This paper focuses on the behavior of two chlorophyll-type semisynthetic photosensitizers for antitumor photodynamic therapy, which, in our opinion, meet the known criteria associated with efficient photodynamic treatment of superficial malignancies. These natural light-sensitive agents obtained from the Spirulina platensis microalgae are nontoxic pure compounds with low manufacturing costs and good stability in a condensed state and solutions. They have high absorption and emission peaks in the optical window of tissue, have appropriate solubility in water, and generate singlet oxygen with a good quantum yield in both aqueous and lipid-like media. These monocationic chlorin photosensitizers use low- and high-density lipoprotein pathways to accumulate in tumor tissues and penetrate mainly the endoplasmic reticulum and mitochondria of tumor cells. The pilot photodynamic treatment of M1 sarcoma-bearing rats with these macrocycles both as individual light-sensitive agents and, especially, in combination with chlorin e6 shows their high potential in antitumor photodynamic therapy.

A polyanionic water-soluble N-confused porphyrin photosensitizer containing four p-sulfonatophenyl groups was synthesized, and its behavior was studied in water and aqueous solutions of the micellar surfactant Tween 80. The antimicrobial photodynamic inactivation study indicated that this photosensitizer efficiently killed Staphylococcus aureus; however, Gram-negative pathogens having an outer lipopolysaccharide membrane were relatively resistant to this compound. The potentiation of photodynamic inactivation by addition of appropriate biocompatible agents increasing permeability of the membrane above was successfully tested and briefly discussed.

The enthalpies of dilution of solutions of hexamethylenetetramine (HMTA), the well-known pharmaceutical urotropine, in water (H2O) and heavy water (D2O) were determined with a new heat conduction calorimeter at 298.15 K. The enthalpy-related homotactic coefficients of pairwise, h22, and triplet, h222, interactions between hydrated solute molecules were computed using the excess thermodynamic function concept (based on the McMillan-Mayer theory formalism). The h22 and h222 values were found to be large and positive in both H2O and D2O due to a partial overlapping of solute hydrophobic hydration shells and appearance of solute - solute correlations at rather large distances. This phenomenon is stronger pronounced in heavy water both for pairwise and for triplet HMTA - HMTA interactions indicating a highly ordered hydration structure in D2O. The established correlation between the h22 values and the corresponding solvent isotope effects, delta h22(H2O -> D2O), for HMTA and tetramethylurea mono- and bicyclic derivatives as solute species confirms the hypothesis of the differentiating effect of a solvent isotopic substitution on both the energetics of solvation and solute - solute interactions in aqueous solutions of proton-accepting non-electrolytes. In other words, the more negative or positive the h22 value due to stronger homo- and heterocomponent D-bonds, the more negative or positive the corresponding isotopic effect is.

In this report, we developed novel chlorin/arylaminoquinazoline conjugates for targeted photodynamic therapy of cancer. The synthesized photosensitizers consisted of chlorin-e6 metallocomplexes (Zn, In, or Pd) conjugated with arylaminoquinazoline ligands with high affinity for epidermal growth factor receptors (EGFR). Additionally, the selectivity and antitumor properties of the conjugates were investigated in the EGFR-expressing A431 human tumor cell line in vitro. Among the tested molecules, the In-containing conjugate effectively inhibited tumor cell proliferation at nanomolar concentrations, a rare property for conventional photosensitizers. In in vivo experiments, the conjugates rapidly accumulated at the tumor site in nude mice bearing A431 xenograft tumors. Subsequent distribution analysis among different tissues was carried out using fluorescence imaging and elemental analysis. Finally, we demonstrated that the most promising In-containing conjugate was capable of inhibiting xenograft tumor growth in mice through combinational therapy. This therapeutic approach, combined with the conjugate's confirmed safety profile, highlights its potential for effective and safe cancer treatment.

In this work, screening studies of the cytotoxic effect of chlorins with fragments of di-, tri-, and pentaethylene glycol at the macrocycle periphery in relation to HeLa, A549, and HT29 cells were performed. It is shown that, despite different hydrophobicity, all the compounds studied have a comparable photodynamic effect. The conjugate of chlorin e6 with pentaethylene glycol, which has the lowest tendency to association among the studied compounds with tropism for low density lipoproteins and the best characteristics of the formation of molecular complexes with Tween 80, has a significant difference in dark and photoinduced toxicity (ratio IC50(dark)/IC50(photo) approximately 2 orders of magnitude for all cell lines), which allows to hope for a sufficiently large "therapeutic window". A study of the interaction of this compound with HeLa cells shows that the substance penetrates the cell and, after red light irradiation induces ROS appearance inside the cell, associated, apparently, with the photogeneration of singlet oxygen. These data indicate that photoinduced toxic effects are caused by damage to intracellular structures as a result of oxidative stress. Programmed type of cell death characterized with caspase-3 induction is prevailing. So, the conjugate of chlorin e6 with pentaethylene glycol is a promising antitumor PS that can be successfully solubilized with Tween 80, which makes it suitable for further in vivo studies.

