The Role of AMPK/mTOR Modulators in the Therapy of Acute Myeloid Leukemia

Rapamycin increases leukemia cell sensitivity to chemotherapy by regulating mTORC1 pathway-mediated apoptosis and autophagy

This study investigated the effect of rapamycin alone and in combination with chemotherapy (doxorubicin and cytarabine) on AML. Human acute monocytic leukemia cell line SHI-1 and NPG AML model mice created by intravenous injection of SHI-1 cell were treated with rapamycin, chemotherapy, or rapamycin plus chemotherapy. Analysis by cell counting kit-8, western blot, flow cytometry, and immunohistochemistry was performed, and results suggested that both rapamycin and chemotherapy inhibited proliferation of SHI-1 cells both in vitro and in vivo, suppressed neoplasm growth in vivo, and promoted survival of NPG AML mice. The antitumor effect of rapamycin plus chemotherapy was better than that of rapamycin alone and chemotherapy alone. In addition, western blot results demonstrated that rapamycin inhibited the phosphorylation of mTOR downstream targets 4EBP1 and S6K1 in SHI-1 cells, and increased the pro-apoptosis-related protein Bax and autophagy-associated proteins Beclin-1, LC3B-II, and ATG5 while reducing the anti-apoptosis-related protein Bcl-2. In conclusion, the results of this study indicate that rapamycin acts synergistically with doxorubicin and cytarabine in AML treatment, and its underlying mechanism might be associated with mTORC1 pathway-mediated apoptosis and autophagy.

The Role of Autophagy and Apoptosis in the Combined Action of Plasma-Treated Saline, Doxorubicin, and Medroxyprogesterone Acetate on K562 Myeloid Leukaemia Cells

The anti-cancer properties of plasma-treated solutions (PTS) and their interaction with drugs are one of the most popular topics in modern plasma medicine. Our research involved comparing the effects of four physiological saline solutions (0.9% NaCl, Ringer’s solution, Hank’s Balanced Salt Solution, Hank’s Balanced Salt Solution with amino acids added in concentrations observed in the human blood) treated with cold atmospheric plasma and studying the combined cytotoxic effect of PTS with doxorubicin and medroxyprogesterone acetate (MPA). Analysis of the effect of the studied agents on the formation of radicals in the incubation medium, the vitality of K562 myeloid leukaemia cells, and the processes of autophagy and apoptosis in them revealed two key findings. The first is that when using PTS and doxorubicin-containing PTS, autophagy is the predominant process in cancer cells. The second is that combining PTS with MPA enhances apoptotic processes. It was hypothesised that while autophagy is stimulated by the accumulation of reactive oxygen species in the cell, apoptosis is stimulated through specific cell progesterone receptors.

Epigenome-wide association studies of occupational exposure to benzene and formaldehyde

Sufficient evidence supports a relationship between certain myeloid neoplasms and exposure to benzene or formaldehyde. DNA methylation could underlie benzene- and formaldehyde-induced health outcomes, but data in exposed human populations are limited. We conducted two cross-sectional epigenome-wide association studies (EWAS), one in workers exposed to benzene and another in workers exposed to formaldehyde. Using HumanMethylation450 BeadChips, we investigated differences in blood cell DNA methylation among 50 benzene-exposed subjects and 48 controls, and among 31 formaldehyde-exposed subjects and 40 controls. We performed CpG-level and regional-level analyses. In the benzene EWAS, we found genome-wide significant alterations, i.e., FWER-controlled P-values <0.05, in the mean and variance of methylation at 22 and 318 CpG sites, respectively, and in mean methylation of a large genomic region. Pathway analysis of genes corresponding to benzene-associated differential methylation sites revealed an impact on the AMPK signalling pathway. In formaldehyde-exposed subjects compared to controls, 9 CpGs in the DUSP22 gene promoter had genome-wide significant decreased methylation variability and a large region of the HOXA5 promoter with 44 CpGs was hypomethylated. Our findings suggest that DNA methylation may contribute to the pathogenesis of diseases related to benzene and formaldehyde exposure. Aberrant expression and methylation of HOXA5 previously has been shown to be clinically significant in myeloid leukaemias. The tumour suppressor gene DUSP22 is a potential biomarker of exposure to formaldehyde, and irregularities have been associated with multiple exposures and diseases.

