Biochemical mechanism of caffeic acid phenylethyl ester (CAPE) selective toxicity towards melanoma cell lines

Cutaneous melanoma and purinergic modulation by phenolic compounds

Cutaneous melanoma is a complex pathology that still has only treatments that lack efficiency and offer many adverse effects. Due to this scenario emerges the need to analyze other possible treatments against this disease, such as the effect of phenolic compounds. These substances have proven antitumor effects, but still have not been fully explored as a form of therapy to combat melanoma. Also, the purinergic receptors, along with its system molecules, take part in the formation of tumors from many pathways, such as the actions of ectoenzymes and receptors activity, especially P2Rs family, and are formed by structures that can be modulated by the phenolic compounds. Therefore, more studies have to be made with the aim of explaining the purinergic system activity in carcinogenesis of cutaneous melanoma and the effects of its modulation by phenolic compound, in order to enable the development of new therapies to combat this aggressive and feared cancer.

Dihydrocaffeic Acid-Is It the Less Known but Equally Valuable Phenolic Acid?

Dihydrocaffeic acid (DHCA) is a phenolic acid bearing a catechol ring and three-carbon side chain. Despite its being found in minor amounts in numerous plants and fungi of different origins, it has attracted the interest of various research groups in many fields of science, from food to biomedical applications. The review article presented herein aims to show a wider audience the health benefits and therapeutic, industrial, and nutritional potential of dihydrocaffeic acid, by sheddinglight on its occurrence, biosynthesis, bioavailability, and metabolism. The scientific literature describes at least 70 different derivatives of dihydrocaffeic acid, both those occurring naturally and those obtained via chemical and enzymatic methods. Among the most frequently used enzymes that were applied for the modification of the parent DHCA structure, there are lipases that allow for obtaining esters and phenolidips, tyrosinases used for the formation of the catechol ring, and laccases to functionalize this phenolic acid. In many studies, both in vitro and in vivo, the protective effect of DHCA and its derivatives on cells subjected to oxidative stress and inflammation were acknowledged.

Modulatory effect of caffeic acid in alleviating diabetes and associated complications

Diabetes mellitus (DM) is one of the most common metabolic disorders characterized by elevated blood glucose levels. Prolonged uncontrolled hyperglycemia often leads to multi-organ damage including diabetic neuropathy, nephropathy, retinopathy, cardiovascular disorders, and diabetic foot ulcers. Excess production of free radicals causing oxidative stress in tissues is often considered to be the primary cause of onset and progression of DM and associated complications. Natural polyphenols can be used to induce or inhibit the expression of antioxidant enzymes such as glutathione peroxidase, heme oxygenase-1, superoxide dismutase, and catalase that are essential in maintaining redox balance, and ameliorate oxidative stress. Caffeic acid (CA) is a polyphenolderived from hydroxycinnamic acid and possesses numerous physiological properties includ-ing antioxidant, anti-inflammatory, anti-atherosclerotic, immune-stimulatory, cardioprotective, antiproliferative, and hepatoprotective activities. CA acts as a regulatory compound affecting numerous biochemical pathways and multiple targets. These include various transcription factors such as nuclear factor-B, tumor necrosis factor-α, interleukin-6, cyclooxygenase-2, and nuclear factor erythroid 2-related factor 2. Therefore, this review summarizes the pharmacological properties, molecular mechanisms, and pharmacokinetic profile of CA in mitigating the adverse effects of DM and associated complications. The bioavailability, drug delivery, and clinical trials of CA have also been discussed.

The Multifaceted Role and Regulation of Nlrp3 Inflammasome in Colitis-Associated Colo-Rectal Cancer: A Systematic Review

Colitis-associated colo-rectal cancer remains the leading cause of mortality in inflammatory bowel diseases, with inflammation remaining one of the bridging points between the two pathologies. The NLRP3 inflammasome complex plays an important role in innate immunity; however, its misregulation can be responsible for the apparition of various pathologies such as ulcerative colitis. Our review focuses on the potential pathways of upregulation or downregulation of the NLRP3 complex, in addition to evaluating its role in the current clinical setting. Eighteen studies highlighted the potential pathways of NLRP3 complex regulation as well as its role in the metastatic process in colo-rectal cancer, with promising results. Further research is, however, needed in order to validate the results in a clinical setting.

Potential Therapeutic Implications of Caffeic Acid in Cancer Signaling: Past, Present, and Future

Caffeic acid (CA) has been present in many herbs, vegetables, and fruits. CA is a bioactive compound and exhibits various health advantages that are linked with its anti-oxidant functions and implicated in the therapy and prevention of disease progression of inflammatory diseases and cancer. The anti-tumor action of CA is attributed to its pro-oxidant and anti-oxidant properties. CA’s mechanism of action involves preventing reactive oxygen species formation, diminishing the angiogenesis of cancer cells, enhancing the tumor cells’ DNA oxidation, and repressing MMP-2 and MMP-9. CA and its derivatives have been reported to exhibit anti-carcinogenic properties against many cancer types. CA has indicated low intestinal absorption, low oral bioavailability in rats, and pitiable permeability across Caco-2 cells. In the present review, we have illustrated CA’s therapeutic potential, pharmacokinetics, and characteristics. The pharmacological effects of CA, the emphasis on in vitro and in vivo studies, and the existing challenges and prospects of CA for cancer treatment and prevention are discussed in this review.

