Biological activities of phthalocyanines--VI. Photooxidation of L-tryptophan by selectively sulfonated gallium phthalocyanines: singlet oxygen yields and effect of aggregation

BOINPYs: facile synthesis and photothermal properties triggered by photoinduced nonadiabatic decay

Photothermal agents (PTAs) represent a core component of photothermal therapy (PTT). However, the current photothermal dyes are almost derived from well-known chromophores such as porphyrins, cyanine, and BODIPYs, and the design of new chromophores as versatile building blocks for PTA is considerably challenging because of the complexity of the modulation of excited-states. Herein, we adopted the concept of photoinduced nonadiabatic decay (PIND) to develop a photothermal boron-containing indoline-3-one-pyridyl chromophore (viz. BOINPY) with a facile one-pot synthesis and high yields. BOINPY derivatives exhibited specific features that fully address the concerns related to the design of PTA. The behavior and mechanism of BOINPYs for generating heat through the conical intersection pathway, which is called PIND, have been well understood through theoretical calculations. After encapsulation into the F127 copolymer, BOINPY@F127 nanoparticles displayed efficient photothermal conversion and performed well in the treatment of solid tumors upon light irradiation with good biocompatibility. This study provides useful theoretical guidance and concrete photothermal chromophores, which offer a versatile strategy embedding tunable properties for the development of diverse high-performance PTA.

Synthesis, characterization and investigation of algal oxidative effects of water-soluble copper phthalocyanine containing sulfonate groups

In this study, the chemical and algicidal properties of the newly synthesized compound (2) were evaluated and its algal oxidative effects were determined in Arthrospira platensis and Chlorella vulgaris. First, we have reported on the synthesis and characterization of highly water-soluble copper (II) phthalocyanine (2), containing sodium 2-mercaptoethanesulfonate (2) substituents at the peripheral positions. Some spectroscopic techniques were used to characterize the new synthesized compound (2). In terms of biological properties, C. vulgaris were more tolerance to compound (2) than A. platensis depending to growth parameters. When SOD (Superoxide dismutase) activity significantly increased at 0.25 ppb and 1.5 ppb concentrations in A. platensis cultures, it increased at 6 ppb concentration in C. vulgaris cultures. GR (Glutathione reductase) activity decreased at 1 ppb and 1.5 ppb concentrations while APX (Ascorbate peroxidase) activity did not show a significant change at any concentrations in A. platensis cultures. GR activity showed a significant increase at 6 ppb concentration, while APX activity increased at all concentrations compared to control in C. vulgaris cultures. MDA (malondialdehyde) and H2O2 content decreased at 1 and 1.5 ppb concentrations but there were significant increases in the proline content at all concentrations compared to the control in A. platensis. MDA, H2O2 and free proline contents showed a significant increase at 0.5 ppb concentration in C. vulgaris. In conclusion, compound (2) have algicidal effects, and also it causes to oxidative stress in these organisms.

The detection sensitivity of commonly used singlet oxygen probes in aqueous environments

The sensitivity for singlet oxygen (¹O₂) of two convenient ¹O₂ probes, 1,3-diphenylisobenzofuran (DPBF) and 9,10-Anthracenediyl-bis(methylene)dimalonic acid (ABDA), has been investigated in different aqueous environments. Both probes are commercially available at reasonable cost and can be used with standard UV-vis spectrometers. Although DPBF is not soluble in neat water and is not specific to the detection of ¹O₂, it has very high, essentially diffusion-limited, reactivity towards ¹O₂; it can trap up to 50% of all ¹O₂ created in alcohol/water or micellar solution, and even more when replacing H₂O by D₂O, which makes it highly useful when the process under investigation does not yield much ¹O₂. On the other hand, ABDA has a much lower reactivity, reacting with only 2% of the singlet oxygen generated in H₂O, as well as a smaller extinction coefficient, resulting in a much smaller spectroscopic response, but is soluble in neat water and is specific for ¹O₂, allowing for discrimination from other reactive oxygen species. The results presented here not only allow a comparative assessment of the usefulness of the two ¹O₂ probes, but also provide a reference for an accurate absolute quantification of the amount of ¹O₂ generated in an experiment from the observed absorbance bleach.