13-Acetoxysarcocrassolide induces apoptosis in human hepatocellular carcinoma cells through mitochondrial dysfunction and suppression of the PI3K/AKT/mTOR/p70S6K signalling pathway

CONTEXT

13-Acetoxysarcocrasside, isolated from the Taiwanese soft coral Sarcophyton crassocaule Moser (Alcyoniidae), has biological activity and induces apoptosis in hepatocellular carcinoma cells.

OBJECTIVE

To elucidate the mechanisms underlying apoptosis induced by 13-acetoxysarcocrasside in HA22T and HepG2 hepatocellular carcinoma cells.

MATERIAL AND METHODS

MTT and morphology assays were employed to assess the anti-proliferative effects of 13-acetoxysarcocrasside (1-5 μM). TUNEL/DAPI staining and annexin V-fluorescein isothiocyanate/propidium iodide staining were used to detect apoptosis. Cells were treated with13-acetoxysarcocrassolide (0, 1, 2, and 4 μM) for 24 h, and the mechanism of cells apoptotic was detected by western blotting. Cells treated with DMSO were the control.

RESULTS

Survival of the cells decreased with the addition of 13-acetoxysarcocrassolide, and at 4 μM cell survival was inhibited by approximately 40%. After treatment of cells with 13-acetoxysarcocrassolide, the incidence of early/late apoptosis to be 0.3%/0.5%∼5.4%/22.7% for HA22T cells, in the HePG2 cells were 0.6%/0.2%∼14.4%/23.7%. Western blotting analysis showed that the expression of Bax, Bad, cleaved caspase 3, cleaved caspase 9, cleaved-PARP-1, cytochrome c, and p-4EBP1 increased with an increasing concentration of 13-acetoxysarcocrasside (0, 1, 2, and 4 μM), whereas that of Bcl-2, Bcl-xL, Mcl-1, p-Bad, p-PI3K, p-AKT, p-mTOR, p-70S6K, p-S6, p-eIF4E, and p-eIF4B decreased.

DISCUSSION AND CONCLUSIONS

Apoptosis induced by 13-acetoxysarcocrassolide in HA22T and HepG2 cells is mediated by mitochondrial dysfunction and inactivation of the PI3K/AKT/mTOR/p70S6K pathway. The potential of 13-acetoxysarcocrassolide as a chemotherapeutic agent should be further assessed for use in human hepatocellular carcinoma treatment.

Quercetin induces autophagy-associated death in HL-60 cells through CaMKKβ/AMPK/mTOR signal pathway

Acute myeloid leukemia (AML) is one of the most common malignancies of the hematopoietic progenitor cell in adults. Quercetin has gained recognition over the years because of its anti-cancer effect with minimal toxicity. Herein, we aim to investigate the anti-leukemia mechanism of quercetin and to decipher the signaling pathway of quercetin in HL-60 leukemic cells. We observed that quercetin induces apoptosis and autophagic cell death, in which both pathways play an important role in suppressing the viability of leukemia cells. Phosphorylated AMPK (p-AMPK) protein expressions are lower in primary AML cells, HL-60 cells, KG-1 and THP-1 cells than in peripheral blood monocular cells. After quercetin treatment, the expression of p-AMPK is increased while the expression of p-mTOR is decreased in a dose-dependent manner. Mechanistically, compound C, an AMPK phosphorylation inhibitor, upregulates the phosphorylation of mTOR and inhibits autophagy and apoptosis in quercetin-induced HL-60 cells, while silencing of CaMKKβ inhibits the quercetin-induced phosphorylation of AMPK, resulting in increased mTOR phosphorylation. Furthermore, silencing of CaMKKβ inhibits the autophagy in HL-60 cells. Taken together, our data delineate that quercetin plays its anti-leukemia role by inhibiting cell viability and inducing apoptosis and autophagy in leukemia cells. Quercetin inhibits the phosphorylation of mTOR by regulating the activity of AMPK, thus playing a role in the regulation of autophagy and apoptosis. CaMKKβ is a potential upstream molecule for AMPK/mTOR signaling pathway, through which quercetin induces autophagy in HL-60 cells.