Potential Therapeutic Implications of Caffeic Acid in Cancer Signaling: Past, Present, and Future

Caffeic acid (CA) has been present in many herbs, vegetables, and fruits. CA is a bioactive compound and exhibits various health advantages that are linked with its anti-oxidant functions and implicated in the therapy and prevention of disease progression of inflammatory diseases and cancer. The anti-tumor action of CA is attributed to its pro-oxidant and anti-oxidant properties. CA’s mechanism of action involves preventing reactive oxygen species formation, diminishing the angiogenesis of cancer cells, enhancing the tumor cells’ DNA oxidation, and repressing MMP-2 and MMP-9. CA and its derivatives have been reported to exhibit anti-carcinogenic properties against many cancer types. CA has indicated low intestinal absorption, low oral bioavailability in rats, and pitiable permeability across Caco-2 cells. In the present review, we have illustrated CA’s therapeutic potential, pharmacokinetics, and characteristics. The pharmacological effects of CA, the emphasis onin vitro and in vivostudies, and the existing challenges and prospects of CA for cancer treatment and prevention are discussed in this review.

Natural products can be used in therapeutic management of COVID-19: Probable mechanistic insights

The unexpected emergence of the new Coronavirus disease (COVID-19) has affected more than three hundred million individuals and resulted in more than five million deaths worldwide. The ongoing pandemic has underscored the urgent need for effective preventive and therapeutic measures to develop anti-viral therapy. The natural compounds possess various pharmaceutical properties and are reported as effective anti-virals. The interest to develop an anti-viral drug against the novel severe acute respiratory syndrome Coronavirus (SARS-CoV-2) from natural compounds has increased globally. Here, we investigated the anti-viral potential of selected promising natural products. Sources of data for this paper are current literature published in the context of therapeutic uses of phytoconstituents and their mechanism of action published in various reputed peer-reviewed journals. An extensive literature survey was done and data were critically analyzed to get deeper insights into the mechanism of action of a few important phytoconstituents. The consumption of natural products such as thymoquinone, quercetin, caffeic acid, ursolic acid, ellagic acid, vanillin, thymol, and rosmarinic acid could improve our immune response and thus possesses excellent therapeutic potential. This review focuses on the anti-viral functions of various phytoconstituent and alkaloids and their potential therapeutic implications against SARS-CoV-2. Our comprehensive analysis provides mechanistic insights into phytoconstituents to restrain viral infection and provide a better solution through natural, therapeutically active agents.

Antiradical properties of curcumin, caffeic acid phenethyl ester, and chicoric acid: a DFT study

The antiradical properties and possible mechanisms of action of the tautomers of curcumin, caffeic acid phenethyl ester (CAPE), and chicoric acid (CA) have been studied within density functional theory (DFT). We calculated global chemical reactivity descriptors from conceptual DFT, pK_a, bioavailability, and toxicity to evaluate the antiradical properties and characterize these species. Our final level of theory is the M06-2X functional with the 6-31 + G* basis set; we selected this level after performing a benchmark calibration and validation among different levels. Solvent effects were modeled via the continuum solvation model based on density (SMD). We used water and pentyl ethanoate as solvents to simulate the physiological conditions. The free radical scavenger capacity was analyzed for three possible oxidative stress mechanisms: single electron transfer (SET), hydrogen atom transfer (HAT), and xanthine oxidase (XO) inhibition. The results indicate that neutral curcumin, CA, and CAPE behave as antireductants. The most favorable mechanism turns out to be HAT, where CA and CAPE stand out. In conclusion, our DFT study strongly indicates that neutral curcumin, CAPE, and CA would very likely perform well as antiradical drugs with recommended therapeutic use, supported by their non-toxic nature.

Production of Caffeic Acid with Co-fermentation of Xylose and Glucose by Multi-modular Engineering in Candida glycerinogenes

Caffeic acid (CA), a natural phenolic compound, has important medicinal value and market potential. In this study, we report a metabolic engineering strategy for the biosynthesis of CA in Candida glycerinogenes using xylose and glucose. The availability of precursors was increased by optimization of the shikimate (SA) pathway and the aromatic amino acid pathway. Subsequently, the carbon flux into the SA pathway was maximized by introducing a xylose metabolic pathway and optimizing the xylose assimilation pathway. Eventually, a high yielding strain CG19 was obtained, which reached a yield of 4.61 mg/g CA from mixed sugar, which was 1.2-fold higher than that of glucose. The CA titer in the 5 L bioreactor reached 431.45 mg/L with a yield of 8.63 mg/g of mixed sugar. These promising results demonstrate the great advantages of mixed sugar over glucose for high-yield production of CA. This is the first report to produce CA in C. glycerinogenes with xylose and glucose as carbon sources, which developed a promising strategy for the efficient production of high-value aromatic compounds.