Solvent and Heavy-Atom Effects on the O2(X3Σg-) → O2(b1Σg+) Absorption Transition

The effect of 16 liquid solvents on both the spectrum and molar absorption coefficient of the X³Σ_g^- → b¹Σ_g⁺ transition in molecular oxygen has been examined. The ability to monitor this weak transition using air or oxygen saturated samples at atmospheric pressure was facilitated by the rapid and efficient O₂(b¹Σ_g⁺) → O₂(a¹Δ_g) transition, which allowed the use of O₂(a¹Δ_g) phosphorescence as a sensitive probe of O₂(b¹Σ_g⁺) production. The results of these O₂(a¹Δ_g) phosphorescence experiments are consistent with the results of independent experiments in which the O₂(a¹Δ_g) thus produced was "trapped" via a chemical reaction. The data recorded were used to calculate rate constants for the O₂(b¹Σ_g⁺) → O₂(X³Σ_g^-) radiative transition, a parameter that is otherwise difficult to directly obtain from such a wide range of solvents using O₂(b¹Σ_g⁺) → O₂(X³Σ_g^-) phosphorescence. The data show that the response of the O₂(b¹Σ_g⁺) → O₂(X³Σ_g^-) radiative transition to solvent is not the same as that of the O₂(b¹Σ_g⁺) → O₂(a¹Δ_g) and O₂(a¹Δ_g) → O₂(X³Σ_g^-) radiative transitions, both of which have been extensively examined over the years. However, our data are consistent with a theoretical model proposed by Minaev for the effect of solvent on radiative transitions in oxygen and, as such, arguably provide one of the final chapters in describing a system that has challenged the scientific community for years.

Glycosylated Metal Phthalocyanines

In the first part; the syntheses of mono-; di-; and tetra-glycosylated phthalonitriles is described; which are the most used starting materials for the preparation of the corresponding glycosylated metal (mostly zinc) phthalocyanines. In the second section; the preparation of symmetric and unsymmetric mono-; tetra-; and octa- glycosylated zinc phthalocyanines are reviewed; in which the sugar is attached to the phthalocyanine macrocycle; either anomerically or via another one of its OH-groups.

Singlet Oxygen Quantum Yields of Different Photosensitizers in Polar Solvents and Micellar Solutions

The singlet oxygen luminescence method and the photochemical methods using 1,3-diphenylisobenzofuran ( DPBF ) or bilirubin ditaurate ( BDT ) as chemical quenchers were employed to determine the single oxygen quantum yields (ΦΔ) of different phthalocyanines and tris(2,2″-bipyridyl)ruthenium(II) dichloride in dimethylformamide ( DMF ) or aqueous micellar solution of 0.1 M CTAC (cetyltrimethylammonium chloride). Additionally, a perylenetetracarboxylic acid diimide derivative was examined in DMF . In a series of tetrasulfonated phthalocyanines ( PTS ) the following order was found: ZnPTS > GaPTS > AlPTS ≈ H 2 PTS > CoPTS . In general, the singlet oxygen quantum yields are higher in DMF than in 0.1 M CTAC/H 2 O . The results obtained with the photochemical systems are comparable with those obtained by the photophysical method.

The photochemical DPBF method results in absolute values of ΦΔ. However, in micellar solution, chain reactions occur when DPBF is used as chemical quencher in the photo-oxidative process. This problem can be overcome by adding sodium thiosulphate which is able to destroy the endoperoxide initially formed. BDT can be used as quencher in different solvents to determine ΦΔ relative to a photosensitizer with known singlet oxygen quantum yield in the respective solvent.

In comparison to the chemical methods the luminescence method exhibits the advantage that side reactions of the quencher are excluded. But normally the ΦΔ values obtained are relative to a reference, since absolute determinations need much larger efforts.

