2-Cyano-3,12-dioxooleana-1,9-dien-28-imidazolide (CDDO-Im) directly targets mitochondrial glutathione to induce apoptosis in pancreatic cancer

Cell-free chromatin particles released from dying cells inflict mitochondrial damage and ROS production in living cells

Mitochondrial damage and the resultant oxidative stress are associated with neurodegenerative diseases, ageing, and cancer. However, the triggers of mitochondrial damage remain unclear. We previously reported that cell-free chromatin particles (cfChPs) released from the billions of cells that die in the body every day can readily enter healthy cells and damage their DNA. Here, we show that cfChPs isolated from the sera of healthy individuals, when applied to NIH3T3 mouse fibroblast cells, cause physical damage to mitochondrial DNA (mtDNA). cfChPs also induce ultrastructural changes, increase mitochondrial mass, alter mitochondrial shape, upregulate mitochondrial outer membrane protein translocase of the outer membrane 20, and change mitochondrial membrane potential. Furthermore, a marked increase was observed in mitochondrial superoxide (ROS) production, as detected by MitoSOX Red, and intracellular superoxide dismutase-1 activation. ROS production was also activated when a conditioned medium containing cfChPs released from hypoxia-induced dying NIH3T3 cells was applied to healthy NIH3T3 cells. ROS activation was significantly reduced when the conditioned medium was pre-treated with three different cfChP-deactivating agents: anti-histone antibody-complexed nanoparticles, DNase I, and the novel pro-oxidant combination of the nutraceuticals resveratrol and copper. Given that 1 × 109-1 × 1012 cells die in the body every day, we hypothesise that cfChPs from dying cells are the major physiological triggers for mtDNA damage and ROS production. Deactivation of cfChPs may provide a novel therapeutic approach to retard ageing and associated degenerative conditions linked to oxidative stress.

The Complex Genetic and Epigenetic Regulation of the Nrf2 Pathways: A Review

Nrf2 is a major transcription factor that significantly regulates-directly or indirectly-more than 2000 genes. While many of these genes are involved in maintaining redox balance, others are involved in maintaining balance among metabolic pathways that are seemingly unrelated to oxidative stress. In the past 25 years, the number of factors involved in the activation, nuclear translocation, and deactivation of Nrf2 has continued to expand. The purpose of this review is to provide an overview of the remarkable complexity of the tortuous sequence of stop-and-go signals that not only regulate expression or repression, but may also modify transcriptional intensity as well as the specificity of promoter recognition, allowing fluidity of its gene expression profile depending on the various structural modifications the transcription factor encounters on its journey to the DNA. At present, more than 45 control points have been identified, many of which represent sites of action of the so-called Nrf2 activators. The complexity of the pathway and the synergistic interplay among combinations of control points help to explain the potential advantages seen with phytochemical compositions that simultaneously target multiple control points, compared to the traditional pharmaceutical paradigm of "one-drug, one-target".

Fluorescent Materials for Monitoring Mitochondrial Biology

Mitochondria play important roles in diverse cellular processes such as energy production, cellular metabolism, and apoptosis to promote cell death. To investigate mitochondria-associated biological processes such as structure, dynamics, morphological change, metabolism, and mitophagy, there exists a continuous demand for visualizing and monitoring techniques elucidating mitochondrial biology and disease-relevancy. Due to the advantages of high sensitivity and practicality, fluorescence phenomena have been most widely used as scientific techniques for the visualization of biological phenomena and systems. In this review, we briefly overview the different types of fluorescent materials such as chemical probes, peptide- or protein-based probes, and nanomaterials for monitoring mitochondrial biology.

Growth inhibition and apoptosis of human multiple myeloma cells induced by 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid derivatives

Multiple myeloma is a blood cell cancer and can cause symptoms such as bone loss and fatigue. Recent studies have shown that the bone marrow microenvironment may mediate tumor proliferation, drug resistance, and migration of the multiple myeloma cells. Synthetic triterpenoids have been used for the treatment of cancer due to their antiproliferative and anti-inflammatory effects. The objective of this study is to examine the effect of 2-cyano-3, 12 dioxoolean-1,9-dien-28-oic acid (CDDO) derivatives on human multiple myeloma cells. Three CDDO derivatives, such as CDDO-methyl ester, CDDO-trifluroethyl amide, and CDDO-imidazolide (Im), were tested on the growth of human multiple myeloma cells. Our results show that all CDDO derivatives decrease the viability of multiple myeloma cells in a dose- and time-dependent manner, with CDDO-Im being the most potent. CDDO-Im was selected to investigate whether its inhibitory effect on multiple myeloma cell growth is due to cell cycle arrest and induction of apoptosis. The results suggest that CDDO-Im may inhibit cell cycle progression in the G0/G1 phase and induce the intrinsic apoptotic pathway. The effect of CDDO-Im on multiple myeloma cells was evaluated in a Transwell model using myeloma cells co-culturing with human HS-5 stromal cells to simulate the bone marrow microenvironment in vitro. The results showed that CDDO-Im induced multiple myeloma cell apoptosis in the presence of HS-5 cells, albeit to a lower extent than in multiple myeloma cells cultured alone. In conclusion, our data suggest that CDDO-Im inhibits the growth of multiple myeloma cells, either cultured alone or co-cultured with bone marrow stromal cells, through the induction of apoptosis.

Activated ERK Signaling Is One of the Major Hub Signals Related to the Acquisition of Radiotherapy-Resistant MDA-MB-231 Breast Cancer Cells

Breast cancer is one of the major causes of deaths due to cancer, especially in women. The crucial barrier for breast cancer treatment is resistance to radiation therapy, one of the important local regional therapies. We previously established and characterized radio-resistant MDA-MB-231 breast cancer cells (RT-R-MDA-MB-231 cells) that harbor a high expression of cancer stem cells (CSCs) and the EMT phenotype. In this study, we performed antibody array analysis to identify the hub signaling mechanism for the radiation resistance of RT-R-MDA-MB-231 cells by comparing parental MDA-MB-231 (p-MDA-MB-231) and RT-R-MDA-MB-231 cells. Antibody array analysis unveiled that the MAPK1 protein was the most upregulated protein in RT-R-MDA-MB-231 cells compared to in p-MDA-MB-231 cells. The pathway enrichment analysis also revealed the presence of MAPK1 in almost all enriched pathways. Thus, we used an MEK/ERK inhibitor, PD98059, to block the MEK/ERK pathway and to identify the role of MAPK1 in the radio-resistance of RT-R-MDA-MB-231 cells. MEK/ERK inhibition induced cell death in both p-MDA-MB-231 and RT-R-MDA-MB-231 cells, but the death mechanism for each cell was different; p-MDA-MB-231 cells underwent apoptosis, showing cell shrinkage and PARP-1 cleavage, while RT-R-MDA-MB-231 cells underwent necroptosis, showing mitochondrial dissipation, nuclear swelling, and an increase in the expressions of CypA and AIF. In addition, MEK/ERK inhibition reversed the radio-resistance of RT-R-MDA-MB-231 cells and suppressed the increased expression of CSC markers (CD44 and OCT3/4) and the EMT phenotype (β-catenin and N-cadherin/E-cadherin). Taken together, this study suggests that activated ERK signaling is one of the major hub signals related to the radio-resistance of MDA-MB-231 breast cancer cells.

