Inhibition of mitochondrial metabolism by methyl-2-cyano-3,12-dioxooleana-1,9-diene-28-oate induces apoptotic or autophagic cell death in chronic myeloid leukemia cells

RTA dh404 Induces Cell Cycle Arrest, Apoptosis, and Autophagy in Glioblastoma Cells

RTA dh404 is a novel synthetic oleanolic acid derivative that has been reported to possess anti-allergic, neuroprotective, antioxidative, and anti-inflammatory properties, and exerts therapeutic effects on various cancers. Although CDDO and its derivatives have anticancer effects, the actual anticancer mechanism has not been fully explored. Therefore, in this study, glioblastoma cell lines were exposed to different concentrations of RTA dh404 (0, 2, 4, and 8 µM). Cell viability was evaluated using the PrestoBlue™ reagent assay. The role of RTA dh404 in cell cycle progression, apoptosis, and autophagy was analyzed using flow cytometry and Western blotting. The expression of cell cycle-, apoptosis-, and autophagy-related genes was detected by next-generation sequencing. RTA dh404 reduces GBM8401 and U87MG glioma cell viability. RTA dh404 treated cells had a significant increase in the percentage of apoptotic cells and caspase-3 activity. In addition, the results of the cell cycle analysis showed that RTA dh404 arrested GBM8401 and U87MG glioma cells at the G2/M phase. Autophagy was observed in RTA dh404-treated cells. Subsequently, we found that RTA dh404-induced cell cycle arrest, apoptosis, and autophagy were related to the regulation of associated genes using next-generation sequencing. Our data indicated that RTA dh404 causes G2/M cell cycle arrest and induces apoptosis and autophagy by regulating the expression of cell cycle-, apoptosis-, and autophagy-related genes in human glioblastoma cells, suggesting that RTA dh404 is a potential drug candidate for the treatment of glioblastoma.

Natural and Semisynthetic Pentacyclic Triterpenes for Chronic Myeloid Leukemia Therapy: Reality, Challenges and Perspectives

Chronic myeloid leukemia (CML) is a neoplasm characterized by BCR-ABL1, an oncoprotein with vital role in leukemogenesis. Its inhibition by tyrosine kinase inhibitors represents the main choice of treatment. However, therapeutic failure is worrying given the lack of pharmacological options. Pentacyclic triterpenes are phytochemicals with outstanding antitumoral properties and have also been explored as a basis for the design of potential leads. In this review, we have gathered and discuss data regarding both natural and semisynthetic pentacyclic triterpenes applied to CML cell treatment. We found consistent evidence that the class of pentacyclic triterpenes in general exerts promising pro-apoptotic and antiproliferative activities in sensitive and resistant CML cells, and thus represents a rich source for drug development. We also analyze the predicted drug-like properties of the molecules, discuss the structural changes with biological implications and show the great opportunities this class represents, as well as the perspectives they provide on drug discovery for CML treatment.

Bardoxolone Methyl Displays Detrimental Effects on Endothelial Bioenergetics, Suppresses Endothelial ET-1 Release, and Increases Endothelial Permeability in Human Microvascular Endothelium

Nrf2 is a master regulator of antioxidant cellular defence, and agents activating the Nrf2 pathway have been tested in various diseases. However, unexpected side effects of cardiovascular nature reported for bardoxolone methyl in patients with type 2 diabetes mellitus and stage 4 chronic kidney disease (the BEACON trial) still have not been fully explained. Here, we aimed to characterize the effects of bardoxolone methyl compared with other Nrf2 activators—dimethyl fumarate and L-sulforaphane—on human microvascular endothelium. Endothelial toxicity, bioenergetics, mitochondrial membrane potential, endothelin-1 (ET-1) release, endothelial permeability, Nrf2 expression, and ROS production were assessed in human microvascular endothelial cells (HMEC-1) incubated for 3 and 24 hours with 100 nM–5 μM of either bardoxolone methyl, dimethyl fumarate, or L-sulforaphane. Three-hour incubation with bardoxolone methyl (100 nM–5 μM), although not toxic to endothelial cells, significantly affected endothelial bioenergetics by decreasing mitochondrial membrane potential (concentrations ≥ 3 μM), decreasing spare respiratory capacity (concentrations ≥ 1 μM), and increasing proton leak (concentrations ≥ 500 nM), while dimethyl fumarate and L-sulforaphane did not exert such actions. Bardoxolone methyl at concentrations ≥ 3 μM also decreased cellular viability and induced necrosis and apoptosis in the endothelium upon 24-hour incubation. In turn, endothelin-1 decreased permeability in endothelial cells in picomolar range, while bardoxolone methyl decreased ET-1 release and increased endothelial permeability even after short-term (3 hours) incubation. In conclusion, despite that all three Nrf2 activators exerted some beneficial effects on the endothelium, as evidenced by a decrease in ROS production, bardoxolone methyl, the most potent Nrf2 activator among the tested compounds, displayed a distinct endothelial profile of activity comprising detrimental effects on mitochondria and cellular viability and suppression of endothelial ET-1 release possibly interfering with ET-1–dependent local regulation of endothelial permeability.

