Arsenic trioxide induces autophagy and antitumor effects in Burkitt's lymphoma Raji cells

Autophagy plays a pro-apoptotic role in arsenic trioxide-induced cell death of liver cancer

OBJECTIVE

The effects of arsenic trioxide (As2O3) on hepatocellular carcinoma have been documented widely. Autophagy plays dual roles in the survival and death of cancer cells. Therefore, we investigated the exact role of autophagy in As2O3-induced apoptosis in liver cancer cells.

METHODS

The viability of hepatoma cells was determined using the MTT assay with or without fetal bovine serum. The rate of apoptosis in liver cancer cells treated with As2O3 was evaluated using flow cytometry, Hoechst 33258 staining, and TUNEL assays. The rate of autophagy among liver cancer cells treated with As2O3 was detected using immunofluorescence, Western blot assay and transmission electron microscopy.

RESULTS

Upon treatment with As2O3, the viability of HepG2 and SMMC-7721 cells was decreased in a time- and dose-dependent manner. The apoptosis rates of both liver cancer cell lines increased with the concentration of As2O3, as shown by flow cytometry. Apoptosis in liver cancer cells treated with As2O3 was also shown by the activation of the caspase cascade and the regulation of Bcl-2/Bax expression. Furthermore, As2O3 treatment induced autophagy in liver cancer cells; this finding was supported by Western blot, immunofluorescence of LC3-II and beclin 1, and transmission electron microscopy. In liver cancer cells, As2O3 inhibited the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) signal pathway that plays a vital role in both apoptosis and autophagy. The PI3K activator SC-79 partially reversed As2O3-induced autophagy and apoptosis. Furthermore, inhibiting autophagy with 3-methyladenine partially reversed the negative effects of As2O3 on cell viability. Serum starvation increased autophagy and amplified the effect of As2O3 on cell death.

CONCLUSION

As2O3 induces apoptosis and autophagy in liver cancer cells. Autophagy induced by As2O3 may have a proapoptotic effect that helps to reduce the viability of liver cancer cells. This study provides novel insights into the effects of As2O3 against liver cancer. Please cite this article as: Deng ZT, Liang SF, Huang GK, Wang YQ, Tu XY, Zhang YN, Li S, Liu T, Cheng BB. Autophagy plays a pro-apoptotic role in arsenic trioxide-induced cell death of liver cancer. J Integr Med. 2024; 22(3): 295-302.

Effect of arsenic trioxide plus etoposide, solumedrol, high‑dose cytarabine and cisplatin chemotherapy on the treatment of relapsed or ref7ractory ALK+ anaplastic large cell lymphoma

It has been reported that arsenic trioxide (ATO) regulates lymphoma cell cycle, apoptosis, autophagy and mitochondrial activity, while it synergizes with other cytotoxic agents. In addition, ATO targets anaplastic lymphoma kinase (ALK)-fusion oncoprotein to repress anaplastic large cell lymphoma (ALCL). The current study aimed to investigate the efficacy and safety of ATO plus etoposide, solumedrol, high-dose cytarabine and cisplatin (ESHAP) chemotherapy compared with ESHAP chemotherapy alone in patients with relapsed or refractory (R/R) ALK⁺ ALCL. A total of 24 patients with R/R ALK⁺ ALCL were enrolled in the present study. Among them, 11 patients were treated with ATO plus ESHAP, while the remaining 13 patients received ESHAP chemotherapy alone. Subsequently, treatment response, event-free survival (EFS), overall survival (OS) and adverse event (AEs) rates were recorded. Both complete response (72.7% vs. 53.8%; P=0.423) and objective response (81.8% vs. 69.2%; P=0.649) rates were higher in the ATO plus ESHAP group compared with the ESHAP group. However, statistical significance was not reached. In addition, EFS was significantly prolonged (P=0.047), while OS was not significantly increased (P=0.261) in the ATO plus ESHAP group compared with the ESHAP group. More specifically, the 3-year accumulating EFS and OS rates were 59.7 and 77.1% in the ATO plus ESHAP group, respectively, and 13.8 and 59.8% in the ESHAP group, respectively. The majority of AEs, such as thrombocytopenia (81.8% vs. 46.2%; P=0.105), fever (81.8% vs. 46.2%; P=0.105) and dyspnea (36.4% vs. 15.4%; P=0.182), were more prevalent in the ATO plus ESHAP group compared with the ESHAP group. However, no statistical significance was observed. In conclusion, the current study indicated that ATO plus ESHAP chemotherapy could exert a superior efficacy compared with ESHAP chemotherapy alone in patients with R/R ALK⁺ ALCL.

