==== Front Molecules Molecules molecules Molecules 1420-3049 MDPI 33271809 10.3390/molecules25235666 molecules-25-05666 Review Biophysical Characterization and Anticancer Activities of Photosensitive Phytoanthraquinones Represented by Hypericin and Its Model Compounds Verebová Valéria 1 Beneš Jiří 2 Staničová Jana 12* Lupiáñez José Antonio Academic Editor Pérez-Jiménez Amalia Academic Editor Rufino-Palomares Eva E. Academic Editor 1 Department of Chemistry, Biochemistry and Biophysics, University of Veterinary Medicine & Pharmacy, Komenského 73, 041 81 Košice, Slovakia; valeria.verebova@uvlf.sk 2 Institute of Biophysics and Informatics, First Faculty of Medicine, Charles University, Kateřinská 1, 121 08 Prague, Czech Republic; jiri.benes@lf1.cuni.cz * Correspondence: jana.stanicova@uvlf.sk; Tel.: +421-915-984-613 01 12 2020 12 2020 25 23 566627 10 2020 28 11 2020 © 2020 by the authors.2020Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Photosensitive compounds found in herbs have been reported in recent years as having a variety of interesting medicinal and biological activities. In this review, we focus on photosensitizers such as hypericin and its model compounds emodin, quinizarin, and danthron, which have antiviral, antifungal, antineoplastic, and antitumor effects. They can be utilized as potential agents in photodynamic therapy, especially in photodynamic therapy (PDT) for cancer. We aimed to give a comprehensive summary of the physical and chemical properties of these interesting molecules, emphasizing their mechanism of action in relation to their different interactions with biomacromolecules, specifically with DNA. natural photosensitive compoundsanticancer activityhypericinemodinquinizarindanthroninteractionDNA ==== Body 1. Photodynamic Therapy Photodynamic therapy (PDT) is part of photochemotherapy and requires the presence of a photosensitive substance (drug, PS), oxygen, and a powerful light source in the area of absorption of the PS used. The main requirements for activating the properties of a PS are its selective accumulation in tumor tissue, high intensity of absorption in the visible and near-infrared region of the spectrum, low level of dark toxicity, and absence of side-effects [1,2]. Selective accumulation and retention of PS in tumor tissues rather than in the surrounding healthy tissue lead to selective destruction of the tumor in PDT, while the surrounding healthy tissue remains intact. Such selectivity is one of the biggest advantages of this method, which may be substituted in some cases for chemotherapy, radiotherapy, or surgery in the treatment of cancer. Due to drug excretion [3] and redistribution, the effective therapeutic dose entering tumor cells is only a fraction of the administered PS. Administration of increased amounts of therapeutics is not possible because they have cytotoxic effects, which could cause significant toxicity in healthy cells. It is very important therefore to find alternative approaches, which increase the efficacy of the drug dose in the tumor and decrease the dose in healthy tissue [4]. Higher selectivity of PSs for tumor cells can be achieved by combining them with transport agents, which preferentially interact with tumor cells, ensure the selective accumulation of the drug within the diseased tissue, and deliver the desired therapeutic drug concentration to a targeted site in the patient’s body. Transport systems commonly used for photosensitizers are polymers, liposomes, oil emulsions, certain metals, some proteins, and carbon-based nanoparticles [5,6,7,8,9,10]. Stable and biocompatible transport systems with a long half-life in the blood are ideal. Selective drug delivery to tumor tissue, transport of nanoparticles containing a PS, and a tumor cell with a receptor is the objectives for achieving high selectivity and low drug concentration [11]. Several research groups have confirmed the hypothesis that one possible approach to achieving these goals is to prepare low-density lipoprotein (LDL)-based particles [12,13,14,15,16,17]. 1.1. PDT in Cancer Therapy PDT has been a promising, non-invasive method for the treatment of certain types of cancer for more than 25 years [18,19,20,21,22,23]; in addition, PDT has also been studied in various non-oncological applications; leishmaniasis [24], psoriasis [25,26], age-related macular degeneration [27,28], hyperplasia [27], restenosis [25], and in cardiology [29], urology [30], immunology [31], ophthalmology [28,32], dental medicine [33,34], and dermatology [35,36]. The combination of light and PS also shows promising results in the treatment of bacterial, fungal, parasitic, and viral infections [37,38,39,40]. The basic process in tumor PDT is shown in the diagram in Figure 1. The photosensitizer is usually administered intravenously (systematically) or topically, and the administration of PS has also been studied orally, mostly in patients with extensive damage (not always caused by cancer) [1,41]. PS accumulates in the tumor tissue, which is subsequently irradiated with a light source of suitable wavelength, leading, in the presence of oxygen, to the formation of reactive oxygen species (ROS) and destruction of tissue and whole cells [1,41], while deactivation of important enzymes occurs and changes in the properties of biomacromolecules [44]. After activation of the photoactive substance by light and its interaction with molecular oxygen, singlet oxygen is formed. The singlet oxygen released in this photochemical reaction is highly toxic and can directly cause the death of tumor cells, through apoptosis, necrosis, or autophagy mechanism [45]. The release of singlet oxygen evokes oxidative stress, increases cytotoxicity, and DNA damage in cancer cells, modifies cellular metabolism, alters cancer cell death signaling pathways [46]. It also damages the blood vessels in tumor cells, resulting in indirect cell death through hypoxia (deficiency of oxygen) or aging (cell starvation). Diffuse distance of singlet oxygen obtained from photobleaching experiments has been appointed as 10–20 nm [47]. More recent time-resolved phosphorescence measurements show higher diffuse distance corresponding to 100 nm [48]. An explanation of this discrepancy was given by Hatz et al. [48] considering a fact that singlet oxygen behaves as a selective rather than reactive intermediate upon encountering other molecules in the cell. Tissue damage depends on the depth of light penetration used to activate the PS. Membranes are damaged by cell death, triggering a number of inflammatory and immune processes, which cascade and cause the death of other tumor cells [49]. However, it was found out that singlet oxygen might cause membrane destruction directly. The cell membrane can be the main target of the singlet oxygen reaction for the bacterial membrane [50] and eukaryotic plasma membrane [51]. After surface irradiation PDT, the deeper connective tissues are only slightly damaged, so the patient’s body can begin to restore the structure and flexibility of the damaged cells, and subsequently the tissues [52,53]. 1.2. Physicochemical Mechanism of PDT The photodynamic effect can be induced by two mechanisms called Type I and Type II (Figure 1—Step 4). After photon absorption, the PS molecule goes from the ground state (S0) to the singlet excited state (S1). From this excited state, the PS can be returned to the ground state by energy emission through non-radiative and/or radiant processes (fluorescence). In its excited state, the PS can also spontaneously move from the singlet state S1 to the excited triplet state (T1) by means of the intersystem conversion process. In this state, the transition to the ground state through a phosphorescence process can occur [54]. The type I mechanism involves electron transfer reactions between the PS molecule in the excited states of S1 and T1 and the substrate. This process results in the formation of ionic radicals, which tend to react immediately with oxygen to form a mixture of highly reactive oxygen radicals, such as superoxide radical (·O2), hydrogen peroxide (H2O2), and hydroxyl radical (·OH), which oxidize a wide range of biomacromolecules [2,55]. The type II mechanism is characterized by energy transfer reactions between PS in the excited triplet state T1 and molecular oxygen, which is also in the triplet ground state (T0). These reactions cause the formation of singlet oxygen (1O2), which is able to rapidly oxidize cellular structures such as proteins, lipids, nucleic acids [56,57], and organelles leading to tumor cell death [58,59]. This also means that PDT may be a useful alternative treatment for cancer cells resistant to chemotherapy [60,61]. The reaction mechanism depends on the following conditions. First, the location of the PS is crucial because most of the ROS are highly reactive and cannot move far from the point of origin before disappearing. Second, the relative number of target biomolecules is important [43]. Davies (2003) calculated the percentage of 1O2 responses in leukocytes: protein 68.5%, ascorbate 16.5%, RNA 6.9%, DNA 5.5%, beta-carotene 0.9%, NADH/NADPH 0.69%, tocopherols 0.5%, reduced glutathione 0.4%, lipids 0.2%, and cholesterol 0.1% [62]. This means that the distribution of 1O2 may vary in different cell targets. Both mechanisms can occur simultaneously. Their proportional representation is significantly influenced by the PS, the substrate, the oxygen concentration, and the binding of PS to the substrate. In addition, the type II mechanism appears to be more efficient as it has a higher rate constant than electron transfer reactions (type I mechanism). As a result, energy transfer to other compounds that can compete with oxygen is less important, so type II is more often dominant [58,63]. 1.3. PDT Applications PDT currently occupies an increasingly important place in clinical medicine. Its most promising application is the treatment of small and superficial tumors, e.g., some types of skin, neck, stomach [64], lung [65,66,67], bronchial [68] or oral cancer [69], esophagus [70,71], bladder [71,72], brain [73], prostate and pleura [74] tumors, breast [75] but also skin disease [76], atherosclerosis, and viral diseases therapy [77], including AIDS [78]. The future of PDT lies in efforts to find or synthesize new photosensitizers with properties allowing their greater selectivity for tumor tissues, and to find new approaches for the specific localization of already-known PS in tumor cells. This should contribute to the wider and more effective application of PDT in clinical practice. Targeted PDT has several advantages they are important in participation in the treatment of oncological diseases. Some of them are listed below: high selectivity, negligible side effects, low level of complications during and after treatment, high quality of life for patients, diagnostics and therapy in one step, and lower financial costs [79]. It can be a convenient complementary therapeutic method to classical surgery, chemotherapy, radiotherapy, and independent limited diagnosis. 