Stereochemical factors in the transport and binding of photosensitizers in biological systems and in photodynamic therapy

Sulfonated Phthalocyanines: Photophysical Properties, in vitro Cell Uptake and Structure-activity Relationships

Aluminium phthalocyanines sulfonated to a different degree ( AlPcS n) and consisting of various isomeric species were studied by spectroscopic techniques to determine their tendencies to form dimers and aggregates. These characteristics were compared with the cell-penetrating properties of the species, using the Ehrlich ascites mouse tumor cell line, to arrive at structure-activity relationships. AlPcS n preparations consisting of the least number of isomeric species exhibited the highest tendency to form dimers and aggregates, whereas the more complex preparations, consisting of many isomeric products, showed more consistent monomeric features in aqueous environments. Uptake in cells was shown to correlate well with the overall hydrophobicity of the preparation and inversely with its degree of aggregation in the extracellular environment. Among the purified, single isomeric AlPcS n the amphiphilic disulfonated AlPcS 2a , enriched in positional isomers featuring sulfonate groups on adjacent phthalic subunits, showed the best membrane-penetrating properties. Even higher cell uptake was observed for the AlPcS 2mix reflecting a combination of optimal lipophilicity and a low degree of aggregation. Similarly, in the case of AlPcS 4, the pure isomeric compound showed less cell uptake than the mixed isomeric preparation of similar hydrophobicity, reflecting the higher degree of aggregation invoked by its symmetrical structure. Our data indicate that mixed sulfonated phthalocyanine preparations may exert higher photodynamic efficacy in biological applications as compared to the pure isomeric constituents.

Evaluation of tetraphenyl-2,3-dihydroxychlorins as potential photosensitizers

A series of β,β-dihydroxychlorins derived from meso-tetraphenylporphyrins (TPPs) have been synthesized. Their in vitro cytotoxicity has been measured and compared to BPDMA (verteporfin). Under the assay conditions BPDMA had an LD 50 (lethal dose to kill 50% of cells) value of 0.007 μM (5 ng/mL). The LD 50 values for the TPP derivatives varied from 1.7 × 10-2 to 9.9 μM depending upon the substituents and their position on the phenyl groups. One example of the dihydroxychlorin prepared from unsubstituted 5,15-diphenylporphyrin was examined and this exhibited an LD 50 of 2.4 × 10-3 μ M !

Like a bolt from the blue: phthalocyanines in biomedical optics

The purpose of this review is to compile preclinical and clinical results on phthalocyanines (Pcs) as photosensitizers (PS) for Photodynamic Therapy (PDT) and contrast agents for fluorescence imaging. Indeed, Pcs are excellent candidates in these fields due to their strong absorbance in the NIR region and high chemical and photo-stability. In particular, this is mostly relevant for their in vivo activation in deeper tissular regions. However, most Pcs present two major limitations, i.e., a strong tendency to aggregate and a low water-solubility. In order to overcome these issues, both chemical tuning and pharmaceutical formulation combined with tumor targeting strategies were applied. These aspects will be developed in this review for the most extensively studied Pcs during the last 25 years, i.e., aluminium-, zinc- and silicon-based Pcs.

Preclinical evaluation of a novel water-soluble chlorin E6 derivative (BLC 1010) as photosensitizer for the closure of the neovessels

In the present study, photodynamic activity of a novel photosensitizer (PS), Chlorin e(6)-2.5 N-methyl-d-glucamine (BLC 1010), was evaluated using the chorioallantoic membrane (CAM) as an in vivo model. After intravenous (i.v.) injection of BLC 1010 into the CAM vasculature, the applicability of this drug for photodynamic therapy (PDT) was assessed in terms of fluorescence pharmacokinetics, i.e. leakage from the CAM vessels, and photothrombic activity. The influence of different PDT parameters including drug and light doses on the photodynamic activity of BLC 1010 has been investigated. It was found that, irrespective of drug dose, an identical continuous decrease in fluorescence contrast between the drug inside and outside the blood vessels was observed. The optimal treatment conditions leading to desired vascular damage were obtained by varying drug and light doses. Indeed, observable damage was achieved when irradiation was performed at light doses up to 5 J/cm(2) 1 min after i.v. injection of drug doses up to 0.5 mg/kg body weight(b.w.). However, when irradiation with light doses of more than 10 J/cm(2) was performed 1 min after injection of drug doses up to 2 mg/kg body weight, this led to occlusion of large blood vessels. It has been demonstrated that it is possible to obtain the desired vascular occlusion and stasis with BLC 1010 for different combinations of drug and/or light doses.

