Gila monsters are strange lizards, both from a physical and chemical point of view. Most people can at least recognize the 5-foot-long lizard by its distinctive bumpy, pink and black scales, stocky body and distinctive stubby tail. Those aren’t their only unique features; they are only one of two known lizard species in the world that can produce venom. Although receiving a bite filled with neurotoxic venom is rarely fatal, it is unpleasant and can cause significant pain, edema, nausea, and vomiting. But the Gila Monster’s spit also contains a substance that now shows promise in detecting extremely difficult-to-find pancreatic tumors.
In rare cases, beta cells responsible for producing insulin in the pancreas can malfunction and form small tumors known as insulinomas. Although relatively benign, these growths can still lower a person’s blood sugar levels due to the overproduction of insulin. This problem is especially problematic for people with diabetes because it can lead to low energy and even fainting. In addition, the tumors are usually smaller than 2.5 cm, making them difficult to locate and diagnose. Now, however, a new PET scan variant appears to accurately assess insulinomas, thanks in large part to the chemical complexity of Gila sample spit.
Before the lizard-inspired solution, identifying patients with insulin was extremely difficult for medical teams. In many cases it takes a long time before its existence is confirmed.
“It is a very challenging disease,” says Marti Boss, first author of a new study published in The Journal of Nuclear Medicine, said in a statement. “We can do blood tests, but they cannot confirm whether a tumor is the cause or where it is located. There are various scans available, such as CT, MRI and PET, but they do not always show the insulinomas.’
“In the past, surgeons would start cutting away parts of the pancreas until they found the tumor. If that were the case, the entire pancreas would be gone,” said Martin Gotthardt, professor of nuclear medicine and co-author of the study. “You can live without a pancreas, but then you suffer from severe diabetes and have to constantly control your blood sugar levels. A better scan was therefore urgently needed.”
Gotthardt and Boss were aware of the promising usefulness of Gila monster saliva. Previous research had shown that a specific chemical found in the spit of the venomous desert-dwelling lizard had a high affinity for binding to a specific molecule in insulinomas known as the GLP1 receptor. But it wasn’t as simple as collecting vials of reptile saliva for use in a laboratory.
“The substance from the saliva was not very stable in the human body,” Gotthardt explains.
To solve this problem, researchers developed a more chemically stable synthetic version known as Extendin, which they then combined with a mildly radioactive tracer used in standard PET scans. From there, they asked 69 adult patients with suspected insulinoma to undergo the Extendin-PET scan. The results were clear: While the basic PET scans detected tumors 65 percent of the time, the new Gila sample-derived option did so with 95 percent accuracy. In cases where the Extendin-PET scan was combined with CT and MRI scans, 13 percent of those insulin identifications were due solely to the Extendin-PET procedure. Once confirmed, surgeons successfully removed all tumors in the affected patients.
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In the future, the team hopes to conduct further research into the benefits of Extendin and how it can be used to treat insulin, as well as introduce the modified PET scans into medical facilities.
“We believe the new scan can replace all other scans,” Boss said. “… [A]All those patients were completely cured after the operation, even though some had been ill for decades.”
