Photosensitized inhibition of growth factor-regulated protein kinases by hypericin

In vitro screening of anti-viral and virucidal effects against SARS-CoV-2 by Hypericum perforatum and Echinacea

Hypericum perforatum and Echinacea are reported to have antiviral activities against several viral infections. In this study, H. perforatum (St. John's Wort) and Echinacea were tested in vitro using Vero E6 cells for their anti-viral effects against the newly identified Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) through its infectious cycle from 0 to 48 h post infection. The hypericin of H. perforatum and the different parts (roots, seeds, aerial) of two types of Echinacea species (Echinacea purpurea and Echinacea angustifolia) were tested for their anti-viral activities to measure the inhibition of viral load using quantitative real-time polymerase chain reaction (qRT-PCR) on cell culture assay. Interestingly, the H. perforatum-Echinacea mixture (1:1 ratio) of H. perforatum and Echinacea was tested as well on SARS-CoV-2 and showed crucial anti-viral activity competing H. perforatum then Echinacea effects as anti-viral treatment. Therefore, the results H. perforatum and Echinacea species, applied in this study showed significant anti-viral and virucidal effects in the following order of potency: H. perforatum, H. perforatum-Echinacea mixture, and Echinacea on SARS-CoV-2 infectious cycle. Additionally, molecular simulation analysis of the compounds with essential proteins (Mpro and RdRp) of the SARS-CoV-2 revealed the most potent bioactive compounds such as Echinacin, Echinacoside, Cyanin, Cyanidin 3-(6''-alonylglucoside, Quercetin-3-O-glucuronide, Proanthocyanidins, Rutin, Kaempferol-3-O-rutinoside, and Quercetin-3-O-xyloside. Thus, based on the outcome of this study, it is demanding the setup of clinical trial with specific therapeutic protocol.

Hypericin, a potential new BH3 mimetic

Many types of cancer such as prostate cancer, myeloid leukemia, breast cancer, glioblastoma display strong chemo resistance, which is supported by enhanced expression of multiple anti-apoptotic Bcl-2, Bcl-XL and Mcl-1 proteins. The viable anti-cancer strategies are based on developing anti-apoptotic Bcl-2 proteins inhibitors, BH3 mimetics. Our focus in past years has been on the investigating a new potential BH3 mimetic, Hypericin (Hyp). Hyp is a naturally occurring photosensitive compound used in photodynamic therapy and diagnosis. We have demonstrated that Hyp can cause substantial effects in cellular ultrastructure, mitochondria function and metabolism, and distribution of Bcl2 proteins in malignant and non-malignant cells. One of the possible mechanisms of Hyp action could be the direct interactions between Bcl-2 proteins and Hyp. We investigated this assumption by in silico computer modelling and in vitro fluorescent spectroscopy experiments with the small Bcl2 peptide segments designed to correspond to Bcl2 BH3 and BH1 domains. We show here that Hyp interacts with BH3 and BH1 peptides in concentration dependent manner, and shows the stronger interactions than known BH3 mimetics, Gossypol (Goss) and ABT-263. In addition, interactions of Hyp, Goss and ABT263, with whole purified proteins Bcl-2 and Mcl-1 by fluorescence spectroscopy show that Hyp interacts stronger with the Bcl-2 and less with Mcl-1 protein than Goss or ABT-263. This suggest that Hyp is comparable to other BH3 mimetics and could be explore as such. Hyp cytotoxicity was low in human U87 MG glioma, similar to that of ABT263, where Goss exerted sufficient cytotoxicity, suggesting that Hyp acts primarily on Bcl-2, but not on Mcl-1 protein. In combination therapy, low doses of Hyp with Goss effectively decreased U87 MG viability, suggesting a possible synergy effect. Overall, we can conclude that Hyp as BH3 mimetic acts primarily on Bcl-2 protein and can be explored to target cells with Bcl-2 over-expression, or in combination with other BH3 mimetics, that target Mcl-1 or Bcl-XL proteins, in dual therapy.

Hypericum triquetrifolium and H. neurocalycinum as Sources of Antioxidants and Multi-Target Bioactive Compounds: A Comprehensive Characterization Combining In Vitro Bioassays and Integrated NMR and LC-MS Characterization by Using a Multivariate Approach

Hypericum triquetrifolium and H. neurocalycinum were evaluated for their phytochemical content and in vitro bioactivity. NMR analyses were performed on the methanol extract of the aerial parts of H. triquetrifolium to establish the main classes of phytoconstituents. Then, LC-DAD-MSⁿ analyses were performed in order to compare the composition of aerial parts and roots extracts of both Hypericum species, obtained using either methanol or water as solvents. Results, processed using multivariate data analysis, showed a significantly higher phenolic content of methanol extracts compared to water extracts, while minor qualitative differences were observed between the two. Distinctive flavonoid and PAC patterns were observed for H. triquetrifolium and H. neurocalycinum, and specific compounds were exclusively detected in one or the other species. Specifically, the phloroglucinols 7-epiclusianone, hyperfirin and hyperforin were present only in H. neurocalycinum, while hyperforin was detected only in H. triquetrifolium. Extracts were assayed using different in vitro tests to evaluate their antioxidant properties and their inhibitory activity against several enzymes, showing significant antioxidant and metal chelating activities. Furthermore, inhibitory properties against acetylcholinesterase, butyrylcholinesterase and tyrosinase were observed. Multivariate approaches were used to correlate biological data with the phytochemical composition of the different extracts. The results, showing positive correlations between specific chemical constituents and the measured bioactivities, represent preliminary data that could guide future studies aimed at isolating bioactive constituents from H. neurocalycinum and H. triquetrifolium for further pharmacological evaluations.

Antiproliferative Effects of St. John's Wort, Its Derivatives, and Other Hypericum Species in Hematologic Malignancies

Hypericum is a widely present plant, and extracts of its leaves, flowers, and aerial elements have been employed for many years as therapeutic cures for depression, skin wounds, and respiratory and inflammatory disorders. Hypericum also displays an ample variety of other biological actions, such as hypotensive, analgesic, anti-infective, anti-oxidant, and spasmolytic abilities. However, recent investigations highlighted that this species could be advantageous for the cure of other pathological situations, such as trigeminal neuralgia, as well as in the treatment of cancer. This review focuses on the in vitro and in vivo antitumor effects of St. John’s Wort (Hypericum perforatum), its derivatives, and other Hypericum species in hematologic malignancies. Hypericum induces apoptosis in both myeloid and lymphoid cells. Other Hypericum targets include matrix metalloproteinase-2, vascular endothelial growth factor, and matrix metalloproteinase-9, which are mediators of cell migration and angiogenesis. Hypericum also downregulates the expression of proteins that are involved in the resistance of leukemia cells to chemotherapeutic agents. Finally, Hypericum and its derivatives appear to have photodynamic effects and are candidates for applications in tumor photodynamic therapy. Although the in vitro studies appear promising, controlled in vivo studies are necessary before we can hypothesize the introduction of Hypericum and its derivatives into clinical practice for the treatment of hematologic malignancies.