Combination treatment with cyclosporin A and arsenic trioxide induce synergistic cell death via non-apoptotic pathway in uterine cervical cancer cells

Cyclosporin A is an immunosuppressive drug with anti-cancer effect. Arsenic trioxide (As₂O₃), a well-known cancer-inhibiting drug, induced cytotoxicity via apoptosis and autophagy. The aim of this study is to evaluate the effect of combinational treatment with cyclosporin A and arsenic trioxide on cell viability inhibition in cervical cancer cells. Using MTT assay and combination index, combinational treatment with cyclosporin A and arsenic trioxide induced a synergistic cytotoxic effect in Caski and SiHa cells. Cyclosporin A and arsenic trioxide triggered cell death via non-apoptotic pathway by using annexin V/propidium iodide (PI) assay. Cyclosporin A and arsenic trioxide combined treatment decreased mitochondrial membrane potential and increase reactive oxygen species (ROS) generation. This co-treatment increased LC3B-II expression and autophagosome formation in cervical cancer cells. This study first demonstrated that combinational treatment with cyclosporin A and As₂O₃ trigger synergistic cytotoxic effect via autophagy in cervical cancer cells.

Parkin, as a Regulator, Participates in Arsenic Trioxide-Triggered Mitophagy in HeLa Cells

Parkin is a well-established synergistic mediator of mitophagy in dysfunctional mitochondria. Mitochondria are the main target of arsenic trioxide (ATO) cytotoxicity, and the effect of mitophagy on ATO action remains unclear. In this study, we used stable Parkin-expressing (YFP-Parkin) and Parkin loss-of-function mutant (Parkin C431S) HeLa cell models to ascertain whether Parkin-mediated mitophagy participates in ATO-induced apoptosis/cell death. Our data showed that the overexpression of Parkin significantly sensitized HeLa cells to ATO-initiated proliferation inhibition and apoptosis; however, the mutation of Parkin C431S significantly weakened this Parkin-mediated responsiveness. Our further investigation found that ATO significantly downregulated two fusion proteins (Mfn1/2) and upregulated fission-related protein (Drp1). Autophagy was also activated as evidenced by the formation of autophagic vacuoles and mitophagosomes, increased expression of PINK1, and recruitment of Parkin to impaired mitochondria followed by their degradation, accompanied by the increased transformation of LC3-I to LC3-II, increased expression of Beclin1 and decreased expression of P62 in YFP-Parkin HeLa cells. Enhanced mitochondrial fragmentation and autophagy indicated that mitophagy was activated. Furthermore, during the process of mitophagy, the overproduction of ROS implied that ROS might represent a key factor that initiates mitophagy following Parkin recruitment to mitochondria. In conclusion, our findings indicate that Parkin is critically involved in ATO-triggered mitophagy and functions as a potential antiproliferative target in cancer cells.

Mechanisms and Therapeutic Strategies of Viral Myocarditis Targeting Autophagy

Viral myocarditis is caused by infection with viruses or bacteria, including coxsackievirus B3 (CVB3), and is characterized by acute or chronic inflammatory responses in the heart. The mortality associated with severe viral myocarditis is considerable. In some patients, viral myocarditis may develop into dilated cardiomyopathy or heart failure. Autophagy is involved in a wide range of physiological processes, including viral infection and replication. In the present review, we focus on the responses of cardiac tissues, cardiomyocytes, and cardiac fibroblasts to CVB3 infection. Subsequently, the effects of altered autophagy on the development of viral myocarditis are discussed. Finally, this review also examined and assessed the use of several popular autophagy modulating drugs, such as metformin, resveratrol, rapamycin, wortmannin, and 3-methyladenine, as alternative treatment strategies for viral myocarditis.

F-box protein FBXO41 plays vital role in arsenic trioxide-mediated autophagic death of cancer cells

Arsenic trioxide (ATO), a potent anti-neoplastic drug, is known to prevent cancer cell growth through induction of autophagic cell death. However, importance of cellular factors in ATO-mediated autophagic cell death is poorly understood. In this study, using biochemical and immunofluorescence techniques, we show that F-box protein FBXO41 plays a critical role in anti-proliferative activity of ATO. Our study reveals the importance of FBXO41 in induction of autophagic death of cancer cells by ATO. Further, we show that the autophagic cell death induced by FBXO41 is distinct and independent of apoptosis and necrosis, showing that FBXO41 may play vital role in inducing autophagic death of apoptosis resistant cancer cells. Overall, our study elucidates the importance of FBXO41 in ATO induced autophagic cell death to prevent cancer progression, which could be explored to develop promising cancer therapeutic strategy.

