Water soluble, core-modified porphyrins. 3. Synthesis, photophysical properties, and in vitro studies of photosensitization, uptake, and localization with carboxylic acid-substituted derivatives

Thiophene Stability in Photodynamic Therapy: A Mathematical Model Approach

Thiophene-containing photosensitizers are gaining recognition for their role in photodynamic therapy (PDT). However, the inherent reactivity of the thiophene moiety toward singlet oxygen threatens the stability and efficiency of these photosensitizers. This study presents a novel mathematical model capable of predicting the reactivity of thiophene toward singlet oxygen in PDT, using Conceptual Density Functional Theory (CDFT) and genetic programming. The research combines advanced computational methods, including various DFT techniques and symbolic regression, and is validated with experimental data. The findings underscore the capacity of the model to classify photosensitizers based on their photodynamic efficiency and safety, particularly noting that photosensitizers with a constant rate 1000 times lower than that of unmodified thiophene retain their photodynamic performance without substantial singlet oxygen quenching. Additionally, the research offers insights into the impact of electronic effects on thiophene reactivity. Finally, this study significantly advances thiophene-based photosensitizer design, paving the way for therapeutic agents that achieve a desirable balance between efficiency and safety in PDT.

Highly Efficient Water-Soluble Photosensitizer Based on Chlorin: Synthesis, Characterization, and Evaluation for Photodynamic Therapy

The clinical applications of many photosensitizers (PSs) are limited because of their poor water solubility, weak tissue penetration, low chemical purity, and severe toxicity in the absence of light. We designed a novel chlorin-based PS (designated as HPS) to achieve fluorescence image-guided photodynamic therapy (PDT) with efficient ROS generation. In addition to its simple fabrication process, HPS has other advantages such as excellent water solubility, strong NIR absorption, and high biocompatibility upon chemical functionalization for enhanced phototherapy. HPS exhibited high photodynamic performance against lung cancer and breast cancer cells by generating a large amount of singlet oxygen (¹O₂) under 654 nm laser irradiation. HPS accumulated into multiple organelles such as mitochondria and the endoplasmic reticulum and triggered cell apoptosis by laser exposure. In the tumor-bearing mice, in vivo, HPS showed an optimal half-life in circulation and achieved fluorescence-image-guided PDT within the irradiation window, resulting in effective tumor growth inhibition and the prolonged survival of animals. Moreover, the antitumor PDT effect of HPS was close to the clinical trial phase II stage of HPPH even at the low dosage of 0.32 mg/kg (under 75 J/cm² laser), while the systemic safety of HPS was much higher. In conclusion, HPS is a novel water-soluble chlorin derivative with excellent PDT potential for clinical transformation.

Photodynamic activity of 2,6-dibrominated dimethylaminophenylbuta-1,3-dienylBODIPY dyes

Mono- and disubstituted 2,6-dibromo-dimethylaminophenylbuta-1,3-dienylBODIPY dyes were successfully prepared, and their in vitro photodynamic activities against MCF-7 breast cancer cells were evaluated with a Thorlabs M660L4 660 nm LED (336 J · cm[Formula: see text]. The IC[Formula: see text] value of the monophenylbuta-1,3-dienylBODIPY was ca. 2.1 [Formula: see text]M, while that of the diphenylbuta-1,3-dienylBODIPY was > 50 [Formula: see text]M. Both dyes exhibited minimal dark toxicity. The results demonstrate that monosubstituted 2,6-dibromo-dimethylaminophenylbuta-1,3-dienylBODIPY dyes merit further in-depth study for use as photosensitizer dyes in photodynamic therapy.

Chemical approaches for the enhancement of porphyrin skeleton-based photodynamic therapy

With the development of photodynamic therapy (PDT), remarkable studies have been conducted to generate photosensitisers (PSs), especially porphyrin PSs. A variety of chemical modifications of the porphyrin skeleton have been introduced to improve cellular delivery, stability, and selectivity for cancerous tissues. This review aims to highlight the developments in porphyrin-based structural modifications, with a specific emphasis on the role of PDT in anticancer treatment and the design of PSs to achieve a synergistic effect on multiple targets.

