MG132, a proteasome inhibitor, induces human pulmonary fibroblast cell death via increasing ROS levels and GSH depletion

Enhanced anticancer effect of carfilzomib by codelivery of calcium peroxide nanoparticles targeting endoplasmic reticulum stress

Encouraged by the clinical success of proteasome inhibitors treating hematological malignancy, continuous efforts are being made to improve their efficacy and expand their applications to solid tumor therapy. In this study, liposomes were used to encapsulate the proteasome inhibitor carfilzomib (CFZ) and calcium peroxide (CaO2) nanoparticles for effective combination therapy targeting the interplay between calcium overload and oxidative stress. Low-dose CaO2 synergistically enhances the anticancer effect of CFZ in the human glioblastoma U-87 MG cells. The reactive oxygen species (ROS) generation and glutathione depletion by low-dose CaO2 complement CFZ-induced ubiquitinated protein accumulation further triggering endoplasmic reticulum (ER) stress leading to calcium overload and mitochondrial dysfunction. The liposome-based codelivery system is capable of transporting CFZ and CaO2 simultaneously to the tumor, and results in a superior antitumor effect in U-87 MG tumor-bearing mice compared with monotherapy. Taken together, CaO2 holds great potential to sensitize proteasome inhibitors in the treatment of solid tumors, and this work also presents a new combination therapy strategy targeting the crosstalk between proteasome inhibitors and oxidative stress for future cancer therapy.

IL-6 Promotes Muscle Atrophy by Increasing Ubiquitin-Proteasome Degradation of Muscle Regeneration Factors After Cerebral Infarction in Rats

Muscle atrophy in pathological or diseased muscles arises from an imbalance between protein synthesis and degradation. Elevated levels of interleukin-6 (IL-6) are a hallmark of ischemic stroke and have been associated with muscle atrophy in certain pathological contexts. However, the mechanisms by which IL-6 induces muscle atrophy in the context of stroke remain unclear. To investigate these effects, we used a rat model of middle cerebral artery occlusion (MCAO) and an in vitro model with the C2C12 cell line to uncover potential molecular mechanisms underlying IL-6-induced muscle atrophy. Our findings revealed elevated protein and serum levels of IL-6, along with increased markers of muscle atrophy, in MCAO rats compared to sham controls. We also observed overactivation of protein ubiquitination pathways and downregulation of muscle regeneration markers in MCAO rats. Further analysis indicated that IL-6 contributes to increased muscle protein ubiquitination. Inhibition of IL-6 signaling led to a significant reduction in infarct size and improved neurological deficit scores. Targeting the IL-6/IL-6R signaling pathway presents a promising therapeutic approach to mitigate muscle atrophy in individuals affected by ischemic stroke.

MG132-mediated Suppression of the Ubiquitin-proteasome Pathway Enhances the Sensitivity of Endometrial Cancer Cells to Cisplatin

BACKGROUND

Tumor cell resistance to cisplatin is a common challenge in endometrial cancer chemotherapy, stemming from various mechanisms. Targeted therapies using proteasome inhibitors, such as MG132, have been investigated to enhance cisplatin sensitivity, potentially offering a novel treatment approach.

OBJECTIVE

The aim of this study was to investigate the effects of MG132 on cisplatin sensitivity in the human endometrial cancer (EC) cell line RL95-2, focusing on cell proliferation, apoptosis, and cell signaling.

METHODS

Human endometrial cancer RL95-2 cells were exposed to MG132, and cell viability was assessed in a dose-dependent manner. The study evaluated the effect of MG132 on cisplatin-induced proliferation inhibition and apoptosis, correlating with caspase-3 activation and reactive oxygen species (ROS) upregulation. Additionally, we examined the inhibition of the ubiquitin-proteasome system and the expression of pro-inflammatory cytokines IL-1β, IL-6, IL-8, and IL-13 during MG132 and cisplatin co-administration.

