Curcumin inhibits the proteasome activity in human colon cancer cells in vitro and in vivo

The ubiquitin/proteasome system-dependent control of mitochondrial steps in apoptosis

Insights into the role of ubiquitin-dependent signaling in the regulation of apoptosis have provided one of the most significant breakthroughs in recent years for cell death research. It has been revealed that all steps in the apoptotic cascade, including transcriptional regulation of apoptotic gene expression, outer mitochondrial membrane permeabilization and caspase activation, are under the control of the ubiquitin/proteasome system. This makes ubiquitin signaling one on the most critical life and death decision checkpoints in mammalian cells. Here we discuss the ubiquitylation-dependent regulation of the mitochondrial steps in apoptosis, with a focus on the role of regulated protein degradation in this process. The newly identified ubiquitylation-dependent processes in the Bcl-2 family-regulated outer mitochondrial membrane permeabilization, as well as the role of mitochondria-associated ubiquitin ligases and other molecular components of the ubiquitin/proteasome system in the control of mitochondrial steps in apoptosis, are discussed.

Chalcone-based small-molecule inhibitors attenuate malignant phenotype via targeting deubiquitinating enzymes

The ubiquitin-proteasome system (UPS) is usurped by many if not all cancers to regulate their survival, proliferation, invasion, angiogenesis and metastasis. Bioflavonoids curcumin and chalcones exhibit anti-neoplastic selectivity through inhibition of the 26S proteasome-activity within the UPS. Here, we provide evidence for a novel mechanism of action of chalcone-based derivatives AM146, RA-9 and RA-14, which exert anticancer activity by targeting deubiquitinating enzymes (DUB) without affecting 20S proteasome catalytic-core activity. The presence of the α,β-unsaturated carbonyl group susceptible to nucleophilic attack from the sulfhydryl of cysteines in the active sites of DUB determines the capacity of novel small-molecules to act as cell-permeable, partly selective DUB inhibitors and induce rapid accumulation of polyubiquitinated proteins and deplete the pool of free ubiquitin. These chalcone-derivatives directly suppress activity of DUB UCH-L1, UCH-L3, USP2, USP5 and USP8, which are known to regulate the turnover and stability of key regulators of cell survival and proliferation. Inhibition of DUB-activity mediated by these compounds downregulates cell-cycle promoters, e.g., cyclin D1 and upregulates tumor suppressors p53, p27(Kip1) and p16(Ink4A). These changes are associated with arrest in S-G 2/M, abrogated anchorage-dependent growth and onset of apoptosis in breast, ovarian and cervical cancer cells without noticeable alterations in primary human cells. Altogether, this work provides evidence of antitumor activity of novel chalcone-based derivatives mediated by their DUB-targeting capacity; supports the development of pharmaceuticals to directly target DUB as a most efficient strategy compared with proteasome inhibition and also provides a clear rationale for the clinical evaluation of these novel small-molecule DUB inhibitors.

Proteasome inhibitors

In May 2003, the US Food and Drug Administration (FDA) granted accelerated approval for the use of the first-in-class proteasome inhibitor bortezomib as a third-line therapy in multiple myeloma, and the European Union followed suit a year later. Bortezomib has subsequently been approved for multiple myeloma as a second-line treatment on its own and as a first-line therapy in combination with an alkylating agent and a corticosteroid. Furthermore, bortezomib has also been approved as a second-line therapy for mantle cell lymphoma. In this chapter, the focus is on the current clinical research on bortezomib, its adverse effects, and the resistance of multiple myeloma patients to bortezomib-based therapy. The various applications of bortezomib in different diseases and recent advances in the development of a new generation of inhibitors that target the proteasome or other parts of the ubiquitin-proteasome system are also reviewed.

Cancer cell signaling pathways targeted by spice-derived nutraceuticals

Extensive research within the last half a century has revealed that cancer is caused by dysregulation of as many as 500 different gene products. Most natural products target multiple gene products and thus are ideally suited for prevention and treatment of various chronic diseases, including cancer. Dietary agents such as spices have been used extensively in the Eastern world for a variety of ailments for millennia, and five centuries ago they took a golden journey to the Western world. Various spice-derived nutraceuticals, including 1'-acetoxychavicol acetate, anethole, capsaicin, cardamonin, curcumin, dibenzoylmethane, diosgenin, eugenol, gambogic acid, gingerol, thymoquinone, ursolic acid, xanthohumol, and zerumbone derived from galangal, anise, red chili, black cardamom, turmeric, licorice, fenugreek, clove, kokum, ginger, black cumin, rosemary, hop, and pinecone ginger, respectively, are the focus of this review. The modulation of various transcription factors, growth factors, protein kinases, and inflammatory mediators by these spice-derived nutraceuticals are described. The anticancer potential through the modulation of various targets is also the subject of this review. Although they have always been used to improve taste and color and as a preservative, they are now also used for prevention and treatment of a wide variety of chronic inflammatory diseases, including cancer.

Semisynthetic neoboutomellerone derivatives as ubiquitin-proteasome pathway inhibitors

The interesting pharmacological properties of neoboutomellerones 1 and 2 were the basis for the assembly of a small library of analogues consisting of natural products isolated from the plant Neoboutonia melleri and of semisynthetic derivatives. As the two enone systems (C23-C24a and C1-C3) and the two hydroxyls groups (C22 and C26) of neoboutomellerones are required for activity, modifications were focused on these functional groups. Biological evaluation by using a cellular assay for proteasome activity provided clues regarding the mechanism of action of these natural products and synthetic derivatives. Certain neoboutomellerone derivatives inhibited the proliferation of human WM-266-4 melanoma tumor cells at submicromolar concentration and warrant evaluation as anticancer agents.

