Cell death response of U87 glioma cells on hypericin photoactivation is mediated by dynamics of hypericin subcellular distribution and its aggregation in cellular organelles

Construction and synergistic anti-tumor study of a tumor microenvironment-based multifunctional nano-drug delivery system

To solve the problems existing in the clinical application of hypericin (Hyp) and tirapazamine (TPZ), a nano-drug delivery system with synergistic anti-tumor functions was constructed using mesoporous silica nanoparticles (MSN) and sodium alginate (SA). The system exhibited excellent stability, physiological compatibility and targeted drug release performance in tumor tissues. In the in vitro and in vivo experiments, Hyp released from MSN killed tumor cells through photodynamic therapy (PDT). The degree of hypoxia in the tumor tissue site was exacerbated, enabling TPZ to fully exert its anti-tumor activity. Our studies suggested that the synergistic effects between the components of the nano-drug delivery system significantly improve the anti-tumor properties of Hyp and TPZ.

Molecular Determinants for Photodynamic Therapy Resistance and Improved Photosensitizer Delivery in Glioma

Gliomas account for 24% of all the primary brain and Central Nervous System (CNS) tumors. These tumors are diverse in cellular origin, genetic profile, and morphology but collectively have one of the most dismal prognoses of all cancers. Work is constantly underway to discover a new effective form of glioma therapy. Photodynamic therapy (PDT) may be one of them. It involves the local or systemic application of a photosensitive compound-a photosensitizer (PS)-which accumulates in the affected tissues. Photosensitizer molecules absorb light of the appropriate wavelength, initiating the activation processes leading to the formation of reactive oxygen species and the selective destruction of inappropriate cells. Research focusing on the effective use of PDT in glioma therapy is already underway with promising results. In our work, we provide detailed insights into the molecular changes in glioma after photodynamic therapy. We describe a number of molecules that may contribute to the resistance of glioma cells to PDT, such as the adenosine triphosphate (ATP)-binding cassette efflux transporter G2, glutathione, ferrochelatase, heme oxygenase, and hypoxia-inducible factor 1. We identify molecular targets that can be used to improve the photosensitizer delivery to glioma cells, such as the epithelial growth factor receptor, neuropilin-1, low-density lipoprotein receptor, and neuropeptide Y receptors. We note that PDT can increase the expression of some molecules that reduce the effectiveness of therapy, such as Vascular endothelial growth factor (VEGF), glutamate, and nitric oxide. However, the scientific literature lacks clear data on the effects of PDT on many of the molecules described, and the available reports are often contradictory. In our work, we highlight the gaps in this knowledge and point to directions for further research that may enhance the efficacy of PDT in the treatment of glioma.

Singlet oxygen lifetime changes in dying glioblastoma cells

Time-resolved phosphorescence detection was employed to determine the lifetime of singlet oxygen in live cells. Using hypericin as a photosensitizer, singlet oxygen was generated in U87MG glioblastoma cells. The phosphorescence of singlet oxygen was detected in aqueous cell suspensions following pulsed laser excitation. Our goal was to eliminate or reduce the problems associated with lifetime measurements in water-based cell suspensions. The apparatus enabled simultaneous singlet oxygen phosphorescence and transient absorption measurements, reducing uncertainty in lifetime estimation. The changes in singlet oxygen lifetime were observed during early and late apoptosis induced by photodynamic action. Our findings show that the effective lifetime of singlet oxygen in the intracellular space of the studied glioblastoma cells is 0.4 μs and increases to 1.5 μs as apoptosis progresses. Another group of hypericin, presumably located in the membrane blebs and the plasma membrane of apoptotic cells, generates singlet oxygen with a lifetime of 1.9 μs.

Imaging of heterogeneity in 3D spheroids of U87MG glioblastoma cells and its implications for photodynamic therapy

BACKGROUND

In recent years, pharmacology and toxicology have emphasised the intention to move from in vivo models to simplified 3D objects represented by spheroidal models of cancer. Mitochondria are one of the subcellular organelles responsible for cell metabolism and are often a lucrative target for cancer treatment including photodynamic therapy (PDT).

METHODS

Hanging droplet-grown glioblastoma cells were forced to form spheroids with heterogeneous environments that were characterised by fluorescence microscopy and flow cytometry using fluorescent probes sensitive to oxidative stress and apoptosis. PDT was induced with hypericin at 590 nm.

RESULTS

It was found that the metabolic activity of the cells in the periphery and core of the spheroid was different. Higher oxidative stress and induction of caspase-3 were observed in the peripheral layers after PDT. These parts were more destabilised and showed higher expression of LC3B, an autophagic marker. However, the response of the whole system to the treatment was controlled by the cells in the core of the spheroids, which were hardly affected by the treatment. It has been shown that the depth of penetration of hypericin into this system is an important limiting step for PDT and the induction of autophagy and apoptosis.

CONCLUSIONS

In this work, we have described the fluorescence imaging of vital mitochondria, caspase-3 production and immunostaining of autophagic LC3B in cells from glioblastoma spheroids before and after PDT. Overall, we can conclude that this model represents an in vitro and in vivo applicable alternative for the study of PDT in solid microtumours.

Effective transport of aggregated hypericin encapsulated in SBA-15 nanoporous silica particles for photodynamic therapy of cancer cells

Photodynamic therapy (PDT) represents an interesting modality for the elimination of damaged biomaterials and cells. This treatment takes advantage of the photosensitizing properties of molecules that are active only when irradiated with light. In the present work, a dual property of hypericin, a hydrophobic molecule with high performance in photodiagnostics and photodynamic therapy, was exploited. The non-fluorescent and photodynamically inactive form of hypericin aggregates was loaded into the nanopores of SBA-15 silica particles. The synthesized particles were characterized by infrared spectroscopy, thermogravimetry, differential thermal analysis, small-angle X-ray scattering and transmission electron microscopy. Hypericin aggregates were confirmed by absorption spectra typical of aggregated hypericin and by its short fluorescence lifetime. Release of hypericin from the particles was observed toward serum proteins, mimicking physiological conditions. Temperature- and time-dependent uptake of hypericin by cancer cells showed gradual release of hypericin from the particles and active cellular transport by endocytosis. A closer examination of SBA-15-hypericin uptake by fluorescence lifetime imaging showed that aggregated hypericin molecules, characterized by a short fluorescence lifetime (∼4 ns), were still present in the SBA-15 particles upon uptake by cells. However, monomerization of hypericin in cancer cells was observed by extending the hypericin fluorescence lifetime by ∼8 ns, preferentially in lipid compartments and the plasma membrane. This suggests a promising prognosis for delayed biological activity of the entire cargo, which was confirmed by effective PDT in vitro. In summary, this work presents an approach for safe, inactive delivery of hypericin that is activated at the target site in cells and tissues.