Singlet Oxygen Quantum Yields of Different Photosensitizers in Polar Solvents and Micellar Solutions

The singlet oxygen luminescence method and the photochemical methods using 1,3-diphenylisobenzofuran ( DPBF ) or bilirubin ditaurate ( BDT ) as chemical quenchers were employed to determine the single oxygen quantum yields (ΦΔ) of different phthalocyanines and tris(2,2″-bipyridyl)ruthenium(II) dichloride in dimethylformamide ( DMF ) or aqueous micellar solution of 0.1 M CTAC (cetyltrimethylammonium chloride). Additionally, a perylenetetracarboxylic acid diimide derivative was examined in DMF . In a series of tetrasulfonated phthalocyanines ( PTS ) the following order was found: ZnPTS > GaPTS > AlPTS ≈ H 2 PTS > CoPTS . In general, the singlet oxygen quantum yields are higher in DMF than in 0.1 M CTAC/H 2 O . The results obtained with the photochemical systems are comparable with those obtained by the photophysical method.

The photochemical DPBF method results in absolute values of ΦΔ. However, in micellar solution, chain reactions occur when DPBF is used as chemical quencher in the photo-oxidative process. This problem can be overcome by adding sodium thiosulphate which is able to destroy the endoperoxide initially formed. BDT can be used as quencher in different solvents to determine ΦΔ relative to a photosensitizer with known singlet oxygen quantum yield in the respective solvent.

In comparison to the chemical methods the luminescence method exhibits the advantage that side reactions of the quencher are excluded. But normally the ΦΔ values obtained are relative to a reference, since absolute determinations need much larger efforts.

Photodynamic therapy against achromic M6 melanocytes: phototoxicity of lipophilic axially substituted aluminum phthalocyanines and hexadecahalogenated zinc phthalocyanines

Lipophilic and axially substituted tri-n-hexylsiloxy aluminum phthalocyanine and cholesteryloxy diphenylsiloxy aluminum phthalocyanine were synthesized and assayed in PDT against M6 melanocytes. In the conditions used (λ > 480 nm , 10 mW cm-2, egg-yolk lecithin or cremophor EL formulation) they both exhibited a higher photodynamic effect than chloroaluminum phthalocyanine. They displayed 2% to 3.5% cell viability at 10-5M dose for 20 min irradiation. Hexadecafluoro zinc phthalocyanine was synthesized to increase the lipophilicity of zinc phthalocyanine, hexadecachloro zinc phthalocyanine was also included because it would theoretically enhance the phototoxicity. In all the delivery systems used, their photodynamic effect against M6 melanocytes was lower in comparison with zinc phthalocyanine and axially substituted aluminum phthalocyanines. A 2 h irradiation treatment with 3 × 10-6 M hexadecafluoro zinc phthalocyanine and 10-5 M hexadecachloro zinc phthalocyanine led to 60% and 15% cell viability respectively. In all cases, the cell killing effect was light-and dose-dependent and was higher in cremophor EL micelles than in the egg-yolk lecithin formulation.

Current status of phthalocyanines in the photodynamic therapy of cancer

Photodynamic therapy is a binary treatment now accepted in clinic for various malignancies in several countries around the world. Phthalocyanine molecules are second-generation photosensitizers with enhanced photophysical and photochemical properties over those of porphyrins. They have been shown to be phototoxic against a number of cell types and tumor models. A great deal of research has been devoted to the elucidation of their mechanism of action and mode of cell death. The present paper reviews phthalocyanine pre-clinical anti-cancer research with emphasis on phthalocyanine induced apoptosis using a silicon phthalocyanine, Pc 4. A brief summary of the latest clinical results using phthalocyanines is presented.

Photodynamic Therapy:In VitroPhotosensitizing Efficacy of Bis(tri-n-hexylsiloxy)silicon Phthalocyanine against Achromic M6 Melanocytes. ESR Study of Active Oxygen Intermediates

The in vitro photodynamic effect of bis(tri-n-hexylsiloxy)silicon phthalocyanine has been evaluated against the melanotic M6 cell line. The results showed that at 10-5M dose, LD50is obtained for a 150 J cm-2light dose and LD90for 540 J cm-2. Electron spin resonance spectroscopy was used with spin traps to study the type I and type II photochemical pathways involved and to detect active oxygen intermediates such as singlet oxygen, oxygen superoxide and hydroxyl radical. The two mechanisms occurred simultaneously and no change was observed when the phthalocyanine was entrapped in liposomes.

