Intrinsic OXPHOS limitations underlie cellular bioenergetics in leukemia

Mapping of Functional Metabolic Phenotypes in Acute Myeloid Leukemia

BACKGROUND

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy with a poor prognosis, particularly in older patients. AML is highly heterogeneous, influenced by various chromosomal, genetic, and epigenetic alterations.

METHODS

This study investigated the metabolic profiles of primary AML cells from 46 patients, focusing on mitochondrial respiration and glycolysis. We hypothesized that the metabolic profiles would reflect distinct disease characteristics. Using Seahorse technology, we measured the oxygen consumption rate (OCR) for mitochondrial respiration and the extracellular acidification rate (ECAR) for glycolysis.

RESULTS

Our results showed significant variability in metabolic activity, with some samples relying more on glycolysis than mitochondrial respiration. Mature AML cells (FAB M4/M5, CD34 negative) exhibited increased rates of both mitochondrial respiration and glycolysis, indicating distinct metabolic adaptations. Higher glycolytic activity was observed in patients with adverse cytogenetic abnormalities. However, no clear associations were found between metabolic profiles and mutations in FLT3 or NPM1.

CONCLUSION

These findings highlight the role of metabolic variability in AML and suggest that targeting specific metabolic pathways could offer therapeutic opportunities, particularly for subgroups like FAB M4/M5 with unique metabolic features. Further studies are needed to refine these therapeutic strategies for clinical application.

Acute myeloid leukemia mitochondria hydrolyze ATP to support oxidative metabolism and resist chemotherapy

OxPhos inhibitors have struggled to show a clinical benefit because of their inability to distinguish healthy from cancerous mitochondria. Herein, we describe an actionable bioenergetic mechanism unique to acute myeloid leukemia (AML) mitochondria. Unlike healthy cells that couple respiration to ATP synthesis, AML mitochondria support inner-membrane polarization by consuming ATP. Matrix ATP consumption allows cells to survive bioenergetic stress. Thus, we hypothesized AML cells may resist chemotherapy-induced cell death by reversing the ATP synthase reaction. In support, BCL-2 inhibition with venetoclax abolished OxPhos flux without affecting mitochondrial polarization. In surviving AML cells, sustained mitochondrial polarization depended on matrix ATP consumption. Mitochondrial ATP consumption was further enhanced in AML cells made refractory to venetoclax, consequential to down-regulations in the endogenous F1-ATPase inhibitor ATP5IF1. Knockdown of ATP5IF1 conferred venetoclax resistance, while ATP5IF1 overexpression impaired F1-ATPase activity and heightened sensitivity to venetoclax. These data identify matrix ATP consumption as a cancer cell-intrinsic bioenergetic vulnerability actionable in the context of BCL-2 targeted chemotherapy.

Adamantane-Quinoxalone Hybrids: Precision Chemotypes and Their Molecular Mechanisms in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive blood cancer with a poor prognosis, especially when diagnosed late. Around 10-15% of cases involve the specific chromosomal abnormality t(8;21), which drives uncontrolled myeloid cell proliferation and contributes to disease onset. Despite advances in AML research and treatment protocols, outcomes for t(8;21) AML remain stagnant, as patients receive standard, nonspecific chemotherapies. This one-size-fits-all approach targets both cancerous and healthy cells, leading to unwanted toxicity and highlighting the urgent need for targeted therapies. In this study, we present a precision chemotype based on a quinoxalone-tethered adamantane framework developed via a metal- and light-free protocol. The compound selectively inhibits t(8;21) AML cell proliferation and induces cell death by disrupting growth and metabolic pathways, as demonstrated through bioassays, RNA sequencing, and proteomic analysis. Notably, it spares other leukemic and solid cancer cells, underscoring its specificity and potential as a targeted therapy for t(8;21) AML.

Mitochondrial abnormalities as a target of intervention in acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive hematological malignancy; it is the most common acute leukemia in adults. AML prognosis is often poor, and relapse often occurs after initial remission. Recurrent genetic abnormalities underlying this disease and the presence of leukemic stem cells complicate disease treatment. However, the complex metabolic reprogramming that enables the unrestrained cell growth seen in these cells may also be their Achilles' heel. In these cells, mitophagy operates as a double-edged sword. On one hand, it provides a source of building blocks for further cell division and serves as a method for removing damaged organelles, promoting cell survival. However, the profound metabolic changes to mitochondria also render these organelles more sensitive to damage and place them precariously close to excess mitophagic activation. This review discusses the dual role mitophagy plays in AML survival, the importance of targeting mitophagy to treat AML, and current progress in the area. The discovery and mechanism of action of multiple compounds that were used to inhibit or stimulate mitophagy and their effects on AML survival are also described. Further, we explore the combination strategy of mitophagy-targeting compounds with existing and/or novel chemotherapeutics to eradicate AML and discuss strategies to uncover new drug targets and novel mitochondria-targeting drugs.

Amino Acid and Glucose Fermentation Maintain ATP Content in Mouse and Human Malignant Glioma Cells

Energy is necessary for tumor cell viability and growth. Aerobic glucose-driven lactic acid fermentation is a common metabolic phenotype seen in most cancers including malignant gliomas. This metabolic phenotype is linked to abnormalities in mitochondrial structure and function. A luciferin-luciferase bioluminescence ATP assay was used to measure the influence of amino acids, glucose, and oxygen on ATP content and viability in mouse (VM-M3 and CT-2A) and human (U-87MG) glioma cells that differed in cell biology, genetic background, and species origin. Oxygen consumption was measured using the Resipher system. Extracellular lactate and succinate were measured as end products of the glycolysis and glutaminolysis pathways, respectively. The results showed that: (1) glutamine was a source of ATP content irrespective of oxygen. No other amino acid could replace glutamine in sustaining ATP content and viability; (2) ATP content persisted in the absence of glucose and under hypoxia, ruling out substantial contribution through either glycolysis or oxidative phosphorylation (OxPhos) under these conditions; (3) Mitochondrial complex IV inhibition showed that oxygen consumption was not an accurate measure for ATP production through OxPhos. The glutaminase inhibitor, 6-diazo-5-oxo-L-norleucine (DON), reduced ATP content and succinate export in cells grown in glutamine. The data suggests that mitochondrial substrate level phosphorylation in the glutamine-driven glutaminolysis pathway contributes to ATP content in these glioma cells. A new model is presented highlighting the synergistic interaction between the high-throughput glycolysis and glutaminolysis pathways that drive malignant glioma growth and maintain ATP content through the aerobic fermentation of both glucose and glutamine.

