Curcumin-induced Apoptosis Research Articles

Curcumin activates a ROS/KEAP1/NRF2/miR-34a/b/c cascade to suppress colorectal cancer metastasis

Curcumin, a natural phytochemical isolated from tumeric roots, represents a candidate for prevention and therapy of colorectal cancer/CRC. However, the exact mechanism of action and the downstream mediators of curcumin’s tumor suppressive effects have remained largely unknown. Here we used a genetic approach to determine the role of the p53/miR-34 pathway as mediator of the effects of curcumin. Three isogenic CRC cell lines rendered deficient for the p53, miR-34a and/or miR-34b/c genes were exposed to curcumin and subjected to cell biological analyses. siRNA-mediated inhibition and ectopic expression of NRF2, as well as Western blot, qPCR and qChIP analyses of its target genes were performed. CRC cells were i.v. injected into NOD/SCID mice and lung-metastases formation was determined by longitudinal, non-invasive imaging. In CRC cells curcumin induced apoptosis and senescence, and suppressed migration and invasion in a p53-independent manner. Curcumin activated the KEAP1/NRF2/ARE pathway by inducing ROS. Notably, curcumin induced miR-34a and miR-34b/c expression in a ROS/NRF2-dependent and p53-independent manner. NRF2 directly induced miR-34a and miR-34b/c via occupying multiple ARE motifs in their promoter regions. Curcumin reverted repression of miR-34a and miR-34b/c induced by IL6 and hypoxia. Deletion of miR-34a and miR-34b/c significantly reduced curcumin-induced apoptosis and senescence, and prevented the inhibition of migration and invasion by curcumin or ectopic NRF2. In CRC cells curcumin induced MET and prevented the formation of lung-metastases in mice in a miR-34a-dependent manner. In addition, we found that curcumin may enhance the therapeutic effects of 5-FU on CRC cells deficient for p53 and miR-34a/b/c. Activation of the KEAP1/NRF2/miR-34a/b/c axis mediates the tumor suppressive activity of curcumin and suggests a new approach for activating miR-34 genes in tumors for therapeutic purposes.

The Role of Thrombomodulin in Estrogen-Receptor-Positive Breast Cancer Progression, Metastasis, and Curcumin Sensitivity.

Estrogen and estrogen receptors (ER) play a key role in breast cancer progression, which can be treated with endocrine therapy. Nevertheless, resistance to endocrine therapies is developed over time. The tumor expression of thrombomodulin (TM) is correlated with favorable prognosis in several types of cancer. However, this correlation has not yet been confirmed in ER-positive (ER+) breast cancer. This study aims to evaluate the role of TM in ER+ breast cancer. Firstly, we found that lower TM expression correlates to poor overall survival (OS) and relapse-free survival (RFS) rates in ER+ breast cancer patients through Kaplan-Meier survival analysis (p < 0.05). Silencing TM in MCF7 cells (TM-KD) increased cell proliferation, migration, and invasion ability. Additionally, TM-KD MCF7 cells showed higher sensitivity (IC50 15 μM) to the anti-cancer agent curcumin than the scrambled control cells. Conversely, overexpression of TM (TM-over) in T47D cells leads to decreased cell proliferation, migration, and invasion ability. Furthermore, TM-over T47D cells showed more resistance (IC50 > 40 μM) to the curcumin treatment. The PI staining, DAPI, and tunnel assay also confirmed that the curcumin-induced apoptosis in TM-KD MCF7 cells was higher (90.34%) than in the scrambled control cells (48.54%). Finally, the expressions of drug-resistant genes (ABCC1, LRP1, MRP5, and MDR1) were determined by qPCR. We found that the relative mRNA expression levels of ABCC1, LRP1, and MDR1 genes after curcumin treatment were higher in scrambled control cells than in TM-KD cells. In conclusion, our results demonstrated that TM plays a suppressive role in the progression and metastasis of ER+ breast cancer, and it regulates curcumin sensitivity by interfering with ABCC1, LRP1, and MDR1 gene expression.

