Oxidative metabolites of curcumin poison human type II topoisomerases

Dry Heating of Curcumin in the Presence of Basic Salts Yields Anti-inflammatory Dimerization Products

Curcumin exerts some of its biological effects via degradation products formed by spontaneous oxidation at physiological, i.e., weakly basic, pH. Here, we analyzed products formed by dry heating of curcumin in the presence of a basic salt (sodium bicarbonate and others). Under the dry heating conditions employed, curcumin was completely consumed, yielding products entirely different from those obtained by autoxidative degradation in buffer. Bioassay-guided fractionation of the reaction mixture was used to identify and isolate compounds with anti-inflammatory activity in a cell-based assay. This provided two dimers of curcumin, dicurmins A and B, featuring a partly saturated naphthalene core that inhibited lipopolysaccharide-induced activation of NF-κB in RAW264.7 cells. Dicurmin A and B are unusual derivatives of curcumin lacking key functional moieties yet exhibit increased anti-inflammatory activity. The process of dry heating of polyphenols in the presence of a basic salt can serve as a novel approach to generating bioactive compounds.

Cobalt-based hybrid nanoparticles loaded with curcumin for ligand-enhanced synergistic nanocatalytic therapy/chemotherapy combined with calcium overload

The therapeutic efficacy of Fenton or Fenton-like nanocatalysts is usually restricted by the inappropriate pH value and limited concentration of hydrogen peroxide (H2O2) at the tumor site. Herein, calcium carbonate (CaCO3)-mineralized cobalt silicate hydroxide hollow nanocatalysts (CSO@CaCO3, CC) were synthesized and loaded with curcumin (CCC). This hybrid system can simultaneously realize nanocatalytic therapy, chemotherapy and calcium overload. With the stabilization of liposomes, CCC is able to reach the tumor site smoothly. The CaCO3 shell first degrades in an acidic tumor environment, releasing Cur and Ca2+, and the pH value of the tumor is increased simultaneously. Then the exposed CSO catalyzes the Fenton-like reaction to convert H2O2 into ˙OH and enhances the cytotoxicity of curcumin (Cur) by catalytically oxidizing it to a ˙Cur radical. Curcumin not only induces the chemotherapy effect but also serves as a nucleophilic ligand and an electron donor in the catalytic system, enhancing the Fenton-like activity of CCC by electron transfer. In addition, calcium overload also amplifies the efficacy of ROS-based therapy. In vitro and in vivo results show that CCC exhibited an excellent synergistic tumor inhibition effect without any clear side effect. This work proposes a novel concept of nanocatalytic therapy/chemotherapy synergistic mechanism by the ligand-induced enhancement of Fenton-like catalytic activity, and inspires the construction of combined therapeutic nanoplatforms and multifunctional nanocarriers for drug and ion delivery in the future.

A drug co-delivery platform made of magnesium-based micromotors enhances combination therapy for hepatoma carcinoma cells

Combination therapy is an emerging strategy to overcome multidrug resistance (MDR) in hepatocellular carcinoma (HCC) chemotherapy treatment. However, the passive diffusion in traditional delivery systems greatly retards the approach and penetration of drugs into hepatocellular carcinoma cells and thus hinders the efficacy of combination therapy. Micro/nanomotors with autonomous locomotion in a tiny scale provide the possibility of tackling this issue. Herein, an active drug delivery micromotor platform delicately designed to load drugs with different physicochemical properties and enhance the drug permeability of cells is demonstrated for HCC chemotherapy treatment. The biocompatible micromotor platform Mg/PLGA/CHI comprised magnesium (Mg) coated with two polymer layers made of poly(lactic-co-glycolic acid) (PLGA) and chitosan (CHI), where the hydrophobic and hydrophilic drugs doxorubicin (Dox) and Curcumin (Cur) were loaded, respectively. The autonomous motion of the micromotors with velocity up to 45 μm s-1 greatly enhanced the diffusion of chemotherapeutic drugs and led to higher extracellular and intracellular drug distribution. Moreover, hydrogen produced during the motion eliminated the excess reactive oxygen species (ROS) in the human hepatocellular carcinoma (HepG2) cells. Compared with inert groups, the absorption of Dox and Cur from the active micromotors was about 2.9 and 1.5 times higher in human hepatocellular carcinoma (HepG2) cells. In addition, the anti-tumor activity also obviously improved at the micromotor concentration of 1 mg mL-1 (cell proliferation was reduced by almost 30%). Overall, this work proposes an approach based on loading different chemotherapy agents on an active delivery system to enhance drug permeability and overcome MDR and provides a potentially effective therapeutic strategy for the treatment of HCC.

Curcumin Inhibition of TGFβ signaling in bone metastatic breast cancer cells and the possible role of oxidative metabolites

TGFβ signaling promotes progression of bone-metastatic (BMET) breast cancer (BCa) cells by driving tumor-associated osteolysis, a hallmark of BCa BMETs, thus allowing for tumor expansion within bone. Turmeric-derived bioactive curcumin, enriched in bone via local enzymatic deconjugation of inactive circulating curcumin-glucuronides, inhibits osteolysis and BMET progression in human xenograft BCa BMET models by blocking tumoral TGFβ signaling pathways mediating osteolysis. This is a unique antiosteolytic mechanism in contrast to current osteoclast-targeting therapeutics. Therefore, experiments were undertaken to elucidate the mechanism for curcumin inhibition of BCa TGFβ signaling and the application of this finding across multiple BCa cell lines forming TGFβ-dependent BMETs, including a possible role for bioactive curcumin metabolites in mediating these effects. Immunoblot analysis of TGFβ signaling proteins in bone tropic human (MDA-SA, MDA-1833, MDA-2287) and murine (4T1) BCa cells revealed uniform curcumin blockade of TGFβ-induced Smad activation due to down-regulation of plasma membrane associated TGFβR2 and cellular receptor Smad proteins that propagate Smad-mediated gene expression, resulting in downregulation of PTHrP expression, the osteolytic factor driving in vivo BMET progression. With the exception of early decreases in TGFβR2, inhibitory effects appeared to be mediated by oxidative metabolites of curcumin and involved inhibition of gene expression. Interestingly, while not contributing to changes in Smad-mediated TGFβ signaling, curcumin caused early activation of MAPK signaling in all cell lines, including JNK, an effect possibly involving interactions with TGFβR2 within lipid rafts. Treatment with curcumin or oxidizable analogs of curcumin may have clinical relevancy in the management of TGFβ-dependent BCa BMETs.

Curcumin Oxidation Is Required for Inhibition of Helicobacter pylori Growth, Translocation and Phosphorylation of Cag A

Curcumin is a potential natural remedy for preventing Helicobacter pylori-associated gastric inflammation and cancer. Here, we analyzed the effect of a phospholipid formulation of curcumin on H. pylori growth, translocation and phosphorylation of the virulence factor CagA and host protein kinase Src in vitro and in an in vivo mouse model of H. pylori infection. Growth of H. pylori was inhibited dose-dependently by curcumin in vitro. H. pylori was unable to metabolically reduce curcumin, whereas two enterobacteria, E. coli and Citrobacter rodentium, which efficiently reduced curcumin to the tetra- and hexahydro metabolites, evaded growth inhibition. Oxidative metabolism of curcumin was required for the growth inhibition of H. pylori and the translocation and phosphorylation of CagA and cSrc, since acetal- and diacetal-curcumin that do not undergo oxidative transformation were ineffective. Curcumin attenuated mRNA expression of the H. pylori virulence genes cagE and cagF in a dose-dependent manner and inhibited translocation and phosphorylation of CagA in gastric epithelial cells. H. pylori strains isolated from dietary curcumin-treated mice showed attenuated ability to induce cSrc phosphorylation and the mRNA expression of the gene encoding for IL-8, suggesting long-lasting effects of curcumin on the virulence of H. pylori. Our work provides mechanistic evidence that encourages testing of curcumin as a dietary approach to inhibit the virulence of CagA.