Anti-tumour potential and selectivity of caffeic acid phenethyl ester in osteosarcoma cells

Osteosarcoma is the most common type of bone cancer, and metastasis is widespread decreasing the survival rate. The search for new therapeutic strategies has increased for phytochemicals due to their potential as antioxidants and anticancer properties. Thus, we evaluated the caffeic acid phenethyl ester (CAPE) and caffeic acid's (CA) anticancer properties on UMR-106 murine osteosarcoma cells. The IC₂₅ and IC₅₀ were 1.3 and 2.7 μM for CAPE and 91.0 and 120.0 μM for CA, respectively. This study shows the potential anticancer properties of CAPE and highlights how a phenethyl ester component addition can improve the pharmacological potency in relation to its precursor CA. Our results showed that CAPE was more efficient and selective in reducing the viability of tumor cells compared to the control osteoblasts (MC3T3-E1) (p < 0.05). In addition, CAPE was 44-fold (IC₂₅) and 70-fold (IC₅₀) more cytotoxic than CA. CAPE also decreased ROS generation and cell migration. In summary, CAPE was more selective for tumor cells, preserving normal ones, suggesting its potential role as an anticancer drug.

Melanization as unfavorable factor in amelanotic melanoma cell biology

The biology of three amelanotic melanoma cell lines (Ab, B16F10, and A375) of different species origin was analyzed during in vitro induced melanization in these cells. Melanin production was induced by DMEM medium characterized by a high level of L-tyrosine (a basic amino acid for melanogenesis). The biodiversity of amelanotic melanoma cells was confirmed by their different responses to melanogenesis induction; Ab hamster melanomas underwent intensive melanization, mouse B16F10 darkened slightly, while human A375 cells did not show any change in melanin content. Highly melanized Ab cells entered a cell death pathway, while slight melanization did not influence cell biology in a significant way. The rapid and high melanization of Ab cells induced apoptosis documented by phosphatidylserine externalization, caspase activation, and mitochondrial energetic state decrease. Melanoma cell type, culture medium, and time of incubation should be taken into consideration during amelanotic melanoma cell culture in vitro. L-tyrosine, as a concentration-dependent factor presented in the culture media, could stimulate some amelanotic melanoma cell lines (Ab, B16F10) to melanin production. The presence of melanin should be considered in the examination of antimelanoma compounds in vitro, because induction of melanin may interfere or be helpful in the treatment of amelanotic melanoma.

Caffeic acid and its derivatives as potential modulators of oncogenic molecular pathways: New hope in the fight against cancer

As a phenolic acid compound, caffeic acid (CA) can be isolated from different sources such as tea, wine and coffee. Caffeic acid phenethyl ester (CAPE) is naturally occurring derivative of CA isolated from propolis. This medicinal plant is well-known due to its significant therapeutic impact including its effectiveness as hepatoprotective, neuroprotective and anti-diabetic agent. Among them, anti-tumor activity of CA has attracted much attention, and this potential has been confirmed both in vitro and in vivo. CA can induce apoptosis in cancer cells via enhancing ROS levels and impairing mitochondrial function. Molecular pathways such as PI3K/Akt and AMPK with role in cancer progression, are affected by CA and its derivatives in cancer therapy. CA is advantageous in reducing aggressive behavior of tumors via suppressing metastasis by inhibiting epithelial-to-mesenchymal transition mechanism. Noteworthy, CA and CAPE can promote response of cancer cells to chemotherapy, and sensitize them to chemotherapy-mediated cell death. In order to improve capacity of CA and CAPE in cancer suppression, it has been co-administered with other anti-tumor compounds such as gallic acid and p-coumaric acid. Due to its poor bioavailability, nanocarriers have been developed for enhancing its ability in cancer suppression. These issues have been discussed in the present review with a focus on molecular pathways to pave the way for rapid translation of CA for clinical use.

Evaluation of the In Vitro Cytotoxic Activity of Caffeic Acid Derivatives and Liposomal Formulation against Pancreatic Cancer Cell Lines

Pancreatic cancer belongs to the most aggressive group of cancers, with very poor prognosis. Therefore, there is an important need to find more potent drugs that could deliver an improved therapeutic approach. In the current study we searched for selective and effective caffeic acid derivatives. For this purpose, we analyzed twelve compounds and evaluated their in vitro cytotoxic activity against two human pancreatic cancer cell lines, along with a control, normal fibroblast cell line, by the classic MTT assay. Six out of twelve tested caffeic acid derivatives showed a desirable effect. To improve the therapeutic efficacy of such active compounds, we developed a formulation where caffeic acid derivative (7) was encapsulated into liposomes composed of soybean phosphatidylcholine and DSPE-PEG₂₀₀₀. Subsequently, we analyzed the properties of this formulation in terms of basic physical parameters (such as size, zeta potential, stability at 4 °C and morphology), hemolytic and cytotoxic activity and cellular uptake. Overall, the liposomal formulation was found to be stable, non-hemolytic and had activity against pancreatic cancer cells (IC₅₀ 19.44 µM and 24.3 µM, towards AsPC1 and BxPC3 cells, respectively) with less toxicity against normal fibroblasts. This could represent a promising alternative to currently available treatment options.