Latent CSN-CRL complexes are crucial for curcumin-induced apoptosis and recruited during adipogenesis to lipid droplets via small GTPase RAB18

The COP9 signalosome (CSN) and cullin-RING ubiquitin ligases (CRLs) form latent CSN-CRL complexes detectable in cells. We demonstrate that the CSN variants CSNCSN7A and CSNCSN7B preferentially bind to CRL3 or CRL4A and CRL4B, respectively. Interestingly, the interacting protein ubiquitin-specific protease 15 exclusively binds to latent CSNCSN7A-CRL3, while p27KIP attaches to latent CSNCSN7B-CRL4A complex. Inhibition of deneddylation by CSN5i-3 or neddylation by MLN4924 do not impede the formation of latent complexes. Latent CSNCSN7A-CRL3 and latent CSNCSN7B-CRL4A/B particles are essential for specific cellular functions. We found that curcumin-induced cell death requires latent CSNCSN7B-CRL4A. Knockout of CSN7B in HeLa cells leads to resistance against curcumin. Remarkably, the small GTPase RAB18 recruits latent CSNCSN7A-CRL3 complex to lipid droplets (LDs), where CRL3 is activated by neddylation, an essential event for LD formation during adipogenesis. Knockdown of CSN7A or RAB18 or destabilization of latent complexes by cutting off CSN7A C-terminal 201-275 amino acids blocks adipogenesis.

Ex vivo explant model of adenoma and colorectal cancer to explore mechanisms of action and patient response to cancer prevention therapies.

Colorectal cancer (CRC) is the second leading cause of cancer death in the UK. Novel therapeutic prevention strategies to inhibit the development and progression of CRC would be invaluable. Potential contenders include low toxicity agents such as dietary-derived agents or repurposed drugs. However, in vitro and in vivo models used in drug development often do not take into account the heterogeneity of tumours or the tumour microenvironment. This limits translation to a clinical setting. Our objectives were to develop an ex vivo method utilizing CRC and adenoma patient-derived explants (PDEs) which facilitates screening of drugs, assessment of toxicity, and efficacy. Our aims were to use a multiplexed immunofluorescence approach to demonstrate the viability of colorectal tissue PDEs, and the ability to assess immune cell composition and interactions. Using clinically achievable concentrations of curcumin, we show a correlation between curcumin-induced tumour and stromal apoptosis (P < .001) in adenomas and cancers; higher stromal content is associated with poorer outcomes. B cell (CD20+ve) and T cell (CD3+ve) density of immune cells within tumour regions in control samples correlated with curcumin-induced tumour apoptosis (P < .001 and P < .05, respectively), suggesting curcumin-induced apoptosis is potentially predicted by baseline measures of immune cells. A decrease in distance between T cells (CD3+ve) and cytokeratin+ve cells was observed, indicating movement of T cells (CD3+ve) towards the tumour margin (P < .001); this change is consistent with an immune environment associated with improved outcomes. Concurrently, an increase in distance between T cells (CD3+ve) and B cells (CD20+ve) was detected following curcumin treatment (P < .001), which may result in a less immunosuppressive tumour milieu. The colorectal tissue PDE model offers significant potential for simultaneously assessing multiple biomarkers in response to drug exposure allowing a greater understanding of mechanisms of action and efficacy in relevant target tissues, that maintain both their structural integrity and immune cell compartments.

Curcumin and Related Compounds in Cancer Cells: New Avenues for Old Molecules.