RESULTS

MG132 exposure significantly reduced cell viability in a dose-dependent manner. It augmented cisplatin- induced proliferation inhibition and enhanced apoptosis, correlating with caspase-3 activation and ROS upregulation. Molecular analysis revealed a profound inhibition of the ubiquitin-proteasome system. MG132 also significantly increased the expression of cisplatin-induced pro-inflammatory cytokines, suggesting a transition from chronic to acute inflammation.

CONCLUSION

MG132 enhances the therapeutic efficacy of cisplatin in human EC cells by suppressing the ubiquitin- proteasome pathway, reducing cell viability, enhancing apoptosis, and shifting the inflammatory response. These findings highlighted the potential of MG132 as an adjuvant in endometrial cancer chemotherapy. Further research is needed to explore detailed mechanisms and clinical applications of this combination therapy.

Inhibition of proteolytic and ATPase activities of the proteasome by the BTK inhibitor CGI-1746

Bruton's tyrosine kinase (BTK) inhibitor, ibrutinib, has been shown to synergize in vitro with proteasome inhibitors (PIs) in reducing the viability of cells derived from B cell malignancies, but the mechanism is not known. We report here that an off-target effect of ibrutinib causes synergy because not all BTK inhibitors exhibited the synergistic effect, and those that synergized did so even in cells that do not express BTK. The allosteric BTK inhibitor CGI-1746 showed the strongest synergy. Co-treatment of cells with CGI-1746 increased PI-induced accumulation of ubiquitin conjugates and expression of heat shock proteins and NOXA and decreased a ratio of reduced to oxidized glutathione. CGI-1746, but not other BTK inhibitors, inhibited ATPase activity and all three peptidase activities of the 26S proteasome. The effect demonstrates a conceptually novel mode of proteasome inhibition that may aid the development of more potent PIs.

Exploring transient global transcriptional changes induced by ascorbic acid revealed via atKAS-seq profiling

Transcription initiates the formation of single-stranded DNA (ssDNA) regions within the genome, delineating transcription bubbles, a highly dynamic genomic process. Kethoxal-assisted single-stranded DNA sequencing (KAS-seq) utilizing N3-kethoxal has emerged as a potent tool for mapping specific guanine positions in ssDNA on a genome-wide scale. However, the original KAS-seq method required the costly Accel-NGS Methyl-seq DNA library kit. This study introduces an optimized iteration of the KAS-seq technique, referred to as adapter-tagged KAS-seq (atKAS-seq), incorporating an adapter tagging strategy. This modification involves integrating sequencing adapters via complementary strand synthesis using random N9 tagging. Additionally, by harnessing the potential of ascorbic acid (ASC), recognized for inducing global epigenetic changes, we employed the atKAS-seq methodology to elucidate critical pathways influenced by short-term, high-dose ASC treatment. Our findings underscore that atKAS-seq enables rapid and precise analyses of transcription dynamics and enhancer activities concurrently. This method offers a streamlined, cost-efficient, and low-input approach, affirming its utility in probing intricate genomic regulatory mechanisms.

Propyl gallate induces cell death in human pulmonary fibroblast through increasing reactive oxygen species levels and depleting glutathione

Propyl gallate (PG) exhibits an anti-growth effect on various cell types. The present study investigated the impact of PG on the levels of reactive oxygen species (ROS) and glutathione (GSH) in primary human pulmonary fibroblast (HPF) cells. Moreover, the effects of N-acetyl cysteine (NAC, an antioxidant), L-buthionine sulfoximine (BSO, a GSH synthesis inhibitor), and small interfering RNA (siRNAs) against various antioxidant genes on ROS and GSH levels and cell death were examined in PG-treated HPF cells. PG (100-800 μM) increased the levels of total ROS and O2·- at early time points of 30-180 min and 24 h, whereas PG (800-1600 μM) increased GSH-depleted cell number at 24 h and reduced GSH levels at 30-180 min. PG downregulated the activity of superoxide dismutase (SOD) and upregulated the activity of catalase in HPF cells. Treatment with 800 μM PG increased the number of apoptotic cells and cells that lost mitochondrial membrane potential (MMP; ΔΨm). NAC treatment attenuated HPF cell death and MMP (ΔΨm) loss induced by PG, accompanied by a decrease in GSH depletion, whereas BSO exacerbated the cell death and MMP (ΔΨm) loss without altering ROS and GSH depletion levels. Furthermore, siRNA against SOD1, SOD2, or catalase attenuated cell death in PG-treated HPF cells, whereas siRNA against GSH peroxidase enhanced cell death. In conclusion, PG induced cell death in HPF cells by increasing ROS levels and depleting GSH. NAC was found to decrease HPF cell death induced by PG, while BSO enhanced cell death. The findings shed light on how manipulating the antioxidant system influence the cytotoxic effects of PG in HPF cells.