Location, Orientation and Aggregation of Bardoxolone-ME, CDDO-ME, in a Complex Phospholipid Bilayer Membrane

Bardoxolone methyl (CDDO-Me), a synthetic derivative of the naturally occurring triterpenoid oleanolic acid, displays strong antioxidant, anticancer and anti-inflammatory activities, according to different bibliographical sources. However, the understanding of its molecular mechanism is missing. Furthermore, CDDO-Me has displayed a significant cytotoxicity against various types of cancer cells. CDDO-Me has a noticeable hydrophobic character and several of its effects could be attributed to its ability to be incorporated inside the biological membrane and therefore modify its structure and specifically interact with its components. In this study, we have used full-atom molecular dynamics to determine the location, orientation and interactions of CDDO-Me in phospholipid model membranes. Our results support the location of CDDO-Me in the middle of the membrane, it specifically orients so that the cyano group lean towards the phospholipid interface and it specifically interacts with particular phospholipids. Significantly, in the membrane the CDDO-Me molecules specifically interact with POPE and POPS. Moreover, CDDO-Me does not aggregates in the membrane but it forms a complex conglomerate in solution. The formation of a complex aggregate in solution might hamper its biological activity and therefore it should be taken into account when intended to be used in clinical assays. This work should aid in the development of these molecules opening new avenues for future therapeutic developments.

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.

Deep insights into the response of human cervical carcinoma cells to a new cyano enone-bearing triterpenoid soloxolone methyl: a transcriptome analysis

Semisynthetic triterpenoids, bearing cyano enone functionality in ring A, are considered now as novel promising anti-tumor agents. However, despite the large-scale studies, their effects on cervical carcinoma cells and, moreover, mechanisms underlying cell death activation by such compounds in this cell type have not been fully elucidated. In this work, we attempted to reconstitute the key pathways and master regulators involved in the response of human cervical carcinoma KB-3-1 cells to the novel glycyrrhetinic acid derivative soloxolone methyl (SM) by a transcriptomic approach. Functional annotation of differentially expressed genes, analysis of their cis^- regulatory sequences and protein-protein interaction network clearly indicated that stress of endoplasmic reticulum (ER) is the central event triggered by SM in the cells. A range of key ER stress sensors and transcription factor AP-1 were identified as upstream transcriptional regulators, controlling the response of the cells to SM. Additionally, by using Gene Expression Omnibus data, we showed the ability of SM to modulate the expression of key genes involved in regulation of the high proliferative rate of cervical carcinoma cells. Further Connectivity Map analysis revealed similarity of SM's effects with known ER stress inducers thapsigargin and geldanamycin, targeting SERCA and Grp94, respectively. According to the molecular docking study, SM could snugly fit into the active sites of these proteins in the positions very close to that of both inhibitors. Taken together, our findings provide a basis for the better understanding of the intracellular processes in tumor cells switched on in response to cyano enone-bearing triterpenoids.

Small molecule grp94 inhibitors block dengue and Zika virus replication

Two major flaviviruses, dengue virus (DENV) and Zika virus (ZIKV), cause severe health and economic burdens worldwide. Recently, genome-wide screenings have uncovered the importance of regulators of the Hrd1 ubiquitin ligase-mediated endoplasmic reticulum (ER)-associated degradation (ERAD) pathway for flavivirus replication in host cells. Here we report the identification of the compound Bardoxolone methyl (CDDO-me) as a potent inhibitor of the Hrd1 ubiquitin ligase-mediated ERAD, which possesses a broad-spectrum activity against both DENV and ZIKV. Cellular thermal shift assay (CETSA) suggested that CDDO-me binds to grp94, a key component of the Hrd1 pathway, at a low nanomolar concentration, whereas interaction was not detected with its paralog Hsp90. CDDO-me and the grp94 inhibitor PU-WS13 substantially suppressed DENV2 replication and the cytopathic effects caused by DENV and ZIKV infection. The antiviral activities of both compounds were demonstrated for all four DENV serotypes and four ZIKV strains in multiple human cell lines. This study defines grp94 as a crucial host factor for flavivirus replication and identified CDDO-me as a potent small molecule inhibitor of flavivirus infection. Inhibition of grp94 may contribute to the antiviral activity of CDDO-me. Further investigation of grp94 inhibitors may lead to a new class of broad-spectrum anti-flaviviral medications.

Nutraceuticals and "Repurposed" Drugs of Phytochemical Origin in Prevention and Interception of Chronic Degenerative Diseases and Cancer

BACKGROUND

Chronic, degenerative diseases are often characterized by inflammation and aberrant angiogenesis. For these pathologies, including rheumatoid arthritis, cardiovascular and autoimmune diseases, cancer, diabetes, and obesity, current therapies have limited efficacy.

OBJECTIVES

The validation of novel (chemo)preventive and interceptive approaches, and the use of new or repurposed agents, alone or in combination with registered drugs, are urgently required.

RESULTS

Phytochemicals (triterpenoids, flavonoids, retinoids) and their derivatives, nonsteroidal anti-inflammatory drugs (aspirin) as well as biguanides (metformin and phenformin) originally developed from phytochemical backbones, are multi-target agents showing antiangiogenic and anti-anti-inflammatory proprieties. Many of them target AMPK and metabolic pathways such as the mTOR axis. We summarize the beneficial effects of several compounds in conferring protection and supporting therapy, and as a paradigm, we present data on terpenoids & biquanides on beer hop xanthohumol and hydroxytryrosol from olive mill waste waters.

CONCLUSIONS

These molecules could be employed for combinatorial chemoprevention and interception approaches or chemoprevention/therapy regimens for cancer and other chronic complex diseases.