Interplay among Oxidative Stress, Methylglyoxal Pathway and S-Glutathionylation

Reactive oxygen species (ROS) are produced constantly inside the cells as a consequence of nutrient catabolism. The balance between ROS production and elimination allows to maintain cell redox homeostasis and biological functions, avoiding the occurrence of oxidative distress causing irreversible oxidative damages. A fundamental player in this fine balance is reduced glutathione (GSH), required for the scavenging of ROS as well as of the reactive 2-oxoaldehydes methylglyoxal (MGO). MGO is a cytotoxic compound formed constitutively as byproduct of nutrient catabolism, and in particular of glycolysis, detoxified in a GSH-dependent manner by the glyoxalase pathway consisting in glyoxalase I and glyoxalase II reactions. A physiological increase in ROS production (oxidative eustress, OxeS) is promptly signaled by the decrease of cellular GSH/GSSG ratio which can induce the reversible S-glutathionylation of key proteins aimed at restoring the redox balance. An increase in MGO level also occurs under oxidative stress (OxS) conditions probably due to several events among which the decrease in GSH level and/or the bottleneck of glycolysis caused by the reversible S-glutathionylation and inhibition of glyceraldehyde-3-phosphate dehydrogenase. In the present review, it is shown how MGO can play a role as a stress signaling molecule in response to OxeS, contributing to the coordination of cell metabolism with gene expression by the glycation of specific proteins. Moreover, it is highlighted how the products of MGO metabolism, S-D-lactoylglutathione (SLG) and D-lactate, which can be taken up and metabolized by mitochondria, could play important roles in cell response to OxS, contributing to cytosol-mitochondria crosstalk, cytosolic and mitochondrial GSH pools, energy production, and the restoration of the GSH/GSSG ratio. The role for SLG and glyoxalase II in the regulation of protein function through S-glutathionylation under OxS conditions is also discussed. Overall, the data reported here stress the need for further studies aimed at understanding what role the evolutionary-conserved MGO formation and metabolism can play in cell signaling and response to OxS conditions, the aberration of which may importantly contribute to the pathogenesis of diseases associated to elevated OxS.

Evaluation of Cytotoxicity and α-Glucosidase Inhibitory Activity of Amide and Polyamino-Derivatives of Lupane Triterpenoids

A series of two new and twenty earlier synthesized branched extra-amino-triterpenoids obtained by the direct coupling of betulinic/betulonic acids with polymethylenpolyamines, or by the cyanoethylation of lupane type alcohols, oximes, amines, and amides with the following reduction were evaluated for cytotoxicity toward the NCI-60 cancer cell line panel, α-glucosidase inhibitory, and antimicrobial activities. Lupane carboxamides, conjugates with diaminopropane, triethylenetetramine, and branched C3-cyanoethylated polyamine methyl betulonate showed high cytotoxic activity against most of the tested cancer cell lines with GI50 that ranged from 1.09 to 54.40 µM. Betulonic acid C28-conjugate with triethylenetetramine and C3,C28-bis-aminopropoxy-betulin were found to be potent micromolar inhibitors of yeast α-glucosidase and to simultaneously inhibit the endosomal reticulum α-glucosidase, rendering them as potentially capable to suppress tumor invasiveness and neovascularization, in addition to the direct cytotoxicity. Plausible mechanisms of cytotoxic action and underlying disrupted molecular pathways were elucidated with CellMinner pattern analysis and Gene Ontology enrichment analysis, according to which the lead compounds exert multi-target antiproliferative activity associated with oxidative stress induction and chromatin structure alteration. The betulonic acid diethylentriamine conjugate showed partial activity against methicillin-resistant S. aureus and the fungi C. neoformans. These results show that triterpenic polyamines, being analogs of steroidal squalamine and trodusquemine, are important substances for the search of new drugs with anticancer, antidiabetic, and antimicrobial activities.

Role of sirtuin-1 (SIRT1) in hypoxic injury in pancreatic β-cells

Islet transplantation (ITx) is being developed as a treatment for type 1 diabetes mellitus, but hypoxic damage to transplanted islet grafts is an important factor affecting successful transplantation. To investigate the role of sirtuin-1 (SIRT1) under hypoxic injury in INS-1 cells, one type of pancreatic β-cell lines, we used SRT1720 and GW4064 for SIRT1 activation. The small interfering RNA SIRT1 (si-SIRT1) was used to suppress SIRT1 gene expression. We measured cell viability, apoptosis, and the levels of inflammatory cytokines, including tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), and reactive oxygen species (ROS), under hypoxic conditions. Real-time PCR and Western blot analysis were performed. Cell viability was significantly reduced to 71% and 40% after 4 and 6 h of hypoxic conditions, respectively. Apoptosis increased significantly 2.8-fold and 5.3-fold after 4 and 6 h of hypoxia, respectively. SIRT1 expression was significantly reduced at the mRNA and protein levels during hypoxia. Hypoxic damage significantly increased the TNF-α, IL-6 and ROS levels in INS-1 cells. However, the reduced cell viability and increased inflammatory cytokines from hypoxic damage were ameliorated by SIRT1 activation in INS-1 cells. These results suggest that SIRT1 is a potential target for the protection of pancreatic β-cells against hypoxic damage during ITx.

Histone methyltransferase G9a inhibitor-loaded redox-responsive nanoparticles for pancreatic ductal adenocarcinoma therapy

Survival data have shown little therapeutic improvement in pancreatic ductal adenocarcinoma (PDAC) over the past several decades, mostly due to aggressive growth and resistance to therapy. Glutathione (GSH) depletion in PDAC may serve as a strategy to suppress tumour malignancy and sensitize tumour cells to therapy. Herein, novel l-cysteine-based poly(disulfide amide) polymers were fabricated to deliver a histone methyltransferase G9a inhibitor (UNC0638) that can simultaneously block GSH biosynthesis and clear cellular GSH levels in PDAC. The optimal UNC0638 nanodrug (NP_UNC0638) had the desired particle size, reasonable drug loading capacity, and GSH-controlled drug release. Moreover, compared to UNC0638 alone, NP_UNC0638 showed better efficacy in inhibiting cell viability, arresting the cell cycle, inducing apoptosis, and suppressing the invasion and self-renewal capacity of PDAC cells. Furthermore, NP_UNC0638 was found to be tumour-specific and well tolerated with no apparent toxicity to vital organs and haematopoietic stem and progenitor cells. Additionally, treatment with NP_UNC0638 provided favourable outcomes in the PDAC xenograft model. Therefore, this work presents a potent drug delivery platform to overcome the GSH-induced malignant potential of PDAC.

Active Particle Based Selective Transport and Release of Cell Organelles and Mechanical Probing of a Single Nucleus

Self-propelling micromotors are emerging as a promising microscale tool for single-cell analysis. The authors have recently shown that the field gradients necessary to manipulate matter via dielectrophoresis can be induced at the surface of a polarizable active ("self-propelling") metallo-dielectric Janus particle (JP) under an externally applied electric field, acting essentially as a mobile floating microelectrode. Here, the application of the mobile floating microelectrode to trap and transport cell organelles in a selective and releasable manner is successfully extended. This selectivity is driven by the different dielectrophoretic (DEP) potential wells on the JP surface that is controlled by the frequency of the electric field, along with the hydrodynamic shearing and size of the trapped organelles. Such selective and directed loading enables purification of targeted organelles of interest from a mixed biological sample while their dynamic release enables their harvesting for further analysis such as gene/RNA sequencing or proteomics. Moreover, the electro-deformation of the trapped nucleus is shown to be in correlation with the DEP force and hence, can act as a promising label-free biomechanical marker. Hence, the active carrier constitutes an important and novel ex vivo platform for manipulation and mechanical probing of subcellular components of potential for single cell analysis.

Epigenetics/epigenomics of triterpenoids in cancer prevention and in health

Triterpenoids are a powerful group of phytochemicals derived from plant foods and herbs. Many reports have shown that they possess chemopreventive and chemotherapeutic effects not only in cell lines and animal models but also in clinical trials. Because epigenetic changes could potentially occur in the early stages of carcinogenesis preceding genetic mutations, epigenetics are considered promising targets in early interventions against cancer using epigenetic bioactive substances. The biological properties of triterpenoids in cancer prevention and in health have multiple mechanisms, including antioxidant and anti-inflammatory activities, cell cycle regulation, as well as epigenetic/epigenomic regulation. In this review, we will discuss and summarize the latest advances in the study of the pharmacological effects of triterpenoids in cancer chemoprevention and in health, including the epigenetic machinery.