Perspective on Improving the Relevance, Rigor, and Reproducibility of Botanical Clinical Trials: Lessons Learned From Turmeric Trials

Plant-derived compounds, without doubt, can have significant medicinal effects since many notable drugs in use today, such as morphine or taxol, were first isolated from botanical sources. When an isolated and purified phytochemical is developed as a pharmaceutical, the uniformity and appropriate use of the product are well defined. Less clear are the benefits and best use of plant-based dietary supplements or other formulations since these products, unlike traditional drugs, are chemically complex and variable in composition, even if derived from a single plant source. This perspective will summarize key points-including the premise of ethnobotanical and preclinical evidence, pharmacokinetics, metabolism, and safety-inherent and unique to the study of botanical dietary supplements to be considered when planning or evaluating botanical clinical trials. Market forces and regulatory frameworks also affect clinical trial design since in the United States, for example, botanical dietary supplements cannot be marketed for disease treatment and submission of information on safety or efficacy is not required. Specific challenges are thus readily apparent both for consumers comparing available products for purchase, as well as for commercially sponsored vs. independent researchers planning clinical trials to evaluate medicinal effects of botanicals. Turmeric dietary supplements, a top selling botanical in the United States and focus of over 400 clinical trials to date, will be used throughout to illustrate both the promise and pitfalls associated with the clinical evaluation of botanicals.

Polyphenols as adjunctive treatments in psychiatric and neurodegenerative disorders: Efficacy, mechanisms of action, and factors influencing inter-individual response

The pathophysiology of psychiatric and neurodegenerative disorders is complex and multifactorial. Polyphenols possess a range of potentially beneficial mechanisms of action that relate to the implicated pathways in psychiatric and neurodegenerative disorders. The aim of this review is to highlight the emerging clinical trial and preclinical efficacy data regarding the role of polyphenols in mental and brain health, elucidate novel mechanisms of action including the gut microbiome and gene expression, and discuss the factors that may be responsible for the mixed clinical results; namely, the role of interindividual differences in treatment response and the potentially pro-oxidant effects of some polyphenols. Further clarification as part of larger, well conducted randomized controlled trials that incorporate precision medicine methods are required to inform clinical efficacy and optimal dosing regimens.

Curcumin loaded sub-30 nm targeting therapeutic lipid nanoparticles for synergistically blocking nasopharyngeal cancer growth and metastasis

Systemic chemotherapy is still the primary treatment for advanced-stage nasopharyngeal carcinoma (NPC), but only limited therapeutic success has been achieved in the past decade because of drug resistance and systemic toxicity. Curcumin (Cur) is an effective alternative to chemotherapeutics because it showed remarkable therapeutic potential in the treatment of NPC. However, lack of tissue specificity and poor penetration in solid tumors are the major obstacles to effective therapy. Therefore, in this work, a self-assembled sub-30 nm therapeutic lipid nanoparticle loaded with Cur, named as Cur@α-NTP-LN, was constructed, specifically targeting scavenger receptor class B member 1 (SR-B1) and enhancing its therapeutic effects on NPC in vivo. Our results showed that Cur@α-NTP-LNs were effective and superior to free Cur on NPC cell-specific targeting, suppressing cell proliferation and inducing cell apoptosis. In vivo and ex vivo optical imaging revealed that Cur@α-NTP-LNs exerted high targeting efficiency, specifically accumulating in NPC xenograft tumors and delivering Cur into the tumor center after systemic administration. Furthermore, Cur@α-NTP-LNs exhibited a remarkable inhibitory effect on the growth of NPC subcutaneous tumors, with over 71 and 47% inhibition compared to Cur- and α-NTP-LNs-treated groups, respectively. In addition, Cur@α-NTP-LNs almost blocked NPC metastasis in a lung metastasis model of NPC and significantly improved the survival rate. Thus, the sub-30 nm Cur@α-NTP-LNs enhanced the solubility of Cur and demonstrated the ability of targeted Cur delivery into the center of the solid NPC tumor, performing synergistic inhibitory effects on the growth of NPC tumor and its metastasis with high efficiency.

Topoisomerase II Poisons: Converting Essential Enzymes into Molecular Scissors

The extensive length, compaction, and interwound nature of DNA, together with its controlled and restricted movement in eukaryotic cells, create a number of topological issues that profoundly affect all of the functions of the genetic material. Topoisomerases are essential enzymes that modulate the topological structure of the double helix, including the regulation of DNA under- and overwinding and the removal of tangles and knots from the genome. Type II topoisomerases alter DNA topology by generating a transient double-stranded break in one DNA segment and allowing another segment to pass through the DNA gate. These enzymes are involved in a number of critical nuclear processes in eukaryotic cells, such as DNA replication, transcription, and recombination, and are required for proper chromosome structure and segregation. However, because type II topoisomerases generate double-stranded breaks in the genetic material, they also are intrinsically dangerous enzymes that have the capacity to fragment the genome. As a result of this dualistic nature, type II topoisomerases are the targets for a number of widely prescribed anticancer drugs. This article will describe the structure and catalytic mechanism of eukaryotic type II topoisomerases and will go on to discuss the actions of topoisomerase II poisons, which are compounds that stabilize DNA breaks generated by the type II enzyme and convert these essential enzymes into "molecular scissors." Topoisomerase II poisons represent a broad range of structural classes and include anticancer drugs, dietary components, and environmental chemicals.

1,2-Naphthoquinone as a Poison of Human Type II Topoisomerases

1,2-Naphthoquinone, a secondary metabolite of naphthalene, is an environmental pollutant found in diesel exhaust particles that displays cytotoxic and genotoxic properties. Because many quinones have been shown to act as topoisomerase II poisons, the effects of this compound on DNA cleavage mediated by human topoisomerase IIα and IIβ were examined. The compound increased the levels of double-stranded DNA breaks generated by both enzyme isoforms and did so better than a series of naphthoquinone derivatives. Furthermore, 1,2-naphthoquinone was a more efficacious poison against topoisomerase IIα than IIβ. Topoisomerase II poisons can be classified as interfacial (which interact noncovalently at the enzyme-DNA interface and increase DNA cleavage by blocking ligation) or covalent (which adduct the protein and increase DNA cleavage by closing the N-terminal gate of the enzyme). Therefore, experiments were performed to determine the mechanistic basis for the actions of 1,2-naphthoquinone. In contrast to results with etoposide (an interfacial poison), the activity of 1,2-naphthoquinone against topoisomerase IIα was abrogated in the presence of sulfhydryl and reducing agents. Moreover, the compound inhibited cleavage activity when incubated with the enzyme prior to the addition of DNA and induced virtually no cleavage with the catalytic core of the enzyme. It also induced stable covalent topoisomerase IIα-DNA cleavage complexes and was a partial inhibitor of DNA ligation. Findings were also consistent with 1,2-naphthoquinone acting as a covalent poison of topoisomerase IIβ; however, mechanistic studies with this isoform were less conclusive. Whereas the activity of 1,2-naphthoquinone was blocked in the presence of a sulfhydryl reagent, it was much less sensitive to the presence of a reducing agent. Furthermore, the reduced form of 1,2-naphthoquinone, 1,2-dihydroxynaphthalene, displayed high activity against the β isoform. Taken together, results suggest that 1,2-naphthoquinone increases topoisomerase II-mediated double-stranded DNA scission (at least in part) by acting as a covalent poison of the human type II enzymes.

Inhibitors of DNA topoisomerases I and II applied to Candida dubliniensis reduce growth, viability, the generation of petite mutants and toxicity, while acting synergistically with fluconazole

The increasing resistance of Candida species to azoles emphasizes the urgent need for new antifungal agents with novel mechanisms of action. The aim of this study was to examine the effect of three DNA topoisomerase inhibitors of plant origin (camptothecin, etoposide and curcumin) on the growth of Candida dubliniensis. The phylogenetic analysis showed a close relationship between the topoisomerase enzymes of C. dubliniensis and Candida albicans. The alignment of the amino acid sequences of topoisomerase I and II of yeasts and humans evidenced conserved domains. The docking study revealed affinity of the test compounds for the active site of topoisomerase I and II in C. dubliniensis. Curcumin and camptothecin demonstrated a stronger in vitro antifungal effect than the reference drugs (fluconazole and itraconazole). Significant synergistic activity between the topoisomerase inhibitors and fluconazole at the highest concentration (750 µM) was observed. Fluconazole induced the petite phenotype to a greater degree than the topoisomerase inhibitors, indicating a tendency to generate resistance. Lower toxicity was found for such inhibitors versus reference drugs on Galleria mellonella larva. The topoisomerase inhibitors exhibited promising antifungal activity, and the DNA topoisomerase enzymes of C. dubliniensis proved to be an excellent model for evaluating new antifungal compounds.

