Investigation of changes in the absorption spectrum of modern chlorine-containing drugs for photodynamic therapy as a result of exposure to laser radiation with a wavelength of 450 nm
Photodynamic therapy (PDT) is promising areas of modern medicine, having a minimum number of side effects and contraindications compared to alternative treatments. Photodynamic therapy uses photosensitizing drugs that contain photosensitizers (PS) that are activated by light, which leads to selective damage to cellular structures and apoptosis. Chlorine-containing photosensitizing drugs have a greater potential for use than other groups of photosensitizing substances (porphyrins), since they better meet the requirements for an ideal PS.
Photobleaching of the photosensitizer is very important for PDT  Information about the degree of photobleaching of the photosensitizer is necessary for choosing the correct tactics of photodynamic therapy .
The study of the spectral-luminescent properties of chlorin e6 (Ce6) for aggregation, and its subsequent effect on the photophysical properties of a chlorine-containing preparation, is a critical moment from the point of view of PDT. The absorption spectrum of Ce6 is characterized by the presence of the following bands: the most intense B-band (Soret band) with a peak at a wavelength of 401 nm, Qx 00- and Qx 01-bands (about 505-510 nm), as well as the Qy 00-band with a peak at a wavelength of about 664 nm. In photodynamic therapy, light sources are mainly used, the wavelength of which falls into the peak of the Qy 00-band. This is because the light with this wavelength penetrates deeply into biological tissue. However, this radiation is not absorbed of photosensitizer as efficiently as the radiation that aligns with its peak of the B-band. The use of sources with a wavelength which aligns with the B-band is limited by the small penetration depth of their radiation into biological tissue. In this regard, the use of radiation with a wavelength which aligns with the B-band, but not corresponding to its absorption peak (non-resonant photodynamic laser action), will make it possible to select the conditions under which the light will penetrate deeper into the biological tissue, but at the same time the absorption of light by the photosensitizer will be higher or at the same level as when exposing to light corresponding the peak of the Qy 00-band.
Goal of investigation: investigation of changes in the absorption spectrum of modern chlorine-containing drugs for photodynamic therapy as a result of exposure to laser radiation with a wavelength of 450 nm
A diode laser with a wavelength of 450 ± 5 nm and an average power of up to 2.0 W was used as a source of laser radiation for non-resonant photodynamic laser action. The absorption spectra (190 - 900 nm) of a modern chlorin-containing photosensitizing drug «Chloderm» (DPT Laboratory LLC, USA) were obtained before and after exposure to laser radiation with λ = 450 ± 5 nm on time (t = 0-20 minutes) and power density (W = 0 - 5.0 kW/cm2) at various concentrations of it an aqueous solution.
The dependences of the absorption coefficient of chlorin-containing photosensitizing drug “Chloderm” at wavelengths corresponding to the maxima of the B- and Qy 00- absorption bands of this photosensitizing drug and at a wavelength λ = 450 ± 5 nm after non-resonant photodynamic laser action on the time and power density of the laser exposure at different the concentrations of their aqueous solution are determined. The coefficient of spectral transformation of the Qy 00-band of chlorin-containing photosensitizing drug “Chloderm” is calculated equal to the ratio of the extinction coefficients at wavelengths that correspond to the conformational states of chlorin e6 in the form of monomer and tetramer. The dependence of the coefficient of spectral transformation Qy 00-band of “Chloderm” before and after non-resonant photodynamic laser action on the time and power density of the laser exposure are represented. The results of the non-resonant photodynamic laser action on drug absorption spectra are compared with the results of the resonant photodynamic action at the peak of the Qy 00-band described in . The prospects for using the non-resonant photodynamic laser action in PDT are discussed.
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