Redistribution of hydrophobic hypericin from nanoporous particles of SBA-15 silica in vitro, in cells and in vivo

Nanoporous silica is nowadays used in various fields of nano- and micro-materials research. The advantage of nanoporous material is that it can be filled with various hydrophilic and hydrophobic molecules, which are then delivered to the target cells and tissues. In the present study, we have studied the interaction of nanoporous silica with hydrophobic and photodynamically active molecule - hypericin. Hypericin was adsorbed on/in SBA-15 silica, which led to the disappearance of its fluorescence due to hypericin aggregate formation. However, it was observed here that hypericin can be easily redistributed from these particles towards proteins and lipids in serum and cells in vitro and in vivo. Moreover, the charged surface character of SBA-15 pores forced the creation of protein/lipid corona on particles. Such complex enabled monomerization of hypericin on the surface of particles presented by fluorescence in the corona and singlet oxygen production suitable for photodynamic therapy (PDT). The PDT efficacy achieved by introducing the new construct into the PDT protocol was comparable to the efficacy of hypericin PDT. In conclusion, this study demonstrates a promising approach for the delivery of hydrophobic photosensitizers to cancer cells by nanoporous silica using fluorescence techniques.

Hypericin: A natural anthraquinone as promising therapeutic agent

BACKGROUND

Hypericin is a prominent secondary metabolite mainly existing in genus Hypericum. It has become a research focus for a quiet long time owing to its extensively pharmacological activities especially the anti-cancer, anti-bacterial, anti-viral and neuroprotective effects. This review concentrated on summarizing and analyzing the existing studies of hypericin in a comprehensive perspective.

METHODS

The literature with desired information about hypericin published after 2010 was gained from electronic databases including PubMed, SciFinder, Science Direct, Web of Science, China National Knowledge Infrastructure databases and Wan Fang DATA.

RESULTS

According to extensive preclinical and clinical studies conducted on the hypericin, an organized and comprehensive summary of the natural and artificial sources, strategies for improving the bioactivities, pharmacological activities, drug combination of hypericin was presented to explore the future therapeutic potential of this active compound.

CONCLUSIONS

Overall, this review offered a theoretical guidance for the follow-up research of hypericin. However, the pharmacological mechanisms, pharmacokinetics and structure activity relationship of hypericin should be further studied in future research.

Photobiomodulation and photodynamic therapy-induced switching of autophagy and apoptosis in human dermal fibroblasts

Nowadays, photobiomodulation (PBM) in combination with chemotherapy or other therapeutic approaches is an attractive adjuvant modality for cancer treatment. Targeted destruction of cancer cells is one of the main advantages of photodynamic therapy (PDT). We have shown in previous studies that the combination of PBM at 808 nm and hypericin-mediated PDT increases PDT efficacy in human glioblastoma cells U87 MG. The study presented here shows significant differences between U87 MG and non-cancerous human dermal fibroblasts (HDF) cells treated by PBM and PDT. This study focuses on mitochondria because PBM mainly affects these organelles. We demonstrated that an interplay between mitochondrial and autophagic proteins plays a crucial role in the response of HDF cells to PBM and PDT. Fluorescence microscopy, flow cytometry, and Western blot analysis were used to examine the autophagic profile of HDF cells after these treatments. An increase in ubiquitin, SQSTM1, LC3BII, and cytochrome c was accompanied by a decrease in M6PR, ATG16L1, and Opa1 in HDF cells exposed to PBM and PDT. Overall, we observed that the switching of autophagy and apoptosis is dose-dependent and also occurs independently of PBM in HDF cells after hypericin-mediated PDT. However, PBM might preferentially induce autophagy in noncancer cells, which might escape apoptosis under certain conditions.

Spheroidal Model of SKBR3 and U87MG Cancer Cells for Live Imaging of Caspase-3 during Apoptosis Induced by Singlet Oxygen in Photodynamic Therapy

Aspects related to the response of cells to photodynamic therapy (PDT) have been well studied in cell cultures, which often grow in monolayers. In this work, we propose a spheroidal model of U87MG and SKBR3 cells designed to mimic superficial tumor tissue, small spheroids (<500 µm) suitable for confocal fluorescence microscopy, and larger spheroids (>500 µm) that can be xenografted onto quail chorioallantoic membrane (CAM) to study the effects of PDT in real time. Hypericin was used as a model molecule for a hydrophobic photosensitizer that can produce singlet oxygen (1O2). 1O2 production by hypericin was detected in SKBR3 and U87MG spheroid models using a label-free technique. Vital fluorescence microscopy and flow cytometry revealed the heterogeneity of caspase-3 distribution in the cells of the spheroids. The levels of caspase-3 and apoptosis increased in the cells of spheroids 24 h after PDT. Lactate dehydrogenase activity was evaluated in the spheroids as the most reliable assay to detect differences in phototoxicity. Finally, we demonstrated the applicability of U87MG spheroids on CAM in photodiagnostics. Overall, the variability and applicability of the prepared spheroid models were demonstrated in the PDT study.

