Effect of arsenic trioxide on viability, proliferation, and apoptosis in human megakaryocytic leukemia cell lines

Influence of Iron on Cytotoxicity and Gene Expression Profiles Induced by Arsenic in HepG2 Cells

The toxicity of arsenic (As) could be influenced by many environmental factors and elements. Iron (Fe) is one of the elements that could be involved in As-induced toxicity. In this study, the interactive effects of Fe and As in HepG2 cells were analyzed based on cytotoxicity and transcriptomic analyses. The results showed that Fe could decrease cell viability and increase mitochondrial depolarization induced by As exposure. Oxidative stress and damage have been proven to be one of the main mechanisms of As toxicity. Our results showed that Fe increased the generation of reactive oxygen species (ROS) and lipid peroxidation product malondialdehyde (MDA) induced by As exposure. Microarray analysis further verified that Fe increased the alteration of gene expression and biological processes related to oxidative stress, cell proliferation, and the apoptotic signaling pathway caused by As exposure. Both results of cytotoxicity and transcriptomic analyses suggest that an increase of Fe in the human body could increase the As-induced toxicity, which should be considered during the health risk assessment of As.

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.

Arsenic induced complete remission in a refractory T-ALL patient with a distinct T-cell clonal evolution without molecular complete remission: A case report

Currently, arsenic trioxide therapy is widely used for the treatment of acute promyelocytic leukemia (APL), relapsed and refractory adult T-cell leukemia/lymphoma and myelodysplastic syndrome. Regarding the broad antitumor activity of arsenic, certain studies have been undertaken to test its efficacy in treating acute T-cell lymphoblastic leukemia (T-ALL) cell lines and patients; however, to the best of our knowledge, no reports document that arsenic is able to induce the remission of T-ALL patients. The present study reports the case of young male patient diagnosed with T-ALL, with no significant response to common chemotherapy regimens, who finally achieved complete remission without minimal residual disease (as detected by flow cytometry) due to arsenic treatment. This result is encouraging, and the present study has shown that malignant TCRαβ⁺ cell clones can be detected at the molecular level using reverse transcription-polymerase chain reaction (PCR) combined with the GeneScan technique. The result is mainly based on the T-cell receptor (TCR) Vβ1 clone (a 190-base pair PCR product that with the same complementarity determining region 3 length can be detected for all samples collected during various statuses) and on undetectable TCR Vγ subfamily members, at the time of disease diagnosis. It is important to analyze the dynamically changing TCR pool in leukemia patients during therapy. Although the molecular mechanism through which arsenic contributes to malignant clone elimination remains unclear in the case presented, the use of arsenic is expected to be effective for clinically treating refractory and relapsed T-ALL patients.

Enhancement of arsenic trioxide-mediated changes in human induced pluripotent stem cells (IPS)

Induced pluripotent stem cells (IPS) are an artificially derived type of pluripotent stem cell, showing many of the same characteristics as natural pluripotent stem cells. IPS are a hopeful therapeutic model; however there is a critical need to determine their response to environmental toxins. Effects of arsenic on cells have been studied extensively; however, its effect on IPS is yet to be elucidated. Arsenic trioxide (ATO) has been shown to inhibit cell proliferation, induce apoptosis and genotoxicity in many cells. Based on ATOs action in other cells, we hypothesize that it will induce alterations in morphology, inhibit cell viability and induce a genotoxic effect on IPS. Cells were treated for 24 hours with ATO (0-9 µg/mL). Cell morphology, viability and DNA damage were documented. Results indicated sufficient changes in morphology of cell colonies mainly in cell ability to maintain grouping and ability to remain adherent. Cell viability decreased in a dose dependent manner. There were significant increases in tail length and moment as well as destruction of intact DNA as concentration increased. Exposure to ATO resulted in a reproducible dose dependent sequence of events marked by changes in morphology, decrease of cell viability, and induction of genotoxicity in IPS.

Arsenic trioxide induces oxidative stress, DNA damage, and mitochondrial pathway of apoptosis in human leukemia (HL-60) cells

Background

Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia (AML), which accounts for approximately 10% of all acute myloid leukemia cases. It is a blood cancer that is formed by chromosomal mutation. Each year in the United States, APL affects about 1,500 patients of all age groups and causes approximately 1.2% of cancer deaths. Arsenic trioxide (ATO) has been used successfully for treatment of APL patients, and both induction and consolidated therapy have resulted in complete remission. Recently published studies from our laboratory have demonstrated that ATO pharmacology as an anti-leukemic drug is associated with cytotoxic and genotoxic effects in leukemia cells.

Methods

In the present study, we further investigated the detailed molecular mechanism of ATO-mediated intrinsic pathway of apoptosis; using HL-60 cells as a test model. Oxidative stress was assessed by spectrophotometric measurements of MDA and GSH levels while genotoxicity was determined by single cell gel electrophoresis (Comet assay). Apoptosis pathway was analyzed by Western blot analysis of Bax, Bcl2 and caspase 3 expression, as well as immunocytochemistry and confocal imaging of Bax and Cyt c translocation and mitochondrial membrane potential depolarization.

Results

ATO significantly (p < 0.05) induces oxidative stress, DNA damage, and caspase 3 activityin HL-60 cells in a dose-dependent manner. It also activated the intrinsic pathway of apoptosis by significantly modulating (p < 0.05) the expression and translocation of apoptotic molecules and decreasing the mitochondrial membrane potential in leukemia cells.

Conclusion

Taken together, our research demonstrated that ATO induces mitochondrial pathway of apoptosis in HL-60 cells. This apoptotic signaling is modulated via oxidative stress, DNA damage, and change in mitochondrial membrane potential, translocation and upregulation of apoptotic proteins leading programmed cell death.

Medical geology of arsenic, selenium and thallium in China

Arsenic (As), selenium (Se) and thallium (Tl) are three trace metals (metalloids) of high concern in China because deficiency or excess expose can cause a range of endemic diseases, such as endemic arsenism, selenosis, Keshan disease (KD), Kashin-Beck disease (KBD) and thallotoxicosis. These specific endemic diseases were attributable for overabundance or deficiency (mainly referring to selenium) of these three elements in the local environment as a result of natural geochemical processes and/or anthropologic activities. The geochemistry and human health impacts of these three trace elements have been intensively studied since the 1970s in China, in terms of geochemical sources, distribution, transportation, health impact pathways, and prevention/remediation measures. Endemic arsenism in China are induced from the exposures of high As in either drinking water or domestic combustion of As-rich coals. Both endemic selenium deficiency and selenosis occurred in China. The KD and KBD were related to the deficiency of Se in the low-Se geological belt with Se contents in soil less than 0.125mg/kg stretching from northeast to southwest of China. Endemic selenosis occurred in areas with high Se concentrations in soils derived from the Se-enriched black carbonaceous siliceous rocks, carbonaceous shale and slate. Endemic Tl poisoning occurred in southwestern China due to Tl contamination in local drinking water and vegetables surrounding the Tl-rich sulfide mineralized areas. Some measures have been taken to control and remedy the endemic diseases with significant effects in reducing health risk and damage of As, Se and Tl. However, the states of the endemic diseases of As, Se and Tl in China are still serious in some areas, and substantial research efforts regarding the health impacts of these elements are further required. This paper reviews the progress of medical geology of As, Se and Tl in China, and provides with some outlooks for future research directions.

Realgar-induced apoptosis of cervical cancer cell line Siha via cytochrome c release and caspase-3 and caspase-9 activation

OBJECTIVE

To explore the molecular mechanism of realgar-induced apoptosis of cervical cancer cells.

METHODS

The cervical cancer cell line Siha was used to determine the cell viability and apoptosis after treatment with realgar using MTT assay and flow cytometry. The activities of caspase-3, -8, and -9 were detected by fluorescence resonance energy transfer technology and colorimetric assay, while the levels of Bcl-2, cytochrome c, and Bax were detected by Western blot method.