In vitro study of disodium cromoglicate as a novel effective hydrotrope solvent for hypericin utilisation in photodynamic therapy

Hypericin (HY) is a naphthodianthrone that naturally occurs in Hypericum perforatum L. It is a promising photosensitiser used in photodynamic therapy for and diagnosis of oncological diseases. However, its hydrophobic character is an obstacle that has prevented its efficient use. The commonly used solvent, dimethyl sulfoxide (DMSO), is a controversial constituent of HY formulations and its use has been rejected by many researchers studying HY both in vitro and in vivo. In this study, we propose the utilisation of hydrotropy to solubilise HY in an aqueous environment. Cromolyn (DSCG) is a non-toxic, well-tolerated, antiallergic drug that has been employed in clinical practice since 1970, and in aqueous solution it acts as a hydrotrope. At a molecular ratio of 1:12,000 HY to DSCG, the compound is able to solubilise HY in aqueous environment. In an HT-29 cell suspension, DSCG (1.8 mmol L-1) considerably enhances the interaction between HY (150 nmol L-1) and HT-29 cells, which leads to an HY fluorescence emission increase with a half-time approximately 2 min compared to 29 min for samples that lack DSCG. Studies using HT-29 adenocarcinoma cells showed that DSCG at a given concentration significantly improved accumulation of HY within cells compared to DMSO (p < 0.05) despite the relative resistance of the HT-29 cell line to HY-PDT. Though no significant difference between total reactive oxygen species production was observed for photoactivated HY dissolved in DMSO and DSCG, significant singlet oxygen generation by photoactivated HY dissolved in a DSCG-containing water solution at the studied molecular ratio was confirmed. We also clarified that DSCG does not act as a scavenger of ABTS and galvinoxyl free radicals. The results from an MTT assay showed that DSCG also significantly enhanced the cytotoxicity of photoactivated HY compared to DMSO (p < 0.05). This study has demonstrated the ability of DSCG to act as a solvent of HY and enhance the effectiveness of HY-PDT compared to the commonly used organic solvent, DMSO.

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.

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.

Targeting the hallmarks of cancer with therapy-induced endoplasmic reticulum (ER) stress

The endoplasmic reticulum (ER) is at the center of a number of vital cellular processes such as cell growth, death, and differentiation, crosstalk with immune or stromal cells, and maintenance of proteostasis or homeostasis, and ER functions have implications for various pathologies including cancer. Recently, a number of major hallmarks of cancer have been delineated that are expected to facilitate the development of anticancer therapies. However, therapeutic induction of ER stress as a strategy to broadly target multiple hallmarks of cancer has been seldom discussed despite the fact that several primary or secondary ER stress-inducing therapies have been found to exhibit positive clinical activity in cancer patients. In the present review we provide a brief historical overview of the major discoveries and milestones in the field of ER stress biology with important implications for anticancer therapy. Furthermore, we comprehensively discuss possible strategies enabling the targeting of multiple hallmarks of cancer with therapy-induced ER stress.

Down-regulation of Bcl-2 and Akt induced by combination of photoactivated hypericin and genistein in human breast cancer cells

Presented experiment considers combination of genistein and photodynamic therapy with hypericin with a view to achieve higher therapeutic outcome in human breast adenocarcinoma cell lines MCF-7 and MDA-MB-231, both identified in our conditions as photodynamic therapy resistant. Since genistein is known to suppress Bcl-2 expression, we predicted that photodynamic therapy with hypericin might benefit from mutual therapeutic combination. In line with our expectations, combined treatment led to down-regulation of Bcl-2 and up-regulation of Bax in both cell lines as well as to suppression of Akt and Erk1/2 phosphorylation induced by photoactivated hypericin in MCF-7 cells. Although Akt and Erk1/2 phosphorylation was not stimulated by photodynamic therapy with hypericin in MDA-MB-231 cells, it was effectively suppressed in combination. Variations in cell death signaling favoring apoptosis were indeed accompanied by cell cycle arrest in G(2)/M-phase, activation of caspase-7, PARP cleavage and increased occurrence of cells with apoptotic morphology of nucleus. All these events corresponded with suppression of proliferation and significantly lowered clonogenic ability of treated cells. In conclusion, our results indicate that pre-treatment with tyrosine kinase inhibitor genistein may significantly improve the effectiveness of photodynamic therapy with hypericin in MCF-7 and MDA-MB-231 breast cancer cells.

Interactive transport, subcellular relocation and enhanced phototoxicity of hypericin encapsulated in guanidinylated liposomes via molecular recognition

Hypericin (HYP), a photocytotoxic phenanthroperylenquinone was encapsulated in liposomes outfitted with guanidinium-bearing lipids to ensure efficient cell binding through molecular recognition with anionic groups resident on the plasma membrane. The uptake of HYP encapsulated in these liposomes by DU145 human prostate cancer cells, was studied employing fluorescence, versus nonguadinylated liposomes and free HYP. The subcellular localization was in all cases studied by confocal microscopy employing specific subcellular organelle probes. The photocytotoxicity of HYP was assessed, 24 h following irradiation with 15 mWcm(-2) light through a GG 495 Schott filter, by a standard tetrazolium to formazan assay (XTT). HYP uptake by DU145 cells was found to be profoundly enhanced by using guanidinylated liposomes. Also the distance of the guanidinium group from the liposomal surface was found to significantly affect HYP loading, subcellular localization and phototoxicity. The two different modes of liposome cell internalization observed, i.e. plasma membrane fusion and endocytosis, were found to greatly affect the phototoxicity of HYP. Molecular recognition was overall appraised as a promising, novel route for photodynamic therapy, profoundly enhancing its efficacy. HYP encapsulated in liposomes-bearing guanidinium groups was more efficiently taken up by cells, leading to enhanced phototoxicity, in contrast to HYP encapsulated in their nonguanidinylated counterparts.