Accumulation and penetration behavior of hypericin in glioma tumor spheroids studied by fluorescence microscopy and confocal fluorescence lifetime imaging microscopy

Glioblastoma WHO IV belongs to a group of brain tumors that are still incurable. A promising treatment approach applies photodynamic therapy (PDT) with hypericin as a photosensitizer. To generate a comprehensive understanding of the photosensitizer-tumor interactions, the first part of our study is focused on investigating the distribution and penetration behavior of hypericin in glioma cell spheroids by fluorescence microscopy. In the second part, fluorescence lifetime imaging microscopy (FLIM) was used to correlate fluorescence lifetime (FLT) changes of hypericin to environmental effects inside the spheroids. In this context, 3D tumor spheroids are an excellent model system since they consider 3D cell-cell interactions and the extracellular matrix is similar to tumors in vivo. Our analytical approach considers hypericin as probe molecule for FLIM and as photosensitizer for PDT at the same time, making it possible to directly draw conclusions of the state and location of the drug in a biological system. The knowledge of both state and location of hypericin makes a fundamental understanding of the impact of hypericin PDT in brain tumors possible. Following different incubation conditions, the hypericin distribution in peripheral and central cryosections of the spheroids were analyzed. Both fluorescence microscopy and FLIM revealed a hypericin gradient towards the spheroid core for short incubation periods or small concentrations. On the other hand, a homogeneous hypericin distribution is observed for long incubation times and high concentrations. Especially, the observed FLT change is crucial for the PDT efficiency, since the triplet yield, and hence the O₂ activation, is directly proportional to the FLT. Based on the FLT increase inside spheroids, an incubation time > 30 min is required to achieve most suitable conditions for an effective PDT.

Autophagy and Apoptosis Induced in U87 MG Glioblastoma Cells by Hypericin-Mediated Photodynamic Therapy Can Be Photobiomodulated with 808 nm Light

Glioblastoma is one of the most aggressive types of tumors. Although few treatment options are currently available, new modalities are needed to improve prognosis. In this context, photodynamic therapy (PDT) is a promising adjuvant treatment modality. In the present work, hypericin-mediated PDT (hypericin-PDT, 2 J/cm²) of U87 MG cells is combined with (2 min, 15 mW/cm² at 808 nm) photobiomodulation (PBM). We observed that PBM stimulates autophagy, which, in combination with PDT, increases the treatment efficacy and leads to apoptosis. Confocal fluorescence microscopy, cytotoxicity assays and Western blot were used to monitor apoptotic and autophagic processes in these cells. Destabilization of lysosomes, mitochondria and the Golgi apparatus led to an increase in lactate dehydrogenase activity, oxidative stress levels, LC3-II, and caspase-3, as well as a decrease of the PKCα and STAT3 protein levels in response to hypericin-PDT subcellular concentration in U87 MG cells. Our results indicate that therapeutic hypericin concentrations can be reduced when PDT is combined with PBM. This will likely allow to reduce the damage induced in surrounding healthy tissues when PBM-hypericin-PDT is used for in vivo tumor treatments.

Alkyl Chain Length in Poly(2-oxazoline)-Based Amphiphilic Gradient Copolymers Regulates the Delivery of Hydrophobic Molecules: A Case of the Biodistribution and the Photodynamic Activity of the Photosensitizer Hypericin

Self-assembled nanostructures of amphiphilic gradient copoly(2-oxazoline)s have recently attracted attention as promising delivery systems for the effective delivery of hydrophobic anticancer drugs. In this study, we have investigated the effects of increasing hydrophobic side chain length on the self-assembly of gradient copolymers composed of 2-ethyl-2-oxazoline as the hydrophilic comonomer and various 2-(4-alkyloxyphenyl)-2-oxazolines as hydrophobic comonomers. We show that the size of the formed polymeric nanoparticles depends on the structure of the copolymers. Moreover, the stability and properties of the polymeric assembly can be affected by the loading of hypericin, a promising compound for photodiagnostics and photodynamic therapy (PDT). We have found the limitation that allows rapid or late release of hypericin from polymeric nanoparticles. The nanoparticles entering the cells by endocytosis decreased the hypericin-induced PDT, and the contribution of the passive process (diffusion) increased the probability of a stronger photoeffect. A study of fluorescence pharmacokinetics and biodistribution revealed differences in the release of hypericin from nanoparticles toward the quail chorioallantoic membrane, a preclinical model for in vivo studies, depending on the composition of polymeric nanoparticles. Photodamage induced by PDT in vivo well correlated with the in vitro results. All formulations studied succeeded in targeting hypericin at cancer cells. In conclusion, we demonstrated the promising potential of poly(2-oxazoline)-based gradient copolymers for effective drug delivery and sequential drug release needed for successful photodiagnostics and PDT in cancer therapy.

Searching for combination therapy by clustering methods: Stimulation of PKC in Golgi apparatus combined with hypericin induced PDT

Cancer cell metabolism is a very attractive target for anticancer treatments. This work focuses on protein kinase C (PKC) signaling in the U87 MG glioma. By means of western blot, fluorescence and time-resolved fluorescence microscopy the correlation between the Golgi apparatus (GA), lysosomes and mitochondria were evaluated. The known regulators of PKC were applied to cancer cells. Phorbol myristate acetate (PMA) was chosen as the activator of PKC. Gö6976, hypericin and rottlerin, the inhibitors of PKCα and PKCδ were selected as well. Stabilization, destabilization processes occurring in cells allow classification of observations into several groups. Multiple versions of hierarchical cluster analysis have been applied and similarities have been found between organelles and PKC regulators. The method identified GA as an extraordinary organelle whose functionality is significantly influenced by PKC regulators as well as oxidative stress. Therefore, combination therapy has been designed according to the results of the cluster analysis. Furthermore, the efficacy of photodynamic therapy mediated by hypericin, and the consequent apoptosis, was significantly increased during the treatment. To our knowledge, this is the first demonstration of the effectiveness of the clustering in the given area.

