Hypericin Derivatives Research Articles

Hypericin and its radio iodinated derivatives - A novel combined approach for the treatment of pediatric alveolar rhabdomyosarcoma cells in vitro.

Alveolar rhabdomyosarcoma (RMA) is a highly malignant soft tissue tumor in children with poor prognosis and failure of established therapies in advanced stages. Therefore, novel treatment options are required. Photodynamic therapy (PDT) has been found useful for the treatment of different tumor entities and might represent such a novel treatment option. A major limitation of PDT remains the restriction to superficial tumor cell layers as illumination with light is essential for the generation of reactive oxygen species. Current research focusses on the development of modified Hypericin (HYP)-based photosensitizers, as well as combining PDT and targeted internal radiotherapy with 131I, to generate an additive anti-tumor effect. A standardized protocol for in vitro Hypericin-PDT was established in RMA cells. The anti-tumor properties of this photosensitizer were analyzed on molecular and metabolic levels. Changes in cell morphology were visualized using bright field-, fluorescence- and scanning-electron microscopy. Iodinated Hypericin derivatives with both radioactive and non-radioactive isotopes 131I/127I were employed to establish a targeted radionuclide therapy and investigate the potential of a combined treatment with PDT. In vitro photodynamic treatment with Hypericin showed a strong anti-tumor efficiency with favorable cellular uptake and compromised cancer cells on metabolic and molecular levels. Iodination of the photosensitizer did not impair the photosensitizer´s properties. Targeted radiotherapy with 131I-HYP led to distinct reductions of tumor viability. A simultaneously performed PDT leads to a reduction of cell viability that begins earlier in time. However, an additive enhancement of the cell viability was not observed in the selected dose range. In this in vitro study, we got a first insight of a possible potential of Hypericin for the treatment of pediatric soft tissue sarcoma. By coupling with radioiodine, we developed a novel approach for a combined anti-tumor treatment. The in vitro experiments lay the foundation for further in vivo experiments, which are needed to study the effects of a sequential administration of 131I-HYP and HYP.

Natural compound inducers of immunogenic cell death.

Accumulating evidence shows that the anti-cancer potential of the immune response that can be activated by modulation of the immunogenicity of dying cancer cells. This regulated cell death process is called immunogenic cell death (ICD) and constitutes a new innovating anti-cancer strategy with immune-modulatory potential thanks to the release of damage-associated molecular patterns (DAMPs). Some conventional clinically-used chemotherapeutic drugs, as well as preclinically-investigated compounds of natural origins such as anthracyclines, microtubule-destabilizing agents, cardiac glycosides or hypericin derivatives, possess such an immune-stimulatory function by triggering ICD. Here, we discuss the effects of ICD inducers on the release of DAMPs and the activation of corresponding signaling pathways triggering immune recognition. We will discuss potential strategies allowing to overcome resistance mechanisms associated with this treatment approach as well as co-treatment strategies to overcome the immunosuppressive microenvironment. We will highlight the potential role of metronomic immune modulation as well as targeted delivery of ICD-inducing compounds with nanoparticles or liposomal formulations to improving the immunogenicity of ICD inducers aiming at long-term clinical benefits.

Progress in the Chemistry of Second Generation Hypericin Based Photosensitizers

Its outstanding ability to generate singlet oxygen or reactive oxygen species upon irradiation with light makes hypericin one of the most powerful photosensitizers to be found in Nature. The most important fields of application of hypericin seem presently to be its use as a photosensitizing antiviral agent to destroy virus particles in blood preparations, to sensitize the destruction of superficial tumors, and its use as a diagnostic tool for fluorescence detection of malignant tissue. Despite all of its benefits and its strong photosensitizing ability, the application of hypericin in photodynamic therapy (PDT) suffers from three main disadvantages: cost intensive isolation from natural sources, limited solubility under physiological conditions, and long wavelength absorption maximum outside the optimum wavelength range for a PDT photosensitizer. Thus, over the last years several efforts have been undertaken to synthesize new hypericin derivatives with increased solubility, a bathochromically shifted long wavelength absorption band, enhanced photosensitizing potential, and applicability to a more widespread field (second generation hypericin based photosensitizers). The objective of this review is to discuss the investigations undertaken in the development of second generation hypericin based photosensitizers. The focus will be on the synthesis of such derivatives as well as on their photochemical properties, their advantages, and disadvantages. Several of these novel synthetic hypericin derivatives have already been tested in vitro and/or in vivo. Accordingly, a summary of the corresponding results will be presented. Keywords: Phenanthroperylene Quinones, Photodynamic Therapy, Photosensitizers, Emodin, Photochemistry, Natural Compounds, Semisynthesis Approaches, Cancer, viruses, retroviruses, microorganisms, photodynamic, photosensitizer, hypericism, HIV infection