Preparation of NIR absorbing axial substituted tin(iv) porphyrins and their photocytotoxic properties

Sn(iv) porphyrins ([Sn(iv)TTP(3PyO)2] (5) and [Sn(iv)TPP(3PyO)2] (6) [tetrathienylporphyrin (TTP), tetraphenylporphyrin (TPP), and pyridyloxy (PyO)]) were prepared and characterized and their photocytotoxicity upon irradiation with 625 nm light has been studied. The presence of the 3PyO axial ligands was found to limit the aggregation and enhance the solubility of 5 and 6 in DMF/H2O (1 : 1). The photophysical properties and photodynamic therapy (PDT) activity of the meso-2-thienyl and meso-phenyl-substituted Sn(iv) porphyrins are compared. 5 and 6 were found to be photocytotoxic in MCF-7 cancer cells when irradiated with a Thorlabs M625L3 LED at 625 nm but remained nontoxic in the dark. The PDT activity of Sn(iv) meso-tetra-2-thienylporphyrin 5 was found to be significantly enhanced relative to its analogous tetraphenylporphyrin 6. There is a marked red-shift of the Q00 band of 5 into the therapeutic window due to the meso-2-thienyl rings, and 5 has an unusually high singlet oxygen quantum yield value of 0.83 in DMF. The results demonstrate that readily synthesized axially ligated Sn(iv) meso-arylporphyrins are potentially suitable for use as singlet oxygen photosensitizers in biomedical applications and merit further in depth investigation in this context.

The effects of bromine atoms on the photophysical and photochemical properties of 3-cinnamoylcoumarin derivatives

Coumarin derivatives modified using bromine atoms linked onto the right benzene ring (mainly in the HOMO) could enhance singlet oxygen generation capability.

Modifications of Porphyrins and Hydroporphyrins for Their Solubilization in Aqueous Media

The increasing popularity of porphyrins and hydroporphyrins for use in a variety of biomedical (photodynamic therapy, fluorescence tagging and imaging, photoacoustic imaging) and technical (chemosensing, catalysis, light harvesting) applications is also associated with the growing number of methodologies that enable their solubilization in aqueous media. Natively, the vast majority of synthetic porphyrinic compounds are not water-soluble. Moreover, any water-solubility imposes several restrictions on the synthetic chemist on when to install solubilizing groups in the synthetic sequence, and how to isolate and purify these compounds. This review summarizes the chemical modifications to render synthetic porphyrins water-soluble, with a focus on the work disclosed since 2000. Where available, practical data such as solubility, indicators for the degree of aggregation, and special notes for the practitioner are listed. We hope that this review will guide synthetic chemists through the many strategies known to make porphyrins and hydroporphyrins water soluble.

Radioiodinated hypericin disulfonic acid sodium salts as a DNA-binding probe for early imaging of necrotic myocardium

Necrotic myocardium imaging can provide great indicators of salvaged myocardial areas for clinical guidances to patients with myocardial infarction (MI). One of the key challenges in necrotic myocardium imaging however, is lack of ideal necrotic imaging tracers for exactly and timely depicting the necrotic myocardium. ¹³¹I-hypericin (¹³¹I-Hyp) is a promising tracer in exact necrotic myocardium delineation. However, it can't clearly image necrotic myocardium until 9h post injection (p.i.) for the high background signals in blood and lung due to the strong lipophilicity. Herein, an optimized ¹³¹I-hypericin-2,5-disulfonic acid sodium salts (¹³¹I-Shyp) probe was synthesized for better pharmacokinetic and biodistribution properties to necrosis imaging. And the related mechanisms of necrotic avidity ability of ¹³¹I-Hyp and ¹³¹I-Shyp were also explored. In the results, ¹³¹I-Shyp still showed selectively high accumulation in both necrotic cells and tissues. Biodistribution data revealed the decreased uptake of ¹³¹I-Shyp in normal organs (lung, spleen and heart) and blood (as shown in pharmacokinetics studies). ¹³¹I-Shyp presented quicker and clearer imaging for necrotic myocardium at 4h p.i. compared with ¹³¹I-Hyp, suggesting that improved hydrophilicity of ¹³¹I-Shyp may be conducive to its better pharmacokinetic and biodistribution properties to imaging. Additionally, DNA competitive binding assays and blocking experiments indicated that E-DNA is the possible target of Shyp and Hyp for their necrosis avidity. ¹³¹I-Shyp may serve as a potential E-DNA targeted probe for necrotic myocardium imaging with molecular specificity for clinical use.

