Autophagy contributes to 4-Amino-2-Trifluoromethyl-Phenyl Retinate-induced differentiation in human acute promyelocytic leukemia NB4 cells

Current Understanding of the Role of Autophagy in the Treatment of Myeloid Leukemia

The most important issues in acute myeloid leukemia are preventing relapse and treating relapse. Although the remission rate has improved to approximately 80%, the 5-year survival rate is only around 30%. The main reasons for this are the high relapse rate and the limited treatment options. In chronic myeloid leukemia patients, when a deep molecular response is achieved for a certain period of time through tyrosine kinase inhibitor treatment, about half of them will reach treatment-free remission, but relapse is still a problem. Therefore, potential therapeutic targets for myeloid leukemias are eagerly awaited. Autophagy suppresses the development of cancer by maintaining cellular homeostasis; however, it also promotes cancer progression by helping cancer cells survive under various metabolic stresses. In addition, autophagy is promoted or suppressed in cancer cells by various genetic mutations. Therefore, the development of therapies that target autophagy is also being actively researched in the field of leukemia. In this review, studies of the role of autophagy in hematopoiesis, leukemogenesis, and myeloid leukemias are presented, and the impact of autophagy regulation on leukemia treatment and the clinical trials of autophagy-related drugs to date is discussed.

ATPR induces acute promyelocytic leukemia cells differentiation and cycle arrest via the lncRNA CONCR/DDX11/PML-RARα signaling axis

Acute promyelocytic leukemia (APL) is a type of acute myeloid leukemia (AML) with a high mortality rate, and the production of PML-RARα fusion protein is the cause of its pathogenesis. Our group has synthesized a novel compound, 4-amino-2-trifluoromethyl-phenyl retinate (ATPR), by structural modification of All-trans retinoic acid (ATRA), which has strong cell differentiation-inducing effects and inhibits the expression of PML-RARα. In this study, acute promyelocytic leukemia NB4 cells before and after ATPR induction were analyzed by whole transcriptome microarray, and the expression of lncRNA CONCR was found to be significantly downregulated. The role of CONCR in ATPR-induced cell differentiation and cycle arrest was explored through overexpression and silencing of CONCR. And then the database was used to predict that CONCR may bind to DEAD/H-Box Helicase 11 (DDX11) protein to further explore the role of CONCR binding to DDX11. The results showed that ATPR could reduce the expression of CONCR, and overexpression of CONCR could reverse the ATPR-induced cell differentiation and cycle blocking effect, and conversely silencing of CONCR could promote this effect. RNA immunoprecipitation (RIP) experiments showed that CONCR could bind to DDX11, the protein expression levels of DDX11 and PML-RARα were elevated after overexpression of CONCR. These results suggest that ATPR can regulate the expression of DDX11 through CONCR to affect the expression of PML-RARα fusion protein, which in turn induces the differentiation and maturation of APL cells.

Potential applications of ferroptosis inducers and regulatory molecules in hematological malignancy therapy

Ferroptosis, a novel form of iron-dependent cell death, has emerged as a potential avenue for promoting tumor cell death by causing cell membrane rupture and the accumulation of lipid peroxides (LPO) in the cell. Since its discovery in 2012, extensive research has been conducted to explore the mechanism of ferroptosis inducers, including erastin, sulfasalazine, and sorafenib. These compounds inhibit system XC-, while Ras-selective lethal small molecule 3 (RSL3) and FION2 specifically target GPX4 to promote ferroptosis. Therefore, targeting ferroptosis presents a promising therapeutic approach for malignant tumors. While the study of ferroptosis in solid tumors has made significant progress, there is limited information available on its role in hematological tumors. This review aims to summarize the molecular mechanisms of ferroptosis inducers and discuss their clinical applications in hematological malignancies. Furthermore, the identification of non-coding RNAs (ncRNAs) and genes that regulate key molecules in the ferroptosis pathway could provide new targets and establish a molecular theoretical foundation for exploring novel ferroptosis inducers in hematological malignancies.