Sidt2 is a key protein in the autophagy-lysosomal degradation pathway and is essential for the maintenance of kidney structure and filtration function

The regulation and homeostasis of autophagy are essential for maintaining organ morphology and function. As a lysosomal membrane protein, the effect of Sidt2 on kidney structure and renal autophagy is still unknown. In this study, we found that the kidneys of Sidt2^-/- mice showed changes in basement membrane thickening, foot process fusion, and mitochondrial swelling, suggesting that the structure of the kidney was damaged. Increased urine protein at 24 h indicated that the kidney function was also damaged. At the same time, the absence of Sidt2 caused a decrease in the number of acidic lysosomes, a decrease in acid hydrolase activity and expression in the lysosome, and an increase of pH in the lysosome, suggesting that lysosomal function was impaired after Sidt2 deletion. The accumulation of autophagolysosomes, increased LC3-II and P62 protein levels, and decreased P62 mRNA levels indicated that the absence of the Sidt2 gene caused abnormal autophagy pathway flow. Chloroquine experiment, immunofluorescence autophagosome, and lysosome fusion assay, and Ad-mcherry-GFP-LC3B further indicated that, after Sidt2 deletion, the production of autophagosomes did not increase, but the fusion of autophagosomes and lysosomes and the degradation of autophagolysosomes were impaired. When incubating Sidt2^-/- cells with the autophagy activator rapamycin, we found that it could activate autophagy, which manifested as an increase in autophagosomes, but it could not improve autophagolysosome degradation. Meanwhile, it further illustrated that the Sidt2 gene plays an important role in the smooth progress of autophagolysosome processes. In summary, the absence of the Sidt2 gene caused impaired lysosome function and a decreased number of acidic lysosomes, leading to formation and degradation disorders of the autophagolysosomes, which eventually manifested as abnormal kidney structure and function. Sidt2 is essential in maintaining the normal function of the lysosomes and the physiological stability of the kidneys.

Metformin and arsenic trioxide synergize to trigger Parkin/pink1-dependent mitophagic cell death in human cervical cancer HeLa cells

Mitochondria are involved in various biological processes including intracellular homeostasis, proliferation, senescence, and death, and mitochondrial mitophagy is closely related to the development and regression of malignant tumors. Recent studies confirmed that the hypoglycemic drug metformin (Met) exerted various antitumor effects, protected neural cells, and improved immunity, while arsenic trioxide (ATO) is an effective chemotherapeutic agent for the clinical treatment of leukemia and various solid tumors. However, the possible combined antitumor effects of Met and ATO and their cellular molecular mechanisms are unclear. We investigated the role of Parkin-mediated mitochondrial mitophagy in the anti-tumor mechanism of Met and ATO by studying the effects of Met and/or ATO on the proliferation and apoptosis of cervical cancer HeLa cells. Both Met and ATO effectively inhibited the proliferative activity of HeLa cells and induced apoptosis by activating Bax and inhibiting Bcl-2. Met and ATO treatment alone or in combination stimulated mitophagosome accumulation in HeLa cells, increased the conversion of microtubule-associated protein light chain 3 (LC3)-I to LC3-II, and decreased levels of the mitophagic lysosomal substrate protein P62. The mitochondrial membrane potential of HeLa cells also decreased, accompanied by activation of the mitochondrial translocase TOM system and the Pink1/Parkin signaling pathway. These results suggested that Met and/or ATO could induce mitophagy in HeLa cells via the Pink1/Parkin signaling pathway, leading to mitophagic apoptosis and inhibition of tumor cell proliferation. The combination of Met and ATO thus has enhanced antitumor effects, suggesting that this combination has potential clinical applications for the treatment of cervical cancer and other tumors.

[Lysosomal membrane protein Sidt2 deletion impairs autophagy in human hepatocytes]

OBJECTIVE

To study the effect of lysosomal membrane protein Sidt2 deletion on autophagy in human hepatocytes.

METHODS

Crispr-Cas9 technology was used to construct a human hepatocyte (HL7702) model of Sidt2 knockout (Sidt2-/-), and the expression levels of the key autophagy proteins LC3II/I, P62 and autophagy-related proteins Atg5, Atg7, and Atg12 were detected.The co-localization of LC3B and P62 in the cells were analyzed with immunofluorescence assay to assess the identification and storage of P62 cargo proteins by the autophagosomes and the degradation of the autophagolysosomes.The co-localization of LC3B and LAMP1 was also determined with immunofluorescence assay to detect the fusion of the autophagosomes with the lysosomes, and LysoTracker was used to trace the acidic lysosomes.

RESULTS

We successfully constructed a HL7702 cell model of Sidt2+/+ and Sidt2-/-, and compared with Sidt2+/+ cells, the Sidt2-/- cell model showed significantly increased expressions of LC3-II/I and P62 (P < 0.01).Immunofluorescence assay showed a significant increase of LC3B and P62 expressions (P < 0.001) and obviously lowered expressions of Atg5, Atg7, and Atg12 in Sidt2-/- cells (P < 0.05).The co-localization of LC3B and P62 and that of LC3B and LAMP1 were both reduced and the number of acidic lysosomes was significantly lowered in Sidt2-/- cells (P < 0.05).

CONCLUSION

Sidt2 gene deletion disturbs the recognition and sequestration of P62 cargo protein by autophagosomes in human hepatocytes.At the same time, the decreased number of acidic lysosomes and the dysfunction of autophagosome and lysosome fusion cause the block of the autophagy-lysosome pathway, leading eventually to LC3B and P62 accumulation and impaired autophagy in the hepatocytes.