Acute myeloid leukemia mitochondria hydrolyze ATP to resist chemotherapy

Despite early optimism, therapeutics targeting oxidative phosphorylation (OxPhos) have faced clinical setbacks, stemming from their inability to distinguish healthy from cancerous mitochondria. Herein, we describe an actionable bioenergetic mechanism unique to cancerous mitochondria inside acute myeloid leukemia (AML) cells. Unlike healthy cells which couple respiration to the synthesis of ATP, AML mitochondria were discovered to support inner membrane polarization by consuming ATP. Because matrix ATP consumption allows cells to survive bioenergetic stress, we hypothesized that AML cells may resist cell death induced by OxPhos damaging chemotherapy by reversing the ATP synthase reaction. In support of this, targeted inhibition of BCL-2 with venetoclax abolished OxPhos flux without impacting mitochondrial membrane potential. In surviving AML cells, sustained polarization of the mitochondrial inner membrane was dependent on matrix ATP consumption. Mitochondrial ATP consumption was further enhanced in AML cells made refractory to venetoclax, consequential to downregulations in both the proton-pumping respiratory complexes, as well as the endogenous F1-ATPase inhibitor ATP5IF1. In treatment-naive AML, ATP5IF1 knockdown was sufficient to drive venetoclax resistance, while ATP5IF1 overexpression impaired F1-ATPase activity and heightened sensitivity to venetoclax. Collectively, our data identify matrix ATP consumption as a cancer-cell intrinsic bioenergetic vulnerability actionable in the context of mitochondrial damaging chemotherapy.

IF1 is a cold-regulated switch of ATP synthase hydrolytic activity to support thermogenesis in brown fat

While mechanisms controlling uncoupling protein-1 (UCP1) in thermogenic adipocytes play a pivotal role in non-shivering thermogenesis, it remains unclear whether F1Fo-ATP synthase function is also regulated in brown adipose tissue (BAT). Here, we show that inhibitory factor 1 (IF1, encoded by Atp5if1), an inhibitor of ATP synthase hydrolytic activity, is a critical negative regulator of brown adipocyte energy metabolism. In vivo, IF1 levels are diminished in BAT of cold-adapted mice compared to controls. Additionally, the capacity of ATP synthase to generate mitochondrial membrane potential (MMP) through ATP hydrolysis (the so-called "reverse mode" of ATP synthase) is increased in brown fat. In cultured brown adipocytes, IF1 overexpression results in an inability of mitochondria to sustain the MMP upon adrenergic stimulation, leading to a quiescent-like phenotype in brown adipocytes. In mice, adeno-associated virus-mediated IF1 overexpression in BAT suppresses adrenergic-stimulated thermogenesis and decreases mitochondrial respiration in BAT. Taken together, our work identifies downregulation of IF1 upon cold as a critical event for the facilitation of the reverse mode of ATP synthase as well as to enable energetic adaptation of BAT to effectively support non-shivering thermogenesis.

Altered metabolism in cancer: insights into energy pathways and therapeutic targets

Cancer cells undergo significant metabolic reprogramming to support their rapid growth and survival. This study examines important metabolic pathways like glycolysis, oxidative phosphorylation, glutaminolysis, and lipid metabolism, focusing on how they are regulated and their contributions to the development of tumors. The interplay between oncogenes, tumor suppressors, epigenetic modifications, and the tumor microenvironment in modulating these pathways is examined. Furthermore, we discuss the therapeutic potential of targeting cancer metabolism, presenting inhibitors of glycolysis, glutaminolysis, the TCA cycle, fatty acid oxidation, LDH, and glucose transport, alongside emerging strategies targeting oxidative phosphorylation and lipid synthesis. Despite the promise, challenges such as metabolic plasticity and the need for combination therapies and robust biomarkers persist, underscoring the necessity for continued research in this dynamic field.

Harnessing Porphyrin Accumulation in Liver Cancer: Combining Genomic Data and Drug Targeting

The liver, a pivotal organ in human metabolism, serves as a primary site for heme biosynthesis, alongside bone marrow. Maintaining precise control over heme production is paramount in healthy livers to meet high metabolic demands while averting potential toxicity from intermediate metabolites, notably protoporphyrin IX. Intriguingly, our recent research uncovers a disrupted heme biosynthesis process termed 'porphyrin overdrive' in cancers that fosters the accumulation of heme intermediates, potentially bolstering tumor survival. Here, we investigate heme and porphyrin metabolism in both healthy and oncogenic human livers, utilizing primary human liver transcriptomics and single-cell RNA sequencing (scRNAseq). Our investigations unveil robust gene expression patterns in heme biosynthesis in healthy livers, supporting electron transport chain (ETC) and cytochrome P450 function without intermediate accumulation. Conversely, liver cancers exhibit rewired heme biosynthesis and a massive downregulation of cytochrome P450 gene expression. Notably, despite diminished drug metabolism, gene expression analysis shows that heme supply to the ETC remains largely unaltered or even elevated with patient cancer progression, suggesting a metabolic priority shift. Liver cancers selectively accumulate intermediates, which are absent in normal tissues, implicating their role in disease advancement as inferred by expression analysis. Furthermore, our findings in genomics establish a link between the aberrant gene expression of porphyrin metabolism and inferior overall survival in aggressive cancers, indicating potential targets for clinical therapy development. We provide in vitro proof-of-concept data on targeting porphyrin overdrive with a drug synergy strategy.

