The sesquiterpene lactone parthenolide induces selective apoptosis of B-chronic lymphocytic leukemia cells in vitro

Anti-Leukemic Attributes of Natural Compounds Targeting Autophagy: A Closer Look into the Molecular Mechanisms

Leukemia is a heterogeneous clonal cancer that affects millions of individuals around the world. Despite substantial breakthroughs in cancer treatment, traditional chemotherapy and radiotherapy remain ineffective, and therapeutic resistance still stands as a big obstacle. As a result, there is an increasing attention being paid currently toward the potency of natural compounds as a complementary or alternative therapy for leukemia. Autophagy, a conserved cellular process where damaged or defective cytosolic components and macromolecules are destroyed and recycled, plays a dual role in promoting or suppressing the continuance of cancer at different junctures of its development. Current studies have reported that autophagy has a cardinal function in the genesis and progression of leukemia, making it a promising target for novel treatments. In this review, we have explored the effectiveness of certain natural compounds, such as curcumin, resveratrol, tanshinone IIA, quercetin, tetrandrine, parthenolide, berberine, pristimerin, and alantolactone, that modulate autophagy and regulate its associated signaling cascades at a molecular level in different types of leukemia. They have been shown to have synergistic effects with conventional chemotherapy, emphasizing their potential as supplementary medicines. However, additional research is required to fully comprehend their mechanisms of action and to maximize their role in clinical perspectives.

Expression and Activity of the NF-κB Subunits in Chronic Lymphocytic Leukaemia: A Role for RelB and Non-Canonical Signalling

BACKGROUND

Canonical NF-κB signalling by p65 (RelA) confers chemo-resistance and poor survival in chronic lymphocytic leukaemia (CLL). The role of non-canonical NF-κB signalling (leading to RelB and p52 subunit activation) in CLL is less understood, but given its importance in other B-cell tumour types, we theorised that RelB and p52 may also contribute to the pathology of CLL.

METHODS

DNA binding activity of all five NF-kB subunits, p65, p50, RelB, p52, and c-Rel, was quantified using ELISA and correlated to ex vivo chemoresistance, CD40L-stimulated signalling (to mimic the lymph node microenvironment), and clinical data.

RESULTS

Importantly, we show for the first time that high basal levels of RelB DNA binding correlate with nuclear RelB protein expression and are associated with del(11q), ATM dysfunction, unmutated IGHV genes, and shorter survival. High levels of nuclear p65 are prevalent in del(17p) cases (including treatment-naïve patients) and also correlate with the outcome. CD40L-stimulation resulted in rapid RelB activation, phosphorylation and processing of p100, and subsequent CLL cell proliferation.

CONCLUSIONS

These data highlight a role for RelB in driving CLL cell tumour growth in a subset of patients and therefore strategies designed to inhibit non-canonical NF-κB signalling represent a novel approach that will have therapeutic benefit in CLL.

Unraveling the therapeutic potential of natural products in the prevention and treatment of leukemia

Leukemia is a heterogeneous group of hematological malignancies distinguished by differentiation blockage and uncontrolled proliferation of myeloid or lymphoid progenitor cells in the bone marrow (BM) and peripheral blood (PB). There are various types of leukemia in which intensive chemotherapy regimens or hematopoietic stem cell transplantation (HSCT) are now the most common treatments associated with severe side effects and multi-drug resistance in leukemia cells. Therefore, it is crucial to develop novel therapeutic approaches with adequate therapeutic efficacy and selectively eliminate leukemic cells to improve the consequences of leukemia. Medicinal plants have been utilized for ages to treat multiple disorders due to their diverse bioactive compounds. Plant-derived products have been used as therapeutic medication to prevent and treat many types of cancer. Over the last two decades, 50 % of all anticancer drugs approved worldwide are from natural products and their derivatives. Therefore this study aims to review natural products such as polyphenols, alkaloids, terpenoids, nitrogen-containing, and organosulfur compounds as antileukemic agents. Current investigations have identified natural products efficiently destroy leukemia cells through diverse mechanisms of action by inhibiting proliferation, reactive oxygen species production, inducing cell cycle arrest, and apoptosis in both in vitro, in vivo, and clinical studies. Current investigations have identified natural products as suitable promising chemotherapeutic and chemopreventive agents. It played an essential role in drug development and emerged as a possible source of biologically active metabolites for therapeutic interventions, especially in leukemia. DATA AVAILABILITY: Data will be made available on request.

Parthenolide and Its Soluble Analogues: Multitasking Compounds with Antitumor Properties

Due to its chemical properties and multiple molecular effects on different tumor cell types, the sesquiterpene lactone parthenolide (PN) can be considered an effective drug with significant potential in cancer therapy. PN has been shown to induce either classic apoptosis or alternative caspase-independent forms of cell death in many tumor models. The therapeutical potential of PN has been increased by chemical design and synthesis of more soluble analogues including dimethylaminoparthenolide (DMAPT). This review focuses on the molecular mechanisms of both PN and analogues action in tumor models, highlighting their effects on gene expression, signal transduction and execution of different types of cell death. Recent findings indicate that these compounds not only inhibit prosurvival transcriptional factors such as NF-κB and STATs but can also determine the activation of specific death pathways, increasing intracellular reactive oxygen species (ROS) production and modifications of Bcl-2 family members. An intriguing property of these compounds is its specific targeting of cancer stem cells. The unusual actions of PN and its analogues make these agents good candidates for molecular targeted cancer therapy.

Antitumor effects of the small molecule DMAMCL in neuroblastoma via suppressing aerobic glycolysis and targeting PFKL

Background

Neuroblastoma (NB) is a common solid malignancy in children that is associated with a poor prognosis. Although the novel small molecular compound Dimethylaminomicheliolide (DMAMCL) has been shown to induce cell death in some tumors, little is known about its role in NB.

Methods

We examined the effect of DMAMCL on four NB cell lines (NPG, AS, KCNR, BE2). Cellular confluence, survival, apoptosis, and glycolysis were detected using Incucyte ZOOM, CCK-8 assays, Annexin V-PE/7-AAD flow cytometry, and Seahorse XFe96, respectively. Synergistic effects between agents were evaluated using CompuSyn and the effect of DMAMCL in vivo was evaluated using a xenograft mouse model. Phosphofructokinase-1, liver type (PFKL) expression was up- and down-regulated using overexpression plasmids or siRNA.