Novel Mechanistic Insights into the Anti-cancer Mode of Arsenic Trioxide

Arsenic, a naturally-occurring toxic element, and a traditionally-used drug, has received a great deal of attention worldwide due to its curative anti-cancer properties in patients with acute promyelocytic leukemia. Among the arsenicals, arsenic trioxide has been most widely used as an anti-cancer drug. Recent advances in cancer therapeutics have led to a paradigm shift away from traditional cytotoxic drugs towards the targeting of proteins closely associated with driving the cancer phenotype. Due to the diverse anti-cancer effects of ATO on different types of malignancies, numerous studies have made efforts to uncover the mechanisms of ATO-induced tumor suppression. From in vitro cellular models to studies in clinical settings, ATO has been extensively studied. The outcomes of these studies have opened doors to establishing improved molecular-targeted therapies for cancer treatment. The efficacy of ATO has been augmented by combination with other drugs. In this review, we discuss recent arsenic-based cancer therapies and summarize the novel underlying molecular mechanisms of the anti-cancer effects of ATO.

Antiangiogenic effect of arsenic trioxide in HUVECs by FoxO3a-regulated autophagy

Arsenic trioxide (ATO) has been shown to have antitumor effect in different tumors, although the underlying mechanisms are not fully understood. Autophagy plays a critical role in tumorigenesis and cancer therapy and has been found to be activated by ATO in different cells. However, the role of autophagy in the antitumor effect of ATO has not yet been elucidated. In this study, we investigated the role of autophagy in the antiangiogenic effect of ATO in human umbilical vein endothelial cells (HUVECs) in vitro and its underlying mechanism. Our data showed that ATO suppresses angiogenesis and induces autophagy in HUVECs through upregulation of forkhead box protein O3 (FoxO3a). Co-incubated with autophagy inhibitor or knockdown of FoxO3a effectively inhibited ATO-induced autophagy and reversed the antiangiogenic effect of ATO, indicating that ATO-induced autophagy plays an antiangiogenic role in HUVECs. Our results highlight the importance of autophagy in the antiangiogenic effect of ATO and provide an improved understanding of the function of ATO.

Arsenic-induced autophagy regulates apoptosis in AML-12 cells

Arsenic (As), a potent toxicant, is known to be a hepatotoxicant. Although As induced liver apoptosis and autophagy, the relationship between apoptosis and autophagy of hepatocytes caused by As remains largely unknown. 3-methyladenine (3-MA) and rapamycin can inhibit and promote autophagy of AML-12 cells, respectively. Hence, in this study, AML-12 cells were treated with different concentrations (0, 2, 4, 6, 8, 10 and 12 μmol/L) of As₂O₃, and 5 mmol/L 3-MA or 100 nmol/L rapamycin were applied to distinguish the effect of autophagy on apoptosis in AML-12. Results showed that exposure to As induced cell apoptosis and autophagy, which were mediated by the significantly altered expression levels of autophagy markers (mTOR, LC3, PI3K and P62), and apoptosis markers (Bcl-2 and caspase-3). Further analysis indicated that a certain dosage of 3-MA and rapamycin decreased apoptosis and the caspase-3 expression, which suggested that As-induced autophagy regulated AML-12 cells apoptosis through the expressions of PI3K, mTOR, P62 and Bcl-2.

Organelle-specific mechanisms of drug-induced autophagy-dependent cell death

The conserved catabolic process of autophagy is an important control mechanism that degrades cellular organelles, debris and pathogens in autolysosomes. Although autophagy primarily protects against cellular insults, nutrient starvation or oxidative stress, hyper-activation of autophagy is also believed to cause autophagy-dependent cell death (ADCD). ADCD is a caspase-independent form of programmed cell death (PCD), characterized by an over-activation of autophagy, leading to prominent self-digestion of cellular material in autolysosomes beyond the point of cell survival. ADCD plays important roles in the development of lower organisms, but also in the response of cancer cells upon exposure of specific drugs or natural compounds. Importantly, the induction of ADCD as an alternative cell death pathway is of special interest in apoptosis-resistant cancer types and serves as an attractive and potential therapeutic option. Although the mechanisms of ADCD are diverse and not yet fully understood, both non-selective (bulk) autophagy and organelle-specific types of autophagy are believed to be involved in this type of cell death. Accordingly, several ADCD-inducing drugs are known to trigger severe mitochondrial damage and endoplasmic reticulum (ER) stress, whereas the contribution of other cell organelles, like ribosomes or peroxisomes, to the control of ADCD is not well understood. In this review, we highlight the general mechanisms of ADCD and discuss the current evidence for mitochondria- and ER-specific killing mechanisms of ADCD-inducing drugs.

