Quercetin decreases intracellular GSH content and potentiates the apoptotic action of the antileukemic drug arsenic trioxide in human leukemia cell lines

Natural products as potential drug treatments for acute promyelocytic leukemia

Acute promyelocytic leukemia (APL), which was once considered one of the deadliest types of leukemia, has become a curable malignancy since the introduction of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) as clinical treatments. ATO, which has become the first-line therapeutic agent for APL, is derived from the natural mineral product arsenic, exemplifying an important role of natural products in the treatment of APL. Many other natural products, ranging from small-molecule compounds to herbal extracts, have also demonstrated great potential for the treatment and adjuvant therapy of APL. In this review, we summarize the natural products and representative components that have demonstrated biological activity for the treatment of APL. We also discuss future directions in better exploring their medicinal value, which may provide a reference for subsequent new drug development and combination therapy programs.

Protective effects of macromolecular polyphenols, metals (zinc, selenium, and copper) - Polyphenol complexes, and different organs with an emphasis on arsenic poisoning: A review

For the potential health benefits and nutritional value, polyphenols are one of the secondary metabolites of plants that have received extensive research. It has anti-inflammatory and cytotoxicity-reducing properties in addition to a high antioxidant content. Macromolecular polyphenols and polysaccharides are biologically active natural polymers with antioxidant and anti-inflammatory potential. Arsenic is an ecologically toxic metalloid. Arsenic in drinking water is the most common way people come into contact with this metalloid. While arsenic is known to cause cancer, it is also used to treat acute promyelocytic leukemia (APL). The treatment's effectiveness is hampered by the adverse effects it can cause on the body. Oxidative stress, inflammation, and the inability to regulate cell death cause the most adverse effects. Polyphenols and other macromolecules like polysaccharides act as neuroprotectants by mitigating free radical damage, inhibiting nitric oxide (NO) production, lowering A42 fibril formation, boosting antioxidant levels, and controlling apoptosis and inflammation. To prevent the harmful effects of toxins, polyphenols and pectin lower oxidative stress, boost antioxidant levels, improve mitochondrial function, control apoptosis, and suppress inflammation. Therefore, it prevents damage to the heart, liver, kidneys, and reproductive system. This review aims to identify the effects of the polyphenols in conjugation with polysaccharides as an ameliorative strategy for arsenic-induced toxicity in various organs.

A Comprehensive Analysis and Anti-Cancer Activities of Quercetin in ROS-Mediated Cancer and Cancer Stem Cells

Reactive oxygen species (ROS) induce carcinogenesis by causing genetic mutations, activating oncogenes, and increasing oxidative stress, all of which affect cell proliferation, survival, and apoptosis. When compared to normal cells, cancer cells have higher levels of ROS, and they are responsible for the maintenance of the cancer phenotype; this unique feature in cancer cells may, therefore, be exploited for targeted therapy. Quercetin (QC), a plant-derived bioflavonoid, is known for its ROS scavenging properties and was recently discovered to have various antitumor properties in a variety of solid tumors. Adaptive stress responses may be induced by persistent ROS stress, allowing cancer cells to survive with high levels of ROS while maintaining cellular viability. However, large amounts of ROS make cancer cells extremely susceptible to quercetin, one of the most available dietary flavonoids. Because of the molecular and metabolic distinctions between malignant and normal cells, targeting ROS metabolism might help overcome medication resistance and achieve therapeutic selectivity while having little or no effect on normal cells. The powerful bioactivity and modulatory role of quercetin has prompted extensive research into the chemical, which has identified a number of pathways that potentially work together to prevent cancer, alongside, QC has a great number of evidences to use as a therapeutic agent in cancer stem cells. This current study has broadly demonstrated the function-mechanistic relationship of quercetin and how it regulates ROS generation to kill cancer and cancer stem cells. Here, we have revealed the regulation and production of ROS in normal cells and cancer cells with a certain signaling mechanism. We demonstrated the specific molecular mechanisms of quercetin including MAPK/ERK1/2, p53, JAK/STAT and TRAIL, AMPKα1/ASK1/p38, RAGE/PI3K/AKT/mTOR axis, HMGB1 and NF-κB, Nrf2-induced signaling pathways and certain cell cycle arrest in cancer cell death, and how they regulate the specific cancer signaling pathways as long-searched cancer therapeutics.

Nanoparticle impregnated self-supporting protein gel for enhanced reduction in oxidative stress: A molecular dynamics insight for lactoferrin-polyphenol interaction

In the present work, lactoferrin (Lf) based nanoparticle incorporated self-supporting gel encapsulating a flavonoid, quercetin (Q), was developed. The complex formation between Lf and Q was assessed using molecular docking and dynamics simulation that lactoferrin and quercetin showed strong interaction and binding supporting hydrophobic interaction. The microscopic, spectroscopic, and x-ray techniques were used to characterize the gel extensively. In vitro drug release was studied to understand the release pattern of quercetin from the protein gel. The viscosity of the gel and its rheological characteristics were determined using a Brookfield viscometer. Ex vivo skin permeation studies using vertical diffusion cells were carried out to understand its skin permeation properties. The gel showed strong anti-oxidant activity using the DPPH scavenging assay. The enhanced effect of the Lf-Q complex on antioxidant enzyme activity (superoxide dismutase, catalase, and malondialdehyde), was supported by molecular dynamics, surface hydrophobicity, and in vitro studies. To investigate the effect of the gel on angiogenesis, the chorioallantoic membrane assay was performed and its compatibility with erythrocytes was also assessed. Suitability for topical administration was assessed using skin irritation studies performed on Sprague Dawley rats. The overall results suggest that the developed NiPG is suitable for cutaneous localization of quercetin with enhanced antioxidant activity.

Plant Polyphenolic Compounds Potentiates Therapeutic Efficiency of Anticancer Chemotherapeutic Drugs: A Review

BACKGROUND

Scientific research continues to develop more efficacious drugs to treat and cure cancer, the dreadful disease threatening the human race. Chemotherapy is an essential means in cancer therapy, however, plant drugs having pharmacological safety, can be used alone or as additions to current chemotherapeutic agents to enhance therapeutic efficacy and minimize chemotherapyinduced adverse effects.

OBJECTIVE

A combination therapy where the synergistic effect on multiple targets is possible has gained significance because a one-drug one-target approach fails to yield the desired therapeutic effect. Therefore, a detailed description of important plant polyphenolic compounds with anticancer activity and their role in potentiating chemotherapeutic efficiency of existing anticancer drugs is provided in this review. Systematically screening combinations of active pharmaceutical ingredients for potential synergy with plant compounds may be especially valuable in cancer therapy.

METHODS

We extensively have gone through reviews and research articles available in the literature. We made use of databases such as Google Scholar, Research Gate, PubMed, Science Direct, etc. The following keywords were used in our literature search: "Chemotherapy, drug development, cancer drugs, plant-derived polyphenolics, synergistic studies, combination therapy, diagnosis and genetics."