RESULTS

Induction of apoptosis by realgar was detected in Siha cell line in a dose-dependent manner. The apoptosis was accompanied by a significant increase in cytochrome c release and activation of caspase-3 and caspase-9 but not caspase-8. Further, the realgar-induced apoptosis was inhibited by a broad-spectrum caspase inhibitor, a caspase-3 inhibitor, and a caspase-9 inhibitor but not by a caspase-8 inhibitor. Bcl-2 and Bax protein expressions were not changed by realgar.

CONCLUSION

The induction of apoptosis by realgar is mediated through a cytochrome c-dependent pathway, which sequentially activates caspase-9 and caspase-3.

Mushroom lectin protects arsenic induced apoptosis in hepatocytes of rodents

Acute and chronic arsenic exposure result in toxicity both in human and animal beings and cause many hepatic and renal manifestations. The present study stated that mushroom lectin prevents arsenic-induced apoptosis. Apoptosis was measured by morphological alterations, cell proliferation index (CPI), phagocytic activity (nitro blue tetrazolium index; NBT), nitric oxide (NO) production, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, DNA fragmentation and caspase-3 activity. Arsenic exposure at 5 μM in the form of sodium arsenite resulted in significant elevation of deformed cells, NO production, TUNEL stained nuclei of hepatocytes, DNA fragmentation and caspase-3 activity. But the CPI and NBT index were significantly declined in arsenic-treated hepatocytes. The beneficial effect of mushroom lectin at 10 μg/mL, 20 μg/mL and 50 μg/mL) showed increased CPI and phagocytic activity. Mushroom lectin at those concentrations reduced deformed cells, NO production, DNA fragmentation and caspase-3 activity of hepatocytes. But significant better protection was observed in 50 μg/mL mushroom lectin-treated hepatocytes. This finding may be of therapeutic benefit in people suffering from chronic arsenic exposure.

Antitumor effect and mechanisms of arsenic trioxide on subcutaneously implanted human gastric cancer in nude mice

We sought to investigate the efficacy of arsenic trioxide (As(2)O(3)) against a human gastric cell line implanted in nude mice in vivo, as well as the mechanism involved. The solid tumor model was created in nude mice with the gastric cancer cell line SGC-7901. The animals were randomly divided into three groups. As(2)O(3) was injected into animals in two arsenic-treated groups (2.5 mg/kg and 5 mg/kg), and the same volume of saline solution was injected into the control group. The inhibitory effect was observed in every group. Apoptotic cells and apoptotic bodies were observed by transmission electron microscope; the fraction of apoptotic cells was detected by TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) under laser confocal technology. The expression of Fas and FasL was detected by immunohistochemical staining. In nude mice, after treatment with 5 mg/kg and 2.5 mg/kg As(2)O(3), approximately 50% and 30% tumor growth inhibition were observed, respectively (P < 0.05 for both treatment groups). Increase in apoptotic cells and apoptotic bodies appeared in As(2)O(3)-treated tumors compared with the control group. The fluorescence intensity levels of apoptotic cells in tumor were significantly higher in the arsenic-treated groups (P < 0.05 for both treatment groups). The fluorescence intensity level of apoptotic cells in the 5-mg/kg group was higher than that in the 2.5-mg/kg group (P < 0.05). The expression of Fas protein increased in dose- and time-dependent manner after the treatment with As(2)O(3), but that of FasL protein showed no significant difference between control and treated groups. As(2)O(3) did not induce hepatic and renal system injury in the nude mice. As(2)O(3) can inhibit the growth of human gastric cell implanted tumor. We ascribe this to upregulation of Fas, which can induce apoptosis of gastric cells.

Preparation of Arsenic Trioxide-Loaded Microemulsion and Its Enhanced Cytotoxicity on MCF-7 Breast Carcinoma Cell Line

In this study, an injectable microemulsion of arsenic trioxide (As2O3-M) was prepared for intratumoral injection and the suppressive effect of As2O3-loaded microemulsion on human breast cancer cells MCF-7 was compared with those of a solution of the drug. Microemulsion was made up of soybean oil as oil phase, a mixture of Brij 58 and Span 80 as surfactants, absolute ethanol as cosurfactant, and bidistilled water containing As2O3 solution as the aqueous phase. Microemulsion formulation contains 5 x 10(-6) M As2O3. The pH of As2O3-M was adjusted to 7.35 +/- 0.1 and the physicochemical stability of the formulation was observed. The particle size distribution and zeta potential of As2O3-M were measured by Zetasizer 3000 HSA. The mean droplet diameters of As2O3-M were determined as 8.6 +/- 0.4 nm. As2O3-M exhibited 13.1 +/- 0.9 mV zeta potential. The formulation was physically stable for 12 months at room temperature when kept in ampule forms, as well as after autoclaving at 110 degrees C for 30 min. The antitumor effects of As2O3-M were examined on human breast cancer cells MCF-7. It was clearly demonstrated that As2O3-M had a significant cytotoxic effect on breast cancer cell lines, and the cytotoxic effect of As2O3-M was significantly more than that of regular As2O3 solutions. Even approximately 3000 times diluted microemulsion formulation loaded with 5 x 10(-6) M As2O3 showed a cytotoxic effect. As a result, this diluted concentration (approximately 1.6 x 10(-9) M) was found 1000 times more effective than regular As2O3 solutions (5 x 10(-6) M). According to the in vitro cytotoxicity studies, we concluded that when As2O3 was incorporated into the microemulsion (As2O3-M), which is a new drug carrier system, it suppresses tumor cell growth on multiple tumor lines. These results indicate that As2O3-M may exert a low cytotoxic effect on normal cells and may be effective as an antitumor agent that induces apoptosis.

Arsenic trioxide

BACKGROUND

The ancient drug, arsenic, has remarkable efficacy in the treatment of relapsed acute promyelocytic leukemia (APL) and this success has led to exploration of its use in other malignancies.

OBJECTIVE

To provide an overview of the mechanism of action of arsenic and summarize its development in the treatment of APL and other malignant disorders.

METHODS

A 20-year search of MEDLINE, EMBASE and Web of Science was conducted.

RESULTS/CONCLUSIONS

A series of clinical trials with arsenic trioxide has confirmed its benefit in the therapy of APL. Its role in the treatment of other malignancies remains to be determined. Careful attention to the clinical management of patients on arsenic trioxide therapy can significantly lessen the risk of major side effects.

Safety and efficacy of arsenic trioxide for patients with advanced metastatic melanoma

BACKGROUND

Arsenic trioxide (ATO) cytotoxicity and apoptosis induction has been demonstrated with numerous cancer cell lines, including human melanoma.

METHODS

A second-line, phase 2, single-arm study of ATO was conducted in patients with inoperable American Joint Committee on Cancer (AJCC) stage IV melanoma. One cycle consisted of a loading dose of 0.32 mg/kg/day for 4 days in Week 1, followed by 0.25 mg/kg/day twice per week for 6 weeks, followed by 1 week of rest, at which time response assessment was performed.

RESULTS

Twenty-one patients (median age, 63.8 years) were accrued. All had stage IV melanoma including M1a (2 patients), M1b (6 patients), and M1c (13 patients) disease. One patient had metastatic choroidal melanoma and 20 patients had cutaneous melanoma. Twenty patients had received prior therapy. Possible treatment-related grade 3 of 4 toxicities (using the National Cancer Institute Common Toxicity Criteria) included 1 case of idiopathic thrombocytopenic purpura and 1 case of elevated lactate dehydrogenase. Four patients did not complete the first cycle of therapy and were not evaluable for response. Among 17 evaluable patients, 1 patient (6%; 95% confidence interval [95% CI], 0-29%) achieved a partial response lasting 7 months, and 10 patients (59%) had disease stabilization after at least 1 cycle, but all eventually developed disease progression. The median time to disease progression was 17 weeks (95% CI, 11-38 weeks) and the median survival was 13 months (95% CI, 12-26 months).

