Arsenic trioxide, a therapeutic agent for APL

Herbal therapy use by cancer patients: a literature review on case reports

Complementary and alternative medicine use is common amongst cancer patients. In many surveys, herbal medicines are amongst the most commonly used group of treatments. Herbal remedies are believed by the general public to be safe, cause less side-effects and less likely to cause dependency. The authors performed a literature review to assess which herbal approaches have had associated cancer case reports and determine which of these have been studied in prospective research. Eighteen case reports of patients having apparent antitumour effects from herbal therapy and 21 case reports of toxic effects of herbs used by cancer patients were identified. Clinicaltrials.gov and MEDLINE (via PubMed) were searched for each of the herbal products identified in these reports. Clinical trials in cancer populations were identified for green tea extracts or compounds (n=34), phytoestrogens (n=27), mistletoe (n=8), Ganoderma lucidum (n=1), noni (n=1) and Silymarin (n=1). Daikenchuto, PC-SPES, Nyoshinsan/TJ and Saw palmetto have also been studied prospectively. In conclusion, some of the herbs with promising case report findings have undergone prospective clinical investigations but many others have either not yet been explored or the results have not been reported in English. Unconventional therapies, such as herbs and minerals, used in ancient medical traditions have led to the identification of active anticancer agents. Mechanisms to support prospective research with such approaches are discussed.

Arsenic trioxide induces a beclin-1-independent autophagic pathway via modulation of SnoN/SkiL expression in ovarian carcinoma cells

Arsenic trioxide (As(2)O(3)), used to treat promyelocytic leukemia, triggers cell death through unknown mechanisms. To further our understanding of As(2)O(3)-induced death, we analyzed its effects on transforming growth factor-β (TGFβ) signaling mediators in ovarian cells. Dysregulated TGFβ signaling is a characteristic of ovarian cancers. As(2)O(3) reduced the protein expression of EVI1, TAK1, SMAD2/3, and TGFβRII while increasing SnoN/SkiL. EVI1 protein was modulated by treatment with the proteasome inhibitors, MG132 and PS-341/Velcade, suggesting that degradation occurs through the ubiquitin-proteasome pathway. The sensitivity of ovarian cells to As(2)O(3)-induced apoptosis correlated with expression of multidrug resistance protein 1. Interestingly, expression of SnoN was similar to LC3-II (autophagy marker), which increased with induction of cytoplasmic vacuolation preceding apoptosis. These vesicles were identified as autophagosomes based on transmission electron microscopy and immunofluorescence staining with EGFP-LC3. The addition of N-acetyl-L-cysteine (ROS scavenger) to As(2)O(3)-treated cells reversed changes in SnoN protein and the autophagic/apoptotic response. In contrast to beclin-1 knockdown, siRNA targeting ATG5, ATG7, and hVps34 markedly reduced autophagy in As(2)O(3)-treated ovarian carcinoma cells. Further, treatment with SnoN siRNA markedly decreased LC3-II levels and increased PARP degradation (an apoptosis marker). Collectively, these findings suggest that As(2)O(3) induces a beclin-1-independent autophagic pathway in ovarian carcinoma cells and implicates SnoN in promoting As(2)O(3)-mediated autophagic cell survival.

Tumor growth inhibition of metastatic nasopharyngeal carcinoma cell lines by low dose of arsenic trioxide via alteration of cell cycle progression and induction of apoptosis

BACKGROUND

Although arsenic trioxide (ATO) has displayed anticancer activity against primary nasopharyngeal carcinoma (NPC), its efficacy in metastatic NPC deserved further investigation because the biological/therapeutic difference in cancer cells probably exists between primary and distant sites.

METHODS

Two human metastatic NPC cell lines (NPC-BM1 and NPC-BM2) were investigated. We measured cellular proliferation, cell cycle, and apoptotic extent of BM1 and BM2 cells treated with ATO in vitro. Furthermore, we evaluated the tumor growth after ATO treatment in vivo.

RESULTS

Low-dose ATO treatment is sufficient to induce an antiproliferative effect, alter the cell cycle, and increase apoptosis in BM1 and BM2 cells. BM1 tumor growth in a xenograft model with low-dose and short-schedule (1 mg/kg/day, intraperitoneal injection for 5 consecutive days) of ATO treatment significantly slowed in vivo.

CONCLUSION

ATO at low dose seems to be an encouraging schedule for palliative treatment of metastatic NPC.

Arsenic trioxide reduces 2,4,6-trinitrobenzene sulfonic acid-induced murine colitis via nuclear factor-κB down-regulation and caspase-3 activation

Arsenic trioxide, As 2O3, already used in human anti-cancer therapy, is also an efficient agent against the autoimmune and inflammatory diseases developed in MRL/lpr mice. Inflammatory bowel diseases (IBDs), notably Crohn’s disease, which remain without efficient treatment, display autoimmune and inflammatory components. We, therefore, hypothesized that As2O 3 may be active on IBDs. Using the 2,4,6-trinitrobenzene sulfonic acid-induced murine model of colitis, we demonstrate that As2O3 used either in a preventive or a curative mode markedly reduced the induced colitis as assessed by macroscopic and microscopic scores, leading to prolonged mice survival. In addition, As2O3 was able to inhibit NF-κB expression and DNA-binding in colon extracts leading to decreased cytokine gene expression (i.e. tumor necrosis factor-α, interleukin(IL)-1β, IL-12, IL-17, IL-18, and IL-23). Interestingly, As2O3 also reduced keratinocyte-derived chemokine (KC), inducible nitric oxide synthase (iNOS) mRNA levels, and myeloperoxidase (MPO) protein expression suggesting an impairment of neutrophils. This was associated with a marked increase of procaspase-3 and induced caspase-3 activation. This caspase-3 co-localized with MPO in the remaining neutrophils suggesting that As2O 3 might have eliminated inflamed cells probably by inducing their apoptosis. These results assessed the potent anti-inflammatory effect of As2O 3, that targets both NF-κB and caspase-3 pathways, and suggests a therapeutic potential for Crohn’s disease and other severe IBDs.

GADD45alpha mediates arsenite-induced cell apoptotic effect in human hepatoma cells via JNKs/AP-1-dependent pathway

Arsenite (As(III)), an effective chemotherapeutic agent for the acute promyelocytic leukemia (APL) and multiple myeloma (MM), might be also a promise for the therapy of other cancers, including the solid tumors. However, the molecular bases of arsenite-induced cytotoxicity in the tumor cells have not been fully defined. In this study, we have disclosed that arsenite effectively induces the apoptotic response in the HepG2 human hepatoma cells by triggering GADD45alpha induction and the subsequent activation of JNKs/AP-1 cell death pathway. However, signaling events relating to GADD45alpha/JNKs/AP-1 pathway activation have not been observed in HL7702 human diploid hepatic cells under the same arsenite exposure condition. Our results thus have illustrated the selective pro-apoptotic role of arsenite in the hepatoma cells by activating GADD45alpha-dependent cell death pathway whereas with little effect on the normal hepatic cells. The approaches to up-regulate GADD45alpha levels might be helpful in improving the chemotherapeutic action of arsenite on certain solid tumors including hepatoma.