2. Plant-Derived Photosensitive Substances Photoactive compounds occurring in medicinal plants with potential utilization in PDT have been found to be less toxic than synthetic agents. The reduction of side effects using natural PSs in cancer treatment is another advantage of this therapeutic approach. However, their clinical applications have been limited by several imperfections such as accumulation in tissues, a lack of chemical purity, or low penetration [80]. Muniyandi et al. [81] have published a comprehensive review article about the role of photoactive phytocompounds in PDT. Phototoxic effects, potential applications in the PDT of cancer of the main natural PSs groups (furanocoumarins, thiophenes, alkaloids, curcumins, polyacetylenes, and anthraquinones) have been described [81]. Our paper focuses on the four anthraquinones, of which hypericin is the most promising PS in the PDT of cancer. With regard to the hydrophobicity of studied anthraquinones, which is important for their penetration through membranes, the following types of PSs have been distinguished. Types of Photosensitive Substances by Hydrophobicity PDT either uses chemotherapeutics commonly applied in chemotherapy, which must also be photosensitive, or new PSs are proposed. All photosensitizers (except uroporphyrin and photophrin), which have been proposed as drugs for use in PDT, interact more or less with serum proteins after intravenous administration. From the point of view of PDT, however, the interaction of the drugs with DNA is also quite important, as it is necessary to disrupt and stop the division of tumor cells, and this can be achieved only through their interaction with DNA [62,82]. In some cases, this interaction is not very significant (as these drugs have a greater affinity for proteins), so it is necessary to find a transporter that will help deliver the drug to the cell nucleus, thereby mediating the drug–DNA interaction [83,84]. Success in the treatment of cancer requires sufficiently hydrophobic drugs to cross the lipid membrane. For this reason, the hydrophobicity of drugs plays an important role in their distribution, metabolism, and excretion from the patient´s body. Due to these facts, we distinguish four groups of drugs with the ability to localize and accumulate in the tumor. Moreover, there are no rigid boundaries between these groups of drugs, and there is some overlapping between them, in some cases a continuous transition. Hydrophobic PSs—compounds requiring the presence of transporters, such as liposomes or Cremophor EL, or Tween 80. They have the ability to localize in the inner lipid part of lipoproteins, mainly in LDL and high-density lipoproteins (HDLs), but also in very-low-density lipoproteins (VLDLs). This group includes phthalocyanines (ZnPC, C1A1PC), naphthalocyanines (isoBOSINC), tin-etiopurpurine (SnET2) [84], and hypericin [85]. Amphiphilic PSs—asymmetric compounds, which can be incorporated into the outer phospholipid and apoprotein layer of lipoprotein particles, e.g., disulfonates (TPPS2a, C1A1PCS2a), lutetium teraphyrin (LuTex), and monoaspartyl chlorine (MACE), which forms a barrier between albumin and HDL [84]. Emodin can be included in this group [86]. Hydrophilic PSs—drugs that predominantly bind to albumins and globulins, e.g., tetra-sulfone derivates of tetraphenylporfin (TPPS3 and TPPS4) and chloroaluminum phthalocyanine (C1A1PCS3 and C1A1PCS4) [84]. Intercalators—drugs that are used mainly in chemotherapy, which intercalate into DNA and are also photoactive, e.g., doxorubicin [87], daunorubicin [88], adriamycin [89], quinizarin [90], and danthron [91]. In this work, we focused in more detail on a very prospective PS in PDT of cancer hypericin. During a study of hypericin molecule incorporation into biomacromolecules (we focused on DNA) model compounds are using for simplification of the problem. Anthraquinones emodin, quinizarin, and danthron represent a significantly smaller part of the larger hypericin molecule with the same chemical groups. This fact facilitates the creation of a proper model for interaction between hypericin and biomacromolecules. Moreover, chosen hypericin derivatives themselves originate from medicinal plants, as the PS can be utilized in PDT and their anticancer effects are known. With respect to the above-mentioned sorting of PSs into groups, they can be representatives of highly hydrophobic (hypericin), mildly hydrophobic (emodin), and intercalating molecules (quinizarin and danthron). Scientists and physicians are currently working on how to increase the effectiveness of cancer treatment. One option that has been shown to be very effective is a combination of therapies (PDT and chemotherapy), which involve the direct or mediated interaction of anticancer drugs with DNA and other bioactive macromolecules (serum albumins, lipoproteins) [92,93,94]. Hypericin, emodin, quinizarin, and danthron are examples of anticancer drugs which are chemotherapeutics synthesized by medicinal plants and PSs, and which can be used, in PDT. The discovery of new natural drugs is very important because they have many benefits for the patients. Drugs derived from medicinal plants are less toxic to the body, their use poses less risk of adverse side effects, does not depends on them, they are suitable for all age groups of patients, and can be easily combined with conventional drugs, i.e., do not show contraindications. 3. Hypericin Hypericin, a naturally occurring pigment, is found in certain plant species of the genus Hypericum. The most important representative is Saint John´s Wort (Hypericum perforatum) from the family Hypericaceae, a plant with golden-yellow flowers that grows to a height of 30–90 cm [95]. Hypericin has also been reported as occurring in some species of Australian insects [96]. Hypericin, 7,14 dione-1,3,4,6,8,12-hexahydroxy 10,11 dimethyl-phenanthrol [1,10,9,8-opgra] perylene (Figure 2) is an aromatic polycyclic dione, which exhibits a wide range of biological activities. It has long been used to treat depression caused by a disorder of the brain neurotransmitters responsible for human moods [98,99]. Hypericin has antiviral [100,101] and antitumor activity [102,103,104,105] and is used to heal wounds, neuralgic sites, and hypertrophic scar [106,107,108]. Hypericin has been demonstrated to be very effective on bacteria [109,110,111,112,113,114]. Studies of hypericin´s antiviral activity confirm that it is known to effectively deactivate enveloped viruses, but it is ineffective against non-enveloped viruses. The antiviral activity of hypericin has been demonstrated against several types of viruses: herpes simplex virus, murine cytomegalovirus, sindbis virus [115,116], hepatitis B [117], anemia, some types of leukemic viruses [118], and HIV [119,120,121], so it has also been used in the clinical treatment of AIDS patients [122]. Hypericin activity depends to a large extent on the presence of light and oxygen. These two factors determine the extent of its antiviral activity and both antiviral and antitumor activities increase significantly after visible light irradiation [123]. Hypericin, together with two other hydroxyquinones, hypocrellin A and calphostin, is characterized by negligible dark toxicity, significant photocytotoxicity to tumor cells, intense absorption at higher wavelengths (>550 nm), higher selectivity for tumor tissues, and faster leaching than hematoporphyrins [124]. Hypericin is soluble in most solvents. In organic solvents (DMSO, ethanol) its solution is red; in basic media, it is green; and in aqueous solutions, it forms purple dispersed particles [125]. The absorption spectrum of hypericin in neutral organic solvents has two main transitions in the visible region, S0→S1 (500–600 nm) and S0→S2 (425–485 nm), and two intense absorption bands. Hypericin forms non-fluorescent aggregates in aqueous solutions. The absorption and fluorescence spectra of hypericin in hexane, chloroform, and toluene are similar to those in water, so it can be assumed that hypericin molecules also form aggregates in these solvents. An indicator of the formation of aggregates in solution is the absence of fluorescence [126]. Several physical and chemical properties of hypericin are shown in Table 1. The photophysics of hypericin is very complicated, and some effort to interpret its photophysical and photochemical properties is necessary to elucidate its pharmacological and biological activities. Phenols are known to be good electron donors, while quinones act as electron acceptors. Hypericin contains both phenolic and quinone moieties. This structural characteristic places it in the group of amphi-electron compounds. The results of experiments suggest that hypericin has the potential to be a good oxidizing and reducing agent [128]. At present, the mechanisms leading to the selective accumulation of hypericin in tumor tissue compared to normal tissue are not known, nor the mechanism of its antiviral and antitumor action has been clearly determined. Thomas et al. proposed a mechanism of hypericin activity that depends on the presence of molecular oxygen, consisting of transferring energy from the excited triplet state of hypericin to the ground state of molecular oxygen, thereby generating oxygen in the singlet state, which is a highly-reactive molecule [129]. Singlet oxygen production has been theoretically confirmed [118] and experimentally demonstrated in organic solvents and lipid media [130,131,132]. Other studies suggest that although oxygen may play an important role in some cases, it is not always necessary for the antiviral activity of hypericin [133]. According to the work of the J.W. Petrich group, the origin of the photoinduced antiviral activity of hypericin may lie in its ability to produce a local pH drop in cells after irradiation [134]. The close relationship between the mechanism of hypericin antitumor activity and photoactivated local acidification in cells has been confirmed in experiments on tumor cell membrane experiments [102]. Hypericin is currently considered as a potential antitumor drug in PDT. It belongs in the group of highly hydrophobic PSs (AlogP = 5.04) [135]. Its cytotoxic and antitumor activity has been demonstrated, and its inhibitory effects on epidermal growth factor-R and a wide range of protein kinases (protein tyrosine kinase, MAP-kinase, and protein kinase C) [136]. The significant photosensitivity properties of hypericin together with its selective uptake in tumor tissues, especially in bladder cancer cells and its minimal cytotoxicity in the dark, are major positive indications for the clinical use of hypericin in the photodynamic cancer treatment [137]. Hypericin is a photosensitizer found in the endoplasmic reticulum, which, when activated by light, mediates the rapid emptying of calcium Ca2+ from the endoplasmic reticulum, which is linked to programmed cell death [138]. Although hypericin has been shown to be a potent inducer of cell death in PDT, some in vivo studies suggest that cells treated with PDT may activate rescue-signaling pathways, which may ultimately lead to tumor survival and recurrence [18,139]. Hypericin is a very good fluorescent probe for super-resolution microscopy [140]. Knowledge of the distribution of this molecule in the individual components of a living system is essential in detecting