Mechanistic Differences in the Inhibition of NF-κB by Turmeric and Its Curcuminoid Constituents

Turmeric extract, a mixture of curcumin and its demethoxy (DMC) and bisdemethoxy (BDMC) isomers, is used as an anti-inflammatory preparation in traditional Asian medicine. Curcumin is considered to be the major bioactive compound in turmeric but less is known about the relative anti-inflammatory potency and mechanism of the other components, their mixture, or the reduced in vivo metabolites. We quantified inhibition of the NF-κB pathway in cells, adduction to a peptide mimicking IκB kinase β, and the role of cellular glutathione as a scavenger of electrophilic curcuminoid oxidation products, suggested to be the active metabolites. Turmeric extracts (IC₅₀ 14.5 ± 2.9 μM), DMC (IC₅₀ 12.1 ± 7.2 μM), and BDMC (IC₅₀ 8.3 ± 1.6 μM), but not reduced curcumin, inhibited NF-κB similar to curcumin (IC₅₀ 18.2 ± 3.9 μM). Peptide adduction was formed with turmeric and DMC but not with BDMC, and this correlated with their oxidative degradation. Inhibition of glutathione biosynthesis enhanced the activity of DMC but not BDMC in the cellular assay. These findings suggest that NF-κB inhibition by curcumin and DMC involves their oxidation to reactive electrophiles, whereas BDMC does not require oxidation. Because it has not been established whether curcumin undergoes oxidative transformation in vivo, oxidation-independent BDMC may be a promising alternative to test in clinical trials.

Safety and efficacy of turmeric extract, turmeric oil, turmeric oleoresin and turmeric tincture from Curcuma longa L. rhizome when used as sensory additives in feed for all animal species

Following a request from the European Commission, the EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety and efficacy of turmeric extract, turmeric oil, turmeric oleoresin and turmeric tincture from Curcuma longa L. rhizome when used as sensory additives in feed and in water for drinking for all animal species. The FEEDAP Panel concludes that the additives under consideration are safe at the maximum proposed use levels: (i) turmeric extract at 15 mg/kg complete feed (or in water for drinking at comparable exposure) for all animal species; (ii) turmeric essential oil at 80 mg/kg feed for veal calves (milk replacer) and 20 mg/kg complete feed (or 20 mg/L) for all other species; (iii) turmeric oleoresin at 30 mg/kg complete feed (or 30 mg/L) for chickens for fattening and laying hens and 5 mg/kg complete feed (or 5 mg/L) for pigs, veal calves, cattle for fattening and dairy cows, sheep, goats, horses, rabbits and fish; (iv) turmeric tincture at 0.8 mL/L water for drinking for poultry, 6 mL per head and day for horses and 0.05 mL tincture/kg complete feed for dogs. No concerns for consumers were identified following the use of the additives at the proposed use level in animal nutrition. Turmeric extract, turmeric oil, turmeric oleoresin and turmeric tincture should be considered as irritants to skin and eyes and the respiratory tract and as skin sensitisers. The use of the additives in feed is not expected to pose a risk for the environment. Since turmeric and its preparations are recognised to flavour food and their function in feed would be essentially the same as that in food, no further demonstration of efficacy is considered necessary.

GZ17-6.02 initiates DNA damage causing autophagosome-dependent HDAC degradation resulting in enhanced anti-PD1 checkpoint inhibitory antibody efficacy

Our studies examined the molecular mechanisms by which the novel cancer therapeutic GZ17-6.02 (NCT03775525) killed GI tumor cells. TZ17-6.02 activated ATM which was responsible for increased phosphorylation of nuclear γH2AX and AMPKα T172. ATM-AMPK signaling was responsible for the subsequent inactivation of mTORC1 and mTORC2, dephosphorylation of ULK1 S757, and increased phosphorylation of ULK1 S317 and of ATG13 S318, which collectively caused enhanced autophagosome formation. GZ17-6.02 interacted with 5-fluorouracil in an additive to greater than additive fashion to kill all of the tested GI tumor cell types. This was associated with greater ATM activation and a greater mammalian target of rapamycin inactivation and autophagosome induction. As a result, autophagy-dependent degradation of multiple histone deacetylase (HDAC) proteins and chaperone proteins occurred. Loss of HDAC expression was causal in reduced expression of programed death ligand 1 (PD-L1), ornithine decarboxylase, and indole amine 2,3-dioxygenase (IDO1) and in the elevated expression of major histocompatibility complex Class IA (MHCA). Treatment with GZ17-6.02 also resulted in enhanced efficacy of a subsequently administered anti-PD1 checkpoint inhibitory antibody. Thus, the primary mode of GZ17-6.02 action is to induce a DNA damage response concomitant with ATM activation, that triggers a series of interconnected molecular events that result in tumor cell death and enhanced immunogenicity.

Role of GOLPH3 and TPX2 in Neuroblastoma DNA Damage Response and Cell Resistance to Chemotherapy

Neuroblastoma (NB) is an aggressive, relapse-prone infancy tumor of the sympathetic nervous system and is the leading cause of death among preschool age diseases, so the search for novel therapeutic targets is crucial. Golgi phosphoprotein 3 (GOLPH3) has been reported to be involved in the development, and in the DNA damage response, of various human cancers. Golgi dispersal is a common feature of DNA damage response in mammalian cells. Understanding how cells react to DNA damage is essential in order to recognize the systems used to escape from elimination. We induced DNA damage in two human neuroblastoma cell lines by curcumin. The exposure of neuroblastoma cells to curcumin induced: (a) up-regulation of GOLPH3⁺ cells; (b) augmentation of double-strand breaks; (c) Golgi fragmentation and dispersal throughout the cytoplasm; (d) increase of apoptosis and autophagy; (e) increased expression of TPX2 oncoprotein, able to repair DNA damage. Primary neuroblastoma samples analysis confirmed these observations. Our findings suggest that GOLPH3 expression levels may represent a clinical marker of neuroblastoma patients’ responsiveness to DNA damaging therapies—and of possible resistance to them. Novel molecules able to interfere with GOLPH3 and TPX2 pathways may have therapeutic benefits when used in combination with standard DNA damaging therapeutic agents in neuroblastoma

Curcumin induces secretion of glucagon-like peptide-1 through an oxidation-dependent mechanism

Curcumin shows antiglycemic effects in animals. Curcumin is chemically unstable at physiological pH, and its oxidative degradation products were shown to contribute to its anti-inflammatory effects. Since the degradation products may also contribute to other effects, we analyzed their role in the antiglycemic activity of curcumin. We quantified curcumin-induced release of glucagon-like peptide 1 (GLP-1) from mouse STC-1 cells that represent enteroendocrine L-cells as a major source of this anti-diabetic hormone. Curcumin induced secretion of GLP-1 in a dose-dependent manner. Two chemically stable analogues of curcumin that do not readily undergo degradation, were less active while two unstable analogues were active secretagogues. Chromatographically isolated spiroepoxide, an unstable oxidative metabolite of curcumin with anti-inflammatory activity, also induced secretion of GLP-1. Stable compounds like the final oxidative metabolite bicyclopentadione, and the major plasma metabolite, curcumin-glucuronide, were inactive. GLP-1 secretion induced by curcumin and its oxidative degradation products was associated with activation of PKC, ERK, and CaM kinase II. Since activity largely correlated with instability of curcumin and the analogues, we tested the extent of covalent binding to proteins in STC-1 cells and found it occurred with similar affinity as N-ethylmaleimide, indicating covalent binding occurred with nucleophilic cysteine residues. These results suggest that oxidative metabolites of curcumin are involved in the antiglycemic effects of curcumin. Our findings support the hypothesis that curcumin functions as a pro-drug requiring oxidative activation to reveal its bioactive metabolites that act by binding to target proteins thereby causing a change in function.

