Inhibition Of Mitochondrial Metabolism Research Articles

Regulation of mitochondrial metabolism during hibernation by reversible suppression of electron transport system enzymes.

Small hibernators cycle between periods of torpor, with body temperature (T b) approximately 5°C, and interbout euthermia (IBE), where T b is approximately 37°C. During entrance into a torpor bout liver mitochondrial respiration is rapidly suppressed by 70% relative to IBE. We compared activities of electron transport system (ETS) complexes in intact liver mitochondria isolated from 13-lined ground squirrels (Ictidomys tridecemlineatus) sampled during torpor and IBE to investigate potential sites of this reversible metabolic suppression. Flux through complexes I-IV and II-IV was suppressed by 40 and 60%, respectively, in torpor, while flux through complexes III-IV and IV did not differ between torpor and IBE. We also measured maximal enzyme activity of ETS enzymes in homogenized isolated mitochondria and whole liver tissue. In isolated mitochondria, activities of complexes I and II were significantly lower in torpor relative to IBE, but complexes III, IV, and V did not differ. In liver tissue, only activity of complex II was suppressed during torpor relative to IBE. Despite the significant differences in both ETS flux and maximal activity, the protein content of complexes I and II did not differ between torpor and IBE. These results suggest that the rapid, reversible suppression of mitochondrial metabolism is due to regulatory changes, perhaps by post-translational modification during entrance into a torpor bout, and not changes in ETS protein content.

Abstract 53: Epigenetic silencing of krebs cycle metabolism in kidney cancer

Abstract Mounting evidence points to alterations in mitochondrial metabolism in renal cell carcinoma (RCC) including recent large-scale transcriptomic data demonstrating loss of tricarboxylic acid (TCA) cycle enzyme expression with aggressive tumors. Using a metabolomics/transcriptomics approach, we identified loss of mRNA expression of PGC-1α and ERR-γ is associated with tumor progression and worsened outcomes in RCC patients. PGC-1α both induces and cooperates with ERR-γ to promote TCA cycle enzyme expression. Additionally, PGC-1α reconstitution in RCC cells reverses the glycolytic phenotype and suppresses invasive phenotypes. Loss of PGC-1α and ERR-γ is through DNA and histone repressive silencing of the transcription factor PRDM16. Loss of PRDM16 is among the most prominent transcriptional changes in metastatic tumor sites. PRDM16 expression in RCC cells restorers TCA cycle enzyme expression, mitigates the Warburg phenotype, and suppresses in vivo tumorigenesis. Collectively, our data uncover a transcription factor network epigenetically silenced in renal cancer resulting in suppression of mitochondrial metabolism. Citation Format: Eun-Young Kho, Carolina B. Livi, Phillip Buckhaults, Francesca Carobbio, Hye-Young Nam, Richard Kirkman, David Crossman, Praveen K. Vayalil, Shi Wei, Ralph J. DeBerardinis, Sunil Sudarshan. Epigenetic silencing of krebs cycle metabolism in kidney cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 53.

Biguanides sensitize leukemia cells to ABT-737-induced apoptosis by inhibiting mitochondrial electron transport

Metformin displays antileukemic effects partly due to activation of AMPK and subsequent inhibition of mTOR signaling. Nevertheless, Metformin also inhibits mitochondrial electron transport at complex I in an AMPK-independent manner, Here we report that Metformin and rotenone inhibit mitochondrial electron transport and increase triglyceride levels in leukemia cell lines, suggesting impairment of fatty acid oxidation (FAO). We also report that, like other FAO inhibitors, both agents and the related biguanide, Phenformin, increase sensitivity to apoptosis induction by the bcl-2 inhibitor ABT-737 supporting the notion that electron transport antagonizes activation of the intrinsic apoptosis pathway in leukemia cells. Both biguanides and rotenone induce superoxide generation in leukemia cells, indicating that oxidative damage may sensitize toABT-737 induced apoptosis. In addition, we demonstrate that Metformin sensitizes leukemia cells to the oligomerization of Bak, suggesting that the observed synergy with ABT-737 is mediated, at least in part, by enhanced outer mitochondrial membrane permeabilization. Notably, Phenformin was at least 10-fold more potent than Metformin in abrogating electron transport and increasing sensitivity to ABT-737, suggesting that this agent may be better suited for targeting hematological malignancies. Taken together, our results suggest that inhibition of mitochondrial metabolism by Metformin or Phenformin is associated with increased leukemia cell susceptibility to induction of intrinsic apoptosis, and provide a rationale for clinical studies exploring the efficacy of combining biguanides with the orally bioavailable derivative of ABT-737, Venetoclax.