Proteasome inhibitors as anticancer agents

INTRODUCTION

The therapeutic targeting of the ubiquitin-proteasome pathway (UPP) through inhibitors of the 20S proteasome core proteolytic activities has revolutionized the treatment of hematological malignancies and is paving the way for its extension to solid tumors.

AREAS COVERED

This review covers the progress made in the field of proteasome inhibitors, ranging from the first-generation bortezomib to the latest second-generation inhibitors such as carfilzomib and ixazomib as well as the proteasome inhibitors in clinical phase such as oprozomib and marizomib. The development of selective and potent proteasome inhibitors with improved pharmacological properties is described from the synthesis to their basic biological, and clinical validation.

EXPERT OPINION

Proteasome inhibitors have transformed the treatment landscape for hematological malignancies and hold great promise for cancer therapy. Combination therapies targeting multiple pathways, the development of novel inhibitors or 'hybrid-inhibitors,' and the optimization of treatment protocols are key areas for future exploration. The extension of proteasome inhibitors for the treatment of solid tumors, and their ability to pass the blood-brain barrier open new possibilities for treating central nervous system cancers. However, managing adverse effects, particularly those affecting the central nervous system, remains a critical consideration and a strategic 'working on' aspect for the near future.

Proteasome inhibitor MG132 enhances the sensitivity of human OSCC cells to cisplatin via a ROS/DNA damage/p53 axis

Cis-diamine-dichloroplatinum II (cisplatin, CDDP) is a key chemotherapeutic regimen in the treatment of oral squamous cell carcinoma (OSCC). However, the therapeutic efficacy of cisplatin in OSCC may be hampered by chemoresistance. Therefore, the development of novel combination therapy strategies to overcome the limitations of CDDP is of great importance. The proteasome inhibitor MG132 exhibits anti-cancer properties against various types of cancer. However, our knowledge of its anti-cancer effects in combination with CDDP in OSCC cells remains limited. In the current study, the synergetic effects of MG132 and CDDP were evaluated in the human CAL27 OSCC cell line. CAL27 cells were treated with CDDP alone or in combination with MG132. The results showed that MG132 significantly reduced cell viability in a dose-dependent manner. Additionally, cell viability was significantly reduced in CAL27 cells treated with 0.2 µM MG132 and 2 µM CDDP compared with cells treated with MG132 or CDDP alone. In addition, MG132 significantly enhanced the CDDP-induced generation of intracellular reactive oxygen species and DNA damage in OSCC cells. Furthermore, treatment with CDDP or MG132 alone notably inhibited colony formation and proliferation of OSCC cells. However, co-treatment of OSCC cells with MG132 and CDDP further hampered colony formation and proliferation compared with cells treated with either MG132 or CDDP alone. Finally, in cells co-treated with MG132 and CDDP, the expression of p53 was markedly elevated and the p53-mediated apoptotic pathway was further activated compared with cells treated with MG132 or CDDP alone, as shown by the enhanced cell apoptosis, Bax upregulation, and Bcl-2 downregulation. Overall, the results of the current study support the synergistic anti-cancer effects of a combination of MG132 and CDDP against OSCC, thus suggesting that the combination of MG132 and CDDP may be a promising therapeutic strategy for the management of OSCC.