6,6'-Dihydroxythiobinupharidine as a poison of human type II topoisomerases

A number of natural products with medicinal properties increase DNA cleavage mediated by type II topoisomerases. In an effort to identify additional natural compounds that affect the activity of human type II topoisomerases, a blind screen of a library of 341 Mediterranean plant extracts was conducted. Extracts from Nuphar lutea, the yellow water lily, were identified in this screen. N. lutea has been used in traditional medicine by a variety of indigenous populations. The active compound in N. lutea, 6,6'-dihydroxythiobinupharidine, was found to enhance DNA cleavage mediated by human topoisomerase IIα and IIβ ∼8-fold and ∼3-fold, respectively. Mechanistic studies with topoisomerase IIα indicate that 6,6'-dihydroxythiobinupharidine is a "covalent poison" that acts by adducting the enzyme outside of the DNA cleavage-ligation active site and requires the N-terminal domain of the protein for its activity. Results suggest that some of the medicinal properties of N. lutea may result from the interactions between 6,6'-dihydroxythiobinupharidine and the human type II enzymes.

The mechanism(s) of action of antioxidants: From scavenging reactive oxygen/nitrogen species to redox signaling and the generation of bioactive secondary metabolites

Small molecule, dietary antioxidants exert a remarkably broad range of bioactivities, and many of these can be explained by the influence of antioxidants on the redox homeostasis. Such compounds help to modulate the levels of harmful reactive oxygen/nitrogen species, and therefore participate in the regulation of various redox signaling pathways. However, upon ingestion, antioxidants usually undergo extensive metabolism that can generate a wide range of bioactive metabolites. This makes it difficult, but otherwise a need, to identify the ones responsible for the different activities of antioxidants. By better understanding their ways of action, the use of antioxidants in therapy can be improved. This review provides a summary on the role of the in vivo metabolic changes and the oxidized metabolites on the mechanisms behind the bioactivity of antioxidants. A special attention is given to metabolites described as products of biomimetic oxidative chemical reactions, which can be considered as models of free radical scavenging. During such reactions a wide variety of metabolites are formed, and they can exert completely different specific bioactivities as compared to their parent antioxidants. This implies that exploring the free radical scavenging-related metabolite fingerprint of each antioxidant molecule, collectively defined here as the scavengome, will lead to a deeper understanding of the bioactivity of these compounds. Furthermore, this paper aims to be a working tool for systematic studies on oxidized metabolic fingerprints of antioxidants, which will certainly reveal an often-neglected segment of chemical space that is a treasury of bioactive compounds.

Antioxidant activity of crude ethanolic extract and fractions of Ziziphus mauritiana Lam. (Rhamnaceae) leaves from Burkina Faso

Background Ziziphus mauritiana Lam. is a plant used in traditional medicine in Burkina Faso in the treatment of several diseases, of which diabetes is characterized by oxidative stress. The aim of this study was to evaluate the in vitro antioxidant potential of the extracts of leaves of this plant. Methods The crude hydroethanolic extract (HEE) of the leaves of Z. mauritiana and their partitionates in n-hexane, dichloromethane, and ethyl acetate, and in the residual aqueous solution (the F1, F2, F3, and F4 fractions, respectively) were first prepared. The content of polyphenols was determined and the antioxidant effects of the extracts were evaluated by their 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity, inhibition of lipid peroxidation (TBARS), and the ferric reducing antioxidant power (FRAP). Results The HEE as well as the F3 and F4 fractions were rich in polyphenols with contents between 58 and 84 mg equivalent gallic acid per 100 mg. The flavonoid content was 4 mg quercetin equivalents in the HEE and the F4 fraction. Except for the F1 fraction, the HEE and the other fractions showed significant DPPH scavenging activity (IC50 between 8 and 12 μg/mL). The IC50 of TBARS by different extracts was in the range 1-5 μg/mL, and the FRAP activity was 7-85 mg ascorbic acid equivalent per 100 mg. Total polyphenol content was highly correlated with the antioxidant activities. Conclusions The HEE, F3, and F4 fractions were found to be the richest in polyphenols and had the best antioxidant activity. The antioxidant activity of the extracts of the leaves of Z. mauritiana is due to these polyphenolic compounds.

A Curcumin Degradation Product, 7-Norcyclopentadione, Formed by Aryl Migration and Loss of a Carbon from the Heptadienedione Chain

Evidence that anti-inflammatory and other biological effects of curcumin may at least in part be mediated by its metabolites underscores the importance of identifying novel transformation products. Spontaneous degradation of curcumin in buffer pH 7.5 results mainly in dioxygenated products with a characteristic cyclopentadione ring composed of carbons 2 through 6 of the former heptadienedione chain. When analyzing degradation reactions of 4'- O-methylcurcumin, a product was identified missing one of the terminal carbons of the heptadienedione moiety while containing a cyclopentadione ring and adjacent hydroxy group typical of curcumin degradation products. Analysis of curcumin autoxidation reactions showed formation of an analogous compound, 7-norcyclopentadione, a degradation product exhibiting net loss of a carbon and gain of an oxygen atom. Removal of the carbon is proposed to occur via a peroxide-linked curcumin dimer in conjunction with radical-mediated 1,2-aryl migration of a guaiacol moiety. Oxidation reactions of demethoxycurcumin gave demethoxy-7-norcyclopentadione, whereas an analogous product was not observed from bis-demethoxycurcumin. Incubation of RAW264.7 macrophage-like cells with curcumin showed the presence of 7-norcyclopentadione, the formation of which was not increased upon activation of the cells with 12- O-tetradecanoylphorbol-13-acetate . 7-Norcyclopentadione is a novel type of degradation product that is most likely formed via autoxidative processes when cells are incubated with curcumin.

Stability and anti-inflammatory activity of the reduction-resistant curcumin analog, 2,6-dimethyl-curcumin

The efficacy of the curry spice compound curcumin as a natural anti-inflammatory agent is limited by its rapid reductive metabolism in vivo. A recent report described a novel synthetic derivative, 2,6-dimethyl-curcumin, with increased stability against reduction in vitro and in vivo. It is also known that curcumin is unstable at physiological pH in vitro and undergoes rapid autoxidative transformation. Since the oxidation products may contribute to the biological effects of curcumin, we tested oxidative stability of 2,6-dimethyl-curcumin in buffer (pH 7.5). The rate of degradation was similar to curcumin. The degradation products were identified as a one-carbon chain-shortened alcohol, vanillin, and two isomeric epoxides that underwent cleavage to vanillin and a corresponding hydroxylated cleavage product. 2,6-Dimethyl-curcumin was more potent than curcumin in inhibiting NF-κB activity but less potent in inhibiting expression of cyclooxygenase-2 in LPS-activated RAW264.7 cells. 2,6-Dimethyl-curcumin and some of its degradation products covalently bound to a peptide that contains the redox-sensitive cysteine of IKKβ kinase, the activating kinase upstream of NF-κB, providing a mechanism for the anti-inflammatory activity. In RAW264.7 cells vanillin, the chain-shortened alcohol, and reduced 2,6-dimethyl-curcumin were detected as major metabolites. These studies provide new insight into the oxidative transformation mechanism of curcumin and related compounds. The products resulting from oxidative transformation contribute to the anti-inflammatory activity of 2,6-dimethyl-curcumin in addition to its enhanced resistance against enzymatic reduction.

Design of pH-sensitive methotrexate prodrug-targeted curcumin nanoparticles for efficient dual-drug delivery and combination cancer therapy

Aim

We designed acid-labile methotrexate (MTX) targeting prodrug self-assembling nanoparticles loaded with curcumin (CUR) drug for simultaneous delivery of multi-chemotherapeutic drugs and combination cancer therapy.