Curcumin and related compounds are known for the large spectrum of activities. The chemical features of these compounds are important for their biological effects with a key role for the thiol-reactive α−β unsaturated carbonyl groups. Curcumin derivatives may overcome the limitation of the bioavailability of the parent compound, while maintaining the key chemical features responsible for biological activities. Curcumin and related compounds show anti-viral, anti-fungal, anti-microbial and anti-tumor activities. The therapeutic effects of curcumin, used as a supplement in cancer therapy, have been documented in various cancer types, in which inhibition of cell growth and survival pathways, induction of apoptosis and other cell death pathways have been reported. Curcumin-induced apoptosis has been linked both to the intrinsic and extrinsic apoptotic pathways. Necroptosis has also been involved in curcumin-induced toxicity. Among curcumin-induced effects, ferroptosis has also been described. The mechanism of curcumin toxicity can be triggered by reactive oxygen species-mediated endoplasmic reticulum stress. Curcumin targets have been identified in the context of the ubiquitin-proteasome system with evidence of inhibition of the proteasome proteolytic activities and cellular deubiquitinases. Curcumin has recently been shown to act on the tumor microenvironment with effects on cancer-associated fibroblasts and immune cells. The related product caffeic acid phenethyl ester has shown promising preclinical results with an effect on the inflammatory microenvironment. Here, we review the mechanisms underlying curcumin and derivatives toxicity towards cancer cells with particular emphasis on cell death pathways and the ubiquitin-proteasome system.

Dasatinib enhances curcumin-induced cytotoxicity, apoptosis and protective autophagy in human schwannoma cells HEI-193: The role of Akt/mTOR/p70S6K signalling pathway.

The present study was carried out in human schwannoma cells (HEI-193) to determine the combined anti-cancer effect of curcumin and dasatinib. Cells were treated with curcumin only, dasatinib only, or the combination of curcumin and dasatinib for 24 hours. Cellular toxicity, cell proliferation, and cell death were determined by LDH, MTT, and trypan blue dye assays, respectively. ELISA based kit was used to determine apoptotic cell death. Western blotting was used to determine the expression of apoptotic and autophagy-associated protein markers. Similarly, expression levels of Akt/mTOR/p70S6K signalling pathway-related proteins were studied using Western blotting. Cell death and apoptosis were significantly higher in HEI-193 cells treated with curcumin and dasatinib combination compared to individual controls. The combination of curcumin and dasatinib significantly enhances autophagy markers compared to individual controls. Furthermore, the combination of curcumin and dasatinib significantly activates Akt/mTOR/p70S6K signalling pathway compared to individual controls. In conclusion, our results suggest that the combination of curcumin and dasatinib significantly enhances cytotoxicity, apoptosis, and protective autophagy in HEI-193 cells through Akt/mTOR/p70S6K signalling pathway.

Curcumin suppresses cell proliferation and triggers apoptosis in vemurafenib‐resistant melanoma cells by downregulating the EGFR signaling pathway

Melanoma is a malignant tumor with aggressive behavior. Vemurafenib, a BRAF inhibitor, is clinically used in melanoma, but resistance to melanoma cytotoxic therapies is associated with BRAF mutations. Curcumin can effectively inhibit numerous types of cancers. However, there are no reports regarding the correlation between curcumin and vemurafenib-resistant melanoma cells. In this study, vemurafenib-resistant A375.S2 (A375.S2/VR) cells were established, and the functional mechanism of the epidermal growth factor receptor (EGFR), serine-threonine kinase (AKT), and the extracellular signal-regulated kinase (ERK) signaling induced by curcumin was investigated in A375.S2/VR cells in vitro. Our results indicated that A375.S2/VR cells had a higher IC50 concentration of vemurafenib than the parental A375.S2 cells. Moreover, curcumin reduced the viability and confluence of A375.S2/VR cells. Curcumin triggered apoptosis via reactive oxygen species (ROS) production, disruption of mitochondrial membrane potential (ΔΨm), and intrinsic signaling (caspase-9/-3-dependent) pathways in A375.S2/VR cells. Curcumin-induced apoptosis was also mediated by the EGFR signaling pathway. Combination treatment with curcumin and gefitinib (an EGFR inhibitor) synergistically potentiated the inhibitory effect of cell viability in A375.S2/VR cells. The present study provides new insights into the therapy of vemurafenib-resistant melanoma and suggests that curcumin might be an encouraging therapeutic candidate for its drug-resistant treatment.