Results

When administered as a single agent, DMAMCL decreased cell proliferation in a time- and dose-dependent manner, increased the percentage of cells in SubG1 phase, and induced apoptosis in vitro, as well as inhibiting tumor growth and prolonging survival in tumor-bearing mice (NGP, BE2) in vivo. In addition, DMAMCL exerted synergistic effects when combined with etoposide or cisplatin in vitro and displayed increased antitumor effects when combined with etoposide in vivo compared to either agent alone. Mechanistically, DMAMCL suppressed aerobic glycolysis by decreasing glucose consumption, lactate excretion, and ATP production, as well as reducing the expression of PFKL, a key glycolysis enzyme, in vitro and in vivo. Furthermore, PFKL overexpression attenuated DMAMCL-induced cell death, whereas PFKL silencing promoted NB cell death.

Conclusions

The results of this study suggest that DMAMCL exerts antitumor effects on NB both in vitro and in vivo by suppressing aerobic glycolysis and that PFKL could be a potential target of DMAMCL in NB.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02330-y.

Anticancer activities of parthenolide in primary effusion lymphoma preclinical models

The sesquiterpene lactone parthenolide is a major component of the feverfew medicinal plant, Tanacetum parthenium. Parthenolide has been extensively studied for its anti-inflammatory and anticancer properties in several tumor models. Parthenolide's antitumor activities depend on several mechanisms but it is mainly known as an inhibitor of the nuclear factor-κB (NF-κB) pathway. This pathway is constitutively activated and induces cell survival in primary effusion lymphoma (PEL), a rare aggressive AIDS-related lymphoproliferative disorder that is commonly caused by the human herpesvirus 8 (HHV-8) infection. The aim of this study is to evaluate the targeted effect of Parthenolide both in vitro and in vivo. Herein, parthenolide significantly inhibited cell growth, induced G₀ /G₁ cell cycle arrest, and induced massive apoptosis in PEL cells and ascites. In addition, parthenolide inhibited the NF-ĸB pathway suppressing IĸB phosphorylation and p65 nuclear translocation. It also reduced the expression of the DNA methylase inhibitor (DNMT1). Parthenolide induced HHV-8 lytic gene expression without inhibiting latent viral gene expression. Importantly, DMAPT, the more soluble parthenolide prodrug, promoted delay in ascites development and prolonged the survival of PEL xenograft mice. This study supports the therapeutic use of parthenolide in PEL and encourages its further clinical development.

The Anti-Leukemic Activity of Natural Compounds

The use of biologically active compounds has become a realistic option for the treatment of malignant tumors due to their cost-effectiveness and safety. In this review, we aimed to highlight the main natural biocompounds that target leukemic cells, assessed by in vitro and in vivo experiments or clinical studies, in order to explore their therapeutic potential in the treatment of leukemia: acute myeloid leukemia (AML), chronic myeloid leukemia (CML), acute lymphocytic leukemia (ALL), and chronic lymphocytic leukemia (CLL). It provides a basis for researchers and hematologists in improving basic and clinical research on the development of new alternative therapies in the fight against leukemia, a harmful hematological cancer and the leading cause of death among patients.

Applications of Sesquiterpene Lactones: A Review of Some Potential Success Cases

Sesquiterpene lactones, a vast range of terpenoids isolated from Asteraceae species, exhibit a broad spectrum of biological effects and several of them are already commercially available, such as artemisinin. Here the most recent and impactful results of in vivo, preclinical and clinical studies involving a selection of ten sesquiterpene lactones (alantolactone, arglabin, costunolide, cynaropicrin, helenalin, inuviscolide, lactucin, parthenolide, thapsigargin and tomentosin) are presented and discussed, along with some of their derivatives. In the authors’ opinion, these compounds have been neglected compared to others, although they could be of great use in developing important new pharmaceutical products. The selected sesquiterpenes show promising anticancer and anti-inflammatory effects, acting on various targets. Moreover, they exhibit antifungal, anxiolytic, analgesic, and antitrypanosomal activities. Several studies discussed here clearly show the potential that some of them have in combination therapy, as sensitizing agents to facilitate and enhance the action of drugs in clinical use. The derivatives show greater pharmacological value since they have better pharmacokinetics, stability, potency, and/or selectivity. All these natural terpenoids and their derivatives exhibit properties that invite further research by the scientific community.

Derivatisation of parthenolide to address chemoresistant chronic lymphocytic leukaemia

Parthenolide is a natural product that exhibits anti-leukaemic activity, however, its clinical use is limited by its poor bioavailability. It may be extracted from feverfew and protocols for growing, extracting and derivatising it are reported. A novel parthenolide derivative with good bioavailability and pharmacological properties was identified through a screening cascade based on in vitro anti-leukaemic activity and calculated "drug-likeness" properties, in vitro and in vivo pharmacokinetics studies and hERG liability testing. In vitro studies showed the most promising derivative to have comparable anti-leukaemic activity to DMAPT, a previously described parthenolide derivative. The newly identified compound was shown to have pro-oxidant activity and in silico molecular docking studies indicate a prodrug mode of action. A synthesis scheme is presented for the production of amine 7 used in the generation of 5f.

Novel Targeted Nano-Parthenolide Molecule against NF-kB in Acute Myeloid Leukemia

The targeted nano-encapsulation of anticancer drugs can improve drug delivery and the selective targeting of cancer cells. Nuclear factor kappa B (NF-kB) is a regulator for different biological responses, including cell proliferation and differentiation. In acute myeloid leukemia (AML), constitutive NF-κB has been detected in more than 50% of cases, enabling leukemic cells to resist apoptosis and stimulate uncontrolled proliferation. We evaluated NF-kB expression in bone marrow samples from 103 patients with AML using quantitative real time polymerase chain reaction (RT-PCR) and found that expression was increased in 80.5% (83 out 103) of these patients with AML in comparison to the control group. Furthermore, overexpressed transmembrane glycoprotein (CD44) on leukemic cells in comparison to normal cells is known to play an important role in leukemic cell engraftment and survival. We designed poly lactide co-glycolide (PLGA) nanoparticles conjugated with antiCD44 and encapsulating parthenolide (PTL), a nuclear factor kappa B (NF-kB) inhibitor, in order to improve the selectivity and targeting of leukemic cells and to spare normal cells. In vitro, in leukemic cell lines Kasumi-1, KG-1a, and THP-1, proliferation was decreased by 40% (** p < 0.01) with 5 µM PLGA-antiCD44-PTL nanoparticles in comparison to the same concentration of free PTL (~10%). The higher uptake of the nanoparticles by leukemic cells was confirmed with confocal microscopy. In conclusion, PLGA-antiCD44-PTL nanoparticles improved the bioavailability and selective targeting of leukemic cells, thus holding promise as a drug delivery system to improve the cure rate of AML.

