Power cut: inhibiting mitochondrial translation to target leukemia

Targeting ATP Synthase by Bedaquiline as a Therapeutic Strategy to Sensitize Ovarian Cancer to Cisplatin

Cisplatin is a common chemotherapeutic drug for treating ovarian cancer, but its clinical efficacy is hampered by intrinsic and acquired resistance. Previous studies had shown inhibiting oxidative phosphorylation overcomes cisplatin resistance in ovarian cancer. Studies reveal that bedaquiline, a clinically available antimicrobial drug, inhibits cancer via targeting mitochondria. This study systematically assessed the efficacy of bedaquiline in ovarian cancer and its underlying mechanism. Using a panel of ovarian cancer cell lines and normal ovary cells, we demonstrated bedaquiline is selective for anti-ovarian cancer activities. Furthermore, the sensitivity varied among different ovarian cancer cell lines regardless of their sensitivity to cisplatin. Bedaquiline inhibited growth, survival and migration, through decreasing levels of ATP synthase subunit, complex V activity, mitochondrial respiration and ATP. We further found that ovarian cancer displayed increased levels of ATP, oxygen consumption rate (OCR), complex V activity and ATP synthase subunits compared to normal counterpart. Combination index analysis showed that bedaquiline and cisplatin is synergistic. Bedaquiline remarkably enhanced the efficacy of cisplatin in inhibiting ovarian cancer growth in mice. Our study provides evidence to repurpose bedaquiline for ovarian cancer treatment and suggests that ATP synthase is a selective target to overcome cisplatin resistance in ovarian cancer.

Monensin inhibits anaplastic thyroid cancer via disrupting mitochondrial respiration and AMPK/mTOR signaling

OBJECTIVE

The clinical management of anaplastic thyroid cancer (ATC) remains challenging and novel treatment methods are needed. Monensin is a carboxyl polyether ionophore that potently inhibits the growth of various cancer types. Our current work investigates whether monensin has selective anti-ATC activity and systematically explores its underlying mechanisms.

METHODS

Proliferation and apoptosis assays were performed using a panel of thyroid cancer cell lines. Mitochondrial biogenesis profiles, ATP levels, oxidative stress, AMPK and mTOR were examined in these cells after monensin treatment.

RESULTS

Monensin is effective to inhibit proliferation and induce apoptosis in a number of thyroid cancer cell lines. The results are consistent across cell lines of varying cellular origins and genetic mutations. Compared to other thyroid cancer cell types, ATC cell lines are the most sensitive to monensin. Of note, monensin used at our experimental concentration affects less of normal cells. Mechanistic studies reveal that monensin acts on ATC cells through disrupting mitochondrial function, inducing oxidative stress and damage, and AMPK activation-induced mTOR inhibition. We further show mitochondrial respiration is a critical target for monensin in ATC cells.

CONCLUSIONS

Our pre-clinical findings demonstrate the selective anti-ATC activities of monensin. This is supported by increasing evidence monensin can to be repurposed as a potential anti-cancer drug.

The subtype-specific molecular function of SPDEF in breast cancer and insights into prognostic significance

Breast cancer (BC) is a molecular diverse disease which becomes the most common malignancy among women worldwide. There are four BC subtypes (Luminal A, Luminal B, HER2‐enriched and Basal‐like) robustly established following gene expression pattern‐based characterization, behave significant differences in terms of their incidence, risk factors, prognosis and therapeutic sensitivity. Thus, there is an urgent need to provide mechanism research, treatment strategies and/or prognosis evaluation based on the patient stratification of BC subtypes. The prostate‐derived ETS factor SPDEF was first identified as an activator of prostate specific antigen, and then, the involvements in many aspects of BC have been proposed. However, the subtype‐specific molecular function of SPDEF in BC and insights into prognostic significance have not been clearly elucidated. This study demonstrated for the first time that SPDEF may play a diversity role in the expression levels, clinicopathologic importance, biological function and prognostic evaluation in BC via bioinformatics and experimental evidence, which mainly depends on different BC subtyping. In summary, our findings would help to better understand the possible mechanisms of various BC subtypes and to find possible candidate genes for prognostic and therapeutic usage.