The transcriptomic response of the coral Acropora digitifera to a competent Symbiodinium strain: the symbiosome as an arrested early phagosome.

Despite the ecological significance of the relationship between reef-building corals and intracellular photosynthetic dinoflagellates of the genus Symbiodinium, very little is known about the molecular mechanisms involved in its establishment. Indeed, microarray-based analyses point to the conclusion that host gene expression is largely or completely unresponsive during the establishment of symbiosis with a competent strain of Symbiodinium. In this study, the use of Illumina RNA-Seq technology allowed detection of a transient period of differential expression involving a small number of genes (1073 transcripts; <3% of the transcriptome) 4h after the exposure of Acropora digitifera planulae to a competent strain of Symbiodinium (a clade B strain). This phenomenon has not previously been detected as a consequence of both the lower sensitivity of the microarray approaches used and the sampling times used. The results indicate that complex changes occur, including transient suppression of mitochondrial metabolism and protein synthesis, but are also consistent with the hypothesis that the symbiosome is a phagosome that has undergone early arrest, raising the possibility of common mechanisms in the symbiotic interactions of corals and symbiotic sea anemones with their endosymbionts.

The mitochondrial metabolism inhibitor CPI-613 in combination with mFOLFIRINOX for pancreatic adenocarcinoma.

264 Background: Stage IV pancreatic cancer is a lethal disease with limited treatment options. Current standard practice is combination chemotherapy with FOLFIRINOX or Gemcitabine + Abraxane. Despite these two new treatment options, the response rate and survival are limited in stage IV pancreatic cancer. The glycolic and mitochondrial metabolisms are aberrant in pancreatic cancer and translate into chemo-resistance. Inhibition of glutamine metabolism can potentially synergize with therapies that increase intracellular reactive oxygen species such as chemotherapy. CPI -613 is a novel anti-mitochondrial developed by Cornerstone Pharmaceuticals. Methods: A phase I clinical trial with mFOLFIRINOX+ CPI-613 in never treated for stage IV pancreatic cancer patients was initiated. The goals of this phase 1trial are: (1) To determine the Maximum Tolerated Dose (MTD) of CPI-613, when used in combination with mFOLFIRINOX, in patients with metastatic pancreatic cancer, (2) To assess the safety of CPI-613/ mFOLFIRINOX combination in patients with metastatic pancreatic cancer, and (3) To obtain preliminary data on efficacy of treatment with CPI-613/ mFOLFIRINOX Results: The MTD for CPI 613 was identified at 500mg/m2. The treatment combination is feasible and well-tolerated. The combination treatment was not found to have higher toxicity than FOLFIRINOX alone. The objective response rate was 53.9 % which is higher than FOLFIRINOX alone (reported as 31.6%). One patient has a complete radiologic and clinical response and two other patients have near complete responses. Conclusions: The preliminary efficacy data of this phase I clinical trial will inform a multi-institutional randomized phase II study of FOLFIRINOX vs. m FOLFIRINOX+ CPI613 in the near future. Clinical trial information: NCT01835041.