Arsenic induces dysfunctional autophagy via dual regulation of mTOR pathway and Beclin1-Vps34/PI3K complex in MLTC-1 cells

Arsenic poisoning and induced potential lesion is a global concern. However, the exact mechanisms underlying its toxicity especially in male reproductive system still remain unclear. Hence, this study aimed to explore the roles of mTOR and Beclin1-Vps34/PI3K complex during As-induced-toxicity using Rapamycin (mTOR inhibitor), Beclin1 siRNA and 3-methyladenine (3-MA, Vps34/PI3K inhibitor) in testicular stromal cells. For this, mouse testis Leydig Tumor Cell lines (MLTC-1) were challenged with As₂O₃ (0, 3, 6 and 9 μM) exposure for 24 hs. Lyso-Tracker Red and Monodansylcadaverine (MDC) staining results depicted a significant accumulation of autophagosomes in MLTC-1 cells exposed to arsenic. Meanwhile, arsenic treatment up-regulated autophagic markers including LC3, Atg7, Beclin1 and Vps34 expressions, mTOR downstream autophagy related genes and the Beclin1-Vps34/PI3K complex associated members. Furthermore, silencing of Beclin1, and inhibition of Vps34/PI3K and mTOR altered the arsenic-induced autophagosomes formation. However, p62, the substrate protein of autophagy, was also up-regulated by arsenic administration independent on Beclin1-Vps34/PI3K complex. Altogether, our results revealed that arsenic exposure induced autophagosomes formation via regulation of the Beclin1-Vps34/PI3K complex and mTOR pathway; the blockage of autophagosomes degradation maybe due to impaired function of lysosomes. Thus, this study provides a novel mechanistic approach with respect to As-induced male reproductive toxicity.

Arsenic trioxide-induced p38 MAPK and Akt mediated MCL1 downregulation causes apoptosis of BCR-ABL1-positive leukemia cells

In this study, we investigated the mechanisms underlying arsenic trioxide (ATO)-induced death of human BCR-ABL1-positive K562 and MEG-01 cells. ATO-induced apoptotic death in K562 cells was characterized by ROS-mediated mitochondrial depolarization, MCL1 downregulation, p38 MAPK activation, and Akt inactivation. ATO-induced BCR-ABL1 downregulation caused Akt inactivation but not p38 MAPK activation. Akt inactivation increased GSK3β-mediated MCL1 degradation, while p38 MAPK-mediated NFκB activation coordinated with HDAC1 suppressed MCL1 transcription. Inhibition of p38 MAPK activation or overexpression of constitutively active Akt increased MCL1 expression and promoted the survival of ATO-treated cells. Overexpression of MCL1 alleviated mitochondrial depolarization and cell death induced by ATO. The same pathway was found to be involved in ATO-induced death in MEG-01 cells. Remarkably, YM155 synergistically enhanced the cytotoxicity of ATO on K562 and MEG-01 cells through suppression of MCL1 and survivin. Collectively, our data indicate that ATO-induced p38 MAPK- and Akt-mediated MCL1 downregulation triggers apoptosis in K562 and MEG-01 cells, and that p38 MAPK activation is independent of ATO-induced BCR-ABL1 suppression.

Arsenic-induced autophagic alterations and mitochondrial impairments in HPG-S axis of mature male mice offspring (F1-generation): A persistent toxicity study

Arsenic (As) has been implicated in causing reproductive toxicity, but the precise cellular pathway through which the As toxicity in mature F1- male mice hypothalamic-pituitary- gonadal- sperm (HPG-S) axis is induced has not well been documented. Hence, parental mice were treated to As₂O₃ (0, 0.2, 2, and 20 ppm in deionized water) from five weeks before mating until weaning, and the male pups from weaning to maturity. Afterward, the markers of oxidative stress, mitochondrial impairment, and autophagy as fundamental mechanisms of cytotoxicity and organ injury were evaluated. Higher As₂O₃ doses (2 and 20 ppm) were a potent inducer of oxidative stress, mitochondrial dysfunction, and autophagy in HPG-S axis. Concomitant with a dose-dependent increase in the number of MDC-labeled autophagic vacuoles in the HPG axis, an adverse dose-dependent effect was observed on the mean body weight, litter size, organ coefficient, and spermatogenesis. Transmission electron microscopy also revealed more autophagosomes at high As₂O₃ dosage. Concomitant with a dose-dependent increment in gene expression of PI3K, Atg5, Atg12, as well as protein expression of Beclin1, LC3- I, II, P62 in HPG axis tissues and Atg12 in the pituitary; a dose-dependent decrease in mTOR gene expression was recorded in the HPG tissues of mature F₁-males. These observations provide direct evidence that oxidative stress-induced mitochondrial impairments and autophagic cell death, through AMPK/TSC/mTOR and LC3 related pathways, are fundamental mechanisms for As₂O₃- induced toxicity on the reproductive system in mature male mice offspring.