Sulfonated phthalocyanines: aggregation and singlet oxygen quantum yield in aqueous solutions

The influence of sulfonation degree (n) and central atom nature on singlet oxygen quantum yield (ΦΔ) were studied for a series of sulfonated phthalocyanine metal complexes MPcS n mix . It was found that in DMSO, where the studied dyes exist as monomers, ΦΔ values are independent of number and position of the sulfogroups and are equal to 0.11 ± 0.02, 0.19 ± 0.03, 0.37 ± 0.05, 0.38 ± 0.05 and 0.68 ± 0.10 for the metal-free and Mg , Gd , Al and Zn complexes, correspondingly. However, in aqueous solutions, aggregation of the dyes determines their photochemical activity. Substitution in adjacent to macrocycle 3 and 6 benzene positions interferes with aggregation compared to 4 and 5 positions, presumably due to enhanced steric hindrances in the former case. In the ZnPcS n mix series (n varied from 2 to 4), as an example, the linear relationship between degree of aggregation and ΦΔ indicates that only the monomer fraction of the dye is responsible for singlet oxygen production. For less sulfonated samples the order of activity of the dyes in water is as follows: H 2 PcS n mix < M II PcS n mix < M III PcS n mix which is in contrast to their tendencies to form aggregates.

Efficient oxidations and photooxidations with molecular oxygen using metal phthalocyanines as catalysts and photocatalysts

Metal phthalocyanines can be very efficient as catalysts and photocatalysts in oxidation reactions using molecular oxygen as oxidant. Different types of soluble low molecular weight or oligomeric and insoluble heterogeneous catalysts and photocatalysts were developed. The heterogeneous metal phthalocyanines exist either impregnated on SiO 2, Al 2 O 3, charcoal and TiO 2 or covalently and coordinatively bound on SiO 2 and organic polymers or ionically bound on an organic ion exchanger. The catalytic oxidations of toxic sulfide and thiol derivative are studied. In addition, toxic phenols were employed as substrates for the photooxidation. Heterogeneous catalysts can exhibit higher activities then low molecular weight phthalocyanines. These systems exhibit a good stability for re-use. Photooxidations are more efficient than oxidations. A Si(IV) phthalocyanine derivative on a polymer ion exchanger is most active and stable. Also some examples for photooxidations in the direction of photochemical synthesis are given.

Can phthalocyanines and their substituted alpha-para-(methoxy)phenyl derivatives act as photosensitizers in photodynamic therapy? A TD-DFT study

A time-dependent density functional theory study (TD-DFT) is presented regarding the substituent effects on the Q-bands of two classes of non-planar phthalocyanines: the alpha-octaphenyl and p-alpha-octamethoxyphenyl substituted compounds, in their free-base and zinc complex forms. Singlet vertical excitation energies, computed at the PBE0/SVP//BP86/SVP level of theory also including bulk solvent effects (COSMO model), resulted within 0.1 eV of experiment. The experimental red-shift for the Q-band, going from the phenylated to the methoxyphenylated case, was well-reproduced theoretically and in the latter case it was found to depend mainly on the nature of the substituents and partly on structure distortion effects. The energetic gap between the singlet ground and first triplet excited state was calculated in solvent to be 1.28 eV for the free-base phthalocyanine (H2Pc) and 1.45 eV for the unsubstituted zinc complex (ZnPc) and lower than 0.98 eV for all the other compounds, which is the energetic lower limit for a molecule to act as photosensitiser in photodynamic therapy according to a Type II reaction mechanism. As a consequence, since this property-requirement for drugs used in photodynamic therapy is not fulfilled by the investigated near-infrared photosensitizers, they cannot be proposed as candidates for their use in this medical treatment.