Curcumin Mediates the Proliferation and Apoptosis of Colorectal Cancer Cells by Downregulating the Expression of Interleukin-1β through the Nuclear Factor-κB Signaling Pathway

Background: Colorectal cancer (CRC) is a frequently occurring malignant tumor, which is mainly observed in elderly men with no significant symptoms at the early stage. Among the malignant tumors of the digestive system, the incidence and mortality of CRC rank second only to hepatic and gastric cancer. Curcumin is an antioxidant and anti-inflammatory compound extracted from the roots of Curcuma longa plant. The antitumor effects of curcumin have been widely reported for various types of cancers, including CRC. Objective: In this study, we aimed to elucidate the protective effects and mechanism of interleukin (IL)-1 β on curcumin-induced apoptosis in SW480 cells. Materials and Methods: Expression levels of IL-1 β in CRC tissues and cells were detected by the quantitative reverse transcription polymerase chain reaction and Western blot assays. Followed by the incubation of cells with curcumin, the effect on IL-1 β was measured. Moreover, after transfection, the effects of IL-1 β on curcumin-induced SW480 cellular processes were analyzed by cell counting kit-8 and flow cytometric analysis. Results: According to the results of this study, IL-1 β was significantly increased in CRC tissues and cells. However, after incubation of the cells with curcumin, IL-1 β was downregulated and overexpression of IL-1 β counteracted the antitumor functions of curcumin in SW480 cells. Further studies have shown that curcumin could promote apoptosis of SW480 cells by inhibiting nuclear factor-κB (NF-κB) signaling pathway. Conclusion: Our study validated that curcumin inhibits SW480 cell proliferation but promotes apoptosis by downregulating the expression of IL-1 β probably through NF-κB signaling pathway. IL-1 β may an important target for the treatment of CRC.

Curcumin induces apoptosis and inhibits the growth of adrenocortical carcinoma: Identification of potential candidate genes and pathways by transcriptome analysis.

Adrenocortical carcinoma (ACC) is an endocrine tumour with high malignancy, high invasiveness and poor prognosis. Curcumin, a major component in turmeric, has been reported to have good efficacy and biological safety in treating cancer. However, the role and mechanism of curcumin in ACC have not yet been fully investigated and were thus the focus of this study. In vitro, ACC SW-13 and NCI-H295R cells were treated with curcumin and their viability, migration and invasion were assessed by CCK-8 and Transwell assays. Apoptosis was detected via flow cytometry and western blotting. High-throughput sequencing and comprehensive bioinformatics analyses were performed to elucidate the molecular processes underlying curcumin activity. In vivo, SW-13 cells were injected into nude mice, and the tumour volumes and weights were observed after 2 weeks of curcumin treatment. Organelle changes were observed by electron microscopy, and potential candidate genes and pathways were analysed by RT-qPCR and western blotting. The role of the CHOP target gene in curcumin-induced ACC cell apoptosis was verified via lentiviral transfection experiments. Curcumin inhibited the viability, migration and invasion, and induced the apoptosis of ACC cells. Transcriptome sequencing analysis showed that curcumin treatment markedly changed the gene expression levels. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses showed that the MAPK and endoplasmic reticulum (ER) stress pathways were the predominant pathways associated with curcumin-induced apoptosis of ACC cells. Subsequent in vivo and in vitro results demonstrated that the JNK, p38 MAPK and ER stress pathways were activated in curcumin-treated ACC cells, and that C/EBP homologous protein induction was responsible for curcumin-induced apoptosis of ACC cells. In summary, curcumin induced ACC cell apoptosis and inhibited tumour growth by activating the JNK, p38 MAPK and ER stress pathways. Thus, curcumin may be a potential therapeutic drug for ACC.

Curcumin induced the cell death of immortalized human keratinocytes (HaCaT) through caspase-independent and caspase-dependent pathways.

