Reinvent Aliphatic Arsenicals as Reversible Covalent Warheads toward Targeted Kinase Inhibition and Non-acute Promyelocytic Leukemia Cancer Treatment.

The success of arsenic in acute promyelocytic leukemia (APL) treatment is hardly transferred to non-APL cancers, mainly due to the low selectivity and weak binding affinity of traditional arsenicals to oncoproteins critical for cancer survival. We present herein the reinvention of aliphatic trivalent arsenicals (As) as reversible covalent warheads of As-based targeting inhibitors toward Bruton's tyrosine kinase (BTK). The effects of As warheads' valency, thiol protection, methylation, spacer length, and size on inhibitors' activity were studied. We found that, in contrast to the bulky and rigid aromatic As warhead, the flexible aliphatic As warheads were well compatible with the well-optimized guiding group to achieve nanomolar inhibition against BTK. The optimized As inhibitors effectively blocked the BTK-mediated oncogenic signaling pathway, leading to elevated antiproliferative activities toward lymphoma cells and xenograft tumor. Our study provides a promising strategy enabling rational design of new aliphatic arsenic-based reversible covalent inhibitors toward non-APL cancer treatment.

Research on different compound combinations of Realgar-Indigo naturalis formula to reverse acute promyelocytic leukemia arsenic resistance by regulating autophagy through mTOR pathway.

ETHNOPHARMACOLOGICAL RELEVANCE: In China, the Chinese patent drug Realgar-Indigo naturalis Formula (RIF) is utilized for the therapy of acute promyelocytic leukemia (APL). Comprising four traditional Chinese herb-Realgar, Indigo naturalis, Salvia miltiorrhiza, and Pseudostellaria heterophylla-it notably includes tetra-arsenic tetra-sulfide, indirubin, tanshinone IIa, and total saponins of Radix Pseudostellariae as its primary active components. Due to its arsenic content, RIF distinctly contributes to the therapy for APL. However, the challenge of arsenic resistance in APL patients complicates the clinical use of arsenic agents. Interestingly, RIF demonstrates a high remission rate in APL patients, suggesting that its efficacy is not significantly compromised by arsenic resistance. Yet, the current state of research on RIF's ability to reverse arsenic resistance remains unclear. AIM OF THE STUDY: To investigate the mechanism of different combinations of the compound of RIF in reversing arsenic resistance in APL. MATERIALS AND METHODS: The present study utilized the arsenic-resistant HL60-PMLA216V-RARα cell line to investigate the effects of various RIF compounds, namely tetra-arsenic tetra-sulfide (A), indirubin (I), tanshinone IIa (T), and total saponins of Radix Pseudostellariae (S). The assessment of cell viability, observation of cell morphology, and evaluation of cell apoptosis were performed. Furthermore, the mitochondrial membrane potential, changes in the levels of PMLA216V-RARα, apoptosis-related factors, and the PI3K/AKT/mTOR pathway were examined, along with autophagy in all experimental groups. Meanwhile, we observed the changes about autophagy after blocking the PI3K or mTOR pathway. RESULTS: Tanshinone IIa, indirubin and total saponins of Radix Pseudostellariae could enhance the effect of tetra-arsenic tetra-sulfide down-regulating PMLA216V-RARα, and the mechanism was suggested to be related to inhibiting mTOR pathway to activate autophagy. CONCLUSIONS: We illustrated that the synergistic effect of different compound combinations of RIF can regulate autophagy through the mTOR pathway, enhance cell apoptosis, and degrade arsenic-resistant PMLA216V-RARα.

[Inhibitory Effect of Metformin and Arsenic Trioxide on KG1a Cell Proliferation].

OBJECTIVE: To investigate the effect of metformin and arsenic trioxide on KG1a cells proliferation of acute myeloid leukemia and its possible mechanism. METHODS: CCK-8 method was used to detect the killing effect of metformin, arsenic trioxide and combined application on KG1a cells. Annexin V-FITC/PI Dual Stain Flow Cytometry was used to detect the effect of combined application on apoptosis of KG1a cells. Western blot was used to detect the expression of intracellular apoptosis-,autophagy-related protein. RESULTS: Metformin and arsenic trioxide alone or in combination could inhibit the proliferation of KG1a cells and induce apoptosis of KG1a cells, and the proliferation inhibition rate and apoptosis rate in the combined drug group were higher than those in the drug group alone(P <0.05). The combination of drugs induced upregulation of Caspase 8 protein and P62 protein expression and was higher than that in the drug group alone(P <0.05). CONCLUSION: Metformin can synergize with arsenic trioxide to kill KG1a cells, and its mechanism of action may be related to inducing apoptosis and enhancing autophagy.

