Therapeutic potential of mitochondrial translation inhibition for treatment of acute myeloid leukemia

A mitochondria-targeted iridium(III) complex-based sensor for endogenous GSH detection in living cells

Glutathione (GSH) plays an important role in maintaining redox homeostasis in biological systems. Development of reliable glutathione sensors is of great significance to better understand the role of biomolecules in living cells and organisms. Based on the advantages of the photophysical properties of iridium complexes, we proposed a "turn-on" phosphorescent sensor. Ir-DNFB has the characteristics of a large Stokes shift, high sensitivity for GSH detection, low cytotoxicity, and extremely short response time, and can specifically analyze glutathione in living cells and highly target endogenous glutathione in mitochondria. The N-H group on the imidazole ring of Ir-DNFB could form a new electrostatic interaction with the α-carboxyl group on the glutamate moiety of glutathione. The nucleophilic attack reaction was regulated by the sulfhydryl group on GSH, following which the ether bond linking the 2,4-dinitrobenzene to probe Ir-DNFB was broken, accompanied with a phosphorescence enhancement. Most importantly, the process of recognizing glutathione was not affected by other amino acids. Overall, this work provided a very useful tool for rapidly distinguishing between normal, inflammatory, and progressive tumor cells.

Targeting mitochondrial metabolism by the mitotoxin bromoxib in leukemia and lymphoma cells

Targeting mitochondrial metabolism represents a promising approach for cancer treatment. Here, we investigated the mitotoxic potential of the polybrominated diphenyl ether bromoxib, a natural compound isolated from the marine sponge Dysidea family. We could show that bromoxib comprised strong cytotoxicity in different leukemia and lymphoma cell lines (such as HL60, HPBALL, Jurkat, K562, KOPTK1, MOLT4, SUPB15 and Ramos), but also in solid tumor cell lines (such as glioblastoma cell lines SJ-GBM2 and TP365MG). Bromoxib activated the mitochondrial death pathway as evidenced by the rapid translocation of Bax to the mitochondria and the subsequent mitochondrial release of Smac. Accordingly, bromoxib-induced apoptosis was blocked in caspase 9 deficient Jurkat cells and Jurkat cells overexpressing the antiapoptotic protein Bcl-2. In addition, we could show that bromoxib functioned as an uncoupler of the electron transport chain with similar rapid kinetics as CCCP in terms of dissipation of the mitochondrial membrane potential (ΔΨm), processing of the dynamin-like GTPase OPA1 and subsequent fragmentation of mitochondria. Beyond that, bromoxib strongly abrogated ATP production via glycolysis as well as oxidative phosphorylation (OXPHOS) by targeting electron transport chain complexes II, III, and V (ATP-synthase) in Ramos lymphoma cells. Thus, bromoxib's potential to act on both cytosolic glycolysis and mitochondrial respiration renders it a promising agent for the treatment of leukemia and lymphoma.

Anti-leukemia effects of omipalisib in acute myeloid leukemia: inhibition of PI3K/AKT/mTOR signaling and suppression of mitochondrial biogenesis

Omipalisib (GSK2126458), a potent dual PI3K/mTOR inhibitor, is reported to exhibit anti-tumor effect in several kinds of cancers. More than 50% of acute myeloid leukemia (AML) patients display a hyperactivation of PI3K/AKT/mTOR signaling. We investigated the anti-proliferative effect of omipalisib in AML cell lines with varied genetic backgrounds. The OCI-AML3 and THP-1 cell lines had a significant response to omipalisib, with IC50 values of 17.45 nM and 8.93 nM, respectively. We integrated transcriptomic profile and metabolomic analyses, and followed by gene set enrichment analysis (GSEA) and metabolite enrichment analysis. Our findings showed that in addition to inhibiting PI3K/AKT/mTOR signaling and inducing cell cycle arrest at the G0/G1 phase, omipalisib also suppressed mitochondrial respiration and biogenesis. Furthermore, omipalisib downregulated several genes associated with serine, glycine, threonine, and glutathione metabolism, and decreased their protein and glutathione levels. In vivo experiments revealed that omipalisib significantly inhibited tumor growth and prolonged mouse survival without weight loss. Gedatolisib and dactolisib, another two PI3K/mTOR inhibitors, exerted similar effects without affecting mitochondria biogenesis. These results highlight the multifaceted anti-leukemic effect of omipalisib, revealing its potential as a novel therapeutic agent in AML treatment.