Hypericum in infection: Identification of anti-viral and anti-inflammatory constituents

The Iowa Center for Research on Botanical Dietary Supplements seeks to optimize Echinacea, Hypericum, and Prunella botanical supplements for human-health benefit, emphasizing antiviral, anti-inflammatory and anti-pain activities. This mini-review reports on ongoing studies on Hypericum. The Center uses the genetically diverse, well-documented Hypericum populations collected and maintained at the USDA-ARS North Central Regional Plant Introduction Station (NCRPIS), and the strength of research in synthetic chemistry at Iowa State University to tap natural diversity, to help discover key constituents and interactions among constituents that impact bioactivity and toxicity. The NCRPIS has acquired more than 180 distinct populations of Hypericum, with a focus on Hypericum perforatum L. (Hypericaceae), representing about 13% of currently recognized taxa. Center chemists have developed novel synthetic pathways for key flavones, acyl phloroglucinols, hyperolactones and a tetralin that have been found in Hypericum, and these compounds are used as standards and for bioactivity studies. Both light-dependent and light-independent anti-viral activities have been identified by using bioactivity-guided fractionation of H. perforatum and a HIV-1 infection test system. Our Center has focused on light-independent activity, potentially due to novel chemicals, and polar fractions are undergoing further fractionation. Anti-inflammatory activity has been found to be light-independent, and fractionation of a flavonoid-rich extract revealed four compounds (amentoflavone, chlorogenic acid, pseudohypericin and quercetin) that interacted in the light to inhibit lipopolysaccharide-induced prostaglandin E(2) activity. The Center continues to explore novel populations of H. perforatum and related species to identify constituents and interactions of constituents that contribute to potential health benefits related to infection.

Molecular modeling and experimental evidence for hypericin as a substrate for mitochondrial complex III; mitochondrial photodamage as demonstrated using specific inhibitors

The effect of hypericin photoactivation on mitochondria of human prostate carcinoma cells was studied using a range of mitochondrial inhibitors. Oligomycin significantly enhanced hypericin phototoxicity while atractyloside and antymicin A conferred a significant protection. Use of myxothiazol did not affect cell survival following hypericin photoactivation. These results signify a protective role for F(1)F(0)-ATP synthase running in reverse mode, and a significant photodamage at the quinone-reducing site of mitochondrial complex III. In light of these results, we performed molecular modeling of hypericin binding to complex III. This revealed three binding sites, two of which coincided with the quinol-oxidizing and quinone-reducing centers. Using submitochondrial particles we examined hypericin as a possible substrate of complex III and compared this to its natural substrate, ubiquinone-10. Our results demonstrate uniquely that hypericin is an efficient substrate for complex III, and this activity is inhibited by myxothiazol and antimycin A. We further demonstrated that hypericin photosensitization completely inactivated complex III with ubiquinone as substrate. The ability to enhance HYP potency by inhibition of F(1)F(0)-ATP synthase or depress HYP efficacy by inhibition at the Qi site of complex III provides a potential to increase the therapeutic index of HYP and amplify its PDT action in tumor cells.

Photosensitizing and radiosensitizing effects of hypericin on human renal carcinoma cells in vitro

The renal cell carcinoma (RCC) is extremely resistant to chemotherapy and radiotherapy. The prognosis of patients with metastatic RCC still remains poor, the median survival is less than 12 months. Therefore, new therapeutic options are desirable. The aim of this study was to investigate the photosensitizing and radiosensitizing effects of hypericin on human RCC cells in vitro. First the RCC-derived cell lines A498 and ACHN were incubated with different concentrations of hypericin. In vitro uptake and intracellular distribution of hypericin were confirmed by fluorescence microscopy. Subsequently cells were illuminated and irradiated with a dose of 2-8 Gy, respectively. Finally, metabolic activity, apoptosis and clonogenic survival were investigated. Uptake of hypericin was observed for almost all cells. Hypericin treatment combined with illumination led to a 94-97% decrease in metabolic activity and caused apoptosis in nearly 100% of RCC cells. Hypericin enhanced the radiosensitivity of A498 cells in vitro. The clonogenic survival after irradiation was significantly reduced by hypericin treatment. Taken together, the photosensitizing and radiosensitizing effects of hypericin on human RCC cells we found in this investigation could be of clinical relevance, e.g. for radiotherapy and intraoperative photodynamic therapy, respectively.

Necrosis predominates in the cell death of human colon adenocarcinoma HT-29 cells treated under variable conditions of photodynamic therapy with hypericin

Photodynamic therapy (PDT) represents a new rapidly-developing anticancer approach based on administration of a non- or weakly-toxic photosensitizer and its activation with light of appropriate wavelength. Hypericin, one of the promising photosensitizers, is known to induce apoptosis with high efficiency in various cell line models. However, here we report the prevalence of necrosis accompanied by suppression of caspase-3 activation in colon adenocarcinoma HT-29 cells exposed to an extensive range of PDT doses evoked by variations in two variables -- hypericin concentration and light dose. Necrosis was the principal mode of cell death despite different PDT doses and the absence of anti-apoptotic Bcl-2 expression, even if the same condition induced caspase-3 activity at similar toxicity in HeLa cells. Introduction of Bcl-2 into HT-29 cells invoked caspase-3 activation, changed the Bcl-X(L) expression pattern, increased the apoptosis ratio with no effect on overall toxicity, and supported arrest in the G(2)/M-phase of cell cycle. Since it is known that Bcl-2 suppression in HT-29 is reversible and linked to the over-expression of mutated p53 and also considering our data, we suggest that the mutation in p53 and events linked to this feature may play a role in cell death signalling in HT-29 colon cancer cells.

Characterization of the interaction of hypericin with protein kinase C in U-87 MG human glioma cells

A fluorescence imaging technique was used to monitor intracellular localization of protein kinase C (PKC) in U-87 MG human glioma cells in the presence of hypericin (Hyp) and phorbol 12-myristate-13-acetate (PMA). It is shown that PKC localization, which reflects its activity, is influenced by Hyp and this influence is different from that observed for PMA which acts as PKC activator. Fluorescence binding experiments were used to determine the binding constants of Hyp to several isoforms of PKC. The obtained values of K(d)s (approximately 100 nM) suggest that Hyp binds with high affinity to PKC. Finally, molecular modeling was used to compare structural models of the interaction of C1B domain of PKC (PKC isoforms alpha, delta, gamma) with Hyp and our previously published model of the (C1B domain PKCgamma)/PMA complex. The influence of Hyp on PKC translocation in U-87 MG cells in comparison with PMA, colocalization fluorescence pattern of Hyp and PKC, the higher binding affinity of Hyp to PKC in comparison with known binding constants of phorbol esters, as well as the binding mode of Hyp and PMA to the C1B domain of PKC suggested by molecular modeling, support the idea that Hyp and PMA might competitively bind to the regulatory domain of PKC.