CONCLUSIONS

ATO as tested in the current trial was found to be well tolerated and had limited activity in patients with metastatic melanoma. The application of this agent in combination with either chemotherapy or agents that target recognized critical signaling and antiapoptotic pathways of melanoma has not yet been performed.

Sub-lethal concentration of arsenic interferes with the proliferation of hepatocytes and induces in vivo apoptosis in Clarias batrachus L

We studied the hepatocellular alterations induced by sub-lethal concentrations (0.50 muM) of arsenic in Indian catfish Clarias batrachus L. Sub-lethal arsenic exposure altered serum aspartate aminotransferase and alkaline phosphatase levels and brought about significant changes in different serum biochemical parameters. Arsenic exposure reduced total hepatocyte protein content and suppressed the proliferation of hepatocytes in a time-dependent manner. Routine histological studies on liver documented arsenic-induced changes characterized by dilated sinusoids, formation of intracellular edema, megalocytosis, vacuolation and appearance of hepatic cells with distorted nuclei. Transmission electron microscopy of hepatocytes further revealed hyperplasia and hypertrophy of mitochondria, development of dilated rough endoplasmic reticulum and changes in peroxisome size with duration of arsenic exposure. Degeneration of mitochondrial cristae and condensation of chromatin was also evident in arsenic-exposed hepatocytes. A significant number of hepatocytes isolated from arsenic-exposed fish stained with annexin V and demonstrated DNA ladder characteristic of apoptosis. Single-cell gel electrophoresis of exposed hepatocytes also revealed the development of comets usually seen in apoptotic cells. Using specific inhibitors it was determined that the arsenic-induced apoptosis of hepatocytes was caspase-mediated, involving the caspase 3 pathway.

Arsenic trioxide induces not only apoptosis but also autophagic cell death in leukemia cell lines via up-regulation of Beclin-1

Although recent data shows that arsenic trioxide (As2O3) is capable of inducing cell death via cell cycle arrest and apoptosis both in acute promyelocytic leukemia (APL) and in non-APL cells, the mechanisms of As2O3-mediated cell death are not fully understood. In this study, we investigated the in vitro effects of As2O3 on cell growth inhibition and cell death in human T-lymphocytic leukemia and myelodysplastic syndrome (MDS) cell lines. As2O3 significantly inhibited the proliferation of Molt-4 and Mutz-1 cells in dose- and time-dependent manner. Autophagic cell death (programmed cell death type II) and apoptosis (programmed cell death type I) were activated together in leukemia cell lines after exposed to As2O3. Numerous large cytoplasmic inclusions and vacuoles were observed in As2O3-treated cells using electron microscope. Furthermore, 3-methyladenine (an autophagy inhibitor) significantly reduced autophagic cell death and sequentially induced apoptosis. Finally, leukemia cells treated with 4 microM As2O3 showed a considerable up-regulation of Beclin-1 (a Bcl-2-interacting protein) expression, which was independent of transcription of mRNA and required protein synthesis. In addition, Molt-4 cells treated with As2O3 exhibited the down-regulation of Bax protein expression, suggesting that Bax may be involved in accumulating of Beclin-1 and triggering autophagic cell death in As2O3-treated leukemia cells. These results may lead to a better understanding of the mechanism of action of As2O3, and provide a suggestion that As2O3 may be of therapeutic value for the treatment of patients with human T-lymphocytic leukemia and myelodysplastic syndrome.

Comparative investigations of sodium arsenite, arsenic trioxide and cadmium sulphate in combination with gamma-radiation on apoptosis, micronuclei induction and DNA damage in a human lymphoblastoid cell line

In the field of radiation protection the combined exposure to radiation and other toxic agents is recognised as an important research area. To elucidate the basic mechanisms of simultaneous exposure, the interaction of the carcinogens and environmental toxicants cadmium and two arsenic compounds, arsenite and arsenic trioxide, in combination with gamma-radiation in human lymphoblastoid cells (TK6) were investigated. Gamma-radiation induced significant genotoxic effects such as micronuclei formation, DNA damage and apoptosis, whereas arsenic and cadmium had no significant effect on these indicators of cellular damage at non-toxic concentrations. However, in combination with gamma-radiation arsenic trioxide induced a more than additive apoptotic rate compared to the sum of the single effects. Here, the level of apoptotic cells was increased, in a dose-dependent way, up to two-fold compared to the irradiated control cells. Arsenite did not induce a significant additive effect at any of the concentrations or radiation doses tested. On the other hand, arsenic trioxide was less effective than arsenite in the induction of DNA protein cross-links. These data indicate that the two arsenic compounds interact through different pathways in the cell. Cadmium sulphate, like arsenite, had no significant effect on apoptosis in combination with gamma-radiation at low concentrations and, at high concentrations, even reduced the radiation-induced apoptosis. An additive effect on micronuclei induction was observed with 1muM cadmium sulphate with an increase of up to 80% compared to the irradiated control cells. Toxic concentrations of cadmium and arsenic trioxide seemed to reduce micronuclei induction. The results presented here indicate that relatively low concentrations of arsenic and cadmium, close to those occuring in nature, may interfere with radiation effects. Differences in action of the two arsenic compounds were identified.

Arsenic trioxide induces apoptosis in cisplatin-sensitive and -resistant ovarian cancer cell lines

Arsenic trioxide (As(2)O(3)), has been used for centuries in traditional Chinese medicine; it has considerable efficacy in the treatment of relapsed acute promyelocytic leukemia, inducing partial differentiation and promoting apoptosis of malignant promyelocytes. Although a number of studies have demonstrated that As(2)O(3) has potent activity against cell growth in a series of leukemia cell lines, little information is available regarding this compound's effect on cell growth in solid tumor cell lines. In this study, we investigated the effects of As(2)O(3)in vitro on ovarian cancer cell lines sensitive (3AO) and resistant (3AO/CDDP) to cisplatin. The 3-(4,5-dimethy-thiazoyl-2-yl)-2,5-diphenyl-tetrazolium bromide assay was used to evaluate cytotoxicity. Flow cytometric analysis was used to determine the apoptosis, cell cycle distribution. We clearly demonstrated that As(2)O(3) induced cell apoptosis and inhibition of cell growth in both the cell lines. Furthermore, we identified that As(2)O(3)-induced apoptosis involved Fas pathway. As(2)O(3) is an active agent against ovarian cancer cells and could be effective in the clinical treatment of ovarian cancer.

In vitro dual effect of arsenic trioxide on hemopoiesis: inhibition of erythropoiesis and stimulation of megakaryocytic maturation

Although the arsenic compounds are now widely utilized in clinics in the treatment of various tumors, their effects on normal hematopoiesis do not seem to have been explored. In the present study, we provide evidence that arsenic trioxide (As(2)O(3)) exerts in vitro a potent inhibitory effect on normal erythropoiesis and a stimulatory action on megakaryocytic differentiation. The effect of As(2)O(3) on erythroid and megakaryocytic differentiation was evaluated on both erythroleukemic cell lines K562 and HEL and on normal hemopoietic progenitor cells (HPCs) induced to selective erythroid or megakaryocytic differentiation. The inhibitory effect of As(2)O(3) on erythropoiesis is related to: (a) the inhibition of Stat5 activation with consequent reduced expression of the target genes Bcl-X(L) and glycophorin-A; (b) the activation of an apoptotic mechanism that leads to the cleavage of the erythroid transcription factors Tal-1 and GATA-1, whose integrity is required for erythroid cell survival and differentiation; (c) the reduced expression of heat shock protein 70, required for GATA-1 integrity. The stimulatory effect of As(2)O(3) on normal megakaryocytopoiesis is seemingly related to upmodulation of GATA-2 expression and to stimulation of MAPK activity. These observations may have implications for the patients undergoing anti-leukemic treatment with this compound.