A role for keratins in supporting mitochondrial organization and function in skin keratinocytes

Mitochondria fulfill essential roles in ATP production, metabolic regulation, calcium signaling, generation of reactive oxygen species (ROS), and additional determinants of cellular health. Recent studies have highlighted a role for mitochondria during cell differentiation, including in skin epidermis. The observation of oxidative stress in keratinocytes from Krt16 null mouse skin, a model for pachyonychia congenita (PC)–associated palmoplantar keratoderma, prompted us to examine the role of Keratin (K) 16 protein and its partner K6 in regulating the structure and function of mitochondria. Electron microscopy revealed major anomalies in mitochondrial ultrastructure in late stage, E18.5, Krt6a/Krt6b null embryonic mouse skin. Follow-up studies utilizing biochemical, metabolic, and live imaging readouts showed that, relative to controls, skin keratinocytes null for Krt6a/Krt6b or Krt16 exhibit elevated ROS, reduced mitochondrial respiration, intracellular distribution differences, and altered movement of mitochondria within the cell. These findings highlight a novel role for K6 and K16 in regulating mitochondrial morphology, dynamics, and function and shed new light on the causes of oxidative stress observed in PC and related keratin-based skin disorders.

Potential Applications of NRF2 Modulators in Cancer Therapy

The nuclear factor erythroid 2-related factor 2 (NRF2)-Kelch-like ECH-associated protein 1 (KEAP1) regulatory pathway plays an essential role in protecting cells and tissues from oxidative, electrophilic, and xenobiotic stress. By controlling the transactivation of over 500 cytoprotective genes, the NRF2 transcription factor has been implicated in the physiopathology of several human diseases, including cancer. In this respect, accumulating evidence indicates that NRF2 can act as a double-edged sword, being able to mediate tumor suppressive or pro-oncogenic functions, depending on the specific biological context of its activation. Thus, a better understanding of the mechanisms that control NRF2 functions and the most appropriate context of its activation is a prerequisite for the development of effective therapeutic strategies based on NRF2 modulation. In line of principle, the controlled activation of NRF2 might reduce the risk of cancer initiation and development in normal cells by scavenging reactive-oxygen species (ROS) and by preventing genomic instability through decreased DNA damage. In contrast however, already transformed cells with constitutive or prolonged activation of NRF2 signaling might represent a major clinical hurdle and exhibit an aggressive phenotype characterized by therapy resistance and unfavorable prognosis, requiring the use of NRF2 inhibitors. In this review, we will focus on the dual roles of the NRF2-KEAP1 pathway in cancer promotion and inhibition, describing the mechanisms of its activation and potential therapeutic strategies based on the use of context-specific modulation of NRF2.

The synthetic oleanane triterpenoid CDDO-Me binds and inhibits pyruvate kinase M2

BACKGROUND

The M2 isoform of the glycolytic enzyme pyruvate kinase (PKM2) is one of the key components in the Warburg effect, and an important regulator of cancer cell metabolism. Elevated PKM2 expression is a hallmark of numerous tumor types, making it a promising target for cancer therapy.

METHODS

Migration of H1299 lung tumor cells treated with synthetic oleanane triterpenoid derivatives CDDO-Me and CDDO-Im was monitored using scratch and transwell assays. Direct binding and inhibition of PKM2 activity by CDDO-Me was demonstrated by pull-down and activity assays. PKM2 localization in the absence and presence of CDDO-Me or CDDO-Im was determined by subcellular fractionation and immunofluorescence microscopy. Involvement of PKM2 in tumor cell migration was assessed using a stable PKM2 knockdown cell line.

RESULTS

We demonstrate that migration of H1299 lung tumor cells is inhibited by CDDO-Me and CDDO-Im in scratch and transwell assays. CDDO-Me binds directly and specifically to recombinant PKM2, leading to a reduction of its catalytic activity. PKM2 knockdown cells exhibit significantly lower migration compared to control cells when subjected to glucose and oxygen deprivation, but not under regular conditions.

CONCLUSIONS

The results suggest that PKM2 expression in a tumor-like environment contributes to cell migration, and that PKM2 activity can be down regulated by synthetic triterpenoid derivatives.

Blebbistatin Inhibits Neomycin-Induced Apoptosis in Hair Cell-Like HEI-OC-1 Cells and in Cochlear Hair Cells

Aging, noise, and ototoxic drug-induced hair cell (HC) loss are the major causes of sensorineural hearing loss. Aminoglycoside antibiotics are commonly used in the clinic, but these often have ototoxic side effects due to the accumulation of oxygen-free radicals and the subsequent induction of HC apoptosis. Blebbistatin is a myosin II inhibitor that regulates microtubule assembly and myosin–actin interactions, and most research has focused on its ability to modulate cardiac or urinary bladder contractility. By regulating the cytoskeletal structure and reducing the accumulation of reactive oxygen species (ROS), blebbistatin can prevent apoptosis in many different types of cells. However, there are no reports on the effect of blebbistatin in HC apoptosis. In this study, we found that the presence of blebbistatin significantly inhibited neomycin-induced apoptosis in HC-like HEI-OC-1 cells. We also found that blebbistatin treatment significantly increased the mitochondrial membrane potential (MMP), decreased ROS accumulation, and inhibited pro-apoptotic gene expression in both HC-like HEI-OC-1 cells and explant-cultured cochlear HCs after neomycin exposure. Meanwhile, blebbistatin can protect the synaptic connections between HCs and cochlear spiral ganglion neurons. This study showed that blebbistatin could maintain mitochondrial function and reduce the ROS level and thus could maintain the viability of HCs after neomycin exposure and the neural function in the inner ear, suggesting that blebbistatin has potential clinic application in protecting against ototoxic drug-induced HC loss.

Synthesis and Anticancer Activity of CDDO and CDDO-Me, Two Derivatives of Natural Triterpenoids

Triterpenoids are natural compounds synthesized by plants through cyclization of squalene, known for their weak anti-inflammatory activity. 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO), and its C28 modified derivative, methyl-ester (CDDO-Me, also known as bardoxolone methyl), are two synthetic derivatives of oleanolic acid, synthesized more than 20 years ago, in an attempt to enhance the anti-inflammatory behavior of the natural compound. These molecules have been extensively investigated for their strong ability to exert antiproliferative, antiangiogenic, and antimetastatic activities, and to induce apoptosis and differentiation in cancer cells. Here, we discuss the chemical properties of natural triterpenoids, the pathways of synthesis and the biological effects of CDDO and its derivative CDDO-Me. At nanomolar doses, CDDO and CDDO-Me have been shown to protect cells and tissues from oxidative stress by increasing the transcriptional activity of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2). At doses higher than 100 nM, CDDO and CDDO-Me are able to modulate the differentiation of a variety of cell types, both tumor cell lines or primary culture cell, while at micromolar doses these compounds exert an anticancer effect in multiple manners; by inducing extrinsic or intrinsic apoptotic pathways, or autophagic cell death, by inhibiting telomerase activity, by disrupting mitochondrial functions through Lon protease inhibition, and by blocking the deubiquitylating enzyme USP7. CDDO-Me demonstrated its efficacy as anticancer drugs in different mouse models, and versus several types of cancer. Several clinical trials have been started in humans for evaluating CDDO-Me efficacy as anticancer and anti-inflammatory drug; despite promising results, significant increase in heart failure events represented an obstacle for the clinical use of CDDO-Me.

Pre-treatment With Fasudil Prevents Neomycin-Induced Hair Cell Damage by Reducing the Accumulation of Reactive Oxygen Species

Ototoxic drug-induced hair cell (HC) damage is one of the main causes of sensorineural hearing loss, which is one of the most common sensory disorders in humans. Aminoglycoside antibiotics are common ototoxic drugs, and these can cause the accumulation of intracellular oxygen free radicals and lead to apoptosis in HCs. Fasudil is a Rho kinase inhibitor and vasodilator that has been widely used in the clinic and has been shown to have neuroprotective effects. However, the possible application of fasudil in protecting against aminoglycoside-induced HC loss and hearing loss has not been investigated. In this study, we investigated the ability of fasudil to protect against neomycin-induced HC loss both in vitro and in vivo. We found that fasudil significantly reduced the HC loss in cochlear whole-organ explant cultures and reduced the cell death of auditory HEI-OC1 cells after neomycin exposure in vitro. Moreover, we found that fasudil significantly prevented the HC loss and hearing loss of mice in the in vivo neomycin damage model. Furthermore, we found that fasudil could significantly inhibit the Rho signaling pathway in the auditory HEI-OC1 cells after neomycin exposure, thus further reducing the neomycin-induced accumulation of reactive oxygen species and subsequent apoptosis in HEI-OC1 cells. This study suggests that fasudil might contribute to the increased viability of HCs after neomycin exposure by inhibition of the Rho signaling pathway and suggests a new therapeutic target for the prevention of aminoglycoside-induced HC loss and hearing loss.

