New PET scanning probe to allow monitoring of the immune system

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Researchers at the University of California Los Angeles (UCLA) Jonsson Comprehensive Cancer Center have modified a common chemotherapy drug to create a new PET probe that will model and measure the immune system in action and monitor response to new therapies.

The discovery, published June 8 in the online edition of Nature Medicine, enables scientists to monitor the immune system at the whole-body level, using 3D advanced visualization technology, as it tries to fight cancer or autoimmune diseases.

Researchers created the probe using a small molecule, called FAC, by slightly altering the molecular structure of gemcitabine, one of the most commonly used chemotherapy drugs. A radiolabel is then added so the cells that take in the probe can be seen during PET scanning, the researchers said.

"This is not a cure or a new treatment, but it will help us to more effectively model and measure the immune system," said Owen Witte, MD, a researcher at UCLA's Jonsson Cancer Center, a Howard Hughes Medical Institute investigator and senior author of the study. "Monitoring immune function using molecular imaging could significantly impact the diagnosis and treatment evaluation of immunological disorders, as well as evaluating whether certain therapies are effective."

Because the probe is labeled with positron emitting particles, cells that take it in glow "hot" under PET scanning, which operates as a molecular camera that enables visualization of biological processes in living organisms. Witte said that eventually researchers hope to be able to monitor the immune systems of patients with FAC and other PET probes.

"This measurement is not invasive—it involves a simple injection of the probe," Witte said. "We could do repetitive scans in a single week to monitor immune response."

If the new PET probe can monitor immune response and response to treatment much more quickly, within a week or two patients would be spared from therapies that aren't working, he concluded.