Newly synthesized curcumin derivatives: crosstalk between chemico-physical properties and biological activity

New curcumin analogues (ester and acid series) were synthesized with the aim to improve the chemical stability in physiological conditions and potential anticancer activity. Cytotoxicity against different tumorigenic cell lines (human ovarian carcinoma cells -2008, A2780, C13*, and A2780/CP, and human colon carcinoma cells HCT116 and LoVo) was tested to evaluate cellular specificity and activity. Physico-chemical properties such as acidity, lipophilicity, kinetic stability, and free radical scavenging activity were investigated to shed light on the structure-activity relationship and provide new attractive candidates for drug development. Most of ester derivatives show IC(50) values lower than curcumin and exhibit selectivity against colon carcinoma cells. Especially they are extremely active after 24 h exposure showing enhanced inhibitory effect on cell viability. The best performances of ester curcuminoids could be ascribed to their high lipophilicity that favors a greater and faster cellular uptake overcoming their apparently higher instability in physiological condition.

Curcumin enhanced antiproliferative effect of mitomycin C in human breast cancer MCF-7 cells in vitro and in vivo

AIM

To investigate the efficacy of mitomycin C (MMC) in combination with curcumin in suppressing human breast cancer in vitro and in vivo.

METHODS

Human breast cancer MCF-7 cells were used. Cell viability was measured using MTT assay. The cell cycle phase was detected with flow cytometric analysis. Cell cycle-associated proteins were examined using Western blot analysis. MCF-7 breast cancer xenografts were established to monitor tumor growth and cell cycle-associated protein expression.

RESULTS

Curcumin inhibited MCF-7 breast cancer cell viability in a concentration-dependent manner (IC(50) value=40 μmol/L). Similarly, MMC inhibited the cell viability with an IC(50) value of 5 μmol/L. Combined treatment of MMC and curcumin showed a synergistic antiproliferative effect. In the presence of curcumin (40 μmol/L), the IC(50) value of MMC was reduced to 5 μmol/L. In MCF-7 xenografts, combined administration of curcumin (100 mg/kg) and MMC (1-2 mg/kg) for 4 weeks produced significantly greater inhibition on tumor growth than either treatment alone. The combined treatment resulted in significantly greater G(1) arrest than MMC or curcumin alone. Moreover, the cell cycle arrest was associated with inhibition of cyclin D1, cyclin E, cyclin A, cyclin-dependent kinase 2 (CDK2) and CDK4, along with the induction of the cell cycle inhibitor p21 and p27 both in MCF-7 cells and in MCF-7 xenografts. These proteins were regulated through p38 MAPK pathway.

CONCLUSION

The results suggest that the combination of MMC and curcumin inhibits MCF-7 cell proliferation and cell cycle progression in vitro and in vivo via the p38 MAPK pathway.

Sensitizing human multiple myeloma cells to the proteasome inhibitor bortezomib by novel curcumin analogs

The proteasome plays a vital role in the degradation of proteins involved in several pathways including the cell cycle, cellular proliferation and apoptosis and is a validated target in cancer treatment. Bortezomib (Velcade^®, PS-341) is the first US FDA approved proteasome inhibitor anticancer drug used in the treatment of refractory multiple myeloma. In spite of its improved efficacy compared to alternative therapies, about 60% of patients do not respond to bortezomib due to the emergence of resistance. We hypothesized that novel small molecules could enhance the proteasome-inhibitory and anticancer activities of bortezomib in resistant multiple myeloma cells in vitro and in vivo. The dietary polyphenol curcumin has been shown to exert anti-cancer activity in several cancer cell lines, but the effects of curcumin in solid tumors have been modest primarily due to poor water solubility and poor bioavailability in tissues remote from the gastrointestinal tract. Here we show that the water-soluble analog of curcumin #12, but not curcumin, in combination with bortezomib could enhance the proteasome-inhibitory effect in multiple myeloma cells. Furthermore, the sensitivity of the myeloma cells to cytotoxic killing in the presence of otherwise sublethal concentrations of bortezomib was enhanced by incubation with the curcumin analog #12. These findings justify further investigation into those combinations that may yield potential therapeutic benefit.

Multitargeting by curcumin as revealed by molecular interaction studies

Curcumin (diferuloylmethane), the active ingredient in turmeric (Curcuma longa), is a highly pleiotropic molecule with anti-inflammatory, anti-oxidant, chemopreventive, chemosensitization, and radiosensitization activities. The pleiotropic activities attributed to curcumin come from its complex molecular structure and chemistry, as well as its ability to influence multiple signaling molecules. Curcumin has been shown to bind by multiple forces directly to numerous signaling molecules, such as inflammatory molecules, cell survival proteins, protein kinases, protein reductases, histone acetyltransferase, histone deacetylase, glyoxalase I, xanthine oxidase, proteasome, HIV1 integrase, HIV1 protease, sarco (endo) plasmic reticulum Ca(2+) ATPase, DNA methyltransferases 1, FtsZ protofilaments, carrier proteins, and metal ions. Curcumin can also bind directly to DNA and RNA. Owing to its β-diketone moiety, curcumin undergoes keto-enol tautomerism that has been reported as a favorable state for direct binding. The functional groups on curcumin found suitable for interaction with other macromolecules include the α, β-unsaturated β-diketone moiety, carbonyl and enolic groups of the β-diketone moiety, methoxy and phenolic hydroxyl groups, and the phenyl rings. Various biophysical tools have been used to monitor direct interaction of curcumin with other proteins, including absorption, fluorescence, Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy, surface plasmon resonance, competitive ligand binding, Forster type fluorescence resonance energy transfer (FRET), radiolabeling, site-directed mutagenesis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), immunoprecipitation, phage display biopanning, electron microscopy, 1-anilino-8-naphthalene-sulfonate (ANS) displacement, and co-localization. Molecular docking, the most commonly employed computational tool for calculating binding affinities and predicting binding sites, has also been used to further characterize curcumin's binding sites. Furthermore, the ability of curcumin to bind directly to carrier proteins improves its solubility and bioavailability. In this review, we focus on how curcumin directly targets signaling molecules, as well as the different forces that bind the curcumin-protein complex and how this interaction affects the biological properties of proteins. We will also discuss various analogues of curcumin designed to bind selective targets with increased affinity.