Synthesis, photophysical properties and biological evaluation of β-alkylaminoporphyrin for photodynamic therapy

A series of β-alkylaminoporphyrins conjugated with different amines at β position (D1-D3) or with electron-donating and electron-withdrawing substituents at phenyl position (D4-D6) were synthesized. Their photophysical and photochemical properties, intracellular localization, photocytotoxicities in vitro and vivo were also investigated. All target compounds exhibited no cytotoxicities in the dark and excellent photocytotoxicities against HeLa cells. Among them, D6 showed the highest phototoxicity and the lowest dark toxicity, which was more phototoxic than Hematoporphyrin monomethyl ether (HMME). In addition, D6 exhibited best photodynamic antitumor efficacy on BALB/c nude mice bearing HeLa tumor. Therefore, D6 is a powerful and promising antitumor photosensitizer for photodynamic therapy.

Photophysical Characterization and in Vitro Phototoxicity Evaluation of 5,10,15,20-Tetra(quinolin-2-yl)porphyrin as a Potential Sensitizer for Photodynamic Therapy

Photodynamic therapy (PDT) is a selective and minimally invasive therapeutic approach, involving the combination of a light-sensitive compound, called a photosensitizer (PS), visible light and molecular oxygen. The interaction of these per se harmless agents results in the production of reactive species. This triggers a series of cellular events that culminate in the selective destruction of cancer cells, inside which the photosensitizer preferentially accumulates. The search for ideal PDT photosensitizers has been a very active field of research, with a special focus on porphyrins and porphyrin-related macrocycle molecules. The present study describes the photophysical characterization and in vitro phototoxicity evaluation of 5,10,15,20-tetra(quinolin-2-yl)porphyrin (2-TQP) as a potential PDT photosensitizer. Molar absorption coefficients were determined from the corresponding absorption spectrum, the fluorescence quantum yield was calculated using 5,10,15,20-tetraphenylporphyrin (TPP) as a standard and the quantum yield of singlet oxygen generation was determined by direct phosphorescence measurements. Toxicity evaluations (in the presence and absence of irradiation) were performed against HT29 colorectal adenocarcinoma cancer cells. The results from this preliminary study show that the hydrophobic 2-TQP fulfills several critical requirements for a good PDT photosensitizer, namely a high quantum yield of singlet oxygen generation (Φ∆ 0.62), absence of dark toxicity and significant in vitro phototoxicity for concentrations in the micromolar range.

Enhancement of two photon absorption properties and intersystem crossing by charge transfer in pentaaryl boron-dipyrromethene (BODIPY) derivatives

Indication of charge transfer and an intersystem crossing mechanism for the B4 compound by using ultrafast pump probe spectroscopy.