Fagopyrin and its derivatives in buckwheat (Fagopyrum sp.)

Fagopyrin and its derivatives are dimerized anthraquinone polyphenolic substances from buckwheat. They act as photosensitizers upon excitation with visible light (540–610nm), which causes phototoxic effect after ingestion of large amounts of buckwheat called fagopyrism (1). According to known structures and transformations of hypericin derivatives from St. John's wort and their similarity to fagopyrin, several forms of fagopyrin derivatives have been postulated as pseudofagopyrin and protofagopyrin (2). It was shown that pre-forms of fagopyrin transform to fagopyrin in plant extract under daylight exposure (3).

The Influence of Cholesterol on the Properties and Permeability of Hypericin Derivatives in Lipid Membranes.

The promising photosensitizing properties of hypericin, a natural quinine substituted with hydroxyl and alkyl groups, have led to the proposal that it can be utilized in photodynamic therapy. Neither the detailed mechanism behind the powerful action of hypericin, arising as a result of light excitation, nor the intracellular localization and transportation of the molecule is yet fully understood. The behavior of hypericin derivatives in a pure dipalmitoylphosphatidylcholine (DPPC) lipid membrane has recently been studied theoretically by means of molecular dynamics simulations. Natural membranes however contain many important constituents-cholesterol being one of the most essential-that influence the function and structure of the membrane, and thereby also the behavior of drug molecules therein. In the present study, we investigated hypericin and its brominated derivatives in membranes containing 9 and 25 mol % cholesterol. The results show that the presence of cholesterol in the membrane affects the permeability of the hypericin molecules and does so differently for the various molecules in the two membranes. Hypericin containing one bromine was found to exhibit the lowest free energy profile for the transport process into the lipids, and also the highest permeability coefficients, indicating that this molecule displays the fastest and easiest diffusion in the membranes. All three molecules were found to accumulate most preferably close to the polar headgroup region in both membranes.

Isolation and functional analysis of cDNAs similar to Hyp-1 involved in hypericin biosynthesis from Hypericum erectum

Hypericin, a naphthodianthrone, has been identified as the principal active compound found in St. John’s wort (Hypericum perforatum L.). To generate a gene resource for hypericin and other valuable metabolites, we generated expressed sequence tags (ESTs) from H. erectum. Analyses of the ESTs enabled us to select three cDNAs, HeHyp1, HeHyp2, and HeHyp3, evidencing significant sequence homology to Hyp-1 that were involved in hypericin biosynthesis from H. erectum. The deduced amino acid sequence of HeHyp1 cDNA exhibits 95 % identity with Hyp-1. The HeHyp2 and HeHyp3 polypeptides also exhibit 81.1 % identity with Hyp-1. The transcripts of HeHyp1, HeHyp2, and HeHyp3 were detected in the root, stem, leaf, flower, and callus cells. Study using recombinant protein suggests that Hyp-1, HeHyp2, and HeHyp3 may be involved in the biosynthetic of hypericin or other emodin derivatives.

Cationic Hypericin Derivatives as Novel Agents with Photobactericidal Activity: Synthesis and Photodynamic Inactivation of Propionibacterium acnes

The present communication describes for the first time the synthesis and preliminary testing of two cationic hypericin derivatives. Uncharged hypericin derivatives with omega,omega'-attached C2-linkers leading to a pyridyl or a 4-dimethylaminophenyl residue were prepared and subsequently quaternized by means of iodomethane. Photobactericidal activity was assessed using Propionibacterium acnes. The quaternary N,N,N-trimethyl-anilinium derivative displayed a pronounced photodynamic inactivation of the bacteria at low incubation concentrations (<100 nm) and a short incubation time (1 h) after illumination with yellow light (590 nm, 20 J cm(-2)), whereas the photobactericidal efficacy of the N-methyl-pyridinium derivative was negligible under identical experimental conditions.