Stressing the ubiquitin-proteasome system without 20S proteolytic inhibition selectively kills cervical cancer cells

Cervical cancer cells exhibit an increased requirement for ubiquitin-dependent protein degradation associated with an elevated metabolic turnover rate, and for specific signaling pathways, notably HPV E6-targeted degradation of p53 and PDZ proteins. Natural compounds with antioxidant properties including flavonoids and triterpenoids hold promise as anticancer agents by interfering with ubiquitin-dependent protein degradation. An increasing body of evidence indicates that their α-β unsaturated carbonyl system is the molecular determinant for inhibition of ubiquitin-mediated protein degradation up-stream of the catalytic sites of the 20S proteasome. Herein we report the identification and characterization of a new class of chalcone-based, potent and cell permeable chemical inhibitors of ubiquitin-dependent protein degradation, and a lead compound RAMB1. RAMB1 inhibits ubiquitin-dependent protein degradation without compromising the catalytic activities of the 20S proteasome, a mechanism distinct from that of Bortezomib. Treatment of cervical cancer cells with RAMB1 triggers unfolded protein responses, including aggresome formation and Hsp90 stabilization, and increases p53 steady state levels. RAMB1 treatment results in activation of lysosomal-dependent degradation pathways as a mechanism to compensate for increasing levels of poly-ubiquitin enriched toxic aggregates. Importantly, RAMB1 synergistically triggers cell death of cervical cancer cells when combined with the lysosome inhibitor Chloroquine.

Curcumin: the potential for efficacy in gastrointestinal diseases

Curcumin is a naturally occurring phytochemical and an extract of turmeric. Extensive in vitro and in vivo data have paved the way for curcumin to become the subject of clinical trials. Curcumin modulates key signalling pathways important in cellular processes. Numerous mechanisms of action have been elucidated. The potential for clinical efficacy is apparent from benign and malignant disease models. Curcumin has potent anti-inflammatory and anti-neoplastic properties used alone and in combination with standard therapies. Early-phase trials have ascertained pharmacological properties and consistently demonstrate it to be safe and well tolerated. However, bioavailability is limited and efficacious doses have not yet been determined. Evidence of efficacy has been derived from animal models or small clinical trials. There is only finite data supporting the use of curcumin in phase III trials with specific diseases (e.g. ulcerative colitis). However, for the vast majority of conditions additional early-phase studies are required to justify larger trials determining efficacy.

Bortezomib as the first proteasome inhibitor anticancer drug: current status and future perspectives

Targeting the ubiquitin-proteasome pathway has emerged as a rational approach in the treatment of human cancer. Based on positive preclinical and clinical studies, bortezomib was subsequently approved for the clinical use as a front-line treatment for newly diagnosed multiple myeloma patients and for the treatment of relapsed/refractory multiple myeloma and mantle cell lymphoma, for which this drug has become the staple of treatment. The approval of bortezomib by the US Food and Drug Administration (FDA) represented a significant milestone as the first proteasome inhibitor to be implemented in the treatment of malignant disease. Bortezomib has shown a positive clinical benefit either alone or as a part of combination therapy to induce chemo-/radio-sensitization or overcome drug resistance. One of the major mechanisms of bortezomib associated with its anticancer activity is through upregulation of NOXA, which is a proapoptotic protein, and NOXA may interact with the anti-apoptotic proteins of Bcl-2 subfamily Bcl-X(L) and Bcl-2, and result in apoptotic cell death in malignant cells. Another important mechanism of bortezomib is through suppression of the NF-κB signaling pathway resulting in the down-regulation of its anti-apoptotic target genes. Although the majority of success achieved with bortezomib has been in hematological malignancies, its effect toward solid tumors has been less than encouraging. Additionally, the widespread clinical use of bortezomib continues to be hampered by the appearance of dose-limiting toxicities, drug-resistance and interference by some natural compounds. These findings could help guide physicians in refining the clinical use of bortezomib, and encourage basic scientists to generate next generation proteasome inhibitors that broaden the spectrum of efficacy and produce a more durable clinical response in cancer patients. Other desirable applications for the use of proteasome inhibitors include the development of inhibitors against specific E3 ligases, which act at an early step in the ubiquitin-proteasome pathway, and the discovery of less toxic and novel proteasome inhibitors from natural products and traditional medicines, which may provide more viable drug candidates for cancer chemoprevention and the treatment of cancer patients in the future.

The novel curcumin analog FLLL32 decreases STAT3 DNA binding activity and expression, and induces apoptosis in osteosarcoma cell lines

Background

Curcumin is a naturally occurring phenolic compound shown to have a wide variety of antitumor activities; however, it does not attain sufficient blood levels to do so when ingested. Using structure-based design, a novel compound, FLLL32, was generated from curcumin. FLLL32 possesses superior biochemical properties and more specifically targets STAT3, a transcription factor important in tumor cell survival, proliferation, metastasis, and chemotherapy resistance. In our previous work, we found that several canine and human osteosarcoma (OSA) cell lines, but not normal osteoblasts, exhibit constitutive phosphorylation of STAT3. Compared to curcumin, we hypothesized that FLLL32 would be more efficient at inhibiting STAT3 function in OSA cells and that this would result in enhanced downregulation of STAT3 transcriptional targets and subsequent death of OSA cells.

Methods

Human and canine OSA cells were treated with vehicle, curcumin, or FLLL32 and the effects on proliferation (CyQUANT^®), apoptosis (SensoLyte^® Homogeneous AMC Caspase- 3/7 Assay kit, western blotting), STAT3 DNA binding (EMSA), and vascular endothelial growth factor (VEGF), survivin, and matrix metalloproteinase-2 (MMP2) expression (RT-PCR, western blotting) were measured. STAT3 expression was measured by RT-PCR, qRT- PCR, and western blotting.

Results

Our data showed that FLLL32 decreased STAT3 DNA binding by EMSA. FLLL32 promoted loss of cell proliferation at lower concentrations than curcumin leading to caspase-3- dependent apoptosis, as evidenced by PARP cleavage and increased caspase 3/7 activity; this could be inhibited by treatment with the pan-caspase inhibitor Z-VAD-FMK. Treatment of OSA cells with FLLL32 decreased expression of survivin, VEGF, and MMP2 at both mRNA and protein levels with concurrent decreases in phosphorylated and total STAT3; this loss of total STAT3 occurred, in part, via the ubiquitin-proteasome pathway.