Cardiovascular Effects of Caffeic Acid and Its Derivatives: A Comprehensive Review

Caffeic acid (CA) and its phenethyl ester (CAPE) are naturally occurring hydroxycinnamic acids with an interesting array of biological activities; e.g., antioxidant, anti-inflammatory, antimicrobial and cytostatic. More recently, several synthetic analogs have also shown similar properties, and some with the advantage of added stability. The actions of these compounds on the cardiovascular system have not been thoroughly explored despite presenting an interesting potential. Indeed the mechanisms underlying the vascular effects of these compounds particularly need clarifying. The aim of this paper is to provide a comprehensive and up-to-date review on current knowledge about CA and its derivatives in the cardiovascular system. Caffeic acid, CAPE and the synthetic caffeic acid phenethyl amide (CAPA) exhibit vasorelaxant activity by acting on the endothelial and vascular smooth muscle cells. Vasorelaxant mechanisms include the increased endothelial NO secretion, modulation of calcium and potassium channels, and modulation of adrenergic receptors. Together with a negative chronotropic effect, vasorelaxant activity contributes to lower blood pressure, as several preclinical studies show. Their antioxidant, anti-inflammatory and anti-angiogenic properties contribute to an important anti-atherosclerotic effect, and protect tissues against ischemia/reperfusion injuries and the cellular dysfunction caused by different physico-chemical agents. There is an obvious shortage of in vivo studies to further explore these compounds' potential in vascular physiology. Nevertheless, their favorable pharmacokinetic profile and overall lack of toxicity make these compounds suitable for clinical studies.

Bioinspired tailoring of fluorogenic thiol responsive antioxidant precursors to protect cells against H2O2-induced DNA damage

Natural antioxidants, like phenolic acids, possess a unique chemical space that can protect cellular components from oxidative stress. However, their polar carboxylic acid chemotype reduces full intracellular antioxidant potential due to limited diffusion through biological membranes. Here, we have designed and developed a new generation of hydrophobic turn-on fluorescent antioxidant precursors that upon penetration of the cell membrane, reveal a more polar and more potent antioxidant core and simultaneously become fluorescent allowing their intracellular tracking. Their activation is stimulated by polarity alteration by sensing intracellular signals and specifically biothiols. In our design, the carboxylic group of phenolic acids that originally restricts cell entrance is derivatized and conjugated through Copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC) to a coumarin derivative that its fluorescence properties are quenched with a biothiol activatable element. This more hydrophobic precursor readily penetrates cell membrane and once inside the cell the antioxidant core is revealed upon sensing glutathione, its fluorescence is restored in a turn-on manner and the generation of a more polar character traps the molecule inside the cell. This turn-on fluorescent antioxidant precursor that can be applied to phenolic acids, was developed for rosmarinic acid and the conjugate was named as RCG. The selectivity and responsiveness of RCG towards the most abundant biothiols was monitored through a variety of biophysical techniques including UV-Vis, fluorescence and NMR spectroscopy. The electrochemical behavior and free radical scavenging capacity of the precursor RCG and the active compound (RC) was evaluated and compared with the parent compound (rosmarinic acid) through cyclic voltammetry and EPR spectroscopy, respectively. The stability of the newly synthesized bioactive conjugate RC was found significantly higher than the parent rosmarinic acid when exposed to oxygen. Cell uptake experiments were conducted and revealed the internalization of RCG. The degree of intracellular DNA protection offered by RCG and its active drug (RC) on exposure to H₂O₂ was also evaluated in Jurkat cells.

Chemopreventive and Chemotherapeutic Effect of Propolis and Its Constituents: A Mini-review

Propolis is a bee wax rich in various phytocomponents and traditionally used to treat various ailments. Propolis is reported to possess an array of biological properties including anti-inflammatory, antioxidant, anti-cancer, and anti-diabetic as well as cardioprotective, hepatoprotective, renoprotective, and derma protective activities. A plethora of studies confirmed that propolis is effective against various types of cancer including head and neck, lung, liver, brain (glioma), pancreas, kidney, prostate, skin (melanoma), breast, oral, esophagus, gastric, colorectal, and bladder cancers. However, many researchers have demonstrated that propolis displays potent chemoprotective/chemopreventive or anti-cancer activity against only a few types of cancers like oral, gastrointestinal, dermal (melanoma), breast, and prostate cancers. Therefore, this mini-review only summarizes the chemopreventive/chemotherapeutic activities of propolis and its updated underlying mechanisms. Taken together, propolis displays potent chemoprotective or anti-cancer effect due to the presence of various phytocomponents which contribute to pro-apoptotic, cytotoxic, anti-proliferative (cell cycle arrest), anti-metastatic, anti-invasive, anti-angiogenic and anti-genotoxic or anti-mutagenic properties along with antioxidant, immunomodulatory, and anti-inflammatory functions. Hence, propolis could be used as an adjuvant for treating various cancers along with standard chemotherapeutic drugs. However, many large-scale clinical studies are needed to justify such applications.

Caffeic Acid Phenethyl Ester Assisted by Reversible Electroporation-In Vitro Study on Human Melanoma Cells

Melanoma is one of the most serious skin cancers. The incidence of this malignant skin lesion is continuing to increase worldwide. Melanoma is resistant to chemotherapeutic drugs and highly metastatic. Surgical resection can only be used to treat melanoma in the early stages, while chemotherapy is limited due to melanoma multi-drug resistance. The overexpression of glutathione S-transferase (GST) may have a critical role in this resistance. Caffeic acid phenethyl ester (CAPE) is a natural phenolic compound, which occurs in many plants. Previous studies demonstrated that CAPE suppresses the growth of melanoma cells and induces reactive oxygen species generation. It is also known that bioactivation of CAPE to its corresponding quinone metabolite by tyrosinase would lead to GST inhibition and selective melanoma cell death. We investigated the biochemical toxicity of CAPE in combination with microsecond electropermeabilization in two human melanoma cell lines. Our results indicate that electroporation of melanoma cells in the presence of CAPE induced high oxidative stress, which correlates with high cytotoxicity. Moreover, it can disrupt the metabolism of cancer cells by inducing apoptotic cell death. Electroporation of melanoma cells may be an efficient CAPE delivery system, enabling the application of this compound, while reducing its dose and exposure time.