The mycotoxin viriditoxin induces leukemia- and lymphoma-specific apoptosis by targeting mitochondrial metabolism

Inhibition of the mitochondrial metabolism offers a promising therapeutic approach for the treatment of cancer. Here, we identify the mycotoxin viriditoxin (VDT), derived from the endophytic fungus Cladosporium cladosporioides, as an interesting candidate for leukemia and lymphoma treatment. VDT displayed a high cytotoxic potential and rapid kinetics of caspase activation in Jurkat leukemia and Ramos lymphoma cells in contrast to solid tumor cells that were affected to a much lesser extent. Most remarkably, human hematopoietic stem and progenitor cells and peripheral blood mononuclear cells derived from healthy donors were profoundly resilient to VDT-induced cytotoxicity. Likewise, the colony-forming capacity was affected only at very high concentrations, which provides a therapeutic window for cancer treatment. Intriguingly, VDT could directly activate the mitochondrial apoptosis pathway in leukemia cells in the presence of antiapoptotic Bcl-2 proteins. The mitochondrial toxicity of VDT was further confirmed by inhibition of mitochondrial respiration, breakdown of the mitochondrial membrane potential (ΔΨm), the release of mitochondrial cytochrome c, generation of reactive oxygen species (ROS), processing of the dynamin-like GTPase OPA1 and subsequent fission of mitochondria. Thus, VDT-mediated targeting of mitochondrial oxidative phosphorylation (OXPHOS) might represent a promising therapeutic approach for the treatment of leukemia and lymphoma without affecting hematopoietic stem and progenitor cells.

Assessment of Platelet Mitochondrial Respiration in a Pediatric Population: A Pilot Study in Healthy Children and Children with Acute Lymphoblastic Leukemia

Characterization of mitochondrial respiration in peripheral blood cells has recently emerged as a potential biomarker for the assessment of the severity of hematological malignancies (HM) in adults. Whether changes in platelet respiratory function occur in children with or without HM it is unknown. The present pilot study was double-aimed: (i) to investigate whether platelet respiration is age-dependent in non-HM children and (ii) to assess the platelet mitochondrial respiration in children with newly diagnosed acute lymphoblastic leukemia (ALL). Blood samples obtained from age-grouped children (10–11, 13–14 and 16–17 years) with non-HM and children with ALL (10–11 years) were used to isolate platelets via differential centrifugation. High-resolution respirometry studies of isolated platelets were performed according to a protocol adapted to evaluate complex I and II-supported respiration. An age-related decrease in respiration was observed in the non-HM pediatric population and had comparable values for the 13–14 and 16–17 years. groups. In children with ALL, a significant increase in C I-supported active respiration and decrease in maximal noncoupled respiration were found at the disease onset. In conclusion, in a pediatric population, platelet mitochondrial respiration is age-dependent. Platelet respiratory dysfunction occurs in children with newly-diagnosed ALL, an observation that warrants further investigation of this change as a disease biomarker.

Mitochondrial metabolism as a target for acute myeloid leukemia treatment

Acute myeloid leukemias (AML) are a group of aggressive hematologic malignancies resulting from acquired genetic mutations in hematopoietic stem cells that affect patients of all ages. Despite decades of research, standard chemotherapy still remains ineffective for some AML subtypes and is often inappropriate for older patients or those with comorbidities. Recently, a number of studies have identified unique mitochondrial alterations that lead to metabolic vulnerabilities in AML cells that may present viable treatment targets. These include mtDNA, dependency on oxidative phosphorylation, mitochondrial metabolism, and pro-survival signaling, as well as reactive oxygen species generation and mitochondrial dynamics. Moreover, some mitochondria-targeting chemotherapeutics and their combinations with other compounds have been FDA-approved for AML treatment. Here, we review recent studies that illuminate the effects of drugs and synergistic drug combinations that target diverse biomolecules and metabolic pathways related to mitochondria and their promise in experimental studies, clinical trials, and existing chemotherapeutic regimens.

