Potential Photosensitizers For Photodynamic Therapy Research Articles

High Singlet Oxygen Generating Benzothienyl‐[b]‐fused BODIPY Nanoaggregates and Photoinduced Apoptosis in Human Carcinoma

AbstractHeavy atom free organic materials absorbing in red to near infrared (NIR) region are potential candidates as photosensitizers (PS) in photodynamic therapy (PDT). PDT relies on many factors and one of them is singlet oxygen generation ability of PS in aqueous medium. In this contribution, we report the synthesis of a new PS i. e., 8‐thienyl bisbenzothieno‐[b]‐fused‐boron‐dipyrromethene (BT‐[b]‐fused BODIPY). This PS shows absorption (λabs) at ~650 nm in toluene while in its water‐dispersible nanoaggregates it is found at ~764 nm. Nanoaggregates of BT‐[b]‐fused BODIPY demonstrated dual advantages, (i) facilitating PS release in the cellular system and (ii) sharply enhanced singlet oxygen efficiency ( ~48 %) in aqueous medium. Intracellular reactive oxygen species (ROS) generation was confirmed by 2′,7′‐dichlorodihydrofluorescein diacetate (DCFDA) assay in A549 cells. In vitro photocytotoxic studies of BT‐[b]‐fused BODIPY are carried out in different carcinomas i. e., MCF‐7 and A549 cells. It has zero dark cell toxicity while half maximal inhibitory concentration (IC50) in MCF‐7 is found to be low (6.08±1.1) μM and 7.41±1.9 μM in A549 on 15 min light exposure. These nanoaggregates induce apoptosis in cancer cells on light irradiation thereby proving it to be a potential PS for PDT.

Interaction between a water-soluble anionic porphyrin and human serum albumin unexpectedly stimulates the aggregation of the photosensitizer at the surface of the albumin

The 5,10,15,20-tetrakis(2,6-difluoro-3-sulfophenyl)porphyrin (TDFPPS4) was reported as a potential photosensitizer for photodynamic therapy. The capacity of the photosensitizers to be carried in the human bloodstream is predominantly determined by its extension of binding, binding location, and binding mechanism to human serum albumin (HSA), influencing its biodistribution and ultimately its photodynamic therapy efficacy in vivo. Thus, the present work reports a biophysical characterization on the interaction between the anionic porphyrin TDFPPS4 and HSA by UV–visible absorption, circular dichroism, steady-state, time-resolved, and synchronous fluorescence techniques under physiological conditions, combined with molecular docking calculations and molecular dynamics simulations. The interaction HSA:TDFPPS4 is spontaneous (ΔG° < 0), strong, and enthalpically driven (ΔH° = −70.1 ± 3.3 kJ mol−1) into subdomain IIA (site I). Curiously, despite the porphyrin binding into an internal pocket, about 50 % of TDFPPS4 structure is still accessible to the solvent, making aggregation in the bloodstream possible. In silico calculations were reinforced by spectroscopic data indicating porphyrin aggregation between bound and unbound porphyrins. This results in an adverse scenario for anionic porphyrins to achieve their therapeutical potential as photosensitizers and control of effective dosages. Finally, a trend of anionic porphyrins to have a combination of quenching mechanisms (static and dynamic) was noticed.

Dual Action of Curcumin as an Anti- and Pro-Oxidant from a Biophysical Perspective.

Curcumin, a natural polyphenol widely used as a spice, colorant and food additive, has been shown to have therapeutic effects against different disorders, mostly due to its anti-oxidant properties. Curcumin also reduces the efficiency of melanin synthesis and affects cell membranes. However, curcumin can act as a pro-oxidant when blue light is applied, since upon illumination it can generate singlet oxygen. Our review aims to describe this dual role of curcumin from a biophysical perspective, bearing in mind its concentration, bioavailability-enhancing modifications and membrane interactions, as well as environmental conditions such as light. In low concentrations and without irradiation, curcumin shows positive effects and can be recommended as a beneficial food supplement. On the other hand, when used in excess or irradiated, curcumin can be toxic. Therefore, numerous attempts have been undertaken to test curcumin as a potential photosensitizer in photodynamic therapy (PDT). At that point, we underline that curcumin-based PDT is limited to the treatment of superficial tumors or skin and oral infections due to the weak penetration of blue light. Additionally, we conclude that an increase in curcumin bioavailability through the using nanocarriers, and therefore its concentration, as well as its topical use if skin is exposed to light, may be dangerous.