Nutraceutical Compounds as Sensitizers for Cancer Treatment in Radiation Therapy

The improvement of diagnostic techniques and the efficacy of new therapies in clinical practice have allowed cancer patients to reach a higher chance to be cured together with a better quality of life. However, tumors still represent the second leading cause of death worldwide. On the contrary, chemotherapy and radiotherapy (RT) still lack treatment plans which take into account the biological features of tumors and depend on this for their response to treatment. Tumor cells' response to RT is strictly-connected to their radiosensitivity, namely, their ability to resist and to overcome cell damage induced by ionizing radiation (IR). For this reason, radiobiological research is focusing on the ability of chemical compounds to radiosensitize cancer cells so to make them more responsive to IR. In recent years, the interests of researchers have been focused on natural compounds that show antitumoral effects with limited collateral issues. Moreover, nutraceuticals are easy to recover and are thus less expensive. On these bases, several scientific projects have aimed to test also their ability to induce tumor radiosensitization both in vitro and in vivo. The goal of this review is to describe what is known about the role of nutraceuticals in radiotherapy, their use and their potential application.

The Melding of Drug Screening Platforms for Melanoma

The global incidence of cancer is rising rapidly and continues to be one of the leading causes of death in the world. Melanoma deserves special attention since it represents one of the fastest growing types of cancer, with advanced metastatic forms presenting high mortality rates due to the development of drug resistance. The aim of this review is to evaluate how the screening of drugs and compounds for melanoma has been performed over the last seven decades. Thus, we performed literature searches to identify melanoma drug screening methods commonly used by research groups during this timeframe. In vitro and in vivo tests are essential for the development of new drugs; however, incorporation of in silico analyses increases the possibility of finding more suitable candidates for subsequent tests. In silico techniques, such as molecular docking, represent an important and necessary first step in the screening process. However, these techniques have not been widely used by research groups to date. Our research has shown that the vast majority of research groups still perform in vitro and in vivo tests, with emphasis on the use of in vitro enzymatic tests on melanoma cell lines such as SKMEL and in vivo tests using the B16 mouse model. We believe that the union of these three approaches (in silico, in vitro, and in vivo) is essential for improving the discovery and development of new molecules with potential antimelanoma action. This workflow would provide greater confidence and safety for preclinical trials, which will translate to more successful clinical trials and improve the translatability of new melanoma treatments into clinical practice while minimizing the unnecessary use of laboratory animals under the principles of the 3R's.

Unraveling the molecular mechanisms and the potential chemopreventive/therapeutic properties of natural compounds in melanoma

Melanoma is the most fatal form of skin cancer. Current therapeutic approaches include surgical resection, chemotherapy, targeted therapy and immunotherapy. However, these treatment strategies are associated with development of drug resistance and severe side effects. In recent years, natural compounds have also been extensively studied for their anti-melanoma effects, including tumor growth inhibition, apoptosis induction, angiogenesis and metastasis suppression and cancer stem cell elimination. Moreover, a considerable number of studies reported the synergistic activity of phytochemicals and standard anti-melanoma agents, as well as the enhanced effectiveness of their synthetic derivatives and novel formulations. However, clinical data confirming these promising effects in patients are still scanty. This review emphasizes the anti-tumor mechanisms and potential application of the most studied natural products for melanoma prevention and treatment.

Lipophilic ester and amide derivatives of rosmarinic acid protect cells against H2O2-induced DNA damage and apoptosis: The potential role of intracellular accumulation and labile iron chelation

Phenolic acids represent abundant components contained in human diet. However, the negative charge in their carboxylic group limits their capacity to diffuse through biological membranes, thus hindering their access to cell interior. In order to promote the diffusion of rosmarinic acid through biological membranes, we synthesized several lipophilic ester- and amide-derivatives of this compound and evaluated their capacity to prevent H2O2-induced DNA damage and apoptosis in cultured human cells. Esterification of the carboxylic moiety with lipophilic groups strongly enhanced the capacity of rosmarinic acid to protect cells. On the other hand, the amide-derivatives were somewhat less effective but exerted less cytotoxicity at high concentrations. Cell uptake experiments, using ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS), illustrated different levels of intracellular accumulation among the ester- and amide-derivatives, with the first being more effectively accumulated, probably due to their extensive hydrolysis inside the cells. In conclusion, these results highlight the hitherto unrecognized fundamental importance of derivatization of diet-derived phenolic acids to unveil their biological potential.

Characterization and Biological Evaluation of Propolis from Poland

In this study, we assessed the therapeutic potential of propolis from Poland and performed chemical analysis by GC–MS, as well as determined its botanical origin. Chemical constituents typical for bud exudates of Populus nigra (section Aigeiros) were determined, however, glycerol esters of phenolic acids, as well as unusually high amounts of p-coumaric and ferulic acid and their benzyl esters, were also detected. These constituents are characteristic for buds of Populus tremula (section Leuce). We also evaluated the antiproliferative effect of propolis extracts against nine human cancer cell lines. Additionally, promising antibacterial activity of the dichloromethane extract (Minimal Inhibitory Concentration MIC values of 0.95–1.24 mg/mL), as well as a moderate antifungal activity (MIC values of 1.25–1.40 mg/mL), was noticed. Propolis from Poland appeared as a rich source of antibacterial and antiproliferative compounds and this confirmed that it is a valuable natural product with the potential to improve human health.