the modes of action of hypericin in biological organisms. The accumulation of hypericin in cells is determined by the diffuse and soluble properties of the molecule. It is known that after the initial accumulation in the cell membranes (20 min), an increased concentration of hypericin in the cell nucleus is observed with increasing time [141]. This indicates the possible interaction of hypericin with nucleic acids, the most essential component of the cell nucleus. Ultraviolet resonance Raman spectroscopy with 257 nm excitation was used to study nucleic acid-hypericin complexes. The excitation used amplifies the vibrational modes of nucleic acid bases. Resonance Raman spectra for complexes of polynucleotides with hypericin showed that hypericin preferentially interacts with purines at the N7 position, and this interaction is stronger in guanine than in adenine [142]. In addition, the spectra of the complex of hypericin with polyrG and calf thymus DNA, which were studied by means of surface-enhanced Raman spectroscopy, are dominated by bands corresponding to hypericin vibrations. Based on the spectra obtained, the importance of the guanine base in the interaction of hypericin with nucleic acid was confirmed. The spectrum of the polyrG complex contains changes similar to those in the spectrum of the DNA complex. Based on these results, it can be assumed that DNA induces changes in the stretching vibrations of the hypericin skeleton associated with the vibrations of the hydroxyl groups, suggesting that the hydroxyl groups of hypericin participate in the interaction with nucleic acid [143]. The mechanism of hypericin distribution in tissues, cells, and cellular organelles is also thought to be a relatively complex process, which is affected by hypericin concentration, incubation time, and properties of biological units. The bio distribution of hypericin in human organisms also depends on the mode of transport in the bloodstream. Hypericin binds to serum proteins, where lipoprotein particles appear to be a more efficient transporter than albumin. The interaction of hypericin with albumin is specific [144], while its interaction with lipoproteins is non-specific [145]. After binding with macromolecules (lipid structures, serum proteins, and sugars), hypericin forms biologically active monomers with an emission band around 600 nm, thus overcoming problems with its solubility in physiological solutions, which is very important in terms of its activity [97,137]. 4. Emodin Emodin, (1,3,8-trihydroxy-6-methylanthraquinone, Figure 3) is an anthraquinone derivate, a naturally-occurring pigment isolated from the underground part of the traditional Chinese medicinal plant Rheum palmatum, which is used mainly for its antitumor, immunosuppressive, antiinflammatory [146], antibacterial, diuretic, laxative [147], antiulcerogenic (antiulcer) [148], and vasorelaxant effects [149]. It is also found in other plant species, such as Cassia, Aloe, and Rhamnus [150,151,152,153,154]. In practice, it is available in the form of an orange crystalline substance. It is insoluble in aqueous media, and it forms aggregates (mostly in the acidic pH range). Emodin shows poor solubility in chloroform, ether, and benzene, but is highly soluble in DMSO and ethanol. The antiviral properties of emodin have also been confirmed, mainly on enveloped viruses. This property of emodin is related to its high affinity for the phospholipid membrane, in which it inhibits hydrophobic interactions between individual hydrocarbon chains [155]. Emodin has been proposed as a major precursor of the microbial metabolic pathway in the isolation of hypericin [156,157]. It is a redox catalyst and plays an important role in many processes, such as electron transport, photosynthesis, or cellular respiration [158]. Its effect on cell death has been widely studied both in the dark and after light activation [155,159]. The stimulatory effects and the prokinetic effect of emodin on gastrointestinal smooth muscle have been described in several studies [147,160]. In recent years, its effect on the contractility of smooth muscle cells has been studied [161,162]. In addition to the pharmacological properties mentioned above, emodin also has toxicological effects. Under aerobic conditions, it is photolabile in visible light and phototoxic in vitro and it can cause testicular toxicity in mice leading to hypospermatogenesis [163,164]. It inhibits protein kinase casein kinase II (CK2). Genetic disorder of the catalytic subunits of CK2 protein kinase leads to changes in sperm shape in mice during spermatogenesis and is also responsible for male infertility [165,166]. Several authors have studied the interaction of emodin with DNA [167,168,169]; for example, it causes the formation of DNA double-strand breaks by stabilizing topoisomerase II-DNA cleavage complexes and inhibiting ATP hydrolysis by topoisomerase II [170]. Emodin has a high binding affinity for serum proteins and is known to bind non-covalently to DNA in intact cells in the presence of serum proteins [159]. The interaction of emodin with proteins has been studied using several techniques surface-enhanced Raman spectroscopy, NMR, fluorescence spectroscopy, circular dichroism, and the stopped-flow method [171,172,173,174]. The formation of emodin–protein complexes is very important with regard to understanding the mode of drug delivery and transport in tumor cells [174]. Emodin belongs in the drug of amphiphilic PSs with mild hydrophobic properties (Alog P = 2.568) [135]. It has an anticancer effect on some types of human liver and lung tumors. However, the molecular mechanisms of emodin-mediated tumor regression have not been precisely defined [150]. Emodin has specific antineuroectodermal tumor activity in vitro and in vivo [175]. It suppresses tyrosine kinase activity on HER-2 breast cancer cells, inhibits the transformation of the phenotype of these cells, and can affect androgen receptors directly by inhibiting cell growth in prostate cancer cells [146]. The antitumor activity of emodin on the human chronic myeloid leukemia cell line K562 has also been demonstrated in vitro and in vivo [176]. Emodin is toxic for glioma cells by inhibiting their proliferation and inducing apoptosis of C6 cells [177]. It is known to increase the sensitivity of tumor cells to chemotherapeutics, but the mechanism of the emodin-mediated chemotherapeutic effect on cancer cells has been the subject of intense study for many years [150,178]. Important physical properties of emodin are listed in Table 1. 5. Quinizarin Quinizarin (1,4-dihydroxyanthraquinone, Figure 4) is a polycyclic aromatic hydrocarbon containing two opposite carboxyl groups (C=O) at positions 9,10. It takes the form of a yellow crystalline substance and occurs in nature in plants (Aloe, Cascara Sagrada, Senna, and rhubarb), fungi, some lichens, and insects [179]. Quinizarin is soluble in basic solutions, acetone, chloroform, and DMSO. It is almost insoluble in aqueous solutions, but its solubility increases with increasing temperature. It is used as a pesticide as a fungicide and as an additive in lubricants [180]. In addition, it is used as a colorant in the food, textile, dyeing, and photographic industries [181]. Quinizarin inhibits HIV proteinase [182] and acts as a mutagenic agent on some mammalian bacteria [183]. Immunological analysis studies have shown that it stimulates the P450 enzyme in rat epithelial and liver cells [184]. The structure of quinizarin has been studied using several spectroscopic methods, such as fluorescence measurements [185], resonance Raman and infrared spectroscopy [186], and X-ray structural analysis [187]. It has planar C2v molecular symmetry and crystallizes in a monoclonal system. Quinizarin is a highly fluorescent substance. The fact that it is almost insoluble in water significantly complicates the application of Raman spectroscopy in its study. However, infrared FT Raman and surface-enhanced Raman spectroscopy can also be used to characterize it in aqueous media [188]. Quinizarin is the simplest model molecule of a chromophore typical of some biologically and pharmaceutically significant compounds, including the antitumor anthracycline antibiotics doxorubicin, daunorubicin, and adriamycin, which are used in antineoplastic therapy. The quinizarin-like quinoid moiety is probably responsible for the cytotoxicity and cardiotoxicity of anthracycline drugs [180]. It is thought to be able to intercalate into DNA [189,190]. We can classify it among the photosensitive intercalators with low hydrophobicity (AlogP = 2.324), which could be applied in PDT [135]. The physical properties of quinizarin are shown in Table 1. 6. Danthron Danthron (1,8-dihydroxyanthraquinone or chrysazine, Figure 5) is a hydroxyanthraquinone that occurs wild in nature found in many plants but also in some insect species (e.g., Pyrrhalta luteola larvae). It is very often isolated from dry leaves and stems of the plant Xyris semifuscata growing in Madagascar [191]. It is commercially available in the form of an orange, red, or red-yellow crystalline powder. Like quinizarin, it is soluble in basic solutions, chloroform, and DMSO. It is practically insoluble in water. Danthron and quinizarin are derivatives of emodin and hypericin. Danthron is part of the anticancer drug aclacinomycin. It is thought to intercalate into DNA and therefore can be used as an example of a low hydrophobicity intercalator (AlogP = 2.324) in PDT. However, it can also be a carcinogen, causing the development of adenoma or adenocarcinoma of the colon and increased incidence of liver cancer cells [191,192]. Danthron is one of the hydroxyanthraquinone derivatives causing topoisomerase II inhibition [193], which is involved in various cellular processes, including chromosome segregation [194], and it is essential for maintaining genome stability [195]. Danthron is used as a laxative [159,196]. It is currently applied as an antioxidant, a fungicide to control powdery mildew, and has an irreplaceable role in the research into anticancer agents. Together with emodin, it is the basic structure of aglycones, which are naturally occurring laxative glycosides [191]. Danthron shows mutagenic activity [197] and indicates mutations in cells of the lymphatic system [192]. Its structure has been studied using fluorescence, resonance Raman and infrared spectroscopy. The danthron crystal is tetragonal and its planar molecule has an asymmetric structure with two different intramolecular O…..O distances. The optical properties of danthron can be discussed in terms of C2v pseudosymmetry [188]. Danthron and quinizarin form two intramolecular hydrogen bonds, which cause small changes in the structure of anthraquinone molecules. The presence of two hydrogen bonds in quinizarin allows for double proton transfer, which can take place in two steps or a one-step process. Conversely, the geometry of the danthron molecule allows only single proton transmission. The structure of danthron and quinizarin has been intensively studied and experimentally determined. For quinizarin, X-ray structural analysis identified the values of the distance O…..O and O…..H bounds, which are 2.57 and 1.77–1.79 Å respectively. This technique helped to define the O…..O distance for danthron and setting its value at 2.49 Å, but it did not provide any information about proton binding [198]. Table 1 shows characteristic physical properties. 