Curcumin is a diketone compound found in turmeric. It is used as food additives and spices, and has anti-proliferation and anti-cancer properties. However, the effect of curcumin on human keratinocytes (KCs) is still unclear. In this study, curcumin dramatically inhibited the cell growth of immortalized human KCs (HaCaT) and arrested the cells at the G2/M phase, with an apoptosis rate of 33.95% after 24 μM curcumin treatment. HaCaT cells showed changes in typical apoptotic morphology and the configuration of nuclear matrix-intermediate filaments (NM-IFs) after treatment with curcumin. We identified 16 differentially expressed nuclear matrix (NM) proteins, including apoptosis inducing factor (AIF) and caspase 3, by 2-DE and MALDI-TOF/TOF mass spectrometry. The expression of AIF decreased in the mitochondria and increased in the nucleus. Immunofluorescence assays showed that AIF was released from the mitochondria to the nucleus. AIF silencing and caspase inhibitor (z-vad-fmk) both lead to HaCaT cells being insensitive to apoptosis induced by curcumin. Meanwhile, after curcumin treatment, mitochondrial membrane depolarization led to cytochrome c release from the mitochondria to the cytoplasm, and the ratio of Bax to Bcl-2 in HaCaT cells was also increased, which subsequently initiated the activation of caspase-3. These results suggest that curcumin-induced apoptosis of HaCaT cells occurs not only through the caspase-dependent pathway but also through the caspase-independent pathway. This discovery enhances the development and utilization of curcumin and provides possible evidence for the treatment of proliferative skin diseases, including skin cancer.

In vitro and in vivo studies on potentiation of curcumin-induced lysosomal-dependent apoptosis upon silencing of cathepsin C in colorectal cancer cells

Cathepsins are lysosomal acid hydrolases that make crucial contributions to tumor progression through a variety of signaling mechanisms, including autophagy, cell survival, chemotherapeutic resistance, and metastasis. Herein, we report that cathepsin C (CTSC) silencing upregulates the anticancer potential of curcumin in colorectal cancer cells (CRCs) both in vitro and in athymic mice xenografts. Curcumin treatment enhances CTSC level in CRCs; however, CTSC silencing with subsequent curcumin treatment (sequential treatment) induces ER stress and autophagic dysregulation accompanied by lysosomal permeabilization and ROS generation. This lysosomal permeabilization triggered the cytosolic CTSB mediated BID-dependent mitochondrial membrane permeabilization and thereby caspase-dependent apoptosis. This phenotype can be rescued by CTSB inhibition and NAC, which further supported the involvement of ROS and CTSB in apoptosis following sequential treatment. Indeed, the sequential CTSC silencing and curcumin treatment also significantly curtailed tumor volume as well as ameliorated cytosolic cyt c and tBID protein levels in tumor tissues compared to those in control and individual treatments of CTSC targeting and on curcumin treatment in nude mice xenografts. The results reveal that CTSC can controls the curcumin-induced cytotoxic insult through autophagy maintenance both in vitro and in athymic mice xenografts, thereby providing an insight into the role of CTSC in chemoprevention of CRCs.

PRP4 Kinase Domain Loss Nullifies Drug Resistance and Epithelial-Mesenchymal Transition in Human Colorectal Carcinoma Cells.

We have investigated the involvement of the pre-mRNA processing factor 4B (PRP4) kinase domain in mediating drug resistance. HCT116 cells were treated with curcumin, and apoptosis was assessed based on flow cytometry and the generation of reactive oxygen species (ROS). Cells were then transfected with PRP4 or pre-mRNA-processing-splicing factor 8 (PRP8), and drug resistance was analyzed both in vitro and in vivo. Furthermore, we deleted the kinase domain in PRP4 using GatewayTM technology. Curcumin induced cell death through the production of ROS and decreased the activation of survival signals, but PRP4 overexpression reversed the curcumin-induced oxidative stress and apoptosis. PRP8 failed to reverse the curcumin-induced apoptosis in the HCT116 colon cancer cell line. In xenograft mouse model experiments, curcumin effectively reduced tumour size whereas PRP4 conferred resistance to curcumin, which was evident from increasing tumour size, while PRP8 failed to regulate the curcumin action. PRP4 overexpression altered the morphology, rearranged the actin cytoskeleton, triggered epithelial-mesenchymal transition (EMT), and decreased the invasiveness of HCT116 cells. The loss of E-cadherin, a hallmark of EMT, was observed in HCT116 cells overexpressing PRP4. Moreover, we observed that the EMT-inducing potential of PRP4 was aborted after the deletion of its kinase domain. Collectively, our investigations suggest that the PRP4 kinase domain is responsible for promoting drug resistance to curcumin by inducing EMT. Further evaluation of PRP4-induced inhibition of cell death and PRP4 kinase domain interactions with various other proteins might lead to the development of novel approaches for overcoming drug resistance in patients with colon cancer.