Susceptibility of acute myeloid leukemia cells to ferroptosis and evasion strategies

Acute myeloid leukemia (AML) is a highly aggressive hematologic malignancy with a 5-year survival rate of less than 30%. Continuous updating of diagnostic and therapeutic strategies has not been effective in improving the clinical benefit of AML. AML cells are prone to iron metabolism imbalance due to their unique pathological characteristics, and ferroptosis is a novel cell death mode that is dominated by three cellular biological processes: iron metabolism, oxidative stress and lipid metabolism. An in-depth exploration of the unique ferroptosis mechanism in AML can provide new insights for the diagnosis and treatment of this disease. This study summarizes recent studies on ferroptosis in AML cells and suggests that the metabolic characteristics, gene mutation patterns, and dependence on mitochondria of AML cells greatly increase their susceptibility to ferroptosis. In addition, this study suggests that AML cells can establish a variety of strategies to evade ferroptosis to maintain their survival during the process of occurrence and development, and summarizes the related drugs targeting ferroptosis pathway in AML treatment, which provides development directions for the subsequent mechanism research and clinical treatment of AML.

Ferroptosis in acute leukemia

ABSTRACT

Ferroptosis is an iron-dependent cell death pathway that is different from apoptosis, pyroptosis, and necrosis. The main characteristics of ferroptosis are the Fenton reaction mediated by intracellular free divalent iron ions, lipid peroxidation of cell membrane lipids, and inhibition of the anti-lipid peroxidation activity of intracellular glutathione peroxidase 4 (GPX4). Recent studies have shown that ferroptosis can be involved in the pathological processes of many disorders, such as ischemia-reperfusion injury, nervous system diseases, and blood diseases. However, the specific mechanisms by which ferroptosis participates in the occurrence and development of acute leukemia still need to be more fully and deeply studied. This article reviews the characteristics of ferroptosis and the regulatory mechanisms promoting or inhibiting ferroptosis. More importantly, it further discusses the role of ferroptosis in acute leukemia and predicts a change in treatment strategy brought about by increased knowledge of the role of ferroptosis in acute leukemia.

Silymarin in combination with ATRA enhances apoptosis induction in human acute promyelocytic NB4 cells

Although all-trans retinoic acid (ATRA) is an efficient pattern in acute promyelocytic leukemia (APL) therapy, further studies are required due to the extant clinical limitations of ATRA. It has been reported that Silymarin, an anti-cancer herbal substance extracted from milk thistle (Silybum marianum), is able to regulate apoptosis in various types of cancer cells through different mechanisms of action. This study investigated the apoptosis-inducing effect of Silymarin (SM) alone and in combination with ATRA on human acute promyelocytic NB4 cells. Examination using MTT assay indicated that SM treatment leads to growth inhibition in NB4 cells in a dose-dependent manner. The IC50 values of SM and ATRA were calculated 90 μM and 2 μM, respectively. Cell cycle analysis by flow cytometry revealed that a more increase in the sub-G1 phase (a sign of apoptosis) when cells were exposed to SM in combination with ATRA. The incidence of apoptosis was confirmed through Hoechst 33258 staining and Annexin V-FITC analysis. The results showed that Silymarin enhances ATRA-induced apoptosis. The flow cytometric analysis also indicated an enhancement in levels of ROS in the treated cells with both compounds. The real-time PCR illustrated that SM targets apoptosis by down-regulation in Survivin and Bcl-2 while up-regulation in Bax. The findings showed that the combination of the two compounds is more effective in the induction of apoptosis in NB4 cells. Molecular docking studies indicated that Sylibin, as a primary compound of the SM, binds to the BH3 domain of Bcl-2 and the BIR domain of Survivin with various affinities. Based on the findings, it seems that SM used alone and in combination with ATRA may be beneficial for inducing apoptosis in APL cells.

