pH-Dependent Modification of Lipophilicity of Porphyrin-type Photosensitizers

Photodynamic disinfection and its role in controlling infectious diseases

Photodynamic therapy is witnessing a revival of its origins as a response to the rise of multi-drug resistant infections and the shortage of new classes of antibiotics. Photodynamic disinfection (PDDI) of microorganisms is making progresses in preclinical models and in clinical cases, and the perception of its role in the clinical armamentarium for the management of infectious diseases is changing. We review the positioning of PDDI from the perspective of its ability to respond to clinical needs. Emphasis is placed on the pipeline of photosensitizers that proved effective to inactivate biofilms, showed efficacy in animal models of infectious diseases or reached clinical trials. Novel opportunities resulting from the COVID-19 pandemic are briefly discussed. The molecular features of promising photosensitizers are emphasized and contrasted with those of photosensitizers used in the treatment of solid tumors. The development of photosensitizers has been accompanied by the fabrication of a variety of affordable and customizable light sources. We critically discuss the combination between photosensitizer and light source properties that may leverage PDDI and expand its applications to wider markets. The success of PDDI in the management of infectious diseases will ultimately depend on the efficacy of photosensitizers, affordability of the light sources, simplicity of the procedures, and availability of fast and efficient treatments.

Chiral Amphiphilic Secondary Amine-Porphyrin Hybrids for Aqueous Organocatalysis

Two chiral proline-derived amphiphilic 5-substituted-10,15,20-tris(4-sulfonatophenyl)porphyrins were prepared, and their pH-dependent supramolecular behavior was studied. In neutral aqueous solutions, the free-base form of the hybrids is highly soluble, allowing enamine-based organocatalysis to take place, whereas under acidic conditions, the porphyrinic protonated core of the hybrid leads to the formation of self-assembled structures, so that the hybrids flocculate and their catalytic activity is fully suppressed. The low degree of chirality transfer observed for aqueous Michael and aldol reactions strongly suggests that these reactions take place under true "in water" organocatalytic conditions. The highly insoluble catalyst aggregates can easily be separated from the reaction products by centrifugation of the acidic reaction mixtures, and after neutralization and desalting, the sodium salts of the sulfonated amine-porphyrin hybrids, retaining their full catalytic activity, can be recovered in high yield.

Impact of lipid composition and photosensitizer hydrophobicity on the efficiency of light-triggered liposomal release

Photo-triggerable liposomes are considered nowadays as promising drug delivery devices due to their potential to release encapsulated drugs in a spatial and temporal manner. In this work, we have investigated the photopermeation efficiency of three photosensitizers (PSs), namely verteporfin, pheophorbide a and m-THPP when incorporated into liposomes with well-defined lipid compositions (SOPC, DOPC or SLPC). By changing the nature of phospholipids and PSs, the illumination of the studied systems was shown to significantly alter their lipid bilayer properties via the formation of lipid peroxides. The system efficiency depends on the PS/phospholipid association, and the ability of the PS to peroxidize acyl chains. Our results demonstrated the possible use of these three clinically approved (or under investigation) PSs as potential candidates for photo-triggerable liposome conception.

Hyperporphyrin effects extended into a J-aggregate supramolecular structure in water

5-(4-Aminophenyl)-10,15,20-tris(4-sulfonatophenyl)porphyrin in acidic water self-assembles into a J-aggregate exhibiting a prominently red-shifted hyperporphyrin-type Q-absorption band at 742 nm.

Non-covalent assembly of meso-tetra-4-pyridyl porphine with single-stranded DNA to form nano-sized complexes with hydrophobicity-dependent DNA release and anti-tumor activity

DNA and porphyrin based therapeutics are important for anti-cancer treatment. The present studies demonstrate single-stranded DNA (ssDNA) assembles with meso-tetra-4-pyridyl porphine (MTP) forming porphyrin:DNA nano-complexes (PDN) that are stable in aqueous solution under physiologically relevant conditions and undergo dissociation with DNA release in hydrophobic environments, including cell membranes. PDN formation is DNA-dependent with the ratio of porphyrin:DNA being approximately two DNA nucleobases per porphyrin. PDN produce reactive oxygen species (ROS) in a light-dependent manner under conditions that favor nano-complex dissociation in the presence of hydrophobic solvents. PDN induce light-dependent cytotoxicity in vitro and anti-tumor activity towards bladder cancer xenografts in vivo. Light-dependent, PDN-mediated cell death results from ROS-mediated localized membrane damage due to lipid peroxidation with mass spectrometry indicating the generation of the lipid peroxidation products 9- and 13-hydroxy octadecanoic acid. Our results demonstrate that PDN have properties useful for therapeutic applications, including cancer treatment.

FROM THE CLINICAL EDITOR

In this study, porphyrin-DNA nanocomplexes were investigated as anti-cancer therapeutics inducing ROS production in a light-dependent manner. Efficacy is demonstrated in vitro as well as a in a bladder cancer xenograft model.