Phosphoproteomics Reveals the AMPK Substrate Network in Response to DNA Damage and Histone Acetylation

AMP-activated protein kinase (AMPK) is a conserved energy sensor that plays roles in diverse biological processes via phosphorylating various substrates. Emerging studies have demonstrated the regulatory roles of AMPK in DNA repair, but the underlying mechanisms remain to be fully understood. Herein, using mass spectrometry-based proteomic technologies, we systematically investigate the regulatory network of AMPK in DNA damage response (DDR). Our system-wide phosphoproteome study uncovers a variety of newly-identified potential substrates involved in diverse biological processes, whereas our system-wide histone modification analysis reveals a link between AMPK and histone acetylation. Together with these findings, we discover that AMPK promotes apoptosis by phosphorylating apoptosis-stimulating of p53 protein 2 (ASPP2) in an irradiation (IR)-dependent manner and regulates histone acetylation by phosphorylating histone deacetylase 9 (HDAC9) in an IR-independent manner. Besides, we reveal that disrupting the histone acetylation by the bromodomain BRD4 inhibitor JQ-1 enhances the sensitivity of AMPK-deficient cells to IR. Therefore, our study has provided a resource to investigate the interplay between phosphorylation and histone acetylation underlying the regulatory network of AMPK, which could be beneficial to understand the exact role of AMPK in DDR.

Cx32 promotes autophagy and produces resistance to SN‑induced apoptosis via activation of AMPK signalling in cervical cancer

The roles of gap junctions (GJs) and its components, connexins, in the autophagy of cervical cancer cells have been rarely investigated. Our previous study demonstrated that connexin 32 (Cx32) exerted an anti‑apoptotic effect on cervical cancer. However, as an important regulator of apoptosis, whether the autophagy is involved in the function of Cx32 on cervical cancer cells is not well defined. The present study aimed to investigate the role of Cx32 on autophagy and apoptosis inhibition in cervical cancer cells. The expression levels of Cx32 and the autophagy‑associated protein LC3‑Ⅱ in paracancerous cervical tissues (n=30) and cervical cancer (n=50) tissues were determined via western blotting. In total, 45 cervical cancer specimens were used to evaluate the clinical relevance of Cx32 and LC3‑Ⅱ. It was found that both Cx32 and LC3‑Ⅱ were upregulated in cervical cancer tissues compared with those in paracancerous cervical tissues. The effect of Cx32 on autophagy was examined by detecting the change of LC3‑Ⅱ using western blotting, transfection with enhanced green fluorescent protein‑LC3 plasmid and transmission electron microscopy analysis. Overexpression of Cx32 significantly enhanced autophagy in HeLa‑Cx32 cells, whereas knockdown of Cx32 suppressed autophagy in C‑33A cells. The flow cytometry results demonstrated that Cx32 inhibited the apoptosis of cervical cancer cells by promoting autophagy. Moreover, Cx32 triggered autophagy via the activation of the AMP‑activated protein kinase (AMPK) signalling, regardless of the presence or absence of GJs. Collectively, it was identified that Cx32 exerted its anti‑apoptotic effect by activating autophagy via the AMPK pathway in cervical cancer, which demonstrates a novel mechanism for Cx32 in human cervical cancer progression.

The Multi-Omic Prognostic Model of Oxidative Stress-Related Genes in Acute Myeloid Leukemia

Background: Acute myeloid leukemia (AML) is one of the most common cancers in the world, and oxidative stress is closely related to leukemia. A lot of effort has been made to improve the prognosis of AML. However, the situation remains serious. Hence, we focused on the study of prognostic genes in AML. Materials and Methods: Prognostic oxidative stress genes were screened out. The gene expression profile of AML patients was downloaded from the The Cancer Genome Atlas (TCGA) database. The oxidative stress-related model was constructed, by which the prognosis of AML patients was predicted using the two GEO GSE23143 datasets and the stability of the GSE71014 authentication model. Results: The prognostic oxidative stress genes were screened out in AML, and the prognostic genes were significantly enriched in a large number of pathways based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. There was a complex interaction between prognostic genes and transcription factors. After constructing the prediction model, the clinical predictive value of the model was discussed in a multi-omic study. We investigated the sensitivity of risk score to common chemotherapeutic agents, the influence of signaling pathways on the prognosis of AML patients, and the correlation of multiple genes with immune score and immune dysfunction. Conclusions: A highly effective prognostic risk model for AML patients was established and validated. The association of prognostic oxidative stress genes with drug sensitivity, signaling pathways, and immune infiltration was explored. The results suggested that oxidative stress genes promised to be potential prognostic biomarkers for AML, which may provide a new basis for disease management.