Quantitative proteomic analysis reveals the perturbation of multiple cellular pathways in HL-60 cells induced by arsenite treatment

Arsenic is ubiquitously present in the environment; it is a known human carcinogen and paradoxically it is also a successful drug for the clinical remission of acute promyelocytic leukemia (APL). The cellular responses induced by arsenite treatment have been investigated for years; however, the precise mechanisms underlying its cytotoxicity and therapeutic activity remain unclear. Here we report the use of mass spectrometry together with stable isotope labeling by amino acids in cell culture (SILAC) for the comparative study of protein expression in HL-60 cells that were untreated or treated with a clinically relevant concentration of arsenite. Our results revealed that, among the 1067 proteins quantified in both forward and reverse SILAC measurements, 56 had significantly altered levels of expression induced by arsenite treatment. These included the up-regulation of core histones, neutrophil elastase, alpha-mannosidase as well as the down-regulation of fatty acid synthase and protein phosphatase 1 alpha. We further demonstrated that the arsenite-induced growth inhibition of HL-60 cells could be rescued by treatment with palmitate, the final product of fatty acid synthase, supporting that arsenite exerts its cytotoxic effect, in part, via suppressing the expression of fatty acid synthase and inhibiting the endogenous production of fatty acid. The results from the present study offered important new knowledge for gaining insights into the molecular mechanisms of action of arsenite.

Gefitinib enhances arsenic trioxide (AS2O3)-induced differentiation of acute promyelocytic leukemia cell line

Gefitinib (Iressa, ZD1839), a selective epidermal growth factor receptor tyrosine kinase inhibitor, inhibits growth, invasion and colony formation of various cancer cells. However, little is known about the effect of combination of gefitinib and arsenic trioxide (ATO) on differentiation of acute promyelocytic leukemia (APL). Therefore, we investigated whether gefitinib had any role in the ATO-induced differentiation of NB4 cells (APL cell line). Gefitinib induced the expression of differentiation markers including CD11b and CD14 in ATO-treated NB4 cells and facilitated ATO-induced morphologic changes and ROS generation. The results were evident that the combination of gefitinib and ATO could induce more effectively the functional differentiation of leukemic cells to macrophage-like cells. Moreover, the ERK pathway was necessary for the enhancement of gefitinib in ATO-induced differentiation, measured by CD11b and CD14 expression on NB4 cells. Therefore, our data indicated that gefitinib can play a potential role as an adjunctive differentiation agent in APL.

Nuclear protein 1 induced by ATF4 in response to various stressors acts as a positive regulator on the transcriptional activation of ATF4

Nuclear protein 1 (NUPR1) was originally identified as p8, a member of the family of HMG-I/Y transcription factors induced in response to various cellular stressors. However, the signaling pathway underlying NUPR1 induction by cellular stresses remains to be established. In this study, we found that the expression of NUPR1 by various stresses induced by activating transcription factor 4 (ATF4). Loss of ATF4 using siRNA significantly diminished NUPR1 expression. Overexpression of ATF4 caused NUPR1 levels to rise. NUPR1 expression was associated with enhanced transcriptional activation of genes of ATF4 downstream, suggesting that the protein promoted the transcription of stress-regulated genes via positive feedback on the ATF4 pathway.

Arsenic trioxide suppresses paclitaxel-induced mitotic arrest

OBJECTIVES

To understand if there exists a functional interaction between arsenic trioxide and paclitaxel in vitro.

MATERIALS AND METHODS

HeLa and HCT116 (rho53(+/+) and rho53(-/-)) cells were treated with As2O3 and/or paclitaxel for various times. Treated cells were collected for analyses using a combination of flow cytometry, fluorescence microscopy and Western blotting.

RESULTS

Because As(2)O(3) is capable of inhibiting tubulin polymerization and inducing mitotic arrest, we examined whether there existed any functional interaction between As(2)O(3) and paclitaxel, a well-known microtubule poison. Flow cytometry and fluorescence microscopy revealed that although As(2)O(3) alone caused a moderate level of mitotic arrest, it greatly attenuated paclitaxel-induced mitotic arrest in cells with p53 deficiency. Western blot analysis showed that As(2)O(3) significantly blocked phosphorylation of BubR1, Cdc20, and Cdc27 in cells treated with paclitaxel, suggesting that arsenic compromised the activation of the spindle checkpoint. Our further studies revealed that the attenuation of paclitaxel-induced mitotic arrest by As(2)O(3) resulted primarily from sluggish cell cycle progression at S phase but not enhanced mitotic exit.

CONCLUSION

The observations that As(2)O(3) has a negative impact on the cell cycle checkpoint activation by taxol should have significant clinical implications because the efficacy of taxol in the clinics is associated with its ability to induce mitotic arrest and subsequent mitotic catastrophe.

Differentiation therapy of leukemia: 3 decades of development

A characteristic feature of leukemia cells is a blockade of differentiation at a distinct stage in cellular maturation. In the 1970s and 1980s, studies demonstrating the capabilities of certain chemicals to induce differentiation of hematopoietic cell lines fostered the concept of treating leukemia by forcing malignant cells to undergo terminal differentiation instead of killing them through cytotoxicity. The first promising reports on this notion prompted a review article on this subject by us 25 years ago. In this review, we revisit this interesting field of study and report the progress achieved in the course of nearly 3 decades. The best proof of principle for differentiation therapy has been the treatment of acute promyelocytic leukemia with all-trans retinoic acid. Attempts to emulate this success with other nuclear hormone ligands such as vitamin D compounds and PPARgamma agonists or different classes of substances such as hematopoietic cytokines or compounds affecting the epigenetic landscape have not been successful on a broad scale. However, a multitude of studies demonstrating partial progress and improvements and, finally, the new powerful possibilities of forward and reverse engineering of differentiation pathways by manipulation of transcription factors support the continued enthusiasm for differentiation therapy of leukemia in the future.

Hypoxia-HIF-1alpha-C/EBPalpha/Runx1 signaling in leukemic cell differentiation

Acute myeloid leukemia (AML), a class of prevalent hematopoietic malignancies, is caused by the acquisition of gene mutations that confer deregulated proliferation, impaired differentiation and a survival advantage of hematopoietic progenitors. More recently, we reported that cobalt chloride (CoCl(2))/iron chelator desferrioxamine (DFO)-mimicked hypoxia or moderate hypoxia (2% and 3% O(2)) can directly trigger differentiation of many subtypes of AML cells. Also, intermittent hypoxia significantly prolongs the survival of the transplanted leukemic mice with differentiation induction of leukemic cells. Additionally, these hypoxia-simulating agents selectively stimulate differentiation in acute promyelocytic leukemic cells induced by arsenic trioxide, an effective second-line drug for this unique type of leukemia. Based on this interesting evidence in vitro and in vivo, the ongoing investigations showed the role of hypoxia-inducible factor-1alpha (HIF-1alpha) protein through its non-transcriptional activity in myeloid cell differentiation, as evidenced by chemical interference, the conditional HIF-1alpha induction, the specific short hairpin RNAs (shRNAs) against HIF-1alpha and HIF-1beta, an essential partner for transcription activity of HIF-1. Furthermore, HIF-1alpha and two hematopoietic transcription factors CCAAT/enhancer binding protein alpha (C/EBPalpha) and Runx1/AML1 interact directly with each other. Such interactions increase the transcriptional activities of C/EBPalpha and Runx1/AML1, while C/EBPalpha competes with HIF-1beta for direct binding to HIF-1alpha protein, and significantly inhibits the DNA-binding ability of HIF-1. As a protein is rapidly responsive to all-trans retinoic acid (ATRA), a classical clinical differentiation-inducing drug for AML, HIF-1alpha also plays a role in ATRA-induced differentiation of leukemic cells.

