ИСТИНА

Photodynamic therapy (PDT), which aroused more than a hundred years ago from the attempts to use photoactive dyes and light for the treatment of some cutaneous diseases, is currently a recognized method to treat cancer, localized infections and some other diseases. PDT destroys cells with reactive oxygen species (ROS) produced during interaction of light with a PDT agent (photosensitizer) accumulated in target cells. Selectivity and safety of treatment is enhanced due to localized irradiation of tissue lesions. In dermatology, PDT is successfully used to cure precancer¬ous states, sun-damaged skin and acne. Healing effect of PDT is complemented with an excellent cosmetic result that is especially valuable in the treatment of soft tissues of a head and neck. PDT is under development for the treatment of cutaneous inflammations and infections. Efficiency of PDT depends extremely on the properties of a photosensitizer (PS). PS are fluorescent dyes, and a confocal spectral imaging (CSI) technique is specifically suitable to assist in development of advanced PS and in optimization of their application. According to the CSI technique a thing tissue section is scanned under microscope, and fluorescence spectra are measured in each point of the specimen with a submicron 3D resolution. It provides an important advantage in comparison with other imaging methods, which measure signal intensity in the filter-selected spectral range, because all spectrum parameters are accessible for an analysis. The spectral analysis allows one to recognize and deconvolve overlapping signals of Rayleigh scattering, intrinsic tissue fluorescence and PS, and finally, to reconstruct spectral images describing a true PS distribution. Moreover, a tissue specificity of the components of complex photosensitizing substances can be revealed. Advances of CSI technique are illustrated in this report with the results of studies of different PS in human malignant tissues. Analysis of PS microdistribution in tissues with the CSI technique as a function of time after PS injection (topical or oral administration) helps to characterize a selectivity of PS accumulation in tumor cells and other tissue structures; to reveal correctly a maximum of time profile of its tumor accumulation and to recognize the features of PS tissue distribution (spatial and temporal) at different ways of PS administration. These data are required to optimize PS applications for tumors of different localization, to choose correctly delay time between PS injection and tumor irradiation with light and to understand a tissue response to PDT. Comparative study of various PS is important to realize how differences in molecular properties would affect tissue distribution, tumor accumulation, and, finally, the overall antitumor effect.