7. Hypericin and Its Derivatives Interaction with DNA In recent years the interaction of hypericin, emodin, quinizarin, and danthron with biomacromolecules has been studied, especially with DNA, LDL, and human serum albumin (HSA) has been investigated [199,200,201,202]. The results of our studies in this area supplement the scientific knowledge on this subject. The measurements indicate that PSs incorporate into DNA, LDL, and HSA, but interact most easily with LDL particles. Distribution of molecules has been studied at two different conditions: (i) DNA–ligand complexes were exposed to the presence of free LDL particles or HSA molecules, respectively and (ii) LDL– or HSA–ligand, respectively, complexes were in the presence of free DNA molecules. From measurements at the first conditions, it is clear that while the fluorescence intensity for the DNA-hypericin complex increases with the addition of LDL to the solution, a less pronounced effect can be observed for the other PSs, DNA–emodin, DNA–quinizarin, and DNA–danthron. Similarly, HSA molecules added to the solution slightly increase the fluorescence intensity in the DNA–hypericin complex. In a competitive environment, they redistribute and rebind from DNA macromolecule to LDL (hypericin) or HSA (emodin, quinizarin, and danthron). In contrast, the fluorescence intensity did not change for the DNA–emodin complex, and a slight decrease in fluorescence has been observed in the DNA–quinizarin and DNA–dantron complexes. The presence of free DNA leads to a decrease in the fluorescence intensity of the LDL–emodin, LDL–quinizarin, and LDL–danthron/HSA–quinizarin and HSA–danthron complexes. For LDL–hypericin and HSA–hypericin complexes, an increase in fluorescence with the addition of DNA was recorded. The fluorescence intensity of the HSA–emodin complex remains unchanged [135]. It is noteworthy that the quenching of fluorescence in the presence of DNA has been observed for intercalating molecules [190]. These results allowed us to state that the molecules of the studied PSs can be extracted from DNA by HSA molecules rather than LDL particles, with the exception of hypericin, where there is a more significant binding from DNA in the presence of LDL particles. Experiments in fluorescence analysis of native and denatured DNA were designed to determine if and how the interaction of hypericin, emodin, quinizarin, and danthron with native and denatured DNA differed. Significant changes were detected for quinizarin and danthron, where fluorescence increased significantly in the presence of denatured DNA. It can be assumed that DNA denaturation increased the distances between the individual quinizarin and danthron molecules (there is a decrease in fluorescence quenching) and helped to better visualize the molecules inside the DNA. This applies in particular to molecules that intercalate into the DNA structure, i.e., quinizarin and danthron. For hypericin and emodin, it has been noted only a slight change in the intensity of fluorescence in the presence of denatured DNA, respectively from which it can again predict a different interaction mode of these PSs with DNA [135]. As a representative of highly hydrophobic PSs, hypericin binds to DNA by means of a large groove [203,204]. A binding constant, whose value was also determined, is 4.0 × 104 L/mol [204]. Emodin, with mild hydrophobic properties, interacts with DNA by binding into a small groove. This interaction is characterized by binding constant 8.1 × 104 L/mol. These ligands are incorporated into the DNA groove with hydrophobic or hydrogen bounds [204]. An intercalating mode of interaction with DNA has been confirmed for quinizarin and danthron, which is very clearly supported by atomic force microscopy measurements. Quinizarin and dathron cause DNA to unwind due to intercalation, increasing the contour length of linear DNA by 10%. By the action of natural photosensitizers studied by us, more rigid molecules of linear DNA have been detected. It is known that this is not only the type of reaction they are involved in. Quinizarin and danthron can also bind to the surface of DNA molecules by means of electrostatic forces. The size of the binding constant of this interaction type for both PSs is 1.1 × 104 L/mol [190]. Cell experiments have been performed with the aim of better understanding the mechanisms of the interaction of hypericin, emodin, quinizarin, and danthron with DNA. Success in the treatment of cancer requires sufficient hydrophobic drugs to cross the lipid membrane. The hydrophobicity of drugs therefore plays an important role in their distribution, metabolism, and excretion from the patient´s body. The main barrier preventing the interaction of nuclear DNA with anticancer drugs is the nuclear envelope. On the other hand, the detoxification process is accompanied by a decrease in drug concentration during the active outflow of these drugs. P-glycoprotein, a member of the transport protein family, is involved in this process [205]. The function of these proteins is to remove toxins from cells [206], so it is possible to regulate drug resistance by manipulating P-glycoprotein activity [207,208]. Another approach to preventing cancer cell resistance to drugs could be based on photochemical activation at a well-defined site/organelle [209]. With this in mind, the intracellular interaction of the drugs discussed here with DNA directly in the nucleus was studied using selective photoactivation and regulation of P-glycoprotein function. Selective photoactivation facilitates entry of emodin, quinizarin, and danthron molecules into the nucleus of tumor cells by means of passive diffusion (this phenomenon has not been observed in the case of hypericin). Inhibition of P-glycoprotein may increase the intracellular concentration of the molecules studied and aid their interaction with DNA. Inhibition of P-glycoprotein stimulates the passive transport of these molecules to the nucleus of tumor cells. In addition, emodin is known to significantly promote the entry of other drugs into the nucleus of tumor cells, with the exception of strongly hydrophobic ones (hypericin-like), which are characterized by a high binding affinity for P-glycoprotein [135]. The treatment of tumor cells with natural photosensitive drugs significantly depends on the degree of hydrophobicity, lipophilicity, and DNA intercalation properties of the drugs used. 8. Conclusions Cancer is a group of diseases characterized by abnormal and uncontrolled cell growth, which can affect a particular tissue or organ in a very aggressive manner and are able to spread to other parts of the body, they can metastasize. Cancer can be treated by classical therapeutic procedures (surgery, chemotherapy, and radiotherapy) and modern, very promising therapeutic methods. These include PDT. These studies show that the most effective way to treat cancer is to combine PDT with traditional therapies, respectively in some cases, PDT can even replace conventional treatment. It is very likely that PDT will be used in the future as the therapeutic approach in the treatment of specific cancers and non-cancerous diseases. This method minimizes the side effects of traditional therapeutic methods, is less invasive, more effective, and affordable. The condition for the successful treatment of cancer with PDT is the disruption of DNA macromolecule, which stops the division of tumor cells. Therefore, it is necessary to find suitable drugs that interact with DNA directly, respectively mediated by transporters that transport them to the nucleus of the tumor cell. A great advantage of newly discovered drugs is that they are natural, easier to prepare, and do not burden the patient´s body as much as synthetically produced drugs. The success of cancer treatment is highly dependent on the application of hydrophobic drugs, which can more easily cross the lipid membrane of tumor cells. Therefore, the interaction of drugs with different hydrophobicity with DNA macromolecule is the subject of many studies. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Author Contributions Conceptualization, J.S. and V.V.; methodology, J.B.; software, J.B.; validation, J.S., V.V. and J.B.; formal analysis, V.V.; investigation, V.V.; resources, V.V.; data curation, J.S.; writing—original draft preparation, V.V.; writing—review and editing, J.S.; visualization, J.B.; supervision, J.S.; project administration, J.S.; funding acquisition, J.S. All authors have read and agreed to the published version of the manuscript. Funding This study was supported by Slovak Research Grant Agency through KEGA project No. 012 UVLF-4/2018. Conflicts of Interest The authors declare no conflict of interest. Figure 1 Scheme of photodynamic therapy (PDT; edited by [42,43]). Figure 2 Two-dimensional (a) and three-dimensional (b) structure of hypericin [97]. Figure 3 Structural formula of emodin. Figure 4 Structural formula of quinizarin. Figure 5 Structural formula of danthron. molecules-25-05666-t001_Table 1Table 1 Physical and chemical properties of selected photosensitizers (hypericin, emodin, quinizarin, and danthron). Photosensitizer Hypericin Emodin Quinizarin Danthron Hydrophobicity high amphiphilic with mild hydrophobicity low Low AlogP 5.040 2.568 2.324 2.324 Absorption maximum in DMSO λmax (nm) 560 600 440 475 430 Fluorescence maximum λexc. (nm) 603 520 540 575 560 440 475 430 Dissociated form (nm) PS0 560 440 475 430 PS1- 600 [127] 480 560 475 PS2- 650 [127] 525 595 500 PS4- 630 [127] PS6- 640 [127] Dissociated constant pKa1 2 [127] 7.2 11.3 10.5 pKa2 7.8 [127] 10.6 12.7 12.9 pKa3 11.5 [127] pKa4 13 [127] ==== Refs References 1. Castano A.P. Demidova T.N. Hamblin M.R. Mechanisms in photodynamic therapy: Part one—photosensitizers, photochemistry and cellular localization Photodiagnosis. Photodyn. Ther. 2004 1 279 293 10.1016/S1572-1000(05)00007-4 25048432 2. Deda D.K. Araki K. Nanotechnology, light and chemical action: An effective combination to kill cancer cells J. Braz. Chem. Soc. 2015 26 2448 2470 10.5935/0103-5053.20150316 3. Allen T.M. Hansen C.B. Demenzes D.E.L. Pharmacokinetics of long circulating liposomes Adv. Drug Deliv. Rev. 1995 16 267 284 10.1016/0169-409X(95)00029-7 4. Loomis K. McNeeley K. Bellamkonda R.V. Nanoparticles with targeting triggered release and imaging functionality for cancer application Soft. Matter. 2011 7 839 856 10.1039/C0SM00534G 5. Reddi E. Role of delivery vehicles for photosensitizers in the photodynamic therapy of tumors J. Photochem. Photobiol. B 1997 37 189 195 10.1016/S1011-1344(96)07404-0 9085566 6. Huntošová V. Buzová D. Petrovajová D. Kasak P. Naďová Z. Jancura D. Sureau F. Miškovský P. Development of a new LDL-based transport system for hydrophobic/amphiphilic drug delivery to cancer cells Int. J. Pharm. 