CONCLUSION

Systematic research studies on screening combinations of plant phytochemicals with potential chemotherapeutic pharmaceuticals shed light on their synergistic effects, mechanisms of actions paving the way to develop more efficient anticancer therapeutics to treat and cure the cancer menace, to nullify chemotherapy-induced adverse effects and our review substantially contributes in this direction.

DJ-1 alleviates anoxia and hypoglycemia injury in cardiac microvascular via AKT and GSH

Cardiac microvascular damage, which is often caused by anoxia and hypoglycemia, is associated with the development of cardiac injury. DJ-1 encodes a peptidase C56 protein family related protein, is has been linked to oxidative stress in various cells such as neurons, COPD epithelial cells, and macrophages. However, the effect of DJ-1 towards oxidative stress caused by anoxia and hypoglycemia of cardiac microvascular endothelial cells (CMEC) remains unclear. In this study, we investigated the role and underlying molecular mechanism of DJ-1 in CMEC with anoxia/hypoglycemic (A/H) injury. We found that the mRNA and the protein expression of DJ-1 in CMEC with A/H injury were significantly downregulated. DJ-1 overexpression by pcDNA.3.1-DJ-1 transfection elevated cell viability while it inhibited LDH leakage, cell apoptosis, caspase-3 activity, ROS level, and MDA contents, while knockdown of DJ-1 has the opposite results. In addition, tube formation was increased in DJ-1 overexpression, while it was decreased in DJ-1 knockdown CMEC with A/H injury. In addition, our results indicated that DJ-1 can regulate glutathione (GSH) levels by modulating AKT activity in CMEC with A/H injury. The downregulation of AKT and GSH may remove the protective role of DJ-1 against A/H injury in CMEC. Taken together, this study showed that DJ-1 upregulation protected CMEC against A/H injury via the AKT/GSH signaling pathway.

Cysteine Depletion, a Key Action to Challenge Cancer Cells to Ferroptotic Cell Death

Cancer cells are characterized as highly proliferative at the expense of enhancement of metabolic rate. Consequently, cancer cells rely on antioxidant defenses to overcome the associated increased production of reactive oxygen species (ROS). The reliance of tumor metabolism on amino acids, especially amino acid transport systems, has been extensively studied over the past decade. Although cysteine is the least abundant amino acid in the cell, evidences described it as one of the most important amino acid for cell survival and growth. Regarding its multi-functionality as a nutrient, protein folding, and major component for redox balance due to its involvement in glutathione synthesis, disruption of cysteine homeostasis appears to be promising strategy for induction of cancer cell death. Ten years ago, ferroptosis, a new form of non-apoptotic cell death, has been described as a result of cysteine insufficiency leading to a collapse of intracellular glutathione level. In the present review, we summarized the metabolic networks involving the amino acid cysteine in cancer and ferroptosis and we focused on describing the recently discovered glutathione-independent pathway, a potential player in cancer ferroptosis resistance. Then, we discuss the implication of cysteine as key player in ferroptosis as a precursor for glutathione first, but also as metabolic precursor in glutathione-independent ferroptosis axis.

Quercetin Triggers Induction of Apoptotic and Lysosomal Death of Sensitive and Multidrug Resistant Leukaemia HL60 Cells

Multidrug resistance (MDR) constitutes the major cause of the failure in anticancer therapy. One of the most important mechanisms leading to the occurrence of MDR is related to the modulation of cellular death pathways. The aim of this study was to determine the effect of quercetin (Q) on triggering the programed death of human promyelocytic leukemia sensitive cells HL60 as well as multidrug resistant HL60/VINC cells overexpressing P-glycoprotein and HL60/MX2 cells characterized by the presence of mutated α isoform of topoisomerase II and the absence of β isoform of this enzyme. Q exerted comparable cytotoxic activities toward sensitive HL60 cells and their MDR counterparts. It was also found that this compound modulated the cellular level of reactive oxygen species (ROS) and led to the marked decrease in cellular GSH level. Furthermore, it was demonstrated that Q used at IC₅₀ and IC₉₀ significantly increased the percentage of sub-G1 subpopulation of all studied leukemia cells causing oligonucleosomal DNA fragmentation. The present study also indicated that Q used at IC₉₀ triggers predominantly programed cell death of sensitive HL60 cells and their MDR counterparts by induction of apoptosis occurring with the involvement of caspase-3 and caspase-8 as well as by lysosome membrane permeabilization-dependent mechanisms.

ROS-Mediated Cancer Cell Killing through Dietary Phytochemicals

Reactive oxygen species (ROS) promote carcinogenesis by inducing genetic mutations, activating oncogenes, and raising oxidative stress, which all influence cell proliferation, survival, and apoptosis. Cancer cells display redox imbalance due to increased ROS level compared to normal cells. This unique feature in cancer cells may, therefore, be exploited for targeted therapy. Over the past few decades, natural compounds have attracted attention as potential cancer therapies because of their ability to maintain cellular redox homeostasis with minimal toxicity. Preclinical studies show that bioactive dietary polyphenols exert antitumor effects by inducing ROS-mediated cytotoxicity in cancer cells. These bioactive compounds also regulate cell proliferation, survival, and apoptotic and antiapoptotic signalling pathways. In this review, we discuss (i) how ROS is generated and (ii) regulated and (iii) the cell signalling pathways affected by ROS. We also discuss (iv) the various dietary phytochemicals that have been implicated to have cancer therapeutic effects through their ROS-related functions.

The Relationship between Pharmacological Properties and Structure- Activity of Chrysin Derivatives

Chrysin is a natural product of a flavonoid compound. Chemically, chrysin consists of two phenyl rings (A and B) and a heterocyclic ring (C). Biologically, chrysin exerts many different physiological activities. In recent years, with the in-depth development for more active drugs, the synthesis and biological activities of chrysin derivatives have been well studied. Besides, structure-activity relationship of chrysin revealed that the chemical construction meets the critical chemical structural necessities of flavonoids for numerous pharmacological activities. It is generally believed that modified chrysin could be more potent than unmodified chrysin. Different modification in the rings of chrysin could possess various degrees of biological activities. This review aims to summarize the mechanism for the activities of chrysin and its derivatives in different rings. We also explored the relationship between biological function and structure-activity of substituted chrysin derivatives with different functional groups. The influence of chrysin derivatives on the proliferation and apoptosis of cancer cells is also investigated. Development of novel drugs based on the biological functions of chrysin could better improve clinical outcomes of affected population, especially for tumor patients and diabetic patients.