Photocytotoxicity, cellular uptake and subcellular localization of amidinophenylporphyrins as potential photodynamic therapeutic agents: An in vitro cell study

The cell-based studies of 5, 10, 15, 20-Tetrakis (4-amidinophenyl) porphyrin (Por1), its Zn complex (Por2) and amidinophenyl bisporphyrin (Por3) were carried out to examine their photocytotoxicity, cellular uptake and sub-cellular localization with human nasopharyngeal carcinoma cell (HK-1), using 5, 10, 15, 20-Tetrakis (N-methyl-4-pyridyl) porphyrin (H2TMPyP) as a reference. These porphyrins showed low dark-cytotoxicity and high photo-cytotoxicity against HK-1. The amphiphilic amidinophenyl bisporphyrin (Por3) displayed better cellular uptake than the single hydrophilic Por1, Por2 and H2TMPyP. As seen from the extent of overlapping of the fluorescence profiles, lysosomal localization of amidinophenylporphyrin Por1-Por3 and mito/lyso localization of the H2TMPyP occurred in the cells. The results suggest these porphyrins with amidine group could be used as potential agents in photodynamic therapy.

Far-red light activatable, multifunctional prodrug for fluorescence optical imaging and combinational treatment

We recently developed “photo-unclick chemistry”, a novel chemical tool involving the cleavage of aminoacrylate by singlet oxygen, and demonstrated its application to visible light-activatable prodrugs. In this study, we prepared an advanced multifunctional prodrug, Pc-(L-CA4)₂, composed of the fluorescent photosensitizer phthalocyanine (Pc), an SO-labile aminoacrylate linker (L), and a cytotoxic drug combretastatin A-4 (CA4). Pc-(L-CA4)₂ had reduced dark toxicity compared with CA4. However, once illuminated, it showed improved toxicity similar to CA4 and displayed bystander effects in vitro. We monitored the time-dependent distribution of Pc-(L-CA4)₂ using optical imaging with live mice. We also effectively ablated tumors by the illumination with far-red light to the mice, presumably through the combined effects of photodynamic therapy (PDT) and released chemotherapy drug, without any sign of acute systemic toxicity.

Synthesis of carboxylate functionalized A3B and A2B2 thiaporphyrins and their application in dye-sensitized solar cells

Thiaporphyrins were effectively applied in dye-sensitized solar cells. Among them, N3S-ECN with an ethynylphenyl linker and cyanoacrylic acid anchor, achieved the highest efficiency of 1.69%.

Synthesis and in vitro biological evaluation of lipophilic cation conjugated photosensitizers for targeting mitochondria

Mitochondria-specific photosensitizers were designed by taking advantage of the preferential localization of delocalized lipophilic cations (DLCs) in mitochondria. Three DLC-porphyrin conjugates: CMP-Rh (a core modified porphyrin-rhodamine B cation), CMP-tPP (a core modified porphyrin-mono-triphenyl phosphonium cation), CMP-(tPP)(2) (a core modified porphyrin-di-tPP cation) were prepared. The conjugates were synthesized by conjugating a monohydroxy core modified porphyrin (CMP-OH) to rhodamine B (Rh B), or either one or two tPPs, respectively, via a saturated hydrocarbon linker. Their ability for delivering photosensitizers to mitochondria was evaluated using dual staining fluorescence microscopy. In addition, to evaluate the efficiency of the conjugates as photosensitizers, their photophysical properties and in vitro biological activities were studied in comparison to those of CMP-OH. Fluorescence imaging study suggested that CMP-Rh specifically localized in mitochondria. On the other hand, CMP-tPP and CMP-(tPP)(2) showed less significant mitochondrial localization. All conjugates were capable of generating singlet oxygen at rates comparable to CMP-OH. Interestingly, all cationic conjugates showed dramatic increase in cellular uptake and phototoxicity compared to CMP-OH. This improved photodynamic activity might be primarily due to an enhanced cellular uptake. Our study suggests that Rh B cationic group is better at least for CMP than tPP as a mitochondrial targeting vector.