2012 436 463 471 10.1016/j.ijpharm.2012.07.005 22814227 7. Hally C. Delcanale P. Nonell S. Viappiani C. Abbruzzetti S. Photosensitizing proteins for antibacterial photodynamic inactivation Transl. Biophotonics 2020 e201900031 10.1002/tbio.201900031 8. Ghorbani J. Rahban D. Aghamiri S. Teymouri A. Bahador A. Photosensitizers in antibacterial photodynamic therapy: An overview Laser Ther. 2018 27 293 302 10.5978/islsm.27_18-RA-01 31182904 9. Buriankova L. Buzova D. Chorvat D. Sureau F. Brault D. Miskovsky P. Jancura D. Kinetics of hypericin association with low-density lipoproteins Photochem. Photobiol. 2011 87 56 63 10.1111/j.1751-1097.2010.00847.x 21114669 10. Lenkavska L. Blascakova L. Jurasekova Z. Macajova M. Bilcik B. Cavarga I. Miskovsky P. Huntosova V. Benefits of hypericin transport and delivery by low- and high-density lipoproteins to cancer cells: From in vitro to ex ovo Photodiagnosis Photodyn. Ther. 2019 25 214 224 10.1016/j.pdpdt.2018.12.013 30597213 11. Konan Y.N. Gurny R. Allemann E. State of the art in the delivery of photosensitizers for photodynamic therapy J. Photochem. Photobiol. B Biol. 2002 66 89 106 10.1016/S1011-1344(01)00267-6 12. Firestone R.A. Low-density lipoprotein as a vehicle for targeting antitumor compounds to cancer cells Bioconjugate Chem. 1994 5 105 113 10.1021/bc00026a002 8031872 13. Versluis A.J. van Geel P.J. Oppellar H. van Berkel T.J. Bijsterbosch M.K. Receptor-mediated uptake of low-density lipoprotein by B16 melanoma cells in vitro and in vivo in mice Br. J. Cancer 1996 4 525 532 10.1038/bjc.1996.396 8761365 14. Rensen P.C. de Vrueh R.L. Kuiper J. Bijsterbosch M.K. Biessen E.A. van Berkel T.J. Recombinant lipoproteins: Lipoprotein-like lipid particles for drug targeting Adv. Drug Deliv. Rev. 2001 47 251 276 10.1016/S0169-409X(01)00109-0 11311995 15. Kader A. Pater. A. Loading anticancer drugs into HDL as well as LDL has little affect on properties of complexes and enhances cytotoxicity to human carcinoma cells J. Control. Release 2002 80 29 44 10.1016/S0168-3659(01)00536-3 11943385 16. Zheng G. Chen J. Li H. Glickson J.D. Rerouting lipoprotein nanoparticles to selected alternate receptors for the targeted delivery of cancer diagnostic and therapeutic agents Proc. Natl. Acad. Sci. USA 2005 102 17757 17762 10.1073/pnas.0508677102 16306263 17. Song L. Li H. Sunar U. Chen J. Corbin I. Yodh A.G. Zheng G. Naphthalocyanine-reconstituted LDL nanoparticles for in vivo cancer imaging and treatment Int. J. Nanomed. 2007 2 767 774 18. Dougherty T.J. Gomer C.J. Henderson B.W. Jori G. Kessel D. Korbelik M. Moan J. Peng Q. Photodynamic therapy J. Natl. Cancer Inst. 1998 90 889 905 10.1093/jnci/90.12.889 9637138 19. Wilson B.C. Patterson M.S. The physics, biophysics and technology of photodynamic therapy Phys. Med. Biol. 2008 53 R61 R109 10.1088/0031-9155/53/9/R01 18401068 20. Yano S. Hirohara S. Obata M. Hagiya Y. Ogura S. Ikeda A. Kataoka H. Tanaka M. Joh T. Current states and future views in photodynamic therapy J. Photochem. Photobiol. C Photochem. Rev. 2011 12 46 67 10.1016/j.jphotochemrev.2011.06.001 21. Lim C.K. Heo J. Shin S. Jeong K. Seo Y.H. Jang W.D. Park C.R. Park S.Y. Kim S. Kwon I.C. Nanophotosensitizers toward advanced photodynamic therapy of cancer Cancer Lett. 2013 334 176 187 10.1016/j.canlet.2012.09.012 23017942 22. Bechet D. Mordon S.R. Guillemin F. Barberi-Heyob M.A. Photodynamic therapy of malignant brain tumours: A complementary approach to conventional therapies Cancer Treat. Rev. 2014 40 229 241 10.1016/j.ctrv.2012.07.004 22858248 23. Benov L. Photodynamic therapy: Current status and future direction Med. Princ. Pract. 2015 24 14 28 10.1159/000362416 24820409 24. Miguel-Gomez L. Vano-Galvan S. Perez-Garcia B. Carrillo-Gijon R. Jaen-Olasolo P. Treatment of folliculitis decalvans with photodynamic therapy: Results in 10 patients J. Am. Acad. Dermatol. 2015 72 1085 1087 10.1016/j.jaad.2015.02.1120 25981008 25. Sharman W.M. Allen C.M. van Lier J.E. Photodynamic therapeutics: Basic principles and clinical applications Drug Discov. Today 1999 4 507 517 10.1016/S1359-6446(99)01412-9 10529768 26. Jin Y. Zhang X. Kang H. Du L. Li M. Nanostructures of an amphiphilic zinc phthalocyanine polymer conjugate for photodynamic therapy of psoriasis Colloids Surf. B 2015 128 405 409 10.1016/j.colsurfb.2015.02.038 27. Sharman W.M. van Lier J.E. Allen C.M. Targeted photodynamic theory via receptor mediated delivery systems Adv. Drug Deliv. Rev. 2004 56 53 76 10.1016/j.addr.2003.08.015 14706445 28. Cruess A.F. Zlateva G. Pleil A.M. Wirostko B. Photodynamic therapy with verteporfin in age-related macular degeneration: A systematic review of efficacy, safety, treatment modifications and pharmacoeconomic properties Acta Ophthalmol. 2009 87 118 132 10.1111/j.1755-3768.2008.01218.x 18577193 29. Rockson S.G. Lorenz D.P. Cheong W.F. Woodburn K.W. Photoangioplasty: An emerging clinical cardiovascular role for photodynamic therapy Circulation 2000 102 591 596 10.1161/01.CIR.102.5.591 10920074 30. Bozzini G. Colin P. Betrouni N. Nevoux P. Ouzzane A. Puech P. Willers A. Mordon S. Photodynamic therapy in urology: What can we do now and where are we heading Photodiagn. Photodyn. Ther. 2012 9 261 273 10.1016/j.pdpdt.2012.01.005 31. Panzarini E. Inguscio V. Dini L. Immunogenic cell death: Can it be exploited in photodynamic therapy for cancer Biomed. Res. Int. 2013 2013 482160 10.1155/2013/482160 23509727 32. Lang G.E. Mennel S. Spital G. Wachtlin J. Jurklies B. Heimann H. Damato B. Meyer C.H. Different indications of photodynamic therapy in ophthalmology Klin. Monbl. Augenheilkd. 2009 226 725 739 10.1055/s-0028-1109514 19603375 33. Trindade A.C. De Figueiredo J.A.P. Steier L. Weber J.B.B. Photodynamic therapy in endodontics: A literature review Photomed. Laser Surg. 2015 33 175 182 10.1089/pho.2014.3776 25719896 34. Vohra F. Al-Kheraif A.A. Qadri T. Hassan M.I.A. Ahmedef A. Warnakulasuriya S. Javed F. Efficacy of photodynamic therapy in the management of oral premalignant lesions. A systematic review Photodiagn. Photodyn. Ther. 2015 12 150 159 10.1016/j.pdpdt.2014.10.001 35. Karrer S. Kohl E. Feise K. Hiepe-Wegener D. Lischner S. Philipp-Dormston W. Podda M. Prager W. Walker T. Szeimies R.M. Photodynamic therapy for skin rejuvenation: Review and summary of the literature-results of a consensus conference of an expert group for aesthetic photodynamic therapy J. Dtsch. Dermatol. Ges. 2013 11 137 148 10.1111/j.1610-0387.2012.08046.x 23190505 36. Fuhrmann G. Serio A. Mazo M. Nair R. Stevens M.M. Active loading into extracellular vesicles significantly improves the cellular uptake and photodynamic effect of porphyrins J. Control. Release 2015 205 35 44 10.1016/j.jconrel.2014.11.029 25483424 37. Baptista M.S. Wainwright M. Photodynamic antimicrobial chemotherapy (PACT) for the treatment of malaria, leishmaniasis and trypanosomiasis Braz. J. Med. Res. 2011 44 1 10 10.1590/S0100-879X2010007500141 38. Goslinski T. Piskorz J. Fluorinated porphyrinoids and their biomedical applications J. Photochem. Photobiol. C Photochem. Rev. 2011 12 304 321 10.1016/j.jphotochemrev.2011.09.005 39. Hanakova A. Bogdanova K. Tomankova K. Pizova K. Malohlava J. Binder S. Bajgar R. Langova K. Kolar M. Mosinger J. The application of antimicrobial photodynamic therapy on S. aureus and E. coli using porphyrin photosensitizers bound to cyclodextrin Microbiol. Res. 2014 169 163 170 10.1016/j.micres.2013.07.005 23899404 40. Baltazar L.M. Ray A. Santos D.A. Cisalpino P.S. Friedman A.J. Nosanchuk J.D. Antimicrobial photodynamic therapy: An effective alternative approach to control fungal injections Front. Microbiol. 2015 6 202 10.3389/fmicb.2015.00202 25821448 41. Bonnett R. Progress with heterocyclic photosensitizers for the photodynamic therapy (PDT) of tomours J. Heterocyclic Chem. 2002 39 455 10.1002/jhet.5570390303 42. Photolitec, LLC Tumor Specific Imaging Therapy Photodynamic Therapy. Available online: http://photolitec.org/Tech_PDT.html (accessed on 10 August 2020) 43. Vatansever F. de Melo W.C.M.A. Avci P. Vecchio D. Sadasivam M. Gupta A. Chandran R. Karimi M. Parizotto N.A. Yin R. Antimicrobial strategies centered around reactive oxygen species—bactericidal antibiotics, photodynamic therapy, and beyond Microbiol. Rev. 2013 37 955 989 10.1111/1574-6976.12026 23802986 44. Henderson B.W. Dougherty T.J. How does photodynamic therapy work Photochem. Photobiol. 1992 55 145 157 10.1111/j.1751-1097.1992.tb04222.x 1603846 45. Agostinis P. Berg K. Cengel K.A. Foster T.H. Girotti A.W. Gollnick S.O. Hahn S.M. Hamblin M.R. Juzeniene A. Kessel D. Photodynamic therapy of cancer: An update CA Cancer J. Clin. 2011 61 250 281 10.3322/caac.20114 21617154 46. Senapathy G.J. George B.P. Abrahamse H. Exloring the role of phytochemicals as potent natural photosensitizers in photodynamic therapy Anticancer Agents Med. Chem. 2020 20 1831 1844 10.2174/1871520620666200703192127 32619181 47. Moan J. Berg K. The photodegradation of porphyrins in cells can be used to estimate the lifetime of singlet oxygen Photochem. Photobiol. 1991 53 549 553 10.1111/j.1751-1097.1991.tb03669.x 1830395 48. Hatz S. Poulsen L. Ogilby P.R. Time-resolved singlet oxygen phosphorescence measurements from photosensitized experiments in single cells: Effects of oxygen diffusion and oxygen concentration Photochem. Photobiol. 2008 84 1284 1290 10.1111/j.1751-1097.2008.00359.x 18435700 49. Nyst H.J. Tan I.B. Stewart F.A. Balm A.J.M. Is photodynamic therapy a good alternative to surgery and radiotherapy in the treatment of head and neck cancer Photodiagnosis Photodyn. Ther. 2009 6 3 11 10.1016/j.pdpdt.2009.03.002 19447366 50. Schafer M. High sensitivity of Deinococcus radiodurans to photodynamically-produced singlet oxygen Int. J. Radiat. Biol. 1998 74 249 253 10.1080/095530098141636 9712554 51. Kochevar I.E. Lambert C.R. Lynch M.C. Tedesco A.C. Comparison of photosensitized plasma membrane damage caused by singlet oxygen and free radicals Biochim. Biophys. Acta 1996 1280 223 230 10.1016/0005-2736(95)00297-9 8639697 52. Barr H. Tralau C.J. Boulos P.B. MacRobert A.J. Tilly R. Bown S.G. The contrasting mechanisms of colonic collagen damage between photodynamic therapy and thermal injury Photochem. Photobiol. 1987 46 795 800 10.1111/j.1751-1097.1987.tb04850.x 3441502 53. Hopper C. Photodynamic therapy. A clinical reality in the treatment of cancer Lancet. Oncol. 2000 1 212 219 10.1016/S1470-2045(00)00166-2 11905638 54. Allison R.R. Bagnato V.S. Sibata C.H. Future of oncologic photodynamic therapy Future Oncol. 2010 6 929 940 10.2217/fon.10.51 20528231 55. Foote C. Mechanisms of photo-oxygenation Porphyrin Localization and Treatment of Tumors 1st ed. Doiron D.R. Gomer C.J. Alan R. Liss New York, NY, USA 1984 3 18 56. Boegheim J.P. Scholte H. Dubbehman T.M. Beems E. Raap A.K. van Steveninck J. Photodynamic effects of hematoporphyrin-derivative on enzyme activities of murine L929 fibroblasts J. Photochem. Photobiol. B 1987 1 61 73 10.1016/1011-1344(87)80006-4 2977616 57. Gibson S.L. Hilf R. Interdependence of fluence, drug, dose and oxygen on hematoporphyrin derivate induced photosensitization of tumor mitochondria Photochem. Photobiol. 