The Progression of Acute Myeloid Leukemia from First Diagnosis to Chemoresistant Relapse: A Comparison of Proteomic and Phosphoproteomic Profiles

Acute myeloid leukemia (AML) is an aggressive hematological malignancy. Nearly 50% of the patients who receive the most intensive treatment develop chemoresistant leukemia relapse. Although the leukemogenic events leading to relapse seem to differ between patients (i.e., regrowth from a clone detected at first diagnosis, progression from the original leukemic or preleukemic stem cells), a common characteristic of relapsed AML is increased chemoresistance. The aim of the present study was to investigate at the proteomic level whether leukemic cells from relapsed patients present overlapping molecular mechanisms that contribute to this chemoresistance. We used liquid chromatography–tandem mass spectrometry (LC–MS/MS) to compare the proteomic and phosphoproteomic profiles of AML cells derived from seven patients at the time of first diagnosis and at first relapse. At the time of first relapse, AML cells were characterized by increased levels of proteins important for various mitochondrial functions, such as mitochondrial ribosomal subunit proteins (MRPL21, MRPS37) and proteins for RNA processing (DHX37, RNA helicase; RPP40, ribonuclease P component), DNA repair (ERCC3, DNA repair factor IIH helicase; GTF2F1, general transcription factor), and cyclin-dependent kinase (CDK) activity. The levels of several cytoskeletal proteins (MYH14/MYL6/MYL12A, myosin chains; VCL, vinculin) as well as of proteins involved in vesicular trafficking/secretion and cell adhesion (ITGAX, integrin alpha-X; CD36, platelet glycoprotein 4; SLC2A3, solute carrier family 2) were decreased in relapsed cells. Our study introduces new targetable proteins that might direct therapeutic strategies to decrease chemoresistance in relapsed AML.

Clinico-pathological significance of Drp1 dysregulation and its correlation to apoptosis in oral cancer patients

Dysregulation in mitochondrial dynamics has been associated with several diseases including cancer. Present study assessed the alteration in mitochondrial fission protein (Drp1) in oral epithelial cells collected from clinically confirmed pre-cancer and cancer patients and further correlates it with the cellular apoptosis signaling. Results indicate the ROS accumulation in OSCC patients is accompanied by several changes including increase in mitochondrial mass, expression of mitochondrial fission protein (Drp1) and alteration in apoptotic signaling. The positive co-relation has been observed between the expressions of anti-apoptotic Bcl-2proteinswith mitochondrial fission protein Drp1. Higher mitochondrial fission in oral cancer cells was also correlated with the increased expression of cell cycle marker CyclinD1 indicating highly proliferative stage of oral cancer cells. The clinical correlation can be extended to develop biomarker for diagram and program in oral cancer management.

Assessment of platelet respiration as emerging biomarker of disease

Mitochondrial dysfunction is currently acknowledged as a central pathomechanism of most common diseases of the 21(st) century. Recently, the assessment of the bioenergetic profile of human peripheral blood cells has emerged as a novel research field with potential applications in the development of disease biomarkers. In particular, platelets have been successfully used for the ex vivo analysis of mitochondrial respiratory function in several acute and chronic pathologies. An increasing number of studies support the idea that evaluation of the bioenergetic function in circulating platelets may represent the peripheral signature of mitochondrial dysfunction in metabolically active tissues (brain, heart, liver, skeletal muscle). Accordingly, impairment of mitochondrial respiration in peripheral platelets might have potential clinical applicability as a diagnostic and prognostic tool as well as a biomarker in treatment monitoring. The aim of this minireview is to summarize current information in the field of platelet mitochondrial dysfunction in both acute and chronic diseases.