HSP90, a Common Therapeutic Target for Suppressing Skin Injury Caused by Exposure to Chemically Diverse Classes of Blistering Agents.

Vesicants such as arsenicals and mustards produce highly painful cutaneous inflammatory and blistering responses, hence developed as chemical weapons during World War I/II. Here, using lewisite and sulfur mustard surrogates, namely phenylarsine oxide (PAO) and 2-chloroethyl ethyl sulfide (CEES), respectively, we defined a common underlying mechanism of toxic action by these two distinct classes of vesicants. Murine skin exposure to these chemicals causes tissue destruction characterized by increase in skin bifold thickness, Draize score, infiltration of inflammatory cells, and apoptosis of epidermal and dermal cells. RNA sequencing analysis identified ∼346 inflammatory genes that were commonly altered by both PAO and CEES, along with the identification of cytokine signaling activation as the top canonical pathway. Activation of several proinflammatory genes and pathways is associated with phosphorylation-dependent activation of heat shock protein 90α (p-HSP90α). Topical treatment with known HSP90 inhibitors SNX-5422 and IPI-504 post PAO or CEES skin challenge significantly attenuated skin damage including reduction in overall skin injury and clinical scores. In addition, highly upregulated inflammatory genes Saa3, Cxcl1, Ccl7, IL-6, Nlrp3, Csf3, Chil3, etc. by both PAO and CEES were significantly diminished by treatment with HSP90 inhibitors. These drugs not only reduced PAO- or CEES-induced p-HSP90α expression but also its client proteins NLRP3 and pP38 and the expression of their target inflammatory genes. Our data confirm a critical role of HSP90 as a shared underlying molecular target of toxicity by these two distinct vesicants and provide an effective and novel medical countermeasure to suppress vesicant-induced skin injury. SIGNIFICANCE STATEMENT: Development of effective and novel mechanism-based antidotes that can simultaneously block cutaneous toxic manifestations of distinct vesicants is important and urgently needed. Due to difficulties in determining the exact nature of onsite chemical exposure, a potent drug that can suppress widespread cutaneous damage may find great utility. Thus, this study identified HSP90 as a common molecular regulator of cutaneous inflammation and injury by two distinct warfare vesicants, arsenicals and mustards, and HSP90 inhibitors afford significant protection against skin damage.

Mutations at proximal cysteine residues in PML impair ATO binding by destabilizing the RBCC domain.

Acute promyelocytic leukemia (APL) is characterized by the fusion gene promyelocytic leukemia-retinoic acid receptor-alpha (PML-RARA) and is conventionally treated with arsenic trioxide (ATO). ATO binds directly to the RING finger, B-box, coiled-coil (RBCC) domain of PML and initiates degradation of the fusion oncoprotein PML-RARA. However, the mutational hotspot at C212-S220 disrupts ATO binding, leading to drug resistance in APL. Therefore, structural consequences of these point mutations in PML that remain uncertain require comprehensive analysis. In this study, we investigated the structure-based ensemble properties of the promyelocytic leukemia-RING-B-box-coiled-coil (PML-RBCC) domains and ATO-resistant mutations. Oligomeric studies reveal that PML-RBCC wild-type and mutants C212R, S214L, A216T, L217F, and S220G predominantly form tetramers, whereas mutants C213R, A216V, L218P, and D219H tend to form dimers. The stability of the dimeric mutants was lower, exhibiting a melting temperature (Tm) reduction of 30 °C compared with the tetrameric mutants and wild-type PML protein. Furthermore, the exposed surface of the C213R mutation rendered it more prone to protease digestion than that of the C212R mutation. The spectroscopic analysis highlighted ATO-induced structural alterations in S214L, A216V, and D219H mutants, in contrast to C213R, L217F, and L218P mutations. Moreover, the computational analysis revealed that the ATO-resistant mutations C213R, A216V, L217F, and L218P caused changes in the size, shape, and flexibility of the PML-RBCC wild-type protein. The mutations C213R, A216V, L217F, and L218P destabilize the wild-type protein structure due to the adaptation of distinct conformational changes. In addition, these mutations disrupt several hydrogen bonds, including interactions involving C212, C213, and C215, which are essential for ATO binding. The local and global structural features induced by these mutations provide mechanistic insight into ATO resistance and APL pathogenesis.