Synthesis, circular dichroism, DNA cleavage and singlet oxygen photogeneration of 4-amidinophenyl porphyrins

5,10,15,20-tetrakis(4-amidinophenyl)porphyrin (Por 1), its Zn complex (Por 2) and its conjugate with a tetraphenylporphyrin to form a bisporphyrin (Por 3) were prepared. The monomeric Por 1 and Por 2 showed both intercalative and external binding with DNA whereas only external DNA binding was seen in the bisporphyrin, Por 3 by circular dichroism and UV-vis. The DNA photocleavage activities of these porphyrins followed the order: Por 1 ~ Por 2 > Por 3, which did not correlate with their measured 1O2 production rates. It suggests 4-amidinophenylporphyrins are promising new photodynamic therapeutic agents.

Structural effects of core-modified porphyrins in dye-sensitized solar cells

A series of core-modified porphyrins with different meso aryl groups ( R 1), anchoring groups ( R 2), and core atoms (X) were studied as light-harvesting sensitizers for dye-sensitized solar cells (DSSCs). DSSCs were fabricated using these porphyrins as well as TiO2 nanoparticles with a particle diameter of around 25 nm. A dense layer of TiO2 was deposited as an interfacial layer on fluorine-doped tin dioxide (FTO) substrates. A TiO2 nanocrystalline film was then deposited on the dense layer by spin coating. The comparison of DSSC performance from different core-modified porphyrins was studied. The UV-vis absorption spectroscopy of porphyrin films attached on TiO2 and porphyrin solutions were also measured. The results indicated that both anchoring and meso aryl groups impacted on cell performance. The cell efficiency was correlated to the absorption of porphyrin films attached on TiO2 at the Soret band.

Synthesis, spectral data, and crystal structure of two novel substitution patterns in dithiaporphyrins

The syntheses, characterizations and crystal structures of 5-(4-tert-butylphenyl)-15,20-diphenyl-10-(4-methoxy)phenyl-21,23-dithiaporphyrin (1b) and 2,3-dimethoxy-10,15-diphenyl-21,23-dithiaporphyrin (2) are described. The cyclization of 2-[1-(4-methoxyphenyl)-1-pyrrolomethyl]-5-(1-phenyl-1-pyrrolomethyl)thiophene and 2-[1-(4-t-butylphenyl)-1-hydroxymethyl]-5-(1-phenyl-1-hydroxymethyl)thiophene gave predominantly the cis-regioisomer, which was characterized by X-ray crystallography.

Synthetic porphyrins bearing β-propionate chains as photosensitizers for photodynamic therapy

Porphyrins with different numbers of β-propionate chains mimicking natural porphyrins were prepared via the 2+2 MacDonald type approach. Photodynamic activity against WiDr colon adenocarcinoma cells showed that activity is related to the number of β-propionate chains, with the derivatives with two carboxylic groups showing higher activity.

Singlet oxygen generation by novel NIR BODIPY dyes

Five novel near-infrared BODIPY dyes were prepared for improved singlet oxygen generation using thiophene and bromine. Theoretical, optical, photostable, and singlet oxygen generation characteristics of these dyes were assessed. Predicted excitation energies by TDDFT calculations were in good agreement (ΔE ≈ 0.06 eV) with experimental data. All five dyes showed both excitation and emission in the NIR range. In particular, two dyes having sulfur and bromine atoms showed efficient singlet oxygen generation with high photostability.

Cell death causes relocalization of photosensitizing fluorescent probes

When cultured cells are treated with fluorescent organelle probes or photosensitizer agents, a characteristic redistribution of fluorescence in cell structures occurs frequently after light irradiation. It is currently assumed that such changes, referred to as relocalizations of the fluorescent compounds, represent an important aspect of the photodynamic process, which is based on the excitation of photosensitizers by light in the presence of oxygen. As cell damage and death result from the oxidative stress induced by photodynamic treatments, we have studied here the redistribution of acridine orange (AO) and 3,3'-dimethyl-oxacarbocyanine (DiOC(1)(3)) fluorescence after incubation of HeLa cell cultures with these compounds followed by blue light irradiation to achieve lethal effects. The relocalization of dyes from their original labeling sites (AO: lysosomes, DiOC(1)(3): mitochondria) to nucleic acid-containing structures (cytoplasm, nuclei and nucleoli) appeared clearly associated with cell death. Therefore, the relocalization phenomenon simply reflects fluorescence changes due to the different affinity of these dyes for living and damaged or dead cells. As fluorescent probes are often photosensitizers, prolonged light exposures using fluorescence microscopy will produce lethal photodynamic effects with relocalization of the fluorescent signal and changes in the cell morphology.