The Influence of Hypericin-Mediated Photodynamic Therapy on Interleukin-8 and -10 Secretion in Colon Cancer Cells

The aim of this study was to measure the secretion of interleukin (IL)-8 and -10 during an elicited immune response following sublethal doses of hypericin-mediated photodynamic therapy (HY-PDT) in experimental models of residual colon cancer cells in vitro. Investigations were performed on the cancer cell lines SW480 and SW620. Each cell line was exposed to 3 different concentrations of the photosensitizer HY and various doses of irradiation. The cell metabolic activity using an MTT assay was performed and then the measurement of IL-8 and IL-10 secretion was achieved using the Bio-Plex ProTMAssay. There was a statistically significant amplification of IL-8 secretion during HY-PDT in the SW620 cell line (at 1 J/cm2: P = .01, 5 J/cm2: P = .002, and 10 J/cm2: P = .025) and a statistically significant decrease in IL-8 during HY-PDT in the SW480 cell line (at 1 J/cm2: P = .05, 5 J/cm2: P = .035, and 10 J/cm2: P = .035). No statistically significant differences in IL-10 concentration were found following HY-PDT in the SW480 (at 1 J/cm2: P > .4, 5 J/cm2: P = .1, and 10 J/cm2: P = .075) or in the SW620 cell line (at 1 J/cm2: P > .4, 5 J/cm2: P > .4, and 10 J/cm2: P > .4). HY-PDT can both eliminate and control a primary tumor via cytotoxic effects, and at sublethal doses, it can affect IL release by colon cancer cells. In this experiment, this influence depended on the level of tumor cell metastatic activity.

A Model In Vitro Study Using Hypericin: Tumor-Versus Necrosis-Targeting Property and Possible Mechanisms

Hypericin (Hyp) had been explored as a tumor-seeking agent for years; however, more recent studies showed its necrosis-avidity rather than cancer-seeking property. To further look into this discrepancy, we conducted an in vitro study on Hyp retention in vital and dead cancerous HepG2 and normal LO2 cell lines by measuring the fluorescence intensity and concentration of Hyp in cells. To question the DNA binding theory for its necrosis-avidity, the subcellular distribution of Hyp was also investigated to explore the possible mechanisms of the necrosis avidity. The fluorescence intensity and concentration are significantly higher in dead cells than those in vital cells, and this difference did not differ between HepG2 and LO2 cell lines. Hyp was taken up in vital cells in the early phase and excreted within hours, whereas it was retained in dead cells for more than two days. Confocal microscopy showed that Hyp selectively accumulated in lysosomes rather than cell membrane or nuclei. Hyp showed a necrosis-avid property rather than cancer-targetability. The long-lasting retention of Hyp in dead cells may be associated with halted energy metabolism and/or binding with certain degraded cellular substrates. Necrosis-avidity of Hyp was confirmed, which may be associated with halted energy metabolism in dead LO2 or HepG2 cells.

Glyco-nanoparticles: New drug delivery systems in cancer therapy

Cancer is known as one of the most common diseases that are associated with high mobility and mortality in the world. Despite several efforts, current cancer treatment modalities often are highly toxic and lack efficacy and specificity. However, the application of nanotechnology has led to the development of effective nanosized drug delivery systems which are highly selective for tumors and allow a slow release of active anticancer agents. Different Nanoparticles (NPs) such as the silicon-based nano-materials, polymers, liposomes and metal NPs have been designed to deliver anti-cancer drugs to tumor sites. Among different drug delivery systems, carbohydrate-functionalized nanomaterials, specially based on their multi-valent binding capacities and desirable bio-compatibility, have attracted considerable attention as an excellent candidate for controlled release of therapeutic agents. In addition, these carbohydrate functionalized nano-carriers are more compatible with construction of the intracellular delivery platforms like the carbohydrate-modified metal NPs, quantum dots, and magnetic nano-materials. In this review, we discuss recent research in the field of multifunctional glycol-nanoparticles (GNPs) intended for cancer drug delivery applications.

Importance of Hypericin-Bcl2 interactions for biological effects at subcellular levels

Hypericin (Hyp) is a naturally occurring compound used as photosensitizer in photodynamic therapy and diagnosis. Recently, we have shown that Hyp presence alone, without illumination, resulted in substantial biological effects at several sub-cellular levels. Hyp induced changes in cellular ultrastructure, mitochondria function and metabolism, and distribution of Bcl2 proteins in malignant and non-malignant cells. The molecular mechanisms that underlie Hyp light-independent effects are still elusive. We have hypothesized that Bcl2-Hyp interactions might be one possible mechanism. We performed molecular docking studies to determine the Hyp-Bcl2 interaction profile. Based on the interaction profiles small Bcl2 peptide segments were selected for further study. We designed small peptides corresponding to Bcl2 BH3 and BH1 domains and tested the binding of Hyp and Bcl2 known inhibitor, ABT263, to the peptides in computer modeling and in vitro binding studies. We employed endogenous tryptophan and tyrosine in the BH3 and BH1 peptides, respectively, and their fluorescent properties to show interaction with Hyp and ABT263. Overall, our results indicate that Hyp can interact with Bcl2 protein at its BH3-BH1 hydrophobic groove, and this interaction may trigger changes in intracellular distribution of Bcl2 proteins. In addition, our computer modeling results suggest that Hyp also interacts with other anti-apoptotic members of Bcl2 family similar to the known BH3 mimetics. Our findings are novel and might contribute to understanding Hyp light-independent effects. In addition, they may substantiate the therapeutic use of Hyp as a BH3 mimetic molecule to enhance other cancer treatments.

Facile fabrication of hypericin-entrapped glyconanoparticles for targeted photodynamic therapy

BACKGROUND

Photodynamic therapy is a safe, noninvasive modality for cancer therapy, in which the photosensitizer (PS) is a crucial component. Hypericin (Hy) is a promising PS; however, its clinical application is significantly limited by its poor hydrophilicity.

MATERIALS AND METHODS

To overcome the clinical application limitation of Hy, a novel strategy is developed here by entrapping Hy into polydopamine (PDA) film formed on the surface of magnetic iron oxide nanoparticles (MNPs) through the self-polymerization of dopamine under alkaline condition. The amount of Hy in the Hy-entrapped PDA-MNP composite nanoparticles (denoted as PHMs) was measured by spectrophotometry. Furthermore, lactose, as the targeting ligand to asialoglycoprotein receptors, was conjugated to the surface of the PHMs by taking advantage of the spontaneous reaction of PDA with amino groups.

