Improved Hypericin solubility via β-cyclodextrin complexation: Photochemical and theoretical study for PDT applications

Hypericin (HY) is a lipophilic photosensitizer (PS) extensively employed for photodynamic therapy (PDT), presenting high absorption in the visible region, chemical and photostability, as well as a good triplet quantum yield. Supramolecular complexation of photosensitizers into cyclodextrins (CD) is promising to improve their poor solubility, compromising their bioavailability and upcoming applications in PDT. This research produced an inclusion complex between HY and β-CD through the co-solvent method. HY became soluble after inclusion into β-CD cavities, besides retaining its fluorescent and singlet oxygen quantum yields (ϕ_f =0.115 and ϕ_Δ= 0.23, respectively), which are essential parameters for PDT uses and are not reported in the literature. By the theoretical analysis, since ΔG < 0, it was easy to conclude that HY inclusion into β-CD is a spontaneous process. Additionally, the complexes presented no changes in excited states after complexation. β-CDHY was 27% more phototoxic than free HY when tested in MCF7 cells using 3 J cm^-2 of irradiation, indicating a better cell uptake of HY. These outcomes suggest that the inclusion complex of HY into β-CD has the potential for use in PDT.

Fundamental electronic changes upon intersystem crossing in large aromatic photosensitizers: free base 5,10,15,20-tetrakis(4-carboxylatophenyl)porphyrin

Free base 5,10,15,20-tetrakis(4-carboxylatophenyl)porphyrin stands for the class of powerful porphyrin photosensitizers for singlet oxygen generation and light-harvesting. The atomic level selectivity of dynamic UV pump – N K-edge probe X-ray absorption spectroscopy in combination with time-dependent density functional theory (TD-DFT) gives direct access to the crucial excited molecular states within the unusual relaxation pathway. The efficient intersystem crossing, that is El-Sayed forbidden and not facilitated by a heavy atom is confirmed to be the result of the long singlet excited state lifetime (Q_x 4.9 ns) and thermal effects. Overall, the interplay of stabilization by conservation of angular momenta and vibronic relaxation drive the de-excitation in these chromophores.

The crucial transient states of free-base porphyrins are characterized by time-resolved X-ray absorption spectroscopy unraveling their unusual relaxation pathway.

Modulation of Temoporfin Distribution in Blood by β-Cyclodextrin Nanoshuttles

Photodynamic therapy represents a more targeted and less invasive alternative cancer treatment to traditional modalities. Temoporfin, as with many photosensitizers, is given by injection into a vein, and its subsequent fate is largely determined by the binding to plasma proteins and interaction with endothelial and blood cells. Thus, it is essential to be able to control and to alter the biodistribution of temoporfin in blood. In the present study, we evaluated the effect of co-administration of temoporfin with randomly methylated β-CD (Me-β-CD) on the distribution of temoporfin in the main subpopulations of blood cells of healthy donors using absorbance spectrophotometry and flow cytometry. We showed that cell-bound temoporfin fraction in blood strongly depends on the concentration of Me-β-CD. In fact, the accumulation of temoporfin in white blood cells was more sensitive than that in red blood cells, due to the higher volume of membranous organelles in white blood cells. Finally, we demonstrated that Me-β-CD significantly increases cellular uptake of temoporfin cancer human Burkitt′s lymphoma Raji cells. The presence of Me-β-CD resulted in a spotted pattern of temoporfin distribution in the plasma membrane compartment. Our results clearly demonstrated that β-CDs derivatives provide new options to modulate temoporfin biodistribution in blood.