Enhanced cytotoxic effects of arsenite in combination with anthocyanidin compound, delphinidin, against a human leukemia cell line, HL-60

Among five major anthocyanin compounds, delphinidin exhibited the most potent and selective cytocidal effect against HL-60, a trivalent arsenic (As(III))-resistant cell line. Co-treatment with delphinidin and As(III) resulted in the reduction of IC₅₀ value for As(III) from 11.2 to 1.5 μM, which was considered as clinically achieved concentrations of As(III). The combination treatment strongly preferred to selectively enhance the cytotoxicity of As(III) against HL-60 cells rather than human peripheral blood mononuclear cells. The induction of apoptosis as evidenced by the increase of sub-G₁ cells, DNA fragmentation, annexin V-positive cells and the activation of caspase-8, -9 and -3 was observed in HL-60 cells co-treated with As(III) and delphinidin. Similar to the activation pattern of caspases, a substantial decrease in the expression level of Bid along with the loss of mitochondrial membrane potential was also observed. These results suggested that the combination treatment triggered a convergence of the intrinsic and extrinsic pathways of apoptosis via the activation of caspase-8 and cleaved Bid. Delphinidin itself significantly decreased the intracellular GSH ([i]GSH) and nuclear factor-κB (NF-κB) binding activity, and further returned As(III)-triggered increment of [i]GSH and enhancement of NF-κB binding activity to control level. Additionally, buthionine sulfoximine, a GSH depletor; JSH-23, a NF-κB inhibitor, also mimicked the capacity of delphinidin to significantly induce the reduction of [i]GSH along with the potentiation of As(III) cytotoxicity in HL-60 cells. These observations suggested that delphinidin-induced sensitization of HL-60 cells to As(III) was caused by the reduction of [i]GSH, which was probably associated with the inhibitory effect of delphinidin on NF-κB binding activity. These findings further suggest that delphinidin-induced sensitization of HL-60 cells to As(III) may lead to dose reduction of As(III) in clinical application, and ultimately contribute to minimizing its side effects.

Quercetrin from Toona sinensis leaves induces cell cycle arrest and apoptosis via enhancement of oxidative stress in human colorectal cancer SW620 cells

Finding effective strategies against colorectal cancer (CRC) is still an emergent health problem. In the present study, we investigated the anticancer activity of quercetrin from Toona sinensis leaves (QTL) and explored the underlying mechanism in human CRC cell line SW620. The cells were treated with various concentrations of QTL and the cytotoxic effects of QTL were determined using the MTT assay. Apoptosis and cell cycle status were detected by flow cytometry. Reactive oxygen species (ROS) levels and mitochondrial membrane potential (∆Ψm) were assessed using DCF-DA and JC-1 fluorescence spectrophotometry, respectively. Western blot analysis was used to quantify the expression of apoptosis-related proteins. RT-PCR was applied to determine the mRNA levels of glutathione peroxidase (GPx) and catalase (CAT). QTL exhibited growth inhibitory effects and caused cell cycle arrest in the G2/M phase, which was accompanied by increased expression of p53 and p21 proteins. QTL promoted apoptosis which was consistent with the upregulated expression of Bax, cytochrome c, caspase-9, Apaf-1 and caspase-3. In addition, QTL induced the loss of mitochondrial membrane potential and triggered ROS generation, as revealed by the downregulated mRNA expression and enzymatic activity of GPx and CAT. Furthermore, both N-acetyl cysteine (NAC) and GSH attenuated the QTL-induced growth inhibition observed in SW620 cells along with the increase of ROS levels. These findings revealed that QTL inhibited the growth of CRC cells and facilitated apoptosis by enhancing oxidative stress. QTL may therefore have potential for use in CRC chemotherapy.

Chrysin and silibinin sensitize human glioblastoma cells for arsenic trioxide

Arsenic trioxide (ATO) is highly efficient in treating acute promyelocytic leukemia. Other malignancies, however, are often less sensitive. Searching for compounds sensitizing arsenic resistant tumours for ATO the plant polyphenols, chrysin and silibinin, and the ATP binding cassette (ABC) transporter inhibitor MK-571, respectively, were investigated in human glioblastoma A-172 cells. The sensitivity of A-172 cells to ATO was characterized by a median cytotoxic concentration of 6 μM ATO. Subcytotoxic concentrations of chrysin, silibinin and MK-571, respectively, remarkably increased the sensitivity of the cells to ATO by factors of 4-6. Isobolographic analysis revealed synergistic interaction of the polyphenols and MK-571, respectively, with ATO. Sensitization by chrysin was associated with depletion of cellular glutathione and increased accumulation of arsenic. In contrast, silibinin and also MK-571 increased the accumulation of arsenic more strongly but without affecting the glutathione level. The increase of arsenic accumulation could be attributed to a decreased rate of arsenic export and, additionally, in the case of silibinin and MK-571, to an increasing amount of irreversibly accumulated arsenic. Direct interaction with ABC transporters stimulating export of glutathione and inhibiting export of arsenic, respectively, are discussed as likely mechanisms of the sensitizing activity of chrysin and silibinin.

Established Human Cell Lines as Models to Study Anti-leukemic Effects of Flavonoids

Despite the extensive work on pathological mechanisms and some recent advances in the treatment of different hematological malignancies, leukemia continues to present a significant challenge being frequently considered as incurable disease. Therefore, the development of novel therapeutic agents with high efficacy and low toxicity is urgently needed to improve the overall survival rate of patients. In this comprehensive review article, the current knowledge about the anticancer activities of flavonoids as plant secondary polyphenolic metabolites in the most commonly used human established leukemia cell lines (HL-60, NB4, KG1a, U937, THP-1, K562, Jurkat, CCRF- CEM, MOLT-3, and MOLT-4) is compiled, revealing clear anti-proliferative, pro-apoptotic, cell cycle arresting, and differentiation inducing effects for certain compounds. Considering the low toxicity of these substances in normal blood cells, the presented data show a great potential of flavonoids to be developed into novel anti-leukemia agents applicable also in the malignant cells resistant to the current conventional chemotherapeutic drugs.

Seasonal Dynamics of Metabolites in Needles of Taxus wallichiana var. mairei

Seasonal variations of the phytochemicals contents in needles of T. wallichiana var. mairei due to the effects of growth meteorological parameters were investigated in this study. The needles of T. wallichiana var. mairei were collected from different months and the contents of taxoids (paclitaxel, 10-deacetylbaccatin III (10-DAB), baccatin III, cephalomannine, 10-deacetyltaxol (10-DAT)), flavones (ginkgetin, amentoflavone, quercetin) and polysaccharides were quantified by ultra performance liquid chromatography (UPLC) and the resonance light scattering (RIL) method. The content of taxoids gave the highest level of 1.77 ± 0.38 mg·g-1 in January, and the lowest value of 0.61 ± 0.08 mg·g-1 in September. Unlike taxoids, the content of flavonoids was the highest in August. The content of polysaccharides reached peak value of 28.52 ± 0.57 mg·g-1 in September, which was two times higher than the lowest content of 9.39 ± 0.17 mg·g-1 in January. The contents of paclitaxel, 10-DAB, 10-DAT and polysaccharides significantly depended on meteorological parameters. The mean of minimum temperature (R = -0.61) and length of daylight (R = -0.60) were significantly correlated to 10-DAB content, while 10-DAT level showed significant correlation with length of daylight (R = -0.70) and relative humidity (R = 0.70). In addition, temperature had significantly negative effect on the content of paclitaxel and a significantly positive effect on that of polysaccharides. This study enriched the knowledge on the accumulation pattern of metabolites and could help us to determine the collecting time of T. wallichiana var. mairei for medicinal use.