Oxygen depletion during in vitro photodynamic therapy: structure-activity relationships of sulfonated aluminum phthalocyanines

Photodynamically induced oxygen depletion has been measured in an Ehrlich ascites mouse tumor cell line using a Clark-type electrode. Cells are loaded with aluminum phthalocyanines, sulfonated to different degrees (A1PcS(n), n = 0,2,3,4) and consisting of various isomeric species. Different cell lines and incubation procedures are used in order to investigate the cellular uptake mechanism. Uptake (in units of molecules/cell), post-irradiation redistribution and A1PcS(n) photodegradation are measured using spectroscopic techniques. For a given sensitizer, the oxygen depletion rate per cell increases sublinearly with uptake and superlinearly with cell density. In order to compare oxygen depletion rates of different compounds, we have defined the biological quantum yield (BQY) as the number of oxygen molecules that disappear per absorbed photon. The BQY is independent of uptake and cell density; therefore, it denotes the intrinsic photoactivity of a sensitizer. Sensitizers with high BQY show efficient post-irradiation intracellular redistribution. Photodegradation during irradiation is similar for all sensitizers (20-30%).

Structure-photodynamic activity relationships of a series of 4-substituted zinc phthalocyanines

Radioiodinated zinc phthalocyanine including [125I]ZnPcI4 and differently sulfonated [65Zn]ZnPcS (ZnPcS4, ZnPcS3, ZnPcS2 and ZnPcS1.75, a mixture of adjacent di and 25% mono) were prepared in order to study cell uptake and release kinetics in EMT-6 cells. The same compounds were evaluated for their in vitro phototoxicity and the biological parameters were compared to partition coefficients to arrive at quantitative structure-activity relationships (QSAR). At 1 microM in 1% serum, at 37 degrees C, all dyes showed rapid cell uptake during the first hour followed by a slow accumulation phase. After 24 h, the highest cellular concentration was observed with the lipophilic ZnPcI4, followed by the amphiphilic ZnPcS2 and ZnPcS1.75. The hydrophilic ZnPcS4 and ZnPcS3 showed lower uptake. Dye release from dye-loaded cells during incubation in dye-free medium could reach up to 60% and was shown to depend mainly on the amount of drug incorporated rather than the type of compound. These results suggest that care should be taken in interpreting dye toxicity data, which involve in vitro cell manipulations in dye-free medium, particularly during in vitro-in vivo protocols. The EMT-6 cell survival after 1 h or 24 h incubation with 1 microM dye in 1% serum followed by exposure to red light was assessed by means of the colorimetric 3-(4,5-dimethylthiazol-2-yl)-diphenyl-tetrazolium bromide (MTT) assay. Photocytotoxicities correlated inversely with the tendencies of the dyes to aggregate. Increased dye uptake by the cells also correlated with their activities, except for the lipophilic ZnPcI4, which showed the highest cell uptake but little phototoxicity. The QSAR between phototoxicity and the log of the partition coefficients (phosphate-buffered saline and n-octanol) gave a parabola with optimal partition values corresponding to the adjacent sulfonated ZnPcS2.

Photodynamic effects on human and chicken erythrocytes studied with microirradiation and confocal laser scanning microscopy

BACKGROUND AND OBJECTIVE

Photodynamic therapy (PDT) of cancers is associated with the destruction of the microvasculature supplying the tumor. The study elucidates the role of red blood cells in PDT-induced vascular injury.

STUDY DESIGN/MATERIALS AND METHODS

Intracellular accumulation of several photosensitizers in human (non-nucleated) and chicken (nucleated) erythrocytes, as well as photodynamic induced hemolysis were studied using 488 nm laser microirradiation (15 microW) and confocal laser scanning fluorescence microscopy.