Photosensitized Generation of Singlet Oxygen (1O2) from Pyropheophorbide a Specifically Bound to All Parallel-Stranded G-Quadruplex DNAs.

Pyropheophorbide a (Pyro-a), a chlorophyll metabolite, is a potential photosensitizer for photodynamic therapy (PDT), but little is known about its interaction with the target molecules for PDT, e.g., nucleic acids. Elucidation of the interaction between photosensitizers and nucleic acids will help us understand the initial process of PDT at the molecular level and hence to develop photosensitizing agents. We found that pyro-a forms a 1:1 complex with an all parallel-stranded G-quadruplex DNA and that pyro-a in the complex exhibits a quantum yield for singlet oxygen generation, with excitation at 664 nm, higher by a factor of ∼10 than that of pyro-a in an aqueous solution. These findings provided novel insights into molecular design of pyro-a-based photosensitizers to enhance their PDT efficacy.

The squaraine derivatives as potential photosensitizers in photodynamic therapy of cancer

The squaraine derivatives as potential photosensitizers in photodynamic therapy of cancer

Benz[e]indole-bearing aminosquaraine dyes: Which of the amines introduced into the squaric ring will be able to induce the best in vitro photodynamic effect?

The introduction of amines into the four-membered central ring of squaraine dyes has proven to be a good way to improve certain attributes of the molecules such as their aqueous solubility, their absorption at higher wavelengths, as well as inducing a more effective interaction with certain biological targets. Therefore this chemical modification has been studied regarding their application in the development of potential photosensitizers for photodynamic therapy. This work presents the synthesis of several N-ethyl chain benz[e]indole-based aminosquaraine dyes with amines of increasing complexity (amino < methylamino < dimethylamino < hydroxyethylamino < hydroxyethylmethylamino < bis(hydroxyethyl)amino), in order to understand the effect of small modifications in the chemical structure on the photobiological activity of these compounds. Within the group of compounds prepared and evaluated, amino- and hydroxyethylamino-bearing dyes were the ones that showed the most interesting in silico and cytotoxicity assay results: low free binding energies for human serum albumin protein, especially hydroxyethylamino for Sudlow site I (−13.58 kcal/mol); higher rates of photocytotoxicity (4–48 times more toxic in the presence of light, depending on the tumor cell line under study) and reasonable rates of tumor selectivity (up to approximately 10 times more photocytotoxic to tumor cells compared to the effects on normal cells). Further studies involving the most promising dyes demonstrated that they are somehow linked or internalized in the mitochondria, that they are little genocytotoxic even after irradiation, that apoptosis, although it occurs, should not be the preferred death mechanism after photodynamic treatment and that a slight increase in the number of cells in the G2/M phase was perceived.

A Star-Shaped Copolymer with Tetra-Hydroxy-Phenylporphyrin Core and Four PNIPAM-b-PMAGA Arms for Targeted Photodynamic Therapy.

The novel thermosensitive star-shaped tetra-hydroxy-phenylporphyrin-cored (THPP) double hydrophilic poly(N-isopropylacrylamide)-b-poly(methylacrylamide glucose) block copolymers (THPP-(PNIPAM-b-PMAGA)4) were synthesized via the reversible addition-fragmentation chain transfer (RAFT) polymerization. Notably, the low critical solution temperatures (LCSTs) of THPP-(PNIPAM-b-PMAGA)4 were above normal body temperature (37 °C) which depended on the hydrophilic PMAGA contents of copolymers. When the temperature was higher than the LCST of the copolymer, the copolymer could be neutralized into micelles in aqueous and could be coated with antitumor drugs and released around tumor cells. The MTT study indicated that THPP-(PNIPAM-b-PMAGA)4 had a low toxicity to L929 and HeLa cells in the absence of light. However, THPP-(PNIPAM-b-PMAGA)4 showed a high toxicity with HeLa cells under light irradiation which could be used as a potential photosensitizer for photodynamic therapy (PDT). In addition, THPP-(PNIPAM-b-PMAGA)4 showed specific a recognition function with Concanavalin A (Con A) to achieve active targeted drug delivery. This work provides a new approach for the development of tumor targeting and chemotherapy/PDT.