Synthesis and metabolism of methylglyoxal, S-D-lactoylglutathione and D-lactate in cancer and Alzheimer's disease. Exploring the crossroad of eternal youth and premature aging

Both cancer and Alzheimer's disease (AD) are emerging as metabolic diseases in which aberrant/dysregulated glucose metabolism and bioenergetics occur, and play a key role in disease progression. Interestingly, an enhancement of glucose uptake, glycolysis and pentose phosphate pathway occurs in both cancer cells and amyloid-β-resistant neurons in the early phase of AD. However, this metabolic shift has its adverse effects. One of them is the increase in methylglyoxal production, a physiological cytotoxic by-product of glucose catabolism. Methylglyoxal is mainly detoxified via cytosolic glyoxalase route comprising glyoxalase 1 and glyoxalase 2 with the production of S-D-lactoylglutathione and D-lactate as intermediate and end-product, respectively. Due to the existence of mitochondrial carriers and intramitochondrial glyoxalase 2 and D-lactate dehydrogenase, the transport and metabolism of both S-D-lactoylglutathione and D-lactate in mitochondria can contribute to methylglyoxal elimination, cellular antioxidant power and energy production. In this review, it is supposed that the different ability of cancer cells and AD neurons to metabolize methylglyoxal, S-D-lactoylglutathione and D-lactate scores cell fate, therefore being at the very crossroad of the "eternal youth" of cancer and the "premature death" of AD neurons. Understanding of these processes would help to elaborate novel metabolism-based therapies for cancer and AD treatment.

Electrophiles modulate glutathione reductase activity via alkylation and upregulation of glutathione biosynthesis

Cells evolved robust homeostatic mechanisms to protect against oxidation or alkylation by electrophilic species. Glutathione (GSH) is the most abundant intracellular thiol, protects cellular components from oxidation and is maintained in a reduced state by glutathione reductase (GR). Nitro oleic acid (NO₂-OA) is an electrophilic fatty acid formed under digestive and inflammatory conditions that both reacts with GSH and induces its synthesis upon activation of Nrf2 signaling. The effects of NO₂-OA on intracellular GSH homeostasis were evaluated. In addition to upregulation of GSH biosynthesis, we observed that NO₂-OA increased intracellular GSSG in an oxidative stress-independent manner. NO₂-OA directly inhibited GR in vitro by covalent modification of the catalytic Cys61, with k_on of (3.45 ± 0.04) × 10³ M⁻¹ s⁻¹, k_off of (4.4 ± 0.4) × 10⁻⁴ s⁻¹, and K_eq of (1.3 ± 0.1) × 10⁻⁷ M. Akin to NO₂-OA, the electrophilic Nrf2 activators bardoxolone-imidazole (CDDO-Im), bardoxolone-methyl (CDDO-Me) and dimethyl fumarate (DMF) also upregulated GSH biosynthesis while promoting GSSG accumulation, but without directly inhibiting GR activity. In vitro assays in which GR was treated with increasing GSH concentrations and GSH depletion experiments in cells revealed that GR activity is finely regulated via product inhibition, an observation further supported by theoretical (kinetic modeling of cellular GSSG:GSH levels) approaches. Together, these results describe two independent mechanisms by which electrophiles modulate the GSH/GSSG couple, and provide a novel conceptual framework to interpret experimentally determined values of GSH and GSSG.

HDAC and Ku70 axis- an effective target for apoptosis induction by a new 2-cyano-3-oxo-1,9-dien glycyrrhetinic acid analogue

Methyl 2-cyano-3,12-dioxo-18β-olean-1,9(11)-dien-30-oate (CDODO-Me, 10d) derived from glycyrrhetinic acid and methyl-2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO-Me) derived from oleanoic acid are potent apoptosis inducers developed to clinical trials. Both compounds have high affinity for reduced  glutathione (GSH), which needs to be overcome to improve their target selectivity. We generated a new 10d analogue methyl 2-cyano-3-oxo-18β-olean-1,9(11), 12-trien-30-oate (COOTO, 10e), which retains high apoptosis inducing ability, while displaying decreased affinity for GSH, and explored the acting targets. We found that it induces Noxa level, reduces c-Flip level and causes Bax/Bak activation. Silencing of either Noxa or Bak significantly attenuated apoptosis induction of 10e. We linked these events due to targeting HDAC3/HDAC6 and Ku70 axis. 10e treatment reduced the levels of HDAC3 and HDAC6 with increased DNA damage/repair marker gamma-H2AX (γ-H2AX) and acetylated Ku70. c-Flip dissociates from acetylated Ku70 undergoing degradation, while Bax dissociates from acetylated Ku70 undergoing activation. Silencing of either HDAC3 or HDAC6 enhanced 10e-induced apoptosis. We reveal a new action cascade of this category of compounds that involves targeting of HADC3/6 proteins and Ku70 acetylation.

Prognostic value, localization and correlation of PD-1/PD-L1, CD8 and FOXP3 with the desmoplastic stroma in pancreatic ductal adenocarcinoma

We examined the prognostic value of programmed cell death-1 (PD-1) and its ligand (PD-L1) together with CD8+ tumor-infiltrating lymphocytes (TILs) and FOXP3+ Tregs in resectable pancreatic ductal adenocarcinoma (PDAC) samples treated with adjuvant chemotherapy. Whole-mount FFPE tissue sections from 145 pancreatectomies were immunohistochemically stained for PD-1, PD-L1, CD8 and FOXP3. Their expression was correlated with clinicopathological characteristics, and overall survival (OS), progression-free survival (PFS), local progression-free survival (LPFS) and distant metastases free-survival (DMFS), in the context of stroma density (haematoxylin-eosin) and activity (alpha-smooth muscle actin) and in regard to intratumoral lymphoid aggregates. The median OS was 21 months after a mean follow-up of 20 months (range, 2-69 months). In multivariate analysis, high PD-1+ TILs expression was associated with better OS (p = 0.049), LPFS (p = 0.017) and DMFS (p = 0.021). Similar findings were observed for CD8+ TILs, whereas FOXP3 and PD-L1 lacked prognostic significance. Although TIL distribution was heterogeneous, tumors of high stroma density had higher infiltration of CD8+ TILs than loose density stroma and vice versa (p < 0.001), whereas no correlation was found with stromal activity. Sixty (41.4%) tumors contained lymphoid aggregates and the presence of PD-1+ TILs was associated with better OS (p = 0.030), LPFS (p = 0.025) and DMFS (p = 0.033), whereas CD8+ TILs only correlated with superior LPFS (p = 0.039). PD-1+ and CD8+ TILs constitute independent prognostic markers in patients with PDAC treated with adjuvant chemotherapy. Our study provides important insight on the role of PD-1/PD-L1 in the context of desmoplastic stroma and could help guide future immunotherapies in PDAC.