Selected polyphenols potentiate the apoptotic efficacy of glycolytic inhibitors in human acute myeloid leukemia cell lines. Regulation by protein kinase activities

Background

The glycolysis inhibitor 2-deoxy-d-glucose (2-DG) is a safe, potentially useful anti-tumour drug, but its efficacy is normally low when used alone. Recent studies indicated that 2-DG stimulates the PI3K/Akt and MEK/ERK defensive pathways, which limits the apoptotic efficacy in tumour cell lines. We hypothesized that co-treatment with selected polyphenols could improve 2-DG-provoked apoptosis by preventing defensive kinase activation.

Methods

Cell proliferation was measured by cell counting or the MTT assay. Cell cycle, apoptosis and necrosis were determined by propidium iodide staining and/or annexin V labeling followed by flow cytometry. Mitochondria pore transition and depolarization were determined by calcein-ATM or rhodamine 123 labeling followed flow cytometry. Intracellular reactive oxygen species and GSH were determined by dichlorodihydrofluorescein diacetate or monochlorobimane labeling followed by flow cytometry or fluorimetry. Expression and phosphorylation of protein kinases were analyzed by the Western blot.

Results

(i) 2-DG-provoked apoptosis was greatly potentiated by co-treatment with the sub-lethal concentrations of the flavonoid quercetin in human HL60 acute myeloblastic leukemia cells. Allowing for quantitative differences, apoptosis potentiation was also obtained using NB4 promyelocytic and THP-1 promonocytic cells, using curcumin or genistein instead of quercetin, and using lonidamine instead of 2-DG, but not when 2-DG was substituted by incubation in glucose-free medium. (ii) Quercetin and 2-DG rapidly elicited the opening of mitochondria pore transition, which preceded the trigger of apoptosis. (iii) Treatments did not affect GSH levels, and caused disparate effects on reactive oxygen species generation, which did not match the changes in lethality. (iv) 2-DG and lonidamine stimulated defensive Akt and ERK phosphorylation/activation, while glucose starvation was ineffective. Polyphenols prevented the stimulation of Akt phosphorylation, and in some cases also ERK phosphorylation. In addition, quercetin and 2-DG stimulated GSK-3α,β phosphorylation/inactivation, although with different isoform specificity. The use of pharmacologic inhibitors confirmed the importance of these kinase modifications for apoptosis.

Conclusions

The present in vitro observations suggest that co-treatment with low concentrations of selected polyphenols might represent a manner of improving the poor anti-tumour efficacy of some glycolytic inhibitors, and that apoptosis potentiation may be at least in part explained by the regulation of defensive protein kinase activities.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-016-0345-y) contains supplementary material, which is available to authorized users.

Aptamer-Functionalized and Backbone Redox-Responsive Hyperbranched Polymer for Targeted Drug Delivery in Cancer Therapy

A novel type of backbone redox-responsive hyperbranched poly(2-((2-(acryloyloxy)ethyl)disulfanyl)ethyl 4-cyano-4-(((propylthio)carbonothioyl)-thio)-pentanoate-co-poly(ethylene glycol) methacrylate) (HPAEG) has been designed and prepared successfully via the combination of reversible addition-fragmentation chain-transfer (RAFT) polymerization and self-condensing vinyl polymerization (SCVP). Owing to the existence of surface vinyl groups, HPAEG could be efficiently functionalized by DNA aptamer AS1411 via Michael addition reaction to obtain an active tumor targeting drug delivery carrier (HPAEG-AS1411). The amphiphilic HPAEG-AS1411 could form nanoparticles by macromolecular self-assembly strategy. Cell Counting Kit-8 (CCK-8) assay illustrated that HPAEG-AS1411 nanoparticles had low cytotoxicity to normal cell line. Flow cytometry and confocal laser scanning microscopy (CLSM) results demonstrated that HPAEG-AS1411 nanoparticles could be internalized into tumor cells via aptamer-mediated endocytosis. Compared with pure HPAEG nanoparticles, HPAEG-AS1411 nanoparticles displayed enhanced tumor cell uptake. When the HPAEG-AS1411 nanoparticles loaded with anticancer drug doxorubicin (DOX) were internalized into tumor cells, the disulfide bonds in the backbone of HPAEG-AS1411 were cleaved by glutathione (GSH) in the cytoplasm, so that DOX was released rapidly. Therefore, DOX-loaded HPAEG-AS1411 nanoparticles exhibited a high tumor cellular proliferation inhibition rate and low cytotoxicity to normal cells. This aptamer-functionalized and backbone redox-responsive hyperbranched polymer provides a promising platform for targeted drug delivery in cancer therapy.

Didymin reverses phthalate ester-associated breast cancer aggravation in the breast cancer tumor microenvironment

The present study demonstrated two novel findings. To the best of our knowledge, it is the first study to demonstrate that regulated upon activation, normal T-cell expressed and secreted (RANTES), produced by breast tumor-associated monocyte-derived dendritic cells (TADCs) following breast cancer cell exposure to phthalate esters, may contribute to the progression of cancer via enhancement of cancer cell proliferation, migration and invasion. Furthermore, the present study revealed that didymin, a dietary flavonoid glycoside present in citrus fruits, was able to reverse phthalate ester-mediated breast cancer aggravation. MDA-MB-231 cells were treated with butyl benzyl phthalate (BBP), di-n-butyl phthalate (DBP) or di-2-ethylhexyl phthalate (DEHP). Subsequently, the conditioned medium (CM) was harvested and cultured with monocyte-derived dendritic cells (mdDCs). Cultures of MDA-MB-231 cells with the conditioned medium of BBP-, DBP- or DEHP-MDA-MB-231 tumor-associated mdDCs (BBP-, DBP- or DEHP-MDA-TADC-CM) demonstrated enhanced proliferation, migration and invasion. Exposure of the MDA-MB-231 cells to DBP induced the MDA-TADCs to produce the inflammatory cytokine RANTES, which subsequently induced MDA-MB-231 cell proliferation, migration and invasion. Depleting RANTES reversed the effects of DBP-MDA-TADC-mediated MDA-MB-231 cell proliferation, migration and invasion. In addition, didymin was observed to suppress phthalate-mediated breast cancer cell proliferation, migration and invasion. The present study suggested that didymin was capable of preventing phthalate ester-associated cancer aggravation.