Microfluidics-free single-cell genomics with templated emulsification

Current single-cell RNA-sequencing approaches have limitations that stem from the microfluidic devices or fluid handling steps required for sample processing. We develop a method that does not require specialized microfluidic devices, expertise or hardware. Our approach is based on particle-templated emulsification, which allows single-cell encapsulation and barcoding of cDNA in uniform droplet emulsions with only a vortexer. Particle-templated instant partition sequencing (PIP-seq) accommodates a wide range of emulsification formats, including microwell plates and large-volume conical tubes, enabling thousands of samples or millions of cells to be processed in minutes. We demonstrate that PIP-seq produces high-purity transcriptomes in mouse-human mixing studies, is compatible with multiomics measurements and can accurately characterize cell types in human breast tissue compared to a commercial microfluidic platform. Single-cell transcriptional profiling of mixed phenotype acute leukemia using PIP-seq reveals the emergence of heterogeneity within chemotherapy-resistant cell subsets that were hidden by standard immunophenotyping. PIP-seq is a simple, flexible and scalable next-generation workflow that extends single-cell sequencing to new applications.

A big picture of the mitochondria-mediated signals: From mitochondria to organism

Mitochondria, well-known for years as the powerhouse and biosynthetic center of the cell, are dynamic signaling organelles beyond their energy production and biosynthesis functions. The metabolic functions of mitochondria, playing an important role in various biological events both in physiological and stress conditions, transform them into important cellular stress sensors. Mitochondria constantly communicate with the rest of the cell and even from other cells to the organism, transmitting stress signals including oxidative and reductive stress or adaptive signals such as mitohormesis. Mitochondrial signal transduction has a vital function in regulating integrity of human genome, organelles, cells, and ultimately organism.

Pan-tissue mitochondrial phenotyping reveals lower OXPHOS expression and function across cancer types

Targeting mitochondrial oxidative phosphorylation (OXPHOS) to treat cancer has been hampered due to serious side-effects potentially arising from the inability to discriminate between non-cancerous and cancerous mitochondria. Herein, comprehensive mitochondrial phenotyping was leveraged to define both the composition and function of OXPHOS across various murine cancers and compared to both matched normal tissues and other organs. When compared to both matched normal tissues, as well as high OXPHOS reliant organs like heart, intrinsic expression of the OXPHOS complexes, as well as OXPHOS flux were discovered to be consistently lower across distinct cancer types. Assuming intrinsic OXPHOS expression/function predicts OXPHOS reliance in vivo, these data suggest that pharmacologic blockade of mitochondrial OXPHOS likely compromises bioenergetic homeostasis in healthy oxidative organs prior to impacting tumor mitochondrial flux in a clinically meaningful way. Although these data caution against the use of indiscriminate mitochondrial inhibitors for cancer treatment, considerable heterogeneity was observed across cancer types with respect to both mitochondrial proteome composition and substrate-specific flux, highlighting the possibility for targeting discrete mitochondrial proteins or pathways unique to a given cancer type.

Mitochondria and Brain Disease: A Comprehensive Review of Pathological Mechanisms and Therapeutic Opportunities

Mitochondria play a vital role in maintaining cellular energy homeostasis, regulating apoptosis, and controlling redox signaling. Dysfunction of mitochondria has been implicated in the pathogenesis of various brain diseases, including neurodegenerative disorders, stroke, and psychiatric illnesses. This review paper provides a comprehensive overview of the intricate relationship between mitochondria and brain disease, focusing on the underlying pathological mechanisms and exploring potential therapeutic opportunities. The review covers key topics such as mitochondrial DNA mutations, impaired oxidative phosphorylation, mitochondrial dynamics, calcium dysregulation, and reactive oxygen species generation in the context of brain disease. Additionally, it discusses emerging strategies targeting mitochondrial dysfunction, including mitochondrial protective agents, metabolic modulators, and gene therapy approaches. By critically analysing the existing literature and recent advancements, this review aims to enhance our understanding of the multifaceted role of mitochondria in brain disease and shed light on novel therapeutic interventions.

Metabolic crosstalk between stromal and malignant cells in the bone marrow niche

Bone marrow is the primary site of blood cell production in adults and serves as the source of osteoblasts and osteoclasts that maintain bone homeostasis. The medullary microenvironment is also involved in malignancy, providing a fertile soil for the growth of blood cancers or solid tumors metastasizing to bone. The cellular composition of the bone marrow is highly complex, consisting of hematopoietic stem and progenitor cells, maturing blood cells, skeletal stem cells, osteoblasts, mesenchymal stromal cells, adipocytes, endothelial cells, lymphatic endothelial cells, perivascular cells, and nerve cells. Intercellular communication at different levels is essential to ensure proper skeletal and hematopoietic tissue function, but it is altered when malignant cells colonize the bone marrow niche. While communication often involves soluble factors such as cytokines, chemokines, and growth factors, as well as their respective cell-surface receptors, cells can also communicate by exchanging metabolic information. In this review, we discuss the importance of metabolic crosstalk between different cells in the bone marrow microenvironment, particularly concerning the malignant setting.