N-Heterocyclic Carbene-Iridium Complexes as Photosensitizers for In Vitro Photodynamic Therapy to Trigger Non-Apoptotic Cell Death in Cancer Cells

A series of seven novel iridium complexes were synthetized and characterized as potential photosensitizers for photodynamic therapy (PDT) applications. Among them, four complexes were evaluated in vitro for their anti-proliferative activity with and without irradiation on a panel of five cancer cell lines, namely PC-3 (prostate cancer), T24 (bladder cancer), MCF7 (breast cancer), A549 (lung cancer) and HeLa (cervix cancer), and two non-cancerous cell models (NIH-3T3 fibroblasts and MC3T3 osteoblasts). After irradiation at 458 nm, all tested complexes showed a strong selectivity against cancer cells, with a selectivity index (SI) ranging from 8 to 34 compared with non-cancerous cells. The cytotoxic effect of all these complexes was found to be independent of the anti-apoptotic protein Bcl-xL. The compound exhibiting the best selectivity, complex 4a, was selected for further investigations. Complex 4a was mainly localized in the mitochondria. We found that the loss of cell viability and the decrease in ATP and GSH content induced by complex 4a were independent of both Bcl-xL and caspase activation, leading to a non-apoptotic cell death. By counteracting the intrinsic or acquired resistance to apoptosis associated with cancer, complex 4a could be an interesting therapeutic alternative to be studied in preclinical models.

In VitroPhotodynamic Activities of Amphiphilic Phthalocyanine‐Amino Appendedβ‐Cyclodextrin Conjugates as Efficient Schiff Base Photosensitizer

AbstractWater‐soluble phthalocyanine has been considered as a potential photosensitizer for photodynamic therapy (PDT) applications. To achieve the best efficiency of phthalocyanine in PDT, amphiphilic zinc phthalocyanine was purposely designed and synthesized by conjugation withβ‐cyclodextrin. Herein, we synthesized two novel zinc phthalocyanine derivatives connected toβ‐cyclodextrin moieties through covalent Schiff base linkage (TFP‐ZnPc/AβCD). In this procedure, aldehyde substituted phthalocyanine and amino‐appendedβ‐cyclodextrins with different length amino side chains were used. The compounds were characterized using FT‐IR,1H NMR, MALDI‐TOF, and UV‐vis. The newly designed photosensitizers did not self‐assemble in water and generated significant singlet oxygenvia1,3‐DPBF (1,3‐diphenylisobenzofuran) bleaching. Simultaneously, longer amino side chains increase1O2production efficiency. The PDT activity of the new TFP‐ZnPc/AβCD complexes was then examined on human breast cancer (MDA‐MB‐231) and fibroblast cells.In vitroresults show that PDT is more effective against cancer cells than normal cells. The new TFP‐ZnPc/AβCD could be an effective PDT drug.

Facile synthesis of porphyrin-conjugates as amphiphilic modified photosensitizer structures of m-THPP bearing carbamate, carboxylate and sulfonate linkers

5,10,15,20-Tetrakis(3-hydroxyphenyl)porphyrin (m-THPP) bearing various nitrogen and sulfur containing heterocycles, aromatic, aliphatic and alicyclic residues covalently linked to the oxygen atom of the meta-hydroxy group of the porphyrin unit were synthesized in good yields as potential photosensitizers for photodynamic therapy (PDT). These new amphiphilic conjugates were designed to use three different polar linkers (carboxylate, sulfonate, and carbamate linker units)via the reaction of m-THPP with nicotinoyl chloride hydrochloride (carboxylate linker), 5-bromothiophene-2-sulfonyl chloride (sulfonate linker), phenyl isocyanate, 3,5-bis(trifluoromethyl)phenyl isocyanate, hexyl isocyanate and cyclohexyl isocyanate (carbamate linker). The heterocycles employed are 5- and 6-membered rings with different solubility characteristics.