AMPK/FIS1-Mediated Mitophagy Is Required for Self-Renewal of Human AML Stem Cells

Leukemia stem cells (LSCs) are thought to drive the genesis of acute myeloid leukemia (AML) as well as relapse following chemotherapy. Because of their unique biology, developing effective methods to eradicate LSCs has been a significant challenge. In the present study, we demonstrate that intrinsic overexpression of the mitochondrial dynamics regulator FIS1 mediates mitophagy activity that is essential for primitive AML cells. Depletion of FIS1 attenuates mitophagy and leads to inactivation of GSK3, myeloid differentiation, cell cycle arrest, and a profound loss of LSC self-renewal potential. Further, we report that the central metabolic stress regulator AMPK is also intrinsically activated in LSC populations and is upstream of FIS1. Inhibition of AMPK signaling recapitulates the biological effect of FIS1 loss. These data suggest a model in which LSCs co-opt AMPK/FIS1-mediated mitophagy as a means to maintain stem cell properties that may be otherwise compromised by the stresses induced by oncogenic transformation.

Therapeutic synergy between tigecycline and venetoclax in a preclinical model of MYC/BCL2 double-hit B cell lymphoma

High-grade B cell lymphomas with concurrent activation of the MYC and BCL2 oncogenes, also known as double-hit lymphomas (DHL), show dismal prognosis with current therapies. MYC activation sensitizes cells to inhibition of mitochondrial translation by the antibiotic tigecycline, and treatment with this compound provides a therapeutic window in a mouse model of MYC-driven lymphoma. We now addressed the utility of this antibiotic for treatment of DHL. BCL2 activation in mouse Eμ-myc lymphomas antagonized tigecycline-induced cell death, which was specifically restored by combined treatment with the BCL2 inhibitor venetoclax. In line with these findings, tigecycline and two related antibiotics, tetracycline and doxycycline, synergized with venetoclax in killing human MYC/BCL2 DHL cells. Treatment of mice engrafted with either DHL cell lines or a patient-derived xenograft revealed strong antitumoral effects of the tigecycline/venetoclax combination, including long-term tumor eradication with one of the cell lines. This drug combination also had the potential to cooperate with rituximab, a component of current front-line regimens. Venetoclax and tigecycline are currently in the clinic with distinct indications: Our preclinical results warrant the repurposing of these drugs for combinatorial treatment of DHL.

The Antibiotic Drug Tigecycline: A Focus on its Promising Anticancer Properties

Tigecycline (TIG), the first member of glycylcycline bacteriostatic agents, has been approved to treat complicated infections in the clinic because of its expanded-spectrum antibiotic potential. Recently, an increasing number of studies have emphasized the anti-tumor effects of TIG. The inhibitory effects of TIG on cancer depend on several activating signaling pathways and abnormal mitochondrial function in cancer cells. The aim of this review is to summarize the cumulative anti-tumor evidence supporting TIG activity against different cancer types, including acute myeloid leukemia (AML), glioma, non-small cell lung cancer (NSCLC), among others. In addition, the efficacy and side effects of TIG in cancer patients are summarized in detail. Future clinical trials are also to be discussed that will evaluate the security and validate the underlying the tumor-killing properties of TIG.

A Phase 1 study of intravenous infusions of tigecycline in patients with acute myeloid leukemia

Acute myeloid leukemia (AML) cells meet the higher energy, metabolic, and signaling demands of the cell by increasing mitochondrial biogenesis and mitochondrial protein translation. Blocking mitochondrial protein synthesis through genetic and chemical approaches kills human AML cells at all stages of development in vitro and in vivo. Tigecycline is an antimicrobial that we found inhibits mitochondrial protein synthesis in AML cells. Therefore, we conducted a phase 1 dose‐escalation study of tigecycline administered intravenously daily 5 of 7 days for 2 weeks to patients with AML. A total of 27 adult patients with relapsed and refractory AML were enrolled in this study with 42 cycles being administered over seven dose levels (50–350 mg/day). Two patients experienced DLTs related to tigecycline at the 350 mg/day level resulting in a maximal tolerated dose of tigecycline of 300 mg as a once daily infusion. Pharmacokinetic experiments showed that tigecycline had a markedly shorter half‐life in these patients than reported for noncancer patients. No significant pharmacodynamic changes or clinical responses were observed. Thus, we have defined the safety of once daily tigecycline in patients with refractory AML. Future studies should focus on schedules of the drug that permit more sustained target inhibition.