Atovaquone at clinically relevant concentration overcomes chemoresistance in ovarian cancer via inhibiting mitochondrial respiration

The poor outcomes in ovarian cancer necessitate new treatments. Strategies to interfere with oxidative phosphorylation have been recently highlighted for the treatment of ovarian tumors. Atovaquone, an approved antimicrobial drug, has demonstrated anti-cancer potential and ability in disrupting mitochondrial function. Here, we investigated the efficacy of atovaquone as single drug and its combination with cisplatin in ovarian cancer. We show that atovaquone at clinically achievable concentrations is active against ovarian cancer bulky and stem-cell like cells via inhibiting growth and colony formation, and inducing caspase-dependent apoptosis. In contrast, atovaquone either does not or inhibits normal cells in a less extent than in ovarian cancer cells. Mechanism studies using multiple independent approaches demonstrate that atovaquone acts on ovarian cancer cells via decreasing mitochondrial complex III which results in mitochondrial respiration inhibition, energy reduction and oxidative stress. In line with in vitro findings, atovaquone alone at non-toxic dose is effective in inhibiting ovarian cancer growth in vivo, and its combination with cisplatin is synergistic. Our study suggests that atovaquone is a promising candidate to the treatment of ovarian cancer. Our work also supports the notion that mitochondrial respiration is a therapeutic target in ovarian cancer.

Quantitative Proteomics Analysis of Berberine-Treated Colon Cancer Cells Reveals Potential Therapy Targets

Simple Summary

Colon cancer is one of the most common malignant tumors and beberine has been found to exert potential anti-colon cancer activity in vitro and in vivo. In this study, by using proteomics and bioinformatics approaches, we report that berberine may inhibit the proliferation of colon cancer cells by regulating mitochondrial translation and ribosome biogenesis, as well as by promoting calcium mobilization and metabolism of fat-soluble vitamins. Moreover, GTPase ERAL1 and mitochondrial ribosomal proteins MRPL11, 15, 30, 37, 40, and 52 have great potential to serve as potential therapeutic targets for colon cancer treatment.

Abstract

Colon cancer is one of the most lethal malignancies worldwide. Berberine has been found to exert potential anti-colon cancer activity in vitro and in vivo, although the detailed regulatory mechanism is still unclear. This study aims to identify the underlying crucial proteins and regulatory networks associated with berberine treatment of colon cancer by using proteomics as well as publicly available transcriptomics and tissue array data. Proteome profiling of berberine-treated colon cancer cells demonstrated that among 5130 identified proteins, the expression of 865 and 675 proteins were changed in berberine-treated HCT116 and DLD1 cells, respectively. Moreover, 54 differently expressed proteins that overlapped in both cell lines were mainly involved in mitochondrial protein synthesis, calcium mobilization, and metabolism of fat-soluble vitamins. Finally, GTPase ERAL1 and mitochondrial ribosomal proteins including MRPL11, 15, 30, 37, 40, and 52 were identified as hub proteins of berberine-treated colon cancer cells. These proteins have higher transcriptional and translational levels in colon tumor samples than that of colon normal samples, and were significantly down-regulated in berberine-treated colon cancer cells. Genetic dependency analysis showed that silencing the gene expression of seven hub proteins could inhibit the proliferation of colon cancer cells. This study sheds a light for elucidating the berberine-related regulatory signaling pathways in colon cancer, and suggests that ERAL1 and several mitochondrial ribosomal proteins might be promising therapeutic targets for colon cancer.

Targeting breast cancer metabolism with a novel inhibitor of mitochondrial ATP synthesis