The chemistry, photophysics and photosensitizing properties of phthalocyanines

Phthalocyanines (Pcs) and naphthalocyanines (Ncs) are being extensively studied as photosensitizers for photodynamic therapy (PDT) of cancer. They strongly absorb clinically useful red light, with maxima around 670 nm and 770 nm respectively. Chelated with appropriate diamagnetic metal ions, they exhibit high triplet yields and long triplet lifetimes. Energy transfer from the triplet dye to ground-state oxygen to yield singlet oxygen appears to be the main photosensitizing pathway in biological systems. Underivatized Pcs and Ncs can be incorporated in liposomes for in vivo administration. Sulphonation renders the dyes water soluble but also enhances dimerization to yield photochemically inactive aggregates. Tumour retention and cell membrane penetration of the dyes are strongly affected by the polarity of the macrocycle as well as the nature of the central metal ion and axial ligands. Among the sulphonated dyes, amphiphilic mono- and disulphonated derivatives exhibit particularly good cell membrane-penetrating properties, although the more highly sulphonated dyes show better tumour retention in vivo. At least in vitro, Pc dyes are more photoactive than the corresponding Nc dyes, which probably reflects the lower photostability of the latter.

Peripheral and axial substitution of phthalocyanines with solketal groups: synthesis and in vitro evaluation for photodynamic therapy

Phthalocyanines (Pcs) are a class of photosensitizers (PSs) with a strong tendency to aggregate in aqueous environment, which has a negative influence on their photosensitizing ability in photodynamic therapy. Pcs with either peripheral or axial solketal substituents, that is, ZnPc(sol)8 and Si(sol)2Pc, respectively, were synthesized and their tendency to aggregate as well as their photodynamic properties in 14C and B16F10 cell lines were evaluated. The results were compared to more hydrophilic silicon Pcs, that is, Si(PEG750)2Pc and Pc4. The order of cellular uptake was Pc4 > ZnPc(sol)8 > Si(PEG750)2Pc > Si(sol2)Pc. In contrast, Si(sol2)Pc showed the highest photocytotoxicity, while ZnPc(sol)8 did not show any photocytotoxicity up to a concentration of 10 microM in both cell types. UV/vis spectroscopy showed that Si(sol)2Pc is less prone to aggregation than ZnPc(sol)8, which can explain the lack of photoactivity of the latter. Si(sol)2Pc was predominantly located in lipid droplets, whereas Si(PEG750)2Pc was homogeneously distributed in the cytosol, which is probably the main cause of their difference in photoactivity. The very high photodynamic efficacy of Si(sol)2Pc makes this PS an interesting candidate for future studies.

Phthalocyanine-mediated photodynamic therapy induces cell death and a G0/G1 cell cycle arrest in cervical cancer cells

We have developed a series of novel photosensitizers which have potential for anticancer photodynamic therapy (PDT). Photosensitizers include zinc phthalocyanine tetra-sulphonic acid and a family of derivatives with amino acid substituents of varying alkyl chain length and degree of branching. Subcellular localization of these photosensitizers at the phototoxic IC(50) concentration in human cervical carcinoma cells (SiHa Cells) was similar to that of the lysosomal dye Lucifer Yellow. Subsequent nuclear relocalization was observed following irradiation with 665nm laser light. The PDT response was characterized using the Sulforhodamine B cytotoxicity assay. Flow cytometry was used for both DNA cell cycle and dual Annexin V-FITC/propidium iodide analysis. Phototoxicity of the derivatives was of the same order of magnitude as for tetrasulphonated phthalocyanine but with an overall trend of increased phototoxicity with increasing amino acid chain length. Our results demonstrate cell death, inhibition of cell growth, and G(0)/G(1) cell cycle arrest during the phthalocyanine PDT-mediated response.

Spectroscopic evidence of monomeric aluminium phthalocyanine tetrasulphonate in aqueous solutions

Aqueous solutions of aluminium phthalocyanine tetrasulphonate (AlPcS(4)) were investigated by means of absorption and fluorescence spectroscopy. The absorption spectrum of AlPcS(4) is independent of concentration in a wide range (from 10(-8) to 10(-4) M). The fluorescence spectrum measured with a standard setup is strongly dependent on AlPcS(4) concentration, and the fluorescence maximum is gradually red-shifted with increasing concentration. Calculations that take into account reabsorption of fluorescence (inner-filter effect) fit the experimental observations at low concentrations (up to 10(-6) M). Disagreement between the calculations and spectra recorded at higher concentrations (above 10(-5) M) shows that the reabsorbed light may be reemitted as fluorescence. The influence of inner-filter effects on the spectral shape was demonstrated by the experiments where a fibre-optic front-face fluorescence setup was applied: Under such conditions the shape of the fluorescence spectra for a high concentration (10(-3) M) coincided with that of a low concentration (10(-8) M). In conclusion, the present spectroscopic results show that AlPcS(4) does not form aggregates and is a very stable compound in aqueous solutions.