Genome stability roles of SUMO-targeted ubiquitin ligases

Post-translational modification of the cell's proteome by ubiquitin and ubiquitin-like proteins provides dynamic functional regulation. Ubiquitin and SUMO are well-studied post-translational modifiers that typically impart distinct effects on their targets. The recent discovery that modification by SUMO can target proteins for ubiquitination and proteasomal degradation sets a new paradigm in the field, and offers insights into the roles of SUMO and ubiquitin in genome stability.

Realgar-induced differentiation is associated with MAPK pathways in HL-60 cells

The clinical efficacy and safety of realgar (arsenic sulfide, As(4)S(4)) in the treatment of acute promyelocytic leukemia in China have given rise to an upsurge in research on the underlying mechanism. We prepared realgar nanoparticles (RNPs) to examine their effect on the differentiation of HL-60 cells. Treatment with RNPs at 6 microM for 72 h induced cell differentiation that was assessed by morphological change, NBT reductive ability, and elevation of CD11b expression at both mRNA and protein levels. The RNP-induced differentiation was synergized, enhanced and suppressed by the inhibition of p38 MAPK, JNK and ERK pathways, respectively. Our findings demonstrate that MAPK signaling pathways are closely related to the RNP-induced differentiation in HL-60 cells.

Arsenic trioxide stimulates SUMO-2/3 modification leading to RNF4-dependent proteolytic targeting of PML

We have recently reported that poly-SUMO-2/3 conjugates are subject to a ubiquitin-dependent proteolytic control in human cells. Here we show that arsenic trioxide (ATO) increases SUMO-2/3 modification of promyelocytic leukemia (PML) leading to its subsequent ubiquitylation in vivo. The SUMO-binding ubiquitin ligase RNF4 mediates this modification and causes disruption of PML nuclear bodies upon treatment with ATO. Reconstitution of SUMO-dependent ubiquitylation of PML by RNF4 in vitro and in a yeast trans vivo system revealed a preference of RNF4 for chain forming SUMOs. Polysumoylation of PML in response to ATO thus leads to its recognition and ubiquitylation by RNF4.

Heterocyclic organobismuth(III) induces apoptosis of human promyelocytic leukemic cells through activation of caspases and mitochondrial perturbation

We have synthesized novel heterocyclic organobismuth compounds that have potent antibacterial properties. In this study, we examined their anticancer activity and addressed the cellular mechanisms involved. Heterocyclic organobismuth compounds showed anticancer activities in various human cancer cell lines. These compounds have particularly potent anticancer activities against leukemia cell lines. One of them, bi-chlorodibenzo [c,f][1,5] thiabismocine (compound 3), inhibited the growth of the human promyelocytic leukemia cell line HL-60 at a concentration of 0.22 microM. Low concentrations of compound 3 (0.22-0.44 microM) induced apoptosis, whereas at a higher concentration (>1.1 microM) it causes acute necrosis. During the apoptosis, caspase-3, -8, and -9 were activated but caspase-12 was not. A broad caspase inhibitor (z-VAD-fmk), and caspase-3 (z-DEVD-fmk) and caspase-9 (z-LEHD-fmk) inhibitors suppressed the compound 3-induced apoptosis, but a caspase-8 inhibitor (z-IETD-fmk) was less effective, suggesting that the caspase-8 activity only partially participates in the apoptosis. In the apoptotic cells, cytochrome c was released from mitochondria to cytosol and a loss of mitochondrial transmembrane potential (DeltaPsi(m)) was detected. Compound 3-induced apoptosis was associated with enhanced generation of intracellular reactive oxygen species (ROS). Pretreatment of the cells with N-acetyl-L-cysteine or catalase suppressed the apoptosis. On the other hand, buthionine sulfoximine enhanced the compound 3-induced collapse of DeltaPsi(m) and apoptosis. Taken together, these results indicate that compound 3 is a potent inducer of apoptosis, triggering a caspase-3-mediated mechanism via the generation of ROS and release of cytochrome c from mitochondria, suggesting a potential mechanism for the anticancer activity of compound 3.

Arsenic trioxide augments Chk2/p53-mediated apoptosis by inhibiting oncogenic Wip1 phosphatase

The oncogenic Wip1 phosphatase (PPM1D) is induced upon DNA damage in a p53-dependent manner and is required for inactivation or suppression of DNA damage-induced cell cycle checkpoint arrest and of apoptosis by dephosphorylating and inactivating phosphorylated Chk2, Chk1, and ATM kinases. It has been reported that arsenic trioxide (ATO), a potent cancer chemotherapeutic agent, in particular for acute promyelocytic leukemia, activates the Chk2/p53 pathway, leading to apoptosis. ATO is also known to activate the p38 MAPK/p53 pathway. Here we show that phosphatase activities of purified Wip1 toward phosphorylated Chk2 and p38 in vitro are inhibited by ATO in a dose-dependent manner. Furthermore, DNA damage-induced phosphorylation of Chk2 and p38 in cultured cells is suppressed by ectopic expression of Wip1, and this Wip1-mediated suppression can be restored by the presence of ATO. We also show that treatment of acute promyelocytic leukemia cells with ATO resulted in induction of phosphorylation and activation of Chk2 and p38 MAPK, which are required for ATO-induced apoptosis. Importantly, this ATO-induced activation of Chk2/p53 and p38 MAPK/p53 apoptotic pathways can be enhanced by siRNA-mediated suppression of Wip1 expression, further indicating that ATO inhibits Wip1 phosphatase in vivo. These results exemplify that Wip1 is a direct molecular target of ATO.

Dissection of mechanisms of Chinese medicinal formula Realgar-Indigo naturalis as an effective treatment for promyelocytic leukemia

To enhance therapeutic efficacy and reduce adverse effects, practitioners of traditional Chinese medicine (TCM) prescribe a combination of plant species/minerals, called formulae, based on clinical experience. Nearly 100,000 formulae have been recorded, but the working mechanisms of most remain unknown. In trying to address the possible beneficial effects of formulae with current biomedical approaches, we use Realgar-Indigo naturalis formula (RIF), which has been proven to be very effective in treating human acute promyelocytic leukemia (APL) as a model. The main components of RIF are realgar, Indigo naturalis, and Salvia miltiorrhiza, with tetraarsenic tetrasulfide (A), indirubin (I), and tanshinone IIA (T) as major active ingredients, respectively. Here, we report that the ATI combination yields synergy in the treatment of a murine APL model in vivo and in the induction of APL cell differentiation in vitro. ATI causes intensified ubiquitination/degradation of promyelocytic leukemia (PML)-retinoic acid receptor alpha (RARalpha) oncoprotein, stronger reprogramming of myeloid differentiation regulators, and enhanced G(1)/G(0) arrest in APL cells through hitting multiple targets compared with the effects of mono- or biagents. Furthermore, ATI intensifies the expression of Aquaglyceroporin 9 and facilitates the transportation of A into APL cells, which in turn enhances A-mediated PML-RARalpha degradation and therapeutic efficacy. Our data also indicate A as the principal component of the formula, whereas T and I serve as adjuvant ingredients. We therefore suggest that dissecting the mode of action of clinically effective formulae at the molecular, cellular, and organism levels may be a good strategy in exploring the value of traditional medicine.