Nitro-fatty acid inhibition of triple-negative breast cancer cell viability, migration, invasion, and tumor growth

Triple-negative breast cancer (TNBC) comprises ∼20% of all breast cancers and is the most aggressive mammary cancer subtype. Devoid of the estrogen and progesterone receptors, along with the receptor tyrosine kinase ERB2 (HER2), that define most mammary cancers, there are no targeted therapies for patients with TNBC. This, combined with a high metastatic rate and a lower 5-year survival rate than for other breast cancer phenotypes, means there is significant unmet need for new therapeutic strategies. Herein, the anti-neoplastic effects of the electrophilic fatty acid nitroalkene derivative, 10-nitro-octadec-9-enoic acid (nitro-oleic acid, NO₂-OA), were investigated in multiple preclinical models of TNBC. NO₂-OA reduced TNBC cell growth and viability in vitro, attenuated TNFα-induced TNBC cell migration and invasion, and inhibited the tumor growth of MDA-MB-231 TNBC cell xenografts in the mammary fat pads of female nude mice. The up-regulation of these aggressive tumor cell growth, migration, and invasion phenotypes is mediated in part by the constitutive activation of pro-inflammatory nuclear factor κB (NF-κB) signaling in TNBC. NO₂-OA inhibited TNFα-induced NF-κB transcriptional activity in human TNBC cells and suppressed downstream NF-κB target gene expression, including the metastasis-related proteins intercellular adhesion molecule-1 and urokinase-type plasminogen activator. The mechanisms accounting for NF-κB signaling inhibition by NO₂-OA in TNBC cells were multifaceted, as NO₂-OA (a) inhibited the inhibitor of NF-κB subunit kinase β phosphorylation and downstream inhibitor of NF-κB degradation, (b) alkylated the NF-κB RelA protein to prevent DNA binding, and (c) promoted RelA polyubiquitination and proteasomal degradation. Comparisons with non-tumorigenic human breast epithelial MCF-10A and MCF7 cells revealed that NO₂-OA more selectively inhibited TNBC function. This was attributed to more facile mechanisms for maintaining redox homeostasis in normal breast epithelium, including a more favorable thiol/disulfide balance, greater extents of multidrug resistance protein-1 (MRP1) expression, and greater MRP1-mediated efflux of NO₂-OA-glutathione conjugates. These observations reveal that electrophilic fatty acid nitroalkenes react with more alkylation-sensitive targets in TNBC cells to inhibit growth and viability.

Mutant spastin proteins promote deficits in axonal transport through an isoform-specific mechanism involving casein kinase 2 activation

Mutations of various genes cause hereditary spastic paraplegia (HSP), a neurological disease involving dying-back degeneration of upper motor neurons. From these, mutations in the SPAST gene encoding the microtubule-severing protein spastin account for most HSP cases. Cumulative genetic and experimental evidence suggests that alterations in various intracellular trafficking events, including fast axonal transport (FAT), may contribute to HSP pathogenesis. However, the mechanisms linking SPAST mutations to such deficits remain largely unknown. Experiments presented here using isolated squid axoplasm reveal inhibition of FAT as a common toxic effect elicited by spastin proteins with different HSP mutations, independent of microtubule-binding or severing activity. Mutant spastin proteins produce this toxic effect only when presented as the tissue-specific M1 isoform, not when presented as the ubiquitously-expressed shorter M87 isoform. Biochemical and pharmacological experiments further indicate that the toxic effects of mutant M1 spastins on FAT involve casein kinase 2 (CK2) activation. In mammalian cells, expression of mutant M1 spastins, but not their mutant M87 counterparts, promotes abnormalities in the distribution of intracellular organelles that are correctable by pharmacological CK2 inhibition. Collectively, these results demonstrate isoform-specific toxic effects of mutant M1 spastin on FAT, and identify CK2 as a critical mediator of these effects.

Perspectives of the Nrf-2 signaling pathway in cancer progression and therapy

The Nuclear factor erythroid2-related factor2 (Nrf2), a master regulator of redox homoeostasis, is a key transcription factor regulating a wide array of genes for antioxidant and detoxification enzymes. It protects organs from various kinds of toxic insults. On the other hand, activation of Nrf2 is also correlated with cancer progression and chemoresistance. Downregulation of Nrf2 activity has attracted an increasing amount of attention as it may provide an alternative cancer therapy. In this review, we examine recent studies on roles of Nrf2 in several pathophysiological conditions emphasising cancer. We discuss elaborately the current knowledge on Nrf2 regulation including KEAP1-dependent and KEAP1-independent cascades. KEAP1/Nrf2 system is a master regulator of cellular response against a variety of environmental stresses. We also highlight several tightly controlled regulations of Nrf2 by numerous proteins, small molecules, toxic metals, etc. In addition, we evaluate the possible therapeutic approaches of increasing chemosensitivity via modulating Nrf2 signaling.

Mitochondria, cholesterol and cancer cell metabolism

Given the role of mitochondria in oxygen consumption, metabolism and cell death regulation, alterations in mitochondrial function or dysregulation of cell death pathways contribute to the genesis and progression of cancer. Cancer cells exhibit an array of metabolic transformations induced by mutations leading to gain-of-function of oncogenes and loss-of-function of tumor suppressor genes that include increased glucose consumption, reduced mitochondrial respiration, increased reactive oxygen species generation and cell death resistance, all of which ensure cancer progression. Cholesterol metabolism is disturbed in cancer cells and supports uncontrolled cell growth. In particular, the accumulation of cholesterol in mitochondria emerges as a molecular component that orchestrates some of these metabolic alterations in cancer cells by impairing mitochondrial function. As a consequence, mitochondrial cholesterol loading in cancer cells may contribute, in part, to the Warburg effect stimulating aerobic glycolysis to meet the energetic demand of proliferating cells, while protecting cancer cells against mitochondrial apoptosis due to changes in mitochondrial membrane dynamics. Further understanding the complexity in the metabolic alterations of cancer cells, mediated largely through alterations in mitochondrial function, may pave the way to identify more efficient strategies for cancer treatment involving the use of small molecules targeting mitochondria, cholesterol homeostasis/trafficking and specific metabolic pathways.

Oleanolic acid derivatives for pharmaceutical use: a patent review

INTRODUCTION

Oleanolic acid belongs to the pentacyclic triterpene family. In China, oleanolic acid has been used as an over the counter (OTC) hepatoprotective drug for decades. Oleanolic acid and its derivatives present a wide variety of biological activities, supporting their pharmaceutical uses for multiple diseases.

AREAS COVERED

Representative patent publications (1971-2015) covering the preparation, pharmaceutical compositions, and medical uses of oleanolic acid and its derivatives are analyzed, with focus on their anticancer, anti-osteoporosis, anti-obesity, anti-diabetic, lipid-lowering, anti-inflammatory, antioxidant, immune-regulatory, and hepatoprotective effects. A large number of Chinese patents have been given particular attention in this review.

EXPERT OPINION

Detailed efficacy studies are highly worth doing to undoubtedly confirm the clinical potential of oleanolic acid and its derivatives. Based on that, it would be critical to identify the key protein targets of the drugs so as to promote drug development and search for new lead compounds. Together, there is a huge potential for drug-repositioning of oleanolic acid, particularly in the areas of metabolic disease and immunological disorders.

Protective Role of Nuclear Factor E2-Related Factor 2 against Acute Oxidative Stress-Induced Pancreatic β -Cell Damage

Oxidative stress is implicated in the pathogenesis of pancreatic β-cell dysfunction that occurs in both type 1 and type 2 diabetes. Nuclear factor E2-related factor 2 (NRF2) is a master regulator in the cellular adaptive response to oxidative stress. The present study found that MIN6 β-cells with stable knockdown of Nrf2 (Nrf2-KD) and islets isolated from Nrf2-knockout mice expressed substantially reduced levels of antioxidant enzymes in response to a variety of stressors. In scramble MIN6 cells or wild-type islets, acute exposure to oxidative stressors, including hydrogen peroxide (H2O2) and S-nitroso-N-acetylpenicillamine, resulted in cell damage as determined by decrease in cell viability, reduced ATP content, morphology changes of islets, and/or alterations of apoptotic biomarkers in a concentration- and/or time-dependent manner. In contrast, silencing of Nrf2 sensitized MIN6 cells or islets to the damage. In addition, pretreatment of MIN6 β-cells with NRF2 activators, including CDDO-Im, dimethyl fumarate (DMF), and tert-butylhydroquinone (tBHQ), protected the cells from high levels of H2O2-induced cell damage. Given that reactive oxygen species (ROS) are involved in regulating glucose-stimulated insulin secretion (GSIS) and persistent activation of NRF2 blunts glucose-triggered ROS signaling and GSIS, the present study highlights the distinct roles that NRF2 may play in pancreatic β-cell dysfunction that occurs in different stages of diabetes.