Inhibitors of mitochondrial respiration and ATP synthesis may promote the selective killing of respiration-competent cancer cells that are critical for tumor progression. We previously reported that CADD522, a small molecule inhibitor of the RUNX2 transcription factor, has potential for breast cancer treatment. In the current study, we show that CADD522 inhibits mitochondrial oxidative phosphorylation by decreasing the mitochondrial oxygen consumption rate (OCR) and ATP production in human breast cancer cells in a RUNX2-independent manner. The enzyme activity of mitochondrial ATP synthase was inhibited by CADD522 treatment. Importantly, results from cellular thermal shift assays that detect drug-induced protein stabilization revealed that CADD522 interacts with both α and β subunits of the F1-ATP synthase complex. Differential scanning fluorimetry also demonstrated interaction of α subunits of the F1-ATP synthase to CADD522. These results suggest that CADD522 might target the enzymatic F1 subunits in the ATP synthase complex. CADD522 increased the levels of intracellular reactive oxygen species (ROS), which was prevented by MitoQ, a mitochondria-targeted antioxidant, suggesting that cancer cells exposed to CADD522 may elevate ROS from mitochondria. CADD522-increased mitochondrial ROS levels were enhanced by exogenously added pro-oxidants such as hydrogen peroxide or tert-butyl hydroperoxide. Conversely, CADD522-mediated cell growth inhibition was blocked by N-acetyl-l-cysteine, a general ROS scavenger. Therefore, CADD522 may exert its antitumor activity by increasing mitochondrial driven cellular ROS levels. Collectively, our data suggest in vitro proof-of-concept that supports inhibition of mitochondrial ATP synthase and ROS generation as contributors to the effectiveness of CADD522 in suppression of tumor growth.

B-cell lymphoma-2 inhibition and resistance in acute myeloid leukemia

Spurred by better understanding of disease biology, improvements in molecular diagnostics, and the development of targeted therapies, the treatment of acute myeloid leukemia (AML) has undergone significant evolution in recent years. Arguably, the most exciting shift has come from the success of treatment with the B-cell lymphoma-2 inhibitor venetoclax. When given in combination with a hypomethylating agent or low dose cytarabine, venetoclax demonstrates high response rates, some of which are durable. In spite of this, relapses after venetoclax treatment are common, and much interest exists in elucidating the mechanisms of resistance to the drug. Alterations in leukemic stem cell metabolism have been identified as a possible escape route, and clinical trials focusing on targeting metabolism in AML are ongoing. This review article highlights current research regarding venetoclax treatment and resistance in AML with a focus on cellular metabolism.

Diabetes-mediated promotion of colon mucosa carcinogenesis is associated with mitochondrial dysfunction

Type 2 diabetes mellitus (T2DM) has been associated with an increased risk of cancer, including colon cancer (CC). However, we recently reported no influence of T2DM on CC prognosis, suggesting that any effect might be at the early stages of tumor development. We hypothesized that T2DM may create an environment in the healthy tissue, which acts as a carcinogenesis driver in agreement with the field of cancerization concept. Here, we focused on early carcinogenesis by analyzing paired tumor and normal colonic mucosa samples from the same patients. The proteome of CC and paired mucosa was quantitatively analyzed in 28 individuals (12 diabetics and 16 nondiabetics) by mass spectrometry with isobaric labeling. Out of 3076 identified proteins, 425 were differentially expressed at the tumor in diabetics compared with nondiabetics. In the adjacent mucosa, 143 proteins were differentially expressed in diabetics and nondiabetics. An enrichment analysis of this signature pointed to mitochondria, ribosome, and translation. Only six proteins were upregulated by diabetes both in tumor and mucosa, of which five were mitochondrial proteins. Differential expression in diabetic versus nondiabetic mucosa was confirmed for MRPL53, MRPL18, and TIMM8B. Higher levels of MRPL18, TIMM8B, and EIF1A were also found in normal colon epithelial cells exposed to high‐glucose conditions. We conclude that T2DM is associated with specific molecular changes in the normal mucosa of CC patients, consistent with field of cancerization in a diabetic environment. The mitochondrial protein signature identifies a potential therapeutic target that could underlie the higher risk of CC in diabetics.

Inhibition of mitochondrial translation selectively targets osteosarcoma

The unique dependence of cancer cells on mitochondrial metabolism has been exploited therapeutically in various cancers but not osteosarcoma. In this work, we demonstrate that inhibition of mitochondrial translation is effective and selective in targeting osteosarcoma. We firstly showed that tigecycline at pharmacological achievable concentrations inhibited growth and induced apoptosis of multiple osteosarcoma cell lines while sparing normal osteoblast cells. Similarly, tigecycline at effective doses that delayed osteosarcoma growth did not cause significant toxicity to mice. We next showed that tigecycline specifically inhibits mitochondrial translation, resulting in defective mitochondrial respiration in both osteosarcoma and normal osteoblast cells. We further confirm mitochondrial respiration as the target of tigecycline using three independent approaches. In addition, we demonstrate that compared to normal osteoblasts, osteosarcoma cells have higher mitochondrial biogenesis. We finally show that specific inhibition of mitochondrial translation via EF-Tu depletion produces the similar anti-osteosarcoma effects of tigecycline. Our work highlights the therapeutic value of targeting mitochondrial metabolism in osteosarcoma and tigecycline as a useful addition to the treatment of osteosarcoma.