Vitamin C enhances the sensitivity of osteosarcoma to arsenic trioxide via inhibiting aerobic glycolysis.

Osteosarcoma (OS) is a common malignant tumor disease in the department of orthopedics, which is prone to the age of adolescents and children under 20 years old. Arsenic trioxide (ATO), an ancient poison, has been reported to play a critical role in a variety of tumor treatments, including OS. However, due to certain poisonous side effects such as cardiotoxicity and hepatotoxicity, clinical application of ATO has been greatly limited. Here we report that low doses of ATO (1 µM) observably reduced the half-effective inhibitory concentration (IC50) of vitamin C on OS cells. Compared with the treatment alone, the synthetic application of vitamin C (VitC, 800 µM) and ATO (1 µM) significantly further inhibited the proliferation, migration, and invasion of OS cells and promoted cell apoptosis in vitro. Meanwhile, we observed that the combined application of VitC and ATO directly suppresses the aerobic glycolysis of OS cells with the decreased production of pyruvate, lactate, and ATP via inhibiting the expression of the critical glycolytic genes (PGK1, PGM1, and LDHA). Moreover, the combination of VitC (200 mg/kg) and ATO (1 mg/kg) with tail vein injection significantly delayed OS growth and migration of nude mice by inhibiting aerobic glycolysis of OS. Thus, our results demonstrate that VitC effectively increases the sensitivity of OS to low concentrations of ATO via inhibiting aerobic glycolysis to alleviate the toxic side effects of high doses of arsenic trioxide, suggesting that synthetic application of VitC and ATO is a promising approach for the clinical treatment of human OS.

AcGlcAs: A Novel P53-Targeting Arsenical with Potent Cellular Uptake and Cancer Cell Selectivity.

Arsenic trioxide (ATO) targets PML/RARα and leads to miraculous success in treating acute promyelocytic leukemia. Notably, ATO also targets p53, the most frequently mutated protein in cancers, through a similar binding mechanism. However, p53-targeting ATO trials are challenging due to the poor cellular uptake and cancer selectivity of ATO. Here, we analyzed the structure-activity relationship of arsenicals and rationally developed a novel arsenical (designated AcGlcAs) by conjugating arsenic to sulfur atoms and tetraacetyl-ß-d-thioglucose. AcGlcAs exhibited remarkable cellular uptake through a thiol-mediated pathway (maximally 127-fold higher than ATO), thereby potently targeting PML/RARα and mutant p53. Among the 55 tested cell lines, AcGlcAs preferentially killed cancer lines rather than normal lines. In preclinical studies, AcGlcAs significantly extended the survival of mice bearing a xenograft tumor with p53 mutation while showing high plasma stability and oral bioavailability. Thus, AcGlcAs is a potential clinical candidate for precisely treating numerous p53-mutated cancers.

Gelling Bodies: Understanding the Mechanisms Underlying Arsenic Trioxide Action.

SUMMARY: The study by Bercier and colleagues investigates the mechanisms of action of arsenic trioxide (ATO). The authors find that ATO promotes transition of PML nuclear bodies to a gel-like state via the PML trimerization domain and a critical cysteine residue. Overall, this work sheds new light onto how PML-RARα, the oncogene of APL, is targeted by ATO for disease eradication. See related article by Bercier et al., p. 2548 (6).

Arsenic Trioxide inhibits Activation of Hedgehog Pathway in Human Neuroblastoma Cell Line SK-N-BE(2) Independent of Itraconazole.