Conclusions

These data demonstrate that the novel curcumin analog FLLL32 has biologic activity against OSA cell lines through inhibition of STAT3 function and expression. Future work with FLLL32 will define the therapeutic potential of this compound in vivo.

Dietary fish oil and curcumin combine to modulate colonic cytokinetics and gene expression in dextran sodium sulphate-treated mice

Both fish oil (FO) and curcumin have potential as anti-tumour and anti-inflammatory agents. To further explore their combined effects on dextran sodium sulphate (DSS)-induced colitis, C57BL/6 mice were randomised to four diets (2 × 2 design) differing in fatty acid content with or without curcumin supplementation (FO, FO+2 % curcumin, maize oil (control, MO) or MO+2 % curcumin). Mice were exposed to one or two cycles of DSS in the drinking-water to induce either acute or chronic intestinal inflammation, respectively. FO-fed mice exposed to the single-cycle DSS treatment exhibited the highest mortality (40 %, seventeen of forty-three) compared with MO with the lowest mortality (3 %, one of twenty-nine) (P = 0·0008). Addition of curcumin to MO increased (P = 0·003) mortality to 37 % compared with the control. Consistent with animal survival data, following the one- or two-cycle DSS treatment, both dietary FO and curcumin promoted mucosal injury/ulceration compared with MO. In contrast, compared with other diets, combined FO and curcumin feeding enhanced the resolution of chronic inflammation and suppressed (P < 0·05) a key inflammatory mediator, NF-κB, in the colon mucosa. Mucosal microarray analysis revealed that dietary FO, curcumin and FO plus curcumin combination differentially modulated the expression of genes induced by DSS treatment. These results suggest that dietary lipids and curcumin interact to regulate mucosal homeostasis and the resolution of chronic inflammation in the colon.

Therapeutic potential of curcumin in gastrointestinal diseases

Curcumin, also known as diferuloylmethane, is derived from the plant Curcuma longa and is the active ingredient of the spice turmeric. The therapeutic activities of curcumin for a wide variety of diseases such as diabetes, allergies, arthritis and other chronic and inflammatory diseases have been known for a long time. More recently, curcumin’s therapeutic potential for preventing and treating various cancers is being recognized. As curcumin’s therapeutic promise is being explored more systematically in various diseases, it has become clear that, due to its increased bioavailability in the gastrointestinal tract, curcumin may be particularly suited to be developed to treat gastrointestinal diseases. This review summarizes some of the current literature of curcumin’s anti-inflammatory, anti-oxidant and anti-cancer potential in inflammatory bowel diseases, hepatic fibrosis and gastrointestinal cancers.

Inhibition of tumor cellular proteasome activity by triptolide extracted from the Chinese medicinal plant 'thunder god vine'

AIMS

The molecular mechanisms of triptolide responsible for its antitumor properties are not yet fully understood. The ubiquitin/proteasome system is an important pathway of protein degradation in cells. This study investigated whether triptolide may inhibit proteasomal activity and induce apoptosis in human cancer cells.

MATERIALS AND METHODS

In vitro proteasome inhibition was measured by incubation of a purified 20S proteasome with triptolide. Human breast and prostate cancer cell lines were also treated with different doses of triptolide for different times, followed by measurement of proteasome inhibition (levels of the chymotrypsin-like activity, ubiquitinated proteins and three well-known proteasome target proteins, p27, IκB-α and Bax) and apoptosis induction (caspase-3 activity and PARP cleavage).

RESULTS

Triptolide did not inhibit the chymotrypsin-like activity of purified 20S proteasome. However, treatment of triptolide was able to cause decreased levels of cellular proteasomal chymotrypsin-like activity and accumulation of ubiquitinated proteins and three well-known proteasome target proteins in human breast and prostate cancer cells, associated with apoptosis induction.

CONCLUSION

It is possible that at least one of metabolites of triptolide has proteasome-inhibitory activity.

α,β-Unsaturated carbonyl system of chalcone-based derivatives is responsible for broad inhibition of proteasomal activity and preferential killing of human papilloma virus (HPV) positive cervical cancer cells

Proteasome inhibitors have potential for the treatment of cervical cancer. We describe the synthesis and biological characterization of a new series of 1,3-diphenylpropen-1-one (chalcone) based derivatives lacking the boronic acid moieties of the previously reported chalcone-based proteasome inhibitor 3,5-bis(4-boronic acid benzylidene)-1-methylpiperidin-4-one and bearing a variety of amino acid substitutions on the amino group of the 4-piperidone. Our lead compound 2 (RA-1) inhibits proteasomal activity and has improved dose-dependent antiproliferative and proapoptotic properties in cervical cancer cells containing human papillomavirus. Further, it induces synergistic killing of cervical cancer cell lines when tested in combination with an FDA approved proteasome inhibitor. Exploration of the potential mechanism of proteasomal inhibition by our lead compound using in silico docking studies suggests that the carbonyl group of its oxopiperidine moiety is susceptible to nucleophilic attack by the γ-hydroxythreonine side chain within the catalytic sites of the proteasome.

Synthesis and identification of new 4-arylidene curcumin analogues as potential anticancer agents targeting nuclear factor-κB signaling pathway

A series of curcumin analogues including new 4-arylidene curcumin analogues (4-arylidene-1,7-bisarylhepta-1,6-diene-3,5-diones) were synthesized. Cell growth inhibition assays revealed that most 4-arylidene curcumin analogues can effectively decrease the growth of a panel of lung cancer cells at submicromolar and low micromolar concentrations. High content analysis technology coupled with biochemical studies showed that this new class of 4-arylidene curcumin analogues exhibits significantly improved NF-κB inhibition activity over the parent compound curcumin, at least in part by inhibiting IκB phosphorylation and degradation via IKK blockage; selected 4-arylidene curcumin analogues also reduced the tumorigenic potential of cancer cells in a clonogenic assay.