Inhibition of mitochondrial translation as a therapeutic strategy for human ovarian cancer to overcome chemoresistance

Aberrant increase in mitochondrial biogenesis is common in human ovarian cancer and has great therapeutic value. In this work, we demonstrate that tigecycline, a FDA-approved broad spectrum antibiotic, selectively targets ovarian cancer cells through inhibition of mitochondrial translation. Tigecycline dose-dependently inhibits proliferation of ovarian cancer cells via arresting them at G2/M phase and induces apoptosis through caspase pathway. At the same concentration, tigecycline either does not or inhibits normal cells in a less extent than ovarian cancer cells. Mechanistically, tigecycline specifically inhibits translation by mitochondrial ribosome but not nuclear or cytosolic ribosome, leading to mitochondrial dysfunction, oxidative stress and damage, AMPK activation and inhibition of mTOR signaling in ovarian cancer cells. We further show that the inhibitory effects on ovarian cancer cell by tigecycline is mediated by its suppression of mitochondrial respiration. Importantly, the combination of tigecycline and cisplatin at sublethal concentration results in much greater efficacy than cisplatin alone in vitro and in vivo. Additionally, the effective dose of tigecycline in ovarian cancer is clinically achievable. Our study suggests that tigecycline is a useful addition to the treatment of ovarian cancer. Our work also highlights the targeted therapeutic potential of mitochondrial respiration in ovarian cancer.

Inhibition of mitochondrial respiration overcomes hepatocellular carcinoma chemoresistance

The clinical management of advanced hepatocellular carcinoma (HCC) is challenging due to its resistance to chemotherapy. In our work, we demonstrate that an antiparasitic drug atovaquone at clinically relevant concentrations is active against chemoresistant HCC. We show that atovaquone inhibits proliferation and induces apoptosis in not only HCC parental cells but also cells exposed to long time culture of chemotherapeutic agents. Consistently, the combination of atovaquone with cisplatin or doxorubicin achieved remarkably greater efficacy than single drug alone. Mechanistically, atovaquone overcomes HCC chemoresistance via supressing mitochondrial respiration and inducing oxidative stress. Atovaquone but not cisplatin or doxorubicin is ineffective in mitochondrial respiration-deficient ρ0, confirming mitochondria as a specific upstream target of atovaquone. Interestingly, we show that prolonged exposure of HCC cells to chemotherapeutic agents induces higher level of mitochondrial respiration, suggesting that tumors which develop chemoresistance after chemotherapy might be more dependent on mitochondrial respiration than primary tumors and explaining the sensitivity of chemoresistant HCC cells to atovaquone. We further show that atovaquone at tolerable does significantly inhibits chemoresistant HCC growth in mice throughout the duration of treatment. In line with in vitro data, we observe the increased oxidative stress in atovaquone-treated tumors. Our findings highlight the dependency of chemoresistant HCC on mitochondrial respiration and demonstrate that atovaquone is a potential drug to overcome HCC chemoresistance.

Gallic acid targets acute myeloid leukemia via Akt/mTOR-dependent mitochondrial respiration inhibition

Gallic acid is one of the many phenolic acids that can be found in dietary substances and traditional medicine herbs. The anti-cancer activities of gallic acid have been shown in various cancers but its underlying molecular mechanisms are not well understood. In this study, we show Akt/mammalian target of rapamycin (mTOR)-dependent inhibition of mitochondrial respiration as a mechanism of gallic acid's action in acute myeloid leukemia (AML). Gallic acid significantly induces apoptosis of AML cell lines, primary mononuclear cells (MNC) and CD34 stem/progenitors isolated form AML patients via caspase-dependent pathway. It also significantly enhances two standard AML chemotherapeutic agents' efficacy in vitro cell culture system and in vivo xenograft model. Gallic acid inhibits dose- and time-dependent mitochondrial respiration, leading to decreased ATP production and oxidative stress. Overexpression of constitutively active Akt restores gallic acid-mediated inhibition of mTOR signaling, mitochondrial dysfunction, energy crisis and apoptosis. Our results demonstrate that mitochondrial respiration inhibition by gallic acid is a consequence of Akt/mTOR signaling suppression. Our findings suggest that combination therapy with gallic acid may enhance antileukemic efficacy of standard chemotherapeutic agents in AML.