The Mitochondrial Metabolism Inhibitor Cpi-613 in Combination with High Dose Ara-C (HDAC) and Mitoxantrone Is Highly Active in Poor Risk Relapsed or Refractory Acute Myeloid Leukemia (AML)

Background: CPI-613 is a first in class agent that inhibits pyruvate dehydrogenase (PDH) and α-ketogluterate dehydrogenase. As a single agent CPI-613 was found to be well tolerated with possible activity in several patients with myeloid malignancies.This trial determined the maximum tolerated dose (MTD), safety, and efficacy of CPI-613 in combination with HDAC and mitoxantrone in patients with relapsed or refractory AML.Methods: CPI-613 was given daily on days 1 through 5 starting at a dose of 500 mg/m2. Beginning on day 3, HDAC at 3,000 mg/m2 (or 1,500 mg/m2 for age ≥60) is administered every 12 hours for 5 total doses and mitoxantrone at 6 mg/m2 is given daily for 3 doses. If residual disease is present on day 14 re-induction with the same or a three day abbreviated course could be given. Patients who achieved a complete remission with or without complete count recovery (CR or CRi) could receive up to a total of two additional consolidation cycles with the goal to get responders to stem cell transplant whenever possible.Results: A total of 67 patients have been enrolled and 65 are evaluable. The median age is 60 (range 21-79). Nineteen patients had refractory disease and 14 received at least 1 previous line of salvage therapy. In patients with relapsed disease the median duration of CR1 was 5 months. Cytogenetics were poor risk in 30 patients, intermediate in 30 and good in 6. One patient had CML in myeloid blast crisis. The overall intention to treat response rate was 48% (26CR+5CRi) with a median survival of 6.4 months. In patients ≥60 years old the CR/CRi rate was 42% (15/36). Surprisingly, the response rate for patients with poor risk cytogenetics was 47% (11CR+3CRi) with a median survival of 5.2 months. In a historical cohort treated with HDAC, mitoxantrone and asparaginase at our institution, only 19% (3/16) of patients with poor risk cytogenetics responded with a median survival of 2.8 months. The MTD of CPI-613 in combination with HDAC and mitoxantrone is 2,500 mg/m2. The dose limiting toxicities were diarrhea and nausea. Nine patients (13%) died on or before day 30. The most common toxicities attributed to CPI-613 were diarrhea and nausea, mainly grade 1 or 2. At the time of this submission thirteen patients have gone on to allogeneic stem cell transplantation. Several patients with circulating blasts had blood samples taken before and after CPI-613 infusion. Three of these patients had increased phosphorylation of PDH consistent with its inhibition. Additionally, two patients demonstrated a robust phosphorylation of adenosine monophosphate-activated protein kinase consistent with depletion of ATP. To explore if loss of p53 function (common in poor risk cytogenetics) affected response we tested CPI-613 alone or with an anthracycline against an AML cell line with and without p53 knockdown. Suppression of p53 function resulted in significant resistance to the anthracycline but no change in response to CPI-613; the combination enhanced cell kill over either agent alone.Conclusions: CPI-613 in combination with HDAC and mitoxantrone is a promising salvage regimen, especially in patients with poor risk cytogenetics. DisclosuresPardee:Novartis: Speakers Bureau; Celgene: Speakers Bureau. Off Label Use: CPI-613 is a novel anticancer agent not currently approved by the FDA. Ellis:Alexion: Speakers Bureau. Manuel:Novartis: Speakers Bureau. Hurd:Merck: Equity Ownership; Pfizer: Equity Ownership; Medtronic: Equity Ownership; Procter and Gamble: Equity Ownership; Bristol Myers Squib: Equity Ownership. Powell:Celgene: Speakers Bureau; Cornerstone Pharmaceuticals: Consultancy.