Design and synthesis of 1,3-diphenylpyrimidine-2,4(1H,3H)-dione derivatives as antitumor agents via elevating ROS production to induce apoptosis

The target compound XS23 have exhibited excellent antitumor cell proliferative activity against multiple tumor cell lines and can induce cancer cell apoptosis by elevating ROS production.

Imbalanced GSH/ROS and sequential cell death

Reactive oxygen species (ROS) are produced in cells during metabolic processes. Excessive intracellular ROS may react with large biomolecules, such as DNA, RNA, proteins, and small biomolecules, that is, glutathione (GSH) and unsaturated fatty acids. GSH has physiological functions, including free radical scavenging, anti-oxidation, and electrophile elimination. The disruption of ROS/GSH balance results in the deleterious oxidation and chemical modification of biomacromolecules, which eventually leads to cell-cycle arrest and proliferation inhibition, and even induces cell death. Imbalanced ROS/GSH may result from a direct increase of ROS, consumption of GSH, intracellular oxidoreductase interference, or thioredoxin activity reduction. Some chemicals including arsenic trioxide (ATO), pyrogallol (PG), and carbobenzoxy-Leu-Leu-leucinal (MG132) could also disrupt the balance of GSH and ROS. This article reviews the occurrence and consequences of the imbalance between GSH and ROS and introduces factors responsible for the disruption of cellular ROS and GSH balance, resulting in cell death. "GSH" and "ROS" were used as keywords to search the relevant literaturess.

Prolonged disturbance of proteostasis induces cellular senescence via temporal mitochondrial dysfunction and subsequent mitochondrial accumulation in human fibroblasts

Proteolytic activity declines with age, resulting in the accumulation of aggregated proteins in aged organisms. To investigate how disturbance in proteostasis causes cellular senescence, we developed a stress-induced premature senescence (SIPS) model, in which normal human fibroblast MRC-5 cells were treated with the proteasome inhibitor MG132 or the vacuolar-type ATPase inhibitor bafilomycin A1 (BAFA1) for 5 days. Time-course studies revealed a significant increase in intracellular reactive oxygen species (ROS) and mitochondrial superoxide during and after drug treatment. Mitochondrial membrane potential initially decreased, suggesting temporal mitochondrial dysfunction during drug treatment, but was restored along with mitochondrial accumulation after drug treatment. AMP-activated protein kinase alpha was notably activated during treatment; thereafter, intracellular ATP levels significantly increased. SIPS induction by MG132 or BAFA1 was partially attenuated by co-treatment with vitamin E or rapamycin, in which the levels of ROS, mitochondrial accumulation, and protein aggregates were suppressed, implying the critical involvement of oxidative stress and mitochondrial function in SIPS progression. Rapamycin co-treatment also augmented the expression of HSP70 and activation of AKT, which could recover proteostasis and promote cell survival, respectively. Our study proposes a possible pathway from the disturbed proteostasis to cellular senescence via excess ROS production as well as functional and quantitative changes in mitochondria.

FOXM1 is a critical driver of lung fibroblast activation and fibrogenesis

While the transcription factor forkhead box M1 (FOXM1) is well known as a proto-oncogene, its potential role in lung fibroblast activation has never been explored. Here, we show that FOXM1 is more highly expressed in fibrotic than in normal lung fibroblasts in humans and mice. FOXM1 was required not only for cell proliferation in response to mitogens, but also for myofibroblast differentiation and apoptosis resistance elicited by TGF-β. The lipid mediator PGE2, acting via cAMP signaling, was identified as an endogenous negative regulator of FOXM1. Finally, genetic deletion of FOXM1 in fibroblasts or administration of the FOXM1 inhibitor Siomycin A in a therapeutic protocol attenuated bleomycin-induced pulmonary fibrosis. Our results identify FOXM1 as a driver of lung fibroblast activation and underscore the therapeutic potential of targeting FOXM1 for pulmonary fibrosis.