Targeting ferroptosis contributes to ATPR-induced AML differentiation via ROS-autophagy-lysosomal pathway

Ferroptosis, a newly discovered form of non-apoptotic cell death, is induced by an excessive degree of iron-dependent lipid peroxide. ATPR, a novel all-trans retinoic acid (ATRA) derivative, has been extensively developed to show superior anticancer effect than ATRA in acute myeloid leukemia (AML). However, whether ferroptosis exists during ATPR treatment of AML remains unclear. Herein, we found that ferroptosis occurred in an AML xenograft mouse model of ATPR treatment. In vitro, ATPR was verified to induce ferroptosis in a dose-dependent manner by proferroptotic protein marker, lipid peroxidation, and lipid ROS, which could be significantly reversed by ferrostatin-1. Using lysosomal inhibitor chloroquine and iron chelator desferrioxamine, we further revealed that ATPR-induced ferroptosis was regulated by autophagy via iron homeostasis, especially Nrf2. Furthermore, targeting ferroptosis contributes to ATPR-induced AML differentiation. In conclusion, these results indicated that ferroptosis play an important role in ATPR-induced differentiation, and suggested that ATPR would provide a potential therapeutic value for AML treatment.

ATPR triggers acute myeloid leukaemia cells differentiation and cycle arrest via the RARα/LDHB/ERK-glycolysis signalling axis

Acute myeloid leukaemia (AML) remains a therapeutic challenge and improvements in chemotherapy are needed. 4‐Amino‐2‐trifluoromethyl‐phenyl retinate (ATPR), a novel all‐trans retinoic acid (ATRA) derivative designed and synthesized by our team, has been proven to show superior anticancer effect compared with ATRA on various cancers. However, its potential effect on AML remains largely unknown. Lactate dehydrogenase B (LDHB) is the key glycolytic enzyme that catalyses the interconversion between pyruvate and lactate. Currently, little is known about the role of LDHB in AML. In this study, we found that ATPR showed antileukaemic effects with RARα dependent in AML cells. LDHB was aberrantly overexpressed in human AML peripheral blood mononuclear cell (PBMC) and AML cell lines. A lentiviral vector expressing LDHB‐targeting shRNA was constructed to generate a stable AML cells with low expression of LDHB. The effect of LDHB knockdown on differentiation and cycle arrest of AML cells was assessed in vitro and vivo, including involvement of Raf/MEK/ERK signalling. Finally, these data suggested that ATPR showed antileukaemic effects by RARα/LDHB/ ERK‐glycolysis signalling axis. Further studies should focus on the underlying leukaemia‐promoting mechanisms and investigate LDHB as a therapeutic target.

LncRNA NR-104098 Inhibits AML Proliferation and Induces Differentiation Through Repressing EZH2 Transcription by Interacting With E2F1

Abundant evidence has illustrated that long non-coding RNA (lncRNA) plays a vital role in the regulation of tumor development and progression. Most lncRNAs have been proven to have biological and clinical significance in acute myeloid leukemia (AML), but further investigation remains necessary. In this study, we investigated lncRNA NR-104098 in AML and its specific mechanism. The microarray analysis was performed on NB4 cells. Based on the related analysis results, we identified that lncRNA NR-104098 is a suppressor gene that is significantly upregulated in AML cells. LncRNA NR-104098 could inhibit proliferation and induce differentiation in AML cells in vitro and also play main role in the mouse xenografts. Mechanically, it was confirmed that lncRNA NR-104098 may effectively inhibit EZH2 transcription by directly binding to E2F1 and recruiting E2F1 to the EZH2 promoter. In addition, ATPR can significantly increase the expression of lncRNA NR-104098, whereas knocking down NR104098 can inhibit the inhibitory effect of ATPR on the proliferation and induction differentiation of AML cells. Taken together, these results lead to deeper insight into the mechanism of ATPR-induced AML differentiation and prevent proliferation by inhibiting EZH2 on the transcriptional level.