The influence of lead and arsenite on the inhibition of human breast cancer MCF-7 cell proliferation by American ginseng root (Panax quinquefolius L.)

American ginseng root (Panax quinquefolius) has a number of purported therapeutic effects, including inhibition of cancer cell proliferation. The ability of environmentally relevant heavy metals to alter ginseng effects on cancer cell growth was the subject of this study. A water extract of American ginseng root was applied alone or in combination with physiologically relevant doses of either lead (Pb) or arsenite to MCF-7 breast cancer cells in vitro and effects on cell proliferation were determined. Ginseng alone produced a significant dose-dependent inhibition of MCF-7 cell proliferation starting at 0.5 mg ml(-1). Treatment of MCF-7 cells with 2.5 microM arsenite significantly decreased MCF-7 cell proliferation (p < 0.01). When cells were treated with arsenite (1.25 or 2.5 microM) in combination with ginseng extract (0.5 mg ml(-1)), there was an apparent synergistic inhibition of cell proliferation. Treatment of MCF-7 breast cancer cells with 50 microM Pb significantly decreased cell proliferation relative to control (p < 0.01), and concomitant ginseng and Pb treatment did not lead to a further decrease. These results suggest that contaminant heavy metals, some of which have been detected in ginseng root extracts or commercial ginseng preparations, may alter the biological activity of ginseng.

In vivo and in vitro treatment of HTLV-1 and HTLV-2 infected cells with arsenic trioxide and interferon-alpha

Adult T-cell leukemia/lymphoma (ATLL) is a malignant lymphoproliferation of mature activated T-cells, mostly CD4, which develops after a long period of latency following Human T cell Lymphotropic virus Type 1 infection. It is characterized by the clonal integration of one or more HTLV-1 proviruses in the tumor cells. There are 4 major subtypes of ATLL: a smoldering type, a chronic type, a lymphoma type and a leukemic/acute type. The survival rate of ATLL patients, especially those who develop the acute leukemic or lymphomas forms, is very poor and such a tumor remains one of the most severe lymphoproliferations. Treatment of ATLL patients using conventional chemotherapy has very limited benefit, since HTLV-1 transformed cells are resistant to most apoptosis-inducing agents. Recently, antiretroviral therapy using the combination of zidovudine (AZT) and interferon alpha (IFN-alpha) has been shown to induce a high complete remission rate and to prolong the survival of ATLL patients. Based on the current physiopathology, other drugs such as arsenic trioxide combined to IFN-alpha have also been demonstrated to synergize in vitro for inducing apoptosis in HTLV-1 infected T cells. Such drugs have now been used in vivo for treating ATLL patients. Both in vitro and in vivo data will be discussed.

Arsenic trioxide therapy in acute promyelocytic leukemia and beyond: from bench to bedside

Arsenic trioxide (As2O3) has a long history of use in medicine. However, it was almost forgotten in Western medicine in the recent centuries. Prompted by reports from China about successful treatment of acute promyelocytic leukemia (APL) with As2O3, there was again increasing interest in this drug in the 1990s. This review summarizes the considerable knowledge about the mechanisms of action of As2O3 that was gained during the last 5-10 years. It is focused in particular on the effects of As2O3 in non-APL cells. Since As2O3 seems to induce apoptosis and inhibits growth in a large variety of cellular targets, it might become an alternative or adjunct drug to conventional chemotherapy. As2O3 can even be effective in cells resistant to conventional cytostatic agents. Insight into the cellular mechanisms, in particular the impact of the redox state on sensitivity towards As2O3 opens the possibility to enhance As2O3 effects by appropriate combination therapies.

Arsenite Delays Progression through Each Cell Cycle Phase and Induces Apoptosis following G2/M Arrest in U937 Myeloid Leukemia Cells

Arsenic is a well known toxicant and carcinogen that is also effective as a chemotherapeutic in the treatment of acute promyelocytic leukemia. Although its effects on humans are well documented, arsenic's mechanism of action is not well understood. Its ability to act as a carcinogen and as a chemotherapeutic seems paradoxical. However, cancer cell transformation and cancer cell destruction can both occur through perturbations of the cell cycle machinery, making cell cycle function a likely target of arsenic action. Arsenic has previously been shown to inhibit cancer cell cycle progression, but the targeted cell cycle phase has been debated. This study was designed to identify the cell cycle phase at which U937 cells are most sensitive to arsenite-induced growth inhibition. Centrifugal elutriation was used to divide asynchronous cell cultures into specific cell cycle phase-enriched fractions. These fractions were monitored for cell cycle phase progression in the presence and absence of sodium arsenite. We found an overall reduction in cell cycle progression rather than induction of arrest at one specific checkpoint. G(2)/M is the phase most sensitive to arsenite-induced apoptosis. However, arsenite profoundly affects U937 cell growth by increasing the length of time it takes cells to transit each phase of the cell cycle. Future study of cell cycle inhibition by arsenic should consider that the effect may not be mediated by the major cell cycle checkpoints. Arsenic's ability to inhibit growth in any cell cycle phase may increase its value as a chemotherapeutic used together with other, more phase-selective agents, such as camptothecin.

Arsenic trioxide liposomes: encapsulation efficiency and in vitro stability

The use of arsenic-containing compounds in cancer therapy is currently being re-considered, after the recent approval of arsenic trioxide (Trisenox) for the treatment of relapsed promyelocytic leukemia (PML). In an attempt to prepare a carrier system to minimize the toxicity of this drug, the aim of this study is to prepare and characterize liposomes encapsulating arsenic trioxide (ATO). For this, we prepared different types of liposomes entrapping ATO: large multilamellar (MLV), sonicated (SUV) and dried reconstituted vesicles (DRV). The techniques used were: thin film hydration, sonication and the DRV method, respectively. Two lipid compositions were studied for each liposome type, EggPC/Chol (1:1) and DSPC/Chol (1:1). After liposome preparation, drug encapsulation was evaluated by measuring arsenic in liposomes. For this, energy-dispersive X-ray fluorescence spectroscopy or atomic absorption was used. In addition, the retention of the drug in the liposomes was evaluated after incubating the liposomes in buffer at 37 degrees C. The experimental results reveal that encapsulation of ATO in liposomes ranges between 0.003 and 0.506 mol/ mol of lipid, and is highest in the DRV vesicles and lowest in the small unilamellar vesicles, as anticipated. Considering the in vitro stability of ATO-encapsulating liposomes: 1) For the PC/Chol liposomes (DRV and MLV), after 24 hours of incubation, more than 70% (or 90% in some cases) of the initially encapsulated amount of ATO was released. 2) The liposomes composed of DSPC/Chol could retain substantially higher amounts of ATO, especially the DRV liposomes (54% retained after 24 h). 3) In the case of PC/Chol, temperature of incubation has no effect on the ATO release after 24 hours, but affects the rate of ATO release in the MLV liposomes, while for the DSPC/Chol liposomes there is a slight increase (statistically insignificant) of ATO release at higher temperature.

The potential of arsenic trioxide in the treatment of malignant disease: past, present, and future

Arsenic trioxide (As2O3) is an effective therapy for acute promyelocytic leukemia (APL), and there has been promising activity noted in other hematologic and solid tumors. The mechanism of action of As2O3 such as differentiation and apoptosis has prompted study into combination therapy. Furthermore, the connection of the sensitivity of diseases such as APL and multiple myeloma to oxidative damage has allowed the investigation of pharmacologic modulation of the cellular redox state for potentiation of As2O3. Continued study of As2O3 as a single-agent and in combination therapy will allow identification of the safest and most effective treatment regimens for malignant disease.