1985 42 367 373 10.1111/j.1751-1097.1985.tb01583.x 3003767 58. Dolmans D.E. Fukumura D. Jain R.K. Photodynamic therapy for cancer Nat. Rev. Cancer 2003 3 380 387 10.1038/nrc1071 12724736 59. Ochsner M. Photophysical and photobiological processes in the photodynamic therapy of tumors J. Photochem. Photobiol. B 1997 39 1 18 10.1016/S1011-1344(96)07428-3 9210318 60. Canti G. Lattuada D. Morelli S. Nicolin A. Cubeddu R. Taroni P. Valentini G. Efficacy of photodynamic therapy against doxorubicin-resistant murine tumors Cancer Lett. 1995 93 255 259 10.1016/0304-3835(95)03818-H 7621437 61. Lofgren L.A. Hallgren S. Nilsson E. Westerborn A. Nilsson C. Reizenstein J. photodynamic therapy for recurrent nasopharyngeal cancer Arch. Otolaryngol. Head Neck Surg. 1995 121 997 1002 10.1001/archotol.1995.01890090039008 7646870 62. Davies M.J. Singlet oxygen-mediated damage to proteins and its consequences Biochem. Biophys. Res. Commun. 2003 305 761 770 10.1016/S0006-291X(03)00817-9 12763058 63. Bicalho L.S. Longo J.P.F. Pereira L.O. Santos M.F.M.A. Azevedo R.B. Photodynamic therapy, a new approach in the treatment of oral cancer Rev. Univ. Ind. Santander. Salud. 2010 42 167 174 64. Yoo J.O. Lim Y.C. Kim Y.M. Ha K.S. Differential cytotoxic responses to low-and high-dose photodynamic therapy in human gastric and bladder cancer cells J. Cell Biochem. 2011 112 3061 3071 10.1002/jcb.23231 21678478 65. Moghissi K. Dixon K. Parson R.J. A controlled trial of Nd-YAG laser vs photodynamic therapy for odvanced malignant bronchial obstruction Laser Med. Sci. 1993 8 269 273 10.1007/BF02547850 66. Kato H. Okunaka T. Shimatani H. Photodynamic therapy for early state bronchogenic carcinoma J. Clin. Laser Med. Surg. 1996 14 235 238 10.1089/clm.1996.14.235 9612188 67. Manoto S.L. Abrahamse H. Effect of a newly synthesized Zn sulfophthalocyanine derivative on cell morphology, viability, proliferation, and cytotoxicity in a human lung cancer cell line (A549) Lasers Med. Sci. 2011 26 523 530 10.1007/s10103-011-0887-0 21279402 68. Jheon S. Lee J.M. Kim J.K. Kim K.H. Seo S.J. Photodynamic therapy for tracheobronchial cancer Photodiagnosis Photodyn. Ther. 2011 6 177 10.1016/j.pdpdt.2011.03.176 69. Grant W.E. MacRobert A.J. Bown S.G. Hopper C. Speight P.M. Photodynamic therapy of oral cancer: Photosensitization with systemic aminolaevulinic acid Lancet 1993 342 147 148 10.1016/0140-6736(93)91347-O 7687318 70. Barr H. Shepherd N.A. Dix A. Roberts D.J.H. Tan W.C. Krasner N. Eradication of high-grade dysplasia in columnar-lined (Barrett´s) oesophagus by photodynamic therapy with endogenously generated protoporphyrin IX Lancet 1996 348 584 585 10.1016/S0140-6736(96)03054-1 8774572 71. Miller J.D. Baron E.D. Scull H. Hsia A. Berlin J.C. McCormick T. Colussi V. Kenney M.E. Cooper K.D. Oleinick N.L. Photodynamic therapy with the phtalocyanin photosensitizer Pc 4: The case experience with preclinical mechanistic and early clinical-tranlational studies Toxicol. Appl. Pharmacol. 2007 224 290 299 10.1016/j.taap.2007.01.025 17397888 72. Nseyo U.O. DeHaven J. Dougherty T.J. Potter W.R. Merrill D.L. Lundahl S.L. Lamm D.L. Photodynamic therapy (PDT) in the treatment of patients with resistant superficial bladder cancer: A long-term experience J. Clin. Laser Med. Surg. 1998 16 61 68 10.1089/clm.1998.16.61 9728133 73. Leon S.P. Folkerth R.D. Black P. Microvessel density is a prognostic indicator for patients with astroglial brain tumors Cancer 1996 77 362 372 10.1002/(SICI)1097-0142(19960115)77:2<362::AID-CNCR20>3.0.CO;2-Z 8625246 74. Zhu T.C. Finlay J.C. The role of photodynamic therapy (PDT) physics Med. Phys. 2008 35 3127 3136 10.1118/1.2937440 18697538 75. George B.P.A. Abrahamse H. A review on novel breast cancer therapies: Photodynamic therapy and plant derived agent induced cell death mechanisms Anticancer Agents Med. Chem. 2016 16 793 801 10.2174/1871520615666151026094028 26499768 76. Kostović K. Pastar Z. Ceović R. Mokos Z.B. Buzina D.S. Stanimirović A. Photodynamic therapy in dermatology: Current treatments and implications Coll. Antropol. 2012 36 1477 1481 23390855 77. Kessel D. Photosensitization of viral particles J. Lab. Clin. Med. 1990 116 428 2212852 78. Tardivo J.P. Del Giglio A. Paschoal L.H. Baptista M.S. New photodynamic therapy protocol to treat AIDS-related Kaposi´s sarcoma Photomed. Laser Surg. 2006 24 528 531 10.1089/pho.2006.24.528 16942436 79. Mĺkvy P. Position and possibilities of photodynamic therapy in oncology Oncology 2007 5 299 301 80. Castano A.P. Demidova T.N. Hamblin M.R. Mechanisms in photodynamic therapy: Part three—Photosensitizer pharmacokinetics, biodistribution, tumor localization and modes of tumor destruction Photodiagnosis Photodyn. Ther. 2005 2 91 106 10.1016/S1572-1000(05)00060-8 25048669 81. Muniyandi K. George B. Parimelazhagan T. Abrahamse H. Role of photoactive phytocompounds in photodynamic therapy of cancer Molecules 2020 25 4102 10.3390/molecules25184102 82. Doherty R.E. Sazanovich I.V. McKenzie L.K. Stasheuski A.S. Coyle R. Baggaley E. Bottomley S. Weinstein J.A. Bryant H.E. Photodynamic killing of cancer cells by a platinum(II) complex with cyclometallating ligand Sci. Rep. 2016 6 22668 10.1038/srep22668 26940077 83. Pouton C.W. Wagstaff K.M. Roth D.M. Moseley G.W. Jans D.A. Targeted delivery to the nucleus Adv. Drug Deliv. Rev. 2007 59 698 717 10.1016/j.addr.2007.06.010 17681634 84. Sobolev A.S. Novel modular transporters delivering anticancer drugs and foreign DNA to the nuclei of target cancer cells J. Buon. 2009 14 Suppl. 1 S33 S42 19785068 85. de Melo W.C.M.A. Lee A.N. Perussi J.R. Hamblin M.R. Electroporation enhances antimicrobial photodynamic therapy mediated by the hydrophobic photosensitizer, hypericin Photodiagnosis Photodyn. Ther. 2013 10 647 650 10.1016/j.pdpdt.2013.08.001 24284122 86. Alves D.S. Pérez-Fons L. Estepa A. Micol V. Membrane-related effects underlying the biological activity of the anthraquinones emodin and barbaloin Biochem. Pharmacol. 2004 68 549 561 10.1016/j.bcp.2004.04.012 15242821 87. Du K. Xia Q. Heng H. Feng F. Temozolomide-doxorubicin conjugate as a double intercalating agent and delivery by apoferritin for glioblastoma chemotherapy ACS Mater. Interfaces 2020 12 34599 34609 10.1021/acsami.0c08531 32648735 88. Mandelli F. Vignetti M. Suciu S. Stasi R. Petti M.C. Meloni G. Muus P. Marmont F. Marie J.P. Labar B. Daunorubicin versus mitoxantrone versus idarubicin as induction and consolidation chemotherapy for adults with acute myeloid leukemia: The EORTC and GIMEMA groups study AML-10 J. Clin. Oncol. 2009 27 5397 5403 10.1200/JCO.2008.20.6490 19826132 89. Wójcik K. Zarebski M. Cossarizza A. Dobrucki J.W. Daunomycin, an antitumor DNA intercalator, influences histone-DNA interactions Cancer Biol. Ther. 2013 14 823 832 10.4161/cbt.25328 23792590 90. Hu X. Cao Y. Yin X. Zhu L. Chen Y. Wang W. Hu J. Design and synthesis of various quinizarin derivatives as potential anticancer agents in acute T lymphoblastic leukemia Bioorganic Med. Chem. 2019 27 1362 1369 10.1016/j.bmc.2019.02.041 30827866 91. Chen H. Zhao C. He R. Zhou M. Liu Y. Guo X. Wang M. Zhu F. Qin R. Li X. Danthron suppresses autophagy and sensitizers pancreatic cancer cells to doxorubicin Toxicol. In Vitro 2019 54 345 353 10.1016/j.tiv.2018.10.019 30389604 92. Wang Y. Yang M. Qian J. Xu W. Wang J. Hou G. Ji L. Suo A. Sequentially self-assembled polysaccharide-based nanocomplexes for combined chemotherapy and photodynamic therapy of breast cancer Carbohydr. Polym. 2019 203 203 213 10.1016/j.carbpol.2018.09.035 30318205 93. Lee H. Han J. Shin H. Han H. Na K. Kim H. Combination of chemotherapy and photodynamic therapy for cancer treatment with sonoporation effects J. Control. Release 2018 283 190 199 10.1016/j.jconrel.2018.06.008 29885415 94. He C. Liu D. Lin W. self-assembled core-shell nanoparticles for combined chemotherapy and photodynamic therapy of resistant head and neck cancers ACS Nano 2015 9 991 1003 10.1021/nn506963h 25559017 95. Gleason H.A. Cronquist A. Manual of Vascular Plants of Northeastern United States and Adjacent Canada 2nd ed. New York Botanical Garden Bronx, New York, NY, USA 1991 910 96. Rahman A. Bioactive natural products (Part C) Studies in Natural Products Chemistry 1st ed. Rahman A. Elsevier Amsterdam, The Netherlands 2000 Volume 22 647 97. Miškovský P. Hypericin—A new antiviral and antitumor photosensitizer: Mechanism of action and interaction with biological macromolecules Curr. Drug Targets 2002 3 55 84 10.2174/1389450023348091 11899265 98. Thornett A. Use of hypericin as antidepressant. Valid measure of antidepressant efficacy in primary care is needed Brit. Med. J. 2000 320 1141 99. Butterweck V. Winterhoff H. Herkenham M. St John´s wort, hypericin, and imipramine: A comparative analysis of mRNA levels in brain areas involved in HPA axis control following short-term and long-term administration in normal and stressed rats Mol. Psychiatry 2001 6 547 564 10.1038/sj.mp.4000937 11526469 100. Eberman R. Alth G. Kreitner M. Kubin A. Natural products derived from plants as potential drugs for the photodynamic destruction of tumor cells J. Photochem. Photobiol. B 1996 36 95 97 10.1016/S1011-1344(96)07353-8 9002245 101. Pengelly A. The Constituents of Medical Plants: An Introduction to the Chemistry and Therapeutics of Herbal Medicine 2nd ed. CABI Publishing Cambridge, UK 2004 20 50 102. Miroššay A. Mirossay L. Tóthová J. Miškovský P. Onderková H. Mojžiš J. Potentiation of hypericin and hypocrellin-induced phototoxicity by omeprazole Phytomedicine 1999 6 311 317 10.1016/S0944-7113(99)80051-8 11962536 103. Cavarga I. Brezani P. Fedorocko P. Miskovsky P. Bobrov N. Longauer F. Rybarova S. Mirossay L. Stubna J. Photoinduced antitumor effect of hypericin can be enhanced by fractionated dosing Photomedicine 2005 12 680 683 10.1016/j.phymed.2004.02.011 104. Plenagl N. Duse L. Seitz B.S. Goergen N. Pinnapireddy S.R. Jedelska J. Brűβler J. Bakowsky U. Photodynamic therapy—hypericin tetraether liposome conjugates and their antitumor and antiangiogenic activity J. Drug Deliv. 2019 26 23 33 10.1080/10717544.2018.1531954 105. Bianchini P. Cozzolino M. Oneto M. Pesce L. Pennacchietti F. Tognolini M. Giorgio C. Nonell S. Cavanna L. Delcanale P. Hypericin-apomyoglobin an enhanced photosensitizer complex for the treatment of tumor cells Biomacromolecules 2019 20 2024 2033 10.1021/acs.biomac.9b00222 30995399 106. Fiebich B.L. Lieb A.H. Inhibition of substance P induced cytokine synthesis by St John´s Wort extracts Pharmacopsychiatry 2001 34 526 528 10.1055/s-2001-15462 11518071 107. Samadi S. Khadivzadeh T. Emami A. Moosavi N.S. Tafaghodi M. Behnam H.R. The effect of Hypericum perforatum on the wound healing and scar of cesarean J. Altern. Complement. Med. 2010 16 113 117 10.1089/acm.2009.0317 20064022 108. Hajhashemi M. Ghanbari Z. Movahedi M. Rafieian M. Keivani A. Haghollahi F. The effect of Achillea millefolium and Hypericum perforatum ointments on episiotomy wound healing in primiparous women J. Matern. Fetal Neonatal Med. 2018 31 63 69 10.1080/14767058.2016.1275549 28027682 109. García I. Ballesta S. Gilaberte Y. Rezusta A. Pascual Á. Antimicrobial photodynamic activity of hypericin against methicillin-susceptible and resistant Staphylococcus aureus biofilms Future Microbiol. 