ATPS-09A MITOCHONDRIAL METABOLISM INHIBITOR RADIO-SENSITIZES GLIOBLASTOMA TUMOURS IN MICE

PENAO (4-(N-(S-penicillaminylacetyl)amino)phenylarsonous acid) is a mitochondrial metabolism inhibitor that is currently in Phase I clinical testing in patients with solid tumors refractory to standard therapy. PENAO is a cysteine mimetic trivalent arsenical that enters cells via an organic ion transporter and accumulates in the mitochondrial matrix where the arsenical moiety cross-links Cys160 and Cys257 on the matrix face of adenine nucleotide translocase (ANT), which inactivates the transporter. ANT inactivation leads to partial uncoupling of oxidative phosphorylation, increase in superoxide production, proliferation arrest and ultimately apoptosis of the cell. PENAO only reacts with ANT when cells are proliferating as Cys160 and Cys257 appear to be disulfide bonded in growth quiescent cells, and so unreactive towards PENAO. PENAO inhibited the proliferation of a panel of 13 glioblastoma cells, including cells from both primary and recurrent tumors, with IC50 values ranging from 0.3-4.5 µM. The IC50 values for proliferation arrest of normal lung fibroblasts and astrocytes are 9 µM and 7 µM, respectively, indicating selectivity for glioblastoma cells. Administration of PENAO (3 mg/kg/day) to mice bearing subcutaneous glioblastoma xenografts resulted in significant inhibition of tumor growth (7 partial and 3 complete responses). Ki67 and TUNEL staining of tumor sections showed that PENAO induced tumor cell growth arrest and death, respectively. Pharmacokinetic analysis demonstrated that PENAO readily crossed the blood-brain-barrier and accumulated specifically in tumor tissue. There were also no signs or symptoms of treatment toxicity. As PENAO induces superoxide production in glioblastoma cells, we hypothesized that PENAO in combination with radiation would synergise. Combining 2 Gy/day radiation (20 Gy total) with intraperitoneal administration of 20 mg/kg/day PENAO, resulted in significant improvement in median survival in an orthotopic glioblastoma murine model. These in-vitro and in-vivo results show that PENAO is a potential new therapeutic for glioblastoma, alone or in combination with radiation therapy

Activity of the mitochondrial metabolism inhibitor cpi-613 in combination with high dose Ara-C (HDAC) and mitoxantrone in high risk relapsed or refractory acute myeloid leukemia (AML).

7015 Background: CPI-613 is a novel agent that targets mitochondrial metabolism. It inhibits mitochondrial respiration in AML cells and in a single agent phase I study was active for several patien...

The Warburg Effect as a VDAC‐Hexokinase‐Mediated Electrical Suppression of Mitochondrial Energy Metabolism

It is known that nearly half of tumor energy metabolism is provided by glycolysis under normal aerobic conditions (the Warburg Effect) that has been attributed to a respiratory impairment in cancer cells. In the last years, the mitochondrial impairment in cancer cells has been explained by the closure of mitochondrial outer membrane VDACs (porins) by free tubulin (as molecular corks) leading to a suppression of mitochondrial metabolism. Here, we further developed a concept that mitochondria in cancer cells are suppressed by the outer membrane potential (OMP) generated by the metabolically‐dependent mechanism involving the functioning of the VDAC‐hexokinase and/or the ANT(adenine nucleotide translocator)‐VDAC‐hexokinase complexes.These complexes and generated OMP allow initiation of glycolysis preferentially by ATP generated in mitochondria. High selectivity of channeling of mitochondrial energy into the cytosol of cancer cells, to only initiate glycolysis, is achieved due to the electrical closure of free VDACs (non‐bound to hexokinase) by the metabolically‐dependent OMP, by a mode preventing turbo acceleration of glycolysis by cytosolic ATP. Even at low values of OMP, not high enough to completely close VDACs, the ATP flux from the mitochondrial intermembrane space should be almost completely suppressed according to Goldman equation. The value of OMP directly generatedby the VDAC‐hexokinase complex, for example, depends on the Gibbs free energy of the hexokinase reaction. It means that VDAC might function as a physiologically important electrical switcher of tumor energy metabolism, allowing a clear explanation of the Warburg Effect mechanism. (Research grants #111852128625 and #520154531565, Colciencias).

High glucose induces mitochondrial dysfunction independently of protein O-GlcNAcylation.

Diabetes is characterized by hyperglycaemia and perturbations in intermediary metabolism. In particular, diabetes can augment flux through accessory pathways of glucose metabolism, such as the hexosamine biosynthetic pathway (HBP), which produces the sugar donor for the β-O-linked-N-acetylglucosamine (O-GlcNAc) post-translational modification of proteins. Diabetes also promotes mitochondrial dysfunction. Nevertheless, the relationships among diabetes, hyperglycaemia, mitochondrial dysfunction and O-GlcNAc modifications remain unclear. In the present study, we tested whether high-glucose-induced increases in O-GlcNAc modifications directly regulate mitochondrial function in isolated cardiomyocytes. Augmentation of O-GlcNAcylation with high glucose (33mM) was associated with diminished basal and maximal cardiomyocyte respiration, a decreased mitochondrial reserve capacity and lower Complex II-dependent respiration (P<0.05); however, pharmacological or genetic modulation of O-GlcNAc modifications under normal or high glucose conditions showed few significant effects on mitochondrial respiration, suggesting that O-GlcNAc does not play a major role in regulating cardiomyocyte mitochondrial function. Furthermore, an osmotic control recapitulated high-glucose-induced changes to mitochondrial metabolism (P<0.05) without increasing O-GlcNAcylation. Thus, increased O-GlcNAcylation is neither sufficient nor necessary for high-glucose-induced suppression of mitochondrial metabolism in isolated cardiomyocytes.