Application of chemometric method and computational analysis in the spectroscopic study of Azure A dimerization

In this contribution we allied chemometric tools and theoretical calculus to comprehend the self-aggregation process of the phenothiazine Azure A (AA), a potential photosensitizer for Photodynamic Therapy. Firstly, due to the high spectral overlap between monomer and dimer, the MCR-ALS method successfully resolve AA's spectra, indicating the formation of a twisted sandwich-like dimer instead of pure H-type aggregate. This chemometric protocol helped not only in the resolution but also in more trustable values of KD. The difference between the KD values after the resolution of the curves was significant, which shows the importance of this procedure. The data extracted from experimental also converged with the informations retrieved from theoretical calculus. The optimization of the AA’s dimer showed the repulsion between the central nitrogen (and at the same time with the sulfur atoms) causes a slight distortion and displacement of one molecule in relation to the other, favoring dimAA-symTRANS, a twisted sandwich-like conformation.The studies also evaluated the impact of salts in the self-aggregation depicting that, besides the ionic strength, polarizable soft anions interact better with cationic species like AA. Thus, soft anions as iodide and bromine causes the most striking impact in self-aggregation. The present study shows the importance in resolve the spectra data set before calculate KD values, role succsesfull developed by MCR-ALS methodology. The approach used here can help in the investigation of others self-aggregation process of photosensitizers and active molecules.

Ruthenium and iridium complexes bearing porphyrin moieties: PDT efficacy against resistant melanoma cells

Porphyrin derivatives present an excellent ability to act as photosensitizers (PS) in photodynamic therapy (PDT). Ruthenium and iridium complexes, mainly containing pyridine ligands, also have been highlighted as potential PS for PDT, due to their photochemical and photophysical properties. The combination of porphyrin derivatives with iridium or ruthenium ions may create singular features and, consequently, improve the PDT effect. In this paper, we report the synthesis, characterization and efficacy of porphyrin derivatives bearing attached ruthenium or iridium terpyridine units to act as PS against resistant melanoma cells (B16F10 cell model). The choice of the porphyrin derivatives to carry out this study was related with their efficacy to generate reactive oxygen species (ROS), the presence of anchoring groups to enable the coordination with ruthenium and iridium metal ions and on the studies of subcellular localization. In the PDT studies, a cell viability decrease was observed in the presence of compounds 4a (ruthenium derivative) and 3b (iridium derivative) at lower concentrations due to the high values of singlet oxygen quantum yield and cellular uptake found. The fluorescence of derivative 3b was observed uniformly dispersed by the cells.

Rational design of mitochondria targeted thiabendazole-based Ir(III) biscyclometalated complexes for a multimodal photodynamic therapy of cancer

Despite their outstanding properties as potential photosensitizers for photodynamic therapy (PDT), Ir(III) biscyclometalated complexes need both further developments to overcome remaining limitations and in-depth investigations into their mechanisms of action to reach clinic application in the treatment of cancer. This work describes the synthesis of a family of Ir(III) complexes of general formula [Ir(C^N)2(N^N′)]Cl (N^N′ = thiabendazole-based ligands; C^N = ppy (2-phenylpyridinate) (Series A), or dfppy (2-(2,4-difluorophenyl)pyridinate) (Series B)) and their evaluation as potential PDT agents. These complexes are partially soluble in water and exhibit cytotoxic activity in the absence of light irradiation versus several cancer cell lines. Furthermore, the cytotoxic activity of derivatives of Series A is enhanced upon irradiation, particularly for complexes [1a]Cl and [3a]Cl, which show phototoxicity indexes (PI) above 20. Endocytosis was established as the uptake mechanism for [1a]Cl and [3a]Cl in prostate cancer cells by flow cytometry. These derivatives mainly accumulate in the mitochondria as shown by colocalization confocal microscopy experiments. Presumably, [1a]Cl and [3a]Cl induce death on cancer cells under irradiation through apoptosis triggered by a multimodal mechanism of action, which likely involves damage over mitochondrial DNA and mitochondrial membrane depolarization. Both processes seem to be the result of photocatalytic oxidation processes.