BACKGROUND: Neuroblastoma (NB) remains associated with a low overall survival rate over the long term. Abnormal activation of the Hedgehog (HH) signaling pathway can activate the transcription of various downstream target genes that promote NB. Both arsenic trioxide (ATO) and itraconazole (ITRA) can inhibit tumor growth. OBJECTIVE: To determine whether ATO combined with ITRA can be used to treat NB with HH pathway activation, we examined the effects of ATO and ITRA monotherapy or combined inhibition of the HH pathway in NB. METHODS: Analysis of CCK8 and flow cytometry showed cell inhibition and cell cycle, respectively. Real-time PCR analysis was conducted to assess the mRNA expression of HH pathway. RESULTS: We revealed that as concentrations of ATO and ITRA increased, the killing effects of both agents on SK-N-BE(2) cells became more apparent. During G2/M, the cell cycle was largely arrested by ATO alone and combined with ITRA, and in the G0/G1 phase by ITRA alone. In the HH pathway, ATO inhibited the transcription of the SHH, PTCH1, SMO and GLI2 genes, however, ITRA did not. Instead of showing synergistic effects in a combined mode, ITRA decreased ATO inhibitory effects. CONCLUSION: We showed that ATO is an important inhibitor of HH pathway but ITRA can weaken the inhibitory effect of ATO. This study provides an experimental evidence for the clinical use of ATO and ITRA in the treatment of NB with HH pathway activation in cytology.

Structural Basis of PML-RARA Oncoprotein Targeting by Arsenic Unravels a Cysteine Rheostat Controlling PML Body Assembly and Function.

PML nuclear bodies (NB) are disrupted in PML-RARA-driven acute promyelocytic leukemia (APL). Arsenic trioxide (ATO) cures 70% of patients with APL, driving PML-RARA degradation and NB reformation. In non-APL cells, arsenic binding onto PML also amplifies NB formation. Yet, the actual molecular mechanism(s) involved remain(s) elusive. Here, we establish that PML NBs display some features of liquid-liquid phase separation and that ATO induces a gel-like transition. PML B-box-2 structure reveals an alpha helix driving B2 trimerization and positioning a cysteine trio to form an ideal arsenic-binding pocket. Altering either of the latter impedes ATO-driven NB assembly, PML sumoylation, and PML-RARA degradation, mechanistically explaining clinical ATO resistance. This B2 trimer and the C213 trio create an oxidation-sensitive rheostat that controls PML NB assembly dynamics and downstream signaling in both basal state and during stress response. These findings identify the structural basis for arsenic targeting of PML that could pave the way to novel cancer drugs. SIGNIFICANCE: Arsenic curative effects in APL rely on PML targeting. We report a PML B-box-2 structure that drives trimer assembly, positioning a cysteine trio to form an arsenic-binding pocket, which is disrupted in resistant patients. Identification of this ROS-sensitive triad controlling PML dynamics and functions could yield novel drugs. See related commentary by Salomoni, p. 2505. This article is featured in Selected Articles from This Issue, p. 2489.

miR-603 promotes cell proliferation and differentiation by targeting TrkB in acute promyelocytic leukemia.

Arsenic trioxide (ATO) treatment effectively prolongs the overall survival of patients with acute promyelocytic leukemia (APL). Mutations in the oncogene PML::RARA were found in patients with ATO-resistant and relapsed APL. However, some relapsed patients do not have such mutations. Here, we performed microarray analysis of samples from newly diagnosed and relapsed APL, and found different microRNA (miRNA) expression patterns between these two groups. Among the differentially expressed miRNAs, miR-603 was expressed at the lowest level in relapsed patients. The expression of miR-603 and its predicted target tropomyosin-related kinase B (TrkB) were determined by PCR and Western blot. Proliferation was measured using an MTT assay, while apoptosis, cell cycle and CD11b expression were analyzed using flow cytometry. In APL patients, the expression of miR-603 was negatively correlated with that of TrkB. miR-603 directly targeted TrkB and downregulated TrkB expression in the APL cell line NB4. miR-603 increased cell proliferation by promoting the differentiation and inhibiting the apoptosis of NB4 cells. This study shows that the miR-603/ TrkB axis may be a potent therapeutic target for relapsed APL.

Dissection of scientific compatibility of Chinese medicinal formula Realgar-Indigo naturalis as an effective treatment for promyelocytic leukemia from the perspective of toxicology.