Genome Scale Modeling to Study the Metabolic Competition between Cells in the Tumor Microenvironment

The tumor's physiology emerges from the dynamic interplay of numerous cell types, such as cancer cells, immune cells and stromal cells, within the tumor microenvironment. Immune and cancer cells compete for nutrients within the tumor microenvironment, leading to a metabolic battle between these cell populations. Tumor cells can reprogram their metabolism to meet the high demand of building blocks and ATP for proliferation, and to gain an advantage over the action of immune cells. The study of the metabolic reprogramming mechanisms underlying cancer requires the quantification of metabolic fluxes which can be estimated at the genome-scale with constraint-based or kinetic modeling. Constraint-based models use a set of linear constraints to simulate steady-state metabolic fluxes, whereas kinetic models can simulate both the transient behavior and steady-state values of cellular fluxes and concentrations. The integration of cell- or tissue-specific data enables the construction of context-specific models that reflect cell-type- or tissue-specific metabolic properties. While the available modeling frameworks enable limited modeling of the metabolic crosstalk between tumor and immune cells in the tumor stroma, future developments will likely involve new hybrid kinetic/stoichiometric formulations.

Pseudo-ginsenoside Rh2 Induces Protective Autophagy in Hepatocellular Carcinoma HepG2 Cells

BACKGROUND

Pseudo-ginsenoside-Rh2 (pseudo-G-Rh2), a novel derivative of ginsenoside Rh2, is reported to exert a pro-apoptotic effect on various malignancies. However, whether this anti-cancer action of pseudo-G-Rh2 involves autophagy remains to be determined and explored.

OBJECTIVES

Investigation of pseudo-G-Rh2-induced apoptosis and autophagy and the underlying mechanism.

METHODS

In the present study, the MTT assay was used for evaluating cell viability and the lactate dehydrogenase (LDH) assay was performed to assess cell toxicity. Autophagy evaluation was performed using monodansylcadaverine (MDC) staining and transmission electron microscopy (TEM). The levels of autophagy-associated and apoptosis-associated proteins were determined using Western blotting. The Annexin V FITC/propidium iodide (PI) assay was used to assess apoptosis.

RESULTS

The Annexin V FITC/PI assay revealed that the percentage of apoptotic cells in HepG2 cells at concentrations 0, 20, 40, and 60 μM was 3.75%±1.37%, 5.70%±1.04%, 12.30%±2.10%, and 34.26%±4.73%, respectively. Pseudo-G-Rh2 was observed to significantly increase the expressions of BAX, cleaved-caspase-3, and cleaved-caspase-9, while it decreased the Bcl-2 expression. MDC and TEM analyses revealed that pseudo-G-Rh2 at concentrations 20, 40, and 60 μM significantly facilitated the accumulation of autophagosomes and autolysosomes within the HepG2 cells. Moreover, pseudo-G-Rh2 significantly increased the expressions of LC3 Ⅱ/LC3 Ⅰ, and Beclin-1 and decreased the expression of p62. The Annexin V FITC/PI assay also revealed that in comparison to the pseudo-G-Rh2 group, the concurrent treatment with pseudo-G-Rh2 and an autophagy inhibitor (CQ or 3-MA) significantly induced distinct apoptosis. In addition, pseudo-G-Rh2 activated AMPK and inhibited the PI3K/Akt/mTOR pathway in a concentration-dependent manner. Pseudo-G-Rh2 is similar to the current patents, which enhanced its anti-cancer activity by combining with autophagy inhibitors.

CONCLUSION

Pseudo-G-Rh2 could induce protective autophagy in HepG2 cells, at least in part, via AMPK and the PI3K/Akt/mTOR pathway.

AICAr, a Widely Used AMPK Activator with Important AMPK-Independent Effects: A Systematic Review

5-Aminoimidazole-4-carboxamide ribonucleoside (AICAr) has been one of the most commonly used pharmacological modulators of AMPK activity. The majority of early studies on the role of AMPK, both in the physiological regulation of metabolism and in cancer pathogenesis, were based solely on the use of AICAr as an AMPK-activator. Even with more complex models of AMPK downregulation and knockout being introduced, AICAr remained a regular starting point for many studies focusing on AMPK biology. However, there is an increasing number of studies showing that numerous AICAr effects, previously attributed to AMPK activation, are in fact AMPK-independent. This review aims to give an overview of the present knowledge on AMPK-dependent and AMPK-independent effects of AICAr on metabolism, hypoxia, exercise, nucleotide synthesis, and cancer, calling for caution in the interpretation of AICAr-based studies in the context of understanding AMPK signaling pathway.