A synthetic triterpenoid CDDO-Im inhibits tumorsphere formation by regulating stem cell signaling pathways in triple-negative breast cancer

Triple-negative breast cancer is associated with poor prognosis because of a high rate of tumor recurrence and metastasis. Previous studies demonstrated that the synthetic triterpenoid, CDDO-Imidazolide (CDDO-Im) induced cell cycle arrest and apoptosis in triple-negative breast cancer. Since a small subpopulation of cancer stem cells has been suggested to be responsible for drug resistance and metastasis of tumors, our present study determined whether the effects of CDDO-Im in triple-negative breast cancer are due to the inhibition of a cancer stem cell subpopulation. CDDO-Im treatment markedly induced cell cycle arrest at G2/M-phase and apoptosis in the triple-negative breast cancer cell lines, SUM159 and MDA-MB-231. Because SUM159 cells were more sensitive to CDDO-Im than MDA-MB-231 cells, the effects of CDDO-Im on the cancer stem cell subpopulation were further investigated in SUM159 cells. SUM159 cells formed tumorspheres in culture, and the cancer stem cell subpopulation, CD24−/EpCAM+ cells, was markedly enriched in SUM159 tumorspheres. The CD24−/EpCAM+ cells in SUM159 tumorspheres were significantly inhibited by CDDO-Im treatment. CDDO-Im also significantly decreased sphere forming efficiency and tumorsphere size in both primary and secondary sphere cultures. PCR array of stem cell signaling genes showed that expression levels of many key molecules in the stem cell signaling pathways, such as Notch, TGF-β/Smad, Hedgehog and Wnt, were significantly down-regulated by CDDO-Im in SUM159 tumorspheres. Protein levels of Notch receptors (c-Notch1, Notch1 and Notch3), TGF-β/Smad (pSmad2/3) and Hedgehog downstream effectors (GLI1) also were markedly reduced by CDDO-Im. In conclusion, the present study demonstrates that the synthetic triterpenoid, CDDO-Im, is a potent anti-cancer agent against triple-negative breast cancer cells by targeting the cancer stem cell subpopulation.

Glutathione: new roles in redox signaling for an old antioxidant

The physiological roles played by the tripeptide glutathione have greatly advanced over the past decades superimposing the research on free radicals, oxidative stress and, more recently, redox signaling. In particular, GSH is involved in nutrient metabolism, antioxidant defense, and regulation of cellular metabolic functions ranging from gene expression, DNA and protein synthesis to signal transduction, cell proliferation and apoptosis. This review will be focused on the role of GSH in cell signaling by analysing the more recent advancements about its capability to modulate nitroxidative stress, autophagy, and viral infection.

Glutathione and mitochondria

Glutathione (GSH) is the main non-protein thiol in cells whose functions are dependent on the redox-active thiol of its cysteine moiety that serves as a cofactor for a number of antioxidant and detoxifying enzymes. While synthesized exclusively in the cytosol from its constituent amino acids, GSH is distributed in different compartments, including mitochondria where its concentration in the matrix equals that of the cytosol. This feature and its negative charge at physiological pH imply the existence of specific carriers to import GSH from the cytosol to the mitochondrial matrix, where it plays a key role in defense against respiration-induced reactive oxygen species and in the detoxification of lipid hydroperoxides and electrophiles. Moreover, as mitochondria play a central strategic role in the activation and mode of cell death, mitochondrial GSH has been shown to critically regulate the level of sensitization to secondary hits that induce mitochondrial membrane permeabilization and release of proteins confined in the intermembrane space that once in the cytosol engage the molecular machinery of cell death. In this review, we summarize recent data on the regulation of mitochondrial GSH and its role in cell death and prevalent human diseases, such as cancer, fatty liver disease, and Alzheimer’s disease.

Oleanolic acid and its synthetic derivatives for the prevention and therapy of cancer: preclinical and clinical evidence

Oleanolic acid (OA, 3β-hydroxyolean-12-en-28-oic acid) is a ubiquitous pentacyclic multifunctional triterpenoid, widely found in several dietary and medicinal plants. Natural and synthetic OA derivatives can modulate multiple signaling pathways including nuclear factor-κB, AKT, signal transducer and activator of transcription 3, mammalian target of rapamycin, caspases, intercellular adhesion molecule 1, vascular endothelial growth factor, and poly (ADP-ribose) polymerase in a variety of tumor cells. Importantly, synthetic derivative of OA, 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO), and its C-28 methyl ester (CDDO-Me) and C28 imidazole (CDDO-Im) have demonstrated potent antiangiogenic and antitumor activities in rodent cancer models. These agents are presently under evaluation in phase I studies in cancer patients. This review summarizes the diverse molecular targets of OA and its derivatives and also provides clear evidence on their promising potential in preclinical and clinical situations.

CDDO-Me: A Novel Synthetic Triterpenoid for the Treatment of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal human malignancy with dismal prognosis and few effective therapeutic options. Novel agents that are safe and effective are urgently needed. Oleanolic acid-derived synthetic triterpenoids are potent antitumorigenic agents, but their efficacy or the mechanism of action for pancreatic cancer has not been adequately investigated. In this study, we evaluated the antitumor activity and the mechanism of action of methyl-2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oate (CDDO-Me), a oleanane-derived synthetic triterpenoid for human pancreatic cancer cell lines. CDDO-Me inhibited the growth of both K-ras mutated (MiaPaca2, Panc1 and Capan2) and wild-type K-ras (BxPC3) pancreatic cancer cells at very low concentrations. The growth inhibitory activity of CDDO-Me was attributed to the induction of apoptosis characterized by increased annexin-V-FITC binding and cleavage of PARP-1 and procaspases-3, -8 and-9. In addition, CDDO-Me induced the loss of mitochondrial membrane potential and release of cytochrome C. The antitumor activity of CDDO-Me was associated with the inhibition of prosurvival p-Akt, NF-κB and mammalian target of rapamycin (mTOR) signaling proteins and the downstream targets of Akt and mTOR, such as p-Foxo3a (Akt) and p-S6K1, p-eIF-4E and p-4E-BP1 (mTOR). Silencing of Akt or mTOR with gene specific-siRNA sensitized the pancreatic cancer cells to CDDO-Me, demonstrating Akt and mTOR as molecular targets of CDDO-Me for its growth inhibitory and apoptosis-inducing activity.

Keap1-Nrf2 signaling pathway: mechanisms of regulation and role in protection of cells against toxicity caused by xenobiotics and electrophiles

The transcription factor Nrf2 governs the expression of a considerable group of genes involved in cell protection against oxidants, electrophiles, and genotoxic compounds. The activity of Nrf2 is sensitive to xenobiotics and endogenous electrophiles. Nrf2 is negatively regulated by specific suppressor protein Keap1, which is also a receptor of electrophiles and adapter for Cul3 ubiquitin ligase. Electrophiles react with critical thiol groups of Keap1 leading to the loss of its ability to inhibit Nrf2. The Keap1-Nrf2 signaling pathway also down-regulates NF-κB transcriptional activity and attenuates cytokine-mediated induction of proinflammatory genes. Pharmacological activation of the Keap1-Nrf2 pathway can be used for treatment and prevention of many diseases. Widely known natural Keap1-Nrf2 activators include curcumin, quercetin, resveratrol, and sulforaphane. The most effective Keap1-Nrf2 activators are synthetic oleanane triterpenoids.

Mitochondrial glutathione: features, regulation and role in disease

BACKGROUND

Mitochondria are the powerhouse of mammalian cells and the main source of reactive oxygen species (ROS) associated with oxygen consumption. In addition, they also play a strategic role in controlling the fate of cells through regulation of death pathways. Mitochondrial ROS production fulfills a signaling role through regulation of redox pathways, but also contributes to mitochondrial damage in a number of pathological states.

SCOPE OF REVIEW

Mitochondria are exposed to the constant generation of oxidant species, and yet the organelle remains functional due to the existence of an armamentarium of antioxidant defense systems aimed to repair oxidative damage, of which mitochondrial glutathione (mGSH) is of particular relevance. Thus, the aim of the review is to cover the regulation of mGSH and its role in disease.

MAJOR CONCLUSIONS

Cumulating evidence over recent years has demonstrated the essential role for mGSH in mitochondrial physiology and disease. Despite its high concentration in the mitochondrial matrix, mitochondria lack the enzymes to synthesize GSH de novo, so that mGSH originates from cytosolic GSH via transport through specific mitochondrial carriers, which exhibit sensitivity to membrane dynamics. Depletion of mGSH sensitizes cells to stimuli leading to oxidative stress such as TNF, hypoxia or amyloid β-peptide, thereby contributing to disease pathogenesis.

