patient could undergo PET scanning about one hour after being injected with the probe, and it might take only about two hours for the probe to be completely eliminated from the body. "The amount of probe is going to be undetectable," he says. "The half-life is very short."
Researchers emphasize that while the probe does not represent a new cure or treatment, the ability to monitor immune system function through molecular imaging could have a significant impact on the diagnosis of immunological disorders as well as on evaluating whether therapies are successful. "There is a wide range of inflammatory diseases, the activity of which is difficult to image with currently available tools," says Johannes Czernin, MD, the director of PET/CT in the UCLA Health System. "If the imaging probe accumulates in inflammation, then the probe might be useful for establishing the extent and degree of inflammation before treatment and subsequently for monitoring responses to anti-inflammatory or immuno-suppressive therapy."
Reference
- Radu C, Shu C, Nair-Gill E, et al. Moledular imaging of lymphoid organs and immune activation by positron emission tomography with a new-labeled 2'-deoxycytidine analog. Nature Medicine 2008; 14:783-788.
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