Interaction of phthalocyanines with lipid membranes: a spectroscopic and functional study on isolated rat liver mitochondria

Nanoparticles Yield Increased Drug Uptake and Therapeutic Efficacy upon Sequential Near-Infrared Irradiation

Nanoparticles offer great opportunities for precision medicine. However, the use of nanoparticles as smart photosensitizers that target tumor biomarkers and are responsive to the tumor microenvironment has yet to be explored. Herein, prostate cancer (PCa)-selective theranostic gold nanoparticles (AuNPs) for precise cancer imaging and therapy are developed. Silicon phthalocyanine, Pc158, was synthesized and deactivated by conjugating it to AuNPs via a biocleavable linker. In vitro and in vivo, the targeted AuNPs show excellent selectivity for PSMA-positive tumor cells. Triggered release of the therapeutic, Pc158, followed by sequential photodynamic therapy (PDT) results in significant inhibition of tumor growth. Further, we demonstrate that multiple sequential PDT greatly enhances nanoparticle uptake and therapeutic efficacy. PSMA is highly expressed in the neovasculature of most other solid tumors in humans, as well as PCa, making this approach of great practical interest for precision PDT in a wide range of cancers.

Alkyl-substituted magnesium phthalocyanine: phototoxicity after excitation of higher electronic states in cells in vitro

Photodynamic tumour therapy (PDT) on the basis of a sequential two-photon excitation of suitable sensitizers is expected 1) to prevent skin phototoxicity caused by day-light and 2) may occur via an oxygen-independent mechanism of photosensitization. Here we investigated cellular uptake, localization and phototoxicity of ( t-butyl )4- PcMg , a promising dye for a sequential two-step activation, in Jurkat cells (human T cell line) and murine hybridoma cells (B cells) in vitro. Pheophorbide a (pheo) was used as a classical Type II reference sensitizer. Excitation of higher singlet states was performed both by direct UV-excitation and by sequential two-step laser excitation in the Q-band with maximum photon flux densities of about 1026 phot.cm−2.s−1. Irradiation of ( t-butyl )4- PcMg in cells in vitro is accompanied by a rapid destruction of the dye, as was proved by confocal fluorescence microscopy. Irradiated cells exhibit a less pronounced decrease of viability and a transient cell cycle arrest of about 24 h. Pheo incubated cells are characterized by a complete stop of proliferation. In contrast, no long-lasting phototoxicity was observed with ( t-butyl )4- PcMg . Low fluorescence levels and rapid photobleaching prevented the identification of intracellular dye-localization. Our data indicate the presence of a radical mechanism as origin of an irreversible dye destruction that accounts for the low phototoxicity of ( t-butyl )4- PcMg .

Photodynamic activity and binding of sulfonated metallophthalocyanines to phospholipid membranes: Contribution of metal-phosphate coordination

Photosensitized efficacy of tetrasulfonated phthalocyanines of zinc, aluminum and nickel (ZnPcS(4), AlPcS(4) and NiPcS(4), respectively) as studied by gramicidin channel (gA) photoinactivation was compared with adsorption of the dyes on the surface of a bilayer lipid membrane as measured by the inner field compensation method. The adsorption of the negatively charged phthalocyanines on diphytanoylphosphatidylcholine (DPhPC) membranes led to formation of a negative boundary potential difference between the membrane/water interfaces. Good correlation was shown between the photodynamic activity and the membrane binding of the three metallophthalocyanines. ZnPcS(4) appeared to be the most potent of these photosensitizers, while NiPcS(4) was completely ineffective. All of these phthalocyanines displayed no binding and negligible gA photoinactivation with membranes formed of glycerol monooleate (GMO), whereas Rose Bengal exhibited significant binding and photodynamic efficacy with GMO membranes. Gramicidin photoinactivation in the presence of AlPcS(4), being insensitive to the ionic strength of the bathing solution, was inhibited by fluoride and attenuated by phosphate ions. A blue shift of the fluorescence peak position of ZnPcS(4) dissolved in ethanol was elicited by phosphate, similarly to fluoride, which was indicative of the coordination interaction of these ions with the central metal atom of the phthalocyanine macrocycle. This interaction was enhanced in the medium modeling the water-membrane interface. The results obtained imply that binding of tetrasulfonated metallophthalocyanines to phospholipid membranes is determined primarily by metal-phosphate coordination.