Retraction: Hepatitis C Virus Core Protein Down-Regulates p21Waf1/Cip1 and Inhibits Curcumin-Induced Apoptosis through MicroRNA-345 Targeting in Human Hepatoma Cells.

Retraction: Hepatitis C Virus Core Protein Down-Regulates p21Waf1/Cip1 and Inhibits Curcumin-Induced Apoptosis through MicroRNA-345 Targeting in Human Hepatoma Cells.

Iron chelation by curcumin suppresses both curcumin-induced autophagy and cell death together with iron overload neoplastic transformation

Iron overload, notably caused by hereditary hemochromatosis, is an excess storage of iron in various organs that causes tissue damage and may promote tumorigenesis. To manage that disorder, free iron depletion can be induced by iron chelators like deferoxamine that are of increasing interest also in the cancer field since iron stock could be a potent target for managing tumorigenesis. Curcumin, a well-known active substance extracted from the turmeric rhizome, destabilizes endoplasmic reticulum, and secondarily lysosomes, thereby increasing mitophagy/autophagy and subsequent apoptosis. Recent findings show that cells treated with curcumin also exhibit a decrease in ferritin, which is consistent with its chemical structure and iron chelating activity. Here we investigated how curcumin influences the intracellular effects of iron overload via Fe-nitriloacetic acid or ferric ammonium citrate loading in Huh-7 cells and explored the consequences in terms of antioxidant activity, autophagy, and apoptotic signal transduction. In experiments with T51B and RL-34 epithelial cells, we have found evidence that curcumin-iron complexation abolishes both curcumin-induced autophagy and apoptosis, together with the tumorigenic action of iron overload.

Curcumin prevents experimental autoimmune encephalomyelitis by inhibiting proliferation and effector CD4+ T cell activation.

Multiple sclerosis (MS) has affected over 2 million people worldwide and it is thought to be initiated by the activated central nervous system (CNS). Reactive CD4+ T cells (TH1, TH17, and Treg phenotypes) are crucial to MS. The TH1 phenotype can promote major histocompatibility complex-II expression and TH17 can induce inflammatory gene expression. Curcumin, a yellow pigment, is found in turmeric rhizomes and has been reported to have various activities, such as anti-proliferative and anti-inflammatory activity. Curcumin has great potential in MS treatment. Little is known about the effect of curcumin on MS. Therefore, we investigated the effect of curcumin on MS, especially on CD4+ T cells. CD4+ T cells (TH1, TH17, and Treg cells) were cultured in Iscove's Modified Dulbecco's Medium (IMDM) medium. Cell proliferation was evaluated by MTT assay. The ability of individual CD4+ T cells to aggregate into viable colony clusters was assessed by clonogenic survival assay. Apoptosis of CD4+ T cells was determined by flow cytometry. The expression of Bcl-2, Bax, and active caspase-3 was detected by Western blotting. The effect of curcumin on the activation molecule was also evaluated by flow cytometry. MTT assay showed that curcumin significantly inhibited CD4+ T cell viability. Furthermore, TH1, TH17, and Treg all showed a dose-dependent but not time-dependent. The results of clonogenic survival assay revealed that curcumin markedly decreased the colony formation ability of CD4+ T cells. Flow cytometry results indicated that curcumin-induced remarkable apoptosis in TH1, TH17, and Treg cells. After treatment with curcumin, the expression of Bcl-2 was decreased and that of Bax and active caspase-3 was increased. Western blotting results also showed that curcumin-induced apoptosis in CD4+ T cells. Hence, our results demonstrated that curcumin inhibited CD4+ T cell proliferation via inducing apoptosis in CD4+ T cells. Meanwhile, flow cytometry results also showed that curcumin directly inhibited CD4+ T cell activation. Curcumin could inhibit CD4+ T cell proliferation and effector cell activation.