RESULTS

Spectrophotometry analysis revealed that the amount of Hy in the PHMs was 72 μmol g-1 PHMs. The fabricated Hy-entrapped glyconanoparticle (Lac-PHM) exhibited excellent water dispersibility, stability, and selectivity for asialoglycoprotein receptors overexpressing HepG2 cells. Atomic absorption spectroscopy analysis showed that the amount of the Lac-PHMs taken in HepG2 cells was 2.1-fold higher than that of the triethylene glycol-modified PHMs. The results of intracellular reactive oxygen species generation detection, cytotoxicity study, and apoptosis detection indicated that the Lac-PHMs had a satisfying photodynamic effect to HepG2 cells.

CONCLUSION

The strategy developed in this work offers great potential for delivery of a variety of hydrophobic PSs.

Sonodynamic therapy: A potential treatment for atherosclerosis

Atherosclerosis (AS), a chronic arterial disease, is one of the major causes of morbidity and mortality worldwide. Several treatment modalities have been demonstrated to be effective in treating AS; however, the mortality rate due to AS remains high. Sonodynamic therapy (SDT) is a promising new treatment using low-intensity ultrasound in combination with sonosensitizers. Although SDT was developed from photodynamic therapy (PDT), it has a stronger tissue-penetrating capability and exhibits a more focused effect on the target lesional site requiring treatment. Furthermore, SDT has been demonstrated to suppress the formation of atheromatous plaques, and it can increase plaque stability both in vitro and in vivo. In this article, we critically summarize the recent literature on SDT, focusing on its possible mechanism of action as well as the existing and newly discovered sonosensitizers and chemotherapeutic agents for the treatment of AS.

In vitro identification of mitochondrial oxidative stress production by time-resolved fluorescence imaging of glioma cells

Oxidative phosphorylation and glycolysis are important features, by which cells could bypass oxidative stress. The level of oxidative stress, and the ability of cells to promote oxidative phosphorylation or glycolysis, significantly determined proliferation or cell demise. In the present work, we have employed selective mitochondrial probe MitoTracker™ Orange CMTM/Ros (MTO) to estimate the level of oxidative stress in cancer cells at different stressed conditions. MTO is partially sensitive to decrease of mitochondrial membrane potential and to reactive oxygen species (ROS) generated in mitochondria. We have demonstrated, that fluorescence lifetime of MTO is much more sensitive to oxidative stress than intensity-based approaches. This method was validated in different cancer cell lines. Our approach revealed, at relatively low ROS levels, that Gö 6976, a protein kinase C (PKC) α inhibitor, and rottlerin, an indirect PKCδ inhibitor, increased mitochondrial ROS level in glioma cell. Their involvement in oxidative phosphorylation and apoptosis was investigated with oxygen consumption rate estimation, western blot and flow-cytometric analysis. Our study brings new insight to identify feeble differences in ROS production in living cells.

Estimation of PKCδ autophosphorylation in U87 MG glioma cells: combination of experimental, conceptual and numerical approaches

Golgi apparatus (GA) is a center for lipid metabolism and the final target of ceramide pathway, which may result in apoptosis. In this work localization of highly hydrophobic hypericin is followed by time-resolved imaging of NBDC₆ (fluorescent ceramide) in U87 MG glioma cells. Decrease of NBDC₆ fluorescence lifetimes in cells indicates that hypericin can also follow this pathway. It is known that both, ceramide and hypericin can significantly influence protein kinase C (PKC) activity. Western blotting analysis shows increase of PKCδ autophosphorylation at Ser645 (p(S645)PKCδ) in glioma cells incubated with 500 nM hypericin and confocal-fluorescence microscopy distinguishes p(S645)PKCδ localization between GA related compartments and nucleus. Experimental and numerical methods are combined to study p(S645)PKCδ in U87 MG cell line. Image processing based on conceptual qualitative description is combined with numerical treatment via simple exponential saturation model which describes redistribution of p(S645)PKCδ between nucleus and GA related compartments after hypericin administration. These results suggest, that numerical methods can significantly improve quantification of biomacromolecules (p(S645)PKCδ) directly from the fluorescence images and such obtained outputs are complementary if not equal to typical used methods in biology.

The flashlights on a distinct role of protein kinase C δ: Phosphorylation of regulatory and catalytic domain upon oxidative stress in glioma cells

Glioblastoma multiforme are considered to be aggressive high-grade tumors with poor prognosis for patient survival. Photodynamic therapy is one of the adjuvant therapies which has been used for glioblastoma multiforme during last decade. Hypericin, a photosensitizer, can be employed in this treatment. We have studied the effect of hypericin on PKCδ phosphorylation in U87 MG cells before and after light application. Hypericin increased PKCδ phosphorylation at tyrosine 155 in the regulatory domain and serine 645 in the catalytic domain. However, use of the light resulted in apoptosis, decreased phosphorylation of tyrosine 155 and enhanced serine 645. The PKCδ localization and phosphorylation of regulatory and catalytic domains were shown to play a distinct role in the anti-apoptotic response of glioma cells. We hypothesized that PKCδ phosphorylated at the regulatory domain is primarily present in the cytoplasm and in mitochondria before irradiation, and it may participate in Bcl-2 phosphorylation. After hypericin and light application, PKCδ phosphorylated at a regulatory domain which is in the nucleus. In contrast, PKCδ phosphorylated at the catalytic domain may be mostly active in the nucleus before irradiation, but active in the cytoplasm after the irradiation. In summary, light-induced oxidative stress significantly regulates PKCδ pro-survival and pro-apoptotic activity in glioma cells by its phosphorylation at serine 645 and tyrosine 155.

Hypericin in the Dark: Foe or Ally in Photodynamic Therapy?