Autophagy regulation and its role in normal and malignant hematopoiesis

Autophagy, the molecular machinery of self-eating, plays a dual role of a tumor promoter and tumor suppressor. This mechanism affects different clinical responses in cancer cells. Autophagy is targeted for treating patients resistant to chemotherapy or radiation. Limited reports investigate the significance of autophagy in cancer therapy, the regulation of hematopoietic and leukemic stem cells and leukemia formation. In the current review, the role of autophagy is discussed in various stages of hematopoiesis including quiescence, self-renewal, and differentiation.

Molecular modelling studies of quinazolinone derivatives as MMP-13 inhibitors by QSAR, molecular docking and molecular dynamics simulations techniques

Matrix metalloproteinase-13 (MMP-13) is an attractive drug target for the treatment of osteoarthritis (OA). In this study, a series of quinazolinone derivatives as MMP-13 inhibitors were firstly systematically studied using QSAR, molecular docking and molecular dynamics (MD) simulation. The reliable CoMFA (q ² = 0.646, r ² = 0.992, R _pred ² = 0.829) and CoMSIA (q ² = 0.704, r ² = 0.992, R _pred ² = 0.839) models were constructed and verified by the Topomer CoMFA model. Results of contour maps indicated that the electrostatic, hydrophobic and H-bond acceptor fields primarily influenced the activity of MMP-13 inhibitors in the models. Several key residues (Ala238, Thr245, Thr247, Met253, Asn215 and Lys140) were identified as important factors to improve the activity and stability of the inhibitor through hydrogen bonding and electrostatic interaction. Based on these results, eight novel quinazolinones (D1-D8) were further designed. Additionally, all designed compounds showed good pharmacokinetic properties by ADMET predictions. Compounds D3 and D8 exhibited excellent predictive activity, and the 10 ns MD simulations analysis revealed that the hydrogen bonding interaction with residues (Ser250 and Gly248) was enhanced, and the small group in R2 and U-shaped conformation was of pivotal importance. These results provided strong guidance for the discovery and design of novel potential MMP-13 inhibitors.

Novel Derivative of Bardoxolone Methyl Improves Safety for the Treatment of Diabetic Nephropathy

Currently, no effective and safe medicines are available to treat diabetic nephropathy (DN). Bardoxolone methyl (CDDO-Me) has displayed promising anti-DN activity as well as serious side effects in clinical trials, probably because the highly reactive α-cyano-α,β-unsaturated ketone (CUK) in ring A of CDDO-Me can covalently bind to thiol functionalities in many biomacromolecules. In this study, we designed and synthesized a γ-glutamyl transpeptidase (GGT)-based and CUK-modified derivative of CDDO-Me (2) to address this issue. 2 can be specifically cleaved by GGT, which is highly expressed in the kidney, to liberate CDDO-Me in situ. It should be noted that 2 exhibited anti-DN efficacy comparable to that of CDDO-Me with much less toxicity in cells and db/db mice, suggesting that its safety is better than CDDO-Me. Our findings not only reveal the therapeutic potential of 2 but also provide a strategy to optimize other synthetic molecules or natural products bearing a pharmacophore like CUK to achieve safer pharmaceutical drugs.

Bardoxolone methyl (CDDO-Me or RTA402) induces cell cycle arrest, apoptosis and autophagy via PI3K/Akt/mTOR and p38 MAPK/Erk1/2 signaling pathways in K562 cells

Chronic myeloid leukemia (CML) treatment remains a challenge due to drug resistance and severe side effect, rendering the need on the development of novel therapeutics. CDDO-Me (Bardoxolone methyl), a potent Nrf2 activator and NF-κB inhibitor, is a promising candidate for cancer treatment including leukemia. However, the underlying mechanism for CDDO-Me in CML treatment is unclear. This study aimed to evaluate the molecular interactome of CDDO-Me in K562 cells using the quantitative proteomics approach stable-isotope labeling by amino acids in cell culture (SILAC) and explore the underlying mechanisms using cell-based functional assays. A total of 1,555 proteins responded to CDDO-Me exposure, including FANCI, SRPK2, XPO5, HP1BP3, NELFCD, Na⁺,K⁺-ATPase 1, etc. in K562 cells. A total of 246 signaling pathways and 25 networks regulating cell survival and death, cellular function and maintenance, energy production, protein synthesis, response to oxidative stress, and nucleic acid metabolism were involved. Our verification experiments confirmed that CDDO-Me down-regulated Na⁺,K⁺-ATPase α1 in K562 cells, and significantly arrested cells in G₂/M and S phases, accompanied by remarkable alterations in the expression of key cell cycle regulators. CDDO-Me caused mitochondria-, death receptor-dependent and ER stress-mediated apoptosis in K562 cells, also induced autophagy with the suppression of PI3K/Akt/mTOR signaling pathway. p38 MAPK/Erk1/2 signaling pathways contributed to both apoptosis- and autophagy-inducing effects of CDDO-Me in K562 cells. Taken together, these data demonstrate that CDDO-Me is a potential anti-cancer agent that targets cell cycle, apoptosis, and autophagy in the treatment of CML.