Biodegradable, Drug-Loaded Nanovectors via Direct Hydration as a New Platform for Cancer Therapeutics

The stabilization and transport of low-solubility drugs, by encapsulation in nanoscopic delivery vectors (nanovectors), is a key paradigm in nanomedicine. However, the problems of carrier toxicity, specificity, and producibility create a bottleneck in the development of new nanomedical technologies. Copolymeric nanoparticles are an excellent platform for nanovector engineering due to their structural versatility; however, conventional fabrication processes rely upon harmful chemicals that necessitate purification. In engineering a more robust (copolymeric) nanovector platform, it is necessary to reconsider the entire process from copolymer synthesis through self-assembly and functionalization. To this end, a process is developed whereby biodegradable copolymers of poly(ethylene glycol)-block-poly(trimethylene carbonate), synthesized via organocatalyzed ring-opening polymerization, undergo assembly into highly uniform, drug-loaded micelles without the use of harmful solvents or the need for purification. The direct hydration methodology, employing oligo(ethylene glycol) as a nontoxic dispersant, facilitates rapid preparation of pristine, drug-loaded nanovectors that require no further processing. This method is robust, fast, and scalable. Utilizing parthenolide, an exciting candidate for treatment of acute lymphoblastic leukemia (ALL), discrete nanovectors are generated that show strikingly low carrier toxicity and high levels of specific therapeutic efficacy against primary ALL cells (as compared to normal hematopoietic cells).

Investigating chemoresistance to improve sensitivity of childhood T-cell acute lymphoblastic leukemia to parthenolide

Current therapies for childhood T-cell acute lymphoblastic leukemia have increased survival rates to above 85% in developed countries. Unfortunately, some patients fail to respond to therapy and many suffer from serious side effects, highlighting the need to investigate other agents to treat this disease. Parthenolide, a nuclear factor kappa (κ)B inhibitor and reactive oxygen species inducer, has been shown to have excellent anti-cancer activity in pediatric leukemia xenografts, with minimal effects on normal hemopoietic cells. However, some leukemia initiating cell populations remain resistant to parthenolide. This study examined mechanisms for this resistance, including protective effects conferred by bone marrow stromal components. T-cell acute leukemia cells co-cultured with mesenchymal stem cells demonstrated significantly enhanced survival against parthenolide (73±11%) compared to cells treated without mesenchymal stem cell support (11±9%). Direct cell contact between mesenchymal cells and leukemia cells was not required to afford protection from parthenolide. Mesenchymal stem cells released thiols and protected leukemia cells from reactive oxygen species stress, which is associated with parthenolide cytotoxicity. Blocking cystine uptake by mesenchymal stem cells, using a small molecule inhibitor, prevented thiol release and significantly reduced leukemia cell resistance to parthenolide. These data indicate it may be possible to achieve greater toxicity to childhood T-cell acute lymphoblastic leukemia by combining parthenolide with inhibitors of cystine uptake.

Mitochondrial and caspase pathways are involved in the induction of apoptosis by nardosinen in MCF-7 breast cancer cell line

Natural products isolated from plants provide a valuable source for expansion of new anticancer drugs. Nardosinen (4,9-dihydroxy-nardosin-6-en) is a natural sesquiterpene extracted from Juniperus foetidissima. Recently, we have reported the cytotoxic effects of nardosinen in various cancer cells. The aim of the current study was to investigate the anticancer features of nardosinen as well as its possible molecular mechanisms of the nardosinen cytotoxic effect on breast tumor cells. MTT assay showed that nardosinen notably inhibited cell proliferation in a dose-dependent manner in MCF-7 breast cancer cells. The growth inhibitory effect of nardosinen was associated with the induction of cell apoptosis, activation of caspase-6, increase of reactive oxygen species (ROS), and loss of mitochondrial membrane potentials (ΔΨm). Western blot assay following treatment with nardosinen showed that the expression levels of the Bax were significantly up-regulated and the expression levels of the Bcl-2 were significantly down-regulated. Our results finally exhibited that nardosinen induces apoptosis in breast cancer cells via the mitochondrial and caspase pathways.

Microenvironmental stromal cells abrogate NF-κB inhibitor-induced apoptosis in chronic lymphocytic leukemia

Nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) is known to play an important role in the pathogenesis of chronic lymphocytic leukemia (CLL). Several NF-κB inhibitors were shown to successfully induce apoptosis of CLL cells in vitro Since the microenvironment is known to be crucial for the survival of CLL cells, herein, we tested whether NF-κB inhibition may still induce apoptosis in these leukemic cells in the presence of protective stromal interaction. We used the specific NF-κB inhibitor dehydroxymethylepoxyquinomicin (DHMEQ). Microenvironmental support was mimicked by co-culturing CLL cells with bone marrow-derived stromal cell lines (HS-5 and M2-10B4). NF-κB inhibition by DHMEQ in CLL cells could be confirmed in both the monoculture and co-culture setting. In line with previous reports, NF-κB inhibition induced apoptosis in the monoculture setting by activating the intrinsic apoptotic pathway resulting in poly (ADP-ribose) polymerase (PARP)-cleavage; however, it was unable to induce apoptosis in leukemic cells co-cultured with stromal cells. Similarly, small interfering ribonucleic acid (siRNA)-mediated RELA downregulation induced apoptosis of CLL cells cultured alone, but not in the presence of supportive stromal cells. B-cell activating factor (BAFF) was identified as a microenvironmental messenger potentially protecting the leukemic cells from NF-κB inhibition-induced apoptosis. Finally, we show improved sensitivity of stroma-supported CLL cells to NF-κB inhibition when combining the NF-κB inhibitor with the SYK inhibitor R406 or the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib, agents known to inhibit the stroma-leukemia crosstalk. We conclude that NF-κB inhibitors are not promising as monotherapies in CLL, but may represent attractive therapeutic partners for ibrutinib and R406.