Structure−Photodynamic Activity Relationships of Substituted Zinc Trisulfophthalocyanines

To identify optimal features of metalated sulfophthalocyanine dyes for their use as photosensitizers in the photodynamic therapy of cancer, we synthesized a series of alkynyl-substituted trisulfonated phthalocyanines and compared their amphiphilic properties to a number of parameters related to their photodynamic potency. Varying the length of the substituted alkynyl side-chain modulates the hydrophobic/hydrophilic properties of the dyes providing a linear relationship between their n-octanol/water partition coefficients and retention times on reversed-phase HPLC. Aggregate formation of the dyes in aqueous solution increased with increasing hydrophobicity while monomer formation was favored by the addition of serum proteins or organic solvent. Trisulfonated zinc phthalocyanines bearing hexynyl and nonynyl substituents exhibited high cellular uptake with strong localization at the mitochondrial membranes, which coincided with effective photocytotoxicity toward EMT-6 murine mammary tumor cells. Further increase in the length of the alkynyl chains (dodecynyl, hexadecynyl) did not improve their phototoxicity, likely resulting from extensive aggregation of the dyes in aqueous medium and reduced cell uptake. Aggregation was evident from shifts in the electronic spectra and reduced capacity to generate singlet oxygen. When monomerized through the addition of Cremophor EL all sulfonated zinc phthalocyanines gave similar singlet oxygen yields. Accordingly, differences in the tendency of the dyes to aggregate do not appear to be a determining factor in their photodynamic potency. Our results confirm that the latter in particular relates to their amphiphilic properties, which facilitate cell uptake and intracellular localization at photosensitive sites such as the mitochondria. Combined, these factors play a significant role in the overall photodynamic potency of the dyes.

Photodynamic properties of amphiphilic derivatives of aluminum tetrasulfophthalocyanine

Photodynamic therapy (PDT) is a promising treatment modality that has recently been accepted in clinics as a curative or palliative therapy for cancer and other nonmalignant conditions. Phthalocyanines (Pc) are attractive photosensitizers for PDT because of their enhanced photophysical and photochemical properties. The overall charge and solubility of Pc play a major role in their potential usefulness for PDT. A series of amphiphilic derivatives of tetrasulfonated aluminum Pc (AlPcS4) was prepared by substituting one of the four sulfonate groups with aliphatic side chains of 4, 8, 12 and 16 carbon atoms. The photodynamic properties of the derivatives were compared with those of AlPcS4 and the adjacent disulfonated aluminum Pc. Parameters studied included reversed-phase high-performance liquid chromatography (HPLC) retention times, capacity to generate singlet oxygen (1O2), in vitro cell uptake and phototoxicity, as well as PDT response of transplantable EMT-6 tumors in mice. The monomerized AlPcS4 derivatives showed similar or higher capacities to generate 1O2 as compared with the parent AlPcS4 as measured from relative L-tryptophan photooxidation yields. A549 cell uptake of the AlPcS4 derivatives decreased in the following order: AlPcS4(C16) > AlPcS4(C12) > AlPcS4(C8) > AlPcS4(C4). Human low-density lipoprotein at high concentrations (40 micrograms/mL) completely prevented uptake, whereas at 4 micrograms/mL uptake was decreased for the more lipophilic compounds and yet remained unaffected for the more hydrophilic dyes. Using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, A549 cell survival was assessed; it showed that photocytotoxic activity varied directly with the HPLC retention times, i.e. more hydrophilic compounds were less phototoxic. As 1O2 yields were similar for the four substituted AlPcS4 derivatives, it was postulated that the increased cytotoxic activity was caused by enhanced subcellular localization as a result of the long aliphatic side chains. These amphiphilic compounds proved to be photodynamically potent against the EMT-6 mouse mammary tumor model implanted in Balb/c mice. At dye doses of 0.2 mumol/kg and a fluence of 400 J/cm2 complete tumor regression was observed with no morbidity. The substitution of AlPcS4 with long aliphatic chains on the macrocycle greatly enhances its photodynamic efficacy both in vitro and in vivo.