GENERAL SIGNIFICANCE

Understanding the regulation of mGSH may provide novel insights to disease pathogenesis and toxicity and the opportunity to design therapeutic targets of intervention in cell death susceptibility and disease. This article is part of a Special Issue entitled Cellular functions of glutathione.

Synthetic oleanane triterpenoids: multifunctional drugs with a broad range of applications for prevention and treatment of chronic disease

We review the rationale for the use of synthetic oleanane triterpenoids (SOs) for prevention and treatment of disease, as well as extensive biological data on this topic resulting from both cell culture and in vivo studies. Emphasis is placed on understanding mechanisms of action. SOs are noncytotoxic drugs with an excellent safety profile. Several hundred SOs have now been synthesized and in vitro have been shown to: 1) suppress inflammation and oxidative stress and therefore be cytoprotective, especially at low nanomolar doses, 2) induce differentiation, and 3) block cell proliferation and induce apoptosis at higher micromolar doses. Animal data on the use of SOs in neurodegenerative diseases and in diseases of the eye, lung, cardiovascular system, liver, gastrointestinal tract, and kidney, as well as in cancer and in metabolic and inflammatory/autoimmune disorders, are reviewed. The importance of the cytoprotective Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1/nuclear factor (erythroid-derived 2)-like 2/antioxidant response element (Keap1/Nrf2/ARE) pathway as a mechanism of action is explained, but interactions with peroxisome proliferator-activated receptor γ (PARPγ), inhibitor of nuclear factor-κB kinase complex (IKK), janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT), human epidermal growth factor receptor 2 (HER2)/ErbB2/neu, phosphatase and tensin homolog (PTEN), the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway, mammalian target of rapamycin (mTOR), and the thiol proteome are also described. In these interactions, Michael addition of SOs to reactive cysteine residues in specific molecular targets triggers biological activity. Ultimately, SOs are multifunctional drugs that regulate the activity of entire networks. Recent progress in the earliest clinical trials with 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) methyl ester (bardoxolone methyl) is also summarized.

The mitochondrial ATP-dependent Lon protease: a novel target in lymphoma death mediated by the synthetic triterpenoid CDDO and its derivatives

Synthetic triterpenoids are multitarget compounds exhibiting promise as preventative and therapeutic agents for cancer. Their proposed mechanism of action is by forming Michael adducts with reactive nucleophilic groups on target proteins. Our previous work demonstrates that the 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and its derivatives promote B-lymphoid cell apoptosis through a mitochondria-mediated pathway linked to mitochondrial protein aggregation. As one function of the Lon protease is to eliminate abnormal mitochondrial proteins, we hypothesized that CDDO-induced protein aggregation and lymphoma apoptosis occur by inactivating this enzyme. Here, we show that CDDO and its derivatives directly and selectively inhibit Lon. CDDO blocks Lon-mediated proteolysis in biochemical and cellular assays, but does not inhibit the 20S proteasome. Furthermore, a biotinylated-CDDO conjugate modifies mitochondrial Lon. A striking common phenotype of CDDO-treated lymphoma cells and Lon-knockdown cells is the accumulation of electron-dense aggregates within mitochondria. We also show that Lon protein levels are substantially elevated in malignant lymphoma cells, compared with resting or activated B cells. Finally, we demonstrate that Lon knockdown leads to lymphoma cell death. Together, these findings suggest that Lon inhibition plays a contributory role in CDDO-induced lymphoma cell death, and support the concept that mitochondrial Lon is a novel anticancer drug target.

Growth inhibitory, apoptotic and anti-inflammatory activities displayed by a novel modified triterpenoid, cyano enone of methyl boswellates

Triterpenoids are pentacyclic secondary metabolites present in many terrestrial plants. Natural triterpenoids have been reported to exhibit anti-inflammatory and anti-carcinogenic activities. Here, we show that modifications of ring A of boswellic acid (2 cyano, 3 enone) resulted in a highly active growth inhibitory, anti-inflammatory, prodifferentiative and anti-tumour triterpenoid compound called cyano enone of methyl boswellates (CEMB). This compound showed cytotoxic activity on a number of cancer cell lines with IC₅₀ ranging from 0.2 to 0.6 μM. CEMB inhibits DNA synthesis and induces apoptosis in A549 cell line at 0.25 μM and 1 μM concentrations, respectively. CEMB induces adipogenic differentiation in 3T3-L1 cells at a concentration of 0.1 μM. Finally, administration of CEMB intra-tumourally significantly inhibited the growth of C6 glioma tumour xenograft in immuno-compromised mice. Collectively, these results suggest that CEMB is a very potent anti-tumour compound.

The Role of PPAR-gamma and Its Interaction with COX-2 in Pancreatic Cancer

In recent years, the study of the peroxisome proliferators activated receptor gamma (PPAR-γ) as a potential target for cancer prevention and therapy has gained a strong interest. However, the overall biological significance of PPAR-γ in cancer development and progression is still controversial. While many reports documented antiproliferative effects in human cancer cell and animal models, several studies demonstrating potential tumor promoting actions of PPAR-γ ligands raised considerable concerns about the role of PPAR-γ in human cancers. Controversy also exists about the role of PPAR-γ in human pancreatic cancers. The current review summarizes the data about PPAR-γ in pancreatic cancer and highlights the biologically relevant interactions between the cyclooxygenase and PPAR system.

Synthetic triterpenoid cyano enone of methyl boswellate activates intrinsic, extrinsic, and endoplasmic reticulum stress cell death pathways in tumor cell lines

We explored the effect of a novel synthetic triterpenoid compound cyano enone of methyl boswellates (CEMB) on various prostate cancer and glioma cancer cell lines. CEMB displayed concentration-dependent cytotoxic activity with submicromolar lethal dose 50% (LD(50)) values in 10 of 10 tumor cell lines tested. CEMB-induced cytotoxicity is accompanied by activation of downstream effector caspases (caspases 3 and 7) and by upstream initiator caspases involved in both the extrinsic (caspase 8) and intrinsic (caspase 9) apoptotic pathways. By using short interfering RNAs (siRNA), we show evidence that knockdown of caspase 8, DR4, Apaf-1, and Bid impairs CEMB-induced cell death. Similar to other proapoptotic synthetic triterpenoid compounds, CEMB-induced apoptosis involved endoplasmic reticulum stress, as shown by partial rescue of tumor cells by siRNA-mediated knockdown of expression of genes involved in the unfolded protein response such as IRE1α, PERK, and ATF6. Altogether, our results suggest that CEMB stimulates several apoptotic pathways in cancer cells, suggesting that this compound should be evaluated further as a potential agent for cancer therapy.

CDDO-imidazolide induces DNA damage, G2/M arrest and apoptosis in BRCA1-mutated breast cancer cells

Breast cancer-associated gene 1 (BRCA1) protein plays important roles in DNA damage and repair, homologous recombination, cell-cycle regulation, and apoptosis. The synthetic triterpenoid 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Imidazolide, CDDO-Im) is a promising anticancer and chemopreventive agent with potent antiproliferative and apoptotic activities against a wide variety of cancer types. However, the mechanisms responsible for the selective apoptotic effects of CDDO-Im in cancer cells remain elusive. In the present work, CDDO-Im induced G2/M arrest and apoptosis in BRCA1-mutated mammary tumor cell lines. Prior to the induction of apoptosis, CDDO-Im induced DNA damage and the phosphorylation of H2AX followed by activation of the DNA damage response. Moreover, CDDO-Im also induced the generation of reactive oxygen species (ROS), which is associated with the induction of DNA damage, in both mouse and human tumor cells containing a BRCA1 mutation. The inhibition of ROS generation by uric acid prevented the induction of DNA damage by CDDO-Im. Furthermore, treatment with CDDO-Im did not induce ROS in nonmalignant MCF-10A breast epithelial cells or in E18-14C-27 breast cancer cells with wild-type BRCA1 genes and was not cytotoxic to normal mouse 3T3 fibroblasts, highlighting a selective therapeutic potential of CDDO-Im for BRCA1-associated breast cancer cells. Altogether, our results show that CDDO-Im induces ROS and subsequent DNA damage, thereby facilitating the activation of the DNA damage checkpoint, G2/M arrest, and finally apoptosis in BRCA1-mutated cancer cells. The particular relevance of these findings to the chemoprevention of cancer is discussed. Cancer Prev Res; 4(3); 425-34. ©2011 AACR.