Succinamide derivatives of melampomagnolide B and their anti-cancer activities

A series of succinamide derivatives of melampomagnolide B have been synthesized by coupling MMB monosuccinate (2) with various heterocyclic amines to afford compounds 3a-3l. MMB monosuccinate was also reacted with terminal diaminoalkanes to afford dimeric succinamido analogs of MMB (4a-4h). These succinamide analogs of MMB were evaluated for their anti-cancer activity against a panel of sixty human cancer cell lines. Analogs 3d-3i and dimers 4f-4g exhibited promising anti-cancer activity with GI50 values ranging from 0.28 to 33.5µM against most of the cell lines in the panel. The dimeric analogs 4f and 4g were identified as lead compounds with GI50 values in the nanomolar range (GI50=280-980nM) against several cell lines in the panel; i.e. leukemia cell lines CCRF-CEM, HL-60(TB), K-562, MOLT-4, RPMI-8226 and SR; and solid tumor cell lines NCI-H522 (non-small cell lung cancer), SW-620 and HCT-116 (colon cancer), LOX IMVI (melanoma), RXF 393 (renal cancer), and MCF7, BT-549 and MDA-MB-468 (breast cancer). Succinamide analogs 3a, 3c-3l and 4b-4h were also evaluated for their apoptotic activity against M9-ENL1 acute myelogenous leukemia cells; compounds 3h-3j and 4g were equipotent with parthenolide, exhibiting LC50 values in the range 4.1-8.1μM. Molecular docking studies indicate that these molecules interact covalently with the highly conserved Cys-46 residue of the N-terminal lobe (1-109) of human IKKβ to inhibit the NFκB transcription factor complex, resulting in down-regulation of anti-apoptotic genes under NFκB control.

Identification of a melampomagnolide B analog as a potential lead molecule for treatment of acute myelogenous leukemia

A series of carbamate derivatives of the antileukemic sesquiterpene melampomagnolide B (MMB) has been synthesized utilizing a 1,2,4-triazole carbamate conjugate of MMB as an intermediate synthon. Five imidazole- and benzimidazole-carbamate analogs of MMB (8a-8e) were prepared and evaluated for anti-leukemic activity against cultured M9 ENL1 AML cells. All the analogs exhibited improved anti-leukemic activity (EC₅₀=0.90-3.93μM) when compared to parthenolide and the parent sesquiterpene, MMB (EC₅₀=7.0μM and 15.5μM, respectively). The imidazole carbamate analog, 8a (EC₅₀=0.9μM), was 16 times more potent than MMB. The comparative bioavailabilities of 8a and MMB were determined in BALB/c mice following oral dosing of these compounds. It has been demonstrated that the absolute plasma bioavailabilities of MMB and 8a were 6.7±0.8%, and 45.5±2%, respectively. These results indicate that, compared to MMB, the PK parameters for 8a display significantly improved bioavailability and exposure after oral administration. Analog 8a is considered to be a potential clinical candidate for treatment of acute myelogenous leukemia.

Cyclic AMP efflux inhibitors as potential therapeutic agents for leukemia

Apoptotic evasion is a hallmark of cancer. We propose that some cancers may evade cell death by regulating 3'-5'-cyclic adenosine monophosphate (cAMP), which is associated with pro-apoptotic signaling. We hypothesize that leukemic cells possess mechanisms that efflux cAMP from the cytoplasm, thus protecting them from apoptosis. Accordingly, cAMP efflux inhibition should result in: cAMP accumulation, activation of cAMP-dependent downstream signaling, viability loss, and apoptosis. We developed a novel assay to assess cAMP efflux and performed screens to identify inhibitors. In an acute myeloid leukemia (AML) model, several identified compounds reduced cAMP efflux, appropriately modulated pathways that are responsive to cAMP elevation (cAMP-responsive element-binding protein phosphorylation, and deactivation of Very Late Antigen-4 integrin), and induced mitochondrial depolarization and caspase activation. Blocking adenylyl cyclase activity was sufficient to reduce effects of the most potent compounds. These compounds also decreased cAMP efflux and viability of B-lineage acute lymphoblastic leukemia (B-ALL) cell lines and primary patient samples, but not of normal primary peripheral blood mononuclear cells. Our data suggest that cAMP efflux is a functional feature that could be therapeutically targeted in leukemia. Furthermore, because some of the identified drugs are currently used for treating other illnesses, this work creates an opportunity for repurposing.

Targeting Thioredoxin Reductase by Parthenolide Contributes to Inducing Apoptosis of HeLa Cells

Parthenolide (PTL), a major active sesquiterpene lactone from the herbal plant Tanacetum parthenium, has been applied in traditional Chinese medicine for centuries. Although PTL demonstrates potent anticancer efficacy in numerous types of malignant cells, the cellular targets of PTL have not been well defined. We reported here that PTL interacts with both cytosolic thioredoxin reductase (TrxR1) and mitochondrial thioredoxin reductase (TrxR2), two ubiquitous selenocysteine-containing antioxidant enzymes, to elicit reactive oxygen species-mediated apoptosis in HeLa cells. PTL selectively targets the selenocysteine residue in TrxR1 to inhibit the enzyme function, and further shifts the enzyme to an NADPH oxidase to generate superoxide anions, leading to reactive oxygen species accumulation and oxidized thioredoxin. Under the conditions of inhibition of TrxRs in cells, PTL does not cause significant alteration of cellular thiol homeostasis, supporting selective target of TrxRs by PTL. Importantly, overexpression of functional TrxR1 or Trx1 confers protection, whereas knockdown of the enzymes sensitizes cells to PTL treatment. Targeting TrxRs by PTL thus discloses an unprecedented mechanism underlying the biological activity of PTL, and provides deep insights to understand the action of PTL in treatment of cancer.

New Sesquiterpene Lactone Dimer, Uvedafolin, Extracted from Eight Yacon Leaf Varieties (Smallanthus sonchifolius): Cytotoxicity in HeLa, HL-60, and Murine B16-F10 Melanoma Cell Lines

Uvedafolin, 1, a new sesquiterpene lactone dimer, was isolated from the leaves of Smallanthus sonchifolius with five related compounds, 2-6, and their cytotoxicity was assessed against three tumor cell lines (HeLa, HL-60, B16-F10 melanoma). The stereostructure of 1 was newly elucidated by ESI-TOF-MS, 1D/2D NMR, and single-crystal X-ray diffraction. Dimers 1 and 2 had the most effective IC50 values, 0.2-1.9 μM, against the three tumor cell lines when compared with monomers 3-6 (IC50 values 0.7-9.9 μM) and etoposide (IC50 values 0.8-114 μM). The ester linkages of two sets of monomers, uvedalin, 5, and sonchifolin, 6, for 1, and enhydrin, 4, and sonchifolin, 6, for 2, as well as the acetyl group at the C-9 position, were essential for the high cytotoxicity. Dimers 1 and 2 would have potential as anticancer agents.

