Effects of endosomal photodamage on membrane recycling and endocytosis

Spatiotemporal metabolic dynamics of the photosensitizer talaporfin sodium in carcinoma and sarcoma

Photodynamic therapy (PDT) using the photosensitizer talaporfin sodium (talaporfin) is a new mode of treatment for cancer. However, the metabolic mechanism of talaporfin has not been clarified. Thus, we investigated the uptake, transportation, and elimination mechanisms of talaporfin in carcinoma and sarcoma. The results showed that talaporfin co‐localized in early endosomes and lysosomes. Talaporfin uptake was via clathrin‐ and caveolae‐dependent endocytosis and a high amount of intracellular ATP was essential. Inhibition of lysosomal enzymes maintained intracellular talaporfin levels. Inhibition of K‐Ras signaling reduced talaporfin uptake in carcinoma and sarcoma cell lines. Talaporfin was taken up by clathrin‐ and caveolae‐dependent endocytosis, translocated from early endosomes to lysosomes, and finally degraded by lysosomes. We also demonstrated that ATP is essential for the uptake of talaporfin and that activation of K‐Ras is involved as a regulatory mechanism. These results provide new insights into the metabolism of talaporfin in cancer cells for the enhancement of PDT for carcinoma and sarcoma.

Membrane reorganization after photochemical internalization to release transferrin-biofunctionalized polystyrene microparticles

Therapeutic drug carriers can drive their cargo to their target cells. However, an obstacle is usually the entrapment of the drug inside the endolysosomal compartment, which physically impedes its actuation by the impossibility of reaching its molecular site of action. To overcome this hurdle, photochemical internalization (PCI) has been proposed, but the extent of PCI-induced membrane disruption and its capability to allow the release of microparticles is unknown. The aim of the present study was to determine if PCI allows the release of microparticles from the endolysosomal compartment to the cytosol and to analyze at the ultrastructural level the effect of PCI on the membrane surrounding the particles. Confocal microscope allowed us to detect that endolysosomal membranes suffered some disruption after PCI, evidenced by the diffusion of soluble transferrin from the endolysosomes to the cytosol and by a decrease of LAMP1-microparticles co-localization. Transmission electron microscopy (TEM) showed a decrease in the number of well-defined membranes around microparticles after PCI, and scanning TEM combined with energy dispersive x-ray revealed an increase in the width of endolysosomal membranes after treatment. These results suggest that endolysosomal membranes suffered an ultrastructure alteration after PCI, enough to liberate soluble transferrin but not the entire microparticles.

Cathepsin B-degradable, NIR-responsive nanoparticulate platform for target-specific cancer therapy

Stimuli-responsive anticancer formulations can promote drug release and activation within the target tumour, facilitate cellular uptake, as well as improve the therapeutic efficacy of drugs and reduce off-target effects. In the present work, indocyanine green (ICG)-containing polyglutamate (PGA) nanoparticles were developed and characterized. Digestion of nanoparticles with cathepsin B, a matrix metalloproteinase overexpressed in the microenvironment of advanced tumours, decreased particle size and increased ICG cellular uptake. Incorporation of ICG in PGA nanoparticles provided the NIR-absorbing agent with time-dependent altered optical properties in the presence of cathepsin B. Having minimal dark toxicity, the formulation exhibited significant cytotoxicity upon NIR exposure. Combined use of the formulation with saporin, a ribosome-inactivating protein, resulted in synergistically enhanced cytotoxicity attributed to the photo-induced release of saporin from endo/lysosomes. The results suggest that this therapeutic approach can offer significant therapeutic benefit in the treatment of superficial malignancies, such as head and neck tumours.

Photodynamic Efficiency: From Molecular Photochemistry to Cell Death

Photodynamic therapy (PDT) is a clinical modality used to treat cancer and infectious diseases. The main agent is the photosensitizer (PS), which is excited by light and converted to a triplet excited state. This latter species leads to the formation of singlet oxygen and radicals that oxidize biomolecules. The main motivation for this review is to suggest alternatives for achieving high-efficiency PDT protocols, by taking advantage of knowledge on the chemical and biological processes taking place during and after photosensitization. We defend that in order to obtain specific mechanisms of cell death and maximize PDT efficiency, PSes should oxidize specific molecular targets. We consider the role of subcellular localization, how PS photochemistry and photophysics can change according to its nanoenvironment, and how can all these trigger specific cell death mechanisms. We propose that in order to develop PSes that will cause a breakthrough enhancement in the efficiency of PDT, researchers should first consider tissue and intracellular localization, instead of trying to maximize singlet oxygen quantum yields in in vitro tests. In addition to this, we also indicate many open questions and challenges remaining in this field, hoping to encourage future research.