Inhibition of cell proliferation and the action mechanisms of arsenic trioxide (As2O3) on human breast cancer cells

Arsenic trioxide (As(2)O(3)) is one of the arsenic compounds found in nature. As(2)O(3) has recently been used to treat patients suffering from retinoic acid receptor (AML). It is of clinical interest to investigate whether As(2)O(3) is also effective in treating solid tumors. Here, we report that As(2)O(3) exhibited inhibitory effects on the proliferation of human breast cancer MCF-7 cells in a dose- and time-dependent manner. The 50% inhibitory concentration (IC(50)) of As(2)O(3) in inhibiting proliferation of MCF-7 cells were 8, 1.8, and 1.2 microM upon 1-, 2-, and 3-day treatment, respectively. In elucidating the underlying action mechanisms, the results of experiments concerning DNA fragmentation and externalization indicated that As(2)O(3) exerted its action on MCF-7 cells via apoptosis, whereas the result of flow cytometry also indicated that As(2)O(3) could induce mitochondrial mediated cell-cycle arrest at G(1) phase. Further studies by Western blot analysis indicated that As(2)O(3) regulated apoptosis and the expression of cell-cycle-related proteins as it upregulated p53 protein level and downregulated bcl-2 protein level. Results in present study indicated that As(2)O(3) might also be a good candidate for treating breast cancer.

Sustained activation of c-jun-terminal kinase (JNK) is closely related to arsenic trioxide-induced apoptosis in an acute myeloid leukemia (M2)-derived cell line, NKM-1

High concentrations (greater than 5 microM) of arsenic trioxide (As(2)O(3)) have been reported to be able to induce apoptosis in several malignant cells. We explored cell lines in which apoptosis was induced with a therapeutic concentration (1-2 microM) of As(2)O(3), and found that 1 microM of As(2)O(3) induced apoptosis in the NKM-1 cell line, which was established from a patient with acute myeloid leukemia (M2). Apoptosis induced by 1 microM of As(2)O(3) in NKM-1 cells was accompanied by an increased cellular content of H(2)O(2), a decreased mitochondrial membrane potential (Deltapsim), and activation of caspase-3. C-Jun-terminal kinase (JNK) was activated only in NKM-1 cells and arsenic-sensitive NB4 cells, but not in arsenic-insensitive HL-60 cells. Activation of JNK in NKM-1 was sustained from 6 to 24 h after As(2)O(3) treatment, and preceded changes in cellular H(2)O(2), Deltapsim, and caspase-3 activation. Moreover, addition of a JNK inhibitor reduced the percentage of apoptotic cells after the As(2)O(3) treatment. Taken together, in the M2 cell line NKM-1, 1 microM of As(2)O(3) induced sustained activation of JNK and apoptosis. This finding may provide a basis to select a subgroup other than acute promyelocytic leukemia, which can benefit from As(2)O(3) treatment.

Opportunities for Trisenox (arsenic trioxide) in the treatment of myelodysplastic syndromes

Arsenic trioxide (ATO) has a long history of efficacy as an antileukemic agent. However, with the advent of modern therapy, it had been relegated to a historical footnote. In the 1990s, investigators in China reported that ATO was safe and had dramatic efficacy in patients with acute promyelocytic leukemia (APL). Preclinical investigations indicate that the biological targets of this novel drug extend to a variety of malignancies other than APL and include induction of apoptosis, nonterminal differentiation, and suppression of proliferation and angiogenesis. The myelodysplastic syndromes (MDSs) present a particular therapeutic challenge. Ineffective hematopoiesis predominates in patients with low-grade prognostic scores. The survival of those patients with high-grade disease is compromised by a high risk of leukemia transformation. Although a number of therapeutic options have been investigated, none has emerged as being broadly efficacious and having an acceptable toxicity profile. No drug has yet received approval by the Food and Drug Administration for this indication. Biologic features of MDS, which include accelerated apoptotic potential, limited maturation capacity, and medullary neovascularity, create a strong scientific rationale for the investigation of ATO in MDS. This report describes the history and scientific basis for ATO treatment of hematologic malignancies, enumerates the potential benefits of ATO in MDS, and discusses the direction of ongoing trials of this novel antineoplastic agent.

Treatment of acute promyelocytic leukemia and other hematologic malignancies with arsenic trioxide: review of clinical and basic studies

Acute promyelocytic leukemia (APL) is now the most potentially curable subtype of acute myeloid leukemia in adults because of the introduction of novel approaches in the management of this disease. All-trans-retinoic acid (ATRA)-based therapy is now the first-choice treatment of patients presenting with de novo APL, and clinical studies have shown that nearly all patients who receive ATRA therapy achieve complete remission. However, approximately 20% to 30% of APL patients eventually have relapses with resistance to further ATRA treatment. Arsenic trioxide (As2O3 [ATO]) has been established as highly effective therapy for patients with APL, even for those with disease refractory to ATRA. Furthermore, results of recent studies have suggested a broad therapeutic potential for ATO in the treatment of hematologic malignancies beyond APL. In this review, we discuss the clinical activity and multiple mechanisms of ATO therapy in the management of APL and other hematologic neoplasms.

The potential effect of short-course high-dose steroid on the maturation and apoptosis of leukemic cells in a child with acute megakaryoblastic leukemia

High-dose methylprednisolone (HDMP) treatment has been shown to induce differentiation of myeloid leukemic cells in children with acute promyelocytic leukemia and other subtypes (FAB AML M1-M2-M4) of acute myeloblastic leukemia. In the present study, a child with acute megakaryoblastic leukemia (AMKL) was given HDMP (30 mg/kg/day) orally in a single dose for the first 4 days of induction therapy. A marked decrease in peripheral blood blast cells and an increase in platelet count associated with a striking change in bone marrow (BM) morphology was observed following a short-course of HDMP treatment alone. BM cells developed distinct morphology characterized by cytoplasmic blebbing and some appeared as platelet producing micromegakaryocytes. Flow cytometric analysis of the BM cells 4 days after HDMP treatment demonstrated a decrease in the percentage of cells co-expressing CD34 and CD117 antigens and a marked increase in CD42a antigen. These changes in BM morphology and immunophenotype may suggest maturation effect of HDMP on megakaryocytic leukemic cells. In addition ultrastructural analysis of BM cells cultured with methylprednisolone (10(-3) and 10(-6) M) for 24 and 48 h showed numerous apoptotic cells. This was coincident with a significant increase in the percentage of annexin positive cells. These results suggest that HDMP treatment may induce differentiation and apoptosis of leukemic cells in a child with AMKL and it could be a promising agent for remission induction of patients with AMKL.

Use of arsenic trioxide (As2O3) in the treatment of patients with acute promyelocytic leukemia: the M. D. Anderson experience

BACKGROUND

Approximately 20-30% of patients with acute promyelocytic leukemia (APL) who are treated with all-trans retinoic acid (ATRA) and an anthracycline develop recurrent disease. It has been reported that arsenic trioxide (As(2)O(3)) is effective in this setting. The authors report the experience of The M. D. Anderson Cancer Center with As(2)O(3) in the treatment of patients with recurrent APL.

METHODS

Twelve patients who developed recurrent APL after treatment with ATRA were included. Patients received intravenous As(2)O(3) 0.15 mg/kg per day until they achieved a complete remission (CR) or up to a maximum of 60 days. Their median age was 44 years (range, 26-72 years), and the median duration of first remission was 52 weeks (range, 23-292 weeks).