Chelation with metal is not essential for antitumor photodynamic activity of sulfonated phthalocyanines

It is generally assumed that a central metal is essential for the efficiency of phthalocyanines in photodynamic therapy (PDT) of cancer. Contrary to the set opinion, the results of the present study indicate that the metal-free sulfonated phthalocyanines (H2PcSn, where n is the number of sulfonate groups per molecule) possess a considerable photoactivity. The relative phototoxicities of H2PcS1.5, H2PcS2.4, H2PcS3.1 and H2PcS3.8 on HEp2 human epidermoid carcinoma cells were 3.3, 20, 3.3 and 1, respectively, thus demonstrating dependence of the activity on the sulfonation degree, known for metallo-PcSn. A significant delay in tumor growth and a decrease in tumor regrowth rate were observed in mice after PDT with H2PcS2.4. The antitumor effect declined in the order H2PcS2.4 > H2PcS3.1 > H2PcS1.5 and vanished for H2PcS3.8. We demonstrate here that the high photodynamic activity of H2PcS2.4 can be explained by its physicochemical properties in living cells and tissues. Thus, H2PcSn (n is about 2) can be considered as a new alternative in PDT of light-accessible neoplasms and further clinic-oriented studies are warranted.

Photodynamic effects of mTHPC on human colon adenocarcinoma cells: photocytotoxicity, subcellular localization and apoptosis

The photodynamic properties of meta-tetra(hydroxyphenyl)chlorin (mTHPC), a promising second-generation photosensitizer, were investigated using a human colon adenocarcinoma cell line (Colo 201 cells). The study on photocytotoxicity using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay showed that mTHPC was an effective photosensitizer on Colo 201 cells. The photocytotoxicity of mTHPC showed both drug and light dose-dependent characteristics. To reach LD50, namely, the dose at which 50% of the cells were killed, only 0.45+/-0.15 microg/mL of mTHPC and 3 J/cm2 of light dose were required. The presence of 10% fetal calf serum in culture medium significantly decreased the incorporation of mTHPC into cells and resulted in the reduction of photodynamic efficacy. Using confocal laser scanning microscopy, mTHPC was first shown to localize in lysosomes rather than in mitochondria. Furthermore, nuclear stainings demonstrated that photodynamic therapy with mTHPC induced apoptosis in Colo 201 cells.

Photodynamic activities of silicon phthalocyanines against achromic M6 melanoma cells and healthy human melanocytes and keratinocytes

Dichlorosilicon phthalocyanine (Cl2SiPc) and bis(tri-n-hexylsiloxy) silicon phthalocyanine (HexSiPc) have been evaluated in vitro as potential photosensitizers for photodynamic therapy (PDT) against the human amelanotic melanoma cell line M6. Each photosensitizer is dissolved in a solvent-PBS mixture, or entrapped in egg-yolk lecithin liposomes or in Cremophor EL micelles. The cells are incubated for 1 h with the sensitizer and then irradiated for 20 min, 1 h or 2 h (lambda > 480 nm, 10 mW cm-2). The photocytotoxic effect is dependent on the photosensitizer concentration and the light dose. Higher phototoxicity is observed after an irradiation of 2 h: treatment with a solution of photosensitizer (2 x 10(-9) M) leads to 10% (HexSiPc in egg-yolk lecithin liposomes) or 20% (Cl2SiPc in DMF-PBS solution) cell viability. After 1 h incubation and 20 min of light exposure, the photodynamic effect is connected with the type of delivery system used. For HexSiPc, lower cell viability is found when this photosensitizer is entrapped in egg-yolk lecithin instead of solvent-PBS or for Cremophor EL micelles with Cl2SiPc. Liposome-delivered HexSiPc leads to lipid damage in M6 cells, illustrated by an increase of thiobarbituric acid-reacting substances (TBARs), but the change is not significant with Cremophor EL. The same is observed for the antioxidative defences after photodynamic stress. The cells irradiated with HexSiPc entrapped in liposomes display an increase of superoxide dismutase (SOD) activity and a decrease of glutathione (GSH) level, glutathione peroxidase (GSHPx) and catalase (Cat) activities.