Mitochondrial mass, a new metabolic biomarker for stem-like cancer cells: Understanding WNT/FGF-driven anabolic signaling

Here, we developed an isogenic cell model of "stemness" to facilitate protein biomarker discovery in breast cancer. For this purpose, we used knowledge gained previously from the study of the mouse mammary tumor virus (MMTV). MMTV initiates mammary tumorigenesis in mice by promoter insertion adjacent to two main integration sites, namely Int-1 (Wnt1) and Int-2 (Fgf3), which ultimately activates Wnt/β-catenin signaling, driving the propagation of mammary cancer stem cells (CSCs). Thus, to develop a humanized model of MMTV signaling, we over-expressed WNT1 and FGF3 in MCF7 cells, an ER(+) human breast cancer cell line. We then validated that MCF7 cells over-expressing both WNT1 and FGF3 show a 3.5-fold increase in mammosphere formation, and that conditioned media from these cells is also sufficient to promote stem cell activity in untransfected parental MCF7 and T47D cells, as WNT1 and FGF3 are secreted factors. Proteomic analysis of this model system revealed the induction of i) EMT markers, ii) mitochondrial proteins, iii) glycolytic enzymes and iv) protein synthesis machinery, consistent with an anabolic CSC phenotype. MitoTracker staining validated the expected WNT1/FGF3-induced increase in mitochondrial mass and activity, which presumably reflects increased mitochondrial biogenesis. Importantly, many of the proteins that were up-regulated by WNT/FGF-signaling in MCF7 cells, were also transcriptionally over-expressed in human breast cancer cells in vivo, based on the bioinformatic analysis of public gene expression datasets of laser-captured patient samples. As such, this isogenic cell model should accelerate the discovery of new biomarkers to predict clinical outcome in breast cancer, facilitating the development of personalized medicine.Finally, we used mitochondrial mass as a surrogate marker for increased mitochondrial biogenesis in untransfected MCF7 cells. As predicted, metabolic fractionation of parental MCF7 cells, via MitoTracker staining, indicated that high mitochondrial mass is a new metabolic biomarker for the enrichment of anabolic CSCs, as functionally assessed by mammosphere-forming activity. This observation has broad implications for understanding the role of mitochondrial biogenesis in the propagation of stem-like cancer cells. Technically, this general metabolic approach could be applied to any cancer type, to identify and target the mitochondrial-rich CSC population.The implications of our work for understanding the role of mitochondrial metabolism in viral oncogenesis driven by random promoter insertions are also discussed, in the context of MMTV and ALV infections.

Feature genes predicting the FLT3/ITD mutation in acute myeloid leukemia

In the present study, gene expression profiles of acute myeloid leukemia (AML) samples were analyzed to identify feature genes with the capacity to predict the mutation status of FLT3/ITD. Two machine learning models, namely the support vector machine (SVM) and random forest (RF) methods, were used for classification. Four datasets were downloaded from the European Bioinformatics Institute, two of which (containing 371 samples, including 281 FLT3/ITD mutation-negative and 90 mutation-positive samples) were randomly defined as the training group, while the other two datasets (containing 488 samples, including 350 FLT3/ITD mutation-negative and 138 mutation-positive samples) were defined as the test group. Differentially expressed genes (DEGs) were identified by significance analysis of the micro-array data by using the training samples. The classification efficiency of the SCM and RF methods was evaluated using the following parameters: Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and the area under the receiver operating characteristic curve. Functional enrichment analysis was performed for the feature genes with DAVID. A total of 585 DEGs were identified in the training group, of which 580 were upregulated and five were downregulated. The classification accuracy rates of the two methods for the training group, the test group and the combined group using the 585 feature genes were >90%. For the SVM and RF methods, the rates of correct determination, specificity and PPV were >90%, while the sensitivity and NPV were >80%. The SVM method produced a slightly better classification effect than the RF method. A total of 13 biological pathways were overrepresented by the feature genes, mainly involving energy metabolism, chromatin organization and translation. The feature genes identified in the present study may be used to predict the mutation status of FLT3/ITD in patients with AML.

