Chlorophyll a in cyclodextrin supramolecular complexes as a natural photosensitizer for photodynamic therapy (PDT) applications

Chlorophyll a (Chl a), an amphipathic porphyrin, was employed as natural photosensitizer for photodynamic therapy applications. Due to its lacking solubility in water and high tendency to aggregate, Chl a was included into different modified cyclodextrins (CDs) to form stable water-soluble supramolecular complexes. To achieve this aim, 2-Hydroxypropyl-beta-cyclodextrin (2-HP-beta-CD), 2-Hydroxypropyl-gamma-cyclodextrin (2-HP-gamma-CD), Heptakis (2,6-di-o-methyl)-beta-cyclodextrin (DIMES) and Heptakis(2,3,6-tri-o-methyl)beta-cyclodextrin (TRIMEB) were used. The chemical physical properties of Chl a/CD complexes in cellular medium were studied by means of UV-Vis absorption spectroscopy. Results demonstrated the good aptitude of 2-HP-gamma-CD, and more particularly of 2-HP-beta-CD, to solubilize the Chl a in cell culture medium in monomeric and photoactive form. Then, Chl a/2-HP-beta-CD and Chl a/2-HP-gamma-CD complexes were evaluated in vitro on human colorectal adenocarcinoma HT-29 cell line, and cytotoxicity and intracellular localization were respectively assessed. Further tests, such as phototoxicity, ROS generation, intracellular localization and mechanism of cell death were then focused exclusively on Chl a/2-HP-beta-CD system. This complex exhibited no dark toxicity and a high phototoxicity toward HT-29 cells inducing cell death via necrotic mechanism. Therefore, it is possible to affirm that Chl a/2-HP-beta-CD supramolecular complex could be a promising and potential formulation for applications in photodynamic therapy.