AICAr, a Widely Used AMPK Activator with Important AMPK-Independent Effects: A Systematic Review

5-Aminoimidazole-4-carboxamide ribonucleoside (AICAr) has been one of the most commonly used pharmacological modulators of AMPK activity. The majority of early studies on the role of AMPK, both in the physiological regulation of metabolism and in cancer pathogenesis, were based solely on the use of AICAr as an AMPK-activator. Even with more complex models of AMPK downregulation and knockout being introduced, AICAr remained a regular starting point for many studies focusing on AMPK biology. However, there is an increasing number of studies showing that numerous AICAr effects, previously attributed to AMPK activation, are in fact AMPK-independent. This review aims to give an overview of the present knowledge on AMPK-dependent and AMPK-independent effects of AICAr on metabolism, hypoxia, exercise, nucleotide synthesis, and cancer, calling for caution in the interpretation of AICAr-based studies in the context of understanding AMPK signaling pathway.

5-aminoimidazole-4-carboxamide ribonucleoside induces differentiation in a subset of primary acute myeloid leukemia blasts

Background

All-trans retinoic acid (ATRA)-based treatment of acute promyelocytic leukemia (APL) is the most successful pharmacological treatment of acute myeloid leukemia (AML). Recent development of inhibitors of mutated isocitrate dehydrogenase and dihydroorotate dehydrogenase (DHODH) has revived interest in differentiation therapy of non-APL AML. Our previous studies demonstrated that 5-aminoimidazole-4-carboxamide ribonucleoside (AICAr) induced differentiation of monocytic cell lines by activating the ATR/Chk1 via pyrimidine depletion. In the present study, the effects of AICAr on the viability and differentiation of primary AML blasts isolated from bone marrow of patients with non-APL AML were tested and compared with the effects of DHODH inhibitor brequinar and ATRA.

Methods

Bone marrow samples were obtained from 35 patients and leukemia blasts were cultured ex vivo. The cell viability was assessed by MTT assay and AML cell differentiation was determined by flow cytometry and morphological analyses. RNA sequencing and partial data analysis were conducted using ClusterProfiler package. Statistical analysis was performed using GraphPad Prism 6.0.

Results

AICAr is capable of triggering differentiation in samples of bone marrow blasts cultured ex vivo that were resistant to ATRA. AICAr-induced differentiation correlates with proliferation and sensitivity to DHODH inhibition. RNA-seq data obtained in primary AML blasts confirmed that AICAr treatment induced downregulation of pyrimidine metabolism pathways together with an upregulation of gene set involved in hematopoietic cell lineage.

Conclusion

AICAr induces differentiation in a subset of primary non-APL AML blasts, and these effects correlate with sensitivity to a well-known, potent DHODH inhibitor.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s12885-020-07533-6.

A phase I study of a dual PI3-kinase/mTOR inhibitor BEZ235 in adult patients with relapsed or refractory acute leukemia

Background

Combined inhibition of phosphatidylinositol 3-kinase (PI3K) and the mammalian target of rapamycin (mTOR) complexes may be an efficient treatment for acute leukemia. The primary objective of this phase I single center open label study was to determine the maximum tolerated dose (MTD) and recommended phase II dose (RP2D) of the dual pan-class I PI3K and mTOR inhibitor BEZ235 in patients with advanced leukemia.

Methods

Herein patients > 18 years of age who had relapsed or showed refractory leukemia were treated with BEZ235 (orally at 300–400 mg BID (cohort − 1/1)) to assess safety, tolerability, preliminary efficacy and pharmacokinetic (PK). Adverse events data and serious adverse events were analyzed and haematological and clinical biochemistry toxicities were assessed from laboratory test parameters. Response was assessed for the first time at the end of cycle 1 (day 29) and after every subsequent cycle. Pharmacokinetic and pharmacodynamic analyses of BEZ235 were also included (BEZ235 plasma levels, phosphorylation of AKT, S6 and 4EBP1). On statistics this trial is a multiple ascending dose study in which a following variant of the 3 + 3 rule (“Rolling Six”), a minimum of 6 and a maximum of 12 patients was recruited for the dose escalation and another 5 were planned for the expansion phase.