Bioactivation of luteolin by tyrosinase selectively inhibits glutathione S-transferase

Glutathione S-transferase (GST) plays a significant role in the metabolism and detoxification of drugs used in treatment of melanoma, resulting in a decrease in drug efficacy. Tyrosinase is an abundant enzyme found in melanoma. In this study, we used a tyrosinase targeted approach to selectively inhibit GST. In the presence of tyrosinase, luteolin (10 μM) showed 87% GST inhibition; whereas in the absence of tyrosinase, luteolin led to negligible GST inhibition. With respect to GSH, both luteolin-SG conjugate and luteolin-quinone inhibited ≥90% of GST activity via competitive reversible and irreversible mixed mechanisms with Ki of 0.74 μM and 0.02 μM, respectively. With respect to CDNB, the luteolin-SG conjugate inhibited GST activity via competitive reversible mechanism and competitively with Ki of 0.58 μM, whereas luteolin-quinone showed irreversible mixed inhibition of GST activity with Ki of 0.039 μM. Luteolin (100 μM) inhibited GST in mixed manner with Ki of 53 μM with respect to GSH and non-competitively with respect to CDNB with Ki of 38 μM. Luteolin, at a concentration range of 5-80 μM, exhibited 78-99% GST inhibition in human SK-MEL-28 cell homogenate. Among the 3 species of intact luteolin, luteolin-SG conjugate, and luteoline-quinone, only the latter two have potential as drugs with Ki < 1 μM, which is potentially achievable in-vivo as therapeutic agents. The order of GST inhibition was luteolin-quinone >> luteolin-SG conjugate >>> luteolin. In summary, our results suggest that luteolin was bioactivated by tyrosinase to form a luteolin-quinone and luteolin-glutathione conjugate, which inhibited GST. For the first time, in addition to intracellular GSH depletion, we demonstrate that luteolin acts as a selective inhibitor of GST in the presence of tyrosinase. Such strategy could potentially be used to selectively inhibit GST, a drug detoxifying enzyme, in melanoma cells.

Biochemical mechanisms of bornyl caffeate induced cytotoxicity in rat pheochromocytoma PC12 cells

The chemopreventive and antineoplastic activities of caffeic acid derivatives are highly dependent on the chemical structures and cancer cell types. The objective of the present study was to investigate the cytotoxicity of bornyl caffeate and the underlying molecular mechanisms in rat pheochromocytoma PC12 cells. Our initial studies demonstrated that bornyl caffeate exhibited potent cytotoxicity in PC12 cells in a concentration- and time-dependent manner. By examining the cell morphology on a fluorescence microscope and detecting the cell surface phosphoserine with Annexin V-FITC, we proposed that bornyl caffeate could induce apoptosis in PC12 cells. We tested this hypothesis by investigating the effects of bornyl caffeate on several apoptosis-related biomarkers. These experiments showed that bornyl caffeate induced the up-regulation of Bax and down-regulation of Bcl-xl, the disruption of mitochondrial membrane potential, the activation of caspase 3 and the cleavage of PARP. Mechanistic studies further revealed that bornyl caffeate caused the depletion of glutathione (GSH), generation of superoxide ion and progressive activation of p38 mitogen-activate protein kinase (MAPK) and c-Jun N-terminal kinase (JNK) in a concentration-dependent manner. In particular, GSH depletion appeared to be the most important mechanism underlying the cytotoxicity of bornyl caffeate. The preservation of the intracellular GSH contents with N-acetyl-L-cysteine (NAC), GSH and vitamin C abolished the effect of bornyl caffeate on the activation of p38 MAPK and JNK, preserved the integrity of mitochondrial membrane and ultimately rescued the cells from drug-induced cell death. These results suggest that bornyl caffeate induces apoptosis in PC12 cells via stimulating the depletion of GSH, the generation of reactive oxygen species (ROS) and the dissipation of mitochondrial transmembrane potential.

Existence of G-quadruplex structures in promoter region of oncogenes confirmed by G-quadruplex DNA cross-linking strategy

Existence of G-quadruplex DNA in vivo always attract widespread interest in the field of biology and biological chemistry. We reported our findings for the existence of G-quadruplex structures in promoter region of oncogenes confirmed by G-quadruplex DNA cross-linking strategy. Probes for selective G-quadruplex cross-linking was designed and synthesized that show high selectivity for G-quadruplex cross-linking. Further biological studies demonstrated its good inhibition activity against murine melanoma cells. To further investigate if G-quadruplex DNA was formed in vivo and as the target, a derivative was synthesized and pull-down process toward chromosome DNAs combined with circular dichroism and high throughput deep sequencing were performed. Several simulated intracellular conditions, including X. laevis oocytes, Ficoll 70 and PEG, was used to investigate the compound's pure cross-linking ability upon preformed G-quadruplex. Thus, as a potent G-quadruplex cross-linking agent, our strategy provided both valuable evidence of G-quadruplex structures in vivo and intense potential in anti-cancer therapy.