Dimers of Melampomagnolide B Exhibit Potent Anticancer Activity against Hematological and Solid Tumor Cells

Novel carbamate (7a-7h) and carbonate (7i, 7j, and 8) dimers of melampomagnolide B have been synthesized by reaction of the melampomagnolide-B-triazole carbamate synthon 6 with various terminal diamino- and dihydroxyalkanes. Dimeric carbamate products 7b, 7c, and 7f exhibited potent growth inhibition (GI50 = 0.16-0.99 μM) against the majority of cell lines in the NCI panel of 60 human hematological and solid tumor cell lines. Compound 7f and 8 exhibited anticancer activity that was 300-fold and 1 × 10(6)-fold more cytotoxic than DMAPT, respectively, at a concentration of 10 μM against rat 9L-SF gliosarcoma cells. Compounds 7a-7j and 8 were also screened against M9-ENL1 and acute myelogenous leukemia (AML) primary cell lines and exhibited 2- to 10-fold more potent antileukemic activity against M9-ENL1 cells (EC50 = 0.57-2.90 μM) when compared to parthenolide (EC50 = 6.0) and showed potent antileukemic activity against five primary AML cell lines (EC50 = 0.76-7.3 μM).

Targeting the Ataxia Telangiectasia Mutated-null phenotype in chronic lymphocytic leukemia with pro-oxidants

Inactivation of the Ataxia Telangiectasia Mutated gene in chronic lymphocytic leukemia results in resistance to p53-dependent apoptosis and inferior responses to treatment with DNA damaging agents. Hence, p53-independent strategies are required to target Ataxia Telangiectasia Mutated-deficient chronic lymphocytic leukemia. As Ataxia Telangiectasia Mutated has been implicated in redox homeostasis, we investigated the effect of the Ataxia Telangiectasia Mutated-null chronic lymphocytic leukemia genotype on cellular responses to oxidative stress with a view to therapeutic targeting. We found that in comparison to Ataxia Telangiectasia Mutated-wild type chronic lymphocytic leukemia, pro-oxidant treatment of Ataxia Telangiectasia Mutated-null cells led to reduced binding of NF-E2 p45-related factor-2 to antioxidant response elements and thus decreased expression of target genes. Furthermore, Ataxia Telangiectasia Mutated-null chronic lymphocytic leukemia cells contained lower levels of antioxidants and elevated mitochondrial reactive oxygen species. Consequently, Ataxia Telangiectasia Mutated-null chronic lymphocytic leukemia, but not tumors with 11q deletion or TP53 mutations, exhibited differentially increased sensitivity to pro-oxidants both in vitro and in vivo. We found that cell death was mediated by a p53- and caspase-independent mechanism associated with apoptosis inducing factor activity. Together, these data suggest that defective redox-homeostasis represents an attractive therapeutic target for Ataxia Telangiectasia Mutated-null chronic lymphocytic leukemia.

Parthenolide inhibits LPS-induced inflammatory cytokines through the toll-like receptor 4 signal pathway in THP-1 cells

Parthenolide (PTL) shows potent anti-inflammatory and anti-cancer activities. In the present study, the molecular mechanisms of PTL's activities were explored in lipopolysaccharide (LPS)-induced human leukemia monocytic THP-1 cells and human primary monocytes. The 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium salt (MTS) assay was used to analyze the effect of PTL on THP-1 cell viability. Enzyme-linked immunosorbent assay was used to determine the effect of PTL on LPS-induced inflammatory cytokine secretion. Flow cytometry and quantitative real-time polymerase chain reaction were used to assess the effect of PTL on LPS-induced toll-like receptor 4 (TLR4) expression. Phosphorylation levels of signaling molecules were determined by western blot analysis. Results showed that PTL <12.5 μM did not significantly affect THP-1 cells viability. LPS treatment led to a marked up-regulation of interleukin (IL)-6, IL-1β, IL-8, IL-12p40, tumor necrosis factor-α, IL-18, and NO in THP-1 cells. However, PTL inhibited the expression of these cytokines in a dose-dependent manner, with IC50 values of 1.091-2.620 μM. PTL blocked TLR4 expression with an IC50 value of 1.373 μM as determined by the flow cytometry analysis, and this blocking effect was verified at both protein and mRNA levels. Up-regulation of phosphorylation levels of extracellular signal-regulated kinase 1/2, Jun N-terminal kinase, p38, nuclear factor κB (NF-κB) p65, and IκBα and up-regulation of expressions of other molecules (inducible nitric oxide synthase, TLR4, and TNF receptor-associated factor 6) induced by LPS were abolished by PTL in a dose-dependent manner. The anti-inflammatory mechanisms of PTL operate partly through the TLR4-mediated mitogen-activated protein kinase and NF-κB signaling pathways. Therefore, TLR4 may be a new target for anti-inflammation therapies.

Parthenolide induces autophagy via the depletion of 4E-BP1

Parthenolide (PTL) is a sesquiterpene lactone isolated from feverfew and exhibits potent antitumor activity against various cancers. Many studies indicate that PTL treatment leads to apoptosis, however, the mechanism has not been defined. Here, we observed that cells underwent autophagy shortly after PTL treatment. Inhibition of autophagy by knocking out autophagy associated gene atg5 blocked PTL-induced apoptosis. Surprisingly, PTL decreased the level of translation initiation factor eIF4E binding protein 1 (4E-BP1) in correlation with autophagy. Ectopic expression or shRNA knockdown of 4E-BP1 further verified the effect of 4E-BP1 on PTL-induced autophagy. Meanwhile, PTL elevated the cellular reactive oxygen species (ROS) which located upstream of the depletion of 4E-BP1, and contributed to the consequent autophagy. This study revealed 4E-BP1 as a trigger for PTL-induced autophagy and may lead to therapeutic strategy to enhance the efficacy of anticancer drugs.

Loss of cooperativity of secreted CD40L and increased dose-response to IL4 on CLL cell viability correlates with enhanced activation of NF-kB and STAT6

Chronic lymphocytic leukemia (CLL) cells fail to enter apoptosis in vivo as opposed to their non-malignant B-lymphocyte counterparts. The ability of CLL cells to escape apoptosis is highly dependent on their microenvironment. Compared to non-malignant B cells, CLL cells are more responsive to complex stimuli that can be reproduced in vitro by the addition of cytokines. To understand the molecular mechanism of the environment-dependent anti-apoptotic signaling circuitry of CLL cells, we quantified the effect of the SDF-1, BAFF, APRIL, anti-IgM, interleukin-4 (IL4) and secreted CD40L (sCD40L) on the survival of in vitro cultured CLL cells and found IL4 and sCD40L to be most efficient in rescuing CLL cells from apoptosis. In quantitative dose-response experiments using cell survival as readout, the binding affinity of IL4 to its receptor was similar between malignant and non-malignant cells. However, the downstream signaling in terms of the amount of STAT6 and its degree of phosphorylation was highly stimulated in CLL cells. In contrast, the response to sCD40L showed a loss of cooperative binding in CLL cells but displayed a largely increased ligand binding affinity. Although a high-throughput microscopy analysis did not reveal a significant difference in the spatial CD40 receptor organization, the downstream signaling showed an enhanced activation of the NF-kB pathway in the malignant cells. Thus, we propose that the anti-apoptotic phenotype of CLL involves a sensitized response for IL4 dependent STAT6 phosphorylation, and an activation of NF-kB signaling due to an increased affinity of sCD40L to its receptor.