Natural Compounds Modulating Mitochondrial Functions

Mitochondria are organelles responsible for several crucial cell functions, including respiration, oxidative phosphorylation, and regulation of apoptosis; they are also the main intracellular source of reactive oxygen species (ROS). In the last years, a particular interest has been devoted to studying the effects on mitochondria of natural compounds of vegetal origin, quercetin (Qu), resveratrol (RSV), and curcumin (Cur) being the most studied molecules. All these natural compounds modulate mitochondrial functions by inhibiting organelle enzymes or metabolic pathways (such as oxidative phosphorylation), by altering the production of mitochondrial ROS and by modulating the activity of transcription factors which regulate the expression of mitochondrial proteins. While Qu displays both pro- and antioxidant activities, RSV and Cur are strong antioxidant, as they efficiently scavenge mitochondrial ROS and upregulate antioxidant transcriptional programmes in cells. All the three compounds display a proapoptotic activity, mediated by the capability to directly cause the release of cytochrome c from mitochondria or indirectly by upregulating the expression of proapoptotic proteins of Bcl-2 family and downregulating antiapoptotic proteins. Interestingly, these effects are particularly evident on proliferating cancer cells and can have important therapeutic implications.

Delphinidin induces cytotoxicity and potentiates cytocidal effect in combination with arsenite in an acute promyelocytic leukemia NB4 cell line

The effects of delphinidin were investigated by focusing on growth inhibition, cell cycle arrest and apoptosis induction in the human acute promyelocytic leukemia (APL) NB4 cell line. Delphinidin exhibited a dose- and time-dependent cytotoxic effect against NB4 cells. Almost no cell cycle arrest, but an apparent increase in the percentage of sub-G1 cells was observed in delphinidin-treated cells. The activation of caspase-8 and -9 was observed as early as 1-h post-exposure to delphinidin, followed by the activation of caspase-3 from 3-h post-exposure. A substantial decrease in the expression level of Bid was also observed as early as 1-h post-exposure. A modest decrease in the mitochondrial membrane potential (ΔΨm) was observed at 3-h post-exposure, followed by a substantial time-dependent decrease in ΔΨm in treated cells. Delphinidin exerted more potent cytotoxicity against NB4 cells than normal peripheral blood mononuclear cells (PBMNCs). In addition, delphinidin in combination with an arsenic derivative arsenite (As(III)), which has demonstrated marked efficacy in patients with APL, achieved an enhanced cytocidal effect against NB4 cells, but lesser on PBMNCs. Treatment of NB4 cells with As(III) plus delphinidin did not increase, but decreased slightly, intracellular arsenic accumulation (As[i]) as compared to that treated with As(III) alone. These results suggested that delphinidin selectively sensitized NB4 cells to As(III), resulting in the enhancement of As(III) cytotoxicity by strengthening intrinsic/extrinsic pathway-mediated apoptosis induction, rather than affecting the As[i] levels. These observations may offer a rationale for the use of delphinidin to improve the clinical efficacy of As(III).

Multi-Target Cytotoxic Actions of Flavonoids in Blood Cancer Cells

To date, cytotoxic effects of flavonoids in various cancer cells are well accepted. However, the intracellular signaling cascades triggered by these natural compounds remain largely unknown and elusive. In this mini- review, the multiplicity of molecular targets of flavonoids in blood cancer cells is discussed by demonstrating the involvement of various signaling pathways in induction of apoptotic responses. Although these data reveal a great potential of flavonoids for the development of novel agents against different types of hematological malignancies, the pleiotropic nature of these compounds in modulation of cellular processes and their interactions certainly need unraveling and further investigation.

Involvement of the modulation of cancer cell redox status in the anti-tumoral effect of phenolic compounds

The association between the anti-tumoral properties of phenolics, the generation of ROS in culture medium and modulation of redox homeostasis was analyzed. In AGS cells, the anti-proliferative effect of quercetin was not reverted by catalase or SOD.

Quercetin induces mitochondrial-derived apoptosis via reactive oxygen species-mediated ERK activation in HL-60 leukemia cells and xenograft

Quercetin is a plant-derived bioflavonoid that was recently shown to have multiple anticancer activities in various solid tumors. Here, novel molecular mechanisms through which quercetin exerts its anticancer effects in acute myeloid leukemia (AML) cells were investigated. Results from Western blot and flow cytometric assays revealed that quercetin significantly induced caspase-8, caspase-9, and caspase-3 activation, poly ADP-ribose polymerase (PARP) cleavage, and mitochondrial membrane depolarization in HL-60 AML cells. The induction of PARP cleavage by quercetin was also observed in other AML cell lines: THP-1, MV4-11, and U937. Moreover, treatment of HL-60 cells with quercetin induced sustained activation of extracellular signal-regulated kinase (ERK), and inhibition of ERK by an ERK inhibitor significantly abolished quercetin-induced cell apoptosis. MitoSOX red and 2',7'-dichlorofluorescin fluorescence, respectively, showed that mitochondrial superoxide and intracellular peroxide levels were higher in quercetin-treated HL-60 cells compared with the control group. Moreover, both N-acetylcysteine and the superoxide dismutase mimetic, MnTBAP, reversed quercetin-induced intracellular reactive oxygen species production, ERK activation, and subsequent cell death. The in vivo xenograft mice experiments revealed that quercetin significantly reduced tumor growth through inducing intratumoral oxidative stress while activating the ERK pathway and subsequent cell apoptosis in mice with HL-60 tumor xenografts. In conclusions, our results indicated that quercetin induced cell death of HL-60 cells in vitro and in vivo through induction of intracellular oxidative stress following activation of an ERK-mediated apoptosis pathway.

Differential effects of polyphenols on proliferation and apoptosis in human myeloid and lymphoid leukemia cell lines

BACKGROUND

Mortality rates for leukemia are high despite considerable improvements in treatment. Since polyphenols exert pro-apoptotic effects in solid tumors, our study investigated the effects of polyphenols in haematological malignancies. The effect of eight polyphenols (quercetin, chrysin, apigenin, emodin, aloe-emodin, rhein, cis-stilbene and trans-stilbene) were studied on cell proliferation, cell cycle and apoptosis in four lymphoid and four myeloid leukemic cells lines, together with normal haematopoietic control cells.

METHODS

Cellular proliferation was measured by CellTiter-Glo(®) luminescent assay; and cell cycle arrest was assessed using flow cytometry of propidium iodide stained cells. Apoptosis was investigated by caspase-3 activity assay using flow cytometry and apoptotic morphology was confirmed by Hoescht 33342 staining.

RESULTS

Emodin, quercetin, and cis-stilbene were the most effective polyphenols at decreasing cell viability (IC50 values of 5-22 μM, 8-33 μM, and 25-85 μM respectively) and inducing apoptosis (AP50 values (the concentration which 50% of cells undergo apoptosis) of 2-27 μM, 19-50 μM, and 8-50 μM respectively). Generally, lymphoid cell lines were more sensitive to polyphenol treatment compared to myeloid cell lines, however the most resistant myeloid (KG-1a and K562) cell lines were still found to respond to emodin and quercetin treatment at low micromolar levels. Non-tumor cells were less sensitive to all polyphenols compared to the leukemia cells.