Synergistic Antitumour Properties of viscumTT in Alveolar Rhabdomyosarcoma

Aqueous mistletoe extracts from the European mistletoe (Viscum album) contain mainly mistletoe lectins and viscotoxins as cytotoxic compounds. Lipophilic triterpene acids, which do not occur in conventional mistletoe preparations, were solubilised with β-cyclodextrins. The combination of an aqueous extract (viscum) and a triterpene-containing extract (TT) recreated a whole mistletoe extract (viscumTT). These extracts were tested on rhabdomyosarcoma in vitro, ex vivo, and in vivo with regard to anticancer effects. Viscum and viscumTT inhibited cell proliferation and induced apoptosis effectively in a dose-dependent manner in vitro and ex vivo, whereas TT showed only moderate inhibitory effects. viscumTT proved to be more effective than the single extracts and displayed a synergistic effect in vitro and a stronger effect in vivo. viscumTT induced apoptosis via the extrinsic and intrinsic pathways, evidenced by the loss of mitochondrial membrane potential and activation of CASP8 and CASP9. CASP10 inhibitor inhibited apoptosis effectively, emphasising the importance of CASP10 in viscumTT-induced apoptosis. Additionally, viscumTT changed the ratio of apoptosis-associated proteins by downregulation of antiapoptotic proteins such as XIAP and BIRC5, thus shifting the balance towards apoptosis. viscumTT effectively reduced tumour volume in patient-derived xenografts in vivo and may be considered a promising substance for rhabdomyosarcoma therapy.

Combined targeting of STAT3 and STAT5: a novel approach to overcome drug resistance in chronic myeloid leukemia

In chronic myeloid leukemia, resistance against BCR-ABL1 tyrosine kinase inhibitors can develop because of BCR-ABL1 mutations, activation of additional pro-oncogenic pathways, and stem cell resistance. Drug combinations covering a broad range of targets may overcome resistance. CDDO-Me (bardoxolone methyl) is a drug that inhibits the survival of leukemic cells by targeting different pro-survival molecules, including STAT3. We found that CDDO-Me inhibits proliferation and survival of tyrosine kinase inhibitor-resistant BCR-ABL1⁺ cell lines and primary leukemic cells, including cells harboring BCR-ABL1^T315I or T315I⁺ compound mutations. Furthermore, CDDO-Me was found to block growth and survival of CD34⁺/CD38⁻ leukemic stem cells (LSC). Moreover, CDDO-Me was found to produce synergistic growth-inhibitory effects when combined with BCR-ABL1 tyrosine kinase inhibitors. These drug-combinations were found to block multiple signaling cascades and molecules, including STAT3 and STAT5. Furthermore, combined targeting of STAT3 and STAT5 by shRNA and STAT5-targeting drugs also resulted in synergistic growth-inhibition, pointing to a new efficient concept of combinatorial STAT3 and STAT5 inhibition. However, CDDO-Me was also found to increase the expression of heme-oxygenase-1, a heat-shock-protein that triggers drug resistance and cell survival. We therefore combined CDDO-Me with the heme-oxygenase-1 inhibitor SMA-ZnPP, which also resulted in synergistic growth-inhibitory effects. Moreover, SMA-ZnPP was found to sensitize BCR-ABL1⁺ cells against the combination ‘CDDO-Me+ tyrosine kinase inhibitor’. Together, combined targeting of STAT3, STAT5, and heme-oxygenase-1 overcomes resistance in BCR-ABL1⁺ cells, including stem cells and highly resistant sub-clones expressing BCR-ABL1^T315I or T315I-compound mutations. Whether such drug-combinations are effective in tyrosine kinase inhibitor-resistant patients with chronic myeloid leukemia remains to be elucidated.

Bardoxolone Methyl and a Related Triterpenoid Downregulate cMyc Expression in Leukemia Cells

Structurally related pentacyclic triterpenoids methyl 2-cyano-3,12-dioxoolean-1,9-dien-28-oate [bardoxolone-methyl (Bar-Me)] and methyl 2-trifluoromethyl-3,11-dioxoolean-1,12-dien-30-oate (CF₃DODA-Me) contain 2-cyano-1-en-3-one and 2-trifluoromethyl-1-en-3-one moieties, respectively, in their A-rings and differ in the position of their en-one structures in ring C. Only Bar-Me forms a Michael addition adduct with glutathione (GSH) and inhibits IKKβ phosphorylation. These differences may be due to steric hindrance by the 11-keto group in CF₃DODA-Me, which prevents Michael addition by the conjugated en-one in the A-ring. In contrast, both Bar-Me and CF₃DODA-Me induce reactive oxygen species in HL-60 and Jurkat leukemia cells, inhibit cell growth, induce apoptosis and differentiation, and decrease expression of specificity proteins (Sp) 1, 3, and 4, and cMyc, and these effects are significantly attenuated after cotreatment with the antioxidant GSH. In contrast to solid tumor-derived cells, cMyc and Sp transcriptions are regulated independently and cMyc plays a more predominant role than Sp transcription factors in regulating HL-60 or Jurkat cell proliferation and differentiation compared with that observed in cells derived from solid tumors.

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.

Ca2+ influx-mediated dilation of the endoplasmic reticulum and c-FLIPL downregulation trigger CDDO-Me-induced apoptosis in breast cancer cells

The synthetic triterpenoid 2-cyano-3, 12-dioxooleana-1, 9(11)-dien-C28-methyl ester (CDDO-Me) is considered a promising anti-tumorigenic compound. In this study, we show that treatment with CDDO-Me induces progressive endoplasmic reticulum (ER)-derived vacuolation in various breast cancer cells and ultimately kills these cells by inducing apoptosis. We found that CDDO-Me-induced increases in intracellular Ca2+ levels, reflecting influx from the extracellular milieu, make a critical contribution to ER-derived vacuolation and subsequent cell death. In parallel with increasing Ca2+ levels, CDDO-Me markedly increased the generation of reactive oxygen species (ROS). Interestingly, there exists a reciprocal positive-regulatory loop between Ca2+ influx and ROS generation that triggers ER stress and ER dilation in response to CDDO-Me. In addition, CDDO-Me rapidly reduced the protein levels of c-FLIPL (cellular FLICE-inhibitory protein) and overexpression of c-FLIPL blocked CDDO-Me-induced cell death, but not vacuolation. These results suggest that c-FLIPL downregulation is a key contributor to CDDO-Me-induced apoptotic cell death, independent of ER-derived vacuolation. Taken together, our results show that ER-derived vacuolation via Ca2+ influx and ROS generation as well as caspase activation via c-FLIPL downregulation are responsible for the potent anticancer effects of CDDO-Me on breast cancer cells.