Metabolism in stem cell-driven leukemia: parallels between hematopoiesis and immunity

Our understanding of cancer metabolism spans from its role in cellular energetics and supplying the building blocks necessary for proliferation, to maintaining cellular redox and regulating the cellular epigenome and transcriptome. Cancer metabolism, once thought to be solely driven by upregulated glycolysis, is now known to comprise multiple pathways with great plasticity in response to extrinsic challenges. Furthermore, cancer cells can modify their surrounding niche during disease initiation, maintenance, and metastasis, thereby contributing to therapy resistance. Leukemia is a paradigm model of stem cell-driven cancer. In this study, we review how leukemia remodels the niche and rewires its metabolism, with particular attention paid to therapy-resistant stem cells. Specifically, we aim to give a global, nonexhaustive overview of key metabolic pathways. By contrasting the metabolic rewiring required by myeloid-leukemic stem cells with that required for hematopoiesis and immune cell function, we highlight the metabolic features they share. This is a critical consideration when contemplating anticancer metabolic inhibitor options, especially in the context of anticancer immune therapies. Finally, we examine pathways that have not been studied in leukemia but are critical in solid cancers in the context of metastasis and interaction with new niches. These studies also offer detailed mechanisms that are yet to be investigated in leukemia. Given that cancer (and normal) cells can meet their energy requirements by not only upregulating metabolic pathways but also utilizing systemically available substrates, we aim to inform how interlinked these metabolic pathways are, both within leukemic cells and between cancer cells and their niche.

The Key Role of Mitochondrial Function in Health and Disease

The role of mitochondrial function in health and disease has become increasingly recognized, particularly in the last two decades. Mitochondrial dysfunction as well as disruptions of cellular bioenergetics have been shown to be ubiquitous in some of the most prevalent diseases in our society, such as type 2 diabetes, cardiovascular disease, metabolic syndrome, cancer, and Alzheimer's disease. However, the etiology and pathogenesis of mitochondrial dysfunction in multiple diseases have yet to be elucidated, making it one of the most significant medical challenges in our history. However, the rapid advances in our knowledge of cellular metabolism coupled with the novel understanding at the molecular and genetic levels show tremendous promise to one day elucidate the mysteries of this ancient organelle in order to treat it therapeutically when needed. Mitochondrial DNA mutations, infections, aging, and a lack of physical activity have been identified to be major players in mitochondrial dysfunction in multiple diseases. This review examines the complexities of mitochondrial function, whose ancient incorporation into eukaryotic cells for energy purposes was key for the survival and creation of new species. Among these complexities, the tightly intertwined bioenergetics derived from the combustion of alimentary substrates and oxygen are necessary for cellular homeostasis, including the production of reactive oxygen species. This review discusses different etiological mechanisms by which mitochondria could become dysregulated, determining the fate of multiple tissues and organs and being a protagonist in the pathogenesis of many non-communicable diseases. Finally, physical activity is a canonical evolutionary characteristic of humans that remains embedded in our genes. The normalization of a lack of physical activity in our modern society has led to the perception that exercise is an "intervention". However, physical activity remains the modus vivendi engrained in our genes and being sedentary has been the real intervention and collateral effect of modern societies. It is well known that a lack of physical activity leads to mitochondrial dysfunction and, hence, it probably becomes a major etiological factor of many non-communicable diseases affecting modern societies. Since physical activity remains the only stimulus we know that can improve and maintain mitochondrial function, a significant emphasis on exercise promotion should be imperative in order to prevent multiple diseases. Finally, in populations with chronic diseases where mitochondrial dysfunction is involved, an individualized exercise prescription should be crucial for the "metabolic rehabilitation" of many patients. From lessons learned from elite athletes (the perfect human machines), it is possible to translate and apply multiple concepts to the betterment of populations with chronic diseases.

A Novel Family of Lysosomotropic Tetracyclic Compounds for Treating Leukemia

Acute myeloid leukemia (AML) is a heterogeneous hematological cancer characterized by poor prognosis and frequent relapses. Aside from specific mutation-related changes, in AML, the overall function of lysosomes and mitochondria is drastically altered to fulfill the elevated biomass and bioenergetic demands. On the basis of previous results, in silico drug discovery screening was used to identify a new family of lysosome-/mitochondria-targeting compounds. These novel tetracyclic hits, with a cationic amphiphilic structure, specifically eradicate leukemic cells by inducing both mitochondrial damage and apoptosis, and simultaneous lysosomal membrane leakiness. Lysosomal leakiness does not only elicit canonical lysosome-dependent cell death, but also activates the terminal differentiation of AML cells through the Ca2+-TFEB-MYC signaling axis. In addition to being an effective monotherapy, its combination with the chemotherapeutic arsenic trioxide (ATO) used in other types of leukemia is highly synergistic in AML cells, widening the therapeutic window of the treatment. Moreover, the compounds are effective in a wide panel of cancer cell lines and possess adequate pharmacological properties rendering them promising drug candidates for the treatment of AML and other neoplasias.

Simultaneous Inhibition of Ceramide Hydrolysis and Glycosylation Synergizes to Corrupt Mitochondrial Respiration and Signal Caspase Driven Cell Death in Drug-Resistant Acute Myeloid Leukemia

Acute myelogenous leukemia (AML), the most prevalent acute and aggressive leukemia diagnosed in adults, often recurs as a difficult-to-treat, chemotherapy-resistant disease. Because chemotherapy resistance is a major obstacle to successful treatment, novel therapeutic intervention is needed. Upregulated ceramide clearance via accelerated hydrolysis and glycosylation has been shown to be an element in chemotherapy-resistant AML, a problem considering the crucial role ceramide plays in eliciting apoptosis. Herein we employed agents that block ceramide clearance to determine if such a "reset" would be of therapeutic benefit. SACLAC was utilized to limit ceramide hydrolysis, and D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-threo-PDMP) was used to block the glycosylation route. The SACLAC D-threo-PDMP inhibitor combination was synergistically cytotoxic in drug-resistant, P-glycoprotein-expressing (P-gp) AML but not in wt, P-gp-poor cells. Interestingly, P-gp antagonists that can limit ceramide glycosylation via depression of glucosylceramide transit also synergized with SACLAC, suggesting a paradoxical role for P-gp in the implementation of cell death. Mechanistically, cell death was accompanied by a complete drop in ceramide glycosylation, concomitant, striking increases in all molecular species of ceramide, diminished sphingosine 1-phosphate levels, resounding declines in mitochondrial respiratory kinetics, altered Akt, pGSK-3β, and Mcl-1 expression, and caspase activation. Although ceramide was generated in wt cells upon inhibitor exposure, mitochondrial respiration was not corrupted, suggestive of mitochondrial vulnerability in the drug-resistant phenotype, a potential therapeutic avenue. The inhibitor regimen showed efficacy in an in vivo model and in primary AML cells from patients. These results support the implementation of SL enzyme targeting to limit ceramide clearance as a therapeutic strategy in chemotherapy-resistant AML, inclusive of a novel indication for the use of P-gp antagonists.