Maintenance of mouse hematopoietic stem cells ex vivo by reprogramming cellular metabolism

AbstractThe difficulty in maintaining the reconstituting capabilities of hematopoietic stem cells (HSCs) in culture outside of the bone marrow microenvironment has severely limited their utilization for clinical therapy. This hurdle is largely due to the differentiation of long-term stem cells. Emerging evidence suggests that energy metabolism plays an important role in coordinating HSC self-renewal and differentiation. Here, we show that treatment with alexidine dihydrochloride, an antibiotic and a selective inhibitor of the mitochondrial phosphatase Ptpmt1, which is crucial for the differentiation of HSCs, reprogrammed cellular metabolism from mitochondrial aerobic metabolism to glycolysis, resulting in a remarkable preservation of long-term HSCs ex vivo in part through hyperactivation of adenosine 5′-monophosphate–activated protein kinase (AMPK). In addition, inhibition of mitochondrial metabolism and activation of AMPK by metformin, a diabetes drug, also decreased differentiation and helped maintain stem cells in culture. Thus, manipulating metabolic pathways represents an effective new strategy for ex vivo maintenance of HSCs.

TASK channels in arterial chemoreceptors and their role in oxygen and acid sensing.

Arterial chemoreceptors play a vital role in cardiorespiratory control by providing the brain with information regarding blood oxygen, carbon dioxide, and pH. The main chemoreceptor, the carotid body, is composed of sensory (type 1) cells which respond to hypoxia or acidosis with a depolarising receptor potential which in turn activates voltage-gated calcium entry, neurosecretion and excitation of adjacent afferent nerves. The receptor potential is generated by inhibition of Twik-related acid-sensitive K+ channel 1 and 3 (TASK1/TASK3) heterodimeric channels which normally maintain the cells’ resting membrane potential. These channels are thought to be directly inhibited by acidosis. Oxygen sensitivity, however, probably derives from a metabolic signalling pathway. The carotid body, isolated type 1 cells, and all forms of TASK channel found in the type 1 cell, are highly sensitive to inhibitors of mitochondrial metabolism. Moreover, type1 cell TASK channels are activated by millimolar levels of MgATP. In addition to their role in the transduction of chemostimuli, type 1 cell TASK channels have also been implicated in the modulation of chemoreceptor function by a number of neurocrine/paracrine signalling molecules including adenosine, GABA, and serotonin. They may also be instrumental in mediating the depression of the acute hypoxic ventilatory response that occurs with some general anaesthetics. Modulation of TASK channel activity is therefore a key mechanism by which the excitability of chemoreceptors can be controlled. This is not only of physiological importance but may also offer a therapeutic strategy for the treatment of cardiorespiratory disorders that are associated with chemoreceptor dysfunction.

Voltage Dependent Anion Channels (VDAC) and Regulation of Mitochondrial Metabolism