Thermochemical data on hydration of the well-established anticancer agent Dioxadet were obtained. Its enthalpies of solution and sublimation at various temperatures were determined calorimetrically, and on their basis the standard enthalpy (ΔhydrH0 = −154.6 ± 3.6 kJ mol−1) and the standard heat capacity (ΔhydrCp0 = 384 ± 80 J mol−1 K−1) of the transfer of the solute from the state of an ideal gas to an aqueous solution at infinite dilution at 298.15 K were calculated.

Because of the antibiotic era is considered to be on the verge of ending and the probability of discovering novel classes of antibiotics is estimated to be low, it is necessary to discover alternative technologies to fight with antibiotic resistant microoorganisms. The key question to be answered in recent years is: will become APDT the alternative to the standard treatment of localized infections to the extent this modality has been adopted by the medical community in treating superficial tumors. Our and many other studies mentioned here do indicate that APDT has a good potential to take an important place in the arsenal of killing resistant microbes. However, much, if not all, will depend on the appearance of the cohort of physicians willing to accept this new paradigm. In this short review, we focus on the most popular chlorin photosensitizers (PSs) used in antimicrobial photodynamic therapy (APDT). The appropriate molecular structures and several important results of photodynamic inactivation of both archival and nosocomial antibiotic resistant microorganisms are given in some detail and briefly discussed. The possible ways of potentiating antimicrobial activity of chlorophyll-based PSs are also analyzed. It has been proven that cationic macroheterocycles are proved to be the most efficient agents for eliminating both Gram-positive and Gram-negative pathogens under appropriate irradiation. Among them chlorophyll derivatives are found to be low toxic to mammalian cells, are destroyed under irradiation and rapidly removed from the body. It has been shown that strong potentiation of APDT by adding inorganic salts or polymers to PS solutions without the growth of dark toxicity will be of special interest in the next years. The development of special dosage forms containing both a PS and a potentiating agent as well as the combination of APDT with traditional methods of treating localized infections may provide additional benefit for many patients.

Enthalpies of dilution of urea (U) solutions in formamide (FA), ethylene glycol (EG) and water were mea- sured calorimetrically in the temperature range between (288.15 and 318.15) K. Based on the results obtained, the enthalpy-homotactic coefficients of pairwise (h22) and triplet (h222) interactions between the solvated U molecules were computed and compared with the similar data for the respective solutions of tetramethylurea (TMU). An analysis was done of how temperature influences the solvophilic and solvophobic effects manifested in the h22 and h222 parameters for U and TMU in the studied organic sol- vents with a spatial H-bonding network.(c) 2022 Elsevier B.V. All rights reserved.

The temperature dependence of the pair and triplet interaction between aromatic amino acid L-Tryptophan (Trp) and glycerol (Gl) or urea (U) in an aqueous medium was studied. For this goal, the enthalpies of solution of Trp in the water-Gl and water-U mixtures were determined in the temperature range of 298.15–328.15 K. The heat capacity values of amino acid solution as well as the partial molal heat capacities were calculated. The virial enthalpic coefficients of pair (Gl–Trp or U–Trp) and triple (Gl–Gl–Trp or U–U–Trp) interactions in aqueous solution were also computed in terms of the excess function concept. The results obtained were used to analyze the solute-non-electrolyte interactions in a liquid phase and their possible influence on stability of protein macromolecules.

A water-soluble monocationic chlorin photosensitizer for antimicrobial photodynamic therapy of superficial localized infections has been proposed. The antimicrobial activity of this compound against planktonic forms of nosocomial antibiotic-resistant gram-negative pathogens, Pseudomonas aeruginosa, Enterobacter cloacae, and Acinetobacter baumannii, has been studied in comparison with the activity of the photosensitizer Fotoran e(6), widely used in the clinical photodynamic therapy of tumors. It has been shown that both photosensitizers possess low dark toxicity; however, the light toxicity of the monocationic chlorin is higher by several orders of magnitude, and it can be proposed as a new agent for the antimicrobial photodynamic therapy.