Calcium signaling induced by 15-deoxy-prostamide-J2 promotes cell death by activating PERK, IP3R, and the mitochondrial permeability transition pore

Melanoma is the deadliest form of skin cancer in the US. Although immunotherapeutic checkpoint inhibitors and small-molecule kinase inhibitors have dramatically increased the survival of patients with melanoma, new or optimized therapeutic approaches are still needed to improve outcomes. 15-deoxy-Δ^12,14-prostamide J₂ (15d-PMJ₂) is an investigational small-molecule that induces ER stress-mediated apoptosis selectively in tumor cells. Additionally, 15d-PMJ2 reduces melanoma growth in vivo. To assess the chemotherapeutic potential of 15d-PMJ₂, the current study sought to uncover molecular pathways by which 15d-PMJ₂ exerts its antitumor activity. B16F10 melanoma and JWF2 squamous cell carcinoma cell lines were cultured in the presence of pharmacological agents that prevent ER or oxidative stress as well as Ca²⁺ channel blockers to identify mechanisms of 15d-PMJ₂ cell death. Our data demonstrated the ER stress protein, PERK, was required for 15d-PMJ₂-induced death. PERK activation triggered the release of ER-resident Ca²⁺ through an IP₃R sensitive pathway. Increased calcium mobilization led to mitochondrial Ca²⁺ overload followed by mitochondrial permeability transition pore (mPTP) opening and the deterioration of mitochondrial respiration. Finally, we show the electrophilic double bond located within the cyclopentenone ring of 15d-PMJ₂ was required for its activity. The present study identifies PERK/IP3R/mPTP signaling as a mechanism of 15d-PMJ₂ antitumor activity.

X-linked inhibitor of apoptosis protein represents a promising therapeutic target for relapsed/refractory ALL

Acute lymphoblastic leukemia (ALL) represents the most frequent malignancy in children, and relapse/refractory (r/r) disease is difficult to treat, both in children and adults. In search for novel treatment options against r/r ALL, we studied inhibitor of apoptosis proteins (IAP) and Smac mimetics (SM). SM-sensitized r/r ALL cells towards conventional chemotherapy, even upon resistance against SM alone. The combination of SM and chemotherapy-induced cell death via caspases and PARP, but independent from cIAP-1/2, RIPK1, TNFα or NF-κB. Instead, XIAP was identified to mediate SM effects. Molecular manipulation of XIAP in vivo using microRNA-30 flanked shRNA expression in cell lines and patient-derived xenograft (PDX) models of r/r ALL mimicked SM effects and intermediate XIAP knockdown-sensitized r/r ALL cells towards chemotherapy-induced apoptosis. Interestingly, upon strong XIAP knockdown, PDX r/r ALL cells were outcompeted in vivo, even in the absence of chemotherapy. Our results indicate a yet unknown essential function of XIAP in r/r ALL and reveal XIAP as a promising therapeutic target for r/r ALL.

Mitochondrial signal transduction

The analogy of mitochondria as powerhouses has expired. Mitochondria are living, dynamic, maternally inherited, energy-transforming, biosynthetic, and signaling organelles that actively transduce biological information. We argue that mitochondria are the processor of the cell, and together with the nucleus and other organelles they constitute the mitochondrial information processing system (MIPS). In a three-step process, mitochondria (1) sense and respond to both endogenous and environmental inputs through morphological and functional remodeling; (2) integrate information through dynamic, network-based physical interactions and diffusion mechanisms; and (3) produce output signals that tune the functions of other organelles and systemically regulate physiology. This input-to-output transformation allows mitochondria to transduce metabolic, biochemical, neuroendocrine, and other local or systemic signals that enhance organismal adaptation. An explicit focus on mitochondrial signal transduction emphasizes the role of communication in mitochondrial biology. This framework also opens new avenues to understand how mitochondria mediate inter-organ processes underlying human health.

Intrinsic adaptations in OXPHOS power output and reduced tumorigenicity characterize doxorubicin resistant ovarian cancer cells

Although the development of chemoresistance is multifactorial, active chemotherapeutic efflux driven by upregulations in ATP binding cassette (ABC) transporters are commonplace. Chemotherapeutic efflux pumps, like ABCB1, couple drug efflux to ATP hydrolysis and thus potentially elevate cellular demand for ATP resynthesis. Elevations in both mitochondrial content and cellular respiration are common phenotypes accompanying many models of cancer cell chemoresistance, including those dependent on ABCB1. The present study set out to characterize potential mitochondrial remodeling commensurate with ABCB1-dependent chemoresistance, as well as investigate the impact of ABCB1 activity on mitochondrial respiratory kinetics. To do this, comprehensive bioenergetic phenotyping was performed across ABCB1-dependent chemoresistant cell models and compared to chemosensitive controls. In doxorubicin (DOX) resistant ovarian cancer cells, the combination of both increased mitochondrial content and enhanced respiratory complex I (CI) boosted intrinsic oxidative phosphorylation (OXPHOS) power output. With respect to ABCB1, acute ABCB1 inhibition partially normalized intact basal mitochondrial respiration between chemosensitive and chemoresistant cells, suggesting that active ABCB1 contributes to mitochondrial remodeling in favor of enhanced OXPHOS. Interestingly, while enhanced OXPHOS power output supported ABCB1 drug efflux when DOX was present, in the absence of chemotherapeutic stress, enhanced OXPHOS power output was associated with reduced tumorigenicity.