Antagonism of proteasome inhibitor-induced heme oxygenase-1 expression by PINK1 mutation

PTEN-induced putative kinase 1 (PINK1) is an integral protein in the mitochondrial membrane and maintains mitochondrial fidelity. Pathogenic mutations in PINK1 have been identified as a cause of early-onset autosomal recessive familial Parkinson’s disease (PD). The ubiquitin proteasome pathway is associated with neurodegenerative diseases. In this study, we investigated whether mutations of PINK1 affects the cellular stress response following proteasome inhibition. Administration of MG132, a peptide aldehyde proteasome inhibitor, significantly increased the expression of heme oxygenase-1 (HO-1) in rat dopaminergic neurons in the substantia nigra and in the SH-SY5Y neuronal cell line. The induction of HO-1 expression by proteasome inhibition was reduced in PINK1 G309D mutant cells. MG132 increased the levels of HO-1 through the Akt, p38, and Nrf2 signaling pathways. Compared with the cells expressing WT-PINK1, the phosphorylation of Akt and p38 was lower in those cells expressing the PINK1 G309D mutant, which resulted in the inhibition of the nuclear translocation of Nrf2. Furthermore, MG132-induced neuronal death was enhanced by the PINK1 G309D mutation. In this study, we demonstrated that the G309D mutation impairs the neuroprotective function of PINK1 following proteasome inhibition, which may be related to the pathogenesis of PD.

Nrf2-ARE signaling provides neuroprotection in traumatic brain injury via modulation of the ubiquitin proteasome system

The nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway exhibits protective effects in a variety of neurological diseases. However, the role of this pathway in traumatic brain injury (TBI) is not fully understood. This study investigates whether the Nrf2-ARE pathway provides neuroprotection following TBI via regulation of the ubiquitin proteasome system (UPS), and examines the involvement of this pathway in redox homeostasis. We found that activation the Nrf2-ARE pathway can mitigate secondary brain injury induced by TBI. Furthermore, we found that inhibiting the Nrf2-ARE pathway weakened the UPS following TBI. Treatment of TBI with the proteasome inhibitor, MG132, increased neuronal apoptosis, and evidence of brain water content was found. These data suggest that the Nrf2-ARE pathway provides neuroprotection following TBI via modulation of the UPS. In addition, the results indicated that the content of glutathione (GSH) was significantly increased after activation of Nrf2, and the level of ROS decreased; however, this effect contradictory in the Nrf2 knockout mice. Further studies found that treatment with the ROS agonist, ferric ammonium citrate (FAC), resulted in additional damage exerted by the ubiquitin proteasome pathways, and a significant increase in the amount of ubiquitinated proteins. In contrast, the activity of the ubiquitin proteasome pathways was vastly enhanced, and the level of ubiquitination proteins was significantly decreased following treatment with the inhibitor, N-acetylcysteine (NAC). The above mentioned results were also verified in in vitro experiments. In conclusion, the activation the Nrf2-ARE pathway improves neurological impairment caused by TBI via modulation of the UPS, and the redox homeostasis is one of the vital regulatory mechanisms.

N-Acetylcysteine in Combination with IGF-1 Enhances Neuroprotection against Proteasome Dysfunction-Induced Neurotoxicity in SH-SY5Y Cells

Ubiquitin proteasome system (UPS) dysfunction has been implicated in the development of many neuronal disorders, including Parkinson's disease (PD). Previous studies focused on individual neuroprotective agents and their respective abilities to prevent neurotoxicity following a variety of toxic insults. However, the effects of the antioxidant N-acetylcysteine (NAC) on proteasome impairment-induced apoptosis have not been well characterized in human neuronal cells. The aim of this study was to determine whether cotreatment of NAC and insulin-like growth factor-1 (IGF-1) efficiently protected against proteasome inhibitor-induced cytotoxicity in SH-SY5Y cells. Our results demonstrate that the proteasome inhibitor, MG132, initiates poly(ADP-ribose) polymerase (PARP) cleavage, caspase 3 activation, and nuclear condensation and fragmentation. In addition, MG132 treatment leads to endoplasmic reticulum (ER) stress and autophagy-mediated cell death. All of these events can be attenuated without obvious reduction of MG132 induced protein ubiquitination by first treating the cells with NAC and IGF-1 separately or simultaneously prior to exposure to MG132. Moreover, our data demonstrated that the combination of the two proved to be significantly more effective for neuronal protection. Therefore, we conclude that the simultaneous use of growth/neurotrophic factors and a free radical scavenger may increase overall protection against UPS dysfunction-mediated cytotoxicity and neurodegeneration.