Targeting Mitochondrial Function to Treat Quiescent Tumor Cells in Solid Tumors

The disorganized nature of tumor vasculature results in the generation of microenvironments characterized by nutrient starvation, hypoxia and accumulation of acidic metabolites. Tumor cell populations in such areas are often slowly proliferating and thus refractory to chemotherapeutical drugs that are dependent on an active cell cycle. There is an urgent need for alternative therapeutic interventions that circumvent growth dependency. The screening of drug libraries using multicellular tumor spheroids (MCTS) or glucose-starved tumor cells has led to the identification of several compounds with promising therapeutic potential and that display activity on quiescent tumor cells. Interestingly, a common theme of these drug screens is the recurrent identification of agents that affect mitochondrial function. Such data suggest that, contrary to the classical Warburg view, tumor cells in nutritionally-compromised microenvironments are dependent on mitochondrial function for energy metabolism and survival. These findings suggest that mitochondria may represent an “Achilles heel” for the survival of slowly-proliferating tumor cells and suggest strategies for the development of therapy to target these cell populations.

A novel formulation of tigecycline has enhanced stability and sustained antibacterial and antileukemic activity

Tigecycline is a broad-spectrum, first-in-class glycylcycline antibiotic currently used to treat complicated skin and intra-abdominal infections, as well as community-acquired pneumonia. In addition, we have demonstrated that tigecycline also has in vitro and in vivo activity against acute myeloid leukemia (AML) due to its ability to inhibit mitochondrial translation. Tigecycline is relatively unstable after reconstitution, and this instability may limit the use of the drug in ambulatory infusions for the treatment of infection and may prevent the development of optimal dosing schedules for the treatment of AML. This study sought to identify a formulation that improved the stability of the drug after reconstitution and maintained its antimicrobial and antileukemic activity. A panel of chemical additives was tested to identify excipients that enhanced the stability of tigecycline in solution at room temperature for up to one week. We identified a novel formulation containing the oxygen-reducing agents ascorbic acid (3 mg/mL) and pyruvate (60 mg/mL), in saline solution, pH 7.0, in which tigecycline (1 mg/mL) remained intact when protected from light for at least 7 days. This formulation also preserved the drug's antibacterial and antileukemic activity in vitro. Moreover, the novel formulation retained tigecycline's antileukemic activity in vivo. Thus, we identified and characterized a novel formulation for tigecycline that preserves its stability and efficacy after reconstitution.

Mitochondria "fuel" breast cancer metabolism: fifteen markers of mitochondrial biogenesis label epithelial cancer cells, but are excluded from adjacent stromal cells

Here, we present new genetic and morphological evidence that human tumors consist of two distinct metabolic compartments. First, re-analysis of genome-wide transcriptional profiling data revealed that > 95 gene transcripts associated with mitochondrial biogenesis and/or mitochondrial translation were significantly elevated in human breast cancer cells, as compared with adjacent stromal tissue. Remarkably, nearly 40 of these upregulated gene transcripts were mitochondrial ribosomal proteins (MRPs), functionally associated with mitochondrial translation of protein components of the OXPHOS complex. Second, during validation by immunohistochemistry, we observed that antibodies directed against 15 markers of mitochondrial biogenesis and/or mitochondrial translation (AKAP1, GOLPH3, GOLPH3L, MCT1, MRPL40, MRPS7, MRPS15, MRPS22, NRF1, NRF2, PGC1-α, POLRMT, TFAM, TIMM9 and TOMM70A) selectively labeled epithelial breast cancer cells. These same mitochondrial markers were largely absent or excluded from adjacent tumor stromal cells. Finally, markers of mitochondrial lipid synthesis (GOLPH3) and mitochondrial translation (POLRMT) were associated with poor clinical outcome in human breast cancer patients. Thus, we conclude that human breast cancers contain two distinct metabolic compartments-a glycolytic tumor stroma, which surrounds oxidative epithelial cancer cells-that are mitochondria-rich. The co-existence of these two compartments is indicative of metabolic symbiosis between epithelial cancer cells and their surrounding stroma. As such, epithelial breast cancer cells should be viewed as predatory metabolic "parasites," which undergo anabolic reprogramming to amplify their mitochondrial "power." This notion is consistent with the observation that the anti-malarial agent chloroquine may be an effective anticancer agent. New anticancer therapies should be developed to target mitochondrial biogenesis and/or mitochondrial translation in human cancer cells.