Elusive Tumors Made Visible by Advanced PET Imaging Tracer

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An international team of scientists have developed a new compound that allows specific tumor types to be made apparent in high resolution using positron emission tomography (PET) imaging.

The tracer has successfully been tested in laboratory mice; giving researchers the incentive to implement and evaluate this new imaging system in clinical trials involving humans.
Imaging techniques used for cancer detection and tracking offer a whole lot more than just data on the scale and location of cancerous cells. There are advanced techniques that additionally typify the tumor cells accurately, for instance, by specific molecules they carry on their surface. Such supplementary information provides clinicianPET Imaging Tracers with critical clues as to the exact kind of cancer they’re facing and allows them to calculate the likelihood of a patient positively responding to a specific form of therapy.

Researchers from ETH Zurich (Switzerland), the Paul Scherrer Institute (PSI; Villigen PSI, Switzerland), and Merck Millipore (Billerica, MA, USA) have now produced a new tracer for PET that connects to the folic acid receptor. This receptor is important because it amasses on the cell’s surface in various cancer types. The PET scan issues data on the size and location of the tumor, in accordance with the density of the folic acid receptors on the cell’s surface. 

The researchers, led by Drs. Simon Ametamey and Roger Schibli, who are both professors at the Institute of Pharmaceutical Sciences at ETH Zurich, have effectively evaluated their new substance in mice with cervical tumors. For the next phase, researchers would like to determine whether the substance proves as equally effective in humans. A precursor study on patients with ovarian, lung and intestinal cancer in several Swiss hospitals, including University Hospital Zurich, is in currently in development; and will be the very first clinical trial on a folic acid receptor marker for PET on patients.

If the substance yields the desired effect, researchers would want to utilize it in order to determine the overall effectiveness of chemotherapy for future cases. More importantly, they now have a new generation of cancer medication in availability that also connects to the folic acid receptor, which then channels the drug into the cancer cells, where it unfolds its therapeutic effect.

“Our PET tracer provides important additional information for this targeted therapeutic approach with cytotoxic substances,” said Ametamey.

However, one drawback of this newly found therapy is that not all cancer cells carry the folic acid receptor. In the matter of cervical, ovarian, and brain tumors, it is about nine out of 10 patients, with lung cancer at 75% and breast cancer at around 50%. In patients without the receptor, the ground-breaking chemotherapy is ineffective.

With the help of this new method, it could be possible to predict whether a patient will respond to certain treatments. Patients whose tumors do not have any folic acid receptors could avoid this therapy and its side effects all together. Furthermore, doctors can employ the new PET tracer to enhance monitoring the progress of therapy and determine whether the tumor size is decreasing.

Yet the new PET tracer isn’t only limited to cancer treatment, but also for showing inflammatory responses in the body; for the folic acid receptor occurs at the surface of specific cells of the immune system, the macrophages, and only if these particular cells are in perceived activated state during an inflammatory response. Therefore, the new marker substance could be utilized to show inflammatory diseases such as arthritis, arteriosclerosis, or inflammatory bowel diseases with PET.

Additionally, a third area of application is also possible with the new tracer: medication development.

“If we’ve got a method to detect chronic inflammatory responses in a noninvasive way, we can test the efficacy of anti-inflammatory medication more effectively,” said Schibli.

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