Researchers at the Institute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences, Saratov State University, and Lomonosov State Academy of Fine Chemical Technology have developed a new kind of composite nanoparticles that can be successfully used to deliver porphyrins to the tissues. Luminescence allows to control the distribution of the nanoparticles in the living tissue while intensifying the photodynamic effect.
In order to generate composite nanoparticles, silver nanocubes from 30 to 60 nanometer in size are produced first. Then, gold-silver nanocells are generated based on the nanocubes, to serve as a foundation for porous nanocoating of silicon dioxide varying from 20 to 100 nanometer in width. After that, the particles are chemically modified and stabilised
Photodynamic therapy (PDT) presents a method of treatment based on the same principle as chemotherapy but with a physical addition. Some substances (termed photosensitisers) cause photochemical reactions in the surrounding solution due to the exposure to the light of certain wavelengths — in particular, they facilitate the shift of oxygen molecules into the excited (singlet) state. Such exited oxygen molecules, in turn, destroy other molecules that are located in their proximity — for example, organic ones. As a result, the number of free radicals in the solution increases. When all the processes described above occur in a living cell, their effect is baneful. If the photosensitiser substance shows an elective affinity to these particular cells that need to be killed — for example, malignant ones — it can be used as a medicine. But its action must be augmented with light exposure of the affected tissue (lasers are currently used for the purpose).
Photosensitisers often happen to be dyes. The very essence of photodynamic therapy was discovered at the turn of the 20th century by German researchers who used an organic dye, acridine. When acridine solution is exposed to light with the wavelength complying with the absorption range of the substance, it can kill infusoria, unicellular organisms dwelling in the solution. Note that the poisonous action of the dye does not manifest without the irradiation. Professor Herman von Tappeiner at the Pharmacology Institute of Munich University who discovered the effect tried to use it to treat fungus infections and skin tumours — with some success. Currently, PDT is used to treat cancer, lymphomas, as well as some bacterial infections (particularly in the cases when the agents of the diseases are resistant to antibiotics). Skin diseases are the most frequent targets of the method as skin is the easiest to expose to light.
The use of PDT poses some technical issues, though. Many substances fit to serve as photosensitisers are hydrophobic due to their chemical nature — that is, that can hardly be dissolved in water. But the inner medium of a human body is in fact a water solution. In order to insure better blood transportation of the reactant and its penetration into the tissues the molecules of the substance get bound to carrier particles. The particles in question must be extremely small — smaller than bacteria. In other words, we are talking nanoparticles.
The research group consisting of experts from the Institute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences, Saratov State University, and State Academy of Fine Chemical Technology developed a new type of composite nanoparticles with the gold-silver core coated with porous silicate layer. The particles are about 40 nanometer in size — just like a small virus. They are successfully used to deliver porphyrins, one of the most important class of photosensitiser substances, to the tissues. In addition, the particles luminesce due to the effect of light of the visible spectrum. First, luminescence helps to manage the distribution of nanoparticles in the living tissues; and second, it can enhance the photodynamic action during the attempts to adjust the correct distance between the molecules of the agent and the metallic core, thus improving the cancer treatment results.
That is not the fist example of using nanotechnologies in malignant tumour treatment. There are reasons to believe that it can offer significant help in solving one of the biggest problems of modern man.
The research was conducted according to the Federal Task Program “Scientific and Pedagogical Resources of Innovative Russia for 2009-2013.
Source of information:
B. N. Khlebtsov, Е. V. Panfilova, V. А. Khanadeev, А. V. Markin, G. S. Terentyuk, V. D. Rumyantseva, А. V. Ivanov, I. P. Shilov, N. G. Khlebtsov: “The Composite Multifunctional Nanoparticles Based on Gold-Silver Nanocells Coated with Silicon Dioxide and Ytterbium Hematoporphyrin.” The Russian Nanotechnologies, vol. 6, #7–8 (in print).