Interactions of cationic and anionic chlorin photosensitizers (PSs) for photodynamic therapy with the potential delivery vehicle, the micellar surfactant Tween 80, were studied by spectrophotometric and fluorescence titration. The formation of PS—Tween 80 complexes in an aqueous solution was demonstrated. Two binding modes of the macrocycles to surfactant micelles, each with its own binding constant and stereochemistry of interactions, are observed in the spectrophotometric titration curves. Regardless of the sign and magnitude of the charge of the PS molecule, water-soluble chlorin macroheterocycles are located in the outer layer of the micelle surrounded by polar oxyethylene groups, into which hydrated iodide ions can penetrate. Cationic PSs were found to be, in general, more accessible to the quencher.

Cancer is one of the leading causes of death worldwide. Despite substantial progress in the understanding of tumor biology, and the appearance of new generations of targeted drugs and treatment techniques, the success achieved in this battle, with some notable exceptions, is still only moderate. Photodynamic therapy (PDT) is a successful but still underestimated therapeutic modality for treating many superficial cancers. In this paper, we focus on the extensive investigation of the monocationic chlorin photosensitizer (PS), considered here as a new photosensitizing agent for both antitumor and antimicrobial PDT. This monocationic chlorin PS (McChl) obtained from methylpheophorbide a (MPh) via a two-step procedure is well soluble in water in the physiological temperature range and forms stable complexes with passive carriers. McChl generates singlet oxygen with a good quantum yield in a lipid-like environment and binds mainly to low- and high-density lipoproteins in a vascular system. A comparison of the photodynamic activity of this agent with the activity of the well-established photosensitizer chlorin e6 (Chl e6) clearly indicates that McChl provides a much more efficient photoinactivation of malignant and microbial cells. The pilot PDT treatment of M1 sarcoma-bearing rats with this PS demonstrates its good potential for further preclinical investigations.

Multidrug resistance of pathogenic microflora is a serious threat to the modern community looking for new approaches to treating superinfections. In this sense, antimicrobial photodynamic therapy (aPDT) is an effective and safe technique considered to be a promising alternative or an important supplement to the traditional clinically applied methods for inactivating antibiotic resistant pathogens. Macroheterocyclic photosensitizers (PS) of three generations are proposed for clinical practice. They are known as the key compounds for PDT able to be localized selectively in microbial cells and to be activated with the red light producing toxic reactive oxygen species (ROS). However, these neutral and anionic PSs possess low affinity towards the outer lipopolysaccharide membrane of Gram-negative bacteria and, consequently, poor ability to kill these pathogens under irradiation. In contrast, cationic PSs containing one or more charged groups, especially those bound to an appropriate carrier, provide efficient inactivation of microorganisms. In this paper, we focus on the study of photophysics, aggregation and photoinduced antimicrobial activity of the water-soluble derivative of deuteroporphyrin-IX, a blood group porphyrin, bearing two cationic trialkylammonium fragments. This potential photosensitizing agent is found to generate singlet oxygen in a non-polar environment and forms stable nano-sized molecular complexes with passive non-ionic carrier Tween 80, localizing in an aqueous surfactant solution as a non-aggregated form in the surface micellar layer. Two different modes of PS/Tween 80 binding characterized by their own stability constants and interaction stoichiometry are observed. Microbiological experiments clearly demonstrate that the increased permeability of the outer bacterial membrane caused by the application of the intramicellar form of the photosensitizer or addition of some potentiation agents leads to pronounced light phototoxicity of the pigment against antibiotic-resistant nosocomial strains of Gram-negative bacterial pathogens.