Novel modified BODIPY–C60 as photosensitizer in photodynamic therapy

We have designed a novel BF2-chelated azadipyrromethene-fullerene dyad as a highly efficient photosensitizer (PS) for photodynamic therapy (PDT) at the B3LYP/6-31G(d) ∼ LANL2DZ theoretical level. The 4,4-difluoro-2,6-diiodo-1,3,5,7-tetramethyl-8-phenyl-4-bora-3a,4a-diaza-s-indacene (2I-BODIPY) with an azido substituent and fullerene (C60) were used to prepare this novel PS (2I-BODIPY-C60). Furthermore, the scrutinized results suggest that PS exhibits intense absorption in the therapeutic window (600–800 nm). The energy of the first triplet excited state (T1) of the photosensitizer lies above the excitation energy of the ground- state molecular oxygen (0.98 eV). On the other hand, the energy gap between the ground state (S0) and the T1 state of the present PS is 1.58 eV. In consideration of these results, 2I-BODIPY-C60 displays an efficiently radiationless intersystem crossing (ISC) and has a sufficient energy for generating singlet molecular oxygen (1O2). Accordingly, 2I-BODIPY-C60 would be proposed as a potential PS for PDT.

3,6,13,16-Tetrapropylporphycene: Rational Synthesis, Complexation, and Halogenation.

We have designed and synthesized 3,6,13,16-tetrapropylporphycene for the first time as its alkyl analogue from ethyl 4-propyl-1H-pyrrole-2-carboxylate. The substituent effect was found to be more intense than reported positional isomeric tetrapropylporphycenes. The freebase porphycene exhibited moderate fluorescence and complexation ability with divalent metal ions, including Zn(II), which displayed an enhanced emission quantum yield (∼30%). The Pd(II) complex and freebase β-tetrabromoporphycene generated singlet oxygen efficiently (75 and 51%, respectively) and, hence, may find application as potential photosensitizers in photodynamic therapy.

Enhanced photodynamic therapy of TiO2/N-succinyl-chitosan composite for killing cancer cells

The aim of this study was to investigate the effect of TiO2/N-succinyl-chitosan composite (TiO2/ NSCS) photodynamic therapy (PDT), while considering the effects of various light sources on the activation of photosensitizer. The methyl thiazolyl tetrazolium assay was used to examine the cell survival rate of the cells. The results showed that glioma cell strain (U251) was the most sensitive cancer cell strain to TiO2/NSCS. When the concentration of TiO2/NSCS was between 0 and 800 μg·mL-1, there was no obvious cytotoxicity to normal liver cells (HL-7702) and U251 cells. During the PDT process, the photokilling effect of TiO2/NSCS on U251 cells under ultraviolet-A (UVA) light irradiation was stronger than that of pure TiO2, and its killing effects were positively correlated with concentration and irradiation time. In addition, both UVA and visible light could excite TiO2/ NSCS, which had significant killing effect on U251 cells. The results of acridine orange/ethidium bromide fluorescent double staining and Annexin V/propidium iodide double staining indicated that TiO2/NSCS under UVA and visible light irradiation could kill U251 cells by inducing apoptosis, and the apoptosis rate of TiO2/NSCS treatment groups was higher than that of TiO2 treatment groups. Therefore, TiO2/NSCS might be used as a potential photosensitizer in PDT.

A2B- and A3-Type Boron(III)Subchlorins Derived from meso-Diethoxycarbonyltripyrrane: Synthesis and Photophysical Exploration.