RESULTS

All 12 patients achieved a CR. The median time to achieve CR was 52 days (range, 27-75 days). Seven of 10 evaluable patients achieved a molecular remission (i.e., polymerase chain reaction [PCR] analysis was negative for the gene encoding fusion of the nuclear receptor for retinoic acid to the PML gene at the time of CR; 70% of patients; 95% confidence interval, 0.35-0.93), and all other patients had negative PCR results after they received post-remission therapy. All patients received subsequent therapy: Four patients received As(2)O(3) alone, six patients received As(2)O(3) with other chemotherapeutic agents, and two patients received idarubicin plus ATRA without As(2)O(3). Eight patients continued in CR after a median follow-up of 24 months (range, 9-45 months). Side effects were mild, except for two patients who developed Grade 2 and 3 peripheral neuropathy, respectively; one of those patients required discontinuation of therapy.

CONCLUSIONS

As(2)O(3) is effective and well tolerated therapy for patients with recurrent APL. Molecular remission may be achieved at the time of CR in the majority of patients, and remissions are durable.

Caspase activation is accelerated by the inhibition of arsenite-induced, membrane rafts-dependent Akt activation

Renewed interest in arsenic has been shown recently due to its dual nature of being a potent toxin and a drug for treatment of acute promyelocytic leukemia (APL) because of its ability to trigger caspase activation. Here, we found that sodium arsenite (NaAsO(2)) also triggers the signal for activation of Akt and downstream glycogen synthase 3beta (GSK3beta). Such Akt/GSK3beta activation was abrogated completely by wortmannin, an inhibitor of PI-3 kinase, and greatly by pertussis toxin, a G-protein inhibitor. Arsenite-induced Akt phosphorylation also was inhibited by sequestrating membrane cholesterol with beta cyclodextrin. Reducing reagents/reactive oxygen species (ROS) scavengers reduced arsenite-induced Akt phosphorylation and beta cyclodextrin reduced arsenite-mediated ROS production, suggesting that arsenite-induced G-protein/Akt/GSK3beta pathway is membrane raft dependent and redox linked. We also found that a combination of a low concentration (1 microM) of arsenite and wortmannin triggers the signal for caspase activation, whereas neither of these elements alone did so. These results suggested that selective blockade of the arsenite-provoked PI-3 kinase/Akt pathway can promote the arsenite-triggered pathway for caspase activation, and this may open a new study area for wider applications of arsenic as a drug for treating various kinds of leukemia.

Arsonoliposomes: effect of arsonolipid acyl chain length and vesicle composition on their toxicity towards cancer and normal cells in culture

Arsonolipid-containing liposomes were investigated in order to characterize the influence of the lipid acyl-chain length and liposome composition on cytotoxicity. Three types of cancer cells (HL-60, C6 and GH3), and two types of normal cells (HUVEC and RAME) were used. Liposomes containing the lauroyl, myristoyl and stearoyl side chain arsonolipids (with different lipid compositions) were incubated with a given number of cells and cell viability was estimated (MTT assay and trypan blue exclusion). Morphological studies were also performed in some cases. In addition, the interaction between some of the prepared arsonoliposomes and HUVEC cells was assessed. Results reveal that all the studied arsonoliposomes cause a dose dependent inhibition of survival in all three malignant cell lines studied (initiated at 10(-6) M). The corresponding toxicity against normal cells (HUVEC and RAME) is much lower for all arsonoliposomes, except for the lauroyl side chain arsonoliposomes which were demonstrated to be relatively toxic towards normal cells, especially RAME. The microscopic observations that these vesicles possibly cause apoptosis of most cell types studied, as well as the different speed of their cytotoxic activity, imply a different mechanism of action for this arsonoliposome type. Taking the results of this study in conjunction with our previous results on arsonoliposome physical stability and cytotoxicity, it is recommended that palmitoyl-arsonolipid arsonoliposomes be used for further investigations in vivo towards the development of an anticancer product.

Megakaryocytic blast crisis as a first presentation of chronic myeloid leukemia

Acute megakaryocytic leukemia (AmegL) corresponds to 5.0-10.0% of all acute myeloid leukemias (AML). Blast crisis as the first presentation of chronic myeloid leukemia (CML) accounts for 10.0% of all cases.

OBJECTIVE

We report a case of megakaryocytic blast crisis as the first presentation of CML.

CASE REPORT

A 25-yr-old-female with a 2-month history of dry cough and a large, non-tender splenomegaly was found to have a hemoglobin concentration of 10.5 g/dL, a hematocritof 33.0%, a white blood cell count (WBC) of 11.4 x 106 L with 38% small blasts, eosinophilia of 5%, basophilia of 8%, and a platelet count of 580 x 109 L. Bone marrow aspiration revealed 24% of blast cells with cytoplasmatic blebs and hyperplastic megakaryocytic lineage with dysplasia. Cytochemical stains were all negative, immunophenotyping studies showed CD41 and CD61 positivity in blast cells. Bone marrow biopsy showed grade II fibrosis. Karyotype revealed 46, XX, t(9,22) (q34.1;q11.2)[20] and the reverse-transcriptase-PCR (RT-PCR) gave rise a product with a size corresponding to the 210 kDa protein (p210). No matched donor was found. After induction therapy 5.9% of blast cells persisted. The patient received Imatinib Mesylate and is doing well after a 12-month follow-up.

DISCUSSION

AmegL as the first presentation of CML is a rare and often fatal event. Some characteristics point towards the diagnosis of a blast crisis instead of AmegL de novo with t(9,22).

Advances in the management of acute promyelocytic leukemia and other hematologic malignancies with arsenic trioxide

Acute promyelocytic leukemia (APL), once considered the most devastating subtype of acute myeloid leukemia, is now the most treatable of all subtypes as a result of intensive research into its molecular pathogenesis. This research has led to a rational approach to treatment in which the use of the differentiating agent all-trans-retinoic acid (ATRA) has proven to be effective first-line treatment for inducing complete remission. Arsenic trioxide (ATO) is currently used to treat relapsed disease, further enhancing survival rates in a patient population for which limited salvage options exist. This review discusses the molecular mechanisms responsible for development of APL and the evolution of treatment options over the last three decades, including the major advances using ATRA and ATO in the last 12 years. The mechanism of action of ATO is also described in view of this agent's potential for broader therapeutic application in a variety of hematologic malignancies.

Involvement of tumor necrosis factor (TNF-α) in arsenic trioxide induced apoptotic cell death of murine myeloid leukemia cells

Arsenic trioxide (As(2)O(3)) has recently been shown to be effective to inhibit the growth and to induce apoptosis in acute promyelocytic leukemia (APL) but not in acute myeloid leukemia (AML) cells. Recently, we have isolated an As(2)O(3) sensitive subclone JCS-16 from the murine myeloid leukemia WEHI 3B (JCS). At the concentrations of 0.3-3 microM, As(2)O(3) induces a dose-dependent cytotoxicity and growth inhibition on the JCS-16 cells. As(2)O(3) also induces apoptotic cell death, as judged by the presence of apoptotic nuclei, at 6 h after treatment. Morphological differentiation was not observed in As(2)O(3) treated JCS cells. Neutralizing anti-TNF-alpha antibody was found to reduce the As(2)O(3)-mediated apoptotic cell death of JCS-16 cells. Growth inhibitory effect of As(2)O(3) was also reduced after the addition of anti-TNF-alpha. In addition, reverse transcription polymerase chain reaction (RT-PCR) and reverse northern blot analysis demonstrated that the expression of TNF receptor (TNF-R2), IL-4, and IL-4R was down-regulate at 1 h after As(2)O(3) treatment. The expression of TNF-alpha and TNF-R1 was not affected. Our results suggest that the autocrine action of TNF-alpha might play a role in As(2)O(3)-induced apoptotic cell death of JCS-16 leukemia cells.