A Natural Combination Extract of Viscum album L. Containing Both Triterpene Acids and Lectins Is Highly Effective against AML In Vivo

Aqueous Viscum album L. extracts are widely used in complementary cancer medicine. Hydrophobic triterpene acids also possess anti-cancer properties, but due to their low solubility they do not occur in significant amounts in aqueous extracts. Using cyclodextrins we solubilised mistletoe triterpenes (mainly oleanolic acid) and investigated the effect of a mistletoe whole plant extract on human acute myeloid leukaemia cells in vitro, ex vivo and in vivo. Single Viscum album L. extracts containing only solubilised triterpene acids (TT) or lectins (viscum) inhibited cell proliferation and induced apoptosis in a dose-dependent manner in vitro and ex vivo. The combination of viscum and TT extracts (viscumTT) enhanced the induction of apoptosis synergistically. The experiments demonstrated that all three extracts are able to induce apoptosis via caspase-8 and -9 dependent pathways with down-regulation of members of the inhibitor of apoptosis and Bcl-2 families of proteins. Finally, the acute myeloid leukaemia mouse model experiment confirmed the therapeutic effectiveness of viscumTT-treatment resulting in significant tumour weight reduction, comparable to the effect in cytarabine-treated mice. These results suggest that the combination viscumTT may have a potential therapeutic value for the treatment AML.

Autophagy collaborates with ubiquitination to downregulate oncoprotein E2A/Pbx1 in B-cell acute lymphoblastic leukemia

B-cell acute lymphoblastic leukemia (B-ALL) accounts for the most cancer incidences in children. We present here that autophagy is downregulated in pediatric B-ALL, suggesting a possible link between autophagy failure and pediatric B-ALL leukemogenesis. With a pediatric t(1;19) B-ALL xenograft mouse model, we show here that activation of autophagy by preventive administration of rapamycin improved the survival of leukemia animals by partial restoration of hematopoietic stem/progenitor cells, whereas treatment of the animals with rapamycin caused leukemia bone marrow cell-cycle arrest. Activation of autophagy in vitro or in vivo by rapamycin or starvation downregulated oncogenic fusion protein E2A/Pbx1. Furthermore, E2A/Pbx1 was found to be colocalized with autophagy marker LC3 in autolysosomes and with ubiquitin in response to autophagy stimuli, whereas autophagy or ubiquitination inhibitor blocked these colocalizations. Together, our data suggest a collaborative action between autophagy and ubiquitination in the degradation of E2A/Pbx1, thereby revealing a novel strategy for targeted preventive or treatment therapy on the pediatric ALL.

Radiation protection of the gastrointestinal tract and growth inhibition of prostate cancer xenografts by a single compound

Normal tissue toxicity markedly reduces the therapeutic index of genotoxic anticancer agents, including ionizing radiation. Countermeasures against tissue damage caused by radiation are limited by their potential to also protect malignant cells and tissues. Here, we tested a panel of signal transduction modifiers for selective radioprotection of normal but not tumor tissues. These included three inhibitors of GSK3 (LiCl, SB216763, and SB415286) and two inhibitors of NF-κB (ethyl pyruvate and RTA 408). Among these, the thiol-reactive triterpenoid RTA 408 emerged as a robust and effective protector of multiple organ systems (gastrointestinal, skin, and hemopoietic) against lethal doses of radiation. RTA 408 preserved survival and proliferation of intestinal crypt cells in lethally irradiated mice while reducing apoptosis incidence in crypts and villi. In contrast, RTA 408 uniformly inhibited growth of established CWR22Rv1, LNCaP/C4-2B, PC3, and DU145 xenografts either alone or combined with radiation. Antitumor effects in vivo were associated with reduced proliferation and intratumoral apoptosis and with inhibition of NF-κB-dependent transcription in PC3 cells. Selective protection of normal tissue compartments by RTA 408 critically depended on tissue context and could not be replicated in vitro. Collectively, these data highlight the potential of RTA 408 as a cytoprotective agent that may be safely used in chemoradiation approaches.

Rapid analysis of glycolytic and oxidative substrate flux of cancer cells in a microplate

Cancer cells exhibit remarkable alterations in cellular metabolism, particularly in their nutrient substrate preference. We have devised several experimental methods that rapidly analyze the metabolic substrate flux in cancer cells: glycolysis and the oxidation of major fuel substrates glucose, glutamine, and fatty acids. Using the XF Extracellular Flux analyzer, these methods measure, in real-time, the oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) of living cells in a microplate as they respond to substrates and metabolic perturbation agents. In proof-of-principle experiments, we analyzed substrate flux and mitochondrial bioenergetics of two human glioblastoma cell lines, SF188s and SF188f, which were derived from the same parental cell line but proliferate at slow and fast rates, respectively. These analyses led to three interesting observations: 1) both cell lines respired effectively with substantial endogenous substrate respiration; 2) SF188f cells underwent a significant shift from glycolytic to oxidative metabolism, along with a high rate of glutamine oxidation relative to SF188s cells; and 3) the mitochondrial proton leak-linked respiration of SF188f cells increased significantly compared to SF188s cells. It is plausible that the proton leak of SF188f cells may play a role in allowing continuous glutamine-fueled anaplerotic TCA cycle flux by partially uncoupling the TCA cycle from oxidative phosphorylation. Taken together, these rapid, sensitive and high-throughput substrate flux analysis methods introduce highly valuable approaches for developing a greater understanding of genetic and epigenetic pathways that regulate cellular metabolism, and the development of therapies that target cancer metabolism.

