Porphyrin-Loaded TyroSpheres for the Intracellular Delivery of Drugs and Photoinduced Oxidant Species

Cellular Imaging and Time-Domain FLIM Studies of Meso-Tetraphenylporphine Disulfonate as a Photosensitising Agent in 2D and 3D Models

Fluorescence lifetime imaging (FLIM) and confocal fluorescence studies of a porphyrin-based photosensitiser (meso-tetraphenylporphine disulfonate: TPPS2a) were evaluated in 2D monolayer cultures and 3D compressed collagen constructs of a human ovarian cancer cell line (HEY). TPPS2a is known to be an effective model photosensitiser for both Photodynamic Therapy (PDT) and Photochemical Internalisation (PCI). This microspectrofluorimetric study aimed firstly to investigate the uptake and subcellular localisation of TPPS2a, and evaluate the photo-oxidative mechanism using reactive oxygen species (ROS) and lipid peroxidation probes combined with appropriate ROS scavengers. Light-induced intracellular redistribution of TPPS2a was observed, consistent with rupture of endolysosomes where the porphyrin localises. Using the same range of light doses, time-lapse confocal imaging permitted observation of PDT-induced generation of ROS in both 2D and 3D cancer models using fluorescence-based ROS together with specific ROS inhibitors. In addition, the use of red light excitation of the photosensitiser to minimise auto-oxidation of the probes was investigated. In the second part of the study, the photophysical properties of TPPS2a in cells were studied using a time-domain FLIM system with time-correlated single photon counting detection. Owing to the high sensitivity and spatial resolution of this system, we acquired FLIM images that enabled the fluorescence lifetime determination of the porphyrin within the endolysosomal vesicles. Changes in the lifetime dynamics upon prolonged illumination were revealed as the vesicles degraded within the cells.

Dynamic photodamage of red blood cell induced by CisDiMPyP porphyrin

It is well-known that oxidative damage in red blood cell (RBC) usually causes morphological changes and increased membrane rigidity. Although many studies have focused on investigating how RBC responds to a photodynamic stimulus, the intermediate steps between membrane damage and hemolysis are not reported. To give a comprehensive insight into changes of RBC membrane property under different oxidative damage levels, we employed the photoactivation of CisDiMPyP porphyrin that primarily generates singlet oxygen ¹O₂ as oxidant species. We found that there were distinguishable characteristic damages depending on the ¹O₂ flux over the membrane, in a way that each impact of photooxidative damage was categorized under three damage levels: mild (maintaining the membrane morphology and elasticity), moderate (membrane elongation and increased membrane elasticity) and severe (wrinkle-like deformation and hemolysis). When sodium azide (NaN₃) was used as a singlet oxygen quencher, delayed cell membrane alterations and hemolysis were detected. The delay times showed that ¹O₂ indeed plays a key role that causes RBC photooxidation by CisDiMPyP. We suggest that the sequence of morphological changes (RBC discoid area expansion, wrinkle-like patterns, and hemolysis) under photooxidative damage occurs due to damage to the lipid membrane and cytoskeletal network proteins.

Validating the predictions of murburn model for oxygenic photosynthesis: Analyses of ligand-binding to protein complexes and cross-system comparisons

In this second half of our treatise on oxygenic photosynthesis, we provide support for the murburn model of the light reaction of photosynthesis and ratify key predictions made in the first part. Molecular docking and visualization of various ligands of quinones/quinols (and their derivatives) with PS II/Cytochrome b₆f complexes did not support chartered 2e-transport role of quinols. A broad variety of herbicides did not show any affinity/binding-based rationales for inhibition of photosynthesis. We substantiate the proposal that disubstituted phenolics (perceived as protonophores/uncouplers or affinity-based inhibitors in the classical purview) serve as interfacial modulators of diffusible reactive (oxygen) species or DR(O)S. The DRS-based murburn model is evidenced by the identification of multiple ADP-binding sites on the extra-membraneous projection of protein complexes and structure/distribution of the photo/redox catalysts. With a panoramic comparison of the redox metabolic machinery across diverse organellar/cellular systems, we highlight the ubiquitous one-electron murburn facets (cofactors of porphyrin, flavin, FeS, other metal centers and photo/redox active pigments) that enable a facile harnessing of the utility of DRS. In the summative analyses, it is demonstrated that the murburn model of light reaction explains the structures of membrane supercomplexes recently observed in thylakoids and also accounts for several photodynamic experimental observations and evolutionary considerations. In toto, the work provides a new orientation and impetus to photosynthesis research. Communicated by Ramaswamy H. Sarma.