Arsenic Trioxide Induces Apoptosis in Chronic Myelogenous Leukemia K562 Cells:Possible Involvement of p38 MAP Kinase

Arsenic trioxide (As(2)O(3)) was recently demonstrated to be an effective inducer of apoptosis in patients with relapsed acute promyelocytic leukemia (APL) as well as in patients with APL in whom all-trans-retinoic acid and conventional chemotherapy failed. Chronic myelogenous leukemia cells are highly resistant to chemotherapeutic drugs. To determine if As(2)O(3) might be useful for the treatment of chronic myelogenous leukemia, we examined the ability of As(2)O(3) to induce apoptosis in K562 cells. In vitro cytotoxicity of As(2)O(3) was evaluated in K562 cells by a MTT assay; the IC(50) value for As(2)O(3) was determined to be 10 microM. When analyzed by agarose gel electrophoresis, the DNA fragments became evident after incubation of the cells with 20 microM As(2)O(3) for 24 h. We also found morphological changes and chromatin condensation of the cells undergoing apoptosis. Activation of caspase-3 was observed 6 h after treatment with 20 microM As(2)O(3) by a Western blot analysis. Next, we examined the MAP kinase-signaling pathway of As(2)O(3)-induced apoptosis in K562 cells. As(2)O(3) at 10 microM strongly induced the activation of p38 and JNK 1/2, while ERK 1/2 was inhibited. In addition, pretreatment of SB203580, a specific inhibitor of p38, inhibited As(2)O(3) induced apoptotic cell death. These results suggest that As(2)O(3) is able to induce the apoptotic activity in K562 cells, and its apoptotic mechanism may be associated with the activation of p38.

P-glycoprotein in acute myeloid leukaemia: therapeutic implications of its association with both a multidrug-resistant and an apoptosis-resistant phenotype

P-glycoprotein (Pgp) expression is an independent prognostic factor for response to remission-induction chemotherapy in acute myeloblastic leukaemia, particularly in the elderly. There are several potential agents for modulating Pgp-mediated multi-drug resistance, such as cyclosporin A and PSC833, which are currently being evaluated in clinical trials. An alternative therapeutic strategy is to increase the use of drugs which are unaffected by Pgp. However, in this review, we explain why this may be more difficult than it appears. Evidence from in vitro studies of primary AML blasts supports the commonly held supposition that chemoresistance may be linked to apoptosis-resistance. We have found that Pgp has a drug-independent role in the inhibition of in vitro apoptosis in AML blasts. Modulation of cytokine efflux, signalling lipids and intracellular pH have all been suggested as ways by which Pgp may affect cellular resistance to apoptosis; these are discussed in this review. For a chemosensitising agent to be successful, it may be more important for it to enhance apoptosis than to increase drug uptake.

The paradox of arsenic: molecular mechanisms of cell transformation and chemotherapeutic effects

Arsenic is a well-documented carcinogen that also appears to be a valuable therapeutic tool in cancer treatment. This creates a paradox for which no unified hypothesis has been reached regarding the molecular mechanisms that determine whether arsenic will act as a carcinogen or as an effectual chemotherapeutic agent. Much of our knowledge with respect to the actions of arsenic has been drawn from epidemiological or clinical studies. The actions of arsenic are likely to be related to cell type, arsenic species, and length and dose of exposure. Arsenic unquestionably induces apoptosis and may specifically target certain tumor cells. Research data strongly suggest that arsenic influences distinct signaling pathways involved in mediating proliferation or apoptosis, including mitogen-activated protein kinases, p53, activator protein-1 or nuclear factor kappa B. The primary purpose of this review is to examine recent findings, from this laboratory and others, that focus on the molecular mechanisms of arsenic's actions in cell transformation and as a therapeutic agent.

Arsenic trioxide and methylprednisolone use different signal transduction pathways in leukemic differentiation

Certain cell lines like HL 60 and K 562 are utilised as leukemic cell models for leukemogenesis research, which differentiate along the granulocytic and/or monocytic pathway when treated with certain inducer molecules. High dose methylprednisolone treatment has been shown to induce in vivo and in vitro differentiation of myeloid leukemia cells to mature granulocytes in patients with acute promyelocytic leukemia (APL) and other subtypes of acute myeloid leukemia (AML). Arsenic trioxide (As(2)O(3)) has been confirmed to have remission induction effects on APL. However, there are conflicting results on the effects with other AML subtypes. Also, it has been well established that the reversible phosphorylation of proteins is a major regulatory mechanism in the signal transduction pathways that control cell growth and differentiation. Serine/threonine protein phosphatases (PP) are major components of phosphorylation. In this study, we investigated the effect of As(2)O(3) on HL 60 and K 562 myeloid leukemic differentiation and compared the signalling cascades of the two inducers with respect to serine/threonine PP 1 and 2A. We utilised PP1 and PP2A inhibitors okadaic acid and calyculin A. In contrast to methylprednisolone, there was no effect of phosphatase inhibitors on As(2)O(3)-induced leukemic differentiation. Incomplete leukemic differentiation occurred with lower As(2)O(3) concentration as 10(-6)M. Unlike As(2)O(3), methylprednisolone induced complete granulocytic and/or monocytic differentiation of HL 60 and K 562 cells via upregulation of PP2A regulatory subunits. Therefore, As(2)O(3) and methylprednisolone are promising agents that have the potential to be used together in myeloid leukemic differentiation therapy.

Dual effects of arsenic trioxide (As2O3) on non-acute promyelocytic leukaemia myeloid cell lines: induction of apoptosis and inhibition of proliferation

Clinical efficacy of As2O3 has been shown in patients with relapsed acute promyelocytic leukaemia (APL). There is evidence that the effects of As2O3 are not restricted to events specific for APL. As2O3 might target mechanisms involved in the pathogenesis of other malignancies. We assessed susceptibility to induction of apoptosis by As2O3 and cytostatics in 22 myeloid and non-myeloid malignant cell lines. As2O3 was used in concentrations of 0.01-10 micromol/l. Cell lines displayed different kinetics of response and different sensitivity to As2O3. The minimum concentration of As2O3 for induction of apoptosis was 0.1 micromol/l. High concentrations of As2O3 (5 micromol/l) induced apoptosis in a large proportion of cells in all cell lines tested. Low (1 micromol/l As2O3) concentrations induced apoptosis in NB-4, HL-60, U-937, CEM, HL-60, KG-1a, PBL-985, ML-2 and MV-4-11, but not in HEL, K-562, KG-1 and Jurkat up to 35 d of incubation. However, the non-apoptotic population of 1 micromol/l As2O3-treated HEL, K-562, K-562 (0.02), K-562(0.1) and Jurkat showed reduced proliferation. CEM as well as its' multidrug-resistant derivatives were sensitive to 1 micromol/l As2O3. In summary, these data demonstrate that As2O3-induced apoptosis is not restricted to cell lines with t(15;17). Apoptosis was induced in vitro by As2O3 concentrations that are achievable in vivo after infusion of well-tolerated As2O3 doses. Thus, As2O3 might be a suitable therapeutic agent for malignancies other than APL provided the adequate dose and duration of As2O3 treatment are used.

Arsonoliposomes, a novel class of arsenic-containing liposomes: effect of palmitoyl-arsonolipid-containing liposomes on the viability of cancer and normal cells in culture

PURPOSE

Arsonolipid-containing liposomes have been recently prepared. The demonstrated antileukemic action of arsenic trioxide prompted us to study their effect on the viability of several types of cancer cells to investigate the possibility of relevant applications. Five different cell types, three malignant (HL-60, C6. and GH3) and two non-malignant (HUVEC and RAME), were used.

METHODS

Liposomes containing the palmitoyl side chain arsonolipid (with different lipid compositions) were incubated with a given number of cells. Cell viability was estimated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-dimethyltetrazolium bromide assay. Morphologic studies were also performed.