Probing the Interactions of Porphyrins with Macromolecules Using NMR Spectroscopy Techniques

Porphyrinic compounds are widespread in nature and play key roles in biological processes such as oxygen transport in blood, enzymatic redox reactions or photosynthesis. In addition, both naturally derived as well as synthetic porphyrinic compounds are extensively explored for biomedical and technical applications such as photodynamic therapy (PDT) or photovoltaic systems, respectively. Their unique electronic structures and photophysical properties make this class of compounds so interesting for the multiple functions encountered. It is therefore not surprising that optical methods are typically the prevalent analytical tool applied in characterization and processes involving porphyrinic compounds. However, a wealth of complementary information can be obtained from NMR spectroscopic techniques. Based on the advantage of providing structural and dynamic information with atomic resolution simultaneously, NMR spectroscopy is a powerful method for studying molecular interactions between porphyrinic compounds and macromolecules. Such interactions are of special interest in medical applications of porphyrinic photosensitizers that are mostly combined with macromolecular carrier systems. The macromolecular surrounding typically stabilizes the encapsulated drug and may also modify its physical properties. Moreover, the interaction with macromolecular physiological components needs to be explored to understand and control mechanisms of action and therapeutic efficacy. This review focuses on such non-covalent interactions of porphyrinic drugs with synthetic polymers as well as with biomolecules such as phospholipids or proteins. A brief introduction into various NMR spectroscopic techniques is given including chemical shift perturbation methods, NOE enhancement spectroscopy, relaxation time measurements and diffusion-ordered spectroscopy. How these NMR tools are used to address porphyrin-macromolecule interactions with respect to their function in biomedical applications is the central point of the current review.

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

We herein describe the comprehensive investigation of the complexation behavior of a guanidinium-modified calix[5]arene pentaisohexyl ether (GC5A) with a variety of typical luminescent dyes. Fluorescein, eosin Y, rose bengal, tetraphenylporphine sulfonate and sulfonated aluminum phthalocyanine were employed as classical aggregation-induced quenching dyes. 2-(p-Toluidinyl)naphthalene-6-sulfonic acid and 1-anilinonaphthalene-8-sulfonic acid were selected as representatives of intramolecular charge-transfer dyes. Phosphated tetraphenylethylene was involved as the classical aggregation-induced emission dye. Sulfonated acedan representing one example of two-photon fluorescent probes, was also investigated. A ruthenium(II) complex with carboxylated bipyridyl ligands was included as a representative candidate of luminescent transition-metal complexes. We determined the association constants of the GC5A-dye complexes by fluorescence titration and discuss the complexation-induced photophysical changes. In addition, a comparison of the complexation behavior of GC5A with that of other macrocycles and potential applications according to the diverse photophysical responses are provided.

Assessment of Cellular Damage by Comet Assay After Photodynamic Therapy in vitro

The aim of this study was analysis of DNA damage in the cell line of the human melanoma G361 after photodynamic therapy (PDT) by comet assay. Photodynamic therapy is based on cytotoxic action of sensitizers (10 µM ZnTPPS4 fixed into 1 mM cyclodextrin hpβCD) and light with a suitable wavelength. Single-cell gel electrophoresis (SCGE, comet assay) is a rapid and sensitive method for detecting DNA strand breaks at the level of single cells. Great amount of DNA damage was detected with the dose of irradiation of 0.1; 0.5 J and 2.5 J.cm-2. Only radiation dose of visible light in the presence of sensitizers can induce DNA breaks of tumour cells. Cells with DNA damage appear as fluorescent comets with tails of DNA fragmentation. In contrast, cells with undamage DNA appear as round spots, because their intact DNA does not migrate out of the cell.

