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.

Monocationic Chlorin as a Promising Photosensitizer for Antitumor and Antimicrobial Photodynamic Therapy.

Cancer is one of the leading causes of death worldwide. Despite substantial progress in the understanding of tumor biology, and the appearance of new generations of targeted drugs and treatment techniques, the success achieved in this battle, with some notable exceptions, is still only moderate. Photodynamic therapy (PDT) is a successful but still underestimated therapeutic modality for treating many superficial cancers. In this paper, we focus on the extensive investigation of the monocationic chlorin photosensitizer (PS), considered here as a new photosensitizing agent for both antitumor and antimicrobial PDT. This monocationic chlorin PS (McChl) obtained from methylpheophorbide a (MPh) via a two-step procedure is well soluble in water in the physiological temperature range and forms stable complexes with passive carriers. McChl generates singlet oxygen with a good quantum yield in a lipid-like environment and binds mainly to low- and high-density lipoproteins in a vascular system. A comparison of the photodynamic activity of this agent with the activity of the well-established photosensitizer chlorin e6 (Chl e6) clearly indicates that McChl provides a much more efficient photoinactivation of malignant and microbial cells. The pilot PDT treatment of M1 sarcoma-bearing rats with this PS demonstrates its good potential for further preclinical investigations.

Accumulation of chlorine e6 derivatives in cells with different level of expression and function activity of multidrug resistance protein P-gp 170.

AIM: This work deals with studying the influence of overexpression and function activity of multidrug transporter protein P-gp 170 on the intracellular accumulation of several porphyrin sensitizers, including chlorin e6 (Chl e6), di- (DME) and trimethyl esters (TME) of Chl e6. METHODS: A parental IM9 cell line and two IM9 drug-resistant IM9 sublines were used. With flow cytometry technique the rates of chlorines accumulation in different IM9 cells and values were related to the extent of multidrug resistance (MDR) phenotype. RESULTS: Using P-gp 170-specific antibodies and fluorescent probe JC-1 an increased expression and function activity of P-gp 170 was detected for drug-resistant cells. It was obtained that drug-resistant IM9 cells accumulated chlorines to a lesser extent than the respective wild type, however the differences did not exceed 30%. Verapamil, cyclosporine, known to reverse the MDR phenotype affects equally IM9-Vinc IM9-Tax and Im9 cells. CONCLUSION: Our results demonstrate that the P-gp 170 does not appear to play a role in the intracellular accumulation of chlorines. Since the enhanced activity of P-gp 170 in tumor cells is a factor of their resistance to the action of various antitumor drugs, we conclude that photodynamic therapy could be useful in killing cells exhibiting the MDR.

Modulation of delayed type hypersensitivity in mice treated with photoproducts of various photosensitizers used in photodynamic therapy.

Photodynamic therapy is frequently accompanied by the induction of immunosuppression. The photochemical mechanisms behind the induction of this immunosuppression are not clear. The purpose of this study was to evaluate the potential of photoproducts of merocyanine 540 (MC540), protoporphyrin IX (PPIX) and hematoporphyrin derivative (HpD) to cause modulation (suppression/activation) of the T cell immune response in vivo. The approach that we have adopted is the pre-irradiation of a photosensitizer solution with the subsequent application of the products of photosensitizer photodegradation in animals. In this approach the photochemical mechanisms of type I and II are not involved in the photosensitized modification of biological targets in vivo. Using the model of delayed type hypersensitivity (DTH) reaction to sheep red blood cells in mice, we have demonstrated that the photoproducts of three essentially different photosensitizers affect T-cell immunity. The HpD photoproducts had a suppressive effect on the DTH, while products of PPIX photodegradation enhanced the DTH nearly twice. Pre-irradiated MC540 strongly modulated the DTH response, i.e. the DTH was enhanced at low doses and inhibited at higher doses. Our results strongly indicate that at least part of the photodynamic therapy-induced immunomodulation may occur via the photobleaching of photosensitizers accompanied by the generation of photoproducts, which can affect T cell immunity.