ATRA induces the differentiation of hepatic progenitor cells by upregulating microRNA-200a

Hepatic progenitor cells (HPCs) are potential seed cells for hepatocyte transplantation treatment of liver diseases. ATRA can induce the differentiation and mature function of hepatic progenitor cells, but the mechanism is still poorly understood. Here, by using microRNA array to analyze the expression profiles of microRNA (miR), we found that miR-200 family molecules in HPCs were upregulated after ATRA treatment, especially miR-200a-3p, 200c-3p, and 141-3p. ATRA induction could downregulate the expression of hepatic stem markers Oct4 and AFP, and improve the expression of hepatic markers ALB, CK18, and TAT, and the activity of ALB-GLuc, as well as indocyanine green uptake and glycogen storage function of HPCs. These above effects of ATRA on HPC differentiation were almost inhibited by blocking of miR-200a-3p, but not miR-200c-3p and 141-3p using antagomir. Cell autophagy is associated with ATRA regulation in HPCs, compared with control group, the expression of LC3 and Beclin1 increased in ATRA-treated HPCs, and orange and red fluorescent spot, which represents autophagy flow, also enhanced after ATRA treatment. However, ATRA-induced cell autophagy level was inhibited in antagomir-200a-3p+ATRA-treated cells. Therefore, the present study indicates that antagomir-200a-3p is related to ATRA-induced hepatic differentiation of HPCs through regulating cell autophagy, supporting the possible use of ATRA as a key inducer in HPC-based therapy of liver diseases.

ATPR-induced differentiation and G0/G1 phase arrest in acute promyelocytic leukemia by repressing EBP50/NCF1 complex to promote the production of ROS

Our previous study has demonstrated that 4-amino-2-trifluoromethyl-phenyl Retinate (ATPR) can induce human leukemia NB4 cells differentiation and G0/G1 phase arrest, but the underlying mechanism is still unclear. In this study, we used proteomics to screen differentially expressed protein profiles in NB4 cells before and after ATPR treatment in vitro. We analyzed the peptides digested from total cellular proteins by reverse phase LC-MS/MS and then performed label-free quantitative analysis. We found 27 significantly up-regulated proteins in the ATPR group compared to the control group. NCF1 was the most significantly changed protein. Immunoprecipitation and double immunofluorescent staining showed that EBP50 bind to NCF1. We further explored the potential molecular mechanism of EBP50/NCF1 complex in ATPR-induced differentiation and G0/G1 phase arrest. The results showed that ATPR remarkably reduced the expression of EBP50 in vivo and in vitro. Interestingly, the reduction of EBP50 contributed to ROS release by modulating the subcellular localization of NCF1. The reduction of EBP50 also contributed to G0/G1 phase arrest by inhibiting CyclinD1, CyclinA2 and CDK4, as well as promoting the differentiation of NB4 cells by increasing the expression of CD11b. Furthermore, we found that the overexpression of EBP50 restrained the effects of ATPR on differentiation and G0/G1 phase arrest in NB4 cells. These results suggest that ATPR-induced differentiation and G0/G1 phase arrest in acute promyelocytic leukemia (APL) by repressing EBP50/NCF1 complex to promote the production of ROS, and the results from in vivo experiments were consistent with those from in vitro studies. Therefore, our finding results suggest that EBP50 may be a new target for ATPR in the treatment of APL.

Role of eIF3a in 4-amino-2-trifluoromethyl-phenyl retinate-induced cell differentiation in human chronic myeloid leukemia K562 cells

4-amino-2-trifluoromethyl-phenyl retinate (ATPR), a novel all-trans retinoic acid (ATRA) derivative designed and synthesized by our team, has been demonstrated its anti-tumor effect through inducing differentiation and inhibiting proliferation. Eukaryotic initiation factor 3a (eIF3a) plays a critical role in affecting tumor cell proliferation and differentiation. However, whether eIF3a is implicated in chronic myeloid leukemia cells differentiation remains unclear. Our results demonstrated that eIF3a could be suppressed by ATPR in K562 cells. The results also confirmed that ATPR could arrest cell cycle in G0/G1 phase and induced differentiation. Moreover, over-expression of eIF3a promoted not only protein expression of c-myc and cyclin D1, but also prevented the expression of p-Raf-1, p-ERK and the myeloid differentiation markers CD11b and CD14 and had an influence on inducing the morphologic mature. However, silencing eIF3a expression by small interfering RNA could have an adverse effect on K562 cells. In addition, PD98059 (a MEK inhibitor) could block cell differentiation of CML cells and contributed to the expression of c-myc and cyclin D1. In conclusion, these results indicated that eIF3a played an important role in ATPR-induced cell differentiation in K562 cells, its mechanism might be related to its ability in regulating the activation of ERK1/2 signaling pathway in vitro.