Sesquiterpene lactones: adverse health effects and toxicity mechanisms

Sesquiterpene lactones (STLs) present a wide range of biological activities, mostly based on their alkylating capabilities, which underlie their therapeutic potential. These compounds are the active constituents of a variety of plants, frequently used as herbal remedies. STLs such as artemisinin and its derivatives are in use as first-line antimalarials while others, such as parthenolide, have recently reached cancer clinical trials. However, the toxicological profile of these compounds must be thoroughly characterized, since the same properties that make STL useful medicines can also cause severe toxicity. STL-containing plants have long been known to induce a contact dermatitis in exposed farm workers, and also to cause several toxic syndromes in farm animals. More recently, concerns are been raised regarding the genotoxic potential of these compounds and the embryotoxicity of artemisinins. A growing number of STLs are being reported to be mutagenic in different in vitro and in vivo assays. As yet no systematic studies have been published, but the genotoxicity of STLs seems to depend not so much on direct DNA alkylation as on oxidative DNA damage and other partially elucidated mechanisms. As the medicinal use of these compounds increases, further studies of their toxic potential are needed, especially those focusing on the structural determinants of genotoxicity and embryotoxicity.

Parthenolide induces caspase-independent and AIF-mediated cell death in human osteosarcoma and melanoma cells

The mechanism of the cytotoxic effect exerted by parthenolide on tumor cells is not clearly defined today. This article shows that parthenolide stimulates in human osteosarcoma MG63 and melanoma SK-MEL-28 cells a mechanism of cell death, which is not prevented by z-VAD-fmk and other caspase inhibitors. In particular treatment with parthenolide rapidly stimulated (1-2 h) reactive oxygen species (ROS) generation by inducing activation of extracellular signal-regulated kinase 1/2 (ERK 1/2) and NADPH oxidase. This event caused depletion of thiol groups and glutathione, NF-κB inhibition, c-Jun N-terminal kinase (JNK) activation, cell detachment from the matrix, and cellular shrinkage. The increase of ROS generation together with the mitochondrial accumulation of Ca(2+) also favored dissipation of Δψm, which seemed primarily determined by permeability transition pore opening, since Δψm loss was partially prevented by the inhibitor cyclosporin A. Staining with Hoechst 33342 revealed in most cells, at 3-5 h of treatment, chromatin condensation, and fragmentation, while only few cells were propidium iodide (PI)-positive. In addition, at this stage apoptosis inducing factor (AIF) translocated to the nucleus and co-localized with areas of condensed chromatin. Prolonging the treatment (5-15 h) ATP content declined while PI-positive cells strongly augmented, denouncing the increase of necrotic effects. All these effects were prevented by N-acetylcysteine, while caspase inhibitors were ineffective. We suggest that AIF exerts a crucial role in parthenolide action. In accordance, down-regulation of AIF markedly inhibited parthenolide effect on the production of cells with apoptotic or necrotic signs. Taken together our results demonstrate that parthenolide causes in the two cell lines a caspase-independent cell death, which is mediated by AIF.

Parthenolide eliminates leukemia-initiating cell populations and improves survival in xenografts of childhood acute lymphoblastic leukemia

Approximately 20% of children with acute lymphoblastic leukemia (ALL) relapse because of failure to eradicate the disease. Current drug efficacy studies focus on reducing leukemia cell burden. However, if drugs have limited effects on leukemia-initiating cells (LICs), then these cells may expand and eventually cause relapse. Parthenolide (PTL) has been shown to cause apoptosis of LIC in acute myeloid leukemia. In the present study, we assessed the effects of PTL on LIC populations in childhood ALL. Apoptosis assays demonstrated that PTL was effective against bulk B- and T-ALL cells, whereas the CD34(+)/CD19(-), CD34(+)/CD7(-), and CD34(-) subpopulations were more resistant. However, functional analyses revealed that PTL treatment prevented engraftment of multiple LIC populations in NOD/LtSz-scid IL-2Rγ(c)-null mice. PTL treatment of mice with established leukemias from low- and high-risk patients resulted in survival and restoration of normal murine hemopoiesis. In only 3 cases, disease progression was significantly slowed in mice engrafted with CD34(+)/CD19(-) or CD34(+)/CD7(-) and CD34(-) cells, but was not prevented, demonstrating that individual LIC populations within patients have different responses to therapy. These observations indicate that PTL may have therapeutic potential in childhood ALL and provide a basis for developing effective therapies that eradicate all LIC populations to prevent disease progression and reduce relapse.

Natural and synthetic α-methylenelactones and α-methylenelactams with anticancer potential

α-Methylene-γ- and δ-lactones, as well as α-methylene-γ- and δ-lactams, are plant-derived compounds often used in traditional medicine for the treatment of inflammatory diseases. In recent years, the anticancer properties of these compounds and the molecular mechanisms of their action have been studied extensively. In the search for modern anticancer drugs, various synthetic analogs of α-methylene-γ- and δ-lactones and lactams have been synthesized and tested for their cytotoxic activity. In this review, we give a brief description of the occurrence and biological activity of such compounds isolated from plants and their diverse synthetic analogs.

Antimyeloma activity of the sesquiterpene lactone cnicin: impact on Pim-2 kinase as a novel therapeutic target

Despite recent advances in therapy, multiple myeloma, the second most common hematologic tumor in the Western world, is still incurable. Identification of substances that display a wide range of tumor-killing activities and target cancer-specific pathways constitute a basis for the development of novel therapies. In this study, we investigate the cytotoxic effect of the natural substance cnicin in multiple myeloma. Cnicin treatment reveals potent antiproliferative effects and induces cell death in cell lines and primary myeloma cells even in the presence of survival cytokines and the tumor microenvironment. Other cell lines of hematopoietic origin also succumb to cell death whereas stromal cells and endothelial cells are unaffected. We show that activation of caspases, accumulation of reactive oxygen species and downregulation of nuclear factor kappa-light-chain-enhancer of activated B cell contribute to the cytotoxic effects of cnicin. Microarray analysis reveals downregulation of Pim-2, a serine/threonine kinase. We provide evidence that Pim-2 constitutes a new survival kinase for myeloma cells in vitro and is highly expressed in malignant but not in normal plasma cells in vivo. Combining cnicin with current standard or experimental therapeutics leads to enhanced cell death. Thus, our data indicate that cnicin induces myeloma cell death via several pathways and reveals Pim-2 as a novel target. These findings provide a rational for further evaluation of cnicin as a new anti-tumor drug and underline the potential of sesquiterpene lactones in tumor therapy.

