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1Drug-free inhibition of cancer cells by visible optical radiation
V. Plavskii*, A. Svechko, O. Dudinova, L. Plavskaya, A. Tretyakova, A. Mikulich, R. Nahorny, T. Ananich, A. Sobchuk, S. Yakimchuk, I. Leusenka
B.I. Stepanov Institute ofPhysics of the National Academy of Sciences of Belarus, Minsk, Belarus
A quarter of a century after establishment of inhibitory effect of blue light on growth of cancer cells, their migration and invasion, many aspects of the mechanism of photophysical and photochemical processes underlying the effect of this physical factor have been quite well studied. However, the most pressing and controversial question remains about molecules that are acceptors of optical radiation, localized in cells and capable of influencing metabolic processes after light absorption [1]. Important information about possible participation of a particular endogenous compound in the implementation of the photobiomodulation effect can be obtained from a comparison of its absorption spectrum and the spectrum of action of optical radiation on cells. In this regard, we studied the spectral-dependent light-induced changes in metabolic activity of HeLa cells, as well as the dependence of the level of ROS formation in cells when exposed to radiation from LED sources peaking at Amax = 395, 405, 415, 445 and 465 nm, in the energy dose range of 1.5-15.0 J/cm2.
It has been shown that the observed spectral-dependent light-induced inhibition of the metabolic activity of cancer cells and the light-induced formation of ROS is due to the changing contribution of endogenous porphyrins and flavins to the total absorption of the influencing radiation when its wavelength changes within the blue spectral region. In this case, the contribution of each endogenous photosensitizer is determined by its concentration, molar absorption coefficient, ROS generation efficacy, spatial localization in the cell near photosensitive molecules and ROS quenchers (interceptors), which have a decisive influence on the efficacy of sensitized processes.
Despite the significantly lower concentration of endogenous porphyrins compared to flavins, tetrapyrrole photosensitizers (protoporphyrin IX, coproporphyrin III, uroporphyrin III, Zn-protoporphyrin IX, Zn-coproporphyrin III) play a decisive role in the generation of ROS and inhibition of the metabolic activity of cancer cells during exposure to blue light, which is confirmed by the higher efficacy of the above processes when exposed to radiation with Amax = 405 nm (corresponding to the maximum of the Soret band of endogenous porphyrins and the local minimum of the absorption band of flavins) in comparison with Amax = 445 nm (corresponding to the long-wavelength maximum of the absorption spectrum of flavins and minimal absorption of porphyrins).
Using specific quenchers (interceptors) of ROS, it was shown, for the first time, that immediately after the cessation of irradiation, the decisive role in light-induced damage to cancer cells is played by singlet oxygen, formed due to the excitation of endogenous photosensitizers, and, to a lesser extent, by hydrogen peroxide. When monitoring the light-induced decrease in the metabolic activity of cells one day after their irradiation, it was found that the decisive role in this process belongs to hydrogen peroxide. It is concluded that the change in the contribution of various types of ROS to the effects of photobiomodulation over time after the cessation of light exposure on cells is explained by a wave of massive secondary production of ROS, and above all, hydrogen peroxide, which, according to literature data, during sensitized processes is recorded in cells several hours later after completion of irradiation.
The effect of blue light on cancer cells is not limited to damage to cellular structures, which ultimately leads to cell death (apoptosis and necrosis). A significant influence on the light-induced decrease in metabolic activity is exerted by changes in cell cycle parameters monitored by flow cytometry: a decrease in the relative number of cells in the G0/G1 stages, an increase in the relative number of cells in the G2/M stages, and their slight increase in the S stage. Moreover, for all studied indicators at the same energy doses, more significant changes are induced by exposure to light with ^max = 405 nm compared to Amax = 445 nm.
[11 V.Y. Plavskii, A.N. Sobchuk, A.V. Mikulich, O.N. Dudinova, L.G. Plavskaya, A.I. Tretyakova, R.K. Nahorny, T.S. Ananich, A.D. Svechko, S.V. Yakimchuk, I.A. Leusenka, Identification by methods of steady-state and kinetic spectrofluorimetry of endogenous porphyrins and flavins sensitizing the formation of reactive oxygen species in cancer cells, Photochem Photobiol, 2024 Jan 23.