CONCLUSIONS

These findings suggest that polyphenols have anti-tumor activity against leukemia cells with differential effects. Importantly, the differential sensitivity of emodin, quercetin, and cis-stilbene between leukemia and normal cells suggests that polyphenols are potential therapeutic agents for leukemia.

Low concentration of quercetin antagonizes the cytotoxic effects of anti-neoplastic drugs in ovarian cancer

Objective

The role of Quercetin in ovarian cancer treatment remains controversial, and the mechanism is unknown. The aim of this study was to investigate the therapeutic effects of Quercetin in combination with Cisplatin and other anti-neoplastic drugs in ovarian cancer cells both in vitro and in vivo, along with the molecular mechanism of action.

Methods

Quercetin treatment at various concentrations was examined in combination with Cisplatin, taxol, Pirarubicin and 5-Fu in human epithelial ovarian cancer C13* and SKOV3 cells. CCK8 assay and Annexin V assay were for cell viability and apoptosis analysis, immunofluorescence assay, DCFDA staining and realtime PCR were used for reactive oxygen species (ROS)-induced injury detection and endogenous antioxidant enzymes expression. Athymic BALB/c-nu nude mice were injected with C13*cells to obtain a xenograft model for in vivo studies. Immunohistochemical analysis was carried out to evaluate the ROS-induced injury and SOD1 activity of xenograft tumors.

Results

Contrary to the pro-apoptotic effect of high concentration (40 µM–100 µM) of Quercetin, low concentrations (5 µM–30 µM) of Quercetin resulted in varying degrees of attenuation of cytotoxicity of Cisplatin treatment when combined with Cisplatin. Similar anti-apoptotic effects were observed when Quercetin was combined with other anti-neoplastic agents: Taxol, Pirarubicin and 5-Fluorouracil (5-Fu). Low concentrations of Quercetin were observed to suppress ROS-induced injury, reduce intracellular ROS level and increase the expression of endogenous antioxidant enzymes, suggesting a ROS-mediated mechanism of attenuating anti-neoplastic drugs. In xenogeneic model, Quercetin led to a substantial reduction of therapeutic efficacy of Cisplatin along with enhancing the endogenous antioxidant enzyme expression and reducing ROS-induced damage in xenograft tumor tissue.

Conclusion

Taken together, these data suggest that Quercetin at low concentrations attenuate the therapeutic effects of Cisplatin and other anti-neoplastic drugs in ovarian cancer cells by reducing ROS damage. Quercetin supplementation during ovarian cancer treatment may detrimentally affect therapeutic response.

Additivity, antagonism, and synergy in arsenic trioxide-induced growth inhibition of C6 glioma cells: effects of genistein, quercetin and buthionine-sulfoximine

Arsenic trioxide (ATO) induces clinical remission in acute promyelocytic leukemia and growth inhibition in various cancer cell lines in vitro. Recently, genistein and quercetin were reported to potentiate ATO-provoked apoptosis in leukemia and hepatocellular carcinoma cells. Genistein acted via enhanced ROS generation and quercetin via glutathione depletion. Searching for potential strategies for the treatment of malignant gliomas in this study the capacity of these flavonoids to sensitize rat C6 astroglioma cells for the cytotoxic action of ATO was investigated. ATO inhibited cell growth in a concentration- and time-dependent manner. This effect was accompanied neither by enhanced radical generation nor lipid peroxidation and was not attributed to apoptosis. ATO treatment concentration-dependently increased glutathione levels. Genistein enhanced radical generation. Combined with ATO it inhibited cell growth additively. Additivity was also obtained after cotreatment with ATO and H2O2. Quercetin acted antagonistically on ATO-induced growth inhibition. Quercetin increased glutathione levels. In contrast, buthionine-sulfoximine (BSO) depleted cellular glutathione and acted synergistically with ATO. In conclusion, in C6 cells neither genistein nor quercetin are suited as sensitizing agent, in contrast to BSO. Depletion of cellular glutathione content rather than an increase of ROS generation plays a central role in the enhancement of ATO-toxicity in C6 cells.

Separation and purification of flavonoid from Taxus remainder extracts free of taxoids using polystyrene and polyamide resin

An efficient separation process of flavonoid from Taxus wallichiana var. mairei remainder extracts free of taxoids was developed in this study. AB-8 macroporous resin and polyamide resin offered the fine adsorption capacity, and its adsorption rate at 30°C fitted well to the Langmuir and Freundich isotherms. Resin dynamic adsorption and desorption experiments were conducted to optimize the separation process of total flavonoids from T. wallichiana var. mairei remainder extracts free of taxoids. The optimum parameters for adsorption by AB-8 resin were as follows: (1) the concentration of flavonoids in a sample solution of 5.61 mg/mL with a processing volume of 2 bed volume (BV) (60 mL); (2) for desorption, ethanol-water (80:20, v/v), with 6 BV as an eluent at a flow rate of 2 BV/h. After a one-run treatment with AB-8 resin, the content of flavonoids was increased 5.10-fold from 4.05 to 20.65%. The optimum parameters for adsorption by polyamide resin were as follows: processing volume of 2 BV (30 mL); for desorption, ethanol-water (70:30, v/v), with 8 BV as an eluent at a flow rate of 2 BV/h. After one-run treatment with polyamide resin, the content of total flavonoids increased from 20.65 to 65.21%. The method will provide a potential approach for large-scale separation and purification of flavonoid for its wide pharmaceutical use.

8-bromo-5-hydroxy-7-methoxychrysin targeting for inhibition of the properties of liver cancer stem cells by modulation of Twist signaling

Emerging evidence has suggested that cancer stem cells with expression of surface biomarkers including CD133 and CD44 have more aggressive biological behavior, including epithelial-mesenchymal transition (EMT), which are closely related to invasion. The upregulation and nuclear relocation of the EMT regulator Twist1 have been implicated in the tumor invasion and metastasis of human hepatocellular carcinoma (HCC). In this study, we aimed to isolate and characterize a small population of CD133+ cells that existed in the HCC cell line SMMC-7721 by MACS and investigated the possible roles of 8-bromo-7-methoxychrysin (BrMC), a synthetic analogue of chrysin, in inhibiting the properties of CD133+ sphere-forming cells (SFCs) derived from the HCC cell line SMMC-7721, namely liver cancer stem cells (LCSCs). Based on the data, BrMC inhibited the proliferation, self-renewal and invasion of LCSCs in vitro and in vivo, downregulated the expression of the LCSC biomarkers CD133 and CD44 and induced EMT by downregulating the expression of Twist and β-catenin in LCSCs. BrMC potentiated the inhibition of LCSCs self-renewal after reduction of twist protein levels, which was attenuated when twist was overexpressed. This study not only provides an important experimental and theoretical basis for investigation of BrMC in LCSCs, but also helps in the development of effective therapeutic medicine for HCC.