Targeting PI4KA sensitizes refractory leukemia to chemotherapy by modulating the ERK/AMPK/OXPHOS axis

Background: The emergence of chemoresistance in leukemia markedly impedes chemotherapeutic efficacy and dictates poor prognosis. Recent evidence has revealed that phosphatidylinositol 4 kinase-IIIα (PI4KA) plays a critical role in tumorigenesis. However, the molecular mechanisms of PI4KA-regulated chemoresistance and leukemogenesis remain largely unknown.

Methods: Liquid chromatography-mass spectrometry (LC-MS), patient samples and leukemia xenograft mouse models were used to investigate whether PI4KA was an effective target to overcome chemoresistance in leukemia. Enzyme-linked immunosorbent assay (ELISA) and molecular mechanics/generalized born surface area (MM/GBSA) method were employed to identify cepharanthine (CEP) as a novel PI4KA inhibitor.

Results: High expression of PI4KA was observed in drug-resistant leukemia cells or in relapsed leukemia patients, which was correlated with poor overall survival. Depletion of PI4KA sensitized drug-resistant leukemia cells to chemotherapeutic drugs in vitro and in vivo by regulating ERK/AMPK/OXPHOS axis. We also identified cepharanthine (CEP) as a novel PI4KA inhibitor, which could undermine the stability of the PI4KA/TTC7/FAM126 complex, enhancing the sensitivity of drug-resistant leukemia cells to chemotherapeutic drugs in vitro and in vivo.

Conclusions: Our study underscored the potential of therapeutic targeting of PI4KA to overcome chemoresistance in leukemia. A combination of the PI4KA inhibitor with classic chemotherapeutic agents could represent a novel therapeutic strategy for the treatment of refractory leukemia.

Bioenergetic Phenotyping of DEN-Induced Hepatocellular Carcinoma Reveals a Link Between Adenylate Kinase Isoform Expression and Reduced Complex I-Supported Respiration

Hepatocellular carcinoma (HCC) is the most common form of liver cancer worldwide. Increasing evidence suggests that mitochondria play a central role in malignant metabolic reprogramming in HCC, which may promote disease progression. To comprehensively evaluate the mitochondrial phenotype present in HCC, we applied a recently developed diagnostic workflow that combines high-resolution respirometry, fluorometry, and mitochondrial-targeted nLC-MS/MS proteomics to cell culture (AML12 and Hepa 1-6 cells) and diethylnitrosamine (DEN)-induced mouse models of HCC. Across both model systems, CI-linked respiration was significantly decreased in HCC compared to nontumor, though this did not alter ATP production rates. Interestingly, CI-linked respiration was found to be restored in DEN-induced tumor mitochondria through acute in vitro treatment with P1, P5-di(adenosine-5′) pentaphosphate (Ap5A), a broad inhibitor of adenylate kinases. Mass spectrometry-based proteomics revealed that DEN-induced tumor mitochondria had increased expression of adenylate kinase isoform 4 (AK4), which may account for this response to Ap5A. Tumor mitochondria also displayed a reduced ability to retain calcium and generate membrane potential across a physiological span of ATP demand states compared to DEN-treated nontumor or saline-treated liver mitochondria. We validated these findings in flash-frozen human primary HCC samples, which similarly displayed a decrease in mitochondrial respiratory capacity that disproportionately affected CI. Our findings support the utility of mitochondrial phenotyping in identifying novel regulatory mechanisms governing cancer bioenergetics.

Detachment of Hexokinase II From Mitochondria Promotes Collateral Sensitivity in Multidrug Resistant Chronic Myeloid Leukemia Cells

Chronic Myeloid Leukemia is a neoplastic disease characterized by the abnormal expansion of hematopoietic cells with compromised functions. Leukemic cells often display a multidrug resistance phenotype, enabling them to evade a number of structurally unrelated cytotoxic compounds. One of those mechanisms relies on the high expression of efflux transporters, such as the ABC proteins, whose activity depends on the hydrolysis of ATP to reduce intracellular drug accumulation. In the present work, we employed a well-known erythroleukemia cell line, K562, and a multidrug resistant derivative cell, FEPS, to evaluate how hexokinase II, a key regulator for the rate-limiting step glycolysis, contributes to the establishment of the multidrug resistance phenotype. We found that multidrug resistant cells primarily resort to glycolysis to generate ATP. Clotrimazole reduced the expression of mitochondrial hexokinase II, which destabilized bioenergetic parameters such as reactive oxygen species production, ATP, and glutathione levels on multidrug resistant cells. This impaired the activity of ABCC1, leading to increased drug accumulation and cell death. In summary, we propose that decoupling of hexokinase II from the mitochondria emerges as a promising strategy to generate collateral sensitivity and aid in the management of chronic myeloid leukemia in chemotherapy-refractory patients.

Skeletal muscle undergoes fiber type metabolic switch without myosin heavy chain switch in response to defective fatty acid oxidation

OBJECTIVE

Skeletal muscle is a heterogeneous and dynamic tissue that adapts to functional demands and substrate availability by modulating muscle fiber size and type. The concept of muscle fiber type relates to its contractile (slow or fast) and metabolic (glycolytic or oxidative) properties. Here, we tested whether disruptions in muscle oxidative catabolism are sufficient to prompt parallel adaptations in energetics and contractile protein composition.