Efficient induction of apoptosis in HeLa cells by a novel cationic porphycene photosensitizer

In the present study we analyze the photobiological properties of 2,7,12-tris(α-pyridinio-p-tolyl)-17-(p-(methoxymethyl)phenyl) porphycene (Py3MeO-TBPo) in Hela cells, in order to assess its potential as a new photosensitizer for photodynamic therapy of cultured tumor cells. Using 0.5 μM Py3MeO-TBPo, flow cytometry studies demonstrated an increase of intracellular drug levels related to the incubation time, reaching a maximum at 18 h. LysoTracker(®) Green (LTG) and MitoTracker(®) Green (MTG) probes were used to identify the subcellular localization. Upon exposure to ultraviolet excitation, red porphycene fluorescence was detected as red granules in the cytoplasm that colocalized with LTG. No significant toxic effects were detected for Py3MeO-TBPo in the dark at concentrations below 1 μM. In contrast, Py3MeO-TBPo combined with red-light irradiation induced concentration- and fluence-dependent HeLa cells inactivation. Besides, all photodynamic protocols assayed induced a clear effect of cell detachment inhibition after trypsin treatment. Both apoptotic and necrotic cell death mechanisms can occur in HeLa cells depending on the experimental protocol. After 18 h incubation with 0.5 μM Py3MeO-TBPo and subsequent red light irradiation (3.6 J/cm(2)), a high number of cells die by apoptosis, as evaluated by morphological alterations, immunofluorescent relocalization of Bax from cytosol to mitochondria, and TUNEL assay. Likewise, immunofluorescence techniques showed that cytochrome c is released from mitochondria into cytosol in cells undergoing apoptosis, which occurs immediately after relocation of Bax in mitochondria. The highest amount of apoptosis appeared 24 h after treatment (70%) and this cell death occurred without cell detachment to the substrate. In contrast, with 0.75 μM Py3MeO-TBPo and 3.6 J/cm(2) irradiation, morphological changes showed a preferential necrotic cell death. Singlet oxygen was identified as the cytotoxic agent involved in cell photoinactivation. Moreover, cell cultures pre-exposed to the singlet oxygen scavenger sodium azide showed pronounced protection against the loss of viability induced by Py3MeO-TBPo and light. Different changes in distribution and organization of cytoskeletal elements (microtubules and actin microfilaments) as well as the protein vinculin, after apoptotic and necrotic photodynamic treatments have been analyzed. Neither of these two cell death mechanisms (apoptosis or necrosis) induced cell detachment. In summary, Py3MeO-TBPo appears to meet the requirements for further scrutiny as a very good photosensitizer for photodynamic therapy: it is water soluble, has a high absorption in the red spectral region (where light penetration in tissue is higher), and is able to induce effective high apoptotic rate (70%) related to the more widely studied photosensitizers.

Inhibition of endocytic processes by photodynamic therapy

BACKGROUND AND OBJECTIVES

Recent studies have demonstrated an effect of photodamage on the endocytic pathway involved in recycling of membrane components. Using a series of agents with known sub-cellular targets, we explored the determinants of photodynamic inhibition of endocytic processes in three cell lines: A murine leukemia, a murine hepatoma, and a non-malignant epithelial cell line of human origin.

STUDY DESIGN/MATERIALS AND METHODS

The PI-3 kinase antagonist wortmannin blocks endosomal processing pathway dependent on this enzyme, providing an indication of the "flux" of endocytosis. Microscopic observations were used to assess the effect of photodamage on this pathway. Photosensitizing agents specific for mitochondrial, endoplasmic reticulum (ER), lysosomal, and endosomal photodamage were employed.

RESULTS

Sub-lethal photodamage directed against endosomes or lysosomes interrupted early steps in this endocytic process in the hepatoma cell line. A mechanism for these effects is proposed. Mitochondrial photodamage could interrupt endocytosis, but at levels that also induced apoptosis. ER photodamage did not affect endocytosis even at lethal levels. Somewhat similar results were obtained with other cell lines, but there were sufficient differences to indicate that the cell phenotype is, in part, a determinant of the endocytic response to PDT.

CONCLUSIONS

PDT is therefore seen to have an effect on endocytic processes. Further work will be needed to delineate the role of these endocytic effects in the array of responses to photodynamic therapy.