Curcumin Attenuates Adipogenesis by Inducing Preadipocyte Apoptosis and Inhibiting Adipocyte Differentiation.

Patients with metabolic syndrome are at an increased risk of developing type 2 diabetes and cardiovascular diseases. The principal risk factor for development of metabolic syndrome is obesity, defined as a state of pathological hyperplasia or/and hypertrophy of adipose tissue. The number of mature adipocytes is determined by adipocyte differentiation from preadipocytes. The purpose of the present study is to investigate the effects of curcumin on adipogenesis and the underlying mechanism. To examine cell toxicity of curcumin, 3T3-L1 preadipocytes were treated with 0–50 µM curcumin for 24, 48, or 72 h, then cell viability was measured using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The effect of curcumin on the cell cycle was determined by flow cytometry. Curcumin-induced cell apoptosis was determined by the TUNEL assay and curcumin-induced caspase activation was measured by immunoblotting. The effect of curcumin on adipocyte differentiation was determined by measuring mitotic clonal expansion (MCE), expression of adipogenic transcription factors, and lipid accumulation. Results showed the viability of preadipocytes was significantly decreased by treatment with 30 µM curcumin, a concentration that caused apoptosis in preadipocytes, as assessed by the TUNEL assay, and caused activation of caspases 8, 9, and 3. A non-cytotoxic dose of curcumin (15 µM) inhibited MCE, downregulated the expression of PPARγ and C/EBPα, prevented differentiation medium-induced β-catenin downregulation, and decreased the lipid accumulation in 3T3-L1 adipocytes. In conclusion, our data show that curcumin can induce preadipocyte apoptosis and inhibit adipocyte differentiation, leading to suppression of adipogenesis.

Downregulation of RBBP6 variant 1 during arsenic trioxide-mediated cell cycle arrest and curcumin-induced apoptosis in MCF-7 breast cancer cells.

Aim:To determine the expression patterns of the RBBP6 spliced variants during arsenic trioxide-mediated cell cycle arrest and curcumin-induced apoptosis in MCF-7 cells.Materials & methods:As2O3 and curcumin were used to study cytotoxicity, cell cycle arrest, apoptosis and the expression of RBBP6 variants. The MUSE Cell Analyser was used to analyze cell cycle arrest, apoptosis and multicaspase activity while apoptosis was further confirmed using microscopy. Semi-quantitative RT-PCR was employed to quantitate the expression of the RBBP6 variants.Results:This study showed that the MCF-7 cells expressed RBBP6 variant 1 but lacked both variant 2 and variant 3. Both As2O3 and curcumin significantly downregulated RBBP6 variant 1 (p < 0.001).Conclusion:RBBP6 variants are promising therapeutic targets.

Curcumin induces apoptotic cell death and protective autophagy by inhibiting AKT/mTOR/p70S6K pathway in human ovarian cancer cells.

Curcumin (Cur), a yellow-colored dietary flavor from the plant (Curcuma longa), has been demonstrated to potentially resist diverse diseases, including ovarian cancer, but drug resistance becomes a major limitation of its success clinically. The key molecule or mechanism associated with curcumin resistance in ovarian cancer still remains unclear. The aim of our study was to investigate the effects of curcumin on autophagy in ovarian cancer cells and elucidate the underlying mechanism. In our study, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), EdU proliferation assay and colony-forming assay were used to assess cell viability. Apoptosis was detected by western blot and flow cytometric analysis of apoptosis. Autophagy was defined by both electron microscopy and immunofluorescence staining markers such as microtubule-associated protein 1 light chain 3 (LC3). Plasmid construction and shRNA transfection helped us to confirm the function of curcumin. Curcumin reduced cell viability and induced apoptotic cell death by MTT assay in human ovarian cancer cell lines SK-OV-3 and A2780 significantly. Electron microscopy, western blot and immunofluorescence staining proved that curcumin could induce protective autophagy. Moreover, treatment with autophagy-specific inhibitors or stable knockdown of LC3B by shRNA could markedly enhance curcumin-induced apoptosis. Finally, the cells transiently transfected with AKT1 overexpression plasmid demonstrated that autophagy had a direct relationship with the AKT/mTOR/p70S6K pathway. Curcumin can induce protective autophagy of human ovarian cancer cells by inhibiting the AKT/mTOR/p70S6K pathway, indicating the synergistic effects of curcumin and autophagy inhibition as a possible strategy to overcome the limits of current therapies in the eradication of epithelial ovarian cancer.