Targeting mitochondrial respiration as a therapeutic strategy for cervical cancer

Targeting mitochondrial respiration has been documented as an effective therapeutic strategy in cancer. However, the impact of mitochondrial respiration inhibition on cervical cancer cells are not well elucidated. Using a panel of cervical cancer cell lines, we show that an existing drug atovaquone is active against the cervical cancer cells with high profiling of mitochondrial biogenesis. Atovaquone inhibited proliferation and induced apoptosis with varying efficacy among cervical cancer cell lines regardless of HPV infection, cellular origin and their sensitivity to paclitaxel. We further demonstrated that atovaquone acts on cervical cancer cells via inhibiting mitochondrial respiration. In particular, atovaquone specifically inhibited mitochondrial complex III but not I, II or IV activity, leading to respiration inhibition and energy crisis. Importantly, we found that the different sensitivity of cervical cancer cell lines to atovaquone were due to their differential level of mitochondrial biogenesis and dependency to mitochondrial respiration. In addition, we demonstrated that the in vitro observations were translatable to in vivo cervical cancer xenograft mouse model. Our findings suggest that the mitochondrial biogenesis varies among patients with cervical cancer. Our work also suggests that atovaquone is a useful addition to cervical cancer treatment, particularly to those with high dependency on mitochondrial respiration.

Antibiotic ivermectin selectively induces apoptosis in chronic myeloid leukemia through inducing mitochondrial dysfunction and oxidative stress

Mitochondria has been a promising target in blood cancer given their unique dependencies on mitochondrial functions compared to normal hematopoietic cells. In line with this concept, we show that an anthelminthic drug ivermectin selectively kills chronic myeloid leukemia (CML) cells via inducing mitochondrial dysfunctions and oxidative stress. Ivermectin is significantly more effective in inducing caspase-dependent apoptosis in CML cell line K562 and primary CML CD34 than normal bone marrow (NBM) CD34 cells. Ivermectin also augments in vitro and in vivo efficacy of standard CML tyrosine kinase inhibitors. Mechanistically, ivermectin inhibits respiratory complex I activity and suppresses mitochondrial respiration in K562 and CML CD34 cells. Interestingly, we demonstrate that mitochondrial respiration are lower in NBM CD34 compared to malignant CD34 cells. In addition, ivermectin also induces mitochondrial dysfunctions in NBM CD34 cells in a similar manner as in CML CD34 cells whereas NBM CD34 cells are significantly less sensitive to ivermectin than CML CD34 cells. These suggest that NBM CD34 cells are more tolerable to mitochondrial dysfunctions than CML CD34 cells. Consistently, ivermectin induces higher levels of oxidative stress and damage in CML than normal counterparts. Antioxidant NAC rescues ivermectin's effects, confirming oxidative stress as the mechanism of its action in CML. Our work provides the fundamental evidence to repurpose ivermectin for CML treatment. Our work also highlights the therapeutic value of targeting mitochondria respiration in CML.

Mitochondrial ribosomes in cancer

Mitochondria play fundamental roles in the regulation of life and death of eukaryotic cells. They mediate aerobic energy conversion through the oxidative phosphorylation (OXPHOS) system, and harbor and control the intrinsic pathway of apoptosis. As a descendant of a bacterial endosymbiont, mitochondria retain a vestige of their original genome (mtDNA), and its corresponding full gene expression machinery. Proteins encoded in the mtDNA, all components of the multimeric OXPHOS enzymes, are synthesized in specialized mitochondrial ribosomes (mitoribosomes). Mitoribosomes are therefore essential in the regulation of cellular respiration. Additionally, an increasing body of literature has been reporting an alternative role for several mitochondrial ribosomal proteins as apoptosis-inducing factors. No surprisingly, the expression of genes encoding for mitoribosomal proteins, mitoribosome assembly factors and mitochondrial translation factors is modified in numerous cancers, a trait that has been linked to tumorigenesis and metastasis. In this article, we will review the current knowledge regarding the dual function of mitoribosome components in protein synthesis and apoptosis and their association with cancer susceptibility and development. We will also highlight recent developments in targeting mitochondrial ribosomes for the treatment of cancer.