Paternal exposure to arsenic resulted in oxidative stress, autophagy, and mitochondrial impairments in the HPG axis of pubertal male offspring

Despite the knowledge of AS-induced reprotoxicity, the literature concerning arsenic trioxide (As₂O₃)-induced oxidative stress and consequent intracellular events, like autophagy process, in the hypothalamic-pituitary- gonadal (HPG) axis of F1- pubertal male mice is sparse to date. Hence, we made an attempt to study the reproductive toxicities and the underlying mechanisms induced by As₂O₃ in the HPG axis of pubertal F1- male mice in correlation with oxidative stress-induced autophagy. Parental mice were challenged with As₂O₃ (0, 0.2, 2, and 20 ppm) from five weeks before mating, and continued till puberty age for the male pups. It was recorded that higher As₂O₃ doses (2 and 20 ppm) were a potent inducer of oxidative stress and autophagy in the HPG axis. Concomitant with a decrease on mean body weight, total antioxidant capacity, and stereology indices, an increase in the number of MDC-labeled autophagic vacuoles, and MDA/GSH ratio in HPG axis of pubertal F1- male mice which were exposed to higher As₂O₃ doses was observed. Meanwhile, concomitant with a dose-dependent increment in the gene expression of ATG3, ATG5, Beclin, as well as protein expression of P62, ATG12, and Beclin in HPG axis tissues; a dose-dependent decrease in PI3K and mTOR gene expression was recorded in the HPG tissues of pubertal F₁-males. Altogether, our observations suggest that higher doses of As₂O₃ have detrimental effects on the functionality of HPG axis in pubertal male mice offspring by increasing MDA/GSH ratio and autophagic cell death-related genes and proteins, as well as by reducing total antioxidant capacity.

Autophagy in Cancer Cell Death

Autophagy has important functions in maintaining energy metabolism under conditions of starvation and to alleviate stress by removal of damaged and potentially harmful cellular components. Therefore, autophagy represents a pro-survival stress response in the majority of cases. However, the role of autophagy in cell survival and cell death decisions is highly dependent on its extent, duration, and on the respective cellular context. An alternative pro-death function of autophagy has been consistently observed in different settings, in particular, in developmental cell death of lower organisms and in drug-induced cancer cell death. This cell death is referred to as autophagic cell death (ACD) or autophagy-dependent cell death (ADCD), a type of cellular demise that may act as a backup cell death program in apoptosis-deficient tumors. This pro-death function of autophagy may be exerted either via non-selective bulk autophagy or excessive (lethal) removal of mitochondria via selective mitophagy, opening new avenues for the therapeutic exploitation of autophagy/mitophagy in cancer treatment.

Hydroxychloroquine reverses the drug resistance of leukemic K562/ADM cells by inhibiting autophagy

Autophagy is an essential metabolic pathway mediated by lysosomal degradation, which is involved in scavenging and recycling senescent or damaged organelles and biological macromolecules in eukaryotic cells. The present study explored the association between the autophagic activity and chemotherapy resistance of leukaemia cells, and the possibility of using autophagy inhibitors to combat leukemic drug resistance. It was found that the levels of basic autophagy in multidrug‑resistant leukaemia cells (K562/ADM) were significantly higher compared with sensitive cells (K562), and that Adriamycin (ADM) was capable of inducing autophagic activity in K562 and K562/ADM cells. K562 and K562/ADM cells were treated with a series of hydroxychloroquine (HCQ) concentrations to inhibit cellular autophagy and detect cell sensitivity to ADM. The results demonstrated that the sensitivity of K562 cells to ADM was mildly enhanced by HCQ, and that the sensitivity of K562/ADM cells to ADM was markedly strengthened by HCQ. In addition, more typical morphological changes associated with apoptosis emerged, and the ratio of Bax/Bcl‑2 and activity of caspase‑3 were markedly increased in K562/ADM cells treated with HCQ. Notably, the expression of mdr1 mRNA and P‑glycoprotein (P‑gp) in drug‑resistant K562/ADM cells was upregulated along with increasing autophagic activity induced by ADM. Furthermore, HCQ significantly reduced the increase in P‑gp expression by inhibiting autophagic activity. Collectively, these findings indicated that the inhibition of autophagy significantly promoted the sensitivity of K562/ADM cells to ADM by facilitating apoptosis. Furthermore, inhibition of autophagy attenuated the expression of P‑gp; therefore, P‑gp may be involved in autophagic regulation in drug‑resistant cells.

Decitabine shows synergistic effects with arsenic trioxide against myelodysplastic syndrome cells via endoplasmic reticulum stress-related apoptosis

Most of the International Prognostic Scoring System (IPSS) high-risk patients with myelodysplastic syndrome partly responded to hypomethylating therapy even with transient remission, while arsenic trioxide (ATO) had partial effect in patients with MDS. Therefore, we sought to investigate the effects and possible mechanisms of the combination of ATO and decitabine (DAC) in MDS cells. In our study, the MUTZ-1 and SKM-1 cells were treated with ATO, DAC or both. Cell viability, cell apoptosis, levels of reactive oxygen species (ROS) and expressions of the endoplasmicreticulum (ER) stress-associated genes and proteins were examined. Results showed the combination of ATO and DAC synergistically inhibited the proliferation and induced apoptosis of MDS cells. Through the RNA-sequence and GSEA gene function analysis, ER stress-related pathway played an important role in apoptosis of MDS cells induced by the combination of ATO and DAC. ER stress-related genes DNA damage inducible transcript 3, GRP78, and activating transcription factor-6 were significantly highly expressed in combination group than those in single agent groups; proteins were confirmed by western blot. The levels of ROS significantly increased in the combination group. Furthermore, the apoptosis of (ATO+DAC) group MDS cells could be partially reversed by antioxidant agent N-acetylcysteine, accompanied by decreased expression of intracellular ROS and ER stress-related genes. These results suggested that the combination of ATO and DAC synergistically induced the apoptosis of MDS cells by increased ROS-related ER stress in MDS cells.