Targeting tumor proteasome with traditional Chinese medicine

The proteasome is a multicatalytic protease complex whose activity is required for the growth of normal or tumor cells. It has been shown that human cancer cells are more sensitive to proteasome inhibition than normal cells, indicating that the proteasome could be a target of chemotherapy. Studies suggest that traditional Chinese medicine (TCM) is an effective approach for cancer treatment. Here we reviewed several TCMs for their potential in treatment of cancer. This short review focuses mainly on the TCMs that potentially target the tumor cellular proteasome and NF-kappaB pathway whose activation is dependent on the proteasome activity.

Amphiphilic curcumin conjugate-forming nanoparticles as anticancer prodrug and drug carriers: in vitro and in vivo effects

Curcumin has been shown to have high cytotoxicity towards various cancer cell lines, but its water insolubility and instability make its bioavailability exceedingly low and, thus, it is generally inactive in in vivo anticancer tests. Here, we report an intracellular-labile amphiphilic surfactant-like curcumin prodrug – curcumin conjugated with two short oligo(ethylene glycol) (Curc-OEG) chains via β-thioester bonds that are labile in the presence of intracellular glutathione and esterase. Curc-OEG formed stable nanoparticles in aqueous conditions and served two roles – as an anticancer prodrug and a drug carrier. As an anticancer prodrug, the formed nanoparticles had a high and fixed curcumin-loading content of 25.3 wt%, and released active curcumin in the intracellular environment. Curc-OEG had high inhibition ability to several cancer cell lines due to apoptosis. Intravenously injected Curc-OEG significantly reduced the tumor weights and tumor numbers in the athymic mice xenografted with intraperitoneal SKOV-3 tumors and subcutaneous (mammary fat pad) MDA-MB-468 tumors. Preliminary systemic toxicity studies found that Curc-OEG did not cause acute and subchronic toxicities to mouse visceral organs at high doses. As drug carriers, Curc-OEG nanoparticles could carry other anticancer drugs, such as doxorubicin and camptothecin, and ship them into drug-resistant cells, greatly enhancing the cytotoxicity of the loaded drug. Thus, Curc-OEG is a promising prototype that merits further study for cancer therapy.

Capsaicin induces apoptosis through ubiquitin-proteasome system dysfunction

Capsaicin is an active component of red pepper having an antiproliferative effect in a variety of cancer cells, which recent evidence suggests due to its ability to induce apoptosis. However, the molecular mechanisms through which capsaicin induces apoptosis are not well understood. Here we demonstrate that capsaicin-induced apoptosis is mediated via the inhibition cellular proteasome function. Treatment of capsaicin to mouse neuro 2a cells results in the inhibition of proteasome activity in a dose- and time-dependent manner that seems to correlate with its effect on cell death. The effect of capsaicin on cellular proteasome function is indirect and probably mediated via the generation of oxidative stress. Exposure of capsaicin also causes increased accumulation of ubiquitinated proteins as wells as various target substrates of proteasome like p53 and Bax and p27. Like many other classical proteasome inhibitors, capsaicin also triggers the intrinsic pathway of apoptosis involving mitochondria and induces neurite outgrowth. Our results strongly support for the use of capsaicin as an anticancer drug.

Superoxide anion and proteasomal dysfunction contribute to curcumin-induced paraptosis of malignant breast cancer cells

Curcumin is considered a pharmacologically safe agent that may be useful in cancer chemoprevention and therapy. Here, we show for the first time that curcumin effectively induces paraptosis in malignant breast cancer cell lines, including MDA-MB-435S, MDA-MB-231, and Hs578T cells, by promoting vacuolation that results from swelling and fusion of mitochondria and/or the endoplasmic reticulum (ER). Inhibition of protein synthesis by cycloheximide blocked curcumin-induced vacuolation and subsequent cell death, indicating that protein synthesis is required for this process. The levels of AIP-1/Alix protein, a known inhibitor protein of paraptosis, were progressively downregulated in curcumin-treated malignant breast cancer cells, and AIP-1/Alix overexpression attenuated curcumin-induced death in these cells. ERK2 and JNK activation were positively associated with curcumin-induced cell death. Mitochondrial superoxide was shown to act as a critical early signal in curcumin-induced paraptosis, whereas proteasomal dysfunction was mainly responsible for the paraptotic changes associated with ER dilation. Notably, curcumin-induced paraptotic events were not observed in normal breast cells, including mammary epithelial cells and MCF-10A cells. Taken together, our findings on curcumin-induced paraptosis may provide novel insights into the mechanisms underlying the selective anti-cancer effects of curcumin against malignant cancer cells.

Curcumin-the paradigm of a multi-target natural compound with applications in cancer prevention and treatment

As cancer is a multifactor disease, it may require treatment with compounds able to target multiple intracellular components. We summarize here how curcumin is able to modulate many components of intracellular signaling pathways implicated in inflammation, cell proliferation and invasion and to induce genetic modulations eventually leading to tumor cell death. Clinical applications of this natural compound were initially limited by its low solubility and bioavailability in both plasma and tissues but combination with adjuvant and delivery vehicles was reported to largely improve bio-availability of curcumin. Moreover, curcumin was reported to act in synergism with several natural compounds or synthetic agents commonly used in chemotherapy. Based on this, curcumin could thus be considered as a good candidate for cancer prevention and treatment when used alone or in combination with other conventional treatments.

Anti-ulcer activity of curcumin on experimental gastric ulcer in rats and its effect on oxidative stress/antioxidant, IL-6 and enzyme activities

OBJECTIVE

To investigate the possible mechanism by which curcumin protects stomach during the acute chronic phase of gastric ulcer disease.

METHODS

The rats were divided into four groups and fasted for 2 days with free access to water. On the third day, the animals were fasted for a further 24 h with no access to water followed by surgery. Rats received different doses of curcumin (20, 40, and 80 mg/kg) or vehicle by oral gavage. Nineteen hours after ulcer induction, the rats were killed by decapitation. Stomach was opened along the greater curvature and ulcerative lesions were counted. Total juice acidity, neutrophils activity, mitochondrial activity, total antioxidants, paraoxonase (PON 1)/arylesterase and total peroxides were evaluated. DNA fragmentation (%) and pro-inflammatory cytokine IL-6 level were measured. The level of different gastro-cytoprotective effectors including total antioxidants and paraoxonase (PON 1)/arylesterase activities was measured.