Photodynamic therapy of cerebral glioma – A review Part I – A biological basis

Photodynamic therapy (PDT) has been investigated extensively in the laboratory for decades, and for over 25 years in the clinical environment, establishing it as a useful adjuvant to standard treatments for many cancers. A combination of both photochemical and photobiological processes occur that lead to the eventual selective destruction of the tumour cells. It is a potentially valuable adjuvant therapy that can be used in conjunction with other conventional therapies for the treatment of cerebral glioma. PDT has undergone extensive laboratory studies and clinical trials with a variety of photosensitizers (PS) and tumour models of cerebral glioma. Many environmental and genetically based factors influence the outcome of the PDT response. The biological basis of PDT is discussed with reference to laboratory and preclinical studies.

Mitochondria are a primary target of hypericin phototoxicity: Synergy of intracellular calcium mobilisation in cell killing

Hypericin, a naturally occurring anthraquinone synthesised by hypericum, upon light activation exhibits photodynamic cytotoxicity attributed mainly to the production of reactive oxygen species. This study aimed to elucidate the primary subcellular targets and mechanistic aspects of hypericin photosensitization in human prostate carcinoma cells. Depletion of intracellular glutathione (>85%) via inhibition of gamma-glutamyl-cysteine synthase had no effect on hypericin (5 microM) phototoxicity, thus precluding any direct oxidative involvement of H2O2. There was no change in intracellular SOD activity immediately after hypericin irradiation (1.5-5 J cm(-2)). Evaluation of the lysosomal enzyme hexosaminidase activity showed: (a) 60% cell loss 22 h following irradiation (1.5 J cm(-2)) and (b) a steady rate of lysosomal leakage to the cytosol (25%), at the same time and irradiation. However, lysosomal damage appears to be a slower process compared to the rapid loss of mitochondrial function, as reflected from parallel tetrazolium to formazan assays. The activity of cytosolic and mitochondrial aconitase, an enzyme exquisitely sensitive to oxidation, revealed a dose correlated loss of activity in the mitochondria immediately following hypericin photoactivation. The use of ionomycin, which modulates both internal Ca2+ stores and external Ca2+ transport during hypericin photosensitization, profoundly enhanced photocytotoxicity. Our data supports a direct mitochondrial hypericin phototoxicity that does not involve glutathione/H2O2 homeostasis. Further a potential synergistic treatment combining mitochondrial targeting of photosensitisers and Ca2+ mobilisation was identified.

Anti-angiogenic activities of hypericin in vivo: potential for ophthalmologic applications

Hypericin, a perihydroxylated dianthraquinone is shown here to be a highly potent inhibitor of angiogenesis in several ocular models examined in rat eyes. Extensive angiogenesis induced in the cornea and iris by intra-ocular administration of FGF-2 was effectively inhibited by a minimum of four dose regimens of hypericin (2 mg/kg) administered via the intraperitoneal route at 48 h intervals. Maximal inhibition was achieved when animal treatment with hypericin was initiated 48 h prior to inoculation of FGF-2. The molecular basis for the hypericin-mediated inhibition of angiogenesis in the anterior eye compartment appears to involve several sites in the cascade leading to angiogenesis. We show that the activating phosphorylation of extracellular signal-regulated MAP kinases (ERK1/2) is inhibited by hypericin in human retinal pigment epithelial cells and in EA.hy926 cells, an endothelial hybridoma expressing endothelial cell properties. ERK1/2 activity is required for the transactivation of hypoxia-inducible factor 1 alpha (HIF-1alpha) and in VEGF-induced blood vessel sprouting. MT1-MMP activity in human microvascular endothelial cells was also inhibited. The findings identify hypericin as a potentially useful agent in the treatment of ophthalmic neovascularization pathogeneses.

Toxicity and drug interactions associated with herbal products: ephedra and St. John's Wort

Health care providers are being increasingly confronted with the use of herbal medications by their patients. It is imperative that patients be questioned regarding herbal preparation use and that health care providers become familiar with these agents. Research into the active components and mechanisms of action of various herbals is ongoing [350]. Long-range studies need to be performed to follow patients for efficacy or toxicity in chronic use [351,352]. Adverse reactions to herbal remedies should be reported to the FDA MedWatch at http://www.fda.gov/medwatch. As withany therapeutic agent, risk of use must always be weighed against potential benefits.

Intracellular signaling mechanisms in photodynamic therapy

In photodynamic therapy (PDT) a sensitizer, light and oxygen are used to induce death of tumor cells and in the treatment of certain noncancerous conditions. Cell death in PDT may occur by apoptosis or by necrosis, depending on the sensitizer, on the PDT dose and on the cell genotype. Some sensitizers that have been used in PDT are accumulated in the mitochondria, and this may explain their efficiency in inducing apoptotic cell death, both in vitro and in vivo. In this review we will focus on the events that characterize apoptotic death in PDT and on the intracellular signaling events that are set in motion in photosensitized cells. Activation of phospholipases, changes in ceramide metabolism, a rise in the cytosolic free Ca2+ concentration, stimulation of nitric oxide synthase (NOS), changes in protein phosphorylation and alterations in the activity of transcription factors and on gene expression have all been observed in PDT-treated cells. Although many of these metabolic reactions contribute to the demise process, some of them may antagonize cell death. Understanding the signaling mechanisms in PDT may provide means to modulate the PDT effects at the molecular level and potentiate its antitumor effectiveness.

Antimetastatic activity of the photodynamic agent hypericin in the dark

A unique property of the photodynamic signal transduction inhibitor hypericin (HY) is high functionality in the dark, which has been shown to result in portfolio of anticancer activities both in vitro and in vivo. Here we show that treatment with HY significantly reduces growth rate of metastases in 2 murine models: breast adenocarcinoma (DA3) and squamous cell carcinoma (SQ2). Focus on metastases was achieved by resection of primary tumors at stages in which micrometastases exist in lungs. Long-term animal survival in DA3 tumor-excised groups increased from 15.6% in controls to 34.5% following supplementary treatment with HY. In mice bearing SQ2 tumor metastases, therapy with HY increased animal survival from 17.7% in controls to 46.1%. Using Laser-induced fluorescence and multipixel spectral image analyses, we demonstrate that HY has a high tendency to accumulate in primary and metastatic tumors; HY content in lungs bearing metastases was approximately 2-fold higher than in the lungs of healthy animals. The tendency of HY to preferentially concentrate in lung metastases, combined with its potent antiproliferative activities, may render HY as a useful supplementary modality in the treatment of metastatic cancer irrespective of photoactivation.

