Verapamil enhances the uptake and the photocytotoxic effect of PII, but not that of tetra(4-sulfonatophenyl)porphine

Studies on function of P-glycoprotein in photodynamic therapy of endometriosis

OBJECTIVE

The aim of the present study was to examine whether the effects of endometriosis-targeted photodynamic therapy (PDT), dependent on 5-aminolevulinic acid (ALA), rely on the presence of P-glycoprotein (P-gp), which is regarded as constituting one of the causes of multidrug resistance phenomenon.

BACKGROUND

The significance of the undertaken studies reflects the complete absence of reports related to the modulation of P-gp activity and efficacy of PDT in patients with endometriosis.

MATERIALS AND METHODS

Tissue samples of normal endometria were obtained from eight women after hysterectomy who were diagnosed with cervical intra-epithelial neoplasia. Fragments of ovarian endometriosis were obtained from 15 women. Epithelial cells were isolated from the material and in in vitro conditions were preincubated with P-gp blocker-verapamil-before ALA-PDT. The cytotoxicity was evaluated using the XTT test, allowing us to estimate cell growth inhibition. Statistical analysis of the results involved the nonparametric Wilcoxon paired rank test and the Mann-Whitney U-test using the Statistica v5 software (p < 0.05). In parallel, P-gp presence in the analyzed material was evaluated using immunohistochemistry.

RESULTS

In normal endometrial epithelium, verapamil was shown to intensify phototoxic effects at 2 and 4 mmol/L ALA (p < 0.05). In endometriotic epithelium, such intensification was noted in all examined concentrations of ALA (p < 0.001). Moreover, the ectopic epithelial cells were more sensitive than eutopic epithelial cells to PDT upon ALA alone, as well as after preincubation with verapamil. Immunohistohemical analysis allowed us to demonstrate the absence of glycoprotein P in normal endometrium. In endometriosis, P-gp was localised in both the epithelium and the stroma of the examined material.

CONCLUSION

Phototoxic effects could be amplified in epithelial cells of endometriotic foci by appropriate action of verapamil and 5-aminolevulinic acid.

An Insight into the Mechanisms of the Phototoxic Response Induced by Cyamemazine in Cultured Fibroblasts and Keratinocytes¶

The phototoxicity of cyamemazine (CMZ, Tercian), a neuroleptic of the phenothiazine family, has recently been reported in humans. CMZ has an absorbance maximum at 267 nm (molar absorptivity, 25,800 M(-1) cm(-1)) but a weaker molar absorptivity in the ultraviolet A (UV-A) region. CMZ exhibits a fluorescence with maximum emission at 535 nm and a quantum yield of 0.11. CMZ is a powerful photosensitizing agent toward HS 68 human skin fibroblasts and NCTC 2544 keratinocytes. At a UV-A radiation dose of 10 J/cm2, innocuous to cells in the absence of CMZ, the LD50 (lethal dose corresponding to 50% killing) are 0.5 and 1 microM for the fibroblasts and the keratinocytes, respectively, after overnight incubation with the drug. Short incubation times do not significantly alter the LD50. The CMZ-induced phototoxicity is accompanied by lipid membrane peroxidation consistent with the amphiphilic character of this photosensitizer. Keratinocytes are an order of magnitude less sensitive to the photosensitized lipid peroxidation than fibroblasts. Microspectrofluorometry reveals that lysosomal membranes are major sites of CMZ incorporation into the two cell lines because a Forster-type resonance energy transfer process occurs from CMZ to LysoTracker Red DND99 (LTR), a specific fluorescent probe of lysosomal membranes. The CMZ-photosensitized destruction of LTR demonstrates that CMZ retains its photosensitizing capacity after its lysosomal uptake.

Encapsulation of p-THPP into nanoparticles: cellular uptake, subcellular localization and effect of serum on photodynamic activity

The cellular uptake, localization and efflux of meso-tetra-(4-hydroxyphenyl)porphyrin (p-THPP)-loaded nanoparticles have been studied in EMT-6 tumor cells. The effect of blood serum on photocytotoxicity has also been evaluated. Sub-130 nm nanoparticles based on poly(D,L-lactide-co-glycolide) (PLGA) (50:50 PLGA and 75:25 PLGA) and poly(D,L-lactide) (PLA) have been examined in comparison with free p-THPP. For all formulations tested, uptake of photosensitizer into cells was dependent on concentration, time and temperature. All nanoparticulate formulations accumulated within the cells to a greater extent relative to free drug. Indeed, the fluorescence intensities measured on EMT-6 cells treated with p-THPP-loaded nanoparticulate formulations were at least two-fold higher than those obtained with free dye. Furthermore, the highest accumulation level was found with PLGA nanoparticles. Fluorescence microscopy revealed that endocytosis is a major intracellular sequestration mechanism of these p-THPP formulations and that these were localized into early and late endosomes. The efflux study performed on both nonirradiated and irradiated cells indicated that free and p-THPP-loaded nanoparticles gradually escaped from EMT-6 cells as a function of time. This was more pronounced when cells were treated with nanoparticles and irradiated, reflecting important photodamage. It was also found that regardless of the nanoparticulate formulations tested, p-THPP photocytotoxicity was influenced by the concentration of the serum.

Evaluation of different photosensitizers for use in photochemical gene transfection

Many potentially therapeutic macromolecules, e.g. transgenes used in gene therapy, are taken into the cells by endocytosis, and have to be liberated from endocytic vesicles in order to express a therapeutic function. To achieve this we have developed a new technology, named photochemical internalization (PCI), based on photochemical reactions inducing rupture of endocytic vesicles. The aim of this study was to clarify which properties of photosensitizers are important for obtaining the PCI effect improving gene transfection. The photochemical effect on transfection of human melanoma THX cells has been studied employing photosensitizers with different physicochemical properties and using two gene delivery vectors: the cationic polypeptide polylysine and the cationic lipid 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). Photochemical treatment by photosensitizers that do not localize in endocytic vesicles (tetra[3-hydroxyphenyl]porphyrin and 5-aminolevulinic acid-induced protoporphyrin IX) do not stimulate transfection, irrespective of the gene delivery vector. In contrast, photosensitizers localized in endocytic vesicles stimulate polylysine-mediated transfection, and amphiphilic photosensitizers (disulfonated aluminium phthalocyanine [AlPcS2a] and meso-tetraphenylporphynes) show the strongest positive effect, inducing approximately 10-fold increase in transfection efficiency. In contrast, DOTAP-mediated transfection is inhibited by all photochemical treatments irrespective of the photosensitizer used. Neither AlPcS2a nor Photofrin affects the uptake of the transfecting DNA over the plasma membrane, therefore photochemical permeabilization of endocytic vesicles seems to be the most likely mechanism responsible for the positive PCI effect on gene transfection.