Berberine enhances inhibition of glioma tumor cell migration and invasiveness mediated by arsenic trioxide

Background

Arsenic trioxide (As₂O₃) exhibits promising anticarcinogenic activity in acute promyelocytic leukemic patients and induces apoptosis in various tumor cells in vitro. Here, we investigated the effect of the natural alkaloid berberine on As₂O₃-mediated inhibition of cancer cell migration using rat and human glioma cell lines.

Methods

The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was used to determine the viability of rat C6 and human U-87 glioma cells after treatment with As₂O₃ or berberine, and after co-treatment with As₂O₃ and berberine. The wound scratch and Boyden chamber assays were applied to determine the effect of As₂O₃ and berberine on the migration capacity and invasiveness of glioma cancer cells. Zymography and Western blot analyses provided information on the effect of As₂O₃ and berberine on the intracellular translocation and activation of protein kinase C (PKC), and some PKC-related downstream factors. Most assays were performed three times, independently, and data were analyzed using ANOVA.

Results

The cell viability studies demonstrated that berberine enhances As₂O₃-mediated inhibition of glioma cell growth after 24 h incubation. Untreated control cells formed a confluent layer, the formation of which was inhibited upon incubation with 5 μM As₂O₃. The latter effect was even more pronounced in the presence of 10 μM berberine. The As₂O₃-mediated reduction in motility and invasion of glioma cells was enhanced upon co-treatment with berberine. Furthermore, it has been reported that PKC isoforms influence the morphology of the actin cytoskeleton, as well as the activation of metalloproteases MT1-MMP and MMP-2, reported to be involved in cancer cell migration. Treatment of glioma cells with As₂O₃ and berberine significantly decreased the activation of PKC α and ε and led to actin cytoskeleton rearrangements. The levels of two downstream transcription factors, myc and jun, and MT1-MMP and MMP-2 were also significantly reduced.

Conclusion

Upon co-treatment of glioma cells with As₂O₃ and berberine, cancer cell metastasis can be significantly inhibited, most likely by blocking the PKC-mediated signaling pathway involved in cancer cell migration. This study is potentially interesting for the development of novel chemotherapeutic approaches in the treatment of malignant gliomas and cancer development in general.

Genetic and epigenetic mechanisms in metal carcinogenesis and cocarcinogenesis: nickel, arsenic, and chromium

Chronic exposure to nickel(II), chromium(VI), or inorganic arsenic (iAs) has long been known to increase cancer incidence among affected individuals. Recent epidemiological studies have found that carcinogenic risks associated with chromate and iAs exposures were substantially higher than previously thought, which led to major revisions of the federal standards regulating ambient and drinking water levels. Genotoxic effects of Cr(VI) and iAs are strongly influenced by their intracellular metabolism, which creates several reactive intermediates and byproducts. Toxic metals are capable of potent and surprisingly selective activation of stress-signaling pathways, which are known to contribute to the development of human cancers. Depending on the metal, ascorbate (vitamin C) has been found to act either as a strong enhancer or suppressor of toxic responses in human cells. In addition to genetic damage via both oxidative and nonoxidative (DNA adducts) mechanisms, metals can also cause significant changes in DNA methylation and histone modifications, leading to epigenetic silencing or reactivation of gene expression. In vitro genotoxicity experiments and recent animal carcinogenicity studies provided strong support for the idea that metals can act as cocarcinogens in combination with nonmetal carcinogens. Cocarcinogenic and comutagenic effects of metals are likely to stem from their ability to interfere with DNA repair processes. Overall, metal carcinogenesis appears to require the formation of specific metal complexes, chromosomal damage, and activation of signal transduction pathways promoting survival and expansion of genetically/epigenetically altered cells.

The role of Akt on arsenic trioxide suppression of 3T3-L1 preadipocyte differentiation

The present study investigates the molecular details of how arsenic trioxide inhibits preadipocyte differentiation and examines the role of Akt/PKB in regulation of differentiation and apoptosis. Continual exposure of arsenic trioxide, at the clinic achievable dosage that does not induce apoptosis, suppressed 3T3-L1 cell differentiation into fat cells by inhibiting the expression of PPARgamma and C/EBPalpha and disrupting the interaction between PPARgamma and RXRalpha, which determines the programming of the adipogenic genes. Interestingly, if we treated the cells for 12 or 24 h and then withdrew arsenic trioxide, the cells were able to differentiate to the comparable levels of untreated cells as assayed by the activity of GAPDH, the biochemical marker of preadipocyte differentiation. Long term treatment blocked the differentiation and the activity of GAPDH could not recover to the comparable levels of untreated cells. Continual exposure of arsenic trioxide caused accumulation in G2/M phase and the accumulation of p21. We found that arsenic trioxide induced the expression and the phosphorylation of Akt/PKB and it inhibited the interaction between Akt/PKB and PPARgamma . Akt/PKB inhibitor appears to block the arsenic trioxide suppression of differentiation. Our results suggested that Akt/PKB may play a role in suppression of apoptosis and negatively regulate preadipocyte differentiation.

RAR and RXR modulation in cancer and metabolic disease

Retinoic acid receptors (RARs) are ligand-controlled transcription factors that function as heterodimers with retinoid X receptors (RXRs) to regulate cell growth and survival. The success of RAR modulation in the treatment of acute promyelocytic leukaemia (APL) has stimulated considerable interest in the development of RAR and RXR modulators. This has been aided by recent advances in the understanding of the biological role of RARs and RXRs and in the design of selective receptor modulators that might overcome the limitations of current drugs. Here, we discuss the challenges and opportunities for therapeutic strategies based on RXR and RAR modulators, with a focus on cancer and metabolic diseases such as diabetes and obesity.

Treatment for chronic myelogenous leukemia: the long road to imatinib

The scientists of today have become accustomed to the extremely rapid pace of progress in the biomedical sciences spurred on by the discovery of recombinant DNA and the advent of automated DNA sequencing and PCR, with progress usually being measured in months or years at most. What is often forgotten, however, are the many prior advances that were needed to reach our present state of knowledge. Here I illustrate this by discussing the scientific discoveries made over the course of the past century and a half that ultimately led to the recent successful development of drugs, particularly imatinib mesylate, to treat chronic myelogenous leukemia.

Leukemia, an effective model for chemical biology and target therapy

The rapid rise of chemical biology aimed at studying signaling networks for basic cellular activities using specific, active small molecules as probes has greatly accelerated research on pathological mechanisms and target therapy of diseases. This research is especially important for malignant tumors such as leukemia, a heterogeneous group of hematopoietic malignancies that occurs worldwide. With the use of a chemical approach combined with genetic manipulation, great progress has been achieved over the past few decades on the biological, molecular and cytogenetic aspects of leukemia, and in its diagnosis and therapy. In particular, discoveries of the clinical effectiveness of all-trans retinoic acid and arsenic trioxide in the treatment of acute promyelocytic leukemia and the kinase inhibitors Imatinib and Dasatinib in the treatment of chronic myelogenous leukemia not only make target therapy of leukemia a reality, but also push mechanisms of leukemogenesis and leukemic cell activities forward. This review will outline advances in chemical biology that help our understanding of the molecular mechanisms of cell differentiation and apoptosis induction and target therapy of leukemia.

