OPTICAL MONITORING OF PHOTOSENSITIZER DIFFUSION INTO TISSUE Alexander V. Khilov1, Mikhail Yu. Kirillin1, Daria A. Loginova1, Alina E. Meller1,2 and Ilya V. Turchin1 1Institute of Applied Physics of Russian Academy of Science, Nizhny Novgorod, Russia 2 Nizhny Novgorod State Medical Academy, Nizhny Novgorod, Russia International Symposium “Saratov Fall Meeting” 26 ― 29 September 2017 Saratov, Russia

Basic PDT principles Therapeutic agents + fluorescent markers for diagnostics = Theranostics Jonathan P. Celli, et al, Chem. Rev. 2010, 110 Photodynamic therapy (PDT) is a modern photochemistry-based approach to the treatment of different pathologies, including cancer. The PDT uses light radiation of a specific wavelength and PS. Light radiation imparts cytotoxicity and photochemical reactions inducing singlet oxygen release followed by necrosis and apoptosis of cancer cells.

PDT benefits Low pain level Good cosmetic results Wide range of permitted PS and light doses Possibility of multiple procedure repetitions Possibility to combine with other treatments For correct choice of PDT regime it is necessary to know the distribution of PS within the treated tissue

Chlorine series photosensitizers Benefits: Fast delivery to tumor (~ 2h) Fast biodegradation (~ 24h) High quantum yield of singlet oxygen Two absorption peaks Two-wavelength probing can provide additional information!

Fluorescence imaging device LED excitation @405 nm and @660 nm CCD camera optical filter Home-made setup for PDT monitoring “Fluovizor” * LED excitation 405 nm 660 nm μa, mm-1 (rat brain) 2.2 0.5 μs, mm-1 (rat brain) 4.5 3.5 The difference in optical properties ** of tissue and PS provides the information about the depth * M. Kleshnin et al, Laser Phys. Lett., 12(11), 2015. ** J. Swartling et al, App. Optics, 44 (10), 2005.

Fluorescence model with diffusion approximation of RTE μa(λ)+μpsa(λ), μs(λ) Tumor R d * For medium radius R >> d lim 𝑑→∞ 𝑆 𝑒𝑚 =𝑐𝑜𝑛𝑠𝑡 (due to limited light penetration) * S. Jacques, J. Biomed. Opt., 15(5), 2010.

Fluorescence model with Monte-Carlo simulations μa(λ)+μpsa(λ), μs(λ) Tumor R μa(λ), μs(λ) Tissue d μa(λ)+μpsa(λ), μs(λ) R μa(λ), μs(λ) d

Effect of tumor invasion depth on fluorescence signals ratio Monte-Carlo simulations vs diffusion approximation Diffusion approximation for different PS concentrations

Phantoms for model experiment Absorption and scattering spectra Phantom + PS Phantom 2% Agar PS emission PS excitation

Results of model experiment Fluorescence for excitation @405 nm Fluorescence for excitation @660 nm Signal ratio

Preliminary in vivo results Experiment on volunteer’s hand Revixan (in gel) as PS Application to skin surface 30 min two-wavelength monitoring Changes in signals ratio Constant PS amount instead of concentration PS Time after application

Preliminary in vivo results via OCT Experiment on volunteer’s hand Revixan (in gel) as PS Application to skin surface OCT monitoring Changes in A-scans and OCT images Control 40 s 50 s 15 min Raw images 𝑵= 𝒊,𝒋 𝑺 𝒊,𝒋 𝒄𝒐𝒏𝒕𝒓 − 𝑺 𝒊,𝒋 𝟐 A-scans Difference in OCT images and first control image Control 2 s Control 45 s Application 40 s Application 50 s Application 15 min Decrease in OCT signal and increase in N reflects PS penetration into tissue

Conclusion Acknowledgement Analytical model for fluorescence from tumor tissue was presented Monte-Carlo simulations verified analytical results Two-wavelength probing can provide information about tumor invasion depth and PS concentration The method can be employed to differentiate for tumor invasion depths up to 2 mm (threshold dependent on optical properties of tissue) Preliminary in vivo results show that ratio of signals changes with PS penetration into tissue and can be used to estimate penetration depth Changes in OCT images reflect Ps penetration into tissue Acknowledgement The study was supported by the Russian Science Foundation (project #17-15-01264)

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