Use of Cyclodextrins in Anticancer Photodynamic Therapy Treatment

Photodynamic therapy (PDT) is mainly used to destroy cancerous cells; it combines the action of three components: a photoactivatable molecule or photosensitizer (PS), the light of an appropriate wavelength, and naturally occurring molecular oxygen. After light excitation of the PS, the excited PS then reacts with molecular oxygen to produce reactive oxygen species (ROS), leading to cellular damage. One of the drawbacks of PSs is their lack of solubility in water and body tissue fluids, thereby causing low bioavailability, drug-delivery efficiency, therapeutic efficacy, and ROS production. To improve the water-solubility and/or drug delivery of PSs, using cyclodextrins (CDs) is an interesting strategy. This review describes the in vitro or/and in vivo use of natural and derived CDs to improve antitumoral PDT efficiency in aqueous media. To achieve these goals, three types of binding modes of PSs with CDs are developed: non-covalent CD⁻PS inclusion complexes, covalent CD⁻PS conjugates, and CD⁻PS nanoassemblies. This review is divided into three parts: (1) non-covalent CD-PS inclusion complexes, covalent CD⁻PS conjugates, and CD⁻PS nanoassemblies, (2) incorporating CD⁻PS systems into hybrid nanoparticles (NPs) using up-converting or other types of NPs, and (3) CDs with fullerenes as PSs.

Viscosity reduction of isotonic solutions of the photosensitizer TPCS2a by cyclodextrin complexation

Meso-tetraphenyl chlorin disulphonate (TPCS_2a) is a photosensitizer (PS) particularly developed and patented for use in the technology of photochemical internalization (PCI) against cancer. TPCS_2a is known to aggregate in aqueous media even at low concentrations (≥0.1 µM) and to form a high-viscosity network at clinically relevant concentrations (mM). The aim of this work was to evaluate the effect of two hydroxypropylated cyclodextrin derivatives of beta and gamma type, respectively i.e. HPβCD and HPγCD, on the aggregation and solubilization of TPCS_2a in isotonic solutions. Samples containing micromolar concentrations of TPCS_2a were studied spectrophotometrically, while samples containing a clinical relevant concentration (10 mM = 9 mg/ml) of TPCS_2a were evaluated by dynamic viscosity measurements. HPβCD was determined to be a more suitable solubilizer of TPCS_2a than HPγCD in aqueous media both in the absence and presence of salt. The complexation stoichiometry between TPCS_2a/HPβCD at micromolar to millimolar concentrations of TPCS_2a was determined to be 1:3 and 1:2 in the absence and presence of isotonic NaCl, respectively. The network of TPCS_2a (10 mM) was broken down in the presence of 3% w/v (= 20 mM) HPβCD, i.e. a 1:2 molar ratio between TPCS_2a and the cyclodextrin. Formation of the inclusion complex resulted in low viscosity samples both in water and in the presence of isotonic NaCl or phosphate buffered saline (PBS) at 25 °C and 37 °C.

Host-guest interactions of cyclodextrins and metalloporphyrins: supramolecular building blocks toward artificial heme proteins

Cyclodextrins are versatile building blocks for a variety of macromolecules due to the inclusion complexes that are formed with hydrophobic organic molecules. Cyclodextrin-porphyrin interactions are of particular interest since cyclodextrins can serve as a non-covalent binding pocket while metalloporphyrins could serve as the heme analogs in the construction of heme protein model compounds. Various approaches to the design and assembly of biomimetic porphyrin constructs are compared and contrasted in this minireview with a particular emphasis on self-assembled and porphyrin-cyclodextrin systems. Several recent advances from our laboratories are described in this context. A sensitive fluorescent binding probe, 6A-N-dansyl-permethylated-β-cyclodextrin (Dan-NH-TMCD), was found to form 2:1 complexes with the meso-tetraphenylporphyrins Mn(III)TCPP , Mn(III)TPPS and Mn(III)TF 4 TMAP with high binding constants. A perPEGylated cyclodextrin, heptakis(2,3,6-tri-O-2-(2-(2-methoxyethoxy)ethoxy)ethyl)-β-cyclodextrin (TPCD), has been shown by 1 H NMR spectroscopy to form a 1:1 complex with H 2 TCPP with a binding constant above 108M-1. Such a strong binding constant is the largest found for a 1:1 complex between a monomeric cyclodextrin and a guest. TPCD was also found to bind Mn(III)TCPP with a binding constant of 1.2 × 106 M -1. A novel, self-assembled hemoprotein model, hemodextrin is also described. The molecular design is based on a PEGylated cyclodextrin scaffold that bears both a heme-binding pocket and an axial ligand that binds an iron porphyrin. The binding constant for Fe (III) TPPS (iron(III) meso-tetra(4-sulfonatophenyl)porphyrin) by py-PPCD was determined to be 2 × 106 M -1. The pyridyl nitrogen of py-PPCD was shown to ligate to the iron center by observing signal changes in the Fe(II) -porphyrin 1 H NMR spectrum. This hemodextrin ensemble, a minimalist myoglobin, was shown to bind dioxygen reversibly and to form a stable ferryl species.