RESULTS

The anti-ulcer activity of curcumin was displayed by attenuating the different ulcerative effectors including gastric acid hyper-secretion, total peroxides, myeloperoxiase (MPO) activity, IL-6 and apoptotic incidence.

CONCLUSION

Curcumin appears to have a propitious protective effect against gastric ulcer development.

Curcumin synergizes with resveratrol to inhibit colon cancer

Development and progression of many malignancies, including colorectal cancer, are associated with activation of multiple signaling pathways. Therefore, inhibition of these signaling pathways with noncytotoxic natural products represents a logical preventive and/or therapeutic approach for colon cancer. Curcumin and resveratrol, both of which inhibit the growth of transformed cells and colon carcinogenesis, were selected to examine whether combining them would be an effective preventive and/or therapeutic strategy for colon cancer. Indeed, the combination of curcumin and resveratrol was found to be more effective in inhibiting growth of p53-positive (wt) and p53-negative colon cancer HCT-116 cells in vitro and in vivo in SCID xenografts of colon cancer HCT-116 (wt) cells than either agent alone. Analysis by Calcusyn software showed synergism between curcumin and resveratrol. The inhibition of tumors in response to curcumin and/or resveratrol was associated with the reduction in proliferation and stimulation of apoptosis accompanied by attenuation of NF-kappaB activity. In vitro studies have further demonstrated that the combinatorial treatment caused a greater inhibition of constitutive activation of EGFR and its family members as well as IGF-1R. Our current data suggest that the combination of curcumin and resveratrol could be an effective preventive/therapeutic strategy for colon cancer.

Cellular signaling perturbation by natural products

Cancer cells are known to have alterations in multiple cellular signaling pathways and because of the complexities in the communication between multiple signaling networks, the treatment and the cure for most human malignancies is still an open question. Perhaps, this is the reason why specific inhibitors that target only one pathway have been typically failed in cancer treatment. However, the in vitro and in vivo studies have demonstrated that some natural products such as isoflavones, indole-3-carbinol (I3C), 3,3'-diindolylmethane (DIM), curcumin, (-)-epigallocatechin-3-gallate (EGCG), resveratrol, lycopene, etc, have inhibitory effects on human and animal cancers through targeting multiple cellular signaling pathways and thus these "natural agents" could be classified as multi-targeted agents. This is also consistent with the epidemiological studies showing that the consumption of fruits, soybean and vegetables is associated with reduced risk of several types of cancers. By regulating multiple important cellular signaling pathways including NF-kappaB, Akt, MAPK, Wnt, Notch, p53, AR, ER, etc, these natural products are known to activate cell death signals and induce apoptosis in pre-cancerous or cancer cells without affecting normal cells. Therefore, non-toxic "natural agents" harvested from the bounties of nature could be useful either alone or in combination with conventional therapeutics for the prevention of tumor progression and/or treatment of human malignancies.

Chemopreventive potential of curcumin in prostate cancer

The long latency and high incidence of prostate carcinogenesis provides the opportunity to intervene with chemoprevention in order to prevent or eradicate prostate malignancies. We present here an overview of the chemopreventive potential of curcumin (diferuloylmethane), a well-known natural compound that exhibits therapeutic promise for prostate cancer. In fact, it interferes with prostate cancer proliferation and metastasis development through the down-regulation of androgen receptor and epidermal growth factor receptor, but also through the induction of cell cycle arrest. It regulates the inflammatory response through the inhibition of pro-inflammatory mediators and the NF-kappaB signaling pathway. These results are consistent with this compound's ability to up-induce pro-apoptotic proteins and to down-regulate the anti-apoptotic counterparts. Alone or in combination with TRAIL-mediated immunotherapy or radiotherapy, curcumin is also reported to be a good inducer of prostate cancer cell death by apoptosis. Curcumin appears thus as a non-toxic alternative for prostate cancer prevention, treatment or co-treatment.

Curcumin induces proapoptotic effects against human melanoma cells and modulates the cellular response to immunotherapeutic cytokines

Curcumin has potential as a chemopreventative and chemotherapeutic agent, but its interactions with clinically relevant cytokines are poorly characterized. Because cytokine immunotherapy is a mainstay of treatment for malignant melanoma, we hypothesized that curcumin could modulate the cellular responsiveness to interferons and interleukins. As a single agent, curcumin induced a dose-dependent increase in apoptosis of human melanoma cell lines, which was most prominent at doses >10 micromol/L. Immunoblot analysis confirmed that curcumin induced apoptosis and revealed caspase-3 processing, poly ADP ribose polymerase cleavage, reduced Bcl-2, and decreased basal phosphorylated signal transducers and activators of transcription 3 (STAT3). Despite its proapoptotic effects, curcumin pretreatment of human melanoma cell lines inhibited the phosphorylation of STAT1 protein and downstream gene transcription following IFN-alpha and IFN-gamma as determined by immunoblot analysis and real time PCR, respectively. Pretreatment of peripheral blood mononuclear cells from healthy donors with curcumin also inhibited the ability of IFN-alpha, IFN-gamma, and interleukin-2 to phosphorylate STAT proteins critical for their antitumor activity (STAT1 and STAT5, respectively) and their respective downstream gene expression as measured by real time PCR. Finally, stimulation of natural killer (NK) cells with curcumin reduced the level of interleukin-12-induced IFN-gamma secretion, and production of granzyme b or IFN-gamma upon coculture with A375 melanoma cells or NK-sensitive K562 cells as targets. These data show that although curcumin can induce apoptosis of melanoma cells, it can also adversely affect the responsiveness of immune effector cells to clinically relevant cytokines that possess antitumor properties.

Fluorocurcumins as cyclooxygenase-2 inhibitor: molecular docking, pharmacokinetics and tissue distribution in mice

PURPOSE

The purpose of the current study was to assess the effect of newly synthesized Curcumin analogs on COX-2 protein by molecular docking studies and by assessments of the effect of one such analog (CDF) on nuclear factor NF-kappaB and PGE(2). In addition, we have determined the pharmacokinetics and tissue distribution of CDF in mice compared to Curcumin.