Voltage dependent anion channels (VDAC) are responsible for permeability of mitochondrial outer membranes to hydrophilic metabolites like ATP, ADP and respiratory substrates. Although previously assumed to remain open, VDAC closure is emerging as an important mechanism for regulation of global mitochondrial function. Acetaldehyde formation from hepatic ethanol metabolism leads to VDAC closure, which suppresses exchange of mitochondrial metabolites and inhibits ureagenesis. In vivo, VDAC closure after ethanol occurs coordinately with mitochondrial depolarization. Together, VDAC closure and uncoupling foster selective and more rapid mitochondrial oxidation of toxic acetaldehyde formed by ethanol metabolism. Glycolysis and suppression of mitochondrial metabolism are metabolic characteristics of cancer cells that promote cell proliferation (Warburg phenomenon). High free αβ-tubulin dimers in cancer cells block VDAC and suppress mitochondrial function, and reversal of tubulin inhibition of VDAC with erastin and erastin-like small molecules has an anti-Warburg effect that hyperpolarizes mitochondria, enhances oxidative phosphorylation and decreases glycolysis. Erastin-like compounds also enhance mitochondria formation of reactive oxygen species in cancer cells, leading eventually to mitochondrial dysfunction and cell death. Thus, VDAC is a key regulator of mitochondrial function (DK073336, DK037034 and 14.Z50.31.0028).

The Mitochondrial Metabolism Inhibitor Cpi-613 Is Highly Active in Combination with High Dose Ara-C (HiDAC) and Mitoxantrone in a Phase I Study for Relapsed or Refractory Acute Myeloid Leukemia (AML)

Background: CPI-613 is a first in class agent that targets mitochondrial metabolism through inhibition of pyruvate dehydrogenase and a-ketogluterate dehydrogenase. In a single agent phase I study CPI-613 was found to be well tolerated and several patients with myeloid malignancies had a response.This trial was designed to determine the maximum tolerated dose, safety, and efficacy of CPI-613 given in combination with HiDAC and mitoxantrone in patients with relapsed or refractory AML.Methods: CPI-613 is given daily on days 1 through 5 starting at a dose of 500 mg/m2. Beginning on day 3, HiDAC at 3,000 mg/m2 (or 1,500 mg/m2 for age ≥60) is administered every 12 hours for 5 doses and mitoxantrone at 6 mg/m2 is given daily for 3 doses. To date the CPI-613 dose has been escalated to 2250 mg/m2. If residual disease is present on day 14 re-induction with the same or a three day abbreviated course can be given. Patients who achieved a complete remission with or without complete count recovery (CR or CRi) could receive additional consolidation cycles with the goal to get responders to stem cell transplant whenever possible.Results: A total of 36 patients have been enrolled to date. The median age is 60 (range 21-76). Eight patients had refractory disease and nine received two or more previous lines of therapy. In patients with relapsed disease where data was available, the median duration of CR1 was 8.4 months. Cytogenetics were poor risk in 17 patients, intermediate in 15, good in 3 and one patient had CML in myeloid blast crisis. The overall intention to treat response rate was 50% (16CR+2CRi). This was the same for patients ≥60 years old with a CR/CRi rate of 50% (10/20). Surprisingly, the response rate was slightly higher for patients with poor risk cytogenetics with a CR/CRi rate of 53% (9/17). In a historical cohort of patients treated with HiDAC, mitoxantrone and asparaginase at our institution, only 25% (4/16) of patients with poor risk cytogenetics achieved a CR/CRi. Median survival for the entire cohort is 6.4 months with a median of 3.1 months of follow-up (see figure 1). Five patients (14%) died on or before day 30. The regimen is well tolerated with no dose limiting toxicities observed to date. Ten patients went on to allogeneic stem cell transplantation (28%). This compares favorably with our historical data where only 17% of patients went on to transplant. Four patients with circulating blasts had blood samples taken on day one, before and after CPI-613 infusion. Three of these patients had demonstrable increases in the level of phosphorylation of pyruvate dehydrogenase complex consistent with its inhibition. Additionally, one patient who cleared her marrow demonstrated robust phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) consistent with depletion of ATP.Conclusions: CPI-613 in combination with HDAC and mitoxantrone is a promising salvage regimen, especially in older patients and those with high risk disease. Induction of AMPK phosphorylation may serve as a predictor of response. This trial continues to accrue patients.Figure 1. Overall survival of all patients. [Display omitted] DisclosuresPardee:Cornerstone Pharmaceuticals: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau. Off Label Use: CPI-613 is a novel mitochondrial metabolism inhibitor.. Powell:Cornerstone Pharmaceuticals: Membership on an entity’s Board of Directors or advisory committees.