METHODS

Mice with defective mitochondrial long-chain fatty acid oxidation (mLCFAO) in the skeletal muscle due to loss of carnitine palmitoyltransferase 2 (Cpt2Sk-/-) were used to model a shift in muscle macronutrient catabolism. Glycolytic and oxidative muscles of Cpt2Sk-/- mice and control littermates were compared for the expression of energy metabolism-related proteins, mitochondrial respiratory capacity, and myosin heavy chain isoform composition.

RESULTS

Differences in bioenergetics and macronutrient utilization in response to energy demands between control muscles were intrinsic to the mitochondria, allowing for a clear distinction of muscle types. Loss of CPT2 ablated mLCFAO and resulted in mitochondrial biogenesis occurring most predominantly in oxidative muscle fibers. The metabolism-related proteomic signature of Cpt2Sk-/- oxidative muscle more closely resembled that of glycolytic muscle than of control oxidative muscle. Respectively, intrinsic substrate-supported mitochondrial respiration of CPT2 deficient oxidative muscles shifted to closely match that of glycolytic muscles. Despite this shift in mitochondrial metabolism, CPT2 deletion did not result in contractile-based fiber type switching according to myosin heavy chain composition analysis.

CONCLUSION

The loss of mitochondrial long-chain fatty acid oxidation elicits an adaptive response involving conversion of oxidative muscle toward a metabolic profile that resembles a glycolytic muscle, but this is not accompanied by changes in myosin heavy chain isoforms. These data suggest that shifts in muscle catabolism are not sufficient to drive shifts in the contractile apparatus but are sufficient to drive adaptive changes in metabolic properties.

Attenuates of NAD+ impair BMSC osteogenesis and fracture repair through OXPHOS

BACKGROUND

Controlling the adipo-osteogenic lineage commitment of bone marrow mesenchymal stem cell (BMSC) in favor of osteogenesis is considered a promising approach for bone regeneration and repair. Accumulating evidence indicates that oxidative phosphorylation (OXPHOS) is involved in regulating cell fate decisions. As an essential cofactor for OXPHOS, nicotinamide adenine dinucleotide (NAD) has been shown to correlate with the differentiation of stem cells. However, whether NAD manipulates BMSC lineage commitment through OXPHOS remains elusive. Therefore, it is critical to investigate the potential role of NAD on energy metabolism in mediating BMSC lineage commitment.

METHODS

In this study, the mitochondrial respiration and intracellular NAD⁺ level were firstly compared between osteogenic and adipogenic cells. For validating the role of NAD in mitochondrial OXPHOS, the inhibitor of NAD⁺ salvage pathway FK866 and activator P7C3 were used to manipulate the NAD⁺ level during osteogenesis. Furthermore, a murine femur fracture model was established to evaluate the effect of FK866 on bone fracture repair.

RESULTS

We elucidated that osteogenic committed BMSCs exhibited increased OXPHOS activity and a decreased glycolysis accompanied by an elevated intracellular NAD⁺ level. In contrast, adipogenic committed BMSCs showed little change in OXPHOS but an upregulated activity in glycolysis and a decline in intracellular NAD⁺ level in vitro. Moreover, attenuates of NAD⁺ via salvage pathway in BMSCs diminished osteogenic commitment due to mitochondria dysfunction and reduced activity of OXPHOS. The cells were rescued by supplementing with nicotinamide mononucleotide. In addition, treatment with NAD⁺ inhibitor FK866 impaired bone fracture healing in vivo.

CONCLUSION

Our data reveals NAD⁺-mediated mitochondrial OXPHOS is indispensable for osteogenic commitment in BMSCs and bone repair, which might provide a potential therapeutic target for bone repair and regeneration.

Clinically Relevant Oxygraphic Assay to Assess Mitochondrial Energy Metabolism in Acute Myeloid Leukemia Patients

Resistant acute myeloid leukemia (AML) exhibits mitochondrial energy metabolism changes compared to newly diagnosed AML. This phenotype is often observed by evaluating the mitochondrial oxygen consumption of blasts, but most of the oximetry protocols were established from leukemia cell lines without validation on primary leukemia cells. Moreover, the cultures and storage conditions of blasts freshly extracted from patient blood or bone marrow cause stress, which must be evaluated before determining oxidative phosphorylation (OXPHOS). Herein, we evaluated different conditions to measure the oxygen consumption of blasts using extracellular flow analyzers. We first determined the minimum number of blasts required to measure OXPHOS. Next, we compared the OXPHOS of blasts cultured for 3 h and 18 h after collection and found that to maintain metabolic organization for 18 h, cytokine supplementation is necessary. Cytokines are also needed when measuring OXPHOS in cryopreserved, thawed and recultured blasts. Next, the concentrations of respiratory chain inhibitors and uncoupler FCCP were established. We found that the FCCP concentration required to reach the maximal respiration of blasts varied depending on the patient sample analyzed. These protocols provided can be used in future clinical studies to evaluate OXPHOS as a biomarker and assess the efficacy of treatments targeting mitochondria.

Targeting Mitochondrial Protein Expression as a Future Approach for Cancer Therapy

Extensive metabolic remodeling is a fundamental feature of cancer cells. Although early reports attributed such remodeling to a loss of mitochondrial functions, it is now clear that mitochondria play central roles in cancer development and progression, from energy production to synthesis of macromolecules, from redox modulation to regulation of cell death. Biosynthetic pathways are also heavily affected by the metabolic rewiring, with protein synthesis dysregulation at the hearth of cellular transformation. Accumulating evidence in multiple organisms shows that the metabolic functions of mitochondria are tightly connected to protein synthesis, being assembly and activity of respiratory complexes highly dependent on de novo synthesis of their components. In turn, protein synthesis within the organelle is tightly connected with the cytosolic process. This implies an entire network of interactions and fine-tuned regulations that build up a completely under-estimated level of complexity. We are now only preliminarily beginning to reconstitute such regulatory level in human cells, and to perceive its role in diseases. Indeed, disruption or alterations of these connections trigger conditions of proteotoxic and energetic stress that could be potentially exploited for therapeutic purposes. In this review, we summarize the available literature on the coordinated regulation of mitochondrial and cytosolic mRNA translation, and their effects on the integrity of the mitochondrial proteome and functions. Finally, we highlight the potential held by this topic for future research directions and for the development of innovative therapeutic approaches.