Arsenic trioxide and proteasome inhibitor bortezomib synergistically induce apoptosis in leukemic cells: the role of protein kinase Cδ

Arsenic trioxide (ATO) and proteasome inhibitor bortezomib have been successfully applied to treat acute promyelocytic leukemia (APL) and multiple myeloma (MM), respectively. Their synergistic effects with other anticancer drugs have been widely studied. Here, we investigated the potential synergy of bortezomib and ATO on Bcr-Abl(+) leukemic K562 cells. The results showed that cotreatment of bortezomib at 32 nM, a half concentration for growth arrest, and ATO at 1 microM, a dose with no significant cytotoxic effect, synergistically induced apoptosis in the cell line, followed by enhanced mitochondrial dysfunction, release of cytochrome c and apoptosis-inducing factor, caspase-3 cleavage and degradation of poly-adenosine diphosphate-ribose polymerase together with the decreased Bcr-Abl protein. These two drugs synergistically induced proteolytic activation of protein kinase Cdelta (PKCdelta) with enhanced activation of two mitogen-activated protein kinases phospho-c-Jun NH(2)-terminal kinase and p38. The specific PKCdelta inhibitor rottlerin markedly decreased bortezomib plus ATO-induced apoptosis, suggesting that PKCdelta plays an important role in bortezomib plus ATO-induced apoptosis. Moreover, apoptosis synergy of bortezomib and ATO could also be seen in some kinds of acute leukemic cell lines and primary cells. Totally, our results indicate that combined regimen of bortezomib and ATO might be a potential therapeutic remedy for the treatment of leukemia.

Arsenic trioxide-induced neuroblastoma cell death is accompanied by proteolytic activation of nuclear Bax

Arsenic trioxide (As(2)O(3)) is toxic to multidrug-resistant neuroblastoma cells in vivo and in vitro. In neuroblastoma, As(2)O(3) does not exert its cell death-promoting effects via a classical apoptotic pathway. A death mechanism involving proteolytic cleavage of Bax to a p18 form seems to be of importance, because inhibition of Bax cleavage coincides with diminished cell death. As existing models of cell death implicate Bax in the intrinsic apoptotic pathway, triggering death after Bax translocation to the mitochondria, we investigated the cellular localization of p18 Bax by subcellular fractionation. After As(2)O(3) treatment, p18 Bax was only present in nuclei-enriched, mitochondria-depleted fractions. Cytoplasmic p21 Bax levels decreased, whereas total (p21 and p18) nuclear Bax increased. Overexpressed p21 Bax localized to the cytoplasm and nuclei, whereas overexpressed p18 Bax localized to extra-nuclear structures only. The inability of overexpressed p18 Bax to locate to the nucleus, and the As(2)O(3)-induced reduction of p21 Bax in the cytosol, suggest an As(2)O(3)-induced mechanism where p18 Bax gets cleaved and 'trapped' in the nucleus. This model is strengthened by the observation that calpain, the protease responsible for p18 Bax generation, is present in the nuclei, and that nuclear calpain is induced by increasing As(2)O(3) and Ca(2+) levels.

An approach to elucidate potential mechanism of renal toxicity of arsenic trioxide

OBJECTIVE

To investigate arsenic trioxide's renal toxicity, we analyzed the gene-expression patterns of primary renal and human kidney cells (HEK293 cell line) following exposure to arsenic trioxide. Moreover, we examined a potential renal toxic mechanism(s) of arsenic trioxide by using a toxicity-related gene and investigated potential treatments to reduce the renal toxicity of arsenic trioxide.

MATERIALS AND METHODS

Arsenic trioxide was exposed to primary renal and HEK293 cells, and the gene-expression analysis was conducted using DNA microarray. Then, reactive oxygen species inhibitors or alpha-lipoic acid were added to HEK293 cells exposed arsenic trioxide and cell viability was determined.

RESULTS

Expression of HMOX1 mRNA increased in a time- and dose-dependent manner, and translation of heme oxygenase 1 protein was also induced. Arsenic trioxide-induced cytotoxicity was inhibited by reactive oxygen species inhibitors. Moreover, superoxide anion was detected in arsenic trioxide-treated HEK293 cells. alpha-Lipoic acid ameliorated arsenic trioxide-induced cytotoxicity and reduced superoxide anion production in HEK293 cells, whereas it had no effect in promyelocytic leukemia cells (HL-60 cells and NB4 cells) and myeloma cells (KMS12BM cells and U266 cells).

CONCLUSIONS

Arsenic trioxide-induced renal toxicity is strongly associated with the increased expression of HMOX1, and the cytotoxic mechanisms of arsenic trioxide involves reactive oxygen species production as well as another pathway. These preliminary results suggest that alpha-lipoic acid may be a suitable agent for prevention or treatment of arsenic trioxide-induced renal toxicity.

Targeted degradation of the AML1/MDS1/EVI1 oncoprotein by arsenic trioxide

Arsenic trioxide (ATO) has been found to be an effective treatment for acute promyelocytic leukemia patients and is being tested for treating other hematologic malignancies. We have previously shown that AML1/MDS1/EVI1 (AME), a fusion gene generated by a t(3;21)(q26;q22) translocation found in patients with chronic myelogenous leukemia during blast phase, myelodysplastic syndrome, or acute myelogenous leukemia (AML), impairs hematopoiesis and eventually induces an AML in mice. Both fusion partners of AME, AML1 and MDS1/EVI1, encode transcription factors and are also targets of a variety of genetic abnormalities in human hematologic malignancies. In addition, aberrant expression of ectopic viral integration site 1 (EVI1) has also been found in solid tumors, such as ovarian and colon cancers. In this study, we examined whether ATO could target AME and related oncoproteins. We found that ATO used at therapeutic levels degrades AME. The ATO treatment induces differentiation and apoptosis in AME leukemic cells in vitro as well as reduces tumor load and increases the survival of mice transplanted with these cells. We further found that ATO targets AME via both myelodysplastic syndrome 1 (MDS1) and EVI1 moieties and degrades EVI1 via the ubiquitin-proteasome pathway and MDS1 in a proteasome-independent manner. Our results suggest that ATO could be used as a part of targeted therapy for AME-, AML1/MDS1-, MDS1/EVI1-, and EVI1-positive human cancers.

Lysosomes and Trivalent Arsenic Treatment in Acute Promyelocytic Leukemia

BACKGROUND

Cells from patients with t(15;17) acute promyelocytic leukemia (APL) express the fusion protein between the promyelocytic leukemia protein and retinoic acid receptor alpha (PML/RAR alpha). Patients with APL respond to differentiation therapy with all-trans-retinoic acid, which induces PML/RAR alpha degradation. When resistance to all-trans-retinoic acid develops, an effective treatment is arsenic trioxide (arsenite), which also induces this degradation. We investigated the mechanism of arsenite-induced PML/RAR alpha degradation.

METHODS

NB4-S1 APL cells were treated with clinically relevant concentrations of arsenite. Lysosomes were visualized with a lysosome-specific dye. Lysosomal protein esterase was measured by immunoblot analysis. Lysosomal cathepsin L was detected by immunogold labeling and transmission electron microscopy, and its activity was measured in cytosolic cellular fractions. In vitro degradation assays of PML/RAR alpha in cell lysates were performed with and without protease inhibitors and assessed by immunoblot analysis. Only nonparametric two-sided statistical analyses were used. The nonparametric Wilcoxon test was used for group comparison, and the nonlinear regression technique was used for analysis of dose-response relationship as a function of arsenite concentration.