xCT expression modulates cisplatin resistance in Tca8113 tongue carcinoma cells

Tongue squamous cell carcinoma (TSCC), which is a subtype of head and neck cancer, is the most common type of oral cancer. Due to its high recurrence rate and chemoresistance, the average survival rate for patients with TSCC remains unsatisfactory. At present, cisplatin (CDDP) is utilized as the first-line treatment for numerous solid neoplasms, including TSCC. CDDP resistance develops in the majority of patients; however, the mechanism of such resistance remains unknown. Therefore, the present study aimed to clarify the mechanism of CDDP resistance and attempted to reduce chemoresistance. The results indicated that CDDP significantly increased expression of xCT, which is the light chain and functional subunit of the glutamate/cysteine transporter system x_c^-, and a subsequent increase in glutathione (GSH) levels was observed. The present study demonstrated that the upregulation of xCT expression and intercellular GSH levels contributed to CDDP resistance in TSCC cells. Furthermore, xCT suppression, induced by small interfering RNA or pharmacological inhibitors, sensitized TSCC cells to CDDP treatment. In conclusion, the present study revealed that CDDP-induced xCT expression promotes CDDP chemoresistance, and xCT inhibition sensitizes TSCC cells to CDDP treatment. These results provide a novel insight into the molecular mechanisms involved in TSCC cell chemoresistance.

Physcion inhibits the metastatic potential of human colorectal cancer SW620 cells in vitro by suppressing the transcription factor SOX2

AIM

Physcion, an anthraquinone derivative, exhibits hepatoprotective, anti-inflammatory, anti-microbial and anti-cancer activities. In this study we examined whether and how physcion inhibited metastatic potential of human colorectal cancer cells in vitro.

METHODS

Human colorectal cancer cell line SW620 was tested. Cell migration and invasion were assessed using a wound healing and Transwell assay, respectively. The expression levels of transcription factor SOX2 in the cells were modulated with shRNA targeting SOX2 and SOX2 overexpressing plasmid. The expression of target molecules involved in epithelial-mesenchymal transition (EMT) process and the signaling pathways was determined with Western blots or qRT-PCR. ROS levels were measured using DCF-DA.

RESULTS

Physcion (2.5, 5 mol/L) did not affect the cell viability, but dose-dependently inhibited the cell adhesion, migration and invasion. Physcion also inhibited the EMT process in the cells, as evidenced by the increased epithelial marker E-cadherin expression, and by decreased expression of mesenchymal markers N-cadherin, vimentin, fibronectin and α-SMA, as well as transcriptional repressors Snail, Slug and Twist. Physcion suppressed the expression of SOX2, whereas overexpression of SOX2 abrogated the inhibition of physcion on metastatic behaviors. Physcion markedly increased ROS production and phosphorylation of AMPK and GSK3β in the cells, whereas the AMPK inhibitor compound C or the ROS inhibitor NAC abolished the inhibition of physcion on metastatic behaviors.

CONCLUSION

Physcion inhibits the metastatic potential of human colorectal cancer cells in vitro via activating ROS/AMPK/GSK3β signaling pathways and suppressing SOX2.

AG4, a compound isolated from Radix Ardisiae Gigantifoliae, induces apoptosis in human nasopharyngeal cancer CNE cells through intrinsic and extrinsic apoptosis pathways