The characterisation of three substituted zinc phthalocyanines of differing charge for use in photodynamic therapy. A comparative study of their aggregation and photosensitising ability in relation to mTHPC and polyhaematoporphyrin

Three substituted zinc (II) phthalocyanines (one anionic, one cationic and one hydrophobic) have been compared to two clinically used photosensitisers, 5,10,15,20-tetra (m-hydroxyphenyl) chlorin (mTHPC) and polyhaematoporphyrin (PHP), as potential agents for photodynamic therapy (PDT). Oxygen-consumption experiments, performed to follow the photo-oxidation of tryptophan, histidine and bovine serum albumin (BSA), suggest that the anionic phthalocyanine is the most efficient photosensitiser. The efficacy of BSA oxidation is much greater than that of tryptophan or histidine, which is partly due to monomerisation of the sensitisers upon binding to BSA. Spectra recorded in aqueous solution reveal that all five compounds are highly aggregated, but monomerisation is induced upon the addition of BSA or methanol. Using a range of methanol-buffer solutions, the aggregation state has been directly related to the efficacy of tryptophan photo-oxidation with maximal rates of oxidation achieved when the sensitiser is monomeric. Using erythrocytes as a simple membrane model, the efficacy of each sensitiser exhibits a different trend from that predicted by oxygen-consumption experiments. The anionic phthalocyanine is the least effective at photohaemolysis, whereas the cationic and hydrophobic phthalocyanines have improved activity over PHP and mTHPC.

Preferential photoinactivation of leukemia cells by aluminum phthalocyanine

The efficacy of chloroaluminum phthalocyanine (AlPc) for photodynamic therapy (PDT) has been evaluated in vitro on acute myeloid leukemia (AML) cells, normal peripheral blood leukocytes (PBL) and mobilized peripheral blood stem cells (mPBSC). The selectivity of the treatment has been evaluated by mixing PBL and TF-1, an erythroleukemic cell line. Upon photoradiation, this photosensitizer leads to a significant and preferential photokilling of leukemia cells in comparison to normal cells. The use of stimulated lymphocytes in PBL/TF-1 mixtures instead of resting cells also leads to a preferential killing towards TF-1 although activated PBL are more affected than resting PBL. The analysis of AlPc intracellular emission by flow cytometry shows that the uptake of the dye by leukemia cells is faster. This good efficacy towards AML and the observed lower phototoxicity towards normal cells (PBL, normal progenitors) suggest that this phthalocyanine is a potential bone marrow purging agent.

Photodynamically generated bovine serum albumin radicals: evidence for damage transfer and oxidation at cysteine and tryptophan residues

Porphyrin-sensitized photoxidation of bovine serum albumin (BSA) results in oxidation of the protein at (at least) two different, specific sites: the Cys-34 residue giving rise to a thiyl radical (RS.); and one or both of the tryptophan residues (Trp-134 and Trp-214) resulting in the formation of tertiary carbon-centred radicals and disruption of the tryptophan ring system. In the case of porphyrins such as hematoporphyrin, which bind at specific sites on BSA, these species appear to arise via long-range transfer of damage within the protein structure, as the binding site is some distance from the ultimate site of radical formation. This transfer of damage is shown to depend on a number of factors including the conformation of the protein, the presence of blocking groups and pH. Alteration of the protein conformation results in radical formation at additional (or alternative) sites, as does blocking of the preferred loci of radical formation. The formation of these thiyl and tryptophan-derived radicals does not lead to significant aggregation or fragmentation of the protein, though it does result in a dramatic enhancement in the susceptibility of the oxidised protein to proteolytic degradation by a range of proteases. The generation of protein-derived radicals also results in an enhancement of photobleaching of the porphyrin, suggesting that protein radical generation is linked to porphyrin photooxidation.