RESULTS

Arsenite treatment destabilized lysosomes in APL cells. Lysosomal proteases, including cathepsin L, were released from lysosomes 5 minutes to 6 hours after arsenite treatment. PML/RAR alpha was degraded by lysate from arsenite-treated APL cells, and the degradation was inhibited by protease inhibitors. At both 6 and 24 hours, substantially fewer arsenite-treated APL cells, than untreated cells, contained cathepsin L clusters, a reflection of cathepsin L delocalization. Cells with cathepsin L clusters decreased as a function of arsenite concentration at rates of -2.03% (95% confidence interval [CI] = -4.01 to -.045; P = .045) and -2.39% (95% CI = -4.54 to -.024; P = .029) in 6- and 24-hour treatment groups, respectively, per 1.0 microM increase in arsenite concentration. Statistically significantly higher cytosolic cathepsin L activity was detected in lysates of arsenite-treated APL cells than in control lysates. For example, the mean increase in cathepsin activity at 6 hours and 1.0 microM arsenite was 26.3% (95% CI = 3.3% to 33%; P < .001), compared with untreated cells.

CONCLUSIONS

In APL cells, arsenite may cause rapid destabilization of lysosomes.

Arsenic trioxide: a promising novel therapeutic agent for lymphoproliferative and autoimmune syndromes in MRL/lpr mice

MRL/lpr mice develop a human lupuslike syndrome and, as in autoimmune lymphoproliferative syndrome (ALPS), massive lymphoproliferation due to inactivation of Fas-mediated apoptosis. Presently, no effective therapy exists for ALPS, and long term, therapies for lupus are hazardous. We show herein that arsenic trioxide (As2O3) is able to achieve quasi-total regression of antibody- and cell-mediated manifestations in MRL/lpr mice. As2O3 activated caspases and eliminated the activated T lymphocytes responsible for lymphoproliferation and skin, lung, and kidney lesions, leading to significantly prolonged survival rates. This treatment also markedly reduced anti-DNA autoantibody, rheumatoid factor, IL-18, IFN-γ, nitric oxide metabolite, TNF-α, Fas ligand, and IL-10 levels and immune-complex deposits in glomeruli. As2O3 restored cellular reduced glutathione levels, thereby limiting the toxic effect of nitric oxide, which is overproduced in MRL/lpr mice. Furthermore, As2O3 protected young animals against developing the syndrome and induced almost total disease disappearance in older affected mice, thereby demonstrating that it is a novel promising therapeutic agent for autoimmune diseases.

Synergistic effect of arsenic trioxide and flt3 inhibition on cells with flt3 internal tandem duplication

Flt3 internal tandem duplication (Flt3-ITD) is a prevalent mutation in acute myeloid leukemia (AML). Flt3-ITD constitutively activates various signaling pathways, including a mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway. Arsenic trioxide (ATO) and MEK inhibition were recently reported to interact synergistically to induce apoptosis in AML cells. In this study, we aimed to clarify whether ATO and Flt3 inhibition would be a more specific and efficient therapy for Flt3-ITD cells. We demonstrate that the combination of ATO and an Flt3 inhibitor, AG1296, profoundly inhibits the growth of Flt3-ITD cells and induces their apoptosis. We further revealed that this combined treatment potently inhibits the ERK activity that might be responsible for cell growth. Moreover, using the Chou-Talalay method, we observed a synergistic growth-inhibitory effect for ATO and AG1296 in Flt3-ITD cells (BaF3-Flt3-ITD, MV4-11, and PL-21 cells), but not in Flt3 wild-type cells (RS4-11 and NB4 cells), for almost all dose ranges tested. Our results provide an experimental basis for a specific and efficient therapy for Flt3-ITD cells that involves combined treatment with Flt3 inhibitors and ATO.

ATR, PML, and CHK2 Play a Role in Arsenic Trioxide-induced Apoptosis

Arsenic trioxide (ATO) is a potent anti-leukemic chemotherapeutic agent for acute promyelocytic leukemia (APL) that results from a t (15, 17) chromosomal translocation that produces PML-RARalpha, a fusion protein between a tumor suppressor PML and the retinoic acid receptor RARalpha. APL patients are initially treated with retinoic acid, but most develop resistance and relapse. In contrast, ATO induces prolonged remissions even in the relapsed cases. However, the molecular mechanisms by which ATO kills the leukemic cells are not fully understood. We find that ATO induces apoptosis, at least in part, by activating proapoptotic kinase Chk2. ATO does this by stimulating ATR (ataxia telangiectasia mutated and Rad3-related) kinase, a Chk2-activating kinase. In conjunction, ATO degrades PML-RARalpha, resulting in the restoration of PML, which is required for autophosphorylation and full activation of Chk2. As a result, the p53-dependent apoptosis pathway is activated. Based on this, we propose that a pathway composed of ATR, PML, Chk2, and p53 plays a role in ATO-mediated apoptosis, a notion that is consistent with the observation that Chk2 is genetically intact and mutations in the p53 gene are extremely rare in APL.

Arsenic trioxide concentration determines the fate of Ewing's sarcoma family tumors and neuroblastoma cells in vitro

Arsenic trioxide (As(2)O(3)) induces both the differentiation and apoptosis of acute promyelocytic leukemia cells in a concentration dependent manner. We assessed the effects of As(2)O(3) in CADO-ES Ewing's sarcoma (ES), JK-GMS peripheral primitive neuroectodermal tumor (PNET), and SH-SY5Y neuroblastoma cells, as they share common histogenetic backgrounds. As(2)O(3) at low concentrations (0.1-1 microM) induced SH-SY5Y differentiation, and whereas PNET cells acquired a slightly differentiated phenotype, change was minimal in ES cells. Extracellular signal-regulated kinase 2 (ERK2) was activated at low As(2)O(3) concentrations, and PD98059, an inhibitor of MEK-1, blocked SH-SY5Y cell differentiation by As(2)O(3). High concentrations (2-10 microM) of As(2)O(3) induced the apoptosis in all three cell lines, and this was accompanied by the activation of c-jun N-terminal kinase. The generation of H(2)O(2) and activation of caspase 3 were identified as critical components of As(2)O(3)-induced apoptosis in all of the above cell lines. Fibroblast growth factor 2 enhanced As(2)O(3)-induced apoptosis in JK-GMS cells. The overall effects of As(2)O(3) strongly suggest that it has therapeutic potential for the treatment of ES/PNET.

Epigenetics and the plasticity of differentiation in normal and cancer stem cells

Embryonic stem cells are characterized by their differentiation to all cell types during embryogenesis. In adult life, different tissues also have somatic stem cells, called adult stem cells, which in specific niches can undergo multipotent differentiation. The use of these adult stem cells has considerable therapeutic potential for the regeneration of damaged tissues. In both embryonic and adult stem cells, differentiation is controlled by epigenetic mechanisms, and the plasticity of differentiation in these cells is associated with transcription accessibility for genes expressed in different normal tissues. Abnormalities in genetic and/or epigenetic controls can lead to development of cancer, which is maintained by self-renewing cancer stem cells. Although the genetic abnormalities produce defects in growth and differentiation in cancer stem cells, these cells have not always lost the ability to undergo differentiation through epigenetic changes that by-pass the genomic abnormalities, thus creating the basis for differentiation therapy. Like normal stem cells, cancer stem cells can show plasticity for differentiation. This plasticity of cancer stem cells is also associated with transcription accessibility for genes that are normally expressed in different tissues, including tissues other than those from which the cancers originated. This broad transcription accessibility can also contribute to the behavior of cancer cells by overexpressing genes that promote cell viability, growth and metastasis.