Bardoxolone methyl (CDDO-Me) as a therapeutic agent: an update on its pharmacokinetic and pharmacodynamic properties

Triterpenoids have been used for medicinal purposes in many Asian countries because of their anti-inflammatory, antioxidant, antiproliferative, anticancer, and anticarcinogenic properties. Bardoxolone methyl, the C-28 methyl ester of 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO) known as CDDO-Me or RTA 402, is one of the derivatives of synthetic triterpenoids. CDDO-Me has been used for the treatment of chronic kidney disease, cancer (including leukemia and solid tumors), and other diseases. In this review, we will update our knowledge of the clinical pharmacokinetics and pharmacodynamics of CDDO-Me, highlighting its clinical benefits and the underlying mechanisms involved. The role of the Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1 (Keap1)/the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway in the therapeutic activities of CDDO-Me will be discussed. CDDO-Me contains α,β-unsaturated carbonyl groups on rings A and C that can generate reversible adducts with the thiol groups of Cys residues in target proteins such as Keap1 and IκB kinase. At low nanomolar concentrations, CDDO-Me protects the cells against oxidative stress via inhibition of reactive oxygen species generation, while CDDO-Me at low micromolar concentrations induces apoptosis by increasing reactive oxygen species and decreasinging intracellular glutathione levels. Through Keap1/Nrf2 and nuclear factor-κB pathways, this agent can modulate the activities of a number of important proteins that regulate inflammation, redox balance, cell proliferation and programmed cell death. In a Phase I trial in cancer patients, CDDO-Me was found to have a slow and saturable oral absorption, a relatively long terminal phase half-life (39 hours at 900 mg/day), nonlinearity (dose-dependent) at high doses (600-1,300 mg/day), and high interpatient variability. As a multifunctional agent, CDDO-Me has improved the renal function in patients with chronic kidney disease associated with type 2 diabetes. CDDO-Me has shown a promising anticancer effect in a Phase I trial. This agent is generally well tolerated, but it may increase adverse cardiovascular events. Presently, it is being further tested for the treatment of patients with chronic kidney disease, cancer, and pulmonary arterial hypertension.

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.

Methyl 3-hydroxyimino-11-oxoolean-12-en-28-oate (HIMOXOL), a synthetic oleanolic acid derivative, induces both apoptosis and autophagy in MDA-MB-231 breast cancer cells

HIMOXOL (methyl 3-hydroxyimino-11-oxoolean-12-en-28-oate) is a synthetic derivative of oleanolic acid (OA). HIMOXOL revealed the highest cytotoxic effect among tested synthetic OA analogs. In this study we focused on elucidating the cytotoxic mechanism of HIMOXOL in MDA-MB-231 breast cancer cells. HIMOXOL reduced MDA-MB-231 cell viability with an IC50 value of 21.08±0.24μM. In contrast to OA, the tested compound induced cell death by activating apoptosis and the autophagy pathways. More specifically, we found that HIMOXOL was able to activate the extrinsic apoptotic pathway, which was proven by observation of caspase-8, caspase-3 and PARP-1 protein activation in Western blot analysis. An increase in the ratio of Bax/Bcl-2 protein levels was also detected. Moreover, HIMOXOL triggered microtubule-associated protein LC3-II expression and upregulated beclin 1. This observed compound activity was modulated by mitogen-activated protein kinases and NFκB/p53 signaling pathways. Together, these data suggest that HIMOXOL, a synthetic oleanolic acid derivative which activates dual cell death machineries, could be a potential and novel chemotherapeutic agent.

Interplay between apoptosis and autophagy, a challenging puzzle: new perspectives on antitumor chemotherapies

Autophagy is a mechanism of protection against various forms of human diseases, such as cancer, in which autophagy seems to have an extremely complex role. In cancer, there is evidence that autophagy may be oncogenic in some contexts, whereas in others it clearly contributes to tumor suppression. In addition, studies have demonstrated the existence of a complex relationship between autophagy and cell death, determining whether a cell will live or die in response to anticancer therapies. Nevertheless, we still need to complete the autophagy-apoptosis puzzle in the tumor context to better address appropriate chemotherapy protocols with autophagy modulators. Generally, tumor cell resistance to anticancer induced-apoptosis can be overcome by autophagy inhibition. However, when an extensive autophagic stimulus is activated, autophagic cell death is observed. In this review, we discuss some details of autophagy and its relationship with tumor progression or suppression, as well as role of autophagy-apoptosis in cancer treatments.