Alterations in sphingolipid composition and mitochondrial bioenergetics represent synergistic therapeutic vulnerabilities linked to multidrug resistance in leukemia

Modifications in sphingolipid (SL) metabolism and mitochondrial bioenergetics are key factors implicated in cancer cell response to chemotherapy, including chemotherapy resistance. In the present work, we utilized acute myeloid leukemia (AML) cell lines, selected to be refractory to various chemotherapeutics, to explore the interplay between SL metabolism and mitochondrial biology supportive of multidrug resistance (MDR). In agreement with previous findings in cytarabine or daunorubicin resistant AML cells, relative to chemosensitive wildtype controls, HL-60 cells refractory to vincristine (HL60/VCR) presented with alterations in SL enzyme expression and lipidome composition. Such changes were typified by upregulated expression of various ceramide detoxifying enzymes, as well as corresponding shifts in ceramide, glucosylceramide, and sphingomyelin (SM) molecular species. With respect to mitochondria, despite consistent increases in both basal respiration and maximal respiratory capacity, direct interrogation of the oxidative phosphorylation (OXPHOS) system revealed intrinsic deficiencies in HL60/VCR, as well as across multiple MDR model systems. Based on the apparent requirement for augmented SL and mitochondrial flux to support the MDR phenotype, we explored a combinatorial therapeutic paradigm designed to target each pathway. Remarkably, despite minimal cytotoxicity in peripheral blood mononuclear cells (PBMC), co-targeting SL metabolism, and respiratory complex I (CI) induced synergistic cytotoxicity consistently across multiple MDR leukemia models. Together, these data underscore the intimate connection between cellular sphingolipids and mitochondrial metabolism and suggest that pharmacological intervention across both pathways may represent a novel treatment strategy against MDR.

Exploring the Leukemogenic Potential of GATA-1S, the Shorter Isoform of GATA-1: Novel Insights into Mechanisms Hampering Respiratory Chain Complex II Activity and Limiting Oxidative Phosphorylation Efficiency

GATA-1 is a key regulator of hematopoiesis. A balanced ratio of its two isoforms, GATA-1_FL and GATA-1_S, contributes to normal hematopoiesis, whereas aberrant expression of GATA-1_S alters the differentiation/proliferation potential of hematopoietic precursors and represents a poor prognostic factor in myeloid leukemia. We previously reported that GATA-1_S over-expression correlates with high levels of the succinate dehydrogenase subunit C (SDHC). Alternative splicing variants of the SDHC transcript are over-expressed in several tumors and act as potent dominant negative inhibitors of SDH activity. With this in mind, we investigated the levels of SDHC variants and the oxidative mitochondrial metabolism in myeloid leukemia K562 cells over-expressing GATA-1 isoforms. Over-expression of SDHC variants accompanied by decreased SDH complex II activity and oxidative phosphorylation (OXPHOS) efficiency was found associated only with GATA-1_S. Given the tumor suppressor role of SDH and the effects of OXPHOS limitations in leukemogenesis, identification of a link between GATA-1_S and impaired complex II activity unveils novel pro-leukemic mechanisms triggered by GATA-1_S. Abnormal levels of GATA-1_S and SDHC variants were also found in an acute myeloid leukemia patient, thus supporting in vitro results. A better understanding of these mechanisms can contribute to identify novel promising therapeutic targets in myeloid leukemia.

Targeted Therapies and Druggable Genetic Anomalies in Acute Myeloid Leukemia: From Diagnostic Tools to Therapeutic Interventions

Acute myeloid leukemia (AML) is a clonal disorder resulting from acquired somatic mutations in hematopoietic progenitor cells that lead to the dysregulation of differentiation and the proliferation of hematopoietic cells [...].

Common Genetic Aberrations Associated with Metabolic Interferences in Human Type-2 Diabetes and Acute Myeloid Leukemia: A Bioinformatics Approach

Type-2 diabetes mellitus (T2D) is a chronic metabolic disorder, associated with an increased risk of developing solid tumors and hematological malignancies, including acute myeloid leukemia (AML). However, the genetic background underlying this predisposition remains elusive. We herein aimed at the exploration of the genetic variants, related transcriptomic changes and disturbances in metabolic pathways shared by T2D and AML, utilizing bioinformatics tools and repositories, as well as publicly available clinical datasets. Our approach revealed that rs11709077 and rs1801282, on PPARG, rs11108094 on USP44, rs6685701 on RPS6KA1 and rs7929543 on AC118942.1 comprise common SNPs susceptible to the two diseases and, together with 64 other co-inherited proxy SNPs, may affect the expression patterns of metabolic genes, such as USP44, METAP2, PPARG, TIMP4 and RPS6KA1, in adipose tissue, skeletal muscle, liver, pancreas and whole blood. Most importantly, a set of 86 AML/T2D common susceptibility genes was found to be significantly associated with metabolic cellular processes, including purine, pyrimidine, and choline metabolism, as well as insulin, AMPK, mTOR and PI₃K signaling. Moreover, it was revealed that the whole blood of AML patients exhibits deregulated expression of certain T2D-related genes. Our findings support the existence of common metabolic perturbations in AML and T2D that may account for the increased risk for AML in T2D patients. Future studies may focus on the elucidation of these pathogenetic mechanisms in AML/T2D patients, as well as on the assessment of certain susceptibility variants and genes as potential biomarkers for AML development in the setting of T2D. Detection of shared therapeutic molecular targets may enforce the need for repurposing metabolic drugs in the therapeutic management of AML.