Design of photosensitizer/cyclodextrin nanoassemblies: spectroscopy, intracellular delivery and photodamage

The engineering of multifunctional nanoparticles carrying photosensitizer drugs (PS) and exposing binding groups for cellular receptors is of increasing interest in therapeutics and diagnostics applications. Natural and modified cyclodextrins (CDs) offer useful scaffolds to bind PS guests by supramolecular interactions. In particular, amphiphilic β-CDs, which form nanoaggregates of diverse shape and size according to the polarity of substituent groups on the rims, include in their different compartments as CD cavity, hydrophilic and hydrophobic portion, PS with different physicochemical properties. PS embedded in cationic amphiphilic CD nanoassemblies are effective in inducing photodynamic damage in cancer cells. For a carrier/PS system to be used in photodynamic therapy (PDT) or photodynamic diagnosis (PDD), the appropriate combination of the delivery characteristics with the preservation of the photodynamic activity of the PS is strictly required. Homogeneous multilayer films based on cationic amphiphilic β-CD entrapping anionic porphyrins can be constructed to exploit interfacial electrostatic interactions between the two components. The capability of CDs to generate restricted microenvironments for PS which can facilitate photoinduced energy transfer with suitable donor molecules was investigated for potential application in fluorescence diagnosis. Besides, recent findings suggest that PDT could represent a useful tool for properly addressing an alternative approach for killing pathogens and combating infections at a clinical level. Finally, modified CDs can bind gold nanoparticles, yielding hybrid organic/inorganic nanoparticles which were studied in water solution and after casting on solid substrates. These binary assemblies could further encapsulate PS or other conventional drugs, opening new intriguing routes on multimodal therapy.

pH-responsive, TiO2-attached porphyrin for singlet oxygen production in an aqueous solution

A pH-responsive, TiO2-attached sensitizer was prepared based on the adsorption of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) onto TiO2 nanoparticles. This colloidally dispersed TiO2-attached TCPP behaves as a single-phase colloidal sensitizer at pH 1.0-3.3 with quantum yields of singlet oxygen production (Phi(Delta)) between 0.20 and 0.25, as a heterogeneous particle sensitizer at pH 3.5-6.0 with Phi(Delta) between 0.25 and 0.50, and as homogeneous free TCPP molecules in alkaline solutions with Phi(Delta) = 0.53. The changes in Phi(Delta) are fully consistent with pH-dependent adsorption of TCPP onto the TiO2 surface. Recovery yields of 99.8% for TCPP and 98.8% for TiO2 were obtained from 1.4 mM TiO2-attached TCPP. We attribute its photosensitization ability to retaining TCPP solubility on the TiO2 surface and, hence, activity. This novel system shows a potential to bridge the gap between easily recoverable and highly efficient sensitizers.

