A commercial ink (left) diffuses far from injection sites (arrows) under mouse skin, but a new colon tattoo ink (right) diffuses much less. Credit: Jordan Yaron, Ph.D.
March is colorectal cancer awareness month, when people older than 50 are reminded to get a colonoscopy, or endoscopic examination of the colon, to detect cancerous and precancerous lesions. If doctors see small polyps during the exam, they usually remove them at the time. However, larger, more complex lesions are often referred to specialists or surgeons for later removal.
“Many times, these are very flat, very subtle lesions, and there’s a need to mark them so that the specialist going in later can find them,” said Rahul Pannala, M.D., a gastroenterologist and associate professor of medicine at the Mayo Clinic Arizona, who is involved in the research.
To do this, doctors inject a commercial ink, typically made of carbon black, a couple of centimeters from the lesion—a process known as endoscopic or colon tattooing. However, the current commercially available inks carry a few disadvantages, according to Pannala.
“The current preparations haven’t changed in many years and they cause a fair amount of scarring when we put them in,” the gastroenterologist explained during a presentation at the spring meeting of the American Chemical Society (ACS). “If there is a significant degree of scaring, it makes it much harder for us to do our procedure.”
Additionally, the current inks diffuse over time so when a specialist goes back in to find the marked lesion, all they find is a broad, black ink spot that is “near-ish” to the cancerous polyp that needs to be removed.
To overcome these limitations, Pannala worked with researchers at Arizona State University (ASU) to design and test new, more effective inks. As bioengineers, Subhadeep Dutta, a graduate student, Kaushal Rege, a chemical engineering professor, and their team brainstormed different approaches and well-established chemistries they could leverage. Ultimately, they settled on metal-derived nanoparticles to give the ink a strong, dark color.
Then, they combined the nanoparticles with different amounts and types of polymers that could adhere to the submucosal surface in the colon. During the conference presentation, Dutta explained it is this protective mucoid polymer coating that distinguishes the ink from current options—and what prevents the ink from diffusing over time.
Dutta and colleagues tested their different formulations first in porcine intestine tissue to study the ex vivo response with respect to imaging contrast and spot retention ability. Then, the team moved on to preclinical studies with live mice, where they injected the ink in the subcutaneous space and observed its effect over a 30-day period.
“So far, in comparison to existing inks, our preclinical studies show the spot size is approximately 4 to 5 times smaller than the commercially available inks used clinically, and it causes minimal inflammation in our experiments in mice,” Dutta told the attendees of the ACS meeting.
Although there have been no obvious signs of inflammation, the scientists are now performing histopathological studies to observe whether any microscopic changes occured in the skin. These studies will also help determine the optimal ink formulation, although Rege says the team has already narrowed it down to a few ideal candidates.
The next step is testing the best inks in actual endoscopic tattoos on live pigs to examine diffusion, contrast and assess overall effectiveness in follow up appointments—just as Pannala does with his human patients.
“If the ink behaves how we expect it to and we can detect it in imaging, then it’s a game changer because we can pinpoint these lesions in a non-invasive manner,” said Pannala. “It opens up a lot of other avenues and opportunities, it’s not limited to just colon cancer. If we’re able to develop an ink that is very precise, we could also use it to mark growths and tumors anywhere in the gut, or even in the pancreas.”