New PET scanning probe makes immune system monitoring possible

June 9th, 2008 - 5:00 pm ICT by ANI  

London, June 9 (ANI): By modifying a common chemotherapy drug, researchers at UCLA’s Jonsson Comprehensive Cancer Center have created a new probe for Positron Emission Tomography (PET), which will not only allow them to monitor the immune system, but also help in checking the response to new therapies.

In this study, researchers created the small molecule, called FAC, by slightly altering the molecular structure of one of the most commonly used chemotherapy drugs, gemcitabine. After this, they added a radiolabel enabling the cells that take in the probe to be seen during PET scanning.

With this discovery, scientists will be able to monitor the immune system of the entire body in 3D and will thus be able to fight some cancers or when it goes awry as it does in autoimmune diseases.

The probe is derived from a fundamental cell biochemical pathway called the DNA Salvage Pathway, which works as a recycling mechanism aiding DNA replication and repair.

While all cells use this pathway to different extents, the pathway is activated at very high levels in lymphocytes and macrophages, the cells of the immune system that initiate immune response.

Thus, Dr. Owen Witte, a researcher at UCLA’s Jonsson Cancer Center , a Howard Hughes Medical Institute investigator and senior author of the study said that the probe accumulates at high levels in those cells.

“This is not a cure or a new treatment, but it will help us to more effectively model and measure the immune system. 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,” Nature Medicine quoted Witte, as saying.

Cells that take the probe are labelled with positron emitting particles, and they glow “hot” under PET scanning, which works a molecular camera allowing visualization of biological processes in living organisms. With further evaluation in animal models, the researchers are looking forward to monitor the immune systems of patients with FAC and other PET probes, said Witte.

“This measurement is not invasive - it involves a simple injection of the probe. We could do repetitive scans in a single week to monitor immune response,” he added.

Using conventional methods like CT and MRI scans, it takes a long time for researchers to know if the patients are responding to therapy or not. However, the PET probe can monitor immune response and response to treatment much more quickly (within a week or two).

“What we wanted to do was to develop new ways to look inside a living organism and gather as much information as we can about the immune system. We wanted to know how cells move from one site in the body to another and find a way to trace them to tumors,” said Caius Radu, an assistant professor of molecular and medical pharmacology, a Jonsson Cancer Center researcher and the first author of the study.

Previous studies required the cells to be modified with “reporter” genes that sequestered a specifically designed PET probe that allowed scientists to monitor them. However, the new probe doesn’t require modified cells, making it easier and less expensive to use and giving it far broader applications than existing probes.

“This probe will tell us things about the immune system that existing probes can’t,” said Radu.

The study is published in the early online edition of the journal Nature Medicine. (ANI)

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