Nanosphere size control by varying the ratio of poly(ester amide) block copolymer blends

HYPOTHESIS

Blending amphiphilic triblock (A-B-A) and diblock (A-B) copolymers comprised of the same hydrophobic tyrosine-derived oligomeric B-block and hydrophilic poly(ethylene glycol) methyl ether (mPEG) A-block can provide highly tunable self-assembled nanosphere particle sizes suitable for biomedical applications.

EXPERIMENT

Triblock and diblock copolymers were synthesized via carbodiimide chemistry and were characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The amount of free PEG present in the purified copolymers was determined using a standard addition calibration curve and GPC peak deconvolution methods. Nanospheres were prepared by co-precipitation of each copolymer and of copolymer blends over a range of mole ratios. Nanospheres were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM) and % polymer recovery post-preparation.

FINDING

Precise synthesis control produced triblock and diblock copolymers with narrow molecular weight distributions and minimal residual reactants. Self-assembled nanosphere particle sizes were 33 nm for the triblock and 129 nm for the diblock, and the size of their blends increased continuously as a function of mole ratio within that biomedically relevant range. Addition of unreacted PEG had minimal impact on either triblock or diblock nanosphere particle sizes whereas addition of unreacted oligomeric B-block increased nanosphere sizes.

Redox-Sensitive and Folate-Receptor-Mediated Targeting of Cervical Cancer Cells for Photodynamic Therapy Using Nanophotosensitizers Composed of Chlorin e6-Conjugated β-Cyclodextrin via Diselenide Linkage

The aim of this study was to fabricate a reactive oxygen species (ROS)-sensitive and folate-receptor-targeted nanophotosensitizer for the efficient photodynamic therapy (PDT) of cervical carcinoma cells. Chlorin e6 (Ce6) as a model photosensitizer was conjugated with succinyl β-cyclodextrin via selenocystamine linkages. Folic acid (FA)-poly(ethylene glycol) (PEG) (FA-PEG) conjugates were attached to these conjugates and then FA-PEG-succinyl β-cyclodextrin-selenocystamine-Ce6 (FAPEGbCDseseCe6) conjugates were synthesized. Nanophotosensitizers of FaPEGbCDseseCe6 conjugates were fabricated using dialysis membrane. Nanophotosensitizers showed spherical shapes with small particle sizes. They were disintegrated in the presence of hydrogen peroxide (H₂O₂) and particle size distribution changed from monomodal distribution pattern to multimodal pattern. The fluorescence intensity and Ce6 release rate also increased due to the increase in H₂O₂ concentration, indicating that the nanophotosensitizers displayed ROS sensitivity. The Ce6 uptake ratio, ROS generation and cell cytotoxicity of the nanophotosensitizers were significantly higher than those of the Ce6 itself against HeLa cells in vitro. Furthermore, the nanophotosensitizers showed folate-receptor-specific delivery capacity and phototoxicity. The intracellular delivery of nanophotosensitizers was inhibited by folate receptor blocking, indicating that they have folate-receptor specificity in vitro and in vivo. Nanophotosensitizers showed higher efficiency in inhibition of tumor growth of HeLa cells in vivo compared to Ce6 alone. These results show that nanophotosensitizers of FaPEGbCDseseCe6 conjugates are promising candidates as PDT of cervical cancer.