Photodynamic treatment and H2O2-induced oxidative stress result in different patterns of cellular protein oxidation

Photodynamic treatment (PDT) is an emerging therapeutic procedure for the management of cancer, based on the use of photosensitizers, compounds that generate highly reactive oxygen species (ROS) on irradiation with visible light. The ROS generated may oxidize a variety of biomolecules within the cell, loaded with a photosensitizer. The high reactivity of these ROS restricts their radius of action to 5-20 nm from the site of their generation. We studied oxidation of intracellular proteins during PDT using the ROS-sensitive probe acetyl-tyramine-fluorescein (acetylTyr-Fluo). This probe labels cellular proteins, which become oxidized at tyrosine residues under the conditions of oxidative stress in a reaction similar to dityrosine formation. The fluorescein-labeled proteins can be visualized after gel electrophoresis and subsequent Western blotting using the antibody against fluorescein. We found that PDT of rat or human fibroblasts, loaded with the photosensitizer Hypocrellin A, resulted in labeling of a set of intracellular proteins that was different from that observed on treatment of the cells with H2O2. This difference in labeling patterns was confirmed by 2D electrophoresis, showing that a limited, yet distinctly different, set of proteins is oxidized under either condition of oxidative stress. By matching the Western blot with the silver-stained protein map, we infer that alpha-tubulin and beta-tubulin are targets of PDT-induced protein oxidation. H2O2 treatment resulted in labeling of endoplasmic reticulum proteins. Under conditions in which the extent of protein oxidation was comparable, PDT caused massive apoptosis, whereas H2O2 treatment had no effect on cell survival. This suggests that the oxidative stress generated by PDT with Hypocrellin A activates apoptotic pathways, which are insensitive to H2O2 treatment. We hypothesize that the pattern of protein oxidation observed with Hypocrellin A reflects the intracellular localization of the photosensitizer. The application of acetylTyr-Fluo may be useful for characterizing protein targets of oxidation by PDT with various photosensitizers.

In-vivo and in-vitro anti-inflammatory effect of Echinacea purpurea and Hypericum perforatum

Echinacea purpurea (L.) Moench and Hypericum perforatum (L.) were evaluated for their anti-inflammatory activity against carrageenan-induced paw oedema in mice. Each drug was administered orally to mice at 30 and 100 mg kg(-1), twice daily. Only the higher dose significantly inhibited, time dependently, the formation of oedema, evaluated as area under the curve (echinacea P < 0.01; hypericum P < 0.05). Western blot analysis showed that in-vivo treatment with these extracts could modulate lipopolysaccharide (LPS) and interferon-gamma induced cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expression in peritoneal macrophages. In particular, treatment with 100 mg kg(-1) hypericum inhibited both iNOS and COX-2 expression, whereas treatment with 100 mg kg(-1) echinacea down-regulated only COX-2 expression. The present study suggests that the anti-inflammatory effect of these extracts could be in part related to their modulation of COX-2 expression.

Hypericin in cancer treatment: more light on the way

Photodynamic therapy (PDT) has been described as a promising new modality for the treatment of cancer. PDT involves the combination of a photosensitizing agent (photosensitizer), which is preferentially taken up and retained by tumor cells, and visible light of a wavelength matching the absorption spectrum of the drug. Each of these factors is harmless by itself, but when combined they ultimately produce, in the presence of oxygen, cytotoxic products that cause irreversible cellular damage and tumor destruction. Hypericin, a powerful naturally occurring photosensitizer, is found in Hypericum perforatum plants, commonly known as St. John's wort. In recent years increased interest in hypericin as a potential clinical anticancer agent has arisen since several studies established its powerful in vivo and in vitro antineoplastic activity upon irradiation. Investigations of the molecular mechanisms underlying hypericin photocytotoxicity in cancer cells have revealed that this photosensitizer can induce both apoptosis and necrosis in a concentration and light dose-dependent fashion. Moreover, PDT with hypericin results in the activation of multiple pathways that can either promote or counteract the cell death program. This review focuses on the more recent advances in the use of hypericin as a photodynamic agent and discusses the current knowledge on the signaling pathways underlying its photocytotoxic action.

St John's wort (Hypericum perforatum L.): a review of its chemistry, pharmacology and clinical properties

The chemical composition of St. John's wort has been well-studied. Documented pharmacological activities, including antidepressant, antiviral, and antibacterial effects, provide supporting evidence for several of the traditional uses stated for St John's wort. Many pharmacological activities appear to be attributable to hypericin and to the flavonoid constituents; hypericin is also reported to be responsible for the photosensitive reactions that have been documented for St. John's wort. With regard to the antidepressant effects of St John's wort, hyperforin, rather than hypericin as originally thought, has emerged as one of the major constituents responsible for antidepressant activity. Further research is required to determine which other constituents contribute to the antidepressant effect. Evidence from randomised controlled trials has confirmed the efficacy of St John's wort extracts over placebo in the treatment of mild-to-moderately severe depression. Other randomised controlled studies have provided some evidence that St John's wort extracts are as effective as some standard antidepressants in mild-to-moderate depression. There is still a need for further trials to assess the efficacy of St John's wort extracts, compared with that of standard antidepressants, particularly newer antidepressant agents, such as the selective serotonin reuptake inhibitors (recent comparative studies with fluoxetine and sertraline have been conducted). Also, there is a need for further studies in well-defined groups of patients, in different types of depression, and conducted over longer periods in order to determine long-term safety. St John's wort does appear to have a more favourable short-term safety profile than do standard antidepressants, a factor that is likely to be important in patients continuing to take medication. Concerns have been raised over interactions between St John's wort and certain prescribed medicines (including warfarin, ciclosporin, theophylline, digoxin, HIV protease inhibitors, anticonvulsants, selective serotonin reuptake inhibitors, triptans, oral contraceptives); advice is that patients taking these medicines should stop taking St John's wort, generally after seeking professional advice as dose adjustment of conventional treatment may be necessary.