Methods

A dual-acting MTX, acting as both an anticancer drug and as a tumor-targeting ligand, was coupled to 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[aldehyde(polyethylene glycol)-2000] via Schiff's base reaction. The synthesized prodrug conjugate (DSPE-PEG-Imine-MTX) could be self-assembled into micellar nanoparticles (MTX-Imine-M) in aqueous solution, which encapsulated CUR into their core by hydrophobic interactions (MTX-Imine-M-CUR).

Results

The prepared MTX-Imine-M-CUR nanoparticles were composed of an inner hydrophobic DSPE/CUR core and an outside hydrophilic bishydroxyl poly (ethyleneglycol) (PEG) shell with a self-targeting MTX prodrug corona. The imine linker between 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[aldehyde(polyethyleneglycol)-2000] and MTX, as a dynamic covalent bond, was strong enough to remain intact in physiological pH, even though it is rapidly cleaved in acidic pH. The MTX-Imine-M-CUR could codeliver MTX and CUR selectively and efficiently into the cancer cells via folate receptor-mediated endocytosis followed by the rapid intracellular release of CUR and the active form of MTX via the acidity of endosomes/lysosomes. Moreover, the MTX-Imine-M-CUR resulted in significantly higher in vitro and in vivo anticancer activity than pH-insensitive DSPE-PEGAmide-MTX assembling nanoparticles loaded with CUR (MTX-Amide-M-CUR), MTX unconjugated DSPE-PEG assembling micellar nanoparticles loaded with CUR (M-CUR), combination of both free drugs, and individual free drugs.

Conclusion

The smart system provided a simple, yet feasible, drug delivery strategy for targeted combination chemotherapy.

HU-331 and Oxidized Cannabidiol Act as Inhibitors of Human Topoisomerase IIα and β

Topoisomerase II is a critical enzyme in replication, transcription, and the regulation of chromatin topology. Several anticancer agents target topoisomerases in order to disrupt cell growth. Cannabidiol is a major non-euphoriant, pharmacologically active component of cannabis. Previously, we examined the cannabidiol derivative HU-331 in order to characterize the mechanism of the compound against topoisomerase IIα. In this current work, we explore whether cannabidiol (CBD) impacts topoisomerase II activity, and we additionally examine the activity of these compounds against topoisomerase IIβ. CBD does not appear to strongly inhibit DNA relaxation and is not a poison of topoisomerase II DNA cleavage. However, oxidation of CBD allows this compound to inhibit DNA relaxation by topoisomerase IIα and β without poisoning DNA cleavage. Additionally, we found that oxidized CBD, similar to HU-331, inhibits ATP hydrolysis and can result in inactivation of topoisomerase IIα and β. We also determined that oxidized CBD and HU-331 are both able to stabilize the N-terminal clamp of topoisomerase II. Taken together, we conclude that while CBD does not have significant activity against topoisomerase II, both oxidized CBD and HU-331 are active against both isoforms of topoisomerase II. We hypothesize that oxidized CBD and HU-331 act against the enzyme through interaction with the N-terminal ATPase domain. According to the model we propose, topoisomerase II inactivation may result from a decrease in the ability of the enzyme to bind to DNA when the compound is bound to the N-terminus.

Functional evaluation of doxorubicin decorated polymeric liposomal curcumin: a surface tailored therapeutic platform for combination chemotherapy

The present study deals with the hypothesis and design of new platform for the accommodation of curcumin and doxorubicin in surface engineered liposomes for combination chemotherapy.

The anti-inflammatory activity of curcumin is mediated by its oxidative metabolites

The spice turmeric, with its active polyphenol curcumin, has been used as anti-inflammatory remedy in traditional Asian medicine for centuries. Many cellular targets of curcumin have been identified, but how such a wide range of targets can be affected by a single compound is unclear. Here, we identified curcumin as a pro-drug that requires oxidative activation into reactive metabolites to exert anti-inflammatory activities. Synthetic curcumin analogs that undergo oxidative transformation potently inhibited the pro-inflammatory transcription factor nuclear factor κB (NF-κB), whereas stable, non-oxidizable analogs were less active, with a correlation coefficient (R²) of IC₅₀versus log of autoxidation rate of 0.75. Inhibition of glutathione biosynthesis, which protects cells from reactive metabolites, increased the potency of curcumin and decreased the amount of curcumin-glutathione adducts in cells. Oxidative metabolites of curcumin adducted to and inhibited the inhibitor of NF-κB kinase subunit β (IKKβ), an activating kinase upstream of NF-κB. An unstable, alkynyl-tagged curcumin analog yielded abundant adducts with cellular protein that were decreased by pretreatment with curcumin or an unstable analog but not by a stable analog. Bioactivation of curcumin occurred readily in vitro, which may explain the wide range of cellular targets, but if bioactivation is insufficient in vivo, it may also help explain the inconclusive results in human studies with curcumin so far. We conclude that the paradigm of metabolic bioactivation uncovered here should be considered for the evaluation and design of clinical trials of curcumin and other polyphenols of medicinal interest.

Potential roles of chemical degradation in the biological activities of curcumin

Substantial pre-clinical and human studies have shown that curcumin, a dietary compound from turmeric, has a variety of health-promoting biological activities. A better understanding of the biochemical mechanisms for the health-promoting effects of curcumin could facilitate the development of effective strategies for disease prevention. Recent studies have shown that in aqueous buffer, curcumin rapidly degrades and leads to formation of various degradation products. In this review, we summarized and discussed the biological activities of chemical degradation products of curcumin, including alkaline hydrolysis products (such as ferulic acid, vanillin, ferulaldehyde, and feruloyl methane), and autoxidation products (such as bicyclopentadione). Though many of these degradation products are biologically active, they are substantially less-active compared to curcumin, supporting that chemical degradation has a limited contribution to the biological activities of curcumin.

Chemical exposure and infant leukaemia: development of an adverse outcome pathway (AOP) for aetiology and risk assessment research

Infant leukaemia (<1 year old) is a rare disease of an in utero origin at an early phase of foetal development. Rearrangements of the mixed-lineage leukaemia (MLL) gene producing abnormal fusion proteins are the most frequent genetic/molecular findings in infant B cell-acute lymphoblastic leukaemia. In small epidemiological studies, mother/foetus exposures to some chemicals including pesticides have been associated with infant leukaemia; however, the strength of evidence and power of these studies are weak at best. Experimental in vitro or in vivo models do not sufficiently recapitulate the human disease and regulatory toxicology studies are unlikely to capture this kind of hazard. Here, we develop an adverse outcome pathway (AOP) based substantially on an analogous disease-secondary acute leukaemia caused by the topoisomerase II (topo II) poison etoposide-and on cellular and animal models. The hallmark of the AOP is the formation of MLL gene rearrangements via topo II poisoning, leading to fusion genes and ultimately acute leukaemia by global (epi)genetic dysregulation. The AOP condenses molecular, pathological, regulatory and clinical knowledge in a pragmatic, transparent and weight of evidence-based framework. This facilitates the interpretation and integration of epidemiological studies in the process of risk assessment by defining the biologically plausible causative mechanism(s). The AOP identified important gaps in the knowledge relevant to aetiology and risk assessment, including the specific embryonic target cell during the short and spatially restricted period of susceptibility, and the role of (epi)genetic features modifying the initiation and progression of the disease. Furthermore, the suggested AOP informs on a potential Integrated Approach to Testing and Assessment to address the risk caused by environmental chemicals in the future.