Investigation of cytotoxic, genotoxic, and apoptotic effects of curcumin on glioma cells

Glioblastoma is a malignant tumor of the brain. The treatment of this tumor is still a challenge. Curcumin has been shown to have therapeutic effects when used to treat malignant diseases. However, the molecular mechanisms of its action are not fully elucidated. We hypothesized that reactive oxygen species (ROS) have a key role in curcumin-induced DNA damage, apoptosis, and cell death. To test our hypothesis, cytotoxic, genotoxic, apoptotic, and ROS-generating effects, as well as mitochondrial membrane potentials of curcumin on rat glioma cells (C-6) and normal fibroblastic cells (L-929) were investigated. We examined concentration-dependent cytotoxic, genotoxic, apoptotic, and ROS generating effects of curcumin at C-6 cells and L-929 cells. The cells were incubated with different doses of curcumin (10-100 µM) for 24 hours. Higher doses of curcumin resulted in greater cellular death of cancer than of normal cells at higher concentrations. Curcumin also induced ROS generation in cancer than normal cells in a concentration-dependent manner. Our results showed that curcumin-induced DNA damage in a dose-dependent manner (p &lt; 0.001). At high curcumin concentration such as 80 µM, the proportions of live cells in cancer and normal cell lines were 11.5 and 44.3, respectively. The higher doses of curcumin resulted in greater apoptosis in cancer than normal cells.This in vitro study provided clear evidence that curcumin induced DNA damage and apoptosis. Cytotoxicity may be due to its pro-oxidant activity in a dose-dependent manner in cancer and normal cells. These activities were higher in cancer cells.

Mechanisms of apoptosis modulation by curcumin: Implications for cancer therapy.

Cancer incidences are growing and cause millions of deaths worldwide. Cancer therapy is one of the most important challenges in medicine. Improving therapeutic outcomes from cancer therapy is necessary for increasing patients' survival and quality of life. Adjuvant therapy using various types of antibodies or immunomodulatory agents has suggested modulating tumor response. Resistance to apoptosis is the main reason for radioresistance and chemoresistance of most of the cancers, and also one of the pivotal targets for improving cancer therapy is the modulation of apoptosis signaling pathways. Apoptosis can be induced by intrinsic or extrinsic pathways via stimulation of several targets, such as membrane receptors of tumor necrosis factor-α and transforming growth factor-β, and also mitochondria. Curcumin is a naturally derived agent that induces apoptosis in a variety of different tumor cell lines. Curcumin also activates redox reactions within cells inducing reactive oxygen species (ROS) production that leads to the upregulation of apoptosis receptors on the tumor cell membrane. Curcumin can also upregulate the expression and activity of p53 that inhibits tumor cell proliferation and increases apoptosis. Furthermore, curcumin has a potent inhibitory effect on the activity of NF-κB and COX-2, which are involved in the overexpression of antiapoptosis genes such as Bcl-2. It can also attenuate the regulation of antiapoptosis PI3K signaling and increase the expression of MAPKs to induce endogenous production of ROS. In this paper, we aimed to review the molecular mechanisms of curcumin-induced apoptosis in cancer cells. This action of curcumin could be applicable for use as an adjuvant in combination with other modalities of cancer therapy including radiotherapy and chemotherapy.