ATP/ADP ratio, the missed connection between mitochondria and the Warburg effect

Non-proliferating cells generate the bulk of cellular ATP by fully oxidizing respiratory substrates in mitochondria. Respiratory substrates cross the mitochondrial outer membrane through only one channel, the voltage dependent anion channel (VDAC). Once in the matrix, respiratory substrates are oxidized in the tricarboxylic acid cycle to generate mostly NADH that is further oxidized in the respiratory chain to generate a proton motive force comprised mainly of membrane potential (ΔΨ) to synthesize ATP. Mitochondrial ΔΨ then drives the release of ATP4− from the matrix in exchange for ADP3− in the cytosol via the adenine nucleotide translocator (ANT) located in the mitochondrial inner membrane. Thus, mitochondrial function in non-proliferating cells drives a high cytosolic ATP/ADP ratio, essential to inhibit glycolysis. By contrast, the bioenergetics of the Warburg phenotype of proliferating cells is characterized by enhanced aerobic glycolysis and the suppression of mitochondrial metabolism. Suppressed mitochondrial function leads to lower production of mitochondrial ATP and hence lower cytosolic ATP/ADP ratios that favor enhanced glycolysis. Thus, the cytosolic ATP/ADP ratio is a key feature that determines if cell metabolism is predominantly oxidative or glycolytic. Here, we describe two novel mechanisms to explain the suppression of mitochondrial metabolism in cancer cells: the relative closure of VDAC by free tubulin and the inactivation of ANT. Both mechanisms contribute to low ATP/ADP ratios that activate glycolysis.

Metabolic suppression in mammalian hibernation: the role of mitochondria.

Hibernation evolved in some small mammals that live in cold environments, presumably to conserve energy when food supplies are low. Throughout the winter, hibernators cycle spontaneously between torpor, with low metabolism and near-freezing body temperatures, and euthermia, with high metabolism and body temperatures near 37°C. Understanding the mechanisms underlying this natural model of extreme metabolic plasticity is important for fundamental and applied science. During entrance into torpor, reductions in metabolic rate begin before body temperatures fall, even when thermogenesis is not active, suggesting active mechanisms of metabolic suppression, rather than passive thermal effects. Mitochondrial respiration is suppressed during torpor, especially when measured in liver mitochondria fuelled with succinate at 37°C in vitro. This suppression of mitochondrial metabolism appears to be invoked quickly during entrance into torpor when body temperature is high, but is reversed slowly during arousal when body temperature is low. This pattern may reflect body temperature-sensitive, enzyme-mediated post-translational modifications of oxidative phosphorylation complexes, for instance by phosphorylation or acetylation.

A phase I study of the mitochondrial metabolism inhibitor CPI-613 in combination with high-dose ara-C (HDAC) and mitoxantrone for relapsed or refractory acute myeloid leukemia (AML).

7028 Background: Altered metabolism is an emerging hallmark of cancer and a possible therapeutic target. CPI-613 is a first in class agent that targets mitochondrial metabolism.This trial was desig...

The mitochondrial pyruvate carrier as a mediator of the Warburg Effect and its impact on cancer growth and metabolism

Background The step between pyruvate production by glycolysis in the cytosol and movement into the mitochondrial matrix has largely been unstudied due to the lack of identity of the genes that mediate this process. The discovery of the Mitochondrial Pyruvate Carrier (MPC) opens this overlooked aspect of metabolism to interrogation. The dispensation of pyruvate represents an important and highly regulated decision within the cell. This is especially true in rapidly proliferating cells including those found in tumors. Given the reliance of cancer cells on glycolysis and the concomitant suppression of mitochondrial metabolism we hypothesize that modulation of the MPC may serve to promote and reinforce the Warburg Effect. Materials and methods Publicly available datasets were queried for differential expression of MPC1 and MPC2 (TGCA and GEO). An array of cell lines representing various cancers were stably infected with MPC1 and MPC2 or empty vector and assayed for growth differences in 2D as well as 3D (soft agar and spheroid formation). Results MPC1 and MPC2 transcript levels are significantly reduced in multiple cancers compared to the adjacent normal tissue including forms of gastric, colon, breast, ovarian, and renal cancers. These expression changes have been confirmed using qPCR and immunoblotting. In addition to altered expression, low MPC correlates with decreased survival across multiple cancer types. We reasoned that cancer cells would reduce MPC expression to promote the Warburg Effect to fuel rapid growth and relied on in vitro cell culture to manipulate MPC expression. The re-expression of MPC1 and MPC2 results in no change in cell viability or apoptosis but causes reduced attachment in culture plates as well as reduced growth in soft agar and spheroids. In addition to the in vitro studies, xenograft models have recapitulated these growth differences. We have confirmed MPC expression produces alterations in metabolism including increased oxygen consumption with pyruvate as a substrate, a reduction in lactate production, and an increase in mitochondrial membrane potential. Conclusions MPC expression is reduced in many types of cancer and its re-expression results in changes in metabolism and growth as measured by multiple assays. As expected, MPC expression facilitates pyruvate movement into the mitochondria and reduces the Warburg Effect. We are now investigating the effect of MPC expression on different cell subpopulations as well as the root cause of the expression changes observed in cancer.

