New tech takes light-based cancer treatment deep inside body

Researchers, including one of Indian-origin, have developed new technology that can allow a cancer treatment, which uses lasers to activate special drugs, to penetrate areas of the body which were previously inaccessible.
Photodynamic therapy (PDT) is an effective treatment for easily accessible tumours such as oral and skin cancer. But the procedure, which uses lasers to activate special drugs called photosensitising agents, is not adept at fighting cancer deep inside the body.
The new technology developed by a team led by University at Buffalo involves using near-infrared beams of light that, upon penetrating deep into the body, are converted into visible light that activates the drug and destroys the tumour.

"We expect this will vastly expand the applications for an effective cancer phototherapy that's already in use," said co-author Tymish Ohulchanskyy, University at Buffalo research associate professor and deputy director for photomedicine at the university's Institute for Lasers, Photonics and Biophotonics (ILPB).
Doctors have used PDT to treat cancer for decades. Cancer cells absorb the drug, which is delivered to the tumour via the bloodstream or locally.
Visible light is then applied to the site, which causes the drug to react with oxygen and create a burst of free radicals that kill the tumour.

However, visible light does not penetrate tissue well. Conversely, near-infrared light penetrates tissue well but does not activate the drugs efficiently.

To solve this problem, some researchers are developing drugs that absorb near-infrared light. This method is limited, however, because stable and efficient near-infrared absorbing photosensitisers are notoriously difficult to synthesise.
The UB-led team took a different approach, which uses the tumour's natural environment to tune the light into the necessary wavelengths.
For example, the near-infrared laser beam interacts with the natural protein collagen, which is found in connective tissues. The interaction changes the near-infrared light to visible light, a process known as second harmonic generation.
Likewise, natural proteins and lipids within the cells interact with near-infrared laser light and change it to visible light through another process called four-wave mixing.

Thus, visible light can be generated in tumours deep inside the body, and it can be absorbed by the drug. This activates the drug, which then destroys the tumour.
The procedure has numerous advantages, said the study's leader, Paras Prasad, SUNY Distinguished Professor in chemistry, physics, electrical engineering, and medicine at UB, and the ILPB's executive director.
"There are no long-term side effects for PDT, it's less invasive than surgery, and we can very precisely target cancer cells," he said.
The study was published in the journal Nature Photonics.