ETHNOPHARMACOLOGICAL RELEVANCE: Realgar-Indigo naturalis formula (RIF), a first-line drug for the treatment of acute promyelocytic leukemia (APL),is also a TCM formula entirely designed based on TCM theories. There have been studies that explain the scientific connotation of the compatibility of RIF from the perspective of pharmacodynamics. However, as one of the arsenic-containing preparations, the safety of realgar is widely concerned, and there has not been systematic studies to explain the scientific connotation of RIF from the perspective of toxicology. AIM OF THIS STUDY: Dissection of scientific compatibility of Chinese medicinal formula Realgar-Indigo naturalis as an effective treatment for promyelocytic leukemia from the perspective of toxicology. MATERIALS AND METHODS: We used normal mice and an APL model to explore (i) the effects of different components on intestinal permeability, (ii) the changes in intestinal flora, and (iii) toxic effects. At the same time, a bionic extraction method was used to study the effects of different components on the dissolution of soluble arsenic in realgar under the acidic environment in the stomach and the alkaline environment in the intestinal tract. RESULTS: Salvia miltiorrhiza Bunge can repair the intestinal mucosal barrier, maintain the homeostasis of intestinal flora, intervene in the dissolution process of realgar, reverse the increase in intestinal permeability and the disturbance of intestinal flora caused by realgar, and reduce toxicity. CONCLUSION: From the perspective of toxicology, we propose new insights into the definition of the roles of each component in the RIF formula, namely realgar is the monarch, Indigo naturalis is the minister, Salvia miltiorrhiza Bungeis the assistant.

ATO Increases ROS Production and Apoptosis of Cells by Enhancing Calpain-Mediated Degradation of the Cancer Survival Protein TG2.

Transglutaminase 2 (TG2) is a critical cancer cell survival factor that activates several signalling pathways to foster drug resistance, cancer stem cell survival, metastasis, inflammation, epithelial-mesenchymal transition, and angiogenesis. All-trans retinoic acid (ATRA) and chemotherapy have been the standard treatments for acute promyelocytic leukaemia (APL), but clinical studies have shown that arsenic trioxide (ATO), alone or in combination with ATRA, can improve outcomes. ATO exerts cytotoxic effects in a variety of ways by inducing oxidative stress, genotoxicity, altered signal transduction, and/or epigenetic modification. In the present study, we showed that ATO increased ROS production and apoptosis ratios in ATRA-differentiated NB4 leukaemia cells, and that these responses were enhanced when TG2 was deleted. The combined ATRA + ATO treatment also increased the amount of nuclear factor erythroid 2-related factor 2 (NRF2) transcription factor, an adaptive regulator of the cellular oxidative stress response, and calpain proteolytic activity, resulting in TG2 degradation and the reduced survival of WT leukaemia cells. We further showed that the induced TG2 protein expression was degraded in the MCF-7 epithelial cell line and primary peripheral blood mononuclear cells upon ATO treatment, thereby sensitising these cell types to apoptotic signals.

MDM2-mediated Inhibitory Effect of Arsenic Trioxide on Small Cell Lung Cancer Cell Line by Degrading Mutant p53.

INTRODUCTION: Small cell lung cancer (SCLC) is featured by a high TP53 mutant rate. Our previous research found that arsenic trioxide (As2O3) could significantly inhibit the growth and metastasis of SCLC. Studies have shown that the degradation of mutant p53 mediated by murine double minute 2 (MDM2) can be induced by As2O3, which probably contributes to the inhibition of SCLC, but the detailed mechanism is still unclear. We aimed to testify that As2O3 can inhibit the growth of SCLC cells by degrading mutant p53 protein via binding to MDM2. METHODS: CCK-8 assay, cell cycle analysis, and western blot of apoptosis markers were used to evaluate the inhibitory effect of As2O3 on NCI-H446 cells (containing mutant p53) and NCI-H1299 cells (p53 null). The effects of As2O3 on p53 and its downstream proteins were identified by western blot using mut-p53-knockdown and overexpressed cell models. MDM2-knockdown cell models were constructed, and western blot, co-IP of mut-p53, and ubiquitin were carried out to explore the mediating effect of MDM2 in As2O3 induced mut-p53 degradation. RESULTS: As2O3 inhibited proliferation and induced cell cycle arrest and apoptosis of SCLC cells in a dose- and timedependent manner. After mut-p53 knockdown or overexpressed, the inhibitory effect of As2O3 was dampened or enhanced. Additionally, As2O3-induced mut-p53 ubiquitination was significantly weakened after MDM2 knockdown. CONCLUSION: As2O3 could inhibit SCLC cells by inhibiting proliferation and inducing cell cycle arrest and apoptosis. These inhibitory effects were achieved at least in part by upregulating MDM2, which, in turn, promotes ubiquitination and degradation of mut-p53.