Oxidative metabolism of curcumin-glucuronide by peroxidases and isolated human leukocytes

Conjugation with glucuronic acid is a prevalent metabolic pathway of orally administrated curcumin, the bioactive diphenol of the spice turmeric. The major in vitro degradation reaction of curcumin is autoxidative transformation resulting in oxygenation and cyclization of the heptadienedione chain to form cyclopentadione derivatives. Here we show that curcumin-glucuronide is much more stable than curcumin, degrading about two orders of magnitude slower. Horseradish peroxidase-catalyzed oxidation of curcumin-glucuronide occurred at about 80% of the rate with curcumin, achieving efficient transformation. Using LC-MS and NMR analyses the major products of oxidative transformation were identified as glucuronidated bicyclopentadione diastereomers. Cleavage into vanillin-glucuronide accounted for about 10% of the products. Myeloperoxidase and lactoperoxidase oxidized curcumin-glucuronide whereas tyrosinase and xanthine oxidase were not active. Phorbol ester-activated primary human leukocytes showed increased oxidative transformation of curcumin-glucuronide which was inhibited by the peroxidase inhibitor sodium azide. These studies provide evidence that the glucuronide of curcumin is not an inert product and may undergo further enzymatic and non-enzymatic metabolism. Oxidative transformation by leukocyte myeloperoxidase may represent a novel metabolic pathway of curcumin and its glucuronide conjugate.

Effects of Stable Degradation Products of Curcumin on Cancer Cell Proliferation and Inflammation

Curcumin is among the most promising dietary compounds for cancer prevention. However, curcumin rapidly degrades in aqueous buffer at physiological pH, making it difficult to understand whether the effects of curcumin are from curcumin itself or its degradation products. Here we studied the antiproliferative and anti-inflammatory effects of curcumin degradation products, including its total degradation products (a mixture containing all stable degradation products of curcumin) and bicyclopentadione (a dominant stable degradation compound of curcumin). Curcumin potently modulated cell proliferation, progression of cell cycle, and apoptosis in MC38 colon cancer cells and inhibited lipopolysaccharide (LPS)-induced inflammatory responses and NF-κB signaling in RAW 264.7 macrophage cells. In contrast, neither the total degradation products of curcumin nor bicyclopentadione had such effects. For example, after 24 h of treatment in MC38 colon cancer cells, 5 μg/mL curcumin inhibited 39.2 ± 1.8% of cell proliferation, whereas its degradation products were inactive. Together, these results suggest that the stable chemical degradation products of curcumin are not likely to play a major role in mediating the biological activities of curcumin.

Novel trifluoromethylated 9-amino-3,4-dihydroacridin-1(2H)-ones act as covalent poisons of human topoisomerase IIα

A number of topoisomerase II-targeted anticancer drugs, including amsacrine, utilize an acridine or related aromatic core as a scaffold. Therefore, to further explore the potential of acridine-related compounds to act as topoisomerase II poisons, we synthesized a series of novel trifluoromethylated 9-amino-3,4-dihydroacridin-1(2H)-one derivatives and examined their ability to enhance DNA cleavage mediated by human topoisomerase IIα. Derivatives containing a H, Cl, F, and Br at C7 enhanced enzyme-mediated double-stranded DNA cleavage ∼5.5- to 8.5-fold over baseline, but were less potent than amsacrine. The inclusion of an amino group at C9 was critical for activity. The compounds lost their activity against topoisomerase IIα in the presence of a reducing agent, displayed no activity against the catalytic core of topoisomerase IIα, and inhibited DNA cleavage when incubated with the enzyme prior to the addition of DNA. These findings strongly suggest that the compounds act as covalent, rather than interfacial, topoisomerase II poisons.

Determining whether curcumin degradation/condensation is actually bioactivation (Review)

Curcumin has been shown to exert therapeutic or protective effects against a variety of diseases, such as cancer, pulmonary diseases, neurological, liver, metabolic, autoimmune, cardiovascular diseases and numerous other chronic ailments. Over 116 clinical studies on curcumin in humans were registered with the US National Institutes of Health in 2015. However, it is mystifying how curcumin can be so effective in the treatment of many diseases since it has very low water solubility and bioavailability. Furthermore, curcumin is not stable under various conditions; its degradation or condensation into different bioactive compounds may be responsible for its biological activities rather than curcumin itself. In this review, we provide evidence of curcumin degradation and condensation into different compounds which have or may have health benefits themselves. Literature reviews strongly suggest that these molecules contribute to the observed health benefits, rather than curcumin itself.

Redox modulation of curcumin stability: Redox active antioxidants increase chemical stability of curcumin

SCOPE

Substantial studies have shown that curcumin, a dietary compound from turmeric, has beneficial effects on many diseases. However, curcumin rapidly degrades at physiological pH, making it difficult to interpret whether the observed actions of curcumin are from curcumin itself or its degradation products. Therefore, it is important to better understand the mechanisms involved in curcumin degradation and the roles of degradation in its biological actions.

METHODS AND RESULTS

Here, we show that a series of redox active antioxidants with diverse chemical structures, including gallic acid, ascorbate (vitamin C), tert-butylhydroquinone (TBHQ), caffeic acid, rosmarinic acid, and Trolox (a water-soluble analog of vitamin E), dramatically increased curcumin stability in phosphate buffer at physiological pH. When treated in basal cell culture medium in MC38 colon cancer cells, curcumin rapidly degraded with a half-life of several minutes and showed a weak antiproliferative effect; co-addition of antioxidants enhanced stability and antiproliferative effect of curcumin. Finally, co-administration of antioxidant significantly increased plasma level of curcumin in animal models.

CONCLUSION

Together, these studies strongly suggest that a redox-dependent mechanism plays a critical role in mediating curcumin degradation. In addition, curcumin itself, instead of its degradation products, is largely responsible for the observed biological actions of curcumin.

Effects of Secondary Metabolites from the Fungus Septofusidium berolinense on DNA Cleavage Mediated by Human Topoisomerase IIα

Two metabolites from the ascomycete fungus Septofusidium berolinense were recently identified as having antineoplastic activity [Ekiz et al. (2015) J. Antibiot. , DOI: 10.1038/ja.2015.84]. However, the basis for this activity is not known. One of the compounds [3,6-dihydroxy-2-propylbenzaldehyde (GE-1)] is a hydroquinone, and the other [2-hydroxymethyl-3-propylcyclohexa-2,5-diene-1,4-dione (GE-2)] is a quinone. Because some hydroquinones and quinones act as topoisomerase II poisons, the effects of GE-1 and GE-2 on DNA cleavage mediated by human topoisomerase IIα were assessed. GE-2 enhanced DNA cleavage ∼4-fold and induced scission with a site specificity similar to that of the anticancer drug etoposide. Similar to other quinone-based topoisomerase II poisons, GE-2 displayed several hallmark characteristics of covalent topoisomerase II poisons, including (1) the inability to poison a topoisomerase IIα construct that lacks the N-terminal domain, (2) the inhibition of DNA cleavage when the compound was incubated with the enzyme prior to the addition of plasmid, and (3) the loss of poisoning activity in the presence of a reducing agent. In contrast to GE-2, GE-1 did not enhance DNA cleavage mediated by topoisomerase IIα except at very high concentrations. However, the activity and potency of the metabolite were dramatically enhanced under oxidizing conditions. These results suggest that topoisomerase IIα may play a role in mediating the cytotoxic effects of these fungal metabolites.

Curcumin-treated cancer cells show mitotic disturbances leading to growth arrest and induction of senescence phenotype

Cellular senescence is recognized as a potent anticancer mechanism that inhibits carcinogenesis. Cancer cells can also undergo senescence upon chemo- or radiotherapy. Curcumin, a natural polyphenol derived from the rhizome of Curcuma longa, shows anticancer properties both in vitro and in vivo. Previously, we have shown that treatment with curcumin leads to senescence of human cancer cells. Now we identified the molecular mechanism underlying this phenomenon. We observed a time-dependent accumulation of mitotic cells upon curcumin treatment. The time-lapse analysis proved that those cells progressed through mitosis for a significantly longer period of time. A fraction of cells managed to divide or undergo mitotic slippage and then enter the next phase of the cell cycle. Cells arrested in mitosis had an improperly formed mitotic spindle and were positive for γH2AX, which shows that they acquired DNA damage during prolonged mitosis. Moreover, the DNA damage response pathway was activated upon curcumin treatment and the components of this pathway remained upregulated while cells were undergoing senescence. Inhibition of the DNA damage response decreased the number of senescent cells. Thus, our studies revealed that the induction of cell senescence upon curcumin treatment resulted from aberrant progression through the cell cycle. Moreover, the DNA damage acquired by cancer cells, due to mitotic disturbances, activates an important molecular mechanism that determines the potential anticancer activity of curcumin.

