Dr.Janusz Dabrowski, Jagiellonian University
"Photodynamic Therapy in Near-Infrared"
Photodynamic therapy requires the combination of a photosensitizer, light and oxygento generate reactive oxygen species (ROS) that destroy the diseased tissue. Theoxidative stress induced by ROS triggers the destruction oftumor cells by apoptosis, necrosisor autophagy. The local inflammation resulting from PDTactivates anti-tumor immune responses capable of causing regression in distant tumors and induce long-term immune memory. These biological processes usually have synergetic effect in PDT but they are strongly dependent on the photosensitizer structure, type of tumor, oxygen availability and light doses. The directionality of light, the eventual affinity of photosensitizers towards tumors and the short diffusion radius of the ROS minimize the damage to healthy tissues, and make of PDT a very well tolerated therapy.
The search for “ideal photosensitizer” focuses on bacteriochlorin derivatives [1-2] because they meet most of desired properties, although earlier studies projected the idea that bacteriochlorins were too labile for PDT. Our bacteriochlorins closely approach the properties of an “ideal photosensitizer”: simple synthesis yielding a pure compound, molar absorption coefficient >100,000 M–1 cm–1 in the phototerapeutic window, controlled photostability, measurable fluorescence, n-octanol:water partition coefficient of 80, very low toxicity in the dark, and high quantum yield of reactive oxygen species.
The focus of this work is to determine and compare photochemical and photobiological properties of structurally related but with various polarity (hydrophilic, amphiphilic or hydrophobic) bacteriochlorins in the context of their application as promising PDT agents. Special attention is given to the description of the properties of NIR absorbing photosensitizers, because they provide the grounds to understand the molecular mechanisms and photodynamic efficacy. The in vitrobiological activity has been investigated against A549, B16F10 and CT26 cancer cells. The pharmacokinetics and biodistribution were studied in various animal models bearing above listed tumors. Exploratory PDT was performed 15 min., 24 h and 72 h after i.v. administration, and led to the complete disappearance of tumors for approximately 2 months and some of the animals treated with the 15 min. protocol were completely cured.The optimal formulation for photosensitizers and their time-dependent cellular uptake were described and characterized by fluorescence microscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM).
We have demonstrated that Pluronic P123 efficiently loads hydrophobic and amphiphilic photosensitizers, increases their stability, improves cellular uptake, biodistribution, pharmacokinetics and enables the efficient photogeneration of hydroxyl radicals resulting in efficient PDT of various types of cancer including pigmented melanoma.  Designed by us photosensitizers with pH-sensitive block copolymers overcome the resistance of melanoma to PDT due to increased selectivity towards tumor and combine effect of oxidative stress in target tissue with a systemic immune response triggered by acute, local inflammation.
1. J. M. Dąbrowski, L. G. Arnaut, Photochem. Photobiol. Sci. 14(2015) 1765.
2. J. M. Dąbrowski, B. Pucelik, L. G. Arnaut et al., Coord. Chem. Rev. 325(2016) 67.
3. B. Pucelik, L. G. Arnaut, G. Stochel, J.M. Dąbrowski, ACS Appl. Mater. Interfaces 8(2016) 22039.