Photosensitizers (PSs) in photodynamic therapy (PDT) are, in most cases, administered systemically with preferential accumulation in malignant tissues; however, exposure of non-malignant tissues to PS may also be clinically relevant, when PS molecules affect the pro-apoptotic cascade without illumination. Hypericin (Hyp) as PS and its derivatives have long been studied, regarding their photodynamic and photocytotoxic characteristics. Hyp and its derivatives have displayed light-activated antiproliferative and cytotoxic effects in many tumor cell lines without cytotoxicity in the dark. However, light-independent effects of Hyp have emerged. Contrary to the acclaimed Hyp minimal dark cytotoxicity and preferential accumulation in tumor cells, it was recently been shown that non-malignant and malignant cells uptake Hyp at a similar level. In addition, Hyp has displayed light-independent toxicity and anti-proliferative effects in a wide range of concentrations. There are multiple mechanisms underlying Hyp light-independent effects, and we are still missing many details about them. In this paper, we focus on Hyp light-independent effects at several sub-cellular levels—protein distribution and synthesis, organelle ultrastructure and function, and Hyp light-independent effects regarding reactive oxygen species (ROS). We summarize work from our laboratories and that of others to reveal an intricate network of the Hyp light-independent effects. We propose a schematic model of pro- and anti-apoptotic protein dynamics between cell organelles due to Hyp presence without illumination. Based on our model, Hyp can be explored as an adjuvant therapeutic drug in combination with chemo- or radiation cancer therapy.

Anti- and Pro-apoptotic Bcl2 Proteins Distribution and Metabolic Profile in Human Coronary Aorta Endothelial Cells Before and After HypPDT

Understanding apoptosis regulatory mechanisms in endothelial cells (ECs) has great importance for the development of novel therapy strategies for cancer and cardiovascular pathologies. An oxidative stress with the generation of reactive oxygen species (ROS) is a common mechanism causing ECs' dysfunction and apoptosis. The generation of ROS can be triggered by various stimuli including photodynamic therapy (PDT). In most PDT treatments, photosensitizer (PS) is administered systemically, and thus, possibility of high exposure to PS in the ECs remains high. PS accumulation in ECs may be clinically relevant even without PDT, if PS molecules affect the pro-apoptotic cascade without illumination. In the present work, we focused on Hypericin (Hyp) and HypPDT effects on the cell viability, oxidative stress, and the distribution of Bcl2 family members in human coronary artery endothelial (HCAEC) cells. Our findings show that the presence of Hyp itself has an effect on cell viability, oxidative stress, and the distribution of Bcl2 family members, without affecting the mitochondria function. In contrast, HypPDT resulted in mitochondria dysfunction, further increase of oxidative stress and effect on the distribution of Bcl2 family members, and in primarily necrotic type of death in HCAEC cells.

Deeper insights into the drug defense of glioma cells against hydrophobic molecules

By means of fluorescence microscopy the intracellular distribution of fluorescent drugs with different hydrophobicity (quinizarin, emodin and hypericin) was studied. Selective photoactivation of these drugs in precisely defined position (nuclear envelope) allowed moderately hydrophobic emodin enter the nucleus. Highly hydrophobic hypericin was predominantly kept in the membranes with no fluorescence observed in the nucleus. The redistribution of quinizarin, emodin and hypericin between lipids, proteins and DNA was studied in solutions and cells. Based on these results was proposed theoretical model of hydrophobic drugs' nuclear internalization after photo-activation. Molecular docking models showed that hypericin has the strongest affinity to P-glycoprotein involved in the cell detoxification. Presence of 10 μM quinizarin, emodin or hypericin increased P-glycoprotein function in U87 MG cells. Moreover, emodin pretreatment allowed quinizarin nuclear internalization without photo-activation, which was not the case for hypericin. The synergy of such pretreatment and photo-activation should lessen the drug doses with simultaneous increase of drug efficacy triggering cell apoptosis/necrosis.

Effect of PKCα expression on Bcl-2 phosphorylation and cell death by hypericin

In order to explain the contribution of the protein kinase Cα (PKCα) in apoptosis induced by photo-activation of hypericin (Hyp), a small interfering RNA was used for post-transcriptional silencing of pkcα gene expression. We have evaluated the influence of Hyp photo-activation on cell death in non-transfected and transfected (PKCα(-)) human glioma cells (U-87 MG). No significant differences were detected in cell survival between non-transfected and transfected PKCα(-) cells. However, the type of cell death was notably affected by silencing the pkcα gene. Photo-activation of Hyp strongly induced apoptosis in non-transfected cells, but the level of necrotic cells in transfected PKCα(-) cells increased significantly. The differences in cell death after Hyp photo-activation are demonstrated by changes in: (i) reactive oxygen species production, (ii) Bcl-2 phosphorylation on Ser70 (pBcl-2(Ser70)), (iii) cellular distributions of pBcl-2(Ser70) and (iv) cellular distribution of endogenous anti-oxidant glutathione and its co-localization with mitochondria. In summary, we suggest that post-transcriptional silencing of the pkcα gene and the related decrease of PKCα level considerably affects the anti-apoptotic function and the anti-oxidant function of Bcl-2. This implies that PKCα, as Bcl-2 kinase, indirectly protects U-87 MG cells against oxidative stress and subsequent cell death.

Differential susceptibility of primary cultured human skin cells to hypericin PDT in an in vitro model

Skin cancer is the most common cancer worldwide, and its incidence rate in South Africa is increasing. Photodynamic therapy (PDT) has been shown to be an effective treatment modality, through topical administration, for treatment of non-melanoma skin cancers. Our group investigates hypericin-induced PDT (HYP-PDT) for the treatment of both non-melanoma and melanoma skin cancers. However, a prerequisite for effective cancer treatments is efficient and selective targeting of the tumoral cells with minimal collateral damage to the surrounding normal cells, as it is well established that cancer therapies have bystander effects on normal cells in the body, often causing undesirable side effects. The aim of this study was to investigate the cellular and molecular effects of HYP-PDT on normal primary human keratinocytes (Kc), melanocytes (Mc) and fibroblasts (Fb) in an in vitro tissue culture model which represented both the epidermal and dermal cellular compartments of human skin. Cell viability analysis revealed a differential cytotoxic response to a range of HYP-PDT doses in all the human skin cell types, showing that Fb (LD50=1.75μM) were the most susceptible to HYP-PDT, followed by Mc (LD50=3.5μM) and Kc (LD50>4μM HYP-PDT) These results correlated with the morphological analysis which displayed distinct morphological changes in Fb and Mc, 24h post treatment with non-lethal (1μM) and lethal (3μM) doses of HYP-PDT, but the highest HYP-PDT doses had no effect on Kc morphology. Fluorescent microscopy displayed cytoplasmic localization of HYP in all the 3 skin cell types and additionally, HYP was excluded from the nuclei in all the cell types. Intracellular ROS levels measured in Fb at 3μM HYP-PDT, displayed a significant 3.8 fold (p<0.05) increase in ROS, but no significant difference in ROS levels occurred in Mc or Kc. Furthermore, 64% (p<0.005) early apoptotic Fb and 20% (p<0.05) early apoptotic Mc were evident; using fluorescence activated cell sorting (FACS), 24h post 3μM HYP-PDT. These results depict a differential response to HYP-PDT by different human skin cells thus highlighting the efficacy and indeed, the potential bystander effect of if administered in vivo. This study contributes toward our knowledge of the cellular response of the epidermis to photodynamic therapies and will possibly enhance the efficacy of future photobiological treatments.

Photoactivation of hypericin decreases the viability of RINm5F insulinoma cells through reduction in JNK/ERK phosphorylation and elevation of caspase-9/caspase-3 cleavage and Bax-to-Bcl-2 ratio

Insulinomas cause neuroglycopenic symptoms, permanent neurological damage and even death. Current available therapies cannot satisfactorily treat malignant insulinomas and some benign insulinomas. The promising phototherapeutic results and harmless side effects of hypericin in some cancer treatments prompted us to explore possible anti-growth activity of photoactivated hypericin against RINm5F insulinoma cells and underlying mechanisms. We now show that detectable and maximal internalization of hypericin in RINm5F insulinoma cells occurred in 20 and 60 min respectively. Hypericin was considerably associated with the plasma membrane, appreciably localized in the sub-plasma membrane region and substantially accumulated in the cytoplasm. Photoactivated hypericin decreased the viability of RINm5F insulinoma cells due to its anti-proliferative and apoptotic actions. Photoactivation of hypericin inhibited cell proliferation reflected by decreased expression of the proliferation marker Ki-67 and cell-cycle arrest in the G₀/G₁-phase. The anti-proliferative effect resulted from down-regulation of phosphorylation of c-Jun N-terminal kinase (JNK) and extracellular-signal-regulated kinase (ERK). Photoactivated hypericin triggered apoptosis through activation of caspase-3 and caspase-9 and elevation of the Bax-to B-cell lymphoma 2 (Bcl-2) ratio. The findings lay a solid foundation for implementation of hypericin-mediated photodynamic therapy in treatment of insulinomas.

Photoexcited hypericin exerts strong antigrowth activity in RINm5F insulinoma cells via inhibition of cell proliferation by reducing JNK/ERK phosphorylation and stimulation of apoptosis by elevating caspase-9/caspase-3 cleavage and Bax-to-Bcl-2 ratio.

The efficacy and mechanism of apoptosis induction by hypericin-mediated sonodynamic therapy in THP-1 macrophages

Purpose

To investigate the sonoactivity of hypericin (HY), together with its sonodynamic effect on THP-1 macrophages and the underlying mechanism.

Materials and methods

CCK-8 was used to examine cell viability. Confocal laser scanning microscopy was performed to assess the localization of HY in cells, reactive oxygen species (ROS) generation, and opening of the mitochondrial permeability transition pore (mPTP) after different treatments. Apoptosis was analyzed using Hoechst–propidium iodide and transmission electron microscopy. Mitochondrial membrane potential (ΔΨm) collapse was detected via fluorescence microscopy. Lipoprotein oxidation was determined in malondialdehyde (MDA) assays. Western blotting was conducted to determine the translocation of BAX and cytochrome C and the expression of apoptosis-related proteins.

Results

HY was sublocalized among the nuclei and the mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosome in the cytosol of THP-1 macrophages. Under low-intensity ultrasound irradiation, HY significantly decreased cell viability and induced apoptosis. Furthermore, greater ROS generation, higher MDA levels, and greater ΔΨm loss were observed in the sonodynamic therapy (SDT) group. Both ROS generation and MDA levels were significantly reduced by the ROS scavenger N-acetyl cysteine (NAC) and the singlet oxygen scavenger sodium azide. Most of the loss of ΔΨm was inhibited by pretreatment with NAC, sodium azide, and the mPTP inhibitor cyclosporin A (CsA). mPTP opening was induced upon SDT but was reduced by pretreatment with bongkrekic acid, 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid disodium, CsA, and NAC. Western blot analyses revealed translocation of BAX and cytochrome C, downregulated expression of Bcl-2, and upregulated expression of cleaved caspase-9, cleaved caspase-3, and cleaved poly(ADP-ribose) polymerase in the SDT group, which were reversed by NAC.

Conclusion

HY mediated SDT-induced apoptosis in THP-1 macrophages via ROS generation. Then, the proapoptotic factor BAX translocated from the cytosol to the mitochondria, increasing the ratio of BAX/Bcl-2, and the mPTP opened to release cytochrome C. This study demonstrated the great potential of HY-mediated SDT for treating atherosclerosis.

St John's Wort (Hypericum perforatum L.) photomedicine: hypericin-photodynamic therapy induces metastatic melanoma cell death

Hypericin, an extract from St John's Wort (Hypericum perforatum L.), is a promising photosensitizer in the context of clinical photodynamic therapy due to its excellent photosensitizing properties and tumoritropic characteristics. Hypericin-PDT induced cytotoxicity elicits tumor cell death by various mechanisms including apoptosis, necrosis and autophagy-related cell death. However, limited reports on the efficacy of this photomedicine for the treatment of melanoma have been published. Melanoma is a highly aggressive tumor due to its metastasizing potential and resistance to conventional cancer therapies. The aim of this study was to investigate the response mechanisms of melanoma cells to hypericin-PDT in an in vitro tissue culture model. Hypericin was taken up by all melanoma cells and partially co-localized to the endoplasmic reticulum, mitochondria, lysosomes and melanosomes, but not the nucleus. Light activation of hypericin induced a rapid, extensive modification of the tubular mitochondrial network into a beaded appearance, loss of structural details of the endoplasmic reticulum and concomitant loss of hypericin co-localization. Surprisingly the opposite was found for lysosomal-related organelles, suggesting that the melanoma cells may be using these intracellular organelles for hypericin-PDT resistance. In line with this speculation we found an increase in cellular granularity, suggesting an increase in pigmentation levels in response to hypericin-PDT. Pigmentation in melanoma is related to a melanocyte-specific organelle, the melanosome, which has recently been implicated in drug trapping, chemotherapy and hypericin-PDT resistance. However, hypericin-PDT was effective in killing both unpigmented (A375 and 501mel) and pigmented (UCT Mel-1) melanoma cells by specific mechanisms involving the externalization of phosphatidylserines, cell shrinkage and loss of cell membrane integrity. In addition, this treatment resulted in extrinsic (A375) and intrinsic (UCT Mel-1) caspase-dependent apoptotic modes of cell death, as well as a caspase-independent apoptotic mode that did not involve apoptosis-inducing factor (501 mel). Further research is needed to shed more light on these mechanisms.

Experimental use of photodynamic therapy in high grade gliomas: a review focused on 5-aminolevulinic acid

Photodynamic therapy (PDT) consists of a laser light exposure of tumor cells photosensitized by general or local administration of a pharmacological agent. Nowadays, PDT is a clinically established modality for treatment of many cancers. 5-Aminolevulinic acid (ALA) induced protoporphyrin IX (PpIX) has proven its rational in fluoro-guided resection of malignant gliomas due to a selective tumor uptake and minimal skin sensitization. Moreover, the relatively specific accumulation of photosensitizing PPIX within the tumor cells has gained interest in the PDT of malignant gliomas. Several experimental and clinical studies have then established ALA-PDT as a valuable adjuvant therapy in the management of malignant gliomas. However, the procedure still requires optimizations in the fields of tissue oxygenation status, photosensitizer concentration or scheme of laser light illumination. In this extensive review, we focused on the methods and results of ALA-PDT for treating malignant gliomas in experimental conditions. The biological mechanisms, the effects on tumor and normal brain tissue, and finally the critical issues to optimize the efficacy of ALA-PDT were discussed.

Proof-of-principle for simple microshelter-assisted buffer exchange in laser tweezers: interaction of hypericin with single cells

Microshelters (i.e. thin dead-end side-arms of fluid channels) are used to aid buffer exchange in optical tweezers experiments. The basic idea is to transfer trapped objects into microshelters during the buffer exchange process. Particles "hidden" in microshelters become insensitive to extreme flow conditions in the main fluid channel, which minimizes the requirements for the applied flow system. The construction scheme of a simple microshelter system is described. The concept has been tested by fluorescence measurements on hypericin interaction with trapped yeast cells in different environments.

Secondary plant products causing photosensitization in grazing herbivores: their structure, activity and regulation

Photosensitivity in animals is defined as a severe dermatitis that results from a heightened reactivity of skin cells and associated dermal tissues upon their exposure to sunlight, following ingestion or contact with UV reactive secondary plant products. Photosensitivity occurs in animal cells as a reaction that is mediated by a light absorbing molecule, specifically in this case a plant-produced metabolite that is heterocyclic or polyphenolic. In sensitive animals, this reaction is most severe in non-pigmented skin which has the least protection from UV or visible light exposure. Photosensitization in a biological system such as the epidermis is an oxidative or other chemical change in a molecule in response to light-induced excitation of endogenous or exogenously-delivered molecules within the tissue. Photo-oxidation can also occur in the plant itself, resulting in the generation of reactive oxygen species, free radical damage and eventual DNA degradation. Similar cellular changes occur in affected herbivores and are associated with an accumulation of photodynamic molecules in the affected dermal tissues or circulatory system of the herbivore. Recent advances in our ability to identify and detect secondary products at trace levels in the plant and surrounding environment, or in organisms that ingest plants, have provided additional evidence for the role of secondary metabolites in photosensitization of grazing herbivores. This review outlines the role of unique secondary products produced by higher plants in the animal photosensitization process, describes their chemistry and localization in the plant as well as impacts of the environment upon their production, discusses their direct and indirect effects on associated animal systems and presents several examples of well-characterized plant photosensitization in animal systems.

In vitro comparison of hypericin and 5-aminolevulinic acid-derived protoporphyrin IX for photodynamic inactivation of medulloblastoma cells

Background

Hypericin (HYP) is a naturally occurring photosensitizer. Cellular uptake and photodynamic inactivation after incubation with this photosensitizer have neither been examined in medulloblastoma cells in vitro, nor compared with 5-aminolevulinic acid-derived protoporphyrin IX (5-ALA-derived PpIX).

Methods

In 3 medulloblastoma cell lines (D283 Med, Daoy, and D341 Med) the time- and concentration-dependent intracellular accumulation of HYP and 5-ALA-derived PpIX was analyzed by fluorescence microscopy (FM) and FACS. Photocytotoxicity was measured after illumination at 595 nm (HYP) and 635 nm (5-ALA-derived PpIX) in D283 Med cells and compared to U373 MG glioma cells.

Results

All medulloblastoma cell lines exhibited concentration- and time-dependent uptake of HYP. Incubation with HYP up to 10 µM resulted in a rapid increase in fluorescence intensity, which peaked between 2 and 4 hours. 5-ALA-derived PpIX accumulation increased in D283 Med cells by 22% over baseline after 5-ALA incubation up to 1.2 mM. Photocytotoxicity of 5-ALA-derived PpIX was higher in D283 Med medulloblastoma compared to U373MG glioma. The [lethal dose (light dose that is required to reduce cell survival to 50% of control)] of 5-ALA-derived PpIX was 3.8 J/cm² in D283 Med cells versus 5.7 J/cm2 in U373MG glioma cells. Photocytotoxicity of HYP in D283 Med cells was determined at 2.5 µM after an incubation time of 2 h and an illumination wavelength of 595 nm. The value was 0.47 J/cm².

Conclusion

By its 5-fold increase in fluorescence over autofluorescence levels HYP has excellent properties for tumor visualization in medulloblastomas. The high photocytotoxicity of HYP, compared to 5-ALA-derived PpIX, is convincingly demonstrated by its 8- to 13-fold lower . Therefore HYP might be a promising molecule for intraoperative visualization and photodynamic treatment of medulloblastomas.