Effect of sesquiterpene lactone coronopilin on leukaemia cell population growth, cell type-specific induction of apoptosis and mitotic catastrophe

OBJECTIVES

The aim of this study was to investigate anti-leukaemic potential of coronopilin, a sesquiterpene lactone from Ambrosia arborescens, and to characterize mechanism(s) underlying its activity.

MATERIALS AND METHODS

The study was conducted on Jurkat and U937, two leukaemia-derived cell lines. Apoptosis and impairment of cell cycle progression were evaluated by flow cytometry and by microscopic analysis. Changes in protein expression and activation were evaluated by western blot analysis. Coronopilin-tubulin covalent adducts were demonstrated by mass spectrometry.

RESULTS

Coronopilin inhibited (IC(50) ≤ 20 μm) leukaemia cell population growth, but displayed poor cytotoxicity to normal white blood cells. On Jurkat cells, coronopilin exerted cell population growth inhibition activity, mainly by triggering caspase-dependent apoptosis. Conversely, in U937 cells, coronopilin's primary response was a robust arrest in G(2) /M. Marked increase in mitotic index and presence of activated cyclin B1/Cdk1 complex, phosphorylated histone H3 at Ser10, and hyperpolymerized tubulin indicated that cells accumulated in mitosis. Prolonged mitotic arrest ultimately resulted in U937 mitotic catastrophe, and dying cells exhibited the features of non-caspase-dependent death.

CONCLUSIONS

  This study demonstrated that coronopilin efficiently inhibited leukaemia cell population growth by triggering cell type-specific responses. Moreover, coronopilin-mediated cell population expansion inhibition was specific to neoplastic cells, as normal white blood cell viability was not significantly affected. Thus, coronopilin may represent an interesting new chemical scaffold upon which to develop new anti-leukaemic agents.

Helenalin bypasses Bcl-2-mediated cell death resistance by inhibiting NF-κB and promoting reactive oxygen species generation

Evasion of cell death by overexpression of anti-apoptotic proteins, such as Bcl-2, is commonly observed in cancer cells leading to a lack of response to chemotherapy. Hence, there is a need to find new chemotherapeutic agents that are able to overcome chemoresistance mediated by Bcl-2 and to understand their mechanisms of action. Helenalin, a sesquiterpene lactone (STL), induces cell death and abrogates clonal survival in a highly apoptosis-resistant Bcl-2 overexpressing Jurkat cell line as well as in two other Bcl-2 overexpressing solid tumor cell lines (mammary MCF-7; pancreatic L6.3pl). This effect is not achieved by directly affecting the mitochondria-protective function of Bcl-2 in the intrinsic pathway of apoptosis since Bcl-2 overexpressing Jurkat cells do not show cytochrome c release and dissipation of mitochondrial membrane potential upon helenalin treatment. Moreover, helenalin induces an atypical form of cell death with necrotic features in Bcl-2 overexpressing cells, neither activating classical mediators of apoptosis (caspases, AIF, Omi/HtrA2, Apaf/apoptosome) nor ER-stress mediators (BiP/GRP78 and CHOP/GADD153), nor autophagy pathways (LC3 conversion). In contrast, helenalin was found to inhibit NF-κB activation that was considerably increased in Bcl-2 overexpressing Jurkat cells and promotes cell survival. Moreover, we identified reactive oxygen species (ROS) and free intracellular iron as mediators of helenalin-induced cell death whereas activation of JNK and abrogation of Akt activity did not contribute to helenalin-elicited cell death. Our results highlight the NF-κB inhibitor helenalin as a promising chemotherapeutic agent to overcome Bcl-2-induced cell death resistance.

p53 and Notch signaling in chronic lymphocytic leukemia: clues to identifying novel therapeutic strategies

The p53 tumor suppressor protein has a key role in the induction of apoptosis of chronic lymphocytic leukemia (CLL) cells. Abnormalities within the p53 pathway identify a subset of patients with a poor prognosis. This review describes recent advances in understanding the mechanisms that regulate p53 levels and the role of p53 in the control of the cell cycle and of apoptosis. The classical model of p53-mediated apoptosis emphasizes the transcriptional activation of proapoptotic genes. In contrast, a novel model emphasizes p53's non-transcriptional actions as the major route of apoptosis induction, whereas its transcriptional arm predominantly upregulates antiapoptotic genes, thus providing a negative feedback mechanism that limits apoptosis. Further studies have identified the Notch pathway as a candidate p53-induced antiapoptotic mechanism. In contrast to the classical model, the novel model predicts that pharmacological inhibition of p53's transcriptional function or of the Notch signaling pathway will augment apoptosis induction by cytotoxic agents. Therapeutic strategies based on the novel model, which we review here for the first time, may significantly augment the antitumor actions of cytotoxic agents in CLL and in other malignancies.

Aberrantly activated anti-apoptotic signalling mechanisms in chronic lymphocytic leukaemia cells: clues to the identification of novel therapeutic targets

Chronic lymphocytic leukaemia (CLL) is the commonest haematological malignancy in the western world and is incurable by cytotoxic therapy. Considerable research effort has identified the signal transduction pathways in CLL cells that contribute to anti-apoptotic signalling. Some pathways are constitutively activated in CLL cells but upregulated in normal cells only when protein tyrosine kinases (PTKs) are activated by ligands. This review describes which PTKs are aberrantly activated in CLL cells and are potential targets for inhibition. Additional potential targets within pathways downstream of these PTKs include Mek/Erk, mTorc1, protein kinase C, PI-3 kinase/Akt, nuclear factor-κB and cyclin-dependent protein kinase. Numerous studies have identified chemical agents and antibodies that selectively kill CLL cells, irrespective of their genetic resistance to conventional chemotherapeutic agents, and which can overcome cytoprotective microenvironmental signalling. These studies have resulted in identification of novel therapies, some of which are currently undergoing clinical trials. In vitro and animal model studies and clinical trials could determine which inhibitors of which targets are the likely to be most effective and least toxic either singly or in combination.