Torsemide increases arsenic concentrations by inhibition of multidrug resistance protein 4 in arsenic trioxide treated acute promyelocytic leukemia patients.

Torsemide is commonly used to relieve edema during the treatment of acute promyelocytic leukemia (APL) with arsenic trioxide (ATO). We explored the effect of torsemide on the plasma concentrations of inorganic arsenic (iAs), monomethylarsonic acid (MMAV) and dimethyarsinic acid (DMAV) in APL patients treated with ATO and clarified its molecular mechanism in rats and cells. The study included 146 APL patients treated with ATO. 60（41.1 %) of these 146 patients were co-administered with torsemide. The treatment of torsemide increased plasma concentrations of iAs (P < 0.05) and DMAV (P < 0.05) in APL patients. The single co-administration of ATO and torsemide in rats significantly increased the plasma concentrations and AUC(0-t) of iAs (P < 0.05) and MMAV (P < 0.05), decreased the urinary excretion rates and the urine concentrations of iAs (P < 0.05) and DMAV (P < 0.05), and enhanced iAs (P < 0.05) and MMAV (P < 0.05) concentrations in the kidneys of rats. In addition, torsemide decreased the expression of multidrug resistance protein 4 (MRP4) in rat kidneys after 7 days of continuous co-administration (P < 0.05). We also treated MRP4-overexpressing HEK293T cells with ATO and different concentrations of torsemide. Torsemide markedly increased the concentrations of iAs, MMAV and DMAV by inhibiting MRP4 compared with ATO alone (P < 0.05). In conclusion, torsemide increased the plasma concentrations of arsenic metabolites in APL patients treated with ATO by inhibiting the transporter MRP4 in a dose-dependent manner.

Bifunctional protein ArsRM contributes to arsenite methylation and resistance in Brevundimonas sp. M20.

BACKGROUND: Arsenic (As) with various chemical forms, including inorganic arsenic and organic arsenic, is the most prevalent water and environmental toxin. This metalloid occurs worldwide and many of its forms, especially arsenite [As(III)], cause various diseases including cancer. Organification of arsenite is an effective way for organisms to cope with arsenic toxicity. Microbial communities are vital contributors to the global arsenic biocycle and represent a promising way to reduce arsenite toxicity. METHODS: Brevundimonas sp. M20 with arsenite and roxarsone resistance was isolated from aquaculture sewage. The arsHRNBC cluster and the metRFHH operon of M20 were identified by sequencing. The gene encoding ArsR/methyltransferase fusion protein, arsRM, was amplified and expressed in Escherichia coli BL21 (DE3), and this strain showed resistance to arsenic in the present of 0.25-6 mM As(III), aresenate, or pentavalent roxarsone. The methylation activity and regulatory action of ArsRM were analyzed using Discovery Studio 2.0, and its functions were confirmed by methyltransferase activity analysis and electrophoretic mobility shift assays. RESULTS: The minimum inhibitory concentration of the roxarsone resistant strain Brevundimonas sp. M20 to arsenite was 4.5 mM. A 3,011-bp arsenite resistance ars cluster arsHRNBC and a 5649-bp methionine biosynthesis met operon were found on the 3.315-Mb chromosome. Functional prediction analyses suggested that ArsRM is a difunctional protein with transcriptional regulation and methyltransferase activities. Expression of ArsRM in E. coli increased its arsenite resistance to 1.5 mM. The arsenite methylation activity of ArsRM and its ability to bind to its own gene promoter were confirmed. The As(III)-binding site (ABS) and S-adenosylmethionine-binding motif are responsible for the difunctional characteristic of ArsRM. CONCLUSIONS: We conclude that ArsRM promotes arsenite methylation and is able to bind to its own promoter region to regulate transcription. This difunctional characteristic directly connects methionine and arsenic metabolism. Our findings contribute important new knowledge about microbial arsenic resistance and detoxification. Future work should further explore how ArsRM regulates the met operon and the ars cluster.