A new nonconjugated naphthalene derivative of meso-tetra-(3-hydroxy)-phenyl-porphyrin as a potential sensitizer for photodynamic therapy

A new 5,10,15,20-tetra-(phenoxy-3-carbonyl-1-amino-naphthyl)-porphyrin was prepared by an isocyanate condensation reaction and its photophysical properties fully evaluated, both in terms of photostability and singlet oxygen production. It shows considerably enhanced photostability when compared with the parent 5,10,15,20-tetra-(3-hydroxy-phenyl)-porphyrin, with the photodegradation quantum yields for T(NAF)PP and T(OH)PP being 4.65×10(-4) and 5.19×10(-3) , respectively. Its photodynamic effect in human carcinoma HT-29 cells was evaluated. The new porphyrin showed good properties as a sensitizer in photodynamic therapy with an in vitro cytotoxicity IC(50) value of 6.80μg mL(-1) for a 24h incubation. In addition to the potential of this compound, the synthetic route used provides possibilities of extension to a wide range of new sensitizers.

Designing photosensitizers for photodynamic therapy: strategies, challenges and promising developments

Photodynamic therapy (PDT) and photodynamic antimicrobial chemotherapy (PACT) are techniques that combine the effects of visible light irradiation with subsequent biochemical events that arise from the presence of a photosensitizing drug (possessing no dark toxicity) to cause destruction of selected cells. Despite its still widespread clinical use, Photofrin® has several drawbacks that limit its general clinical use. Consequently, there has been extensive research into the design of improved alternative photosensitizers aimed at overcoming these drawbacks. While there are many review articles on the subject of PDT and PACT, these have focused on the photosensitizers that have been used clinically, with little emphasis placed on how the chemical aspects of the molecule can affect their efficacy as PDT agents. Indeed, many of the PDT/PACT agents used clinically may not even be the most appropriate within a given class. As such, this review aims to provide a better understanding of the factors that have been investigated, while aiming at improving the efficacy of a molecule intended to be used as a photosensitizer. Recent publications, spanning the last 5 years, concerning the design, synthesis and clinical usage of photosensitizers for application in PDT and PACT are reviewed, including 5-aminolevulinic acid, porphyrins, chlorins, bacteriochlorins, texaphyrins, phthalocyanines and porphycenes. It has been shown that there are many important considerations when designing a potential PDT/PACT agent, including the influence of added groups on the lipophilicity of the molecule, the positioning and nature of these added groups within the molecule, the presence of a central metal ion and the number of charges that the molecule possesses. The extensive ongoing research within the field has led to the identification of a number of potential lead molecules for application in PDT/PACT. The development of the second-generation photosensitizers, possessing shorter periods of photosensitization, longer activation wavelengths and greater selectivity for diseased tissue provides hope for attaining the ideal photosensitizer that may help PDT and PACT move from laboratory investigation to clinical practice.