RESULTS

Cells incubated with anionic hydrophilic compounds TPPS4 and Pd-TPPS4 exhibited no fluorescence before irradiation, but developed strong and sustained fluorescence in the cellular and nuclear membranes following photoinduced membrane damage. In contrast, microirradiation of Photofrin-incubated erythrocytes showed instantaneous fluorescence which decreased due to photodegradation. For the cationic hydrophilic dye methylene blue, significant fluorescence was detected only in the nucleus. Following ALA incubation, large intercellular differences were observed in fluorescence in the red spectral region. Photofrin induced the most efficient hemolysis. Higher radiant exposures were required for lysis of nucleated rather than of non-nucleated red blood cells, except in the case of methylene blue.

CONCLUSION

Laser microbeams were used, for the first time, to study photodynamic cell damage. Erythrocytes were shown to be primary targets in PDT. Damage to red blood cells could be responsible for hemostasis in the vascular bed of a tumor, which was reported by many groups.

Structure-activity relationship of porphines for photoinactivation of bacteria

The antibacterial photodynamic effects of uncharged (o-tetrahydroxyphenyl porphine [THPP], m-THPP and p-THPP), cationic (5,10,15,20-tetra[4-N-methylpyridyl]porphine [TMPyP]) and anionic (5,10,15,20-tetra[4-sulfonatophenyl porphine] [TPPS4]) porphines on Staphylococcus aureus and Escherichia coli bacteria inactivation were examined. The results show that uncharged porphines provoked antibacterial photodynamic activity on S. aureus, and also on E. coli in the presence of the membrane-disorganizing peptide polymixin B nonapeptide (PMNP). The TMPyP compound was highly photoactive toward gram-positive bacteria but only marginally effective on gram-negative cells, whereas TPPS4 showed no activity on either gram-positive or gram-negative bacteria. The photoactivity of TMPyP is due to the electrostatic attraction between the positively charged sensitizer molecule and the negatively charged membrane of the gram-positive target cells. For TPPS4, the inactivity toward gram-positive bacteria is due to electrostatic repulsion between the charged sensitizer molecule and the cell membrane. For gram-negative bacteria, the inactivity is conceivably due to preferential (electrostatic) binding to the positively charged PMNP, which is an adjuvant for membrane disorganization, but has no effect on cell viability. For hydrophobic sensitizers, the photoactivity depends on the state of aggregation. The extent of deaggregation of the different THPP isomers was determined by fluorescence measurements of bound sensitizers and could be positively correlated with their photoinactivation capacity. We conclude that the structure-activity relationships of these porphines are affected by their net charge and by aggregation.

Photodynamic effects of the cationic porphyrin, mesotetra(4N-methylpyridyl)porphine, on microtubules of HeLa cells

The treatment of HeLa human carcinoma cells with mesotetra(4N-methylpyridyl)porphine (T4MPyP) and blue light led to damage of the microtubules (MTs). The morphologies of interphase MTs and the mitotic spindle apparatus were analysed by immunofluorescence staining of alpha-tubulin. The extent of MT damage depended on the light dose and the time after photodynamic treatment. After a period of 1 h after irradiation with doses of 0.3 or 1.5 J cm-2 (sublethal conditions, corresponding to survival rates of 90% and 60% respectively), the normal MT network arrangement of interphase cells and the mitotic spindle apparatus of many cells were clearly affected. However, these effects were found to be transient, and several hours after irradiation most MTs resumed control morphology. Higher irradiation doses (4.5 J cm-2, lethal conditions, less than 10% cell survival) resulted in the irreversible alteration of interphase and mitotic MTs. The change in MT organization appeared to be the reason for the observed increase in the mitotic index (MI) after sublethal doses. The largest increase in MI was detected 6 h after treatment (twofold increase over untreated cells) for both sublethal light doses. Most of the cells in mitosis corresponded to metaphase, the number of ana-telophase cells being greatly reduced for the first hours after irradiation with a dose of 1.5 J cm-2. The results, which resemble those observed with inhibitors of MT assembly, suggest that MTs might represent an important target for T4MPyP action.