Inhibition of human DNA topoisomerase IIα by two novel ellipticine derivatives

Ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole) is an antineoplastic agent that intercalates into DNA and alters topoisomerase II activity. Unfortunately, this compound displays a number of adverse properties. Therefore, to investigate new ellipticine-based compounds for their potential as topoisomerase II-targeted drugs, we synthesized two novel derivatives, N-methyl-5-demethyl ellipticine (ET-1) and 2-methyl-N-methyl-5-demethyl ellipticinium iodide (ET-2). As determined by DNA decatenation and cleavage assays, ET-1 and ET-2 act as catalytic inhibitors of human topoisomerase IIα and are both more potent than the parent compound. Neither compound impairs the ability of the type II enzyme to bind its DNA substrate. Finally, the potency of ET-1 and ET-2 as catalytic inhibitors of topoisomerase IIα appears to be related to their ability to intercalate into the double helix.

Co-delivery of doxorubicin and curcumin by pH-sensitive prodrug nanoparticle for combination therapy of cancer

Ample attention has focused on cancer drug delivery via prodrug nanoparticles due to their high drug loading property and comparatively lower side effects. In this study, we designed a PEG-DOX-Cur prodrug nanoparticle for simultaneous delivery of doxorubicin (DOX) and curcumin (Cur) as a combination therapy to treat cancer. DOX was conjugated to PEG by Schiff's base reaction. The obtained prodrug conjugate could self-assemble in water at pH 7.4 into nanoparticles (PEG-DOX NPs) and encapsulate Cur into the core through hydrophobic interaction (PEG-DOX-Cur NPs). When the PEG-DOX-Cur NPs are internalized by tumor cells, the Schiff's base linker between PEG and DOX would break in the acidic environment that is often observed in tumors, causing disassembling of the PEG-DOX-Cur NPs and releasing both DOX and Cur into the nuclei and cytoplasma of the tumor cells, respectively. Compared with free DOX, free Cur, free DOX-Cur combination, or PEG-DOX NPs, PEG-DOX-Cur NPs exhibited higher anti-tumor activity in vitro. In addition, the PEG-DOX-Cur NPs also showed prolonged blood circulation time, elevated local drug accumulation and increased tumor penetration. Enhanced anti-tumor activity was also observed from the PEG-DOX-Cur-treated animals, demonstrating better tumor inhibitory property of the NPs. Thus, the PEG-DOX-Cur prodrug nanoparticle system provides a simple yet efficient approach of drug delivery for chemotherapy.

Chemical conjugation of 2-hexadecynoic acid to C5-curcumin enhances its antibacterial activity against multi-drug resistant bacteria

The first total synthesis of a C5-curcumin-2-hexadecynoic acid (C5-Curc-2-HDA, 6) conjugate was successfully performed. Through a three-step synthetic route, conjugate 6 was obtained in 13% overall yield and tested for antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) strains. Our results revealed that 6 was active against eight MRSA strains at MICs that range between 31.3 and 62.5 μg/mL. It was found that the presence of 2-hexadecynoic acid (2-HDA, 4) in conjugate 6 increased 4-8-fold its antibacterial activity against MRSA strains supporting our hypothesis that the chemical connection of 4 to C5-curcumin (2) increases the antibacterial activity of 2 against Gram-positive bacteria. Combinational index (CIn) values that range between 1.6 and 2.3 were obtained when eight MRSA strains were treated with an equimolar mixture of 2 and 4. These results demonstrated that an antagonistic effect is taking place. Finally, it was investigated whether conjugate 6 can affect the replication process of S. aureus, since this compound inhibited the supercoiling activity of the S. aureus DNA gyrase at minimum inhibitory concentrations (MIC) of 250 μg/mL (IC50=100.2±13.9 μg/mL). Moreover, it was observed that the presence of 4 in conjugate 6 improves the anti-topoisomerase activity of 2 towards S. aureus DNA gyrase, which is in agreement with results obtained from antibacterial susceptibility tests involving MRSA strains.

Degradation of Curcumin: From Mechanism to Biological Implications

Curcumin is the main bioactive ingredient in turmeric extract and widely consumed as part of the spice mix curry or as a dietary supplement. Turmeric has a long history of therapeutic application in traditional Asian medicine. Biomedical studies conducted in the past two decades have identified a large number of cellular targets and effects of curcumin. In vitro curcumin rapidly degrades in an autoxidative transformation to diverse chemical species, the formation of which has only recently been appreciated. This paper discusses how the degradation and metabolism of curcumin, through products and their mechanism of formation, provide a basis for the interpretation of preclinical data and clinical studies. It is suggested that the previously unrecognized diversity of its degradation products could be an important factor in explaining the polypharmacology of curcumin.

Effects of Olive Metabolites on DNA Cleavage Mediated by Human Type II Topoisomerases

Several naturally occurring dietary polyphenols with chemopreventive or anticancer properties are topoisomerase II poisons. To identify additional phytochemicals that enhance topoisomerase II-mediated DNA cleavage, a library of 341 Mediterranean plant extracts was screened for activity against human topoisomerase IIα. An extract from Phillyrea latifolia L., a member of the olive tree family, displayed high activity against the human enzyme. On the basis of previous metabolomics studies, we identified several polyphenols (hydroxytyrosol, oleuropein, verbascoside, tyrosol, and caffeic acid) as potential candidates for topoisomerase II poisons. Of these, hydroxytyrosol, oleuropein, and verbascoside enhanced topoisomerase II-mediated DNA cleavage. The potency of these olive metabolites increased 10–100-fold in the presence of an oxidant. Hydroxytyrosol, oleuropein, and verbascoside displayed hallmark characteristics of covalent topoisomerase II poisons. (1) The activity of the metabolites was abrogated by a reducing agent. (2) Compounds inhibited topoisomerase II activity when they were incubated with the enzyme prior to the addition of DNA. (3) Compounds were unable to poison a topoisomerase IIα construct that lacked the N-terminal domain. Because hydroxytyrosol, oleuropein, and verbascoside are broadly distributed across the olive family, extracts from the leaves, bark, and fruit of 11 olive tree species were tested for activity against human topoisomerase IIα. Several of the extracts enhanced enzyme-mediated DNA cleavage. Finally, a commercial olive leaf supplement and extra virgin olive oils pressed from a variety of Olea europea subspecies enhanced DNA cleavage mediated by topoisomerase IIα. Thus, olive metabolites appear to act as topoisomerase II poisons in complex formulations intended for human dietary consumption.

Redox nanoparticles inhibit curcumin oxidative degradation and enhance its therapeutic effect on prostate cancer

Curcumin is a phytochemical with diverse molecular targets and is well known for its anti-tumor potential. However, it has limited application in cancer therapy because curcumin undergoes rapid oxidative degradation at physiological conditions resulting in poor stability and bio-availability. In this study, we were able to suppress curcumin's oxidative degradation by encapsulating it in a nanoparticle that also acts as a radical scavenger. We prepared curcumin-loaded pH-sensitive redox nanoparticles (RNP(N)) by self-assembling amphiphilic block copolymers conjugated with reactive oxygen species (ROS) scavenging nitroxide radicals to ensure the delivery of minimally degraded curcumin to target regions. In vitro analysis confirmed that the entrapment of both curcumin and nitroxide radicals in the hydrophobic core of RNP(N) suppressed curcumin degradation in conditions mimicking the physiological environment. Evaluation of apoptosis-related molecules in the cells, such as ceramides, caspases, apoptosis-inducing factor, and acid ceramidase revealed that curcumin loaded RNP(N) induced strong apoptosis compared to free curcumin. Lastly, intravenous injection of curcumin loaded RNP(N) suppressed tumor growth in vivo, which is due to the increased bio-availability and significant ROS scavenging at tumor sites. These results demonstrated that RNP(N) is a promising drug carrier with unique ROS-scavenging abilities, and it is able to overcome the crucial hurdle of curcumin's limitations to enhance its therapeutic potential.

