Photosensitizing effects and physicochemical properties of chlorophyll a derivatives with hydrophilic oligoethylene glycol fragments at the macrocycle periphery

In this work, screening studies of the cytotoxic effect of chlorins with fragments of di-, tri-, and pentaethylene glycol at the macrocycle periphery in relation to HeLa, A549, and HT29 cells were performed. It is shown that, despite different hydrophobicity, all the compounds studied have a comparable photodynamic effect. The conjugate of chlorin e6 with pentaethylene glycol, which has the lowest tendency to association among the studied compounds with tropism for low density lipoproteins and the best characteristics of the formation of molecular complexes with Tween 80, has a significant difference in dark and photoinduced toxicity (ratio IC50(dark)/IC50(photo) approximately 2 orders of magnitude for all cell lines), which allows to hope for a sufficiently large "therapeutic window". A study of the interaction of this compound with HeLa cells shows that the substance penetrates the cell and, after red light irradiation induces ROS appearance inside the cell, associated, apparently, with the photogeneration of singlet oxygen. These data indicate that photoinduced toxic effects are caused by damage to intracellular structures as a result of oxidative stress. Programmed type of cell death characterized with caspase-3 induction is prevailing. So, the conjugate of chlorin e6 with pentaethylene glycol is a promising antitumor PS that can be successfully solubilized with Tween 80, which makes it suitable for further in vivo studies.

Solvation, Cancer Cell Photoinactivation and the Interaction of Chlorin Photosensitizers with a Potential Passive Carrier Non-Ionic Surfactant Tween 80

Cancer and drug-resistant superinfections are common and serious problems afflicting millions worldwide. Photodynamic therapy (PDT) is a successful and clinically approved modality used for the management of many neoplastic and nonmalignant diseases. The combination of the light-activated molecules, so-called photosensitizers (PSs), with an appropriate carrier, is proved to enhance PDT efficacy both in vitro and in vivo. In this paper, we focus on the solvation of several potential chlorin PSs in the 1-octanol/phosphate saline buffer biphasic system, their interaction with non-ionic surfactant Tween 80 and photoinactivation of cancer cells. The chlorin conjugates containing d-galactose and l-arginine fragments are found to have a much stronger affinity towards a lipid-like environment compared to ionic chlorins and form molecular complexes with Tween 80 micelles in water with two modes of binding. The charged macrocyclic PSs are located in the periphery of surfactant micelles near hydrophilic head groups, whereas the d-galactose and l-arginine conjugates are deeper incorporated into the micelle structure occupying positions around the first carbon atoms of the hydrophobic surfactant residue. Our results indicate that both PSs have a pronounced affinity toward the lipid-like environment, leading to their preferential binding to low-density lipoproteins. This and the conjugation of chlorin e₆ with the tumor-targeting molecules are found to enhance their accumulation in cancer cells and PDT efficacy.