RACK1 deficiency synergizes with all-trans retinoic acid to induce apoptosis in human acute promyelocytic leukemia cells

As a classic differentiation agent, all-trans retinoic acid (ATRA) has been widely used in the treatment of acute promyelocytic leukemia (APL). However, the clinical application of ATRA has strict limitations, for its severe side effects due to the accumulation of peripheral blood leukocytes. The scaffold protein RACK1 (Receptor for activated C kinase 1), which regulates multiple signaling pathways, has been proposed to contribute to the survival of leukemic progenitors. But it remains unclear whether it is also involved in the oncogenic growth of APL. In the present study, we demonstrate that silencing of endogenous RACK1 expression synergized with ATRA to promote the death of NB4 and HL-60 APL cells without effect on cell differentiation induced by ATRA. Interestingly, RACK1 knockdown combined with ATRA treatment mainly induces apoptosis. It is distinct to the necrotic cell death induced by idarubicin in combination with ATRA, a regimen extensively used in the clinic to prevent neutrophil accumulation. Further exploration revealed that the lysosome-autophagy pathway is likely to be responsible for the anti-apoptotic role of RACK1. Taken together, our findings indicate that RACK1 is essential in maintaining the malignant features of APL, and targeting RACK1 may have promising therapeutic implications in the treatment of APL.

Ginkgo biloba exocarp extracts induces autophagy in Lewis lung cancer cells involving AMPK / mTOR / p70S6k signaling pathway

OBJECTIVES

Ginkgo biloba L. is called a living fossil plant, and could be used for the treatment of cancer thousands of years ago in China. The extracts prepared from the Ginkgo biloba exocarp (Ginkgo biloba exocarp extracts, GBEE) has a significant anti-cancer effect. Autophagy plays an important role in the occurrence and development of cancer as programmed cell death (PCD) type II. Thus it would be interesting to study the effects and mechanisms of GBEE inducing autophagy in Lewis lung cancer (LLC) cells.

METHODS

MTT method was used to detect the inhibitory effect of GBEE on LLC cells. Monodansylcadaverine (MDC) staining method was applied to observe the formation of acidic vacuoles in cells. The ultrastructure of LLC cells was observed using transmission electron microscope (TEM) to confirm the formation of autophagosomes. Quantify reverse transcription-polymerase chain reaction (qRT-PCR) was used to detect the mRNA levels of Beclin1 and Atg5. Western Blot was used to detect the protein levels of Beclin1, Atg5, LC3I/II, p-AMPK, AMPK, p-mTOR, mTOR, p-p70S6k and p70S6K in LLC cells.

RESULTS

GBEE (5-160μg/mL) inhibited the proliferation of LLC cells in vitro with the half maximal inhibitory concentration (IC50) value of 161.26μg/mL. The formation and activation of acidic vacuoleswere increased by the action of GBEE (10, 20 and 40μg/mL) on LLC cells. The autophagosomes were also increased. Meanwhile, it up-regulated both the mRNA and protein levels of Beclin1 and Atg5. The ratio of LC3-I/LC3-II protein was down-regulated. In addition, the protein level of p-AMPK was increased, and the p-mTOR and p-p70S6K was decreased. But the AMPK, mTOR and p70S6K proteins were not significantly changed.

CONCLUSIONS

The inhibitory effect of GBEE on LLC is associate with inducing autophagy in LLC cells, which may be closely relevant to the regulation of AMPK/mTOR/p70S6k signaling pathways.