3β-O-{α-L-Pyran rhamnose-(1→3)-[β-D-xylopyranose-(1→2)]-β-D-glucopyranose-(1→4)-[β-D-lucopyranose-(1→2)]-α-L-pyran arabinose}-cyclamiretin A (AG4) is a saponin component obtained from the Giantleaf Ardisia Rhizome (Rhizoma Ardisiae Gigantifoliae). The present study aimed to investigate the antitumor potential of AG4 and its possible mechanisms in human nasopharyngeal carcinoma cells (CNE). We exposed tumor cells to AG4 to investigate which cell line was the most sensitive to AG4. Cell viability was assessed using the MTT reduction assay, and the effects of AG4 on apoptosis, reactive oxygen species (ROS) content, mitochondrial membrane potential (MMP), and cell cycle were detected using a flow cytometer; the glutathione, superoxide dismutase and malondialdehyde activities were measured using colorimetric methods. The relative expressions of Bax, Bad, Bid, Bcl-2, and Fas mRNA were calculated using the (Equation is included in full-text article.)comparative method by real-time PCR studies and protein was detected by western blotting. AG4 markedly inhibited the growth of CNE cells by decreasing cell proliferation, inducing apoptosis, and blocking the cell cycle in the S phase. The release of caspase-3, caspase-8, and caspase-9 was stimulated by AG4 in CNE, and the decreased proliferation induced by AG4 was blocked by the inhibitor of pan caspase (Z-VAD-FMK). Moreover, the MMP was decreased in AG4-treated cells, and AG4-induced cell apoptosis was accompanied by a rapid and lasting increase in ROS, which was abolished by N-acetyl-L-cysteine (NAC); glutathione, superoxide dismutase, and malondialdehyde were regulated by AG4. AG4 inhibited Bcl-2 mRNA and protein expression and stimulated Bax, Bad, Bid, Fas mRNA, and protein expression in CNE cultures, suggesting an effect at the transcriptional and protein level. In addition, both the FasL inhibitor (AF-016) and the Bcl-2 family inhibitor (GX15-070) could prevent the cell apoptosis induced by AG4. The findings suggested that AG4-induced apoptosis in CNE cells involved a death receptor pathway and a Bcl-2 family-mediated mitochondrial signaling pathway by decreasing the MMPs in an ROS-dependent manner and regulating genes and proteins relative to apoptosis; also, regulation of cell cycles may also play a role in the antitumor mechanism of AG4.

Proteasome inhibitor MG-132 enhances histone deacetylase inhibitor SAHA-induced cell death of chronic myeloid leukemia cells by an ROS-mediated mechanism and downregulation of the Bcr-Abl fusion protein

Recently, there has been progress in the treatment of chronic myeloid leukemia (CML). However, novel therapeutic strategies are required in order to address the emerging problem of imatinib resistance. Histone deacetylase inhibitors (HDACi) and proteasome inhibitors are promising alternatives, and may be amenable to integration with current therapeutic approaches. However, the mechanisms underlying the interaction between these two agents remain unclear. The present study assessed the cytotoxic effect of the HDACi, suberoylanilide hydroxamic acid (SAHA), in combination with the proteasome inhibitor, MG-132, in imatinib-sensitive K562 and imatinib-resistant K562G cells, and investigated the mechanism underlying this effect. Cell viability was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method and protein expression levels were determined by western blotting. Reactive oxygen species (ROS) generation levels were observed under a fluorescence microscope The results indicated that SAHA and MG-132 act in a synergistic manner to induce cell death in K562 and K562G cells. This effect was associated with Bcr-Abl downregulation and the production of ROS. Notably, the ROS scavenger, N-acetyl-L-cysteine, almost fully reversed the cell death and Bcr-Abl downregulation that was induced by the combination of SAHA and MG-132. By contrast, the pan-caspase inhibitor, z-VAD-fmk, only partially reversed the cell death induced by these two drugs in CML cells. These results indicated that increased intracellular ROS levels are important in the induction of cell death and the downregulation of Bcr-Abl. In conclusion, the present results suggested that combined SAHA and MG-132 may be a promising treatment for CML.