RESULTS

Our results reveal that arsonoliposomes cause a dose (initiated at 10(-6) M)- and time-dependent inhibition of survival in all three malignant cell lines studied. No significant effect on the survival of the normal cells studied was observed at these, as well as at 10-fold higher. concentrations, although arsenic trioxide was toxic to HUVEC cells at equivalent arsenic concentrations. Microscopy studies reveal that although morphologic changes were initiated in HL-60 and C6 cells after incubation with arsonoliposomes, no changes in HUVEC and RAME cells were observed.

CONCLUSIONS

Considering the numerous advantages of liposomal systems in therapeutics, it is concluded that the arsonoliposome system is very interesting and future applications should be exploited by further studies.

Clinical trials of arsenic trioxide in hematologic and solid tumors: overview of the National Cancer Institute Cooperative Research and Development Studies

Arsenic trioxide inhibits growth and promotes apoptosis in many different cancer cell lines. The National Cancer Institute is working cooperatively with research centers across the U.S. to evaluate its clinical activity in hematologic malignancies, such as acute promyelocytic leukemia, acute myeloid leukemia, acute lymphocytic leukemia, chronic myelogenous leukemia, non-Hodgkin's lymphoma, Hodgkin's disease, chronic lymphocytic leukemia, myelodysplastic syndrome, and multiple myeloma. It is also supporting research in solid tumors, such as advanced hormone-refractory prostate cancer and renal cell cancer and in cervical cancer and refractory transitional cell carcinoma of the bladder. The safety and pharmacokinetics of arsenic trioxide are also being evaluated in pediatric patients with refractory leukemia and lymphoma. The results of these ongoing studies should provide important insights into the clinical utility of arsenic trioxide in these diseases.

Apoptosis induced by arsenic trioxide in leukemia U937 cells is dependent on activation of p38, inactivation of ERK and the Ca2+-dependent production of superoxide

The mechanism of the induction of apoptosis by arsenic trioxide (As2O3), which was demonstrated recently to be an effective inducer of apoptosis in patients with leukemia, was examined in detail in human leukemia U937 cells. Upon treatment of U937 cells with 50 microM of As2O3, complete inactivation of the kinases ERK1 and ERK2 was detected within 30 min. p38 was activated within 3 hr, and the maximum activity was detected at 6 hr, when DNA fragmentation remained undetectable. Experiments with transfected cells that expressed constitutively activated MEK1 and a specific inhibitor of p38 also suggested that inactivation of ERKs and activation of p38 might be associated with the induction of apoptosis by As2O3. In contrast to the inactivation of ERKs and the activation of p38, activation of JNK by As2O3 appeared to protect cells against the induction of apoptosis. Treatment of U937 cells with As2O3 also caused the Ca2+-dependent production of superoxide and intracellular acidification and a decrease in the mitochondrial membrane potential at the early stages of induction of apoptosis by As2O3. These changes preceded the release of cytochrome c from mitochondria and the activation of caspase-3. It should be possible to exploit the unusual characteristics of the mechanism of induction of apoptosis by As2O3 in U937 cells by making use of synergistic effects of this compound with other inducers of apoptosis.

Arsenic trioxide induces dose- and time-dependent apoptosis of endothelium and may exert an antileukemic effect via inhibition of angiogenesis

Arsenic trioxide (As2O3) has recently been used successfully in the treatment of acute promyelocytic leukemia and has been shown to induce partial differentiation and apoptosis of leukemic cells in vitro. However, the mechanism by which As2O3 exerts its antileukemic effect remains uncertain. Emerging data suggest that the endothelium and angiogenesis play a seminal role in the proliferation of liquid tumors, such as leukemia. We have shown that activated endothelial cells release cytokines that may stimulate leukemic cell growth. Leukemic cells, in turn, can release endothelial growth factors, such as vascular endothelial growth factor (VEGF). On the basis of these observations, we hypothesized that As2O3 may interrupt a reciprocal loop between leukemic cells and the endothelium by direct action on both cell types. We have shown that treatment of proliferating layers of human umbilical vein endothelial cells (HUVECs) with a variety of concentrations of As2O3results in a reproducible dose- and time-dependent sequence of events marked by change to an activated morphology, up-regulation of endothelial cell adhesion markers, and apoptosis. Also, treatment with As2O3 caused inhibition of VEGF production in the leukemic cell line HEL. Finally, incubation of HUVECs with As2O3 prevented capillary tubule and branch formation in an in vitro endothelial cell–differentiation assay. In conclusion, we believe that As2O3 interrupts a reciprocal stimulatory loop between leukemic cells and endothelial cells by causing apoptosis of both cell types and by inhibiting leukemic cell VEGF production.

Arsenic trioxide induces dose- and time-dependent apoptosis of endothelium and may exert an antileukemic effect via inhibition of angiogenesis

Arsenic trioxide (As2O3) has recently been used successfully in the treatment of acute promyelocytic leukemia and has been shown to induce partial differentiation and apoptosis of leukemic cells in vitro. However, the mechanism by which As2O3 exerts its antileukemic effect remains uncertain. Emerging data suggest that the endothelium and angiogenesis play a seminal role in the proliferation of liquid tumors, such as leukemia. We have shown that activated endothelial cells release cytokines that may stimulate leukemic cell growth. Leukemic cells, in turn, can release endothelial growth factors, such as vascular endothelial growth factor (VEGF). On the basis of these observations, we hypothesized that As2O3 may interrupt a reciprocal loop between leukemic cells and the endothelium by direct action on both cell types. We have shown that treatment of proliferating layers of human umbilical vein endothelial cells (HUVECs) with a variety of concentrations of As2O3results in a reproducible dose- and time-dependent sequence of events marked by change to an activated morphology, up-regulation of endothelial cell adhesion markers, and apoptosis. Also, treatment with As2O3 caused inhibition of VEGF production in the leukemic cell line HEL. Finally, incubation of HUVECs with As2O3 prevented capillary tubule and branch formation in an in vitro endothelial cell–differentiation assay. In conclusion, we believe that As2O3 interrupts a reciprocal stimulatory loop between leukemic cells and endothelial cells by causing apoptosis of both cell types and by inhibiting leukemic cell VEGF production.

Arsenic trioxide therapy for relapsed acute promyelocytic leukemia: an useful salvage therapy

Arsenic trioxide (As2O3) was recently identified as a very potent agent against acute promyelocytic leukemia (APL). Intravenous infusion of 10 mg As2O3 daily for one to two months can induce significant complete remission (CR) of APL, and there is no cross drug-resistance between As2O3 and other antileukemic agents, including all-trans retinoic acid (ATRA). The CR rate of relapsed and/or refractory APL patients who received As2O3 treatment ranged from 52.3% to 93.3%. The median duration to CR ranged from 38 to 51 days, with accumulative As2O3 dosage of 340-430 mg. Although most adverse reactions of As2O3 treatment were tolerable, certain infrequent but severe toxicities related to As2O3 were observed, including renal failure, hepatic damage, cardiac arrhythmia and chronic neuromuscular degeneration, which should be monitored carefully. As2O3 can induce partial differentiation and subsequent apoptosis of APL cells through degradation of wild type PML and PML/RAR alpha chimeric proteins and possible anti-mitochondrial effects. Like the treatment of ATRA in APL, early relapses from As2O3 treatment within a few months were not infrequently seen, indicating that rapid emerging resistance to As2O3 can occur. Nevertheless, the PML/RAR alpha fusion protein was reported to disappear in some APL patients who received As2O3, and who might earn long-survival. However, the follow-up is still too short to draw the conclusion. Intriguingly, it has been shown that As2O3 can also induce apoptosis of other non-APL tumor cells with clinical achievable concentrations. However, the detailed molecular mechanisms are not yet fully understood. Further studies regarding to the pharmacological characters, clinical efficacies, toxicities, apoptogenic mechanisms, and spectrum of anti-tumor activity of As2O3 are warranted.