Involvement of Mitochondrial Damage and Oxidative Stress in Apoptosis Induced by Betulin Plus Arsenic Trioxide in Neuroblastoma Cells.

BACKGROUND/AIM: Arsenic trioxide (As2O3), a potent toxin in traditional Chinese medicine, has been utilized as an anticancer agent in Chinese culture for over a millennium. Betulin, commonly extracted from the bark of birch trees, has been identified for its pharmacological properties, including antibacterial, anti-inflammatory, antitumor, and antiviral activities. The aim of this study was to determine the efficacy and underlying anticancer signaling cascade induced by As2O3 and betulin in neuroblastoma cells. MATERIALS AND METHODS: SK-N-SH cells were treated with As2O3 with or without betulin. Cell viability and apoptotic signaling were assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, measurement of mitochondrial membrane potential (MMP) loss and reactive oxygen species (ROS), and quantitative western blotting analysis. Student's t-test in addition to one- or two-way analysis of variance was used to examine significant differences between comparison groups. RESULTS: The combined treatment of As2O3 plus betulin was more effective than single treatments in suppressing cell viability and induction of apoptosis, which correlated well with elevated ROS levels. The apoptotic signaling cascade of As2O3 plus betulin was revealed as ROS elevation and relative loss of MMP, leading to the cleavage of caspase-3 and -9. As2O3 plus betulin treatment also reduced the expression of BCL2 apoptosis regulator, BH3-interacting domain death agonist, and BCL2-like-1. CONCLUSION: The novel combination of As2O3 plus betulin has the potential to serve as a practical anti-neuroblastoma drug.

Arsenic trioxide-induced cytotoxicity in A549 cells: The role of necroptosis.

INTRODUCTION: Lung cancer is one of the deadliest cancers globally. Arsenic trioxide (ATO) is still present as a highly effective drug in treating acute promyelocytic leukemia (APL). Chemotherapy resistance is one of the major problems in cancer therapy. Necroptosis, can overcomes resistance to apoptosis, and can promote cancer treatment. This study examines the necroptosis pathway in A549 cancer cells exposed to ATO. METHODS: We used the MTT test to determine the ATO effects on the viability of A549 cells at three different time intervals. Also, the reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) were performed in three-time intervals. The effect of ATO on apoptosis was evaluated by Annexin V / PI staining and, the RIPK1 and MLKL gene expression were measured by Real-Time PCR. RESULTS: The ATO has dose and time-dependent cytotoxic effects, so at 24, 48, and 72 h, the IC50 doses were 33.81 '11.44 '2.535 µM respectively. A 50 µM ATO is the most appropriate to increase the MMP loss significantly at all three times. At 24 and 48 h after exposure of cells to ATO, the ROS levels increased. The RIPK1 gene expression increased significantly compared to the control group at concentrations of 50 and 100 µM; however, MLKL gene expression decreased. CONCLUSIONS: The A549 cells, after 48 h exposure to ATO at 50 and 100 µM, induces apoptosis and necroptosis. Due to the reduced expression of MLKL, it can be concluded that ATO is probably effective in the metastatic stage of cancer cells.

Potential of natural products in combination with arsenic trioxide: Investigating cardioprotective effects and mechanisms.

Over the past few decades, clinical trials conducted worldwide have demonstrated the efficacy of arsenic trioxide (ATO) in the treatment of relapsed acute promyelocytic leukemia (APL). Currently, ATO has become the frontline treatments for patients with APL. However, its therapeutic applicability is severely constrained by ATO-induced cardiac side effects. Any cardioprotective agents that can ameliorate the cardiac side effects and allow exploiting the full therapeutic potential of ATO, undoubtedly gain significant attention. The knowledge and use of natural products for evidence-based therapy have grown rapidly in recent years. Here we discussed the potential mechanism of ATO-induced cardiac side effects and reviewed the studies on cardiac side effects as well as the research history of ATO in the treatment of APL. Then, We summarized the protective effects and underlying mechanisms of natural products in the treatment of ATO-induced cardiac side effects. Based on the efficacy and safety of the natural product, it has a promising future in the development of cardioprotective agents against ATO-induced cardiac side effects.