Co-treatment with quercetin and 1,2,3,4,6-penta-O-galloyl-β-D-glucose causes cell cycle arrest and apoptosis in human breast cancer MDA-MB-231 and AU565 cells

Breast cancer is the most universal cancer in women, but the medications for breast cancer usually cause serious side effects and offer no effective treatment for triple-negative breast cancer. Here, we investigated the growth inhibitory effects of gallic acid (GA), (-)-epigallocatechin gallate (EGCG), or 1,2,3,4,6-penta-O-galloyl-β-D-glucose (5GG) combined with quercetin (Que) on breast cancer cells. In this study, we tested the combined effects of these compounds on estrogen receptor (ER)/human epidermal growth factor 2 (Her2)-negative (MDA-MB-231), ER-positive/Her2-negative (BT483), and ER-negative/Her2-positive (AU565) breast cancer cells. After treatment of each cell line with these compounds, we found that Que combined with 5GG induced S-phase arrest and apoptosis in MDA-BM-231 cells through downregulation of S-phase kinase protein 2 expression, but induced G2/M-phase arrest and apoptosis in AU565 cells through downregulation of Her2 expression. Additionally, Que combined with 5GG was more effective in inhibiting MDA-MB-231 cell growth than Que combined with EGCG (5GG analogue) or GA. The combination of 5GG and Que can offer great potential for the chemoprevention of ER-negative breast cancer.

The effect of MAPK inhibitors and ROS modulators on cell growth and death of H₂O₂-treated HeLa cells

Reactive oxygen species (ROS) influence the signaling of mitogen‑activated protein kinases (MAPKs) involved in cell survival and death. In the present study, the toxicological effect of hydrogen peroxide (H2O2) on HeLa cervical cancer cells was evaluated following treatment with MAPK inhibitors [MAP kinase or ERK kinase (MEK), c‑Jun N‑terminal kinase (JNK) or p38], N‑acetyl cysteine (NAC) and propyl gallate (PG) (well‑known antioxidants), or L‑buthionine sulfoximine [BSO; an inhibitor of glutathione (GSH) synthesis]. Treatment with 100 µM H2O2 inhibited the growth of HeLa cells and induced cell death, which was accompanied by loss of the mitochondrial membrane potential (MMP; ΔΨm). H2O2 did not induce any specific phase arrests of the cell cycle. ROS levels increased, while GSH levels decreased in H2O2‑treated HeLa cells after 1 and 24 h of treatment. The MAPK inhibitors enhanced H2O2‑induced HeLa cell death, while only p38 inhibitor increased ROS levels. Both NAC and PG attenuated H2O2‑induced HeLa cell growth inhibition and death together with the suppression of ROS levels. BSO increased ROS levels in H2O2‑treated HeLa cells without increasing cell death. The levels of MMP (ΔΨm) loss and GSH depletion were not closely associated with the levels of apoptosis in HeLa cells treated with the MAPK inhibitors, NAC, PG or BSO, in the presence of H2O2. In conclusion, H2O2 induced HeLa cell growth inhibition and death. MAPK inhibitors generally enhanced H2O2‑induced HeLa cell death. In particular, p38 inhibitor increased ROS levels in H2O2‑treated HeLa cells, while NAC and PG attenuated H2O2‑induced HeLa cell death by suppressing ROS levels.

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

MG132 as a proteasome inhibitor can induce apoptotic cell death in lung cancer cells. However, little is known about the toxicological cellular effects of MG132 on normal primary lung cells. Here, we investigated the effects of N-acetyl cysteine (NAC) and vitamin C (well known antioxidants) or L-buthionine sulfoximine (BSO; an inhibitor of GSH synthesis) on MG132-treated human pulmonary fibroblast (HPF) cells in relation to cell death, reactive oxygen species (ROS) and glutathione (GSH). MG132 induced growth inhibition and death in HPF cells, accompanied by the loss of mitochondrial membrane potential (MMP; ΔΨ_m). MG132 increased ROS levels and GSH-depleted cell numbers in HPF cells. Both antioxidants, NAC and vitamin C, prevented growth inhibition, death and MMP (ΔΨ_m) loss in MG132-treated HPF cells and also attenuated ROS levels in these cells. BSO showed a strong increase in ROS levels in MG132-treated HPF cells and slightly enhanced the growth inhibition, cell death, MMP (ΔΨ_m) loss and GSH depletion. In addition, NAC decreased anonymous ubiquitinated protein levels in MG132-treated HPF cells. Furthermore, superoxide dismutase (SOD) 2, catalase (CTX) and GSH peroxidase (GPX) siRNAs enhanced HPF cell death by MG132, which was not correlated with ROS and GSH level changes. In conclusion, MG132 induced the growth inhibition and death of HPF cells, which were accompanied by increasing ROS levels and GSH depletion. Both NAC and vitamin C attenuated HPF cell death by MG132, whereas BSO slightly enhanced the death.

Synergism between arsenite and proteasome inhibitor MG132 over cell death in myeloid leukaemic cells U937 and the induction of low levels of intracellular superoxide anion

Increased oxygen species production has often been cited as a mechanism determining synergism on cell death and growth inhibition effects of arsenic-combined drugs. However the net effect of drug combination may not be easily anticipated solely from available knowledge of drug-induced death mechanisms. We evaluated the combined effect of sodium arsenite with the proteasome inhibitor MG132, and the anti-leukaemic agent CAPE, on growth-inhibition and cell death effect in acute myeloid leukaemic cells U937 and Burkitt's lymphoma-derived Raji cells, by the Chou-Talalay method. In addition we explored the association of cytotoxic effect of drugs with changes in intracellular superoxide anion (O₂⁻) levels. Our results showed that combined arsenite+MG132 produced low levels of O₂⁻ at 6h and 24h after exposure and were synergic on cell death induction in U937 cells over the whole dose range, although the combination was antagonistic on growth inhibition effect. Exposure to a constant non-cytotoxic dose of 80μM hydrogen peroxide together with arsenite+MG132 changed synergism on cell death to antagonism at all effect levels while increasing O₂⁻ levels. Arsenite+hydrogen peroxide also resulted in antagonism with increased O₂⁻ levels in U937 cells. In Raji cells, arsenite+MG132 also produced low levels of O₂⁻ at 6h and 24h but resulted in antagonism on cell death and growth inhibition. By contrast, the combination arsenite+CAPE showed high levels of O₂⁻ production at 6h and 24 h post exposure but resulted in antagonism over cell death and growth inhibition effects in U937 and Raji cells. We conclude that synergism between arsenite and MG132 in U937 cells is negatively associated to O₂⁻ levels at early time points after exposure.

Casticin-induced apoptosis involves death receptor 5 upregulation in hepatocellular carcinoma cells

AIM: To investigate the apoptotic activities of casticin in hepatocellular carcinoma (HCC) cells and its molecular mechanisms.