Photodynamic therapy (PDT) is still considered to be a promising antitumor modality whose potential is not fully disclosed. This unique combination of visible light, molecular oxygen and a light-sensitive molecule, i.e. a photosensitizer (PS), leads to a generation of reactive oxygen species inducing direct tumor cell death, damage to tumor microvasculature and induction of a local inflammatory reaction. A much higher selectivity of tumor targeting during PDT can be achieved by the PS binding to appropriate delivery vehicles with pronounced af-finity to tumor tissue. Blood lipoproteins are often considered to be such agents enhancing PS tumor accumu-lation. Here, we focus on the interaction between a series of charged chlorin PSs synthesized on a chlorophyll a platform with blood transport proteins. The ability of PS molecules to form molecular complexes with potential carries - biocompatible polymers or surfactants is also considered and briefly discussed. Our experimental studies do indicate that a charge sign, number and relative position of charged groups in the macrocyclic molecule strongly influence the PS-protein interaction. The monocationic chlorin PS with a pronounced hydrophobic surface is found to be delivered by lipoproteins, while trianionic chlorin e6 is preferentially associated with serum albumin. The addition of biocompatible micellar or polymeric carriers widely used to improve biocompatibility of many drugs remains an elution profile almost unchanged despite strong PS-carrier binding. It is important that both di-and tricationic chlorins are not associated with any transport proteins and the mechanism of their accumulation in tumors must be different from other PSs. Taking into account that lipoproteins are highly important carriers for PS molecules in antitumor photodynamic therapy, we can make an important conclusion that chlorins bearing one cationic group at a certain position of a macrocycle are more efficient photosensitizing agents compared to anionic or polycationic macrocycles.

Aggregation studies of a photosensitizer (PS), tricationic chlorin (H2Chl3+), and its interaction with passive delivery vehicles Tween 80 and polyvinylpyrrolidone (PVP) in aqueous solutions have been carried out using 1D and 2D NMR spectroscopy, which has been shown to be a powerful tool for detecting both nanoaggregates at about 10–3 mole/kg and associates formed in solutions of H2Chl3+ at PS concentration lower by two orders of magnitude. NMR spectroscopy also can be used to identify molecular fragments of PS responsible for aggregation. The addition of solubilizers Tween 80 and PVP leads to the destruction of the PS nanoaggregates and formation of stable complexes with potential carriers, while the associated forms of the macrocycle may be retained in the solution. These results are consistent with the adsorption, fluorescence, and dynamic light scattering data. The molecular complex of water-soluble H2Chl3+ ions with the PVP macromolecule in aqueous solution is additionally stabilized by hydrogen bonding of the amide NH proton of the photosensitizer and oxygen atom of the polymer carbonyl group.

In this experimental work the acute toxicity of a chemically modified derivative of the natural pigment chlorophyll a called monocationic chlorin e6, which is a promising photosensitizer (PS) for antimicrobial and antitumor photodynamic therapy, was studied using white rats. The advantages of the PS under investigation are an intense absorption in the long-wavelength region of the visible spectrum, a sufficiently high quantum yield of singlet oxygen generation, pronounced amphiphilic properties along with an appropriate solubility in water, and a high level of photocytotoxic- ity in relation to both malignant HeLa cells and antibiotic-resistant hospital strains of E. сoli bacteria., P. aerugenosa and others. It has been shown that the value of LD50 of the considered PS can be calculated as the value of 100 mg/kg. In the reproduced experimental model of acute toxicity, pathomorphological changes in the vital organs of laboratory animals indicate a pronounced vasopathic effect of the drug with the development of cerebral edema and respiratory distress syndrome, which have become the main signs of thanatogenesis.

This review presents a wide range of tetrapyrrole photosensitizers used for photodynamic therapy (PDT), antimicrobial photodynamic therapy, photoinactivation of pathogens. Methods of synthesis and design of new photosensitizers with greater selectivity of accumulation in tumor tissue and increased photoinduced antitumor activity are considered. The issues of studying the properties of new photosensitizers, their photoactivity, the ability to generate singlet oxygen, and the possibility of using targeted photodynamic therapy in clinical practice are discussed. The review examines the work on PDT by national and foreign researchers.

The interaction of the dicationic photosensitizers (PSs) of the porphyrin {13(3),17(3)-bis-N-(2-N',N',N'-trimethylammonioethylamide) diiodide of deuteroporphyrin-IX} and chlorin {3(1),3(2)-bis-(N,N,N-trimethylammoniomethyl)-13(1)-N-methylamide-15(2),17(3)-dimethyl ester of chlorin e 6 diiodide} types with a nonionic surfactant Tween 80 (a potential delivery means) in the region of spherical micelles was studied by spectrophotometric and fluorescent titration. It was found that stable PS–Tween 80 complexes formed, with two binding modes with their own interaction constants and stoichiometry revealed on the titration curves; the most probable reasons for this are discussed. It was concluded that PS molecules lie in the outer layer of the micelle, where they are surrounded by polar oxyethylene groups and where hydrated iodide ions can penetrate. In the presence of various electrolytes, the size of Tween 80 micelles changed, which was detected by dynamic light scattering.