CC BY
0Skin optical clearing in vivo: application for photodynamic
therapy
V.D. Genin1'2*. D.K. Tuchina12, A.B. Bucharskaya23, E.A. Genina12, N.A. Navolokin3, D.A. Mudrak3, G.N. Maslyakova3, V.V. Tuchin124
1-Department of Optics and Biophotonics, Saratov State University, Astrakhanskaya St., 83, 410012 Saratov,
Russia
2- Laboratory of Laser Molecular Imaging and Machine Learning, Tomsk State University, 36 Lenin Ave.,
634050 Tomsk, Russia
3- Department of Pathological Anatomy, Saratov State Medical University, Bolshaya Kazachaya St., 112,
410012 Saratov, Russia
4- Institute of Precision Mechanics and Control Problems of the Russian Academy of Sciences, Federal Research Center "Saratov Scientific Center of the RAS", Rabochaya St., 24, 410028 Saratov, Russia
* versetty2005@yandex.ru
A promising method for increasing the selectivity of laser treatment of tumors is the combination of photodynamic therapy (PDT) using a photosensitizer, coupled with the technique of optical clearing (OC) of biotissues. A photosensitizer delivered to the tumor helps to provide locally photosensitivity of the tumor, as the use of an optical clearing agent (OCA) reduces the damage of healthy tissues located on the path of laser beam and increases light penetration to deep tumors. The mechanism of OCA action is to match the refractive indices of the tissue structural components and interstitial fluid to reduce tissue scattering.
The aim of the study was to investigate diffuse reflectance spectra changes in the healthy skin in vivo under action of OC and tumor region after the PDT with and without OC in rats with transplanted cholangiocarcinoma of the PC-1 line.
Diffuse reflectance spectra were measured using fiber-optical spectrometers in the spectral range of 400-2100 nm. The measured skin reflection spectra were used to determine the effective optical density of the skin.
The values of the characteristic diffusion time, effective diffusion coefficient and effective skin permeability coefficient of volunteers in vivo for 70% glycerol solution as an OCA were obtained.
For PDT, Photosens solution in saline with a concentration of 2 mg/ml was used as a photosensitizer. A mixture of 70% glycerol, 5% DMSO, 25% water was used as the OCA.
When the tumor volume reached 3±0.3 cm3, the rats were intratumorally injected with Photosens solution at a dose of 0.4±0.05 ml. Then rats were divided into two groups. The rats in the first group (PDT group) were exposed to PDT only: 10-30 min after Photosens injection, the tumors were irradiated percutaneously with a 662 nm laser at a power density of 0.5 W/cm2 for 15 min. The rats in the second group (PDT+OC group) were exposed to OC before the same PDT exposition: OCA was applied to the surface of the skin over the tumor and treated with a therapeutic sonophoresis device for 5 min with the following parameters: 1.2 W, 1 MHz, and 50% duty cycle. Sonophoresis was used as an enhancer of the OCA diffusion into the skin. The temperature of local heating of the tumor was monitored using a thermal imager. During the procedures, the temperature on the surface of the skin above the tumor did not exceed 40°C. Diffuse reflectance spectra were measured at different stages of the experiment and analyzed.
The work was supported by RSF grant 23-14-00287.