Saxifragifolin D induces the interplay between apoptosis and autophagy in breast cancer cells through ROS-dependent endoplasmic reticulum stress

Breast cancer is the leading cause of cancer death among females, and novel chemotherapeutic drugs for treating breast cancer are needed urgently. Saxifragifolin D (SD) was isolated by our group from Androsace umbellata which is commonly used to treat solid tumor. In this study, we evaluated its growth inhibitory effect on breast cancer cells and explored the underlying molecular mechanisms. Our results showed that SD inhibited the growth of both MCF-7 and MDA-MB-231 cells significantly. Mechanistic studies demonstrated that SD induced apoptosis through mitochondrial apoptotic pathway. Evidence of SD-induced autophagy included the occurrence of autophagic vacuoles, up-regulation of LC3-II, Beclin1 and Vps34. Inhibition of autophagy by bafilomycin A1 or Beclin1 siRNA pretreatment decreased the ratio of apoptosis, indicating that autophagy induction contributes to apoptosis and is required for the latter. SD was also found to induce endoplasmic reticulum stress, accompanied by ROS production, increase of intracellular calcium and up-regulation of Bip, IRE1α and XBP-1s. Inhibition of endoplasmic reticulum stress by N-acetyl-l-cysteine, tauroursodeoxycholic acid or IRE1α siRNA pretreatment could suppress both apoptosis and autophagy. Besides, increases in CHOP, calnexin, calpain, p-JNK and p-Bcl-2 were followed by subsequent dissociation of Beclin1 from Bcl-2, further suggesting endoplasmic reticulum stress to be the common signaling pathway shared by SD-induced apoptosis and autophagy. In conclusion, SD inhibits breast cancer cell growth and induces interplay between apoptosis and autophagy through ROS-mediated endoplasmic reticulum stress. It will provide molecular bases for developing SD into a drug candidate for the treatment of breast cancer.

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.

Rac2-MRC-cIII-generated ROS cause genomic instability in chronic myeloid leukemia stem cells and primitive progenitors

Chronic myeloid leukemia in chronic phase (CML-CP) is induced by BCR-ABL1 oncogenic tyrosine kinase. Tyrosine kinase inhibitors eliminate the bulk of CML-CP cells, but fail to eradicate leukemia stem cells (LSCs) and leukemia progenitor cells (LPCs) displaying innate and acquired resistance, respectively. These cells may accumulate genomic instability, leading to disease relapse and/or malignant progression to a fatal blast phase. In the present study, we show that Rac2 GTPase alters mitochondrial membrane potential and electron flow through the mitochondrial respiratory chain complex III (MRC-cIII), thereby generating high levels of reactive oxygen species (ROS) in CML-CP LSCs and primitive LPCs. MRC-cIII-generated ROS promote oxidative DNA damage to trigger genomic instability, resulting in an accumulation of chromosomal aberrations and tyrosine kinase inhibitor-resistant BCR-ABL1 mutants. JAK2(V617F) and FLT3(ITD)-positive polycythemia vera cells and acute myeloid leukemia cells also produce ROS via MRC-cIII. In the present study, inhibition of Rac2 by genetic deletion or a small-molecule inhibitor and down-regulation of mitochondrial ROS by disruption of MRC-cIII, expression of mitochondria-targeted catalase, or addition of ROS-scavenging mitochondria-targeted peptide aptamer reduced genomic instability. We postulate that the Rac2-MRC-cIII pathway triggers ROS-mediated genomic instability in LSCs and primitive LPCs, which could be targeted to prevent the relapse and malignant progression of CML.

Targeted inhibition of tumor proliferation, survival, and metastasis by pentacyclic triterpenoids: potential role in prevention and therapy of cancer

Over the last two decades, extensive research on plant-based medicinal compounds has revealed exciting and important pharmacological properties and activities of triterpenoids. Fruits, vegetables, cereals, pulses, herbs and medicinal plants are all considered to be biological sources of these triterpenoids, which have attracted great attention especially for their potent anti-inflammatory and anti-cancer activities. Published reports in the past have described the molecular mechanism(s) underlying the various biological activities of triterpenoids which range from inhibition of acute and chronic inflammation, inhibition of tumor cell proliferation, induction of apoptosis, suppression of angiogenesis and metastasis. However systematic analysis of various pharmacological properties of these important classes of compounds has not been done. In this review, we describe in detail the pre-clinical chemopreventive and therapeutic properties of selected triterpenoids that inhibit multiple intracellular signaling molecules and transcription factors involved in the initiation, progression and promotion of various cancers. Molecular targets modulated by these triterpenoids comprise, cytokines, chemokines, reactive oxygen intermediates, oncogenes, inflammatory enzymes such as COX-2, 5-LOX and MMPs, anti-apoptotic proteins, transcription factors such as NF-κB, STAT3, AP-1, CREB, and Nrf2 (nuclear factor erythroid 2-related factor) that regulate tumor cell proliferation, transformation, survival, invasion, angiogenesis, metastasis, chemoresistance and radioresistance. Finally, this review also analyzes the potential role of novel synthetic triterpenoids identified recently which mimic natural triterpenoids in physical and chemical properties and are moving rapidly from bench to bedside research.

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.

A new development of triterpene acid-containing extracts from Viscum album L. displays synergistic induction of apoptosis in acute lymphoblastic leukaemia

OBJECTIVES

Aqueous Viscum album L. extracts are widely used for anti-cancer therapies. Due to their low solubility, triterpenes (which are known to act on cancers), do not occur in aqueous extracts in significant amounts. Using cyclodextrins, we have found it possible to solubilize mistletoe triterpene acids and to determine their effects on acute lymphoblastic leukaemia (ALL) in vitro and in vivo.