Tectorigenin, an isoflavone of Pueraria thunbergiana Benth., induces differentiation and apoptosis in human promyelocytic leukemia HL-60 cells

Cytotoxic effects of six isoflavonoids, tectorigenin, glycitein, tectoridin, glycitin, 6''-O-xylosyltectoridin, and 6''-O-xylosylglycitin isolated from the flower of Pueraria thunbergiana Benth. together with genistein, a known differentiation and apoptosis inducer, were examined. Among these isoflavonoids, tectorigenin and genistein exhibited cytotoxicity against various human cancer cells; glycitein showed only mild cytotoxicity. These results suggest that the isoflavone structure and 5-hydroxyl group are crucial for the cytotoxic properties and that glycosides are inactive. Moreover, tectorigenin induced differentiation of human promyelocytic leukemia HL-60 cells to granulocytes and monocytes/macrophages, and caused apoptotic changes of DNA in the cells, as did genistein. Tectorigenin also inhibited autophosphorylation of epidermal growth factor (EGF) receptor by EGF and decreased the expression of Bcl-2 protein, with less activity than genistein. From these results, tectorigenin may be a possible therapeutic agent for leukemia.

Anti-cancer activities of hypericin in the dark

The potent photodynamic properties of hypericin (HY) elicit a range of light-dependent virucidal and tumoricidal activities. Yet, a relatively low reduction/oxidation potential endows HY with electron accepting and donating properties enabling it to act as both an oxidizing and a reducing agent. HY can thus compete as an electron acceptor from bioenergized reduction/oxidation reactions generating its excitation energy for biological activities from physiological reduction/oxidation reactions in the absence of light. Our studies show that HY can inhibit the growth of highly metastatic murine breast adenocarcinoma and squamous cell carcinoma tumors in culture. Furthermore, we show that HY can interfere with the growth of these tumors in mice reducing tumor size and prolonging animal survival in complete absence of light. While there is no evidence that HY induces apoptosis in these cells in the dark, 3H-thymidine incorporation into DNA was significantly reduced indicating effects that are apparently cytostatic in nature compared to the cytocidal effects of HY with light.

The structure of hypericin in solution. Searching for hypericin's 1,6 tautomer

Hypericin in organic solvents displays two types of electronic spectra: one type which shows a distinct solvatochromic effect, the stable form, and the other, the unstable form, which lacks this property. The latter type is formed in dry nonprotic solvents (e.g. tetrahydrofuran, EtOAc) and can be converted to the stable form on addition of protic solvents. In order to establish the tautomeric structure of the unstable form we applied conventional nuclear magnetic resonance techniques as well as two-dimensional gradient-enhanced heteronuclear multiple-quantum correlation, gradient-enhanced ROESY and one-dimensional nuclear Overhauser effect difference experiments. All these techniques pointed to the fact that the unstable form has the 7,14-diketo tautomeric structure, like the stable form, and not the 1,6-diketo structure. Electronic spectroscopy indicated that the unstable form has acidic properties and therefore possesses two free OH groups at C3 and C4 at the bay region of the molecule.

Hypericin and photodynamic therapy decreases human pancreatic cancer in vitro and in vivo

BACKGROUND

The treatment of pancreatic cancer has remained dismal despite advances in medical and surgical care. Recent preclinical data have revealed that hypericin, a photochemical dye, is activated by green light and generates toxic radical species in tumors. We hypothesized that interstitial hypericin and laser phototherapy would decrease pancreatic cancer growth.

METHODS

MiaPaCa-2 and PANC-1 cells were grown in tissue culture. In vitro experiments were performed with addition of 10 microg of hypericin/500,000 cancer cells. Cells were incubated with hypericin for 2 h. Cells were then exposed to KTP532 green laser light for 1 min at 0.6 W using a cylindrical diffuser tip. Cell growth was measured by MTT assay 24 h after laser treatment, N = 12. MiaPaCa-2 cells were implanted subcutaneously and orthotopically in pancreas of nude mice. After 5 weeks, both tumors were injected with 100 microg of hypericin followed by insertion of a cylindrical diffuser tip into the tumor center. Mice received 200J KTP laser light at 1.0 W in two sites. Tumors were measured before and 4 weeks after laser treatment.

RESULTS

Both in vitro and in vivo mice data showed a significant decrease in growth of pancreatic cancer. Pancreatic cancer cell growth was suppressed by 66.1 +/- 0.2%, n = 12, P < 0.01, ANOVA. Subcutaneous shoulder tumors were suppressed by 91.2 +/- 2.3%, n = 12, P < 0.001, and orthotopically grown pancreatic tumors were suppressed by 42.2 +/- 8.1%, n = 12, P < 0.05, compared to pretreatment sizes. Data expressed as percentage reduction vs paired controls in the MTT assay and vs pre-photodynamic therapy in mice experiments. Paired Student's t tests were performed vs pretreatment sizes.

CONCLUSION

Both in vitro and in vivo results revealed a significant decrease in pancreatic cancer cell growth. Laser or dye alone had no effect, indicating that intratumor hypericin and laser therapy may prove useful in unresectable pancreatic cancer.

Signaling pathways in cell death and survival after photodynamic therapy

Photodynamic therapy (PDT) is a cytotoxic treatment, which can induce cells to initiate a rescue response, or to undergo cell death, either apoptosis or necrosis. The many signaling pathways involved in these processes are the topic of this review. The subcellular localization of the photosensitizer has been shown to be a key factor in the outcome of PDT. Mitochondrial localized photosensitizers are able to induce apoptosis very rapidly. Lysosomal localized photosensitizers can elicit either a necrotic or an apoptotic response. In the plasma membrane, a target for various photosensitizers, rescue responses, apoptosis and necrosis is initiated. Several protein phosphorylation cascades are involved in the regulation of the response to PDT. Finally, a number of stress-induced proteins play a role in the rescue response after PDT. Notably, the induction of apoptosis by PDT might not be crucial for an optimal outcome. Recent studies indicate that abrogation of the apoptotic pathway does alter the clonogenic survival of the cells after PDT. Further studies, both in vitro and especially in vivo could lead to more efficient combination therapies in which signaling pathways, involved in cell death or rescue, are either up- or downregulated before PDT.