Cyclodextrin carriers of positively charged porphyrin sensitizers

The cationic sensitizer 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) forms supramolecular complexes with native, per-methylated, sulfonated and dimethyl-sulfonated cyclodextrins (CDs). Binding interactions were proved by NMR, mass spectra, capillary zone electrophoresis, UV-Vis and fluorescence spectroscopy. The 2D-NMR experiments on native CDs indicate that the interaction of TMPyP with the external CD surface is the dominant binding mode. The high binding affinity of TMPyP towards sulfonated CDs is due to electrostatic interactions. Binding is accompanied by an increase of the TMPyP basicity. Whereas betaCD does not affect the lifetime of the TMPyP triplet states, binding with sulfonated CDs causes the protonation of the TMPyP triplet states even in neutral solution. The diprotonated anionic sensitizer 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPSH(2)(2+)) forms host-guest complexes with native betaCD and gammaCD, similarly as in its non-protonated state. The positive charge of pyrrole nitrogen atoms does not significantly influence the mode of the interaction. In contrast to TMPyP, the lifetimes of the triplet states of bound TPPSH(2)(2+) to native CDs increase.

Photophysical properties of glucoconjugated chlorins and porphyrins and their associations with cyclodextrins

Glucoconjugated analogues of the meta-hydroxyphenyl porphyrin (m-THPP) and meta-hydroxyphenyl chlorin (m-THPC) has been recently synthesized. The characteristics of their triplet states have been determined with regard to their involvement in the photodynamic (PDT) efficiency. In the case of porphyrin derivatives, triplet quantum yields (Phi(T)) were ranging from 0.42 to 0.55 and triplet life times (tau(T)) from 1 to 5 micros. High reaction rate constants (k(q)) with molecular oxygen (k(q): 1.2-1.6 x 10(9)s(-1)) have been found. The triplet lifetimes of chlorin derivatives were about four times higher than those of porphyrins whereas the Phi(T) and k(q) values remained quite similar. Singlet oxygen yields of glucosylated and non-glucosylated porphyrins and chlorins were not significantly different within experimental errors (Phi(Delta)((1)O(2)): 0.41-0.58). Furthermore, it has been shown that glucoconjugated photosensitizers could undergo associations with the methyl-beta-cyclodextrin (Me-beta-CD) which exhibit high triplet lifetimes and singlet oxygen yields ranging from 0.27 to 0.48.

Photodynamic therapy with zinc-tetra(p-sulfophenyl)porphyrin bound to cyclodextrin induces single strand breaks of cellular DNA in G361 melanoma cells

The basis of photodynamic therapy (PDT) is the phototoxicity resulting from co-action of light, sensitizer and oxygen. In this study we demonstrate in vitro phototoxicity measurement on G361 cell lines using ZnTPPS(4) sensitizer bound to cyclodextrin hpbetaCD. We have proved its photodamage effect on cancer cell lines in the visible region of spectrum. We used the halogen lamp (24V/250W) as a source of radiation. After 24h incubation of cell cultures with 10 microM ZnTPPS(4) and 1mM cyclodextrine hpbetaCD, the cells were irradiated for 7.5 min at the total irradiation dose of 12.5 Jcm(-2). Analysis of DNA damage in the cell line after PDT was proved by comet assay and using inversion fluorescent microscope with image analysis. This treatment method gave rise to DNA damage. The used radiation dose of visible light in the absence of sensitizers does not induce DNA breaks in tumour cells. In conclusion, binding of ZnTPPS(4) sensitizer to cyclodextrin hpbetaCD may improve the efficacy of PDT for the treatment of malign melanoma.

In vitro toxicity testing of supramolecular sensitizers for photodynamic therapy

We report the phototoxicity of meso-tetrakis(4-sulphonatophenyl)porphine (TPPS4) and zinc metallocomplex (ZnTPPS4) sensitizers in the presence or absence of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on G361human melanoma cells. Morphological changes in cell cultures have been evaluated using inversion fluorescent microscope and image analysis. Viability of cells was determined by means of molecular probes for fluorescence microscopy (LIVE/DEAD kit- double staining with Calcein AM and Ethidium Homodimer). The quantitative changes of cell viability in relation to sensitizers concentrations and irradiation doses were proved by fluorometric measurement with fluoroscan Ascent. We found that the most effective sensitizer is ZnTPPS4 bound to HP-beta-CD, since the IC50 value was 12.5 g/ml at the dose of light radiation of 10 J/cm2.