Photodynamic therapy of cerebral glioma – A review Part I – A biological basis

Photodynamic therapy (PDT) has been investigated extensively in the laboratory for decades, and for over 25 years in the clinical environment, establishing it as a useful adjuvant to standard treatments for many cancers. A combination of both photochemical and photobiological processes occur that lead to the eventual selective destruction of the tumour cells. It is a potentially valuable adjuvant therapy that can be used in conjunction with other conventional therapies for the treatment of cerebral glioma. PDT has undergone extensive laboratory studies and clinical trials with a variety of photosensitizers (PS) and tumour models of cerebral glioma. Many environmental and genetically based factors influence the outcome of the PDT response. The biological basis of PDT is discussed with reference to laboratory and preclinical studies.

Interaction of tetraphenyl-porphyrin derivatives with DPPC-liposomes: an EPR study

The effect of the symmetry and polarity of the porphyrin molecules on their membrane localization and interaction with membrane lipids were investigated by electron paramagnetic resonance (EPR). For this purpose, two glycoconjugated tetraphenyl porphyrin derivatives were selected, respectively, symmetrically and asymmetrically substituted. Small unilamellar liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and spin labeled stearic acids were prepared. The spin probe was located at the 5th or 7th or 12th or 16th position of the hydrocarbon chain in order to monitor various regions of the lipid bilayer. EPR spectra of porphyrin-free and porphyrin-bound liposomes were recorded at various temperatures below and above the phase transition temperature of DPPC. The effect on membrane fluidity proved to be stronger with the asymmetrical porphyrin derivative than with the symmetrical one. The rigidity increased when the spin label was near lipid head groups. The difference observed between control and porphyrin-treated samples when measured below the main lipid transition temperature disappeared at higher temperature. When the spin label was near the end of the hydrophobic tails, the symmetrical porphyrin derivative caused increase in fluidity, while the asymmetrical one slightly decreased it. To explain this phenomenon we propose that the asymmetrical derivative exerts a stronger ordering effect caused by its fluorophenyl group located at the level of the lipid heads, which is attenuated to the hydrophobic tails. The perturbing effect of the symmetric derivative could not lead to similar extent of ordering at the head groups and looses the hydrocarbon chains deeper in the membrane.

The Influence of Depleted Glutathione Levels on the Photodynamic Action of Zinc Phthalocyanine in CHO K1 Cells

OBJECTIVE

The current study focuses on any influence that depletion of endogenous glutathione in CHO K1 cells may have on the photodynamic action of zinc phthalocyanine (ZnPc).

MATERIALS AND METHODS

Two lasers--a HeNe laser, 632.5 nm, maximum power output 3.5 mW, and a Toshiba semiconducting laser, 670 nm, maximum power of 7 mW--were used. Chinese Hamster Ovary cells (CHO K1) were exposed to light, 2-10 J. Cellular reduced glutathione levels [GSH] were depressed prior to exposure to ZnPc and laser light, using buthionine sulphoximine, a potent inhibitor of gamma-glutamylcysteine synthetase. The influence of hypoxic intracellular conditions was studied by reduction of oxygen content of cells by 80% following purging of cell cultures with nitrogen.

RESULTS

In well-aerated cells, doubling times are reduced by the photodynamic action of ZnPc by 29 +/- 6%, fig 2 (p = 0.01). Cells with lowered [GSH] do not show this effect (p = 0.1). When hypoxic cells are studied at normal [GSH], no photodynamic effect is observed (p = 0.1). When cell viability is studied, using the 670-nm laser, a photodynamic effect is observed, (80% fall from controls, p < 0.001), irrespective of the cellular [GSH] level for a single dose of 6 J. This effect is observed in cells with normal [GSH], for varied doses of 2 J and higher (63% fall at 2 J, p < 0.001).

CONCLUSIONS

Lowered [GSH] was observed to depress the photodynamic effect of ZnPc when cell-doubling times were the endpoint. The photostimulating effect of ZnPc was similarly suppressed by hypoxic conditions. When cell viability was the endpoint, then a photodynamic effect of ZnPc was observed irrespective of the endogenous [GSH] values.