In vitro study of the photocytotoxicity of bathochromically-shifted hypericin derivatives

Hypericin has excellent photosensitizing properties and displays favorable tumouritropic characteristics, but at the same time exhibits minimal dark toxicity. As such, the compound is a promising photosensitizer in the context of clinical photodynamic therapy (PDT). The present study was undertaken to investigate whether a newly-synthesized series of hypericin derivatives with a bathochromic shift shows promise for future PDT applications. Potentially these structures offer an advantage over the parent compound by being photo-activated by red light, which penetrates deeper into tumour tissue. Our results show that 3 compounds (a dibenzoxazole, a pyridazinone, and especially a dibenzthiazole derivative of hypericin), designed to exhibit a bathochromic shift in their absorption spectrum, demonstrated an efficient singlet oxygen yield and intracellular uptake, and concomitantly a potent photocytotoxic effect under white-light conditions. These results indicate that it is possible to synthesize bathochromically-shifted compounds based on hypericin chemistry which maintain their PDT potential. However, the data also show that the present derivatives are only poor photosensitizers when used under red-light conditions.

Hypericinoid Pigments In Millericrinids From the Lower Kimmeridgian Of the Holy Cross Mountains (Poland)

Abstract Purple to violet colored millericrinids (Crinoidea) are described from the lower Kimmeridgian of the Malogoszcz quarry, Holy Cross Mountains, Poland. By chemical analysis using high-performance liquid chromatography, ultraviolet/visible spectroscopy, and mass spectrometry, the organic compounds were characterized as a homologous series of hypericinoid pigments ranging from C28H12O8 (fringelite F) to C36H28O8. The results indicate that hypericinoid pigments were more widespread in millericrinids than previously known. The presence of new hypericin derivatives in the fossil crinoids with characteristic alkyl side chains shows that Mesozoic hypericinoid pigments were closely related to recent crinoidal pigments.

Synthesis and in vitro/vivo Evaluation of Iodine-123/124 Labelled Hypericin Derivatives

To evaluate the potential of radioiodine labelled hypericin as a malignant glioma imaging agent, U-251 MG, U-373 MG, C6 glioma and fibroblast were treated with a I-123 labelled hypericin derivative and C6 glioma transplanted nude mouse were injected with a I-124 labelled hypericin derivative for a micro PET imaging. 2- Iodohypericin was prepared as a reference compound. In this paper, we describe the syntheses of 2- iodohypericin and 2-[<TEX>$^{123}I/^{124}I$</TEX>]iodohypericin and the results of a corresponding biological evaluation. In all glioma cell lines, 2-[<TEX>$^{123}I$</TEX>]iodohypericin uptake was increased in a time dependant manner and an accumulation of 2-[<TEX>$^{124}I$</TEX>]iodohypericin was observed in C6 glioma bearing nude mouse. These results suggest that radioiodine labelled hypericin can visualize a PKC overexpressed malignant glioma.

ω,ω′-Appended nucleo-base derivatives of hypericin

ω,ω′-Disubstituted hypericin derivatives with the nucleo-bases thymine, cytosine, and adenine in these positions were prepared starting from tri-O-methyl-ω-bromoemodin. The most promising derivative proved to be that with a thymine moiety. It displayed the best solubility of the three products together with a potency to produce singlet oxygen and/or reactive oxygen species comparable to the parent compound hypericin. In addition, although no specific interaction with DNA or poly(2′-deoxyadenylic acid) could be detected, it proved to be significantly better accumulating in the nucleus of prostatic cancer LNCaP cells than hypericin making it a promising candidate for a second-generation photodynamic hypericin agent.