Arsenic trioxide induces apoptosis in human colorectal adenocarcinoma HT-29 cells through ROS

PURPOSE

Treatment with arsenic trioxide (As(2)O(3)) results in a wide range of cellular effects that includes induction of apoptosis, inhibition of cell growth, promotion or inhibition of cellular differentiation, and inhibition of angiogenesis through a variety of mechanisms. The mechanisms of As(2)O(3)-induced cell death have been mainly studied in hematological cancers, and those mechanisms in solid cancers have yet to be clearly defined. In this study, the mechanisms by which As(2)O(3) induces apoptosis in human colorectal adenocarcinoma HT-29 cells were investigated.

MATERIALS AND METHODS

To examine the levels of apoptosis, HT-29 cells were treated with As(2)O(3) and then we measured the percentage of Annexin V binding cells, the amount of ROS production and the mitochondrial membrane potential. Western blot analysis was performed to identify the activated caspases after As(2)O(3) exposure, and we compared the possible target molecules of apoptosis. As(2)O(3) treatment induced the loss of the mitochondrial membrane potential and an increase of ROS, as well as activation of caspase-3, -7, -9 and -10.

RESULTS

As(2)O(3) induced apoptosis via the production of reactive oxygen species and the loss of the mitochondrial membrane potential. As(2)O(3) induced the activation of caspase-3, -7, -9 and -10. Furthermore, As(2)O(3) treatment downregulates the Mcl-1 and Bcl-2 expressions, and the release of cytochrome c and an apoptosis-inducing factor (AIF). Pretreating the HT-29 cells with N-acetyl-L-cysteine, which is a thiol-containing antioxidant, inhibited the As(2)O(3)-induced apoptosis and caspase activation.

CONCLUSION

Taken together, these results suggest that the generation of reactive oxygen species (ROS) by As(2)O(3) might play an important role in the regulation of As(2)O(3)-induced apoptosis. This cytotoxicity is mediated through a mitochondria-dependent apoptotic signal pathway in HT-29 cells.

Lysophosphatidic acid acyltransferase-beta: a novel target for induction of tumour cell apoptosis

Phosphatidic acid (PA) is a component of cellular membranes that is also a mediator of certain cell signalling functions associated with oncogenesis. These include ras/raf/Erk and Akt/mTor [1-3]. The authors have investigated whether it would be possible to interrupt these known oncogenic pathways through the inhibition of lysophosphatidic acid acyltransferase (LPAAT), an enzyme that catalyses the biosynthesis of PA. The expression and activity of the LPAAT-beta isoform are elevated in human tumours, and the respective gene displays transforming capacity when overexpressed in vitro. Inhibition by either genetic means or by isoform-specific small molecules results in a block to cell signalling pathways and apoptosis. Furthermore, the small-molecule inhibitors of LPAAT-beta are not cytotoxic to a number of normal cell types, including primary bone marrow progenitors, indicating a differential dependence of tumour cells on LPAAT-beta function. These discoveries indicate that LPAAT-beta represents a potential novel cancer therapy target.

Mitochondria: pharmacological manipulation of cell death

Cell death by apoptosis or necrosis is often important in the etiology and treatment of disease. Since mitochondria play important roles in cell death pathways, these organelles are potentially prime targets for therapeutic intervention. Here we discuss the mechanisms through which mitochondria participate in the cell death process and also survey some of the pharmacological approaches that target mitochondria in various ways.

Arsenic trioxide: an anti cancer missile with multiple warheads

The proven efficacy of ATO in the treatment of APL and the emerging importance of ATO in other diseases prompted extensive studies of the mechanisms of action of ATO in APL and in other types of cancers. In this review we will focus on downstream events in ATO-induced intrinsic and extrinsic apoptotic pathways with an emphasis on the role of pro-apoptotic and anti-apoptotic proteins and the role of p53 in ATO-induced apoptosis including its effect on cell cycle, its anti-mitotic effect and the role of apoptosis inducing factors (AIF) in ATO-induced apoptosis, chromatin condensation and nuclear fragmentation in myeloma cells as a model.

Arsenic trioxide (As(2)O(3)) induces apoptosis through activation of Bax in hematopoietic cells

This study explores the roles of Bax and other Bcl-2 family members play in arsenic trioxide (As(2)O(3))-induced apoptosis. We showed that As(2)O(3) treatment triggered Bax conformational change and subsequent translocation from cytosol to mitochondria to form various multimeric homo-oligomers in IM-9 cells. On the other hand, human leukemic Jurkat cells deficient in Bax showed dramatically reduced apoptosis in response to As(2)O(3). Stable overexpression of Bcl-2 in IM-9 cells (IM-9/Bcl-2) inhibited As(2)O(3)-mediated Bax activation and apoptosis, and this inhibition could be partially averted by cell-permeable Bid-Bcl-2 homology (BH)3 peptide. Meanwhile, Bax conformational change and oligomerization induced by As(2)O(3) were not inhibited by the pancaspase inhibitor z-VAD-fmk, although Bid cleavage could be completely abolished. Bax activation by As(2)O(3) seemed to require stress-induced intracellular reactive oxygen species (ROS), since the ROS scavengers (N-acetyl-L-cysteine and lipoic acid) could completely block the conformational change and translocation of Bax from cytosol to mitochondria. These data suggest that As(2)O(3) might exert the cell killing in part by inducing Bax activation through a Bcl-2-suppressible pathway in hematopoietic cells that is caspase independent and intracellular ROS regulated.

Retinoic acid and arsenic trioxide cooperate for apoptosis through phosphorylated RXR alpha

Arsenite trioxide (As2O3) induces apoptosis in several cell lines by disturbing key signal transduction pathways through its oxidative properties. Here, we report that As2O3 also induces the phosphorylation of the retinoid receptor RXRalpha, subsequent to oxidative damages and the activation of the stress-activated protein kinases cascade (JNKs). We also report that RA amplifies both As2O3-induced phosphorylation of RXRalpha and apoptosis. Taking advantage of 'rescue' F9 cell lines expressing RXRalpha mutated at its phosphorylation sites, in an RXRalpha null background, we provide evidence that RXRalpha is a key element involved in that potentiating effect. Finally, we demonstrate that As2O3 also abrogates the transactivation of RA-target genes.