MATERIALS AND METHODS

A C.B-17/SCID model of pre-B ALL (NALM-6) was used to test efficacy and mechanisms of treatment with lectin- and triterpene acid containing preparations in vivo. Cytotoxicity of increasing concentrations of V. album L. preparations was assessed in vitro. Apoptosis was determined using mitochondrial membrane potential measurements, annexin V/PI, western blot analyses and caspase inhibitor assays.

RESULTS

Solubilized triterpene acid- or lectin-containing V. album L. extracts inhibited cell proliferation and demonstrated cytotoxic properties in vitro. Annexin V/PI and mitochondrial membrane potential assays indicated that dose-dependent induction of apoptosis was the main mechanism. Combination (viscumTT) of lectin- (viscum) and triterpene-containing (TT) extracts resulted in greatest induction of apoptosis. Furthermore, caspase activity demonstrated that these extracts were able to induce apoptosis through both caspase-8 and -9 dependent pathways. In vivo experimentation showed that treatment of mice with viscumTT combination prolonged mean survival to 50.5 days compared to 39.3 days in the phosphate-buffered saline group.

CONCLUSION

Here for the first time, we have demonstrated that either solubilized triterpene acids or lectins and combinations thereof, induce dose-dependent apoptosis in the ALL cell line NALM-6 via caspase-8 and -9 dependent pathways.

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.

Global targeting of subcellular heat shock protein-90 networks for therapy of glioblastoma

Drug discovery for complex and heterogeneous tumors now aims at dismantling global networks of disease maintenance, but the subcellular requirements of this approach are not understood. Here, we simultaneously targeted the multiple subcellular compartments of the molecular chaperone heat shock protein-90 (Hsp90) in a model of glioblastoma, a highly lethal human malignancy in urgent need of fresh therapeutic strategies. Treatment of cultured or patient-derived glioblastoma cells with Shepherdin, a dual peptidomimetic inhibitor of mitochondrial and cytosolic Hsp90, caused irreversible collapse of mitochondria, degradation of Hsp90 client proteins in the cytosol, and tumor cell killing by apoptosis and autophagy. Stereotactic or systemic delivery of Shepherdin was well tolerated and suppressed intracranial glioma growth via inhibition of cell proliferation, induction of apoptosis, and reduction of angiogenesis in vivo. These data show that disabling Hsp90 cancer networks in their multiple subcellular compartments improves strategies for drug discovery and may provide novel molecular therapy for highly recalcitrant human tumors.

Triterpenoids as new promising anticancer drugs

Triterpenoids are structurally diverse organic compounds, characterized by a basic backbone modified in multiple ways, allowing the formation of more than 20 000 naturally occurring triterpenoid varieties. Several triterpenoids, including ursolic and oleanolic acid, betulinic acid, celastrol, pristimerin, lupeol, and avicins possess antitumor and anti-inflammatory properties. To improve antitumor activity, some synthetic triterpenoid derivatives have been synthesized, including cyano-3,12-dioxooleana-1,9 (11)-dien-28-oic (CDDO), its methyl ester (CDDO-Me), and imidazolide (CDDO-Im) derivatives. Of these, CDDO, CDDO-Me, and betulinic acid have shown promising antitumor activities and are presently under evaluation in phase I studies. Triterpenoids are highly multifunctional and the antitumor activity of these compounds is measured by their ability to block nuclear factor-kappaB activation, induce apoptosis, inhibit signal transducer, and activate transcription and angiogenesis.

Autophagy facilitates the development of breast cancer resistance to the anti-HER2 monoclonal antibody trastuzumab

Autophagy has been emerging as a novel cytoprotective mechanism to increase tumor cell survival under conditions of metabolic stress and hypoxia as well as to escape chemotherapy-induced cell death. To elucidate whether autophagy might also protect cancer cells from the growth inhibitory effects of targeted therapies, we evaluated the autophagic status of preclinical breast cancer models exhibiting auto-acquired resistance to the anti-HER2 monoclonal antibody trastuzumab (Tzb). We first examined the basal autophagic levels in Tzb-naive SKBR3 cells and in two pools of Tzb-conditioned SKBR3 cells (TzbR), which optimally grow in the presence of Tzb doses as high as 200 µg/ml Tzb. Fluorescence microscopic analyses revealed that the number of punctate LC3 structures -a hallmark of autophagy- was drastically higher in Tzb-refractory cells than in Tzb-sensitive SKBR3 parental cells. Immunoblotting analyses confirmed that the lipidation product of the autophagic conversion of LC3 was accumulated to high levels in TzbR cells. High levels of the LC3 lipidated form in Tzb-refractory cells were accompanied by decreased p62/sequestosome-1 protein expression, a phenomenon characterizing the occurrence of increased autophagic flux. Moreover, increased autophagy was actively used to survive Tzb therapy as TzbR pools were exquisitely sensitive to chemical inhibitors of autophagosomal formation/function. Knockdown of LC3 expression via siRNA similarly resulted in reduced TzbR cell proliferation and supra-additively interacted with Tzb to re-sensitize TzbR cells. Sub-groups of Tzb-naive SKBR3 parental cells accumulated LC3 punctate structures and decreased p62 expression after treatment with high-dose Tzb, likely promoting their own resistance. This is the first report showing that HER2-overexpressing breast cancer cells chronically exposed to Tzb exhibit a bona fide up-regulation of the autophagic activity that efficiently works to protect breast cancer cells from the growth-inhibitory effects of Tzb. Therapeutic targeting autophagosome formation/function might represent a novel molecular avenue to reduce the emergence of Tzb resistance in HER2-dependent breast carcinomas.