Synthesis and preliminary biological evaluation of a 99mTc‐labeled hypericin derivative as a necrosis avid imaging agent

AbstractMono‐[123I]iodohypericin and mono‐[123I]iodohypericin monocarboxylic acid are iodine‐123‐labeled hypericin derivatives which have shown great promise in preclinical studies as necrosis avid imaging agents in animal models of infarction. In view of the more attractive properties of a 99mTc‐labeled hypericin derivative, we have synthesized a conjugate of protohypericin monocarboxylic acid with S‐benzoylmercaptoacetyldiglycyl‐diaminopentane in an overall yield of 15%. The conjugate was labeled with technetium‐99m by exchange labeling at pH 10 in a labeling yield of 95% followed by photocyclization to yield 99mTc‐mercaptoacetyldiglycyl‐1,5‐diaminopentylene hypericincarboxamide (99mTc‐13). The negatively charged 99mTc‐13 complex was purified by reversed phase high‐pressure liquid chromatography and the log P7.4 was determined to be 2.36. In normal NMRI mice, the complex showed slow hepatobiliary clearance while plasma clearance was rapid. The tracer was evaluated in rats with reperfused hepatic infarction by ex vivo autoradiography, gamma counting and histochemical techniques. Unlike the radioiodinated hypericin derivatives, the new tracer agent did not show preferential uptake in necrotic tissue on autoradiography and gamma counting techniques. Conjugation of hypericin with a 99mTc‐chelate, resulting in a change in size, charge and lipophilicity, had a profound effect on the necrosis avidity of the tracer agent. The results show that 99mTc‐13 is not suitable for imaging necrosis. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Hypericin Derivatives: Substituent Effects on Radical-anion Formation

The electron-transfer properties of the hypericin derivatives, dibromo-, hexaacetyl-, hexamethyl- and desmethylhypericin, were studied. Cyclovoltammetric measurements revealed that dibromo- and desmethylhypericin have almost the same redox potentials as the parent hypericin. Substitution of the hydroxyl groups by acetoxy leads to less negative E½ values, whereas methoxy substitution induces more negative values. Electron paramagnetic resonance (EPR)/electron nuclear double resonance/general TRIPLE spectroscopy and quantum mechanical calculations were used to establish the structure of the one-electron reduced stages of hypericin derivatives. Proton loss in the bay region, already demonstrated for hypericin, was also found for dibromo- and desmethylhypericin. The spin and charge of the radical ions are predominately confined to the central biphenoquinone moiety of the hypericin skeleton. Generation of the radical ions by in situ electrolysis indicates that the redox potentials of hypericin, dibromo- and desmethylhypericin, containing hydroxyls at the 1, 3, 4, 6, 8 and 13 positions, largely depend on the solvent. With phosphate-buffered saline (pH 7.4)/dimethylsulfoxide (DMSO) as the solvent the EPR spectra of the corresponding radical ions appear at markedly lower potentials than in pure DMSO and N,N′-dimethylformamide. However, this effect is not observable for hexaacetyl- and hexamethylhypericin-lacking hydroxyl groups. In all cases the EPR data and calculations revealed the presence of 7,14 tautomers.

Towards Second Generation Hypericin Based Photosensitizers for Photodynamic Therapy

Its outstanding ability to generate singlet oxygen or reactive oxygen species upon irradiation with light makes hypericin one of the most powerful photosensitizers to be found in nature. The most important fields of application of hypericin seem presently to be its use as a photosensitizing anti-viral agent to destroy virus particles in blood preparations, to sensitize the destruction of superficial tumors, and its use as a diagnostic tool for fluorescence detection of malignant tissue. Despite of all of its benefits and its strong photosensitizing ability, the application of hypericin in photodynamic therapy (PDT) suffers from three main disadvantages: cost expensive isolation, limited solubility under physiological conditions, long wavelength absorption maximum outside the optimum wavelength range for a photosensitizer. Thus, over the last decade several efforts have been undertaken to synthesize new hypericin derivatives with increased solubility, bathochromically shifted long wavelength absorption band, enhanced photosensitizing potential, and applicability in a more widespread field (second generation hypericin based photosensitizers). The objective of this review is to discuss the investigations undertaken in the development of second generation hypericin based photosensitizers. The focus will be on the synthesis aspects of such derivatives as well as on their photochemical properties, their advantages, and disadvantages. Several of these novel synthetic hypericin derivatives have already been tested in vitro and/or in vivo. Accordingly, also a summary of the corresponding results will be presented.