From elementary reactions to chemical relevance in the photodynamic therapy of cancer

Theories of radiationless conversions and of chemical processes were employed to design better photosensitizers for photodynamic therapy (PDT). In addition to photostability and intense absorption in the near infrared, these photosensitizers were required to generate high yields of long-lived triplet states that could efficiently transfer their energy, or an electron, to molecular oxygen. The guidance provided by the theories was combined with the ability to synthesize large quantities of pure photosensitizers and with the biological screening of graded hydrophilicities/lipophilicities. The theoretical prediction that halogenated sulfonamide tetraphenylbacteriochlorins could satisfy all the criteria for ideal PDT photosensitizers was verified experimentally.

Temoporfin (Foscan®, 5,10,15,20-tetra(m-hydroxyphenyl)chlorin)--a second-generation photosensitizer

This review traces the development and study of the second-generation photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin through to its acceptance and clinical use in modern photodynamic (cancer) therapy. The literature has been covered up to early 2011.

Photosensitizing properties of chlorins in solution and in membrane-mimicking systems

The photosensitizing properties of three chlorins, meso-tetra(3-hydroxyphenyl)chlorin (m-THPC), chlorin e6 (Ce6) and meso-tetraphenylchlorin substituted by two adjacent sulfonated groups (TPCS(2a)) are compared in solution and when incorporated in dioleoyl-sn-phosphatidylcholine (DOPC) liposomes. In solution, the three chlorins possess a similar efficacy to generate singlet oxygen (quantum yield approximately 0.65). The formation of conjugated dienes was used to determine their ability to induce the peroxidation of methyl linoleate as a target of singlet oxygen. In ethanol solution, the apparent quantum yield for this process is the same for the three chlorins and its value agrees with that expected from the known rates for the decay of singlet oxygen and its reaction with methyl linoleate. When incorporated in liposomes, the order of efficacy is m-THPC > TPCS(2a) > Ce6. This order is tentatively assigned to the relative embedment of the photosensitizer within the lipidic bilayer, TPCS(2a) and Ce6 being anchored by their negative chains nearer to the water-lipid interface. The photoinduced permeation of the lipidic bilayer by these chlorins was investigated by measuring the release of carboxyfluorescein entrapped into DOPC liposomes. The charged chlorins, in particular TPCS(2a), are the most efficient, a result discussed in relation with the technology of photochemical internalization, PCI.

The history of PDT in Norway Part one: Identification of basic mechanisms of general PDT

Photodynamic therapy (PDT) is now an established treatment of malignant and premalignant dysplasias. A number of first and second generation photosensitizers have been studied in Norway. The aim has been to improve PDT efficiency and applicability. Many critical details regarding the mechanisms of PDT were elucidated by researchers in Norway. In this review we focus on the most important findings related to these basic mechanisms, such as generation of singlet oxygen, estimations of its lifetime, the oxygen effect itself, the subcellular localization of photosensitizers with different properties, their photodegradation during PDT and their tumour selectivity.

Redistribution of Foscan? from plasma proteins to model membranes

Photodynamic therapy is a comparatively novel modality of tumours treatment that includes simultaneous action of photosensitizers, light and oxygen. Photosensitizer redistribution between plasma proteins and biomembranes define photosensitizers interaction with cells, their intracellular localization and kinetics of sensitizers accumulation in the tumour. Present study investigates the kinetics of Foscan release from plasma proteins to model membranes using fluorescence resonance energy transfer (FRET) from label, covalently bound to protein, to sensitizer. We have demonstrated very slow kinetics of Foscan release from protein complexes with rate constants of (1.7 +/- 0.1) x 10(-3) s(-1) for albumin and (1.6 +/- 0.3) x 10(-4) s(-1) for high-density lipoproteins (HDL). Foscan redistributes by both collision and diffusion-mediated transfer from complexes with HDL, with bimolecular rate constant k(out) = (8.8 +/- 1.4) x 10(-2) M(-1) s(-1). Thermodynamic considerations proposed that sensitizer release from HDL into the aqueous medium is unfavourable and collision mechanism appeared to be a preferred mode of transfer in biological environment. Slow rates of Foscan redistribution from plasma proteins should be considered while planning dosimetry protocol of Foscan-PDT.

pH dependent uptake of porphyrin-type photosensitizers by solid tumor cells in vitro is not induced by modification of transmembrane potential

The uptake of HpIX, TPPS2a and mTHPC by WiDr, THX cells and skin fibroblasts at pH 7.4 and 6.8 was compared. In the absence of serum, the uptake of HpIX was higher at lower pH. The difference was significant in WiDr cells (P < 0.01) and skin fibroblasts (P < 0.05). TPPS2a nor mTHPC showed any pH dependent uptake. Lowering the extracellular pH resulted in a significant depolarization (3-8 mV) of the cells. Application of tetraethylammonium chloride did not affect the cellular uptake of any of the photosensitizers. We conclude that the pH dependent uptake of photosensitizers is not mainly related to altered transmembrane potential.