Methods for detecting circulating cancer stem cells (CCSCs) as a novel approach for diagnosis of colon cancer relapse/metastasis

Cancer stem cells (CSCs) are believed to be resistant to currently available therapies and may be responsible for relapse of cancer in patients. Measuring circulating tumor cells (CTCs) in the blood of patients has emerged as a non-invasive diagnostic procedure for screening patients who may be at high risk for developing metastatic cancers or relapse of the cancer disease. However, accurate detection of CTCs has remained a problem, as epithelial-cell markers used to date are not always reliable for detecting CTCs, especially during epithelial-mesenchymal transition. As CSCs are required to initiate metastatic tumors, our goal was to optimize and standardize a method for identifying circulating CSCs (CCSCs) in patients, using established CSC markers. Here, we report for the first time the detection of CCSCs in the blood of athymic nude mice, bearing metastatic tumors, and in the blood of patients positive for colonic adenocarcinomas. Using a simple and non-expensive method, we isolated a relatively pure population of CSCs (CD45-/CK19+), free of red blood cells and largely free of contaminating CD45+ white blood cells. Enriched CCSCs from patients with colon adenocarcinomas had a malignant phenotype and co-expressed CSC markers (DCLK1/LGR5) with CD44/Annexin A2. CSCs were not found in the blood of non-cancer patients, free of colonic growths. Enriched CCSCs from colon cancer patients grew primary spheroids, suggesting the presence of tumor-initiating cells in the blood of these patients. In conclusion, we have developed a novel diagnostic assay for detecting CSCs in circulation, which may more accurately predict the risk of relapse or metastatic disease in patients. As CSCs can potentially initiate metastatic growths, patients positive for CCSCs can be treated with inhibitory agents that selectively target CSCs, besides conventional treatments, to reduce the risk of relapse/metastatic disease for improving clinical outcomes.

Preventive and therapeutic effects of MG132 by activating Nrf2-ARE signaling pathway on oxidative stress-induced cardiovascular and renal injury

So far, cardiovascular and renal diseases have brought us not only huge economic burden but also serious society problems. Since effective therapeutic strategies are still limited, to find new methods for the prevention or therapy of these diseases is important. Oxidative stress has been found to play a critical role in the initiation and progression of cardiovascular and renal diseases. In addition, activation of nuclear-factor-E2-related-factor-2- (Nrf2-) antioxidant-responsive element (ARE) signaling pathway protects cells and tissues from oxidative damage. As a proteasomal inhibitor, MG132 was reported to activate Nrf2 expression and function, which was accompanied with significant preventive and/or therapeutic effect on cardiovascular and renal diseases under most conditions; therefore, MG132 seems to be a potentially effective drug to be used in the prevention of oxidative damage. In this paper, we will summarize the information available regarding the effect of MG132 on oxidative stress-induced cardiovascular and renal damage, especially through Nrf2-ARE signaling pathway.

Astrocyte plasticity revealed by adaptations to severe proteotoxic stress

Neurodegeneration is characterized by an accumulation of misfolded proteins in neurons. It is less well appreciated that glia often also accumulate misfolded proteins. However, glia are highly plastic and may adapt to stress readily. Endogenous adaptations to stress can be measured by challenging stressed cells with a second hit and then measuring viability. For example, subtoxic stress can elicit preconditioning or tolerance against second hits. However, it is not known if severe stress that kills half the population can elicit endogenous adaptations in the remaining survivors. Glia, with their resilient nature, offer an ideal model in which to test this new hypothesis. The present study is the first demonstration that astrocytes surviving one LC50 hit of the proteasome inhibitor MG132 were protected against a second MG132 hit. ATP loss in response to the second hit was also prevented. MG132 caused compensatory rises in stress-sensitive heat shock proteins. However, stressed astrocytes exhibited an even greater rise in ubiquitin-conjugated proteins upon the second hit, illustrating the severity of the proteotoxicity and verifying the continued impact of MG132. Despite this stress, MG132-pretreated astrocytes were completely prevented from losing glutathione with the second hit. Furthermore, inhibiting glutathione synthesis rendered astrocytes sensitive to the second hit, unmasking the cumulative impact of two hits by removal of an endogenous adaptation. These findings suggest that stressed astrocytes become progressively harder to kill by virtue of antioxidant defenses. Such plasticity may permit astrocytes under severe stress to better support neurons and help explain the protracted nature of neurodegeneration.