Condensed Emodin Derivatives and Their Applicability for the Synthesis of a Fused Heterocyclic Hypericin Derivative

AbstractInvestigations on the bifunctionalization of emodin at C(6) and C(7) with respect to the synthesis of a new class of fused heterocyclic hypericin derivatives were undertaken. The synthesis of such complex anthraquinone derivatives is possible by applying a Marschalk‐type reaction with emodin‐6‐carbaldehyde as the key step. The newly synthesized pyridazinone‐fused hypericin derivative possesses a satisfying bathochromically shifted absorption maximum making it a promising candidate for further investigations concerning a possible application in photodynamic therapy. Furthermore, the herein described strategy for the bifunctionalization of emodin provides a novel route for the synthesis of anthraquinone derivatives that are difficult to obtain by other methods.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)

First preclinical evaluation of mono-[123I]iodohypericin as a necrosis-avid tracer agent

We have labelled hypericin, a polyphenolic polycyclic quinone found in St. John's wort (Hypericum perforatum), with( 123)I and evaluated mono-[(123)I]iodohypericin (MIH) as a potential necrosis-avid diagnostic tracer agent. MIH was prepared by an electrophilic radioiodination method. The new tracer agent was evaluated in animal models of liver infarction in the rat and heart infarction in the rabbit using single-photon emission computed tomography (SPECT), triphenyltetrazolium chloride (TTC) histochemical staining, serial sectional autoradiography and microscopy, and radioactivity counting techniques. Using in vivo SPECT imaging, hepatic and cardiac infarctions were persistently visualised as well-defined hot spots over 48 h. Preferential uptake of the tracer agent in necrotic tissue was confirmed by perfect match of images from post-mortem TTC staining, autoradiography (ARX) and histology. Radioactivity concentration in infarcted tissues was over 10 times (liver; 3.51% ID/g in necrotic tissue vs 0.38% ID/g in normal tissue at 60 h p.i.) and over 6 times (myocardium; 0.36% ID/g in necrotic tissue vs 0.054% ID/g in normal tissue; ratios up to 18 for selected parts on ARX images) higher than in normal tissues. The results suggest that hypericin derivatives may serve as powerful necrosis-avid diagnostic agents for assessment of tissue viability.

9,12‐Dibenzothiazolylhypericin and 10,11‐Dibenzothiazolyl‐10,11‐didemethylhypericin: Photochemical Properties of Hypericin Derivatives Depending on the Substitution Site.

AbstractFor Abstract see ChemInform Abstract in Full Text.

An Efficient Route to Emodic Amine and Analogous O‐Methyl Protected Derivatives Starting from Emodin.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Route to Amino Functionalized Hypericin Derivatives and their Chemical and Photochemical Properties Pertaining to Photodynamic Therapy

Syntheses of amino functionalized hypericin derivatives could be achieved starting from the recently prepared emodin derived 1,3,8-trimethoxy-6-amino-9,10-anthraquinone. Our strategies for the preparation of 10,11-didemethyl-10,11-diaminohypericin, 10,11-didemethyl-10,11-di(acetylamino) hypericin, and its hypericinoidic diazepine derivative include synthetical modifications on the levels of the anthraquinone, anthron, and the phenanthroperylenequinone system itself. The chemical as well as photochemical properties of these unique hypericin derivatives, which might constitute new photodynamic therapy agents, are reported.

Effects of halogen substitution on the photochemical properties of hypericin

Hypericin (hyp) displays photodynamic activity under the influence of visible light, which has opened up new possibilities of utilizing hypericin derivatives as potential photodynamic therapy agents. In the current work, the effects of halogen substitution were considered through a detailed computational study of bromine, chlorine, and fluorine substitution on the geometrical structure, and electronic and phototoxic properties of the hypericin molecule by the use of density functional theory, integral equation formalism polarized continuum models, and a time-dependent formalism (TD-DFT) to the study of singlet and triplet excited states. It is concluded that the effect of halogen substitution is primarily an increase of the electron affinities and thereby increased quantum efficiency of superoxide formation of importance in photodynamic therapy.