Therapeutic Modulation of Autophagy in Leukaemia and Lymphoma

Haematopoiesis is a tightly orchestrated process where a pool of hematopoietic stem and progenitor cells (HSPCs) with high self-renewal potential can give rise to both lymphoid and myeloid lineages. The HSPCs pool is reduced with ageing resulting in few HSPC clones maintaining haematopoiesis thereby reducing blood cell diversity, a phenomenon called clonal haematopoiesis. Clonal expansion of HSPCs carrying specific genetic mutations leads to increased risk for haematological malignancies. Therefore, it comes as no surprise that hematopoietic tumours develop in higher frequency in elderly people. Unfortunately, elderly patients with leukaemia or lymphoma still have an unsatisfactory prognosis compared to younger ones highlighting the need to develop more efficient therapies for this group of patients. Growing evidence indicates that macroautophagy (hereafter referred to as autophagy) is essential for health and longevity. This review is focusing on the role of autophagy in normal haematopoiesis as well as in leukaemia and lymphoma development. Attenuated autophagy may support early hematopoietic neoplasia whereas activation of autophagy in later stages of tumour development and in response to a variety of therapies rather triggers a pro-tumoral response. Novel insights into the role of autophagy in haematopoiesis will be discussed in light of designing new autophagy modulating therapies in hematopoietic cancers.

The suppressive effect of arsenic trioxide on TET2-FOXP3-Lyn-Akt axis-modulated MCL1 expression induces apoptosis in human leukemia cells

Arsenic trioxide (ATO) has been reported to inhibit the activity of Ten-eleven translocation methylcytosine dioxygenase (TET). TET modulates FOXP3 expression, while dysregulation of FOXP3 expression promotes the malignant progression of leukemia cells. We examined the role of TET-FOXP3 axis in the cytotoxic effects of ATO on the human acute myeloid leukemia cell line, U937. ATO-induced apoptosis in U937 cells was characterized by activation of caspase-3/-9, mitochondrial depolarization, and MCL1 downregulation. In addition, ATO-treated U937 cells showed ROS-mediated inhibition of TET2 transcription, leading to downregulation of FOXP3 expression and in turn, suppression of FOXP3-mediated activation of Lyn and Akt. Overexpression of FOXP3 or Lyn minimized the suppressive effect of ATO on Akt activation and MCL1 expression. Promoter luciferase activity and chromatin immunoprecipitation assays revealed the crucial role of Akt-mediated CREB phosphorylation in MCL1 transcription. Further, ATO-induced Akt inactivation promoted GSK3β-mediated degradation of MCL1. Transfection of constitutively active Akt expression abrogated ATO-induced MCL1 downregulation. MCL1 overexpression lessened the ATO-induced depolarization of mitochondrial membrane and increased the viability of ATO-treated cells. Thus, our data suggest that ATO induces mitochondria-mediated apoptosis in U937 cells through its suppressive effect on TET2-FOXP3-Lyn-Akt axis-modulated MCL1 transcription and protein stabilization. Our findings also indicate that the same pathway underlies ATO-induced death in human leukemia HL-60 cells.

Autophagy in cancer: a complex relationship

Macroautophagy is the process by which cells package and degrade cytosolic components, and recycle the breakdown products for future use. Since its initial description by Christian de Duve in the 1960s, significant progress has been made in understanding the mechanisms that underlie this vital cellular process and its specificity. Furthermore, macroautophagy is linked to pathologic conditions such as cancer and is being studied as a therapeutic target. In this review, we will explore the connections between autophagy and cancer, which are tumor- and context-dependent and include the tumor microenvironment. We will highlight the importance of tumor compartment-specific autophagy in both cancer aggressiveness and treatment.

Arsenic trioxide inhibits glioma cell growth through induction of telomerase displacement and telomere dysfunction

Glioblastomas are resistant to many kinds of treatment, including chemotherapy, radiation and other adjuvant therapies. As₂O₃ reportedly induces ROS generation in cells, suggesting it may be able to induce telomerase suppression and telomere dysfunction in glioblastoma cells. We show here that As₂O₃ induces ROS generation as well as telomerase phosphorylation in U87, U251, SHG4 and C6 glioma cells. It also induces translocation of telomerase from the nucleus to the cytoplasm, thereby decreasing total telomerase activity. These effects of As₂O₃ trigger an extensive DNA damage response at the telomere, which includes up-regulation of ATM, ATR, 53BP1, γ-H₂AX and Mer11, in parallel with telomere fusion and 3′-overhang degradation. This ultimately results in induction of p53- and p21-mediated cell apoptosis, G2/M cell cycle arrest and cellular senescence. These results provide new insight into the antitumor effects of As₂O₃ and can perhaps contribute to solving the problem of glioblastoma treatment resistance.