Caffeic acid phenethyl ester inhibits alpha-melanocyte stimulating hormone-induced melanin synthesis through suppressing transactivation activity of microphthalmia-associated transcription factor

Caffeic acid phenethyl ester (1), a natural compound found in various plants and propolis, is a well-known anti-inflammatory, immunomodulatory, and cytotoxic agent. The present study aimed to investigate the molecular events underlying the antimelanogenic activity of 1 in alpha-melanocyte stimulating hormone (α-MSH)-stimulated B16-F10 melanoma cells. In this investigation, 1 effectively reduced α-MSH-stimulated melanin synthesis by suppressing expression of melanogenic enzymes such as tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2), although this compound did not directly inhibit tyrosinase enzyme activity. On the other hand, the expression and nuclear translocation of microphthalmia-associated transcription factor (MITF) as a key transcription factor for tyrosinase expression regulating melanogenesis were not affected by treatment with 1. The upstream signaling pathways including cAMP response element-binding protein (CREB), glycogen synthase kinase-3β (GSK-3β), and Akt for activation and expression of MITF were also not influenced by 1. Interestingly, 1 inhibited transcriptional activity of a tyrosinase promoter by suppressing the interaction of MITF protein with an M-box containing a CATGTG motif on the tyrosinase promoter. Given the important role of MITF in melanogenesis, suppression of 1 on the function of MITF to transactivate tyrosinase promoter may present a novel therapeutic approach to treat hyperpigmentation disorders.

Caffeic acid production enhancement by engineering a phenylalanine over-producing Escherichia coli strain

Caffeic acid is a plant-specific phenylpropanoic acid with multiple health-improving effects reported, and its therapeutic derivatives have also been studied throughout the last decade. To meet its market need and achieve high-level production, microbial production of caffeic acid approaches have been developed in metabolically engineered Escherichia coli. In our previous work, we have established the first artificial pathway that realized de novo production of caffeic acid using E. coli endogenous 4-hydroxyphenylacetate 3-hydroxylase (4HP3H). In this work, we exploited the catalytic potential of 4HPA3H in the whole-cell bioconversion study and produced 3.82 g/L (461.12 mg/L/OD) caffeic acid from p-coumaric acid, a direct precursor. We further engineered a phenylalanine over-producer into a tyrosine over-producer and then introduced the artificial pathway. After adjusting the expression strategy and optimizing the inoculants timing, de novo production of caffeic acid reached 766.68 mg/L. Both results from the direct precursor and simple carbon sources represent the highest titers of caffeic acid from microbial production so far.

Caffeic acid phenethyl ester suppresses melanoma tumor growth by inhibiting PI3K/AKT/XIAP pathway

Melanoma is highly metastatic and resistant to chemotherapeutic drugs. Our previous studies have demonstrated that caffeic acid phenethyl ester (CAPE) suppresses the growth of melanoma cells and induces reactive oxygen species generation. However, the exact mechanism of the growth suppressive effects of CAPE was not clear. Here, we determined the potential mechanism of CAPE against melanoma in vivo and in vitro. Administration of 10 mg/kg/day CAPE substantially suppressed the growth of B16F0 tumor xenografts in C57BL/6 mice. Tumors from CAPE-treated mice showed reduced phosphorylation of phosphoinositide 3-kinase, AKT, mammalian target of rapamycin and protein level of X-linked inhibitor of apoptosis protein (XIAP) and enhanced the cleavage of caspase-3 and poly (ADP ribose) polymerase. In order to confirm the in vivo observations, melanoma cells were treated with CAPE. CAPE treatment suppressed the activating phosphorylation of phosphoinositide 3-kinase at Tyr 458, phosphoinositide-dependent kinase-1 at Ser 241, mammalian target of rapamycin at Ser 2448 and AKT at Ser 473 in B16F0 and SK-MEL-28 cells in a concentration and time-dependent study. Furthermore, the expression of XIAP, survivin and BCL-2 was downregulated by CAPE treatment in both cell lines. Significant apoptosis was observed by CAPE treatment as indicated by cleavage of caspase-3 and poly (ADP ribose) polymerase. AKT kinase activity was inhibited by CAPE in a concentration-dependent manner. CAPE treatment increased the nuclear translocation of XIAP, indicating increased apoptosis in melanoma cells. To confirm the involvement of reactive oxygen species in the inhibition of AKT/XIAP pathway, cells were treated with antioxidant N-acetyl-cysteine (NAC) prior to CAPE treatment. Our results indicate that NAC blocked CAPE-mediated AKT/XIAP inhibition and protected the cells from apoptosis. Because AKT regulates XIAP, their interaction was examined by immunoprecipitation studies. Our results show that CAPE treatment decreased the interaction of AKT with XIAP. To establish the involvement of AKT in the apoptosis-inducing effects of CAPE, cells were transfected with AKT. Our results revealed that AKT overexpression attenuated the decrease in XIAP and significantly blocked CAPE-mediated apoptosis. Similarly, overexpression of XIAP further decreased CAPE-induced apoptosis. Taken together, our results suggest that CAPE suppresses phosphoinositide 3-kinase/AKT/XIAP pathway leading to apoptosis in melanoma tumor cells in vitro and in vivo.