Temperature-induced changes in fluorescence properties as a probe of porphyrin microenvironment in lipid membranes. 1. The partition of hematoporphyrin and protoporphyrin in liposomes

Temperature-induced fluorescence changes were studied for hematoporphyrin and protoporphyrin, incorporated into liposomes of dipalmitoylphosphoglycerocholine (Pam2GroPCho) or dimiristoylphosphoglycerocholine (Myr2GroPCho). In some cases, cholesterol or cardiolipin were added to the vesicles for better mimicking the lipid composition of biological membranes. The experimental conditions were appropriately chosen in order to reproduce different possible configurations of the porphyrin molecule in lipid membranes: namely, at the polar water/headgroups, headgroups/lipid and lipid/lipid interfaces. A peculiar feature observed in some of the above liposomal systems was the appearance of discontinuities in the Arrhenius plots of the fluorescence quantum yields, with relevant changes of the values of activation energies. These discontinuities were due to an increase of the fluorescence signal in a temperature range corresponding to the transition of the different lipids from the gel-to-liquid crystal state. The observed phenomena are consistent with the formation of non-covalent linear dimers or linear higher aggregates of the porphyrin molecules. The intermolecular contacts required for the formation of these species are favoured by at least three situations: disruption of the ordered lipid structure during the gel-to-liquid crystal phase transition; competition of other polar groups (e.g., the -OH group of cholesterol) with the porphyrin carboxylate groups for the polar phospholipid headgroups; and steric constraints due to overcrowding of porphyrin molecules in a restricted space.

Temperature-induced changes in fluorescence properties as a probe of porphyrin microenvironment in lipid membranes. 2. The partition of hematoporphyrin and protoporphyrin in mitochondria

The temperature dependence of hematoporphyrin and protoporphyrin fluorescence quantum yields (phi F) was studied after delivery to whole mitochondria or isolated inner (IMM) and outer (OMM) mitochondrial membranes, obtained from liver of Wistar rats. These studies are very sensitive to variations of the porphyrin lipid environment. Before incorporation, the porphyrins were dissolved in 0.01 M sodium phosphate, 0.15 M NaCl, pH 7.4) NaCl/Pi (only hematoporphyrin) or dispersed into liposomes of dipalmitoylphosphoglycerocholine (Pam2GroPCho), sometimes enriched with cholesterol or cardiolipin. Whole mitochondria show higher incorporation capacity of hematoporphyrin and protoporphyrin than isolated IMM and OMM, probably because additional, energy-sensitive transport mechanisms for the porphyrin uptake occur in intact organelles. A small decrease in protoporphyrin uptake is observed in OMM in comparison with IMM; in contrast, the decrease in hematoporphyrin uptake by OMM is rather significant. A comparison between the results obtained with IMM, OMM and whole mitochondria show that both porphyrins, when released to the intact organelles, preferentially localize in the IMM, irrespective of the lipid carrier used. NaCl/Pi-dissolved hematoporphyrin probably interacts with some membrane proteins, due to the similarity of the Arrhenius plots with those obtained for liposome-entrapped human serum albumin/hematoporphyrin complexes which were used as models to mimic hematoporphyrin-membrane protein binding sites. Liposomal hematoporphyrin and protoporphyrin bind to lipid domains. Hematoporphyrin accumulates in specific, localized lipid regions, perhaps in the boundary lipids area surrounding some inner-mitochondrial carriers; protoporphyrin accomodates in more rigid, lipid areas. On these bases, the higher photoactivity of hematoporphyrin, previously observed in mitochondria, in comparison with protoporphyrin, can be easily explained. Formation of linear dimers/aggregates, endowed with higher phi F than that of the monomers, are postulated to occur for both porphyrins only in the inner mitochondrial membrane.

Photophysical properties of porphyrins in biological membranes

This review illustrates the photophysical properties of some porphyrins, especially those used for biomedical applications, in relation to their photosensitizing efficiency in biological membranes. Porphyrin absorption and luminescence properties are mainly examined. The factors influencing the affinity of porphyrins for biological membranes, including the dye hydrophobicity, the charge and aggregation state, the pH of the medium and the physicochemical properties of the dye environment, are discussed. These factors determine the differences in the photophysical properties of porphyrins in biological membranes. Particular attention is paid to the porphyrin aggregation state: only monomeric species and possibly planar end-to-end aggregates are endowed with significant photosensitizing ability. Many conclusions presented are based on data obtained on membrane model systems such as micelles or liposomes which can mimic specific situations occurring in cells.