Differences of basic and induced autophagic activity between K562 and K562/ADM cells

Patients with acute myeloid leukemia (AML) often have a poor prognosis due to drug resistance, which is regarded as a tough problem during the period of clinical therapeutics. It has been reported that autophagy, an important event in various cellular processes, plays a crucial role in mediating drug-resistance to cancer cells. Our study attempts to comparatively investigate the differences of basic and induced autophagic activity between drug-sensitive and multidrug-resistant AML cells. The level of basic autophagy in K562/ADM cells was higher than that in K562 cells, which could be characterized by more cytosolic contents-packaged autophagic vacuoles in K562/ADM cells when compared to that in K562 cells. The observation of MDC staining showed that the fluorescent intensity of autophagosomes in K562/ADM cells was stronger than that in K562 cells. The expression of Beclin1 and the ratio of LC3-II to LC3-I were distinctly higher in K562/ADM cells, however, P62 protein was relatively lower in K562/ADM cells. Furthermore, we found that nutrient depletion could induce autophagic activity of both cell lines. However, autophagic activity of K562/ADM cells was always maintained at a higher level in contrast with K562 cells. ADM (Adriamycin) was also capable of inducing autophagic activity of K562 and K562/ADM cells, but the autophagic alteration in K562 cells appeared earlier. Taken together, our findings suggest that autophagy exerts an important effect on formation and maintenance of drug-resistance in AML cells.

Ouabain induces apoptosis and autophagy in Burkitt's lymphoma Raji cells

The steroid Na+/K+-ATPase blocker ouabain has been shown to exhibit cytotoxic effects in various tumor cell systems. This study aimed to determine the effects of ouabain on Burkitt's lymphoma Raji cells. Ouabain treatment of Raji cells significantly inhibited cell proliferation in a dose-dependent manner and increased the morphological changes associated with apoptosis. Additionally, increased numbers of both early and late apoptotic cells were observed by annexin V-FITC/PI flow cytometry assay. Increased levels of caspase-3 and cleaved-caspase-3, higher Bax activity and decreased expression of the anti-apoptotic protein Bcl-2 were detected in ouabain-treated Raji cells. Vacuole accumulation was also observed in transmission electron microscope (TEM) images of ouabain-treated Raji cells, indicating that these cells were undergoing autophagy. Expression of the autophagy-related proteins LC3-II and Beclin-1 was upregulated in ouabain-treated Raji cells. These results suggest that ouabain may promote cell death in Raji cells by inducing pathways associated with apoptosis and autophagy. Our study also provides novel evidence that ouabain may be an effective agent for treating Burkitt's lymphoma.

Insulin resistance contributes to multidrug resistance in HepG2 cells via activation of the PERK signaling pathway and upregulation of Bcl-2 and P-gp

Liver tumorigenesis frequently causes insulin resistance which may be used as an independent risk factor for evaluation of survival and post-surgery relapse of liver cancer patients. In the present study, HepG2/IR, an insulin resistant HepG2 cell line, was established by exposing HepG2 cells to 0.5 µmol/l of insulin for 72 h, and comparison of HepG2/IR with the parental HepG2 cells indicated that the HepG2/IR cells showed significantly enhanced resistance to the most frequently used chemotherapeutics for solid tumors, such as cisplatin, 5-fluorouracil, vincristine and mitomycin. Flow cytometric analysis of cisplatin-treated HepG2/IR cells showed a significantly decreased hypodiploid peak and a significantly downregulated expression level of pro-apoptotic protein caspase-3 compared with the parental HepG2 cells. Our data further showed swollen endoplasmic reticulum (ER) in the cisplatin-treated HepG2/IR cells with significantly increased levels of glucose-regulated protein 78 (GRP78), phosphorylated protein kinase R-like ER kinase (p-PERK) and P-glycoprotein (P-gp). There was also an upregulated expression of anti-apoptotic protein B-cell lymphoma 2 (Bcl-2) whereas no significant change was observed for CCAAT-enhancer-binding protein homologous protein (CHOP), which is known to be induced by ER stress and to mediate apoptosis. Our results demonstrated that insulin resistance in HepG2 cells promoted a protective unfolded protein response and upregulated the expression of ER chaperone protein GRP78, which resulted in the phosphorylation of PERK kinase to activate the PERK-mediated ER stress signal transduction pathway and the upregulation of Bcl-2 and P-gp, leading to the inhibition of the caspase-3-dependent apoptosis pathway and to the survival of liver tumor cells.