METHODS

Molecular docking on COX-2 protein was assessed by standard computer modeling studies. PGE(2) assay in conditioned media was done utilizing high sensitivity immunoassay kit following manufacturer's instructions, while NF-kappaB was done by routine EMSA. Serum pharmacokinetics and tissue distribution studies were carried out using the validated high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS) methods.

RESULTS

The molecular docking showed that fluorocurcumin analogs do not introduce any major steric changes compared to the parent Curcumin molecule, which was consistent with down-regulation of NF-kappaB and reduced PGE(2) levels in cells treated with CDF. Pharmacokinetic parameters revealed that CDF had better retention and bioavailability and that the concentration of CDF in the pancreas tissue was 10-fold higher compared to Curcumin.

CONCLUSION

Our observations clearly suggest that the bioavailability of CDF is much superior compared to Curcumin, suggesting that CDF would be clinically useful.

Potent and selective inhibition of the tumor marker AKR1B10 by bisdemethoxycurcumin: probing the active site of the enzyme with molecular modeling and site-directed mutagenesis

A human member of the aldo-keto reductase (AKR) superfamily, AKR1B10, shares high sequence identity with aldose reductase (AR), and was recently identified as a therapeutic target in the treatment of several types of cancer. We have compared the inhibitory effects of plant components on recombinant AKR1B10 and AR. AKR1B10 was inhibited by curcuminoids, magnolol, honokiol and resveratrol, with IC(50) values of 0.06-5 microM, which were lower than their values for AR. Among them, bisdemethoxycurcumin was the most potent competitive inhibitor (K(i)=22 nM) with the highest selectivity (85-fold versus AR), and acted as an effective inhibitor in cellular level. In contrast, demethoxycurcumin and curcumin showed >3-fold less potency and selectivity. Molecular docking studies of the curcuminoids in the AKR1B10-NADP(+) complex and site-directed mutagenesis of the putative binding residues suggest that Gln114, Val301 and Gln303 are important for determining the inhibitory potency and selectivity of the curcuminoids.

Harnessing the fruits of nature for the development of multi-targeted cancer therapeutics

Cancer cells exhibit deregulation in multiple cellular signaling pathways. Therefore, treatments using specific agents that target only one pathway usually fail in cancer therapy. The combination treatments using chemotherapeutic agents with distinct molecular mechanisms are considered more promising for higher efficacy; however, using multiple agents contributes to added toxicity. Emerging evidence has shown that some "natural products" such as isoflavones, indole-3-carbinol (I3C) and its in vivo dimeric product 3,3'-diindolylmethane (DIM), and curcumin among many others, have growth inhibitory and apoptosis inducing effects on human and animal cancer cells mediated by targeting multiple cellular signaling pathways in vitro without causing unwanted toxicity in normal cells. Therefore, these non-toxic "natural products" from natural resources could be useful in combination with conventional chemotherapeutic agents for the treatment of human malignancies with lower toxicity and higher efficacy. In fact, recently increasing evidence from pre-clinical in vivo studies and clinical trials have shown some success in support of the use of rational design of multi-targeted therapies for the treatment of cancers using conventional chemotherapeutic agents in combination with "natural products". These studies have provided promising results and further opened-up newer avenues for cancer therapy. In this review article, we have succinctly summarized the known effects of "natural products" especially by focusing on isoflavones, indole-3-carbinol (I3C) and its in vivo dimeric product 3,3'-diindolylmethane (DIM), and curcumin, and provided a comprehensive view on the molecular mechanisms underlying the principle of cancer therapy using combination of "natural products" with conventional therapeutics.

Curcumin and cancer cells: how many ways can curry kill tumor cells selectively?

Cancer is a hyperproliferative disorder that is usually treated by chemotherapeutic agents that are toxic not only to tumor cells but also to normal cells, so these agents produce major side effects. In addition, these agents are highly expensive and thus not affordable for most. Moreover, such agents cannot be used for cancer prevention. Traditional medicines are generally free of the deleterious side effects and usually inexpensive. Curcumin, a component of turmeric (Curcuma longa), is one such agent that is safe, affordable, and efficacious. How curcumin kills tumor cells is the focus of this review. We show that curcumin modulates growth of tumor cells through regulation of multiple cell signaling pathways including cell proliferation pathway (cyclin D1, c-myc), cell survival pathway (Bcl-2, Bcl-xL, cFLIP, XIAP, c-IAP1), caspase activation pathway (caspase-8, 3, 9), tumor suppressor pathway (p53, p21) death receptor pathway (DR4, DR5), mitochondrial pathways, and protein kinase pathway (JNK, Akt, and AMPK). How curcumin selectively kills tumor cells, and not normal cells, is also described in detail.

Clinical development of novel proteasome inhibitors for cancer treatment

BACKGROUND

Emerging evidence demonstrates that targeting the tumor proteasome is a promising strategy for cancer therapy.

OBJECTIVE

This review summarizes recent results from cancer clinical trials using specific proteasome inhibitors or some natural compounds that have proteasome-inhibitory effects.

METHODS

A literature search was carried out using PubMed. Results about the clinical application of specific proteasome inhibitors and natural products with proteasome-inhibitory activity for cancer prevention or therapy were reviewed.

RESULTS/CONCLUSION

Bortezomib, the reversible proteasome inhibitor that first entered clinical trials, has been studied extensively as a single agent and in combination with glucocorticoids, cytotoxic agents, immunomodulatory drugs and radiation as treatment for multiple myeloma and other hematological malignancies. The results in some cases have been impressive. There is less evidence of bortezomib's efficacy in solid tumors. Novel irreversible proteasome inhibitors, NPI-0052 and carfilzomib, have also been developed and clinical trials are underway. Natural products with proteasome-inhibitory effects, such as green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG), soy isoflavone genistein, and the spice turmeric compound curcumin, have been studied alone and in combination with traditional chemotherapy and radiotherapy against various cancers. There is also interest in developing these natural compounds as potential chemopreventive agents.