Oxidative Transformation of Demethoxy- and Bisdemethoxycurcumin: Products, Mechanism of Formation, and Poisoning of Human Topoisomerase IIα

Extracts from the rhizome of the turmeric plant are widely consumed as anti-inflammatory dietary supplements. Turmeric extract contains the three curcuminoids, curcumin (≈80% relative abundance), demethoxycurcumin (DMC; ≈15%), and bisdemethoxycurcumin (BDMC; ≈5%). A distinct feature of pure curcumin is its instability at physiological pH, resulting in rapid autoxidation to a bicyclopentadione within 10-15 min. Here, we describe oxidative transformation of turmeric extract, DMC, and BDMC and the identification of their oxidation products using LC-MS and NMR analyses. DMC autoxidized over the course of 24 h to the expected bicyclopentadione diastereomers. BDMC was resistant to autoxidation, and oxidative transformation required catalysis by horseradish peroxidase and H2O2 or potassium ferricyanide. The product of BDMC oxidation was a stable spiroepoxide that was equivalent to a reaction intermediate in the autoxidation of curcumin. The ability of DMC and BDMC to poison recombinant human topoisomerase IIα was significantly increased in the presence of potassium ferricyanide, indicating that oxidative transformation was required to achieve full DNA cleavage activity. DMC and BDMC are less prone to autoxidation than curcumin and contribute to the enhanced stability of turmeric extract at physiological pH. Their oxidative metabolites may contribute to the biological effects of turmeric extract.

Synthesis of novel C5-curcuminoid-fatty acid conjugates and mechanistic investigation of their anticancer activity

The first synthesis of C5-curcumin-fatty acid (C5-Curc-FA) conjugates was successfully performed. Through a two-step synthetic route, 10 analogs were synthesized for a structure-activity relationship (SAR) study. It was found that C5-Curc-FA conjugates containing either decanoic acid or palmitic acid moieties were cytotoxic against colorectal adenocarcinoma cell (CCL-229) at IC50s ranging from 22.5 to 56.1μg/mL, being 5c the most active C5-Curc-FA conjugate. Our results strongly suggests that a decanoic acid moiety at the meta position in C5-Curc-FA conjugates is important for their anticancer activity effect. Possible mechanisms for the anticancer activity of C5-Curc-FA conjugates were also investigated including apoptosis induction, mitochondrial damage and caspases activation. It was shown that 5c inhibited the luminescence activity of NFκB, a key signaling molecule involved in cell apoptosis and cell proliferation, at IC50=18.2μg/mL. In addition, it was demonstrated that 5c displayed significant apoptotic effect at GI50=46.0μg/mL in colorectal adenocarcinoma cell line (ATCC CCL-222), which can be explained by the significant mitochondrial membrane permeabilization and caspases 3 and 7 activation effect of 5c. Finally, it was investigated that C5-Curc-FA conjugates can affect the replication process of cancer cells, since compounds 5c, 5e, and 6c inhibited the relaxing activity of the human DNA topoisomerase I at minimum inhibitory concentrations (MICs) that range from 50 to 250μg/mL. Our results strongly support the hypothesis that the inhibition of both NFκB and DNA topoisomerase I by C5-Curc-FA conjugates is associated with their anticancer activity.

Unraveling curcumin degradation: autoxidation proceeds through spiroepoxide and vinylether intermediates en route to the main bicyclopentadione

Curcumin is a dietary anti-inflammatory and chemopreventive agent consisting of two methoxyphenol rings connected by a conjugated heptadienedione chain. Curcumin is unstable at physiological pH and rapidly degrades in an autoxidation reaction to a major bicyclopentadione product in which the 7-carbon chain has undergone oxygenation and double cyclization. Early degradation products (but not the final bicyclopentadione) mediate topoisomerase poisoning and possibly many other activities of curcumin, but it is not known how many and what autoxidation products are formed, nor their mechanism of formation. Here, using [(14)C2]curcumin as a tracer, seven novel autoxidation products, including two reaction intermediates, were isolated and identified using one- and two-dimensional NMR and mass spectrometry. The unusual spiroepoxide and vinylether reaction intermediates are precursors to the final bicyclopentadione product. A mechanism for the autoxidation of curcumin is proposed that accounts for the addition and exchange of oxygen that have been determined using (18)O2 and H2(18)O. Several of the by-products are formed from an endoperoxide intermediate via reactions that are well precedented in lipid peroxidation. The electrophilic spiroepoxide intermediate formed a stable adduct with N-acetylcysteine, suggesting that oxidative transformation is required for biological effects mediated by covalent adduction to protein thiols. The spontaneous autoxidation distinguishes curcumin among natural polyphenolic compounds of therapeutic interest; the formation of chemically diverse reactive and electrophilic products provides a novel paradigm for understanding the polypharmacological effects of curcumin.

Catalytic core of human topoisomerase IIα: insights into enzyme-DNA interactions and drug mechanism

Coordination between the N-terminal gate and the catalytic core of topoisomerase II allows the proper capture, cleavage, and transport of DNA during the catalytic cycle. Because the activities of these domains are tightly linked, it has been difficult to discern their individual contributions to enzyme-DNA interactions and drug mechanism. To further address the roles of these domains, we analyzed the activity of the catalytic core of human topoisomerase IIα. The catalytic core and the wild-type enzyme both maintained higher levels of cleavage with negatively (as compared to positively) supercoiled plasmid, indicating that the ability to distinguish supercoil handedness is embedded within the catalytic core. However, the catalytic core alone displayed little ability to cleave DNA substrates that did not intrinsically provide the enzyme with a transport segment (i.e., substrates that did not contain crossovers). Finally, in contrast to interfacial topoisomerase II poisons, covalent poisons did not enhance DNA cleavage mediated by the catalytic core. This distinction allowed us to further characterize the mechanism of etoposide quinone, a drug metabolite that functions primarily as a covalent poison. Etoposide quinone retained some ability to enhance DNA cleavage mediated by the catalytic core, indicating that it still can function as an interfacial poison. These results further define the distinct contributions of the N-terminal gate and the catalytic core to topoisomerase II function. The catalytic core senses the handedness of DNA supercoils during cleavage, while the N-terminal gate is critical for capturing the transport segment and for the activity of covalent poisons.

Upregulation of extrinsic apoptotic pathway in curcumin-mediated antiproliferative effect on human pancreatic carcinogenesis

Pancreatic cancer is one of the most lethal human cancers, with almost identical incidence and mortality rates. Curcumin, derived from the rhizome of Curcuma longa, has a long history of use as coloring agent and for a wide variety of disorders. Here, the antiproliferative activity of curcumin and its modulatory effect on gene expression of pancreatic cancer cell lines were investigated. The effect of curcumin on cellular proliferation and viability was monitored by sulphurhodamine B assay. Apoptotic effect was evaluated by flow cytometry and further confirmed by measuring amount of cytoplasmic histone-associated DNA fragments. Analysis of gene expression was performed with and without curcumin treatment using microarray expression profiling techniques. Array results were confirmed by real-time PCR. ingenuity pathway analysis (IPA) has been used to classify the list of differentially expressed genes and to indentify common biomarkergenes modulating the chemopreventive effect of curcumin. Results showed that curcumin induces growth arrest and apoptosis in pancreatic cancer cell lines. Its effect was more obvious on the highly COX-2 expressing cell line. Additionally, the expression of 366 and 356 cancer-related genes, involved in regulation of apoptosis, cell cycle, metastasis, was significantly altered after curcumin treatment in BxPC-3 and MiaPaCa-2 cells, respectively. Our results suggested that up-regulation of the extrinsic apoptotic pathway was among signaling pathways modulating the growth inhibitory effects of curcumin on pancreatic cancer cells. Curcumin effect was mediated through activation of TNFR, CASP 8, CASP3, BID, BAX, and down-regulation of NFκB, NDRG 1, and BCL2L10 genes.