Mito-DCA: A Mitochondria Targeted Molecular Scaffold for Efficacious Delivery of Metabolic Modulator Dichloroacetate

Tumor growth is fueled by the use of glycolysis, which normal cells use only in the scarcity of oxygen. Glycolysis makes tumor cells resistant to normal death processes. Targeting this unique tumor metabolism can provide an alternative strategy to selectively destroy the tumor, leaving normal tissue unharmed. The orphan drug dichloroacetate (DCA) is a mitochondrial kinase inhibitor that has the ability to show such characteristics. However, its molecular form shows poor uptake and bioavailability and limited ability to reach its target mitochondria. Here, we describe a targeted molecular scaffold for construction of a multiple DCA loaded compound, Mito-DCA, with three orders of magnitude enhanced potency and cancer cell specificity compared to DCA. Incorporation of a lipophilic triphenylphosphonium cation through a biodegradable linker in Mito-DCA allowed for mitochondria targeting. Mito-DCA did not show any significant metabolic effects toward normal cells but tumor cells with dysfunctional mitochondria were affected by Mito-DCA, which caused a switch from glycolysis to glucose oxidation and subsequent cell death via apoptosis. Effective delivery of DCA to the mitochondria resulted in significant reduction in lactate levels and played important roles in modulating dendritic cell (DC) phenotype evidenced by secretion of interleukin-12 from DCs upon activation with tumor antigens from Mito-DCA treated cancer cells. Targeting mitochondrial metabolic inhibitors to the mitochondria could lead to induction of an efficient antitumor immune response, thus introducing the concept of combining glycolysis inhibition with immune system to destroy tumor.

Are long chain acyl CoAs responsible for suppression of mitochondrial metabolism in hibernating 13-lined ground squirrels?

Hibernation in 13-lined ground squirrels (Ictidomys tridecemlineatus) is associated with a substantial suppression of whole-animal metabolism. We compared the metabolism of liver mitochondria isolated from torpid ground squirrels with those from interbout euthermic (IBE; recently aroused from torpor) and summer euthermic conspecifics. Succinate-fuelled state 3 respiration, calculated relative to mitochondrial protein, was suppressed in torpor by 48% and 44% compared with IBE and summer, respectively. This suppression remains when respiration is expressed relative to cytochrome c oxidase activity. We hypothesized that this suppression was caused by inhibition of succinate transport at the dicarboxylate transporter (DCT) by long-chain fatty acyl CoAs that may accumulate during torpor. We predicted, therefore, that exogenous palmitoyl CoA would inhibit respiration in IBE more than in torpor. Palmitoyl CoA inhibited respiration ~70%, in both torpor and IBE. The addition of carnitine, predicted to reverse palmitoyl CoA suppression by facilitating its transport into the mitochondrial matrix, did not rescue the respiration rates in IBE or torpor. Liver mitochondrial activities of carnitine palmitoyl transferase did not differ among IBE, torpor and summer animals. Although palmitoyl CoA inhibits succinate-fuelled respiration, this suppression is likely not related exclusively to inhibition of the DCT, and may involve additional mitochondrial transporters such as the adenine-nucleotide transporter.