New difluoro Knoevenagel condensates of curcumin, their Schiff bases and copper complexes as proteasome inhibitors and apoptosis inducers in cancer cells

PURPOSE

Emerging evidence clearly suggests the potential chemopreventive and anti-tumor activity of a well known "natural agent" curcumin. However, studies have shown that curcumin is not readily bioavailable, and thus the tissue bioavailability of curcumin is also poor except for gastrointestinal track. Because of the potential biological activity of curcumin, many studies have attempted for making a better analog of curcumin that is equally effective or better with increased bioavailability, which was the purpose of our current study.

METHODS

We have designed and synthesized new difluoro Knoevenagel condensates of curcumin and Schiff bases along with their copper (II) complexes and evaluated their biological activities with respect to the inhibitory effects on purified rabbit 26S proteasome, and growth inhibition and induction of apoptosis in colon and pancreatic cancer cell lines.

RESULTS

All copper complexes possess distorted square planar geometries with 1:1 metal to ligand stoichiometry with reversible copper redox couple. The difluoro compound CDF exhibited inhibitory effects on purified rabbit 20S proteasome or cellular 26S proteasome, and caused both growth inhibition of cancer cell lines and induced apoptotic cell death in our preliminary assessment.

CONCLUSION

Our results suggest that our newly synthesized classes of curcumin analogs could be useful as chemopreventive and/or therapeutic agents against cancers.

Possible contribution of beta-glycosidases and caspases in the cytotoxicity of novel glycoconjugates in colon cancer cells

Glycoconjugates represent a recent trend in cancer chemotherapy that adopts the concept of selective prodrug/drug targeting of tumor cells by selectively binding to specific transmembrane glucose transporters. Following preferential uptake of sugar conjugates into cancer cells, they are presumably subject to enzymatic cleavage by specific beta-glycosidases to liberate the free active cytotoxic aglycones that act selectively on cancer cells and spare other noncancerous ones. In this sense, the cytotoxicity of an array of newly synthesized glycoconjugates, including curcumin beta-glucoside, perillyl alcohol beta-glucoside, perillyl alcohol beta-galactoside, diethylstilbesterol beta-glucoside and diethylstilbesterol beta-galactoside have been investigated over 24-96 h in a panel of human colon cancer cells namely, Caco-2, HT29 and T84 cells. The role of beta-glycosidases and caspases in the bioactivation and cytotoxicity of these compounds has been addressed in the current study. All the glycoconjugates have proven cytotoxic efficacy in a time-dependent manner. Curcumin beta-glucoside was the most potent amongst all glycoconjugates tested. The sensitivity rank order of tumor cells towards all beta-glucosides was Caco-2 > HT29 > T84. This sensitivity ranking was well correlated with beta-glucosidase activity assessed in these cell lines. Unlike perillyl alcohol galactoside, the cytotoxicity rank order for diethylstilbesterol beta-galactoside was not coping with the beta-galactosidase activity detected. Apoptosis was assessed by fluorometric assay of caspase-3 and caspase-9 activities. Initiation and activation of apoptosis were increased in all colon cancer cells following exposure to most of the glycoconjugates, and this was well correlated with the cytotoxicity rank order of these prodrugs. Enzymatic cleavage of glycoconjugates was accomplished using a host of hydrolytic enzymes and cleavage kinetics was determined using HPLC. The glycoconjugates were only cleaved by beta-glucosidases and beta-galactosidases, but not by pancreatic lipase or hepatic esterase. Taken together, one could conclude that beta-glucosidases and beta-galactosidases are crucial for the bioactivation and cytotoxicity of these glycoconjugates. Also, initiation and activation of apoptosis in tumor cells may contribute, at least partly, for the cytotoxicity of these sugar conjugates.

Dietary curcumin and limonin suppress CD4+ T-cell proliferation and interleukin-2 production in mice

Phytochemicals may reduce chronic inflammation and cancer risk in part by modulating T-cell nuclear factor-kappaB (NF-kappaB) activation. Therefore, we examined the effects of curcumin (Cur) and limonin (Lim) feeding on NF-kappaB-dependent CD4(+) T-cell proliferation. DO11.10 transgenic mice (n = 5-7) were fed diets containing 1% Cur or 0.02% Lim combined with either (n-6) PUFA [5% corn oil (CO)] or (n-3) PUFA [4% fish oil+1% corn oil (FO)] for 2 wk, followed by splenic CD4(+) T-cell isolation and stimulation with ovalbumin peptide 323-339 (OVA) and antigen-presenting cells from mice fed a conventional nonpurified rodent diet. Both Cur and Lim diets suppressed (P < 0.05) NF-kappaB p65 nuclear translocation in activated CD4(+) T-cells. In contrast, activator protein-1 (c-Jun) and nuclear factor of activated T-cells c1 were not affected compared with the CO control diet (no Cur or Lim). CD4(+) T-cell proliferation in response to either mitogenic anti-CD3/28 monoclonal antibodies (mAb) or antigenic stimulation by OVA was also suppressed (P < 0.05) by Cur as assessed by carboxyfluorescein succinimidyl ester staining. In contrast, interleukin-2 production was not directly associated with NF-kappaB status. Interestingly, dietary combination with FO enhanced the suppressive effects (P < 0.05) of Cur or Lim with respect to CD4(+) T-cell proliferation in response to anti-CD3/28 mAb. These results suggest that combination chemotherapy (FO+Cur or Lim) may favorably modulate CD4(+) T-cell-mediated inflammation.

In vitro schistosomicidal activity of curcumin against Schistosoma mansoni adult worms

The in vitro schistosomicidal activity of curcumin (doses ranging from 5 to 100 microM) was carried out against Schistosoma mansoni adult worms. Curcumin (at 50 and 100 microM) caused death of all worms. When tested at the doses of 5 and 20 microM, it decreased the worm viability in comparison with negative (Roswell Memorial Park Institute (RPMI) 1640 medium alone or RPMI 1640 medium with 10% dimethyl sulfoxide) and positive (heat-killed worms at 56 degrees C or praziquantel 10 microM) control groups. All pairs of coupled adult worms were separated into individual male and female by the action of curcumin at the doses of 20 to 100 microM. When tested at 5 and 10 microM, curcumin reduced egg production by 50% in comparison with the positive control group. It is the first time that the schistosomicidal activity has been reported for curcumin.