Results

Twenty-four patients with ALL (n = 11) or AML (n = 12) or CML-BP (n = 1) were enrolled. All patients had failed one (n = 5) or more lines of therapy (n = 5) and 14 patients were in refractory / refractory relapse. No formal MTD was defined, stomatitis and gastrointestinal toxicity at 400 mg BID dose was considered incompatible with prolonged treatment. The RP2D of BEZ235 was defined as 300 mg BID. Four of 24 patients showed clinical benefit. Twenty-two of 24 patients discontinued because of progression, (median time to progression 27 days (4d-112d). There was no association between PK parameters and efficacy or tolerability.

Conclusions

Combined inhibition of PI3K and mTOR inhibits a clinically meaningful driver pathway in a small subset of patients with ALL, with no benefit in patients with AML.

Trial registration

ClinicalTrials.gov, identifier NCT01756118. retrospectively registered 19th December 2012, https://clinicaltrials.gov/ct2/show/NCT01756118.

Integrated molecular signaling involving mitochondrial dysfunction and alteration of cell metabolism induced by tyrosine kinase inhibitors in cancer

Cancer cells have unlimited replicative potential, insensitivity to growth-inhibitory signals, evasion of apoptosis, cellular stress, and sustained angiogenesis, invasiveness and metastatic potential. Cancer cells adequately adapt cell metabolism and integrate several intracellular and redox signaling to promote cell survival in an inflammatory and hypoxic microenvironment in order to maintain/expand tumor phenotype. The administration of tyrosine kinase inhibitor (TKI) constitutes the recommended therapeutic strategy in different malignancies at advanced stages.

There are important interrelationships between cell stress, redox status, mitochondrial function, metabolism and cellular signaling pathways leading to cell survival/death. The induction of apoptosis and cell cycle arrest widely related to the antitumoral properties of TKIs result from tightly controlled events involving different cellular compartments and signaling pathways. The aim of the present review is to update the most relevant studies dealing with the impact of TKI treatment on cell function. The induction of endoplasmic reticulum (ER) stress and Ca²⁺ disturbances, leading to alteration of mitochondrial function, redox status and phosphatidylinositol 3-kinase (PI3K)-protein kinase B (Akt)-mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) signaling pathways that involve cell metabolism reprogramming in cancer cells will be covered. Emphasis will be given to studies that identify key components of the integrated molecular pattern including receptor tyrosine kinase (RTK) downstream signaling, cell death and mitochondria-related events that appear to be involved in the resistance of cancer cells to TKI treatments.

Targeting Metabolic Reprogramming in Acute Myeloid Leukemia

The cancer metabolic reprogramming allows the maintenance of tumor proliferation, expansion and survival by altering key bioenergetics, biosynthetic and redox functions to meet the higher demands of tumor cells. In addition, several metabolites are also needed to perform signaling functions that further promote tumor growth and progression. These metabolic alterations have been exploited in different cancers, including acute myeloid leukemia, as novel therapeutic strategies both in preclinical models and clinical trials. Here, we review the complexity of acute myeloid leukemia (AML) metabolism and discuss how therapies targeting different aspects of cellular metabolism have demonstrated efficacy and how they provide a therapeutic window that should be explored to target the metabolic requirements of AML cells.

The ribonucleoside AICAr induces differentiation of myeloid leukemia by activating the ATR/Chk1 via pyrimidine depletion

Metabolic pathways play important roles in proliferation and differentiation of malignant cells. 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAr), a precursor in purine biosynthesis and a well-established activator of AMP-activated protein kinase (AMPK), induces widespread metabolic alterations and is commonly used for dissecting the role of metabolism in cancer. We have previously reported that AICAr promotes differentiation and inhibits proliferation of myeloid leukemia cells. Here, using metabolic assays, immunoblotting, flow cytometry analyses, and siRNA-mediated gene silencing in leukemia cell lines, we show that AICAr-mediated differentiation was independent of the known metabolic effects of AMPK, including glucose consumption, but instead depends on the activation of the DNA damage–associated enzyme checkpoint kinase 1 (Chk1) induced by pyrimidine depletion. LC/MS/MS metabolomics analysis revealed that AICAr increases orotate levels and decreases uridine monophosphate (UMP) levels, consistent with inhibition of UMP synthesis at a step downstream of dihydroorotate dehydrogenase (DHODH). AICAr and the DHODH inhibitor brequinar had similar effects on differentiation markers and S-phase arrest, and genetic or pharmacological Chk1 inactivation abrogated both of these effects. Our results delineate an AMPK-independent effect of AICAr on myeloid leukemia differentiation that involves perturbation of pyrimidine biosynthesis and activation of the DNA damage response network.