2015 10 347 356 10.2217/fmb.14.114 25812458 110. Engelhardt V. Krammer B. Plaetzer K. Antibacterial photodynamic therapy using water-soluble formulations of hypericin or mTHPC is effective in inactivation of Staphylococcus aureus Photochem. Photobiol. Sci. 2010 9 365 369 10.1039/b9pp00144a 20221463 111. Yow C. Tang H.M. Chu E.S. Huang Z. Hypericin-mediated photodynamic antimicrobial effect on clinically isolated pathogens Photochem. Photobiol. 2012 88 626 632 10.1111/j.1751-1097.2012.01085.x 22233203 112. Rodríguez-Amigo B. Delcanale P. Rotger G. Juárez-Jiménez J. Abbruzzetti S. Summer A. Agut M. Luque F.J. Nonell S. Viappiani C. The complex of hypericin with β-lactoglobulin has antimicrobial activity with perspective applications in dairy industry J. Dairy Sci. 2015 98 89 94 10.3168/jds.2014-8691 25465550 113. Delcanale P. Rodríguez-Amigo B. Juárez-Jiménez J. Luque F.J. Abbruzzetti S. Agut M. Nonell S. Viappiani C. Tuning the local solvent composition at a drug carrier surface: Effect of dimethyl sulfoxide/water mixture on the photofunctional properties of hyperici-β-lactoglobulin Mat. Chem. B 2017 5 1633 1641 10.1039/C7TB00081B 114. Pezzuoli D. Cozzolino M. Montali C. Brancaleon L. Bianchini P. Zantedeschi M. Bonardi S. Viappiani C. Abbruzzetti S. Serum albumins are efficient delivery systems for the photosensitizer hypericin in photosensitization-based treatments against Staphylococcus aureus Food Control. 2018 94 254 262 10.1016/j.foodcont.2018.07.027 115. Lopez-Bazzocchi I. Hudson J.B. Towers G.H. Antiviral activity of photoactive plant pigment hypericin Photochem. Photobiol. 1991 54 95 98 10.1111/j.1751-1097.1991.tb01990.x 1658826 116. Hudson J.B. Lopez-Bazzocchi I. Towers G.H. Antiviral activities of hypericin Antivir. Res. 1991 15 101 112 10.1016/0166-3542(91)90028-P 1650164 117. Moraleda G. Wu T.T. Jilbert A.R. Aldrich C.E. Condreay L.D. Larsen S.H. Tang J.C. Colacino J.M. Mason W.S. Inhibition of duck hepatitis B virus replication by hypericin Antivir. Res. 1993 20 235 247 10.1016/0166-3542(93)90023-C 8470884 118. Guedes R.C. Eriksson L.A. Effects of halogen substitution on the photochemical properties of hypericin J. Photochem. Photobiol. A Chem. 2006 178 41 49 10.1016/j.jphotochem.2005.06.018 119. Meruelo D. Lavie G. Lavie D. Therapeutic agents with dramatic antiretroviral activity and little toxicity at effective doses: Aromatic polycyclic diones hypericin and pseudohypericin Proc. Natl. Acad. Sci. USA 1988 85 5230 5234 10.1073/pnas.85.14.5230 2839837 120. Hudson J.B. Imperial V. Haugland R.P. Diwu Z. Antiviral activities of photoactive perylenequinones Photochem. Photobiol. 1997 65 352 354 10.1111/j.1751-1097.1997.tb08570.x 9066311 121. Xu Y. Lu C. Raman spectroscopy study on structure of human immunodeficiency virus (HIV) and hypericin-induced photosensitive damage of HIV Sci. China Ser. C 2005 48 117 132 122. Gulick R.M. McAuliffe V. Holden-Wiltse J. Crumpacker C. Liebes L. Stein D.S. Meehan P. Hussey S. Forcht J. Valentine F.T. Phase I studies of hypericin, the active compound in St. John´s Wort, as an antiretroviral agent in HIV-infected adults: AIDS clinical trials group protocols 150 and 258 Ann. Intern. Med. 1999 130 510 514 10.7326/0003-4819-130-6-199903160-00015 10075619 123. Kerb R. Reum T. Brockmöller J. Bauer S. Roots I. No clinically relevant photosensitization after single-dose and steady state in treatment with hypericum extract in man Eur. J. Clin. Pharmacol. 1995 49 A156 124. Diwu Z. Novel therapeutic and diagnostic applications of hypocrellins and hypericins Photochem. Photobiol. 1995 61 529 539 10.1111/j.1751-1097.1995.tb09903.x 7568399 125. Wynn J.L. Cotton T.M. Spectroscopic properties of hypericin in solution and at surfaces J. Phys. Chem. 1995 99 4317 4323 10.1021/j100012a063 126. Yamazaki T. Ohta N. Yamazaki I. Song P.S. Excited-state properties of hypericin: Electronic spectra and fluorescence decay kinetics J. Phys. Chem. 1993 97 7870 7875 10.1021/j100132a013 127. Keša P. Antalík M. Determination of pKa constants of hypericin in aqueous solution of the anti-allergic hydrotropic drug Cromolyn disodium salt Chem. Phys. Lett. 2017 676 112 117 10.1016/j.cplett.2017.03.059 128. Redepenning J. Tao N. Measurement of formal potentials for hypericin in dimethylsulfoxide Photobiol. 1993 58 532 535 10.1111/j.1751-1097.1993.tb04927.x 8248327 129. Thomas C. Pardini R.S. Oxygen dependence of hypericin-induced phototoxicity to EMT6 mouse mammary carcinoma cells Photochem. Photobiol. 1992 55 831 837 10.1111/j.1751-1097.1992.tb08531.x 1409890 130. Ehrenberg B. Anderson J.L. Foote C.S. Kinetics and yield of singlet oxygen photosensitized by hypericin inorganic and biological media Photochem. Photobiol. 1998 68 135 140 10.1111/j.1751-1097.1998.tb02479.x 9723207 131. Roslaniec M. Weitman H. Freeman D. Mazur Y. Ehrenberg B. Liposome binding constant and singlet oxygen quantum yields of hypericin, tetrahydroxyhelianthrone and their derivatives: Studies in organic solutions and in liposomes J. Photochem. Photobiol. B Biol. 2000 57 149 158 10.1016/S1011-1344(00)00090-7 132. Gbur P. Dedič R. Jancura D. Miškovský P. Hala J. Time-resolved luminescence and singlet oxygen formation under illumination of hypericin in acetone J. Lumin. 2008 128 765 767 10.1016/j.jlumin.2007.11.073 133. Fehr M.J. Carpenter S.L. Petrich J.W. The role of oxygen in the photoinduced antiviral activity of hypericin Bioorg. Med. Chem. Lett. 1994 4 1339 1344 10.1016/S0960-894X(01)80357-7 134. Carpenter S. Fehr J.M. Kraus G.A. Petrich J.W. Chemiluminescent activation of the antiviral activity of hypericin: A molecular flashlight Proc. Natl. Acad. Sci. USA 1994 91 12273 12277 10.1073/pnas.91.25.12273 7991618 135. Verebová V. Belej D. Joniová J. Jurašeková Z. Miškovský P. Kožár T. Horváth D. Staničová J. Huntošová V. Deeper insights into the drug defense of glioma cells against hydrophobic molecules Int. J. Pharm. 2016 503 56 67 10.1016/j.ijpharm.2016.02.042 26940808 136. de Witte P. Agostinis P. Van Lint J. Merlevede W. Vandenheede J.R. Inhibition of epidermal growth factor receptor tyrosine kinase activity by hypericin Biochem. Pharmacol. 1993 46 1929 1936 10.1016/0006-2952(93)90633-8 8267642 137. Agostinis P. Vantieghem A. Merlevede W. de Witte P. Hypericin in cancer treatment: More light on the way Int. J. Biochem. Cell Biol. 2002 34 221 241 10.1016/S1357-2725(01)00126-1 11849990 138. Buytaert E. Callewaert G. Hendrickx N. Scorrano L. Hartmann D. Missiaen L. Vandenheede J.R. Heirman I. Grooten J. Agostinis P. Role of endoplasmic reticulum depletion and multidomain proapoptic BAX and BAK proteins in shaping cell death after hypericin-mediated photodynamic therapy Faseb. J. 2006 20 756 758 10.1096/fj.05-4305fje 16455754 139. Ferrario A. von Tiehl K. Wong S. Luna M. Gomer C.J. Cyclooxygenase-2 inhibitor treatment enhances photodynamic therapy-mediated tumor response Cancer Res. 2002 62 3956 3961 12124326 140. Delcanale P. Pennacchietti F. Maestrini G. Rodríguez-Amigo B. Bianchini P. Diaspro A. Iagatti A. Patrizi B. Foggi P. Agut M. Subdiffraction localization of a nanostructured photosensitizer in bacterial cells Sci. Rep. 2015 5 15564 10.1038/srep15564 26494535 141. Miškovský P. Sureau F. Chinsky L. Turpin P.Y. Subcellular distribution of hypericin in human cancer cells Photochem. Photobiol. 1995 62 546 549 10.1111/j.1751-1097.1995.tb02382.x 8570710 142. Miškovský P. Chinsky L. Wheeler G.V. Turpin P.Y. Hypericin site specific interactions within polynucleotides used as DNA model compounds J. Biomol. Struct. Dyn. 1995 13 547 552 10.1080/07391102.1995.10508865 8825735 143. Sánchez-Cortés S. Miškovský P. Jancura D. Bertoluzza A. Specific interactions of antiretroviraly active drug hypericin with DNA as studied by surface-enhanced resonance Raman spectroscopy J. Phys. Chem. 1996 100 1938 1944 10.1021/jp951980q 144. Das K. Smirnov A.V. Wen J. Miškovský P. Petrich J.W. Photophysics of hypericin and hypocrellin A in complex with subcellular components: Interactions with human serum albumin Photochem. Photobiol. 1999 69 633 645 10.1111/j.1751-1097.1999.tb03339.x 10378001 145. Senthil V. Jones L.R. Senthil K. Grossweiner L.J. Hypericin photosensitization in aqueous model system Photochem. Photobiol. 1994 59 40 47 10.1111/j.1751-1097.1994.tb04999.x 8127939 146. Mijatovic S. Maksimovic-Ivanic D. Radovic J. Milijkovic D. Kaludjerovic G.N. Sabo T.J. Trajkovic V. Aloe emodin decreases the ERK-dependent anticancer activity of cisplatin Cell Mol. Life Sci. 2005 62 1275 1282 10.1007/s00018-005-5041-3 15905960 147. Ma T. Qi Q.H. Yang W.X. Xu J. Dong Z.L. Contractile effects and antracellular Ca2+ signaling induced by emodin in circular smooth muscle cells of rat colon World J. Gastroenterol. 2003 9 1804 1807 10.3748/wjg.v9.i8.1804 12918125 148. Janeczko M. Masčyk M. Kubiński K. Golczyk H. Emodin, a natural inhibitor of protein kinase CK2, suppresses growth, hyphal development, and biofilm formation of Candida Albicans Yeast 2017 34 253 265 10.1002/yea.3230 28181315 149. Huang H.C. Lee C.R. Lee Chao P.D. Chen C.C. Chu S.H. Vasorelaxant effects of emodin, an antraquinone from a Chinese herb Eur. J. Pharmacol. 1991 205 289 294 1667913 150. Su Y.T. Chang H.L. Shyue S.K. Hsu S.L. Emodin induces apoptosis in human lung adenocarcinoma cells through a reactive oxygen species-dependent mitochondrial signaling pathway Biochem. Pharmacol. 2005 70 229 241 10.1016/j.bcp.2005.04.026 15941563 151. Chukwujelwu J.C. Coombes P.H. Mulholland D.A. van Staden J. Emodin, an antibacterial anthraquinone from the roots of Cassia occidentalis S. Afr. J. Bot. 2006 72 295 297 10.1016/j.sajb.2005.08.003 152. Srinivas G. Babykutty S. Sathiadevan P.P. Srinivas P. Molecular mechanism of emodin action: Transition from laxative ingredient to an antitumor agent Med. Res. Rev. 2007 27 591 608 10.1002/med.20095 17019678 153. Fernand V.E. Dinh D.T. Washington S.J. Fakayode S.O. Loss J.N. van Ravenswaay R.O. Warner I.M. Determination of pharmacologically active compounds in root extracts of Cassia Alata L. by use of high performance liquid chromatography Talanta 2008 74 896 902 10.1016/j.talanta.2007.07.033 18371725 154. Hennebelle T. Weniger B. Joseph H. Sahpaz S. Bailleul F. Senna alata Fitoterapia 2009 80 385 393 10.1016/j.fitote.2009.05.008 19446609 155. Andersen D.O. Weber N.D. Wood S.G. Hughes B.G. Murray B.K. North J.A. In vitro virucidal activity of selected anthraquinones and anthraquinone derivatives Antiviral Res. 1991 16 185 196 10.1016/0166-3542(91)90024-L 1665961 156. Kusari S. Lamshöft M. Zühlke S. Spiteller M. An endophytic fungus from hypericum perforatum that produces hypericin J. Nat. Prod. 2008 71 159 162 10.1021/np070669k 18220354 157. Karioti A. Bilia A.R. Hypericins as potential leads for new therapeutics Int. J. Mol. Sci. 2010 11 562 594 10.3390/ijms11020562 20386655 158. Bogdanska A. Chmurzyński L. Ossowski T. Liwo A. Jeziorek D. Protolytic equilibria of dihydroxyanthraquinones in non-aqueous solutions Anal. Chim. Acta 1999 402 339 343 10.1016/S0003-2670(99)00546-2 159. Mueller S.O. Lutz W.K. Stopper H. Factors affecting the genotoxic potency ranking of natural anthraquinones in mammalian cell culture systems Mutat. Res. 1998 414 125 129 10.1016/S1383-5718(98)00047-3 9630566 160. Li J. Yang W. Hu W. Wang J. Jin Z. Wang X. Xu W. Effects of emodin on the activity of K channel in guinea pig taenia coli smooth muscle cells Acta Pharm. Sin. 1998 33 321 325 161. Ma T. Qi Q.H. Xu J. Dong Z.L. Yang W.X. Signal pathways involved in emodin-induced contraction of smooth muscle cells from rat colon World J. Gastroenterol. 