The effect of anti-CD44 monoclonal antibodies on differentiation and proliferation of human acute myeloid leukemia cells

Acute myeloid leukemia (AML) is a clonal malignant disease characterized by an increasing number of immature myeloid cells arrested at various stages of granulocytic and monocytic differentiation. The stage of the blockage defines distinct AML subtypes (AML1 to AML5 are the most frequent ones). There is increasing evidence that the malignant clone is maintained by rare AML stem cells endowed with self-renewal capacity, which through extensive proliferation coupled to partial differentiation, generate leukemic progenitors and blasts, of which the vast majority have limited proliferative capacity. Contrarily to chemotherapy alone, which is still unable to cure most AML patients, the differentiation therapy, which consists in releasing the differentiation blockage of leukemic blasts, has succeeded, when it is combined with chemotherapy, to greatly improve the survival of AML3 patients, using retinoic acid as differentiating agent. However, this molecule is ineffective in other AML subtypes, which are the most frequent. We have shown that specific monoclonal antibodies (mAbs, H90 and A3D8) directed to the CD44 cell surface antigen, that is strongly expressed on human AML blasts, are capable of triggering terminal differentiation of leukemic blasts in AML1 to AML5 subtypes. These results have raised the perspective of developing a CD44-targeted differentiation therapy in most AML cases. Interestingly, these anti-CD44 mAbs can also induce the differentiation of AML cell lines, inhibit their proliferation and, in some cases, induce their apoptotic death. These results suggest that H90 and/or A3D8 mAbs may be capable to inhibit the proliferation of leukemic progenitors, to promote the differentiation of the leukemic stem cells at the expense of their self-renewal, and, perhaps, to induce their apoptotic death, thereby contributing to decrease the size of the leukemic clone. The challenges of an anti-CD44 based differentiation therapy in AML, and its importance in relation to the new other therapies developed in this malignancy, are discussed in this review.

Anthraquinones sensitize tumor cells to arsenic cytotoxicity in vitro and in vivo via reactive oxygen species-mediated dual regulation of apoptosis

Cellular oxidation/reduction state affects the cytotoxicity of a number of chemotherapeutic agents, including arsenic trioxide. Reactive oxygen species (ROS), the major intracellular oxidants, may be a determinant of cellular susceptibility to arsenic. Our previous studies showed that a naphthoquinone and an anthraquinone (emodin) displayed the capability of producing ROS and facilitating arsenic cytotoxicity in both leukemia and solid tumor cell lines. We therefore attempted to test emodin and several other kinds of anthraquinone derivatives on EC/CUHK1, a cell line derived from esophageal carcinoma, and on a nude mouse model, with regard to their effects and mechanisms. Results showed that anthraquinones could produce ROS and sensitize tumor cells to arsenic both in vivo and in vitro. The combination of emodin and arsenic promoted the major apoptotic signaling events, i.e., the collapse of the mitochondrial transmembrane potential, the release of cytochrome c, and the activation of caspases 9 and 3. Meanwhile a combination of emodin and arsenic suppressed the activation of transcription factor NF-kappaB and downregulated the expression of a NF-kappaB-specific antiapoptotic protein, survivin. These two aspects could be antagonized by the antioxidant N-acetyl-L-cysteine. Therefore anthraquinones exert their effects via a ROS-mediated dual regulation, i.e., the enhancement of proapoptosis and the simultaneous inhibition of antiapoptosis. In vivo study showed that emodin made the EC/CUHK1 cell-derived tumors more sensitive to arsenic trioxide with no additional systemic toxicity and side effects. Taken together, these results suggest an innovative and safe chemotherapeutic strategy that uses natural anthraquinone derivatives as ROS generators to increase the susceptibility of tumor cells to cytotoxic therapeutic agents.

Phosphorylation of PML by mitogen-activated protein kinases plays a key role in arsenic trioxide-mediated apoptosis

The promyelocytic leukemia (PML) protein is a potent growth suppressor and proapototic factor, whereas aberrant fusions of PML and retinoic acid receptor (RAR)-alpha are causal agents in human acute promyelocytic leukemia. Arsenic trioxide (As(2)O(3)) treatment induces apoptosis in acute promyelocytic leukemia cells through an incompletely understood mechanism. We report here that As(2)O(3) treatment induces phosphorylation of the PML protein through a mitogen-activated protein (MAP) kinase pathway. Increased PML phosphorylation is associated with increased sumoylation of PML and increased PML-mediated apoptosis. Conversely, MAP kinase cascade inhibitors, or the introduction of phosphorylation or sumoylation-defective mutations of PML, impair As(2)O(3)-mediated apoptosis by PML. We conclude that phosphorylation by MAP kinase cascades potentiates the antiproliferative functions of PML and helps mediate the proapoptotic effects of As(2)O(3).

Essential role of the voltage-dependent anion channel (VDAC) in mitochondrial permeability transition pore opening and cytochrome c release induced by arsenic trioxide

The precise molecular mechanism underlying arsenic trioxide (As(2)O(3))-induced apoptosis is a subject of extensive study. Here, we show that clinically relevant doses of As(2)O(3) can induce typical apoptosis in IM-9, a multiple myeloma cell line, in a Bcl-2 inhibitable manner. We confirmed that As(2)O(3) directly induced cytochrome c (cyto c) release from isolated mouse liver mitochondria via the mitochondrial permeability transition pore, and we further identified the voltage-dependent anion channel (VDAC) as a biological target of As(2)O(3) responsible for eliciting cyto c release in apoptosis. First, pretreatment of the isolated mitochondria with an anti-VDAC antibody specifically prevented As(2)O(3)-induced cyto c release. Second, in proteoliposome experiments, VDAC by itself was sufficient to mediate As(2)O(3)-induced cyto c release, which could be specifically inhibited by Bcl-X(L). Third, As(2)O(3) induced mitochondria membrane potential (DeltaPsim) reduction and cyto c release only in the VDAC-expressing, but not in the VDAC-deficient yeast strain. Finally, we found that As(2)O(3) induced the increased expression and homodimerization of VDAC in IM-9 cells, but not in Bcl-2 overexpressing cells, suggesting that VDAC homodimerization could potentially determine its gating capacity to cyto c, and Bcl-2 blockage of VDAC homodimerization represents a novel mechanism for its inhibition of apoptosis.

Arsenic trioxide-induced mitotic arrest and apoptosis in acute promyelocytic leukemia cells

Arsenic trioxide (As(2)O(3)), an effective drug for the treatment of acute promyelocytic leukemia (APL), can induce apoptosis and partial differentiation in APL cells in vitro and in vivo. However, As(2)O(3) also induces apoptosis in cancer cells other than APL with complex mechanisms, which seem to be cell type dependent. In this study, we report that APL cells (NB4 cell line) are arrested at early mitotic phase before the collapse of mitochondrial transmembrane potential (Deltavarphi(m)) and apoptosis after treatment with pharmacological concentrations (1.0-2.0 micro M) of As(2)O(3). We have also made the following new discoveries: (1) 0.5 micro M As(2)O(3) that fails to induce apoptosis has no effects on cell cycle distribution. (2) With inhibition of As(2)O(3)-induced Deltavarphi(m) collapse and apoptosis, dithiothreitol also effectively inhibits As(2)O(3)-induced mitotic arrest, suggesting that both As(2)O(3)-induced apoptosis and mitotic arrest involve proteins with thiol groups. (3) 1.5 mM caffeine that relieves cells from G(2)/M arrest also inhibits As(2)O(3)-induced Deltavarphi(m) collapse and apoptosis, (4) 1.0 micro M As(2)O(3) increases the expression of both cyclin B(1) and hCDC20 whereas it inhibits Tyr15 phosphorylation of p34(cdc2). In conclusion, our results strongly support that there is a tight link between As(2)O(3)-induced apoptosis and mitotic arrest, the latter being one of common mechanisms for As(2)O(3)-induced apoptosis in cancer cells.