Parthenolide inhibits TRIF-dependent signaling pathway of Toll-like receptors in RAW264.7 macrophages

Toll-like receptors (TLRs) play an important role in induction of innate immune responses for host defense against invading microbial pathogens. Microbial component engagement of TLRs can trigger the activation of myeloid differential factor 88 (MyD88)- and toll-interleukin-1 receptor domain-containing adapter inducing interferon-β (TRIF)-dependent downstream signaling pathways. Parthenolide, an active ingredient of feverfew (Tanacetum parthenium), has been used for centuries to treat many chronic diseases. Parthenolide inhibits the MyD88-dependent pathway by inhibiting the activity of inhibitor-κB kinase. However, it is not known whether parthenolide inhibits the TRIF-dependent pathway. To evaluate the therapeutic potential of parthenolide, its effect on signal transduction via the TRIF-dependent pathway of TLRs induced by lipopolysaccharide (LPS) or polyinosinic-polycytidylic acid (poly [I:C]) was examined. Parthenolide inhibited nuclear factor-κB and interferon regulatory factor 3 activation induced by LPS or poly[I:C], and the LPS-induced phosphorylation of interferon regulatory factor 3 as well as interferon-inducible genes such as interferon inducible protein-10. These results suggest that parthenolide can modulate TRIF-dependent signaling pathways of TLRs, and may be the basis of effective therapeutics for chronic inflammatory diseases.

The NF-kappaB inhibitor LC-1 has single agent activity in multiple myeloma cells and synergizes with bortezomib

Multiple myeloma remains incurable with conventional therapeutics. Thus, new treatments for this condition are clearly required. In this study we evaluated the novel NF-kappaB inhibitor LC-1 in multiple myeloma cell lines and plasma cells derived from multiple myeloma patients. LC-1 was cytotoxic to multiple myeloma cell lines H929, U266, and JJN3, and induced apoptosis in a dose-dependent manner with an overall LD(50) of 3.6 micromol/L (+/-1.8) after 48 hours in culture. Primary multiple myeloma cells, identified by CD38 and CD138 positivity, had a mean LD(50) for LC-1 of 4.9 micromol/L (+/-1.6); normal bone marrow cells were significantly less sensitive to the cytotoxic effects of LC-1 (P = 0.0002). Treatment of multiple myeloma cell lines with LC-1 resulted in decreased nuclear localization of the NF-kappaB subunit Rel A and the inhibition of NF-kappaB target genes. In addition, LC-1 showed synergy with melphalan, bortezomib, and doxorubicin (combination indices of 0.72, 0.61, and 0.78, respectively), and was more effective when cells were cultured on fibronectin. These data show that LC-1 has activity in multiple myeloma cell lines and primary multiple myeloma cells, and its ability to inhibit NF-kappaB seems important for its cytotoxic effects. Furthermore, LC-1-induced transcriptional suppression of survivin and MCL1 provides a potential explanation for its synergy with conventional agents.

Targeting mitochondria for cancer therapy

Mitochondria are the cells' powerhouse, but also their suicidal weapon store. Dozens of lethal signal transduction pathways converge on mitochondria to cause the permeabilization of the mitochondrial outer membrane, leading to the cytosolic release of pro-apoptotic proteins and to the impairment of the bioenergetic functions of mitochondria. The mitochondrial metabolism of cancer cells is deregulated owing to the use of glycolytic intermediates, which are normally destined for oxidative phosphorylation, in anabolic reactions. Activation of the cell death machinery in cancer cells by inhibiting tumour-specific alterations of the mitochondrial metabolism or by stimulating mitochondrial membrane permeabilization could therefore be promising therapeutic approaches.

NF-kappaB as a therapeutic target in chronic lymphocytic leukemia

IMPORTANCE OF THE FIELD

NF-kappaB includes a family of transcription factors that play a critical role in the biology of normal lymphocytes and it is aberrantly activated in chronic lymphocytic leukemia (CLL) cells. Here, we review the role of constitutive NF-kappaB activation in CLL pathogenesis and its potential as a therapeutic target for CLL treatment.

AREAS COVERED IN THIS REVIEW

This review highlights the different strategies reported to inhibit NF-kappaB signaling in CLL cells. They include both IkappaB kinase inhibitors and several natural compounds that act at different steps of the pathway.

WHAT THE READER WILL GAIN

Targeting NF-kappaB leads to apoptosis of CLL cells, corroborating the role of NF-kappaB in the survival and clonal expansion of these tumoral cells. Moreover, several studies confirmed a synergistic effect between NF-kappaB inhibitors and other antitumoral agents and that inhibition of NF-kappaB could overcome the microenvironmental protection of CLL cells.

TAKE HOME MESSAGE

NF-kappaB is a relevant target in CLL and inhibitors of this prosurvival pathway, alone or in combination, represent a novel therapeutic strategy for the treatment of CLL patients.

Nrf2 responses and the therapeutic selectivity of electrophilic compounds in chronic lymphocytic leukemia

Recent studies show that redox-active small molecules are selectively cytotoxic to chronic lymphocytic leukemia (CLL). Although elevated levels of reactive oxygen species in CLL cells have been implicated, the molecular mechanism underlying this selectivity is unclear. In other cell types, the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway regulates the oxidative stress response. We found elevated Nrf2 signaling in untreated CLL cells compared with normal lymphocytes. Therefore, we tested 27 known electrophilic and antioxidant compounds with drug-like properties and determined their CLL-selective cytotoxicity and effect on Nrf2 signaling. The selected compounds were from five distinct structural classes; alpha-beta unsaturated carbonyls, isothiocyanates, sulfhydryl reactive metals, flavones, and polyphenols. Our results show that compounds containing alpha-beta unsaturated carbonyls, sulfhydryl reactive metals, and isothiocyanates are strong activators of Nrf2 in a reporter assay system and in primary human CLL based on increased expression of the Nrf2 target heme oxygenase-1. alpha-beta Unsaturated carbonyl-containing compounds were selectively cytotoxic to CLL, and loss of the alpha-beta unsaturation abrogated Nrf2 activity and CLL toxicity. The alpha-beta unsaturated carbonyl containing compounds ethacrynic acid and parthenolide activated Nrf2 in normal peripheral blood mononuclear cells, but had a less potent effect in CLL cells. Furthermore, ethacrynic acid bound directly to the Nrf2-negative regulator Kelch-like ECH-associated protein 1 (Keap1) in CLL cells. These experiments document the presence of Nrf2 signaling in human CLL and suggest that altered Nrf2 responses may contribute to the observed selective cytotoxicity of electrophilic compounds in this disease.

Semisynthetic derivatives of sesquiterpene lactones by palladium-catalyzed arylation of the alpha-methylene-gamma-lactone substructure

The palladium-catalyzed arylation of different alpha-methylene-gamma-lactone-containing sesquiterpene lactones was shown to produce E-olefin coupling products selectively in moderate to excellent yields. Biological evaluation of these semisynthetic sesquiterpene lactone derivatives in HeLa cells showed interesting antiproliferative profiles and provided initial structure-activity data.