2004 10 1476 1479 10.3748/wjg.v10.i10.1476 15133857 162. Chen D. Xiong Y. Wang L. Lv B. Lin Y. Characteristics of emodin on modulating the contractility of jejunal smooth muscle Can. J. Physiol. Pharmacol. 2012 90 455 462 10.1139/y2012-004 22452333 163. Vargas F. Fraile G. Velásquez M. Correia H. Fonseca G. Marin M. Marcano E. Sánchez Y. Studies on the photostability and phototoxicity of aloe-emodin, emodin and rhein Pharmazie 2002 57 399 404 12116877 164. Oshida K. Hirakata M. Maeda A. Miyoshi T. Miyamoto Y. Toxicological effect of emodin in mouse testicular gene expression profile J. Appl. Toxicol. 2011 31 790 800 10.1002/jat.1637 21319176 165. Xu X. Toselli A. Russell L.D. Seldin D.C. Globozospermia in mice lacking the casein kinase II α´catalytic subunit Nat. Genet. 1999 23 118 121 10.1038/12729 10471512 166. Escalier D. Silvius D. Xu X. Spermatogenesis of mice lacking CK2alpha´failure of germ cell survival and characteristic modifications of the spermatid nucleus Mol. Reprod. Dev. 2003 66 190 201 10.1002/mrd.10346 12950107 167. Wang L. Lin L. Ye B. Electrochemical studies of the interaction of the anticancer herbal drug emodin with DNA J. Pharm. Biomed. Anal. 2006 42 625 629 10.1016/j.jpba.2006.05.017 16828249 168. Bi S. Zhang H. Qiao C. Sun Y. Liu C. Studies of interaction of emodin and DNA in the presence of ethidium bromide by spectroscopic method Spectrochim. Acta A Mol. Biomol. Spectrosc. 2008 69 123 129 10.1016/j.saa.2007.03.017 17548242 169. Saito S.T. Silva G. Pungartnik C. Brendel M. Study of DNA-emodin interaction by FTIR and UV-Vis spectroscopy J. Photochem. Photobiol. B: Biol. 2012 111 59 63 10.1016/j.jphotobiol.2012.03.012 170. Li Y. Luan Y. Qi X. Li M. Gong L. Xue X. Wu X. Wu Y. Chen M. Xing G. Emodin triggers DNA double-strand breaks by stabilizing topoisomerase II-DNA cleavage complexes and by inhibiting ATP hydrolysis of topoisomerase II Toxicol. Sci. 2010 118 435 443 10.1093/toxsci/kfq282 20855424 171. Fabriciova G. Sanchez-Cortes S. Garcia-Ramos J.V. Miskovsky P. Surface-enhanced Raman spectroscopy study of the interaction of the antitumoral drug emodin with serum albumin Biopolymers 2004 74 125 130 10.1002/bip.20058 15137109 172. Bi S.Y. Song D.O. Kan Y.H. Xu D. Tian Y. Zhou X. Zhang H.Q. Spectroscopic characterization of effective components anthraquinones in Chinese medicinal herbs binding with serum albumins Spectrochim. Acta A: Biomol. Spectrosc. 2005 62 203 212 10.1016/j.saa.2004.12.049 173. Koistinen K.M. Soininen P. Venalainen T.A. Hayrinen J. Laatikainen R. Perakyla M. Tervahauta A.I. Karenlampi S.O. Birch PR-10c interacts with several biologically important ligands Phytochemistry 2005 66 2524 2533 10.1016/j.phytochem.2005.09.007 16246382 174. Sevilla P. Rivas J.M. García-Blanco F. García-Ramos J.V. Sánchez-Cortés S. Identification of the antitumoral drug emodin binding sites in bovine serum albumin by spectroscopic methods BBA-Proteins Proteom. 2007 1774 1359 1369 10.1016/j.bbapap.2007.07.022 175. Pecere T. Gazzola M.V. Mucignat C. Parolin C. Dalla V.F. Cavaggioni A. Basso G. Diaspro A. Salvato B. Carli M. Aloe-emodin is a new type of anticancer agent with selective activity against neuroectodermal tumors Cancer Res. 2000 60 2800 2804 10850417 176. Chun-Guan W. Jun-Qing Y. Bei-Zhong L. Dan-Ting J. Chong W. Liang Z. Dan Z. Yan W. Anti-tumor activity of emodin against human chronic myelocytic leukemia K562 cell lines in vitro and in vivo Eur. J. Pharmacol. 2010 627 33 41 10.1016/j.ejphar.2009.10.035 19857484 177. Kuo T.C. Yang J.S. Lin M.W. Hsu S.C. Lin J.J. Lin H.J. Hsia T.C. Liao L. Yang M.D. Fan M.J. Emodin has cytotoxic and pretoctive effect in rat c6 glioma cells: Roles of Mdr1a and nuclear factor κB in cell survival J. Pharmacol. Exp. Ther. 2009 330 736 744 10.1124/jpet.109.153007 19549930 178. Ko J.C. Su Y.J. Lin S.T. Jhan J.Y. Ciou S.C. Cheng C.M. Lin Y.W. Suppression of ERCC1 and Rad51 expression through ER1/2 inactivation is essential in emodin-mediated cytotoxicity in human non-small cell lung cancer cells Biochem. Pharmacol. 2010 79 655 664 10.1016/j.bcp.2009.09.024 19799875 179. Chemicalland21 Quinizarin Available online: http://www.chemicalland21.com/specialtychem/finechem/QUINIZARIN.htm (accessed on 7 September 2020) 180. Quinti L. Allen N.S. Edge M. Murphy B.P. Perotti A. A study of the strongly fluorescent species formed by the interaction of the dye 1,4-dihydroxyanthraquinone (quinizarin) with A(III) J. Photochem. Photobiol. A Chem. 2003 155 79 91 10.1016/S1010-6030(02)00360-X 181. Yohida M. Chemistry and hair dyes application of dihydroxy derivates of anthraquinone and naphtoquinone Prog. Org. Coat. 1997 31 63 72 10.1016/S0300-9440(97)00019-2 182. Brinkworth R.I. Fairle D.P. Hydroxyquinones are competitive nonpeptide inhibitors of HIV-1 proteinase Biochim. Biophys. Acta 1995 1253 5 8 10.1016/0167-4838(95)00183-U 7492599 183. Brown J.P. A review of the genetic effects of naturally occurring flavonoids, anthraquinones and related compounds Mutat. Res. 1980 75 243 277 10.1016/0165-1110(80)90029-9 6770263 184. Longo V. Amato G. Salvetti A. Gervasi P.G. Heterogenous effect of anthraquinones on drug-metabolizing enzymes in the liver and small intestine of rat Chem. Biol. Interact. 2000 126 63 77 10.1016/S0009-2797(00)00154-X 10826654 185. Carter T.P. Gillispie G.D. Connoll M.A. Intramolecular hydrogen bonding in substituted anthraquinones by laser-induced fluorescence. 1. 1,4-dihydroxyanthraquinone (quinizarin) J. Phys. Chem. 1982 86 192 196 10.1021/j100391a012 186. Smulevich G. Angeloni L. Giovannardi S. Marzocchi M.P. Resonance Raman and polarized light infrared spectra of 1,4-dihydroxyanthraquinone, vibrational studies of the ground and excited electronic states Chem. Phys. 1982 65 313 322 10.1016/0301-0104(82)85207-5 187. Nigam G. Deppisch B. Redetermination of the structure of 1,4-dihydroxyanthraquinone (C14 H8 O4 ) Z. Kristallogr. 1980 151 185 191 10.1524/zkri.1980.151.3-4.185 188. Fabriciová G. Garcia-Ramos J.V. Miškovský P. Sanchez-Cortes S. Absorption and acidic behavior of anthraquinone drugs quinizarin and danthron on Ag nanoparticles studied by Raman spectroscopy Vib. Spectrosc. 2004 34 273 281 10.1016/j.vibspec.2004.01.001 189. Bondy G.S. Armstrong C.L. Dawson B.A. Héroux-Metcalf C. Neville G.A. Rogers C.G. Toxicity of structurally related anthraquinones and anthrones to mammalian-cell in vitro Toxicol. In Vitro 1994 8 329 335 10.1016/0887-2333(94)90153-8 20692923 190. Verebová V. Adamčík J. Danko P. Podhradský D. Miškovský P. Staničová J. Anthraquinones quinizarine and danthron unwind negatively supercoiled DNA and lengthen linear DNA Biochem. Biophys. Res. Commun. 2014 444 50 55 10.1016/j.bbrc.2014.01.007 24434150 191. IARC Dantron (chrysazin; 1,8-dihydroxyanthraquinone) Pharmaceutical Drugs International Agency for Research on Cancer Lyon, France 1990 265 275 192. Mueller S.O. Stopper H. Dekant W. biotransformation of the anthraquinones emodin and chrysophanol by cytochrome P450 enzymes. Bioactivation to genotoxic metabolites Drug Metab. Dispos. 1998 26 540 546 9616189 193. Müller S.O. Eckert I. Lutz W.K. Stopper H. Genotoxicity of the laxative drug components emodin, aloe-emodin and danthron in mammalian cells: Topoisomerase II mediated Mutat. Res. Genet. Toxicol. 1996 371 165 173 10.1016/S0165-1218(96)90105-6 194. Downes C.S. Mullinger A.M. Johnson R.T. Inhibitors of DNA topoisomerase II prevent chromatid separation in mammalians cells but do not prevent exit from mitosis Proc. Natl. Acad. Sci. USA 1991 88 8895 8899 10.1073/pnas.88.20.8895 1656458 195. Wang J.R. Caron P.R. Kim R.A. The role of DNA topoisomerases in recombination and genomic stability: A double-edged sword Cell 1990 62 403 406 10.1016/0092-8674(90)90002-V 2165864 196. Neimeikaité-Čéniené A. Sergediené E. Nivinskas H. Čénas N. Cytotoxicity of natural hydroxyanthraquinones: Role of oxidative stress Z. Naturforsch. C 2002 57 822 827 10.1515/znc-2002-9-1012 12440719 197. Lieberman D.F. Fink R.C. Schaefer F.L. Mulcahy R.J. Stark A. Mutagenicity of anthraquinone and hydroxylated anthraquinones in the Ames/Salmonella microsome system Appl. Environ. Microbiol. 1982 43 1354 1359 10.1128/AEM.43.6.1354-1359.1982 7103489 198. Ferreiro M.L. Rodriguez-Otero J. Ab inition study of the intramolecular proton transfer in dihydroxyanthraquinones J. Mol. Struct. 2001 542 63 77 10.1016/S0166-1280(00)00811-3 199. Ansari S.S. Khan R.H. Naqvi S. Probing the intermolecular interactions into serum albumin and anthraquinone systems: A spectroscopic and docking approach J. Biomol. Struct. Dyn. 2018 36 3362 3375 10.1080/07391102.2017.1388284 28974158 200. Jutkova A. Chorvat D. Miskovsky P. Jancura D. Datta S. Encapsulation of anticancer drug curcumin and co-loading with photosensitizer hypericin into lipoproteins investigated by fluorescence resonance energy transfer Int. J. Pharm. 2019 564 369 378 10.1016/j.ijpharm.2019.04.062 31022501 201. Kozsup M. Dömötör O. Nagy S. Farkas E. Enyedy E.A. Buglyó P. Synthesis, characterization and albumin binding capabilities of quinizarin containing ternary cobalt(III) complexes J. Inorg. Biochem. 2020 204 110963 10.1016/j.jinorgbio.2019.110963 31874363 202. Crlikova H. Kostrhunova H. Pracharova J. Kozsup M. Nagy S. Buglyó P. Brabec V. Kasparkova J. Antiproliferative, DNA binding, and cleavage properties of dinuclear Co(III) complexes containing the bioactive quinizarin ligand J. Biol. Inorg. Chem. 2020 25 339 350 10.1007/s00775-020-01765-4 32112290 203. Kočišová E. Chinsky L. Miškovský P. Sequence specific interaction of the photoactive drug hypericin depends on the structural arrangement and the stability of the structure containing its specific 5´AG3´target: A resonance Raman spectroscopy study J. Biomol. Struct. Dyn. 1999 17 51 59 10.1080/07391102.1999.10508340 10496421 204. Staničová J. Verebová V. Strejčková A. Potential anticancer agent hypericin and its model compound emodin: Interaction with DNA Čes. Slov. Farm. 2016 65 28 31 205. Gottesman M.M. Fojo T. Bates S.E. Multidrug resistance in cancer: Role of ATP-dependent transporters Nat. Rev. Cancer 2002 2 48 58 10.1038/nrc706 11902585 206. Aller S.G. Yu J. Ward A. Weng Y. Chittaboina S. Zhou R.P. Harrell P.M. Trinh Y.T. Zhang Q.H. Urbatsch I.L. Structure of P-glycoprotein reveals a molecular basis for poly-specific drug binding Science 2009 323 1718 1722 10.1126/science.1168750 19325113 207. Regina A. Demeule M. Laplante A. Jodoin J. Dagenais C. Berthelet F. Moghrabi A. Beliveau R. Multidrug resistance in brain tumors: Roles of the blood-brain barrier Cancer Metastasis Rev. 2001 20 13 25 10.1023/A:1013104423154 11831641 208. Szaflarski W. Sujka-Kordowska P. Januchowski R. Wojtowicz K. Andrzejewska M. Nowicki M. Zabel M. Nuclear localization of P-glycoprotein is responsible for protection of the nucleus from doxorubicin in the resistant LoVo cell line Biomed. Pharmacother. 2013 67 497 502 10.1016/j.biopha.2013.03.011 23602050 209. Weyergang A. Berstad M.E. Bull-Hansen B. Olsen C.E. Selbo P.K. Berg K. Photochemical activation of drug for the treatment of therapy-resistant cancers Photochem. Photobiol. Sci. 2015 14 1465 1475 10.1039/C5PP00029G 25849953