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.

BCL-2 inhibition impairs mitochondrial function and targets oral tongue squamous cell carcinoma

Purpose

To understand the role of Bcl-2 overexpression in oral tongue squamous cell carcinoma (OTSCC) patients and investigate the efficacy of targeting Bcl-2 in OTSCC.

Methods

The expression level of Bcl-2 on normal tongue cells and OTSCC cells were measured by real-time PCR and western blotting. The functional roles of Bcl-2 were examined by MTS, flow cytometry and xenograft cancer mouse model. Mechanism studies were performed by analyzing mitochondrial functions in a panel of OTSCC cell lines.

Results

Bcl-2 is up-regulated at mRNA and protein levels in a panel of OTSCC cell lines compared to normal tongue epithelial cells (NTEC). Importantly, overexpression of Bcl-2 confers resistance of OTSCC cells to chemotherapeutic drug cisplatin treatment. Overexpression of Bcl-2 in NTEC significantly increased cell growth. In contrast, inhibition of Bcl-2 by genetic and pharmacological approaches inhibits proliferation and induces apoptosis in OTSCC cells. Mechanistically, Bcl-2 inhibitor ABT-199 impairs mitochondrial functions as shown by the decreased levels of mitochondrial membrane potential, mitochondrial respiration and ATP, and the increased levels of ROS in OTSCC cells. In addition, ABT-199 inhibits proliferation and induces apoptosis and mitochondrial dysfunctions in NTEC cells, but to a less extent than in OTSCC cells. We further show that ABT-199 augments the effects of cisplatin in eliminating OTSCC cells in in vitro tongue cancer cellular system and in vivo tongue cancer xenograft mouse model.

Conclusions

Inhibition of Bcl-2 effectively targets OTSCC cells through inhibiting proliferation and inducing apoptosis. Inhibition of Bcl-2 also augments the inhibitory effects of cisplatin in vitro and in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s40064-016-3310-2) contains supplementary material, which is available to authorized users.

Niclosamide suppresses renal cell carcinoma by inhibiting Wnt/β-catenin and inducing mitochondrial dysfunctions

PURPOSE

To investigate the effects of anthelminthic drug niclosamide in renal cell carcinoma (RCC) and the underlying mechanisms of its action.

METHODS

The effects of niclosamide on the proliferation and apoptosis of RCC cells were examined in vitro and in vivo by using MTS, colony formation assay, flow cytometry and xenograft cancer mouse model. Mechanism studies were performed by analyzing Wnt/β-catenin signaling and mitochondrial functions in a panel of RCC cell lines.

RESULTS

We show that niclosamide effectively targets two RCC cell lines through inhibiting proliferation and anchorage-independent colony formation, and inducing apoptosis. It also enhances the inhibitory effects of chemotherapeutic drug cisplatin in two independent in vivo RCC xenograft mouse models. Mechanistically, niclosamide decreases β-catenin levels and therefore suppresses Wnt/β-catenin activities. Overexpression of β-catenin partially reverses the inhibitory effects of niclosamide in RCC cells, demonstrating that besides β-catenin, other mechanisms are involved in niclosamide's anti-cancer activity. Indeed, we further show that niclosamide induces mitochondrial dysfunctions as shown by the decreased level of mitochondrial membrane potential and respiration, resulting in decreased ATP levels and increased reactive oxygen species (ROS) levels.

CONCLUSIONS

Our findings support the inhibitory effects of niclosamide in cancer and provide better understanding on its underlying mechanism. Our data suggests that niclosamide is a useful addition to the treatment armamentarium for RCC.