The first direct fabrication of A2B- and A3-type B(III)subchlorins from meso-ethoxycarbonyl-substituted tripyrrane has been realized by condensation with appropriate acid chlorides (benzoyl chloride, butyryl chloride, and ethyl chlorooxoacetate). The aliphatic acid chloride-based annulation reaction is new to subporphyrinoid chemistry. The phenyl (6a)- or n-propyl (6b)-substituted derivatives could be oxidized to the corresponding B(III)subporphyrins upon refluxing with DDQ, whereas the triethoxycarbonyl moiety (6c) was found to be resistant to oxidation and exhibits the most red-shifted absorption (587 nm) and emission (604 nm). The study indicates that absorption and emission behaviors of the B(III)subchlorin can be tuned by the introduction of electron-rich or electron-deficient substituents at the meso-position. B(III)subchlorins 6a and 6c generate singlet oxygen efficiently (44 and 40%, respectively) and, thus, may find application as potential photosensitizers in photodynamic therapy (PDT).

Anticancer Activity, DNA Binding, and Photodynamic Properties of a N∧C∧N-Coordinated Pt(II) Complex.

In the effort to discover new targets and improve the therapeutic efficacy of metal-containing anticancer compounds, transition metal complexes that can elicit cytotoxicity when irradiated with light of a proper wavelength and, then, candidates as potential photosensitizers for photodynamic therapy are actively being investigated. In this work, the cytotoxicity in the dark and the photophysical properties of the complex Pt(N∧C∧N)Cl, where the N∧C∧N ligand is 2,6-dipyrido-4-methyl-benzene chloride, are investigated in detail by means of a series of theoretical levels, that is density functional theory and its time-dependent extension together with molecular dynamics (MD) simulations. In the dark, cytotoxicity has been explored by simulating the steps of the mechanism of action of classical Pt(II) complexes. The suitability of the investigated complex to act as a photosensitizer has been verified by calculating spectroscopic properties for both the unperturbed complex and its aquated and guanine-bound forms. Furthermore, using MD simulation outcomes as a starting point, the photophysical properties of DNA-intercalated and -bound complexes have been evaluated with the goal of establishing how intercalation and binding affect sensitization activity.

A valproic acid-modified platinum diimine complex as potential photosensitizer for photodynamic therapy

Histone deacetylase inhibitors have often been used in combination treatment of various types of cancers due to their non-genotoxic epigenetic potential. Valproic acid (VPA) is a well-known histone deacetylase inhibitor. Conjugate of VPA with a phtoactive platinum diimine complex through an ester bond has been fabricated to potentiate the photocytotoxicity of the photosensitizer. Its capability to generate singlet oxygen, behavior in the presence of esterase, and photocytotoxicity in tumor cells have also been studied. The results revealed that the novel VPA-modified platinum diimine complex could produce singlet oxygen efficiently and release VPA in the presence of porcine liver esterase. The results also suggested that incorporation of VPA moiety into the platinum diimine complex might significantly enhance the cytotoxicity of the complex.

Potential of Cyanine Derived Dyes in Photodynamic Therapy.

Photodynamic therapy (PDT) is a method of cancer treatment that leads to the disintegration of cancer cells and has developed significantly in recent years. The clinically used photosensitizers are primarily porphyrin, which absorbs light in the red spectrum and their absorbance maxima are relatively short. This review presents group of compounds and their derivatives that are considered to be potential photosensitizers in PDT. Cyanine dyes are compounds that typically absorb light in the visible to near-infrared-I (NIR-I) spectrum range (750–900 nm). This meta-analysis comprises the current studies on cyanine dye derivatives, such as indocyanine green (so far used solely as a diagnostic agent), heptamethine and pentamethine dyes, squaraine dyes, merocyanines and phthalocyanines. The wide array of the cyanine derivatives arises from their structural modifications (e.g., halogenation, incorporation of metal atoms or organic structures, or synthesis of lactosomes, emulsions or conjugation). All the following modifications aim to increase solubility in aqueous media, enhance phototoxicity, and decrease photobleaching. In addition, the changes introduce new features like pH-sensitivity. The cyanine dyes involved in photodynamic reactions could be incorporated into sets of PDT agents.