Synthesis and pro-apoptotic activity of novel glycyrrhetinic acid derivatives

Triterpenoids are used for medicinal purposes in many countries. Some, such as oleanolic and glycyrrhetinic acids, are known to be anti-inflammatory and anticarcinogenic. However, the biological activities of these naturally occurring molecules against their particular targets are weak, so the synthesis of new synthetic analogues with enhanced potency is needed. By combining modifications to both the A and C rings of 18βH-glycyrrhetinic acid, the novel synthetic derivative methyl 2-cyano-3,12-dioxo-18βH-olean-9(11),1(2)-dien-30-oate was obtained. This derivative displays high antiproliferative activity in cancer cells, including a cell line with a multidrug-resistance phenotype. It causes cell death by inducing the intrinsic caspase-dependent apoptotic pathway.

Synthesis and antitumor evaluation of methyl spongoate analogs

A series of novel methyl spongoate (1) analogs has been synthesized and evaluated for their in vitro cytotoxic properties. It was found that the nature of the C-20 side chain had significant effects on their bioactivities and some analogs showed higher cytotoxicity than 1 against A549, HCT-116, HepG2, SW-1990, MCF-7 and NCI-H460 tumor cell lines. The pharmacological results confirmed that the α,β-unsaturated carbonyl moiety, a Michael acceptor in ring A, plays a pivotal role in the cytotoxic effect of these derivatives. The compiled pharmacological data may be useful for the design of novel analogous anticancer drugs.

Synthetic triterpenoids prolong survival in a transgenic mouse model of pancreatic cancer

Pancreatic cancer is the fourth leading cause of cancer-related deaths in the United States and is nearly always fatal. Whereas early detection offers the most promising approach for reducing the mortality of this disease, there is still a need to develop effective drugs for the prevention and treatment of pancreatic cancer. We tested two promising classes of noncytotoxic drugs, synthetic oleanane triterpenoids and rexinoids, for the prevention of carcinogenesis in the highly relevant LSL-Kras(G12D/+);LSL-Trp53(R127H/+);Pdx-1-Cre (KPC) mouse model of pancreatic cancer. KPC transgenic mice closely recapitulate the genetic mutations, clinical symptoms, and histopathology found in human pancreatic cancer. Beginning at 4 weeks of age, mice were fed powdered control diet or a diet containing the triterpenoids CDDO-methyl ester (CDDO-Me) or CDDO-ethyl amide, the rexinoid LG100268 (LG268), or the combination, until the mice displayed overt symptoms of pancreatic cancer. CDDO-Me, LG268, the combination of CDDO-Me and LG268, and the combination of CDDO-ethyl amide and LG268, all significantly (P < 0.05) increased survival in the KPC mice by 3 to 4 weeks. Recent studies have shown that gemcitabine, the current standard of care for human pancreatic cancer, does not extend survival in KPC mice. In cell lines developed from the KPC mice, the triterpenoids directly interact with both signal transducer and activator of transcription 3 and IκB kinase (IKK) to decrease constitutive interleukin-6 secretion, inhibit constitutive signal transducer and activator of transcription 3 phosphorylation, and block the degradation of IκBα when challenged with tumor necrosis factor α. These results suggest that oleanane triterpenoids and rexinoids have the potential to prevent pancreatic cancer.

Synthetic triterpenoids target the Arp2/3 complex and inhibit branched actin polymerization

Synthetic triterpenoids are anti-tumor agents that affect numerous cellular functions including apoptosis and growth inhibition. Here, we used mass spectrometric and protein array approaches and uncovered that triterpenoids associate with proteins of the actin cytoskeleton, including actin-related protein 3 (Arp3). Arp3, a subunit of the Arp2/3 complex, is involved in branched actin polymerization and the formation of lamellipodia. 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO)-Im and CDDO-Me were observed to 1) inhibit the localization of Arp3 and actin at the leading edge of cells, 2) abrogate cell polarity, and 3) inhibit Arp2/3-dependent branched actin polymerization. We confirmed our drug effects with siRNA targeting of Arp3 and observed a decrease in Rat2 cell migration. Taken together, our data suggest that synthetic triterpenoids target Arp3 and branched actin polymerization to inhibit cell migration.

Mesenchymal stromal cells alone or expressing interferon-beta suppress pancreatic tumors in vivo, an effect countered by anti-inflammatory treatment

BACKGROUND AIMS

Because of the inflammatory nature and extensive stromal compartment in pancreatic tumors, we investigated the role of mesenchymal stromal cells (MSC) to engraft selectively in pancreatic carcinomas and serve as anti-tumor drug delivery vehicles to control pancreatic cancer progression.

METHODS

Human pancreatic carcinoma cells, PANC-1, expressing renilla luciferase were orthotopically implanted into SCID mice and allowed to develop for 10 days. Firefly luciferase-transduced MSC or MSC expressing interferon (IFN)-beta were then injected intraperitoneally weekly for 3 weeks. Mice were monitored by bioluminescent imaging for expression of renilla (PANC-1) and firefly (MSC) luciferase.

RESULTS

MSC selectively homed to sites of primary and metastatic pancreatic tumors and inhibited tumor growth (P=0.032). The production of IFN-beta within the tumor site by MSC-IFN-beta further suppressed tumor growth (P=0.0000083). Prior studies indicated that MSC home to sites of inflammation; therefore, we sought to alter the tumor microenvironment through treatment with a potent anti-inflammatory agent. After treatment, inflammation-associated mediators were effectively down-regulated, including NFkappaB, vascular endothelial growth factor (VEGF) and interleukin (IL)-6 as well as chemokines involved in MSC migration (CCL3 and CCL25). Treatment with the anti-inflammatory agent CDDO-Me before and after MSC-IFN-beta injections resulted in reduction of MSC in the tumors and reversed the positive effect of tumor inhibition by MSC-IFN-beta alone (P=0.041).

CONCLUSIONS

These results suggest that MSC exhibit innate anti-tumor effects against PANC-1 cells and can serve as delivery vehicles for IFN-beta for the treatment of pancreatic cancer. However, these beneficial effects may be lost in therapies combining MSC with anti-inflammatory agents.

Role of peroxisome proliferator-activated receptor-gamma and its coactivator DRIP205 in cellular responses to CDDO (RTA-401) in acute myelogenous leukemia

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a member of the nuclear receptor (NR) family of transcription factors with important regulatory roles in cellular growth, differentiation, and apoptosis. Using proteomic analysis, we showed expression of PPARgamma protein in a series of 260 newly diagnosed primary acute myelogenous leukemia (AML) samples. Forced expression of PPARgamma enhanced the sensitivity of myeloid leukemic cells to apoptosis induced by PPARgamma agonists 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and 15-deoxy-(12,14)-15DPGJ(2), through preferential cleavage of caspase-8. No effects on cell cycle distribution or differentiation were noted, despite prominent induction of p21 in PPARgamma-transfected cells. In turn, antagonizing PPARgamma function by small interfering RNA or pharmacologic PPARgamma inhibitor significantly diminished apoptosis induction by CDDO. Overexpression of coactivator protein DRIP205 resulted in enhanced differentiation induction by CDDO in AML cells through PPARgamma activation. Studies with DRIP205 deletion constructs showed that the NR boxes of DRIP205 are not required for this coactivation. In a phase I clinical trial of CDDO (RTA-401) in leukemia, CDDO induced an increase in PPARgamma mRNA expression in six of nine patient samples; of those, induction of differentiation was documented in four patients and that of p21 in three patients, all expressing DRIP205 protein. In summary, these findings suggest that cellular levels of PPARgamma regulate induction of apoptosis via caspase-8 activation, whereas the coactivator DRIP205 is a determinant of induction of differentiation, in response to PPARgamma agonists in leukemic cells.