Pyrvinium selectively targets blast phase-chronic myeloid leukemia through inhibition of mitochondrial respiration

The use of BCR-ABL1 tyrosine kinase inhibitors (TKI) has led to excellent clinical responses in patients with chronic phase chronic myeloid leukemia (CML). However these inhibitors have been less effective as single agents in the terminal blast phase (BP). We show that pyrvinium, a FDA-approved anthelminthic drug, selectively targets BP-CML CD34⁺ progenitor cells. Pyrvinium is effective in inducing apoptosis, inhibiting colony formation and self-renewal capacity of CD34⁺ cells from TKI-resistant BP-CML patients, while cord blood CD34⁺ are largely unaffected. The effects of pyrvinium are further enhanced upon combination with dasatinib, a second generation BCR-ABL1 TKI. In a CML xenograft model pyrvinium significantly inhibits tumor growth as a single agent, with complete inhibition in combination with dasatinib. While pyrvinium has been shown to inhibit the Wnt/β-catenin signalling pathway via activation of casein kinase 1α, we find its activity in CML is not dependent on this pathway. Instead, we show that pyrvinium localizes to mitochondria and induces apoptosis by inhibiting mitochondrial respiration. Our study suggests that pyrvinium is a useful addition to the treatment armamentarium for BP-CML and that targeting mitochondrial respiration may be a potential therapeutic strategy in aggressive leukemia.

Therapeutic effects of antibiotic drug mefloquine against cervical cancer through impairing mitochondrial function and inhibiting mTOR pathway

Targeting mitochondria is an attractive strategy for cancer therapy due to the essential roles of mitochondria in cancer cell energy metabolism. In this study, we show that mefloquine, an antibiotic drug, effectively targets cervical cancer cells through impairing mitochondrial function. Mefloquine dose-dependently induces apoptosis and inhibits proliferation and anchorage-independent colony formation of multiple cervical cancer cell lines. Mefloquine alone inhibits cervical tumor growth in vivo and its combination with paclitaxel is synergistic in inhibiting tumor growth. Mechanistically, mefloquine inhibits mitochondrial function via inhibiting mitochondrial respiration, decreasing membrane potential, increasing ROS generation, and decreasing ATP level. We further show that mefloquine suppresses activation of mTOR signaling pathway in HeLa cells. However, the inhibitory effects of mefloquine on survival, colony formation, and ATP are abolished in mitochondrial respiration-deficient HeLa ρ⁰ cells, demonstrating that mefloquine acts on cervical cancer cells via targeting mitochondrial respiration. Inhibition of mTOR signaling pathway by mefloquine was also reversed in HeLa ρ⁰ cells, suggesting deactivation of mTOR pathway as a consequence of mitochondria function disruption. Our work suggests that mefloquine is a potential candidate for cervical cancer treatment. Our work also highlights the therapeutic value of anti-mitochondria and establishes the association of mitochondrial function and the activation of mTOR signaling pathway in cervical cancer cells.

Structure and Function of the Mitochondrial Ribosome

Mitochondrial ribosomes (mitoribosomes) perform protein synthesis inside mitochondria, the organelles responsible for energy conversion and adenosine triphosphate production in eukaryotic cells. Throughout evolution, mitoribosomes have become functionally specialized for synthesizing mitochondrial membrane proteins, and this has been accompanied by large changes to their structure and composition. We review recent high-resolution structural data that have provided unprecedented insight into the structure and function of mitoribosomes in mammals and fungi.

Repositioning of antibiotic levofloxacin as a mitochondrial biogenesis inhibitor to target breast cancer

Targeting mitochondrial biogenesis has become a potential therapeutic strategy in cancer due to their unique metabolic dependencies. In this study, we show that levofloxacin, a FDA-approved antibiotic, is an attractive candidate for breast cancer treatment. This is achieved by the inhibition of proliferation and induction of apoptosis in a panel of breast cancer cell lines while sparing normal breast cells. It also acts synergistically with conventional chemo drug in two independent in vivo breast xenograft mouse models. Importantly, levofloxacin inhibits mitochondrial biogenesis as shown by the decreased level of mitochondrial respiration, membrane potential and ATP. In addition, the anti-proliferative and pro-apoptotic effects of levofloxacin are reversed by acetyl-L-Carnitine (ALCAR, a mitochondrial fuel), confirming that levofloxacin's action in breast cancer cells is through inhibition of mitochondrial biogenesis. A consequence of mitochondrial biogenesis inhibition by levofloxacin in breast cancer cells is the deactivation of PI3K/Akt/mTOR and MAPK/ERK pathways. We further demonstrate that breast cancer cells have increased mitochondrial biogenesis than normal breast cells, and this explains their different sensitivity to levofloxacin. Our work suggest that levofloxacin is a useful addition to breast cancer treatment. Our work also establish the essential role of mitochondrial biogenesis on the activation of PI3K/Akt/mTOR and MAPK/ERK pathways in breast cancer cells.