Photocytotoxicity of hypericin in normoxic and hypoxic conditions

The normoxic and hypoxic photocytotoxicity of hypericin has been examined on A431 cells as assessed by the Neutral Red method, using cell-culture flasks made of polystyrene and glass, different hypericin concentrations and light fluences. Using polystyrene flasks, lower hypoxic photoactivities of hypericin than those in normoxic conditions are seen under low fluence. In these conditions the hypoxic photocytotoxic effect can be (partially) rescued by increasing the fluence. However, a completely different outcome is observed when using glass flasks, since most of the hypoxic photocytotoxicity is lost under these conditions. The differences can be explained in terms of efficiency of deoxygenation of the medium present in polystyrene or glass flasks. Polystyrene holds large amounts of oxygen that effuses very slowly. Glass, on the other hand, does not cause this inconvenience. Therefore the type of material of the container used to investigate the oxygen dependency of the photobiological activity of photosensitizers dramatically influences the outcome of the hypoxic experiments. Our results unequivocally prove that the cytotoxic effect induced by photoactivated hypericin is completely oxygen dependent. Hence hypericin does not differ from other phototherapeutics used in photodynamic therapy of cancer, since haematoporphyrin derivative and the second-generation photosensitizers used all seem to depend on the presence of oxygen for their antitumour activity.

Investigation of the absorption of hypericin into the skin of hairless mice

The skin absorption of hypericin was evaluated in hairless mice to develop an optimised hypericin topical formulation that could be used in the clinical study of psoriasis. Hypericin (0.01-1.0%) in Beeler basis, polyethylene glycol ointment, carbopol gel, cetomacrogol cream, petrolatum or emulsifying ointment, with and without skin-absorption enhancers (isopropylidene glycerol and diethylene glycol monoethyl ether), was tested in-vivo on hairless mice skin. Using a skin-stripping technique and the intrinsic fluorescence of hypericin under standardised UV365 irradiation, it was demonstrated that the absorption of hypericin very much depended on the vehicle used. The concentrations of hypericin in the skin were then estimated by HPLC analysis. For this purpose, two vehicles were employed, with which hypericin penetrated the skin of hairless mice well (emulsifying ointment with isopropylidene glycerol) or very poorly (polyethylene glycol ointment). In the case of emulsifying ointment with isopropylidene glycerol (0.05% hypericin), a substantial concentration of hypericin (8.6+/-3.2 microg g(-1)) (mean +/- s.d., n = 5) was found in the skin. With polyethylene glycol ointment, however, only a limited hypericin skin concentration (0.38+/-0-34 microg g(-1), n = 5) was achieved. These results show that emulsifying ointment with polyethylene glycol holds promise as an effective topical vehicle for the treatment of skin diseases, such as psoriasis, with hypericin.

Inhibition of the CD8+ T cell-mediated cytotoxicity reaction by hypericin: potential for treatment of T cell-mediated diseases

The cytotoxicity reaction of murine CD8 T lymphocytes has been found to be strongly inhibited by nanomolar concentrations of hypericin, a lipophilic dianthraquinone with photodynamic properties. Cytotoxic T lymphocyte (CTL)-induced target cell apoptosis, as well as exocytosis of cytolytic granules from these cells, were ablated by hypericin, administered at the onset of the reaction, without affecting CTL viability. The inhibition of cytolysis occurred without the light irradiation which is essential for photosensitization. The findings suggest that the action of hypericin targets the effector CTL; however, apoptosis induced in murine L-cells with recombinant tumor necrosis factor (TNF)-alpha was also prevented by hypericin. Since hypericin is a known inhibitor of protein kinase C, MAP kinase and at least one other tyrosine kinase, this inhibitory activity could play a role in the down-modulation of CTL-induced cytotoxicity. Furthermore, our studies show that the action of hypericin induces rapid dephosphorylation of phospholipids associated with low-density membranes in CTL, but not with membranes of the cytotoxic granules. The ability of hypericin to interfere with cytotoxicity may render it useful in the treatment of T cell-mediated diseases.

Skin photosensitization with topical hypericin in hairless mice

Hypericin, a naturally occurring photosensitizer, exhibits interesting in vitro photobiological activities, which suggest that the compound is a potential antipsoriatic agent. In this study, the possibility of hypericin penetrating the skin in photo-active concentrations has been studied. Hypericin is incorporated in either emulsifying ointment supplemented with solketal (hypericin content: 0.05%) or in polyethylene glycol (PEG) ointment (hypericin content: 0.5%) and applied to the skin of hairless mice for 4 h. After removing excess ointment, the mice are then irradiated with different light doses using a 500 W halogen lamp. As a positive control, intraperitoneally (i.p.) administered hypericin (10 and 40 mg/kg) has also been tested. Erythema, desquamation and erosions are demonstrated in the mice treated with hypericin in emulsifying ointment with solketal using a light dose of at least 4.5 J/cm2. In general, these reactions correlate well with those of i.p. administered hypericin (40 mg/kg), indicating that hypericin incorporated in emulsifying ointment with solketal is well absorbed by the skin of the mice. However, for the i.p. administered hypericin (40 mg/kg), we could not evaluate phototoxic reactions in the group of animals that received a light dose of 108 J/cm2, as they all died 12-24 h after irradiation, indicating extreme photosensitization with systemic hypericin at higher light doses. On the contrary, there is no measurable skin photosensitivity induced by hypericin when incorporated in PEG ointment or when 10 mg/kg hypericin is i.p. administered. Our results show that hypericin incorporated in a suitable vehicle can be delivered to the skin in photo-active concentrations. Using a vehicle such as emulsifying ointment with solketal, it will be possible to explore the photo-activity of hypericin in the treatment of psoriasis and other skin diseases.

Regulation of Na+-K+-2Cl- cotransport by protein phosphorylation in ferret erythrocytes

1. Na+-K+-2Cl- cotransport in ferret erythrocytes was measured as the bumetanide-sensitive uptake of 86Rb. 2. The resting cotransport rate was high but could be increased threefold by treating erythrocytes with calyculin A, a potent inhibitor of serine/threonine phosphatases. Twenty nanomolar was sufficient to maximally and rapidly (within 4 min) stimulate transport. 3. The effects of several kinase inhibitors were tested. High concentrations of K-252a, K-252b, calphostin C and hypericin caused less than 20 % inhibition. Staurosporine (IC50, 0.06 microM) and 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1; IC50, 2.5 microM) were more potent but still only partially (40-50 %) inhibited transport, an effect mimicked by reducing ionized intracellular Mg2+ concentration to submicromolar levels. Genistein may inhibit all transport at a sufficiently high dose (IC50, 0.36 mM) perhaps by directly inhibiting the transporter. 4. Staurosporine, PP1 and the removal of Mg2+ all prevented subsequent stimulation by calyculin A, and all inhibited calyculin-stimulated transport by 20-30 %. The effects of staurosporine, PP1 and Mg2+ removal were not additive. 5. The phosphatase that dephosphorylates the cotransporter is probably Mg2+ (or possibly Ca2+ or Mn2+) sensitive and not the target for calyculin A. The data suggest that this phosphatase is inhibited by phosphorylation, and that it is the regulation of this process which is affected by calyculin A and the kinase inhibitors tested here. Phosphorylation of the phosphatase is probably regulated by members of the Src family of tyrosine kinases.