METHODS: PLC/PRF/5 and Hep G2 cell lines were cultured in vitro and the inhibitory effect of casticin on the growth of cells was detected by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolim bromide (MTT) assay. The apoptotic cell death was examined using the cell apoptosis enzyme linked immunosorbent assay (ELISA) detection kit, flow cytometry (FCM) after propidium iodide (PI) staining and DNA agarose gel electrophoresis. The caspase activities were measured using ELISA. Reactive oxygen species (ROS) production was evaluated by FCM after dichlorodihydrofluorescein diacetate (DCFH-DA) probe labeling. Intracellular glutathione (GSH) content was measured using a glutathione assay kit. The expression of death receptor (DR)4 and DR5 proteins was analyzed by Western blotting and FCM.

RESULTS: Casticin significantly inhibited the growth of human HCC (PLC/PRF/5 and Hep G2) cells in a dose-dependent manner (P < 0.05). Casticin increased the percentage of the sub-G1 population in HCC cells in a concentration-dependent manner. The potency of casticin to PLC/PRF/5 cells was higher than that of 5-flurouracil (26.8% ± 4.8% vs 17.4% ± 5.1%) at 10 μmol/L for 24 h. Casticin increased the levels of Histone/DNA fragmentation and the levels of active caspase-3, -8 and -9 in a concentration-dependent manner (P < 0.05). Treatment with 30 μmol/L casticin for 24 h resulted in the formation of a DNA ladder. Casticin reduced the GSH content (P < 0.05), but did not affect the level of intracellular ROS in PLC/PRF/5 and Hep G2 cells. The thiol antioxidants, acetylcysteine (NAC) and GSH restored GSH content and attenuated casticin-induced apoptosis. In contrast, the nonthiol antioxidants, butylated hydroxyanisole and mannitol failed to do so. In the HCC cells treated with casticin for 24 h, DR5 protein level was increased. The expression of DR5 protein induced by casticin was inhibited by NAC. Pretreatment with DR5/Fc chimera protein, a blocking antibody, effectively attenuated the induction of apoptosis by casticin.

CONCLUSION: Casticin-induced apoptosis of HCC cells is involved in GSH depletion and DR5 upregulation.

Potentiation of arsenic trioxide-induced apoptosis by 8-bromo-7-methoxychrysin in human leukemia cells involves depletion of intracellular reduced glutathione

The novel chrysin analog 8-bromo-7-methoxychrysin (BrMC) has been reported to induce apoptosis of various cancer cell lines. Arsenic trioxide (ATO) treatment induces clinical remission in acute promyelocytic leukemia patients. The combination of ATO with other agents has been shown to improve therapeutic effectiveness in vitro and in vivo. In this report, the mechanism of apoptosis induced by treatment with ATO alone or in combination with BrMC was studied in U937, HL-60, and Jurkat cells. Our results demonstrated that BrMC cooperated with ATO to induce apoptosis in human leukemia cells. This co-treatment caused mitochondrial transmembrane potential dissipation and stimulated the mitochondrial apoptotic pathway, as evidenced by cytochrome c release, down-regulation of X-linked inhibitor of apoptosis (XIAP) and Bcl-XL, and up-regulation of Bax. BrMC alone or in combination with ATO, decreased Akt phosphorylation as well as intracellular reduced glutathione (GSH) content. The thiol antioxidant N-acetylcysteine and exogenous GSH restored GSH content and attenuated apoptosis induced by co-treatment with ATO plus BrMC. In contrast, the non-thiol antioxidant butylated hydroxyanisole and mannitol failed to do so. These findings suggest that GSH depletion explains at least in part the potentiation of ATO-induced apoptosis by BrMC.

Synergistic Apoptosis-Inducing Antileukemic Effects of Arsenic Trioxide and Mucuna macrocarpa Stem Extract in Human Leukemic Cells via a Reactive Oxygen Species-Dependent Mechanism

The objective of this study was to examine the potential of enhancing the antileukemic activity of arsenic trioxide (ATO) by combining it with a folk remedy, crude methanolic extract of Mucuna macrocarpa (CMEMM). Human leukemia cells HL-60, Jurkat, and Molt-3 were treated with various doses of ATO, CMEMM, and combinations thereof for 24 and 48 h. Results indicated that the combination of 2.5 μM ATO and 50 μg/mL CMEMM synergistically inhibited cell proliferation in HL-60 and Jurkat cell lines. Apoptosis triggered by ATO/CMEMM treatment was confirmed by accumulation of cells in the sub-G₁ phase in cell cycle analyses, characteristic apoptotic nuclear fragmentation, and increased percentage of annexin V-positive apoptotic cells. Such combination treatments also led to elevation of reactive oxygen species (ROS). The antioxidants N-acetyl cysteine (NAC), butylated hydroxytoluene, and α-tocopherol prevented cells from ATO/CMEMM-induced apoptosis. The ATO/CMEMM-induced activation of caspase-3 and caspase-9 can be blocked by NAC. In summary, these results suggest that ATO/CMEMM combination treatment exerts synergistic apoptosis-inducing effects in human leukemic cells through a ROS-dependent mechanism and may provide a promising antileukemic approach in the future.

Arsenic trioxide and radiation enhance apoptotic effects in HL-60 cells through increased ROS generation and regulation of JNK and p38 MAPK signaling pathways

The induction of apoptotic cell death is a significant mechanism of tumor cells under the influence of radio-/chemotherapy, and resistance to these treatments has been linked to some cancer cell lines with a low propensity for apoptosis. The present study aimed to investigate the enhanced effects and mechanisms in apoptosis and the cycle distribution of HL-60 cells, a human leukemia cell line lacking a functional p53 protein, after combination treatment with arsenic trioxide (ATO) and irradiation (IR). Our results indicated that combined treatment led to increased cytotoxicity and apoptotic cell death in HL-60 cells, which was correlated with the activation of cdc-2 and increased expression of cyclin B, the induction of intracellular reactive oxygen species (ROS) generation, the loss of mitochondria membrane potential, and the activation of caspase-3. The combined treatment of HL-60 cells pre-treated with Z-VAD or NAC resulted in a significant reduction in apoptotic cells. In addition, activation of JNK and p38 MAPK may be involved in combined treatment-mediated apoptosis. The data suggest that a combination of IR and ATO could be a potential therapeutic strategy against p53-deficient leukemia cells.

Dequalinium induces human leukemia cell death by affecting the redox balance

Dequalinium, an amphiphilic quinolinium derivative, selectively accumulates in mitochondria and displays anticancer activity in cells from different malignancies. Previous studies indicate a differential DQA-induced cytotoxicity in NB4 and K562 human leukemia cells as a consequence of an early disturbance in mitochondrial function. Results in this paper show that DQA induces a concentration-dependent oxidative stress by decreasing GSH level and increasing ROS in a cell type specific way. Inhibitors of the JNK and p38 stress regulated kinases potentiate DQA-induced NB4 cell death suggesting a protective function for these enzymes. K562 cells with relatively high GSH levels remained resistant to DQA action.