Mitochondrial dependency in progression of acute myeloid leukemia

Acute myeloid leukemia (AML) is a clonal hematopoietic malignant disorder which arises due to dysregulated differentiation, uncontrolled growth and inhibition of apoptosis leading to the accumulation of immature myeloid progenitor in the bone marrow. The heterogeneity of the disease at the molecular and cytogenetic level has led to the identification of several alteration of biological and clinical significance. One of the alterations which have gained attention in recent times is the altered energy and metabolic dependency of cancer originally proposed by Warburg. Mitochondria are important cell organelles regulating cellular energetic level, metabolism and apoptosis which in turn can affect cell proliferation and differentiation, the major manifestations of diseases like AML. In recent times the importance of mitochondrial generated ATP and mitochondrial localized metabolic pathways has been shown to play important role in the progression of AML. These studies have also demonstrated the clinical significance of mitochondrial targets for its effectiveness in combating relapsed or refractory AML. Here we review the importance of the mitochondrial dependency for the progression of AML and the emergence of the mitochondrial molecular targets which holds therapeutic importance.

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.

Mitochondrial translational inhibitors in the pharmacopeia

The vast majority of energy necessary for cellular function is produced in the mitochondria by the phosphorylation of ADP to ATP. Other critical mitochondrial functions include apoptosis and free-radical production. Chemical agents, including those found in the modern pharmacopeia, may impair mitochondrial function by a number of mechanisms. The mitochondria are vulnerable to environmental injury because of their complex physical structure, electrochemical properties of the inner mitochondrial membrane (IMM), dual genetic control from both mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) and inherent properties of the translational and transcriptional machinery. Mitochondria have evolved from alpha-proteobacteria and the residual structural similarity to bacterial translational machinery has left the mtDNA genes vulnerable to inhibition by commonly used translation-targeted antibiotics. Many of these medications cause adverse effects in otherwise healthy people, but there are also examples where particular gene mutations may predispose to increased drug toxicity. It is hoped that preclinical pharmacogenetic and functional studies of mitochondrial toxicity, along with personalized genomic medicine, will improve both our understanding of the spectrum of disease caused by inhibition of mitochondrial translation and improve the safe and effective use of antibiotics that inhibit bacterial and human mitochondrial translation. This article is part of a Special Issue entitled: Mitochondrial Gene Expression.

Is cancer a metabolic rebellion against host aging? In the quest for immortality, tumor cells try to save themselves by boosting mitochondrial metabolism

Aging drives large systemic reductions in oxidative mitochondrial function, shifting the entire body metabolically towards aerobic glycolysis, a.k.a, the Warburg effect. Aging is also one of the most significant risk factors for the development of human cancers, including breast tumors. How are these two findings connected? One simplistic idea is that cancer cells rebel against the aging process by increasing their capacity for oxidative mitochondrial metabolism (OXPHOS). Then, local and systemic aerobic glycolysis in the aging host would provide energy-rich mitochondrial fuels (such as L-lactate and ketones) to directly "fuel" tumor cell growth and metastasis. This would establish a type of parasite-host relationship or "two-compartment tumor metabolism", with glycolytic/oxidative metabolic-coupling. The cancer cells ("the seeds") would flourish in this nutrient-rich microenvironment ("the soil"), which has been fertilized by host aging. In this scenario, cancer cells are only trying to save themselves from the consequences of aging, by engineering a metabolic mutiny, through the amplification of mitochondrial metabolism. We discuss the recent findings of Drs. Ron DePinho (MD Anderson) and Craig Thomspson (Sloan-Kettering) that are also consistent with this new hypothesis, linking cancer progression with metabolic aging. Using data mining and bioinformatics approaches, we also provide key evidence of a role for PGC1a/NRF1 signaling in the pathogenesis of (1) two-compartment tumor metabolism, and (2) mitochondrial biogenesis in human breast cancer cells.