Effect of liposomal confinement on photochemical properties of photosensitizers with varying hydrophilicity

Preferential tumor localization and the aggregation state of photosensitizers (PSs) can depend on the hydrophilic/hydrophobic nature of the molecule and affect their phototoxicity. In this study, three PSs of different hydrophilicity are introduced in liposomes to understand the structure-photochemistry relationship of PSs in this cellular model system. Absorbance and fluorescence spectra of amphiphilic aluminum (III) phthalocyanine disulfonate chloride adjacent isomer (Al-2), hydrophilic aluminum (III) phthalocyanine chloride tetrasulfonic acid (Al-4), and lipophilic 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide (HPPH) are compared in a liposomal confined state with free PS in bulk solution. For fluorescence measurements, a broad range of concentrations of both bulk and liposomal confined PSs are examined to track the transition from monomers to dimers or higher order aggregates. Epifluorescence microscopy, absorbance, and fluorescence measurements all confirm different localization of the PSs in liposomes, depending on their hydrophilicity. In turn, the localization affects the aggregation of molecules inside the liposome cell model. Data obtained with such cellular models could be useful in optimizing the photochemical properties of photosensitizing drugs based on their structure-dependent interactions with cellular media and subcellular organelles.

Effect of liposomal confinement on photothermal and photo-oximetric fluorescence lifetimes of photosensitizers with varying hydrophilicity

The time-resolved fluorescence of photosensitizers (PSs) of varying hydrophobicities, di-and tetrasulfonated Al phthalocyanines (Al-2 and Al-4), and Photochlor (HPPH), was investigated in liposomes used as cell-mimetic models. Using frequency-and time-domain apparatus, the fluorescence lifetime, tau(fluo), was compared for PSs free in aqueous solution and in a liposome-associated state at varied temperatures (25 to 78 degrees C) and oxygen concentrations (0-190 microM). The analysis of tau(fluo) revealed different decay behaviors for the free-solution and liposome-confined PSs, most significantly for the lipophilic HPPH. Hydrophilic PS drugs (Al-4, Al-2) were less affected by the liposomal confinement, depending on the relative hydrophilicity of the compound and the consequent localization in liposomes. Changes in the emission decay due to confinement were detected as differences in the lifetime between the bulk solution and the liposome-localized PS in response to heating and deoxygenation. Specifically, hydrophilic Al-4 produced an identical lifetime trend as a function of temperature both in solu and in a liposome-confined state. Hydrophobic HPPH exhibited a fundamental transformation in its fluorescence decay kinetics, transitioning from a multiexponential (in free solution) to single-exponential (in liposome) decay. Deoxygenation resulted in a ubiquitous tau(fluo) increase for all PSs in free solution, while the opposite, a tau(fluo) decrease, occurred in all liposomal PSs.

Photodynamic activity of substituted zinc trisulfophthalocyanines: role of plasma membrane damage

We recently reported that variations in cellular phototoxicity among a series of alkynyl-substituted zinc trisulfophthalocyanines (ZnPcS3Cn) correlates with their hydrophobicity, with the most amphiphilic derivatives showing the highest cell uptake and phototoxicity. In this study we address the role of the plasma membrane in the photodynamic response as it relates to the overall hydrophobicity of the photosensitizer. The membrane tracker dye 1-[4(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH), which is incorporated into plasma membranes by endocytosis, was used to establish plasma membrane uptake by EMT-6 cells of the ZnPcS3C, by colocalization, and TMA-DPH membrane uptake rates after photodynamic therapy were used to quantify membrane damage. TMA-DPH colocalization patterns show plasma membrane uptake of the photosensitizers after short 1 h incubation periods. TMA-DPH plasma membrane uptake rates after illumination of the photosensitizer-treated cells show a parabolic relationship with photosensitizer hydrophobicity that correlates well with the phototoxicity of the ZnPcS3C,. After a 1 h incubation period, overall phototoxicity correlates closely with the postillumination rate of TMA-DPH incorporation into the cell membrane, suggesting a major role of plasma membrane damage in the overall PDT effect. In contrast, after a 24 h incubation, phototoxicity shows a stronger but imperfect correlation with total cellular photosensitizer uptake rather than TMA-DPH membrane uptake, suggesting a partial shift in the cellular damage responsible for photosensitization from the plasma membrane to intracellular targets. We conclude that plasma membrane localization of the amphiphilic ZnPcS3C6-C9 is a major factor in their overall photodynamic activity.