Lipophilic caffeic acid derivatives protect cells against H2O2-Induced DNA damage by chelating intracellular labile iron

Naturally occurring cinnamic acid derivatives are ubiquitously distributed in the plant kingdom, and it has been proposed that their consumption contributes to the maintenance of human health. However, the molecular mechanisms underlying their health keeping effects remain unknown. In the present investigation, we evaluated the capacity of several cinnamic acid derivatives (trans-cinnamic, p-coumaric, caffeic and ferulic acids, as well as caffeic acid-methyl and -propyl esters) to protect cells from oxidative stress-induced DNA damage. It was observed that effective protection was based on the ability of each compound to (i) reach the intracellular space and (ii) chelate intracellular "labile" iron. These results support the notion that numerous lipophilic iron chelating compounds, present abundantly in plant-derived diet components, may protect cells in conditions of oxidative stress and in this way be important contributors toward maintenance of human health.

In vitro antitrypanosomal activity of some phenolic compounds from propolis and lactones from Fijian Kawa (Piper methysticum)

During our search to discover new antitrypanosomal compounds, eight known plant compounds (three phenolic compounds and five kawa lactones) were evaluated for in vitro activity against Trypanosoma brucei brucei. Among them, we found two phenolic compounds and three kawa lactones possessing an α-pyrone influenced antitrypanosomal property. In particular, β-phenethyl caffeate, farnesyl caffeate and dihydrokawain exhibited high or moderate selective and potent antitrypanosomal activity in vitro. We detail here the antitrypanosomal activity and cytotoxicities of the compounds, in comparison with two commonly used antitrypanosomal drugs (eflornithine and suramin). Our findings represent the first report of the promising trypanocidal activity of these compounds.

Hormetics: dietary triggers of an adaptive stress response

A series of dietary ingredients and metabolites are able to induce an adaptive stress response either by generation of reactive oxygen species (ROS) and/or via activation of the Nrf2/Keap1 stress response network. Most of the molecules belong to activated Michael acceptors, electrophiles capable to S-alkylate redox sensitive cysteine thiols. This review summarizes recent advances in the (re)search of these compounds and classifies them into distinct groups. More than 60 molecules are described that induce the Nrf2 network, most of them found in our daily diet. Although known as typical antioxidants, a closer look reveals that these molecules induce an initial mitochondrial or cytosolic ROS formation and thereby trigger an adaptive stress response and hormesis, respectively. This, however, leads to higher levels of intracellular glutathione and increased expression levels of antioxidant enzymes such as glutathione peroxidase, thioredoxin reductase, and superoxide dismutase. According to this principle, the author suggests the term hormetics to describe these indirect antioxidants.

The metabolic bioactivation of caffeic acid phenethyl ester (CAPE) mediated by tyrosinase selectively inhibits glutathione S-transferase

Glutathione S-transferase (GST) and multidrug resistance-associated proteins (MRPs) play major roles in drug resistance in melanoma. In this study, we investigated caffeic acid phenethyl ester (CAPE) as a selective GST inhibitor in the presence of tyrosinase, which is abundant in melanoma cells. Tyrosinase bioactivates CAPE to an o-quinone, which reacts with glutathione to form CAPE-SG conjugate. Our findings indicate that 90% CAPE was metabolized by tyrosinase after a 60-min incubation. LC-MS/MS analyses identified a CAPE-SG conjugate as a major metabolite. In the presence of tyrosinase, CAPE (10-25μM) showed 70-84% GST inhibition; whereas in the absence of tyrosinase, CAPE did not inhibit GST. CAPE-SG conjugate and CAPE-quinone (25μM) demonstrated ⩾85% GST inhibition via reversible and irreversible mechanisms, respectively. Comparing with CDNB and GSH, the non-substrate CAPE acted as a weak, reversible GST inhibitor at concentrations >50μM. Furthermore, MK-571, a selective MRP inhibitor, and probenecid, a non-selective MRP inhibitor, decrease the IC(50) of CAPE (15μM) by 13% and 21%, apoptotic cell death by 3% and 13%, and mitochondrial membrane potential in human SK-MEL-28 melanoma cells by 10% and 56%, respectively. Moreover, computational docking analyses suggest that CAPE binds to the GST catalytic active site. Caffeic acid, a hydrolyzed product of CAPE, showed a similar GST inhibition in the presence of tyrosinase. Although, as controls, 4-hydroxyanisole and L-tyrosine were metabolized by tyrosinase to form quinones and glutathione conjugates, they exhibited no GST inhibition in the absence and presence of tyrosinase. In conclusion, both CAPE and caffeic acid selectively inhibited GST in the presence of tyrosinase. Our results suggest that intracellularly formed quinones and glutathione conjugates of caffeic acid and CAPE may play major roles in the selective inhibition of GST in SK-MEL-28 melanoma cells. Moreover, the inhibition of MRP enhances CAPE-induced toxicity in the SK-MEL-28 melanoma cells.

Phenylpropanoids in radioregulation: double edged sword

Radiotherapy, frequently used for treatment of solid tumors, carries two main obstacles including acquired radioresistance in cancer cells during radiotherapy and normal tissue injury. Phenylpropanoids, which are naturally occurring phytochemicals found in plants, have been identified as potential radiotherapeutic agents due to their anti-cancer activity and relatively safe levels of cytotoxicity. Various studies have proposed that these compounds could not only sensitize cancer cells to radiation resulting in inhibition of growth and cell death but also protect normal cells against radiation-induced damage. This review is intended to provide an overview of recent investigations on the usage of phenylpropanoids in combination with radiotherapy in cancer treatment.