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on imaging applications, Tsien says.
One idea is to start with MRI images. That tool is the best for whole body scanning for tumors, because it doesn’t expose the patient to any radiation that can accumulate and cause problems over time, and it provides high resolution images. But it’s not very sensitive, which requires a lot of gadolinium probes in a contrast agent to help a doctor see the difference between a tumor and healthy tissue. Radioactive tracers are very sensitive and easy to see, but pose a danger to the patient with accumulation over time, he says.
Avelas enters this picture with what it calls a fluorescent “Activatable Cell-Penetrating Peptide.” Tsien showed me on his laptop a picture of a surgeon looking at a tumor without any of these fluorescent-tagged peptides, and he asked me if I could tell the difference between the tumor and the healthy part (I couldn’t). Then he overlaid images with a blue dye for the tumor, and a green dye for the healthy parts, and it was crystal clear.
This kind of imaging has been used by a surgical collaborator, UCSD’s Quyen Nguyen, who has shown that the Avelas peptides enabled her to clearly define the boundaries of the tumor, and completely remove them surgically, which helped experimental mice live longer after surgery. This is one of the age-old problems with cancer surgery—failing to cut out the whole tumor can leave tiny metastases behind to flourish, while cutting too much out can cause disability in the patient.
“Surgeons fear that they are getting near some nerves. They are not that easy to distinguish,” Tsien says. “If you cut the patient’s nerves, the patient can lose motor function, gets paralyzed, lose sensation. That can be for the rest of your life.”
The demand for sharper contrast agents is growing as surgery becomes more roboticized, thanks to companies like Sunnyvale, CA-based Intuitive Surgical. Doctors who use laparoscopes mounted with cameras to perform operations have less and less ability to function on feel, and need to compensate by seeing better, Tsien says. Imaging for surgery, is “the low-hanging fruit,” Tsien says.
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