The effect of hypericin and hypocrellin-A on lipid membranes and membrane potential of 3T3 fibroblasts

Hypericin (HY) and Hypocrellin-A (HA) photosensitization induce rapid depolarization of plasma membrane in 3T3 cells as revealed by confocal microspectrofluorimetry using diO-C5(3) fluorescent probe. HY and HA are also able to rigidify the lipid membrane of DMPC liposomes as indicated by the decrease of pyrene excimer fluorescence used as a marker of the lipid membrane fluidity. We have also observed a nonspecific inhibition of Na+,K+-ATPase activity due to the HY and HA photosensitization. The described effects are concentration- and light dose-dependent and generally more pronounced for HA than for HY. All these observations suggest that the lipid membranes can play an important role in the photosensitization process induced by HY and HA at the cellular level. It can be hypothesized that for HA and HY the secondary mechanism following type I or type II photosensitization process can be the peroxidation of membrane lipids as well, and thus intracellular membranes seem to be one of the most important targets of these photosensitizers.

The activation of the c-Jun N-terminal kinase and p38 mitogen-activated protein kinase signaling pathways protects HeLa cells from apoptosis following photodynamic therapy with hypericin

In this study, we elucidate signaling pathways induced by photodynamic therapy (PDT) with hypericin. We show that PDT rapidly activates JNK1 while irreversibly inhibiting ERK2 in several cancer cell lines. In HeLa cells, sustained PDT-induced JNK1 and p38 mitogen-activated protein kinase (MAPK) activations overlap the activation of a DEVD-directed caspase activity, poly(ADP-ribose) polymerase (PARP) cleavage, and the onset of apoptosis. The caspase inhibitors benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD-fmk) and benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone (zDEVD-fmk) protect cells against apoptosis and inhibit DEVD-specific caspase activity and PARP cleavage without affecting JNK1 and p38 MAPK activations. Conversely, stable overexpression of CrmA, the serpin-like inhibitor of caspase-1 and caspase-8, has no effect on PDT-induced PARP cleavage, apoptosis, or JNK1/p38 activations. Cell transfection with the dominant negative inhibitors of the c-Jun N-terminal kinase (JNK) pathway, SEK-AL and TAM-67, or pretreatment with the p38 MAPK inhibitor PD169316 enhances PDT-induced apoptosis. A similar increase in PDT-induced apoptosis was observed by expression of the dual specificity phosphatase MKP-1. The simultaneous inhibition of both stress kinases by pretreating cells with PD169316 after transfection with either TAM-67 or SEK-AL produces a more pronounced sensitizing effect. Cell pretreatment with the p38 inhibitor PD169316 causes faster kinetics of DEVD-caspase activation and PARP cleavage and strongly oversensitizes the cells to apoptosis following PDT. These observations indicate that the JNK1 and p38 MAPK pathways play an important role in cellular resistance against PDT-induced apoptosis with hypericin.

A photodynamic pathway to apoptosis and necrosis induced by dimethyl tetrahydroxyhelianthrone and hypericin in leukaemic cells: possible relevance to photodynamic therapy

The mechanism of cell death induction by dimethyl tetrahydroxyhelianthrone (DTHe), a new second-generation photodynamic sensitizer, is analysed in human leukaemic cell lines in comparison with the structurally related hypericin. DTHe has a broad range of light spectrum absorption that enables effective utilization of polychromatic light. Photosensitization of HL-60 cells with low doses of DTHe (0.65 microM DTHe and 7.2 J cm(-2) light energy) induced rapid apoptosis of > or =90% of the cells. At doses > or =2 microM, dying cells assumed morphological necrosis with perinucleolar condensation of chromatin in HL-60 and K-562 cell lines. Although nuclear fragmentation that is characteristic to apoptosis was prevented, DNA digestion to oligonucleosomes proceeded unhindered. Such incomplete apoptosis was more prevalent with the related analogue hypericin throughout most doses of photosensitization. Despite hypericin being a stronger photosensitizer, DTHe exhibited advantageous phototoxic properties to tumour cells, initiating apoptosis at concentrations about threefold lower than hypericin. Photosensitization of the cells induced dissociation of the nuclear envelope, releasing lamins into the cytosol. DTHe also differed from hypericin in effects exerted on the nuclear lamina, causing release of an 86-kDa lamin protein into the cytosol that was unique to DTHe. Within the nucleus, nuclear envelope lamin B underwent covalent polymerization, which did not affect apoptotic nuclear fragmentation at low doses of DTHe. At higher doses, polymerization may have been extensive enough to prevent nuclear collapse. Hut-78, CD4+ cells were resistant to the photodynamically activated apoptotic pathway. Beyond the tolerated levels of photodynamic damage, these cells died exclusively via necrosis. Hut-78 cells overexpress Bcl-X(L) as well as a truncated Bcl-X(L)tr isoform that could contribute to the observed resistance to apoptosis.

Photocytotoxic effect of pseudohypericin versus hypericin

Pseudohypericin and hypericin, the major photosensitizing constituents of Hypericum perforatum, are believed to cause hypericism. Since hypericin has been proposed as a photosensitizer for photodynamic cancer therapy, the photocytotoxicity of its congener pseudohypericin has been investigated. The presence of foetal calf serum (FCS) or albumin extensively inhibits the photocytotoxic effect of pseudohypericin against A431 tumour cells, and is associated with a large decrease in cellular uptake of the compound. These results suggest that pseudohypericin, in contrast to hypericin, interacts strongly with constituents of FCS, lowering its interaction with cells. Since pseudohypericin is two to three times more abundant in Hypericum than hypericin and the bioavailabilities of pseudohypericin and hypericin after oral administration are similar, these results suggest that hypericin, and not pseudohypericin, is likely to be the constituent responsible for hypericism. Moreover, the dramatic decrease of photosensitizing activity of pseudohypericin in the presence of serum may restrict its applicability in clinical situations.