New frontiers of photodynamic therapy
Deep dive
NanoNewsNet based on UB materials: Going beyond the surfacePhotodynamic therapy is an effective method of treating easily accessible cancers, such as tumors of the oral cavity or skin.
But this method, in which lasers are used to activate special drugs called photosensitizing agents, is not adapted to fight deep cancerous tumors. Fortunately, the situation is changing for the better thanks to technology that can bring photodynamic therapy (PDT) to previously inaccessible areas.
Described in the journal Nature Photonics (Kachynski et al., Photodynamic therapy by in situ nonlinear photon conversion), the new approach involves the use of near-infrared light beams, which, when penetrating deep into tissues, are converted into visible light, activating the drug and destroying the tumor.
"We believe that this will significantly expand the use of this effective method of anti–cancer therapy, which is already being used," says study co-author Timish Ohulchansky, PhD, research professor at the University of Buffalo (University at Buffalo, UB), Deputy director for Photomedicine of the Institute of Lasers, Photonics and Biophotonics (Institute for Lasers, Photonics and Biophotonics, ILPB) UB.
Doctors have been using PDT to treat cancer for decades. Cancer cells absorb the drug, which is delivered to the tumor by injection into the blood or locally. Then visible light is directed at the tumor, which causes the drug to react with oxygen and create a flurry of free radicals that kill the tumor.
Unfortunately, visible light does not penetrate well into the tissues. On the contrary, near-infrared light penetrates well into tissues, but it cannot activate drugs effectively enough.
To solve this problem, a number of scientists are developing drugs that absorb near-infrared light. However, this approach also has its limitations, because stable and effectively absorbing such light photosensitizers are notorious for difficulties with their synthesis.
Researchers from UB approached the solution of this problem from the other side. To adjust the light to the required wavelength, they used a naturally surrounding tumor microenvironment.
Thus, the light of the near-IR laser interacts with the natural protein collagen, located in the connective tissue. This interaction turns near–infrared light into visible light, a process known as second harmonic generation. In a similar way, natural proteins and lipids inside cells interact with the light of a near-infrared laser. In this case, its transformation into visible light occurs in a process known as four-wave mixing.
Thus, visible light is generated in deep tumors and can be absorbed by the drug. The activated drug further destroys the tumor.
In the laser-irradiated area (white square) there are both living (green) and dead (red)
cancer cells that died as a result of radiation. (Photo: University at Buffalo)
According to the head of the study Paras Prasad, PhD, professor of chemistry, physics, electrical engineering and medicine UB, executive director of ILPB, this method has many advantages.
"PDT has no long–term side effects, it is less invasive than surgery, and allows you to target cancer cells very precisely," he explains